Open Transmission Projects
New Transmission Facilities
Minimum Design Requirements
Draft Language for Future BPM
1
1.0 Definitions
1.1 Absolute Transmission Circuit Limit
An MVA loading limit above which a Transmission Circuit cannot be
loaded for any period of time. This limit is the lesser of i) the Relay Trip
Load Level and, ii) the Maximum Power Transfer Limit. This limit is an
upper bound on all other Transmission Circuit ratings.
1.2 Circuit Breaker Assembly
Applicable to circuit breakers in a ring bus, breaker-and-a-half bus, and
double-breaker bus configuration. Consists of a circuit breaker and all
conductor and load carrying equipment electrically in series with the
circuit breaker (where “in series” means it carries the same current level as
the circuit breaker or a current level proportional to the current level
carried by the circuit breaker). The following are substation load carrying
elements typically in series with a Circuit Breaker:

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Bus Conductor
Jumper Conductor
Lead Conductor
Connectors
Disconnect Switches
Circuit Breaker Bushings
Current Transformers (bushing or standalone)
Current Transformer Secondary Elements (only elements that
monitor circuit breaker flows):
o Breaker Failure Relay Overcurrent Fault Detectors
o Breaker Ammeters
o Breaker Current Transducers
1.3 Emergency Conditions
An operating state where i) at least one normally energized Transmission
Element is out-of-service, ii) at least one Generation Element and/or
switchable Transmission Element (e.g., shunt capacitor bank, series
capacitor bypass breaker, etc.) is needed but is unavailable, and/or iii) the
system is otherwise configured in an abnormal state (e.g., a normally
closed breaker is open, a normally open breaker is closed, etc.).
1.4 Generation Element
One or more generating units, associated generator step-up transformers,
associated generator lead lines, and, if applicable, associated generator
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collector systems that ultimately interconnect to the Transmission System
via a single terminal at the interconnecting transmission substation.
1.5 Maximum Allowable Emergency Operating Temperature
The maximum temperature allowed for a Transmission Circuit Conductor
during Emergency Conditions. This temperature is less than or equal to
the Maximum Conductor Sag Temperature and greater than or equal to the
Maximum Allowable Normal Operating Temperature. The degree to
which this temperature exceeds the Maximum Allowable Normal
Operating Temperature is a function of the amount of risk the asset owner
is willing to assume with regard to the accelerated loss of tensile strength
and/or accelerated creep elongation that may occur when operation above
the Maximum Allowable Normal Operating Temperatures is permitted
during Emergency Conditions.
1.6 Maximum Allowable Normal Operating Temperature
The maximum temperature allowed for a Transmission Circuit Conductor
under Normal Conditions that ensures continuous operation at this
temperature will not reduce the expected life span of the conductor via
accelerated loss of tensile strength or accelerated creep elongation. This
temperature is less than or equal to the Maximum Conductor Sag
Temperature and the Maximum Allowable Emergency Operating
Temperature.
1.7 Maximum Conductor Sag Temperature
The maximum temperature allowed for a Transmission Circuit Conductor
to ensure NESC vertical clearance requirements are satisfied when
operating at this temperature.
1.8 Maximum Power Transfer Limit
The maximum amount of power that can be theoretically transferred
across a specific Transmission Circuit given the Transmission Circuit
series reactance and assuming the sending-end and receiving-end voltage
magnitudes are equal to the nominal operating voltage level. This transfer
level occurs at an angular displacement of 90 degrees between the
sending-end and receiving-end terminal voltages and cannot be exceeded.
1.9 Normal Conditions
An operating state where all Transmission Elements and Generation
Elements are operated in their normal configuration or otherwise available
if needed.
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1.10
Relay Trip Load Level
The minimum MVA load level at a Transmission Circuit terminal that is
necessary to cause a relay trip of the Transmission Circuit terminal given
the angle between the terminal voltage and the current flow into the line is
between -30 and + 30. A Relay Trip Load Level applies only when a
line trip can occur without the pickup of a non-load responsive relay
element (e.g., differential relay, phase comparison relay, etc.). The Relay
Trip Load Level is based on 87% of the actual primary setting of the relay
to account for instrument transformer error and relay setting drift, which is
consistent with NERC PRC-023-3.
1.11
Series Compensation Device
A series capacitor, series reactor, or similar series FACTs device
connected between two Transmission System Buses, a Transmission
System Bus and a Transmission Circuit terminal, or a Transmission
System Bus and a Transmission Transformer terminal, and used generally
to alter the impedance of a Transmission Circuit or Transmission
Transformer, control the flow of power on the transmission system, and/or
control the available fault current level on the transmission system.
1.12
Shunt Compensation Device
A shunt capacitor bank, shunt reactor bank, static VAR compensator
(SVC), static synchronous compensator (STATCOM), synchronous
condenser, or other shunt device installed for the purpose of controlling
voltage and power factor via injecting or withdrawing reactive power into
and out of the transmission system.
1.13
Substation Terminal Equipment
All load carrying equipment within a substation that is in series with a
two-terminal Transmission Circuit, one leg of a three-terminal
Transmission Circuit, or Generation Element that terminates at the
substation (where “in series” means it carries the same current level as the
Transmission Circuit, Transmission Circuit leg, or Generation Element or
a current level proportional to the current level carried by the
Transmission Circuit, Transmission Circuit leg, or Generation element).
The following are substation load carrying elements typically in series
with a Transmission Circuit or Generation Element:



Bus Conductor
Riser Conductor
Jumper Conductor
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

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
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
1.14
First Span Conductor
Connectors
Line or Generator Switches
Wave Traps
Circuit Breakers (if straight bus configuration)
Circuit Breaker Disconnect Switches (if straight bus
configuration)
Circuit Breaker Leads (if straight bus configuration)
Circuit Breaker Bushings (if straight bus configuration)
Circuit Breaker Current Transformers (if straight bus
configuration)
Standalone Current Transformers
Current Transformer Secondary Elements (only elements that
monitor Transmission Circuit or Generation Element flows and
are not connected to monitor the residual flow of all three
current transformers):
o Line or Generator Phase Protective Relay Elements
o Line or Generator Ammeters
o Other Line or Generator Flow Meters
o Line or Generator Current Transducers
Substation Terminal Equipment Ampere Rating
Applies to each substation terminal of a two terminal Transmission
Circuit, the connected substation terminal of a specific three-terminal
Transmission Circuit leg, or the substation terminal of a Generation
Element and is equal to the lowest ampere rating of all Substation
Terminal Equipment associated with (i.e., in series with) a specific
Transmission Circuit, Transmission Circuit leg, or Generation Element
1.15
Summer Conductor Sag Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the maximum amount of
electrical current, expressed in amperes, that can be carried by each
Transmission Circuit Conductor on a sustained basis under i) summer
ambient temperatures and ii) zero wind speed without exceeding the
Maximum Conductor Sag Temperature.
1.16
Summer Continuous Conductor Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the maximum amount of
electrical current, expressed in amperes, that can be carried by each
Transmission Circuit Conductor on a sustained basis under i) summer
ambient temperatures and ii) wind conditions not more favorable than
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wind speeds of 2.0 feet per second striking the conductor perpendicularly
without exceeding the Maximum Allowable Normal Operating
Temperature.
1.17
Summer Emergency Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the lesser of the i) Summer
Conductor Sag Ampere Rating, ii) Summer Stressed Conductor Ampere
Rating, iii) lowest nameplate continuous current rating for all
Transmission Circuit Switching Devices installed on the Transmission
Circuit (or leg), or iv) the smallest Substation Terminal Equipment
Ampere Rating for any substation terminal associated with the
Transmission Circuit (or leg).
1.18
Summer Emergency MVA Rating
Applies to an entire two terminal Transmission Circuit or to each leg of a
three-terminal Transmission Circuit and is equal to the lesser of i) the
Summer Emergency Thermal MVA Rating or ii) the Voltage and Stability
Loadability Rating, if applicable.
1.19
Summer Emergency Thermal MVA Rating
Applies to an entire two terminal Transmission Circuit or to each leg of a
three-terminal Transmission Circuit and is equal to the MVA that is
transferred when i) the voltages are balanced, ii) the voltage magnitudes
are equal to the nominal operating voltage level, iii) the phase currents are
balanced, and iv) the phase current magnitudes are equal to the Summer
Emergency Ampere Rating.
1.20
Summer Normal Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the lesser of the i) Summer
Conductor Sag Ampere Rating, ii) Summer Continuous Conductor
Ampere Rating, iii) lowest nameplate continuous current rating for all
Transmission Circuit Switching Devices installed on the Transmission
Circuit (or leg), or iv) the smallest Substation Terminal Equipment
Ampere Rating for any substation terminal associated with the
Transmission Circuit (or leg).
1.21
Summer Normal MVA Rating
Applies to an entire two terminal Transmission Circuit or to each leg of a
three-terminal Transmission Circuit and is equal to the lesser of i) the
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Summer Normal Thermal MVA Rating or ii) the Voltage and Stability
Loadability Rating, if applicable.
1.22
Summer Normal Thermal MVA Rating
Applies to an entire two terminal Transmission Circuit or to each leg of a
three-terminal Transmission Circuit and is equal to the MVA that is
transferred when i) the voltages are balanced, ii) the voltage magnitudes
are equal to the nominal operating voltage level, iii) the phase currents are
balanced, and iv) the phase current magnitudes are equal to the Summer
Normal Ampere Rating.
1.23
Summer Short-term Emergency Ampere Rating
An optional rating that applies to a two-terminal Transmission Circuit or
to each leg of a three-terminal Transmission Circuit and may be
determined by the facility owner based on the lessor of i) the maximum
amount of electrical current that can be carried by each Transmission
Circuit Conductor under summer ambient temperatures and conditions for
a limited period of time without exceeding the Maximum Conductor Sag
Temperature based on a pre-specified initial conductor temperature equal
to the Maximum Allowable Normal Operating Temperature and ii) the
maximum amount of electrical current that can be carried by each
Transmission Circuit Conductor under summer ambient temperatures and
conditions for a limited period of time on an infrequent basis without
exposing the conductor to significant or otherwise unacceptable reductions
in conductor life span due to accelerated loss of tensile strength and/or
accelerated creep elongation. The Summer Short-term Emergency
Ampere Rating also includes a maximum time duration applicable to each
incident where loading is above the Summer Emergency Ampere Rating
but not in excess of the Summer Short-term Emergency Ampere Rating.
1.24
Summer Short-term Emergency MVA Rating
An optional rating that applies to an entire two terminal Transmission
Circuit or to each leg of a three-terminal Transmission Circuit and is equal
to the lesser of i) the Summer Short-term Emergency Thermal MVA
Rating or ii) the Absolute Transmission Circuit Limit. The Summer
Short-term Emergency MVA Rating must also include a maximum time
duration which is equal to the maximum time duration associated with the
Summer Short-term Emergency Thermal MVA Rating.
1.25
Summer Short-term Emergency Thermal MVA Rating
An optional rating that applies to an entire two terminal Transmission
Circuit or to each leg of a three-terminal Transmission Circuit and is equal
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to the MVA that is transferred when i) the voltages are balanced, ii) the
voltage magnitudes are equal to the nominal operating voltage level, iii)
the phase currents are balanced, and iv) the phase current magnitudes are
equal to the Summer Short-term Emergency Ampere Rating. The
Summer Short-term Emergency Thermal MVA Ratings must also include
a maximum time duration which is equal to the maximum time duration
associated with the Summer Short-term Emergency Ampere Rating.
1.26
Summer Stressed Conductor Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the maximum amount of
electrical current, expressed in amperes, that can be carried by each
Transmission Circuit Conductor on a sustained basis under i) summer
ambient temperatures and ii) wind conditions not more favorable than
wind speeds of 2.0 feet per second striking the conductor perpendicularly
without exceeding the Maximum Allowable Emergency Operating
Temperature.
1.27
Terminal Equipment Rating Class
An industry standard continuous current rating that applies to substation
equipment such as circuit breakers, switches, wave traps, current
transformer primaries, and other similar equipment. Several terminal
equipment rating classes are available for various voltage levels. Table 1
in Attachment A is a summary of the most common Terminal Equipment
Rating Classes currently used in North America and the Terminal
Equipment Rating Classes to be used by MISO in determining minimum
design requirements.
1.28
Transmission Circuit
An AC three-phase electrical circuit operating at a transmission voltage
level and containing two or more substation terminals that is used to
transfer electrical energy between the terminating substations and is
associated with a single zone of protection within the transmission system.
1.29
Transmission Circuit Conductor
The conductor or set of bundled or paralleled conductors associated with
any one of the three phases of a Transmission Circuit that is used to
transport electrical energy between the terminals of the Transmission
Circuit.
1.30
Transmission Circuit Switching Device
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A non-fault interrupting switch in series with the Transmission Circuit
Conductors, located external to a substation, and typically mounted on a
transmission structure.
1.31
Transmission Element
A Transmission Circuit, Transmission Physical Bus, Transmission
Transformer, Series Compensation Device, Shunt Compensation Device,
transmission bus-tie breaker, or HVDC converter.
1.32
Transmission Line
One or more Transmission Circuits and associated facilities (right-of-way,
structures, conductors, shield wires, insulators, and hardware) extending
from one location to another, where such locations could be substation
terminals or other points. A Transmission Line can contain multiple
Transmission Circuits (i.e., several Transmission Circuits can be carried
on common structures) and a Transmission Circuit can be installed on
multiple Transmission Lines (i.e., several single and multi-circuit
Transmission Lines can carry the same Transmission Circuit).
1.33
Transmission Physical Bus
A physical bus made up of conductors operating at a transmission voltage
level and located within a substation for the purpose of physically
interconnecting the terminals of three or more Transmission Elements
and/or Generation Elements directly. A Transmission Physical Bus is
associated with only one zone of protection. Examples of Transmission
Physical Buses are single-zone straight buses or one of the two buses in a
breaker-and-a-half or double-breaker bus configuration. A Transmission
Physical Bus is always part of a Transmission System Bus and sometimes
may correspond to an entire Transmission System Bus.
1.34
Transmission System Bus
An electrical hub made up of one or more elements located within a
substation for the purpose of interconnecting the terminals of three or
more Transmission Elements and/or Generation Elements directly or
through zero impedance devices. A Transmission System Bus may span
multiple zones of protection. Examples of Transmission System Buses are
straight buses, multiple straight buses interconnected by normally closed
tie breakers, ring buses, breaker-and-a-half buses, and double breaker
buses. A Transmission System Bus may or may not include one or more
Transmission Physical Buses.
1.35
Transmission Transformer
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A multi winding power transformer, autotransformer, voltage regulating
transformer, or phase angle regulating transformer connected between at
least two or more Transmission System Buses or between a Transmission
System Bus and a Transmission Circuit terminal, Series Compensation
Device terminal, or HVDC Converter terminal. Generator step-up
transformers, station service transformers, station auxiliary transformers,
transformers serving the distribution system, and transformers serving
transmission level end-use load are not defined as Transmission
Transformers.
1.36
Voltage and Stability Loadability Rating
A maximum MW rating for a Transmission Circuit based on voltage and
stability considerations rather than conductor thermal loading
considerations. This rating defaults to the Absolute Transmission Circuit
Limit, which is an upper bound on this rating, unless there are special
circumstances where planning studies determine a lower rating for specific
facilities is appropriate.
1.37
Winter Conductor Sag Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the maximum amount of
electrical current, expressed in amperes, that can be carried by each
Transmission Circuit Conductor on a sustained basis under i) winter
ambient temperatures and ii) zero wind speed without exceeding the
Maximum Conductor Sag Temperature.
1.38
Winter Continuous Conductor Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the maximum amount of
electrical current, expressed in amperes, that can be carried by each
Transmission Circuit Conductor on a sustained basis under i) winter
ambient temperatures and ii) wind conditions not more favorable than
wind speeds of 2.0 feet per second striking the conductor perpendicularly
without exceeding the Maximum Allowable Normal Operating
Temperature.
1.39
Winter Emergency Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the lesser of the i) Winter
Conductor Sag Ampere Rating, ii) Winter Stressed Conductor Ampere
Rating, iii) lowest nameplate continuous current rating for all
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Transmission Circuit Switching Devices installed on the Transmission
Circuit (or leg), or iv) the smallest Substation Terminal Equipment
Ampere Rating for any substation terminal associated with the
Transmission Circuit (or leg).
1.40
Winter Emergency MVA Rating
Applies to an entire two terminal Transmission Circuit or to each leg of a
three-terminal Transmission Circuit and is equal to the lesser of i) the
Winter Emergency Thermal MVA Rating or ii) the Voltage and Stability
Loadability Rating, if applicable.
1.41
Winter Emergency Thermal MVA Rating
Applies to an entire two terminal Transmission Circuit or to each leg of a
three-terminal Transmission Circuit and is equal to the MVA that is
transferred when i) the voltages are balanced, ii) the voltage magnitudes
are equal to the nominal operating voltage level, iii) the phase currents are
balanced, and iv) the phase current magnitudes are equal to the Winter
Emergency Ampere Rating.
1.42
Winter Normal Ampere Rating
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the lesser of the i) Winter
Conductor Sag Ampere Rating, ii) Winter Continuous Conductor Ampere
Rating, iii) lowest nameplate continuous current rating for all
Transmission Circuit Switching Devices installed on the Transmission
Circuit (or leg), or iv) the smallest Substation Terminal Equipment
Ampere Rating for any substation terminal associated with the
Transmission Circuit (or leg).
1.43
Winter Normal MVA Rating
Applies to an entire two terminal Transmission Circuit or to each leg of a
three-terminal Transmission Circuit and is equal to the lesser of i) the
Winter Normal Thermal MVA Rating or ii) the Voltage and Stability
Loadability Rating, if applicable.
1.44
Winter Normal Thermal MVA Rating
Applies to an entire two terminal Transmission Circuit or to each leg of a
three-terminal Transmission Circuit and is equal to the MVA that is
transferred when i) the voltages are balanced, ii) the voltage magnitudes
are equal to the nominal operating voltage level, iii) the phase currents are
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balanced, and iv) the phase current magnitudes are equal to the Winter
Normal Ampere Rating.
1.45
Winter Short-term Emergency Ampere Rating
An optional rating that applies to a two-terminal Transmission Circuit or
to each leg of a three-terminal Transmission Circuit and may be
determined by the facility owner based on the lesser of i) the maximum
amount of electrical current that can be carried by each Transmission
Circuit Conductor under winter ambient temperatures and conditions for a
limited period of time without exceeding the Maximum Conductor Sag
Temperature based on a pre-specified initial conductor temperature equal
to the Maximum Allowable Normal Operating Temperature and ii) the
maximum amount of electrical current that can be carried by each
Transmission Circuit Conductor under winter ambient temperatures and
conditions for a limited period of time on an infrequent basis without
exposing the conductor to significant or otherwise unacceptable reductions
in conductor life due to accelerated loss of tensile strength and/or
accelerated creep elongation. The Winter Short-term Emergency Ampere
Rating also includes a maximum time duration applicable to each incident
where loading is above the Winter Emergency Ampere Rating but not in
excess of the Winter Short-term Emergency Ampere Rating.
1.46
Winter Short-term Emergency MVA Rating
An optional rating that applies to an entire two terminal Transmission
Circuit or to each leg of a three-terminal Transmission Circuit and is equal
to the lesser of i) the Winter Short-term Emergency Thermal MVA Rating
or ii) the Absolute Transmission Circuit Limit. The Winter Short-term
Emergency MVA Ratings must also include a maximum time duration
which is equal to the maximum time duration associated with the Winter
Short-term Emergency Thermal MVA Rating.
1.47
Winter Short-term Emergency Thermal MVA Rating
An optional rating that applies to an entire two terminal Transmission
Circuit or to each leg of a three-terminal Transmission Circuit and is equal
to the MVA that is transferred when i) the voltages are balanced, ii) the
voltage magnitudes are equal to the nominal operating voltage level, iii)
the phase currents are balanced, and iv) the phase current magnitudes are
equal to the Winter Short-term Emergency Ampere Rating. The Winter
Short-term Emergency Thermal MVA Ratings must also include a
maximum time duration which is equal to the maximum time duration
associated with the Winter Short-term Emergency Ampere Rating.
1.48
Winter Stressed Conductor Ampere Rating
12
Applies to a two-terminal Transmission Circuit or to each leg of a threeterminal Transmission Circuit and is equal to the maximum amount of
electrical current, expressed in amperes, that can be carried by each
Transmission Circuit Conductor on a sustained basis under i) winter
ambient temperatures and ii) wind conditions not more favorable than
wind speeds of 2.0 feet per second striking the conductor perpendicularly
without exceeding the Maximum Allowable Emergency Operating
Temperature.
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2.0 New Transmission Line Facilities
2.1 Transmission Proposal Request Specifications
Listed below are the minimum Transmission Proposal Request specifications for
New Transmission Line Facilities which will be included in all Transmission
Proposal Requests and additional Transmission Proposal Request specifications
for New Transmission Line Facilities which may be included in some
Transmission Proposal Requests depending on specific circumstances.
2.1.1
Minimum Transmission Proposal Request Specifications
The Transmission Proposal Request (TPR) shall always specify the
following requirements for each new Transmission Circuit associated with
a New Transmission Line Facility:
2.1.2

Nominal Operating kV

Terminal Locations (Substation and Transmission System Bus)

Minimum Summer Emergency Ampere Rating

Minimum Summer Emergency MVA Rating

Minimum Winter Emergency Ampere Rating

Minimum Winter Emergency MVA Rating
Additional Transmission Proposal Request Specifications
A Transmission Proposal Request (TPR) may specify the following
additional information for each new Transmission Circuit associated with
a New Transmission Line Facility when determined appropriate based on
specific circumstances:

Maximum Positive Sequence Impedance for Transmission Circuits.
This parameter will typically be specified under one of the following
two scenarios only:
o Transmission Circuits where planning reliability analyses
determines that potential voltage or stability issues are possible
based on excessive length of the circuit relative to the operating
voltage and/or the strength of the system at the terminals and
thus a maximum impedance constraint is required for the
Transmission Circuit.
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o Transmission Circuits where a maximum impedance constraint
is necessary to ensure the project performs as expected with
regard to congestion relief.

Multi-circuit Transmission Structures
The TPR may specify the use of structures with spare circuit positions
for a New Transmission Line Facility or specific portions thereof (such
as river crossings or congested areas). Specification of multi-circuit
structures may occur when there is a high probability of the need to
install an additional circuit in the future and incorporating spare
positions on the New Transmission Line Facility structures will
significantly reduce the cost of adding the future circuit. It is expected
that this practice will be limited to making sure existing structures can
be modified to accommodate additional circuits if and when needed.
For example, a single-circuit New Transmission Line Facility would
be specified to have sufficient right-of-way to add a second circuit and
would be constructed to facilitate adding the second circuit without
replacing any existing plant. For a monopole structure, this could be
accomplished by sizing poles so that additional davit arms could be
installed without replacing the existing poles or removing and
reinstalling the existing davit arms. For an H-frame structure, this
could be accomplished by sizing poles so that that a second circuit
could be installed under the first circuit without any modification to
the first circuit. Specifying future expansion flexibility in a TPR is
subject to applicable Federal, state, and local laws and regulations.

Fiber Optic Shield Wires
The use of fiber optic shield wires for communications assisted
protection schemes will be specified if required by the interconnecting
incumbent Transmission Owners that own the substation terminals.
2.2 Methods for Determining Minimum Design Requirements of New
Transmission Line Facilities
2.2.1
Minimum Transmission Circuit Emergency Load Ratings
Minimum emergency load ratings will be determined by MISO for
each Transmission Circuit associated with a New Transmission Line
Facility for both the summer and winter seasons.
2.2.1.1 Minimum Transmission Circuit Emergency Ampere
Ratings
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The minimum Transmission Circuit emergency ampere ratings
will be determined by MISO as follows:

Scenario 1: Single Interconnecting Transmission
Owner
If the new Transmission Circuit is connected to a single
incumbent Transmission Owner system at all terminals
and the incumbent Transmission Owner has a single
standard emergency ampere rating for newly
constructed Transmission Circuits at the applicable
voltage level, then the minimum emergency ampere
rating will be set equal to the Transmission Owner’s
standard emergency ampere rating.
If the new Transmission Circuit is connected to a single
incumbent Transmission Owner system at all terminals
and the incumbent Transmission Owner has multiple
standard emergency ampere ratings for newly
constructed Transmission Circuits at the applicable
voltage level, then the minimum emergency ampere
rating will be set equal to the greater of i) the
Transmission Owner’s lowest standard emergency
ampere rating and ii) the minimum emergency ampere
rating listed in Table 2 of Attachment A for the
applicable voltage level.
If the new Transmission Circuit is connected to a single
incumbent Transmission Owner system at all terminals
and the incumbent Transmission Owner has no standard
emergency ampere ratings for newly constructed
Transmission Circuits at the applicable voltage level,
then the minimum emergency ampere rating will be set
equal to the minimum emergency ampere rating listed
in Table 2 of Attachment A for the applicable voltage
level.
Should the Transmission Owner have one or more
standard emergency MVA rating levels for newly
constructed Transmission Circuits at the applicable
voltage level but no standard emergency ampere
ratings, MISO will infer standard emergency ampere
ratings based on the following formula:
Inferred Standard Ampere Rating
16
= (Standard MVA Rating * 1000)
/ (Nominal kV * 31/2)
(1)
It is important to note that MISO reserves the right to
specify a higher minimum emergency ampere rating
than what would be determined by the procedure above
if a higher minimum emergency ampere rating is
necessary to ensure the project adequately addresses the
Transmission Issues that drive the justification of the
project.

Scenario 2: Multiple Interconnecting Transmission
Owners
If the new Transmission Circuit is connected between
two different incumbent Transmission Owner systems
and each of the incumbent Transmission Owners have a
single standard emergency ampere rating for newly
constructed Transmission Circuits at the applicable
voltage level, then the minimum emergency ampere
rating will be set equal to the greatest of the individual
Transmission Owner’s standard emergency ampere
ratings.
If the new Transmission Circuit is connected between
two different incumbent Transmission Owner systems,
designated as TO System A and TO System B, and TO
System A has a single standard emergency ampere
rating for newly constructed Transmission Circuits at
the applicable voltage level while TO System B has
multiple standard emergency ampere ratings for newly
constructed Transmission Circuits at the applicable
voltage level, then the minimum emergency ampere
rating will be set equal to the greater of i) the standard
emergency ampere rating for the applicable voltage
level for TO System A , ii) the lowest standard
emergency ampere rating for the applicable voltage
level for TO System B, and iii) the minimum
emergency ampere rating listed in Table 2 of
Attachment A for the applicable voltage level.
If the new Transmission Circuit is connected between
two different incumbent Transmission Owner systems,
designated as TO System A and TO System B, and
each of the Transmission Owners have multiple
standard emergency ampere ratings for newly
17
constructed Transmission Circuits at the applicable
voltage level, then the minimum emergency ampere
rating will be set equal to the greater of i) the lowest
standard minimum emergency ampere rating for TO
System A for the applicable voltage level, ii) the lowest
standard minimum emergency ampere rating for TO
System B for the applicable voltage level, and iii) the
minimum emergency ampere rating listed in Table 2 of
Attachment A for the applicable voltage level.
If the new Transmission Circuit is connected between
two different incumbent Transmission Owner systems,
designated as TO System A and TO System B, and TO
System A has a single standard emergency ampere
ratings for newly constructed Transmission Circuits at
the applicable voltage level while TO System B has no
standard emergency ampere ratings for newly
constructed Transmission Circuits at the applicable
voltage level, then the minimum emergency ampere
rating will be set equal to the greater of i) the standard
minimum emergency ampere rating for TO System A
for the applicable voltage level and ii) the minimum
emergency ampere rating listed in Table 2 of
Attachment A for the applicable voltage level.
If the new Transmission Circuit is connected between
two different incumbent Transmission Owner systems,
designated as TO System A and TO System B, and TO
System A has multiple standard emergency ampere
ratings for newly constructed Transmission Circuits at
the applicable voltage level while TO System B has no
standard emergency ampere ratings for newly
constructed Transmission Circuits at the applicable
voltage level, then the minimum emergency ampere
rating will be set equal to the greater of i) the lowest
standard minimum emergency ampere rating for TO
System A for the applicable voltage level and ii) the
minimum emergency ampere rating listed in Table 2 of
Attachment A for the applicable voltage level.
If the new Transmission Circuit is connected between
two different incumbent Transmission Owner systems
and neither of the incumbent Transmission Owners
have standard emergency ampere ratings for newly
constructed Transmission Circuits at the applicable
voltage level, then the minimum emergency ampere
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rating will be set equal to the minimum emergency
ampere rating listed in Table 2 of Attachment A for the
applicable voltage level.
Should either or both of the Transmission Owners have
one or more standard emergency MVA rating levels for
newly constructed Transmission Circuits at the
applicable voltage level but no standard emergency
ampere ratings, MISO will infer standard emergency
ampere ratings based on the following formula:
Inferred Standard Ampere Rating
= (Standard MVA Rating * 1000)
/ (Nominal kV * 31/2)
(1)
It is important to note that MISO reserves the right to
specify a higher minimum emergency ampere rating
than the rating that would be determined by the
procedure above if a higher minimum emergency
ampere rating is necessary to ensure the project
adequately addresses the Transmission Issues that drive
the justification of the project.
2.2.1.2 Minimum Transmission Circuit Emergency Thermal MVA
Rating Requirements
The minimum Transmission Circuit emergency thermal MVA
ratings will be determined by MISO using the following
formulae:
SETMVA’ = (NOKV * SEAR’ * 31/2) / 1000
(2)
where
SETMVA’ = Minimum Summer Emergency Thermal
MVA Rating
NOKV = Nominal Operating kV ()
SEAR’ = Minimum Summer Emergency Ampere Rating
WETMVA’ = (NOKV * WEAR’ * 31/2) / 1000
where
19
(3)
WETMVA’ = Minimum Winter Emergency Thermal MVA
Rating
WEAR’ = Minimum Winter Emergency Ampere Rating
2.2.1.3 Minimum Transmission Circuit Emergency MVA Rating
Requirements
The minimum Transmission Circuit emergency MVA ratings will be
determined by MISO as the lesser of the emergency thermal MVA
ratings and the Voltage and Stability Loadability Rating. The Voltage
and Stability Loadability Rating will default to the Absolute
Transmission Circuit Limit unless planning studies determine that a
lower rating is appropriate for the Transmission Circuit to ensure
reliability and stability.1 In determining the Absolute Transmission
Circuit Limit, MISO will calculate it as equal to the estimated
Maximum Power Transfer Limit since the Relay Trip Load Level will
not yet be known2. The estimated Maximum Power Transfer Limit
will be determined by MISO as follows based on a worst case sendingend and receiving-end voltage magnitude of 0.95 per unit, an angular
displacement of 90, and the estimated positive sequence reactance
used to model the Transmission Circuit in the power flow and
production costs models:
MPTL* = 0.9025 * NOMKV2 / X1LINE*
(4)
where
MPTL* = Estimated Maximum Power Transfer Limit (MW)
X1LINE* = Estimated Positive Sequence Line Reactance ()3
The Absolute Transmission Circuit Limit will be set equal to the
estimated Maximum Power Transfer Limit and the Voltage & Stability
Loadability Rating will be set equal to the lesser of the Absolute
Transmission Circuit Limit and any voltage and stability limit
1
It is important to note that voltage and stability loadability limits are often applied to interfaces rather than
individual Transmission Circuits, and if planning studies determine that such a rating should be applied to an
interface as a result of the project rather than to the Transmission Circuit in question, the Voltage and Stability
Loadability Rating for the Transmission Circuit will default to the Absolute Transmission Circuit Limit.
2
This requires the substation terminal owners, who have the responsibility to protect the Transmission Circuit, to
design a protection system that is compliant with PRC-023-3 based on the minimum emergency load ratings
specified in the Transmission Proposal Request. This may necessitate the use of schemes other than the
substation owner’s standard schemes, such as schemes with non-load responsive relay elements or load
encroachment features.
3
In cases where MISO specifies a maximum positive sequence reactance in the Transmission Proposal Request for
the Transmission Circuit in question, this value will be set equal to the specified maximum reactance.
20
identified in the planning process. These calculations are summarized
by equations (5) and (6) as follows:
ATCL = MPTL*
(5)
where
ATCL = Absolute Transmission Circuit Limit
VSLR = Minimum {ATCL, PIVSL}
(6)
where
VSLR = Voltage & Stability Loadability Rating
PIVSL = Planning Identified Voltage and Stability Limit
NOTE: VSLR = ATCL if there is no PIVSL
The seasonal minimum emergency MVA ratings will be set equal to
the minimum of the appropriate seasonal minimum emergency thermal
MVA ratings and the Voltage & Stability Loadability Rating as
illustrated in equations (7) and (8) below:
SEMVA’ = Minimum {SETMVA’, VSLR}
(7)
where
SEMVA’ = Minimum Summer Emergency MVA Rating
WEMVA’ = Minimum {WETMVA’, VSLR}
(8)
where
WEMVA’ = Minimum Winter Emergency MVA Rating
2.2.2
Minimum Transmission Circuit Normal Load Ratings
The minimum Transmission Circuit normal load ratings will not be
specified by MISO in the Transmission Proposal Request. However,
the methodology that must be used by the New Transmission Proposal
Applicant to determine such ratings must adhere to the normal load
rating calculation methodology outlined in Sections 2.3.4 through
2.3.6 of this document.
2.2.3
Transmission Circuit Emergency Load Rating Duration
21
Transmission Circuit emergency load ratings are long-term emergency
ratings and as such will not be limited to any specific duration.
Therefore, in performing the risk assessment to determine Maximum
Allowable Emergency Operating Temperature, the New Transmission
Proposal Applicant must consider the probability of contingencies,
including the potential duration of such contingencies, that could risk
exposing the Transmission Circuit Conductor to temperatures in
excess of the Maximum Allowable Normal Operating Temperatures
for sustained periods of time should there be a prolonged contingency
duration4. For Transmission Circuits limited by Maximum Conductor
Sag Temperatures, there is no reason for a duration limit since the
method for calculating ratings assumes the conductor temperature, and
thus the conductor sag, has reached a new equilibrium state.
Therefore, no duration limitations shall be specified for emergency
load ratings with the exception that duration limitations can be
specified for the optional short-term ratings, if specified in New
Transmission Proposals, where such short-term ratings are designed to
allow time for short-term system adjustments following a contingency.
2.3 Requirements Applicable to New Transmission Proposal Applicants for
Specifying Design Parameters for New Transmission Line Facilities in New
Transmission Proposals
2.3.1
Calculation of Transmission Circuit Emergency Ampere Ratings
The emergency ampere rating of a Transmission Circuit shall be
driven solely by the selected conductor. Once the conductor is
selected and emergency ampere ratings are determined, all other load
carrying equipment and materials associated with the Transmission
Circuit, including jumpers, splices, other connectors, and Transmission
Circuit Switching Devices, must be selected with continuous ampere
ratings equal to or greater than the calculated emergency ampere rating
for the conductor. Substation Terminal Equipment is covered under a
different section of this document.
2.3.1.1 Required Conductor Rating Methodology
In developing New Transmission Proposals, New Transmission
Proposal Applicants must follow the methodology outlined in IEEE
4
There is no requirement for the Maximum Allowable Emergency Operating Temperature to be greater than the
Maximum Allowable Normal Operating Temperature (although it cannot be less), thus any decision to allow a
higher Maximum Allowable Emergency Operating Temperature and the selection of such a temperature must
consider the fact that there will be no expectation that emergency load ratings will be constrained to any specific
duration within the operating horizon.
22
738-2012 (or the version in effect at the time the Transmission
Proposal Request is posted) to calculate emergency ampere ratings for
Transmission Circuit Conductors. The New Transmission Proposal
Applicant must specify both a Summer Emergency Ampere Rating
and a Winter Emergency Ampere Rating. The Summer Emergency
Ampere Rating must be calculated assuming an ambient temperature
not less than 40C (104 F) whereas the Winter Emergency Ampere
Rating must be calculated assuming an ambient temperature not less
than 10C (50F). The actual ambient temperatures used must be
specified in the New Transmission Proposal Request and must comply
with the above minimum temperature requirements.
The Summer Emergency Ampere Rating shall be determined as the
lower of the Summer Conductor Sag Ampere Rating and the Summer
Stressed Conductor Ampere Rating. Likewise, the Winter Emergency
Ampere Rating will be determined as the lower of the Winter
Conductor Sag Ampere Rating and the Winter Stressed Conductor
Ampere Rating.
2.3.1.2 Conductor Sag Ampere Ratings
The Summer Conductor Sag Ampere Rating and the Winter Conductor
Sag Ampere Rating are based on the Maximum Conductor Sag
Temperature, which is the conductor temperature that results in
maximum allowable sag based on i) NESC vertical clearance
requirements, ii) the design of the Transmission Line, and iii) an
assumption that there is no wind available to aid conductor heat loss
and thus natural convection must be assumed in lieu of wind for
convective conductor heat loss. These two ratings differ only in the
ambient temperatures used to calculate the ratings.5 The rationale for
determining the Summer Conductor Sag Ampere Rating and the
Winter Conductor Sag Ampere Rating assuming a zero wind speed is
to ensure NESC clearance requirements are met at all times for all
possible combinations of wind speeds and wind/conductor angles, not
just for average or typical conditions.
The Summer Conductor Sag Ampere Rating shall be calculated based
on the following parameters:
o Maximum Conductor Sag Temperature
o Ambient Temperature of 40C (104 F)
o Wind Speed of 0.0 feet per second
5
The owner may elect to specify certain other variables differently for the winter and summer rating calculations
as well, such as the azimuth and altitude of the sun, but is not required to do so.
23
The Winter Conductor Sag Ampere Rating shall be calculated based
on the following parameters:
o Maximum Conductor Sag Temperature
o Ambient Temperature of 10C (50 F)
o Wind Speed of 0.0 feet per second
2.3.1.3 Stressed Conductor Ampere Ratings
The Summer Stressed Conductor Ampere Rating and the Winter
Stressed Conductor Rating are based on the Maximum Allowable
Emergency Operating Temperature and wind conditions determined
by the New Transmission Proposal Applicant but not more favorable6
than a wind speed of 2.0 feet per second striking the conductor
perpendicularly. The Maximum Allowable Emergency Operating
Temperature is the lesser of the Maximum Conductor Sag
Temperature and the maximum conductor temperature the New
Transmission Proposal Applicant is willing to allow based on a risk
assessment of potential accelerated conductor loss-of-life due to
excessive loss-of-strength or excessive creep elongation that may
occur over the life of the conductor when operating the conductor at
temperatures above the Maximum Allowable Normal Operating
Temperature from time to time. When the Maximum Allowable
Emergency Operating Temperature is equal to the Maximum
Conductor Sag Temperature, there is no need to calculate the stressed
conductor ratings since the conductor sag ampere ratings will be worst
case. When the Maximum Allowable Emergency Operating
Temperature is lower than the Maximum Conductor Sag Temperature,
then both the stressed conductor ampere ratings and the conductor sag
ampere ratings should be calculated and the lesser of the stressed
conductor ampere rating or the conductor sag ampere rating becomes
the emergency ampere rating
The Summer Stressed Conductor Ampere Rating is calculated based
on the following parameters:
o Maximum Allowable Emergency Operating Temperature
o Ambient Temperature of 40C (104 F)
o Wind conditions not more favorable than a wind speed of 2.0
feet per second striking the conductor perpendicularly
6
The phrase “not more favorable than” means that the wind conditions used by the New Transmission Proposal
Applicant to determine the stressed conductor ampere rating, if different than a wind speed of 2.0 feet per second
and a wind direction angle of 90 degrees with respect to the conductor direction, must not yield a higher
convective heat loss than would be calculated if a wind speed of 2.0 feet per second and a wind direction angle of
90 degrees were used with all other variables being the same.
24
The Winter Stressed Conductor Ampere Rating is calculated based on
the following parameters:
o Maximum Allowable Emergency Operating Temperature
o Ambient Temperature of 10C (50 F)
o Wind conditions not more favorable than a wind speed of 2.0
feet per second striking the conductor perpendicularly
2.3.2
Calculation of Actual Transmission Circuit Emergency Thermal
MVA Ratings
The actual Transmission Circuit emergency thermal MVA ratings will
be calculated by New Transmission Proposal Applicant using the
following formulae:
SETMVA = (NOKV * SEAR * 31/2) / 1000
(9)
where
SETMVA = Summer Emergency Thermal MVA Rating
SEAR = Summer Emergency Ampere Rating
WETMVA = (NOKV * WEAR * 31/2) / 1000
(10)
where
WETMVA = Winter Emergency Thermal MVA Rating
WEAR = Winter Emergency Ampere Rating
2.3.3
Calculation of Actual Transmission Circuit Emergency MVA
Ratings
The Transmission Circuit emergency MVA ratings will be calculated
by New Transmission Proposal Applicant using the following
formulae:
SEMVA = Minimum {SETMVA, VSLR}
where
SEMVA = Summer Emergency MVA Rating
25
(11)
VSLR = Voltage & Stability Loadability Rating determined by
MISO and specified in the Transmission Proposal
Request
WEMVA = Minimum {WETMVA, VSLR}
(12)
where
WEMVA = Winter Emergency MVA Rating
2.3.4
Calculation of Actual Transmission Circuit Normal Ampere
Ratings
The actual normal ampere ratings of a Transmission Circuit shall be
calculated in a similar manner as the emergency ampere ratings as
detailed in the sections below.
2.3.4.1 Required Conductor Rating Methodology
As with emergency ampere ratings, New Transmission Proposal
Applicants must follow the methodology outlined in IEEE 738-2012
(or the version in effect at the time the Transmission Proposal Request
is posted) to calculate normal ampere ratings for Transmission Circuit
Conductors. The New Transmission Proposal Applicant must specify
both a Summer Normal Ampere Rating and a Winter Normal Ampere
Rating. The Summer Normal Ampere Rating must be calculated
assuming an ambient temperature not less than 40C (104 F) whereas
the Winter Normal Ampere Rating must be calculated assuming an
ambient temperature not less than 10C (50F). The actual ambient
temperatures used must be specified in the Transmission Proposal
Request and must comply with the above minimum temperature
requirements.
The Summer Normal Ampere Rating shall be determined as the lower
of the Summer Conductor Sag Ampere Rating and the Summer
Continuous Conductor Ampere Rating. Likewise, the Winter Normal
Ampere Rating will be determined as the lower of the Winter
Conductor Sag Ampere Rating and the Winter Continuous Conductor
Ampere Rating. The conductor sag ratings used to determine the
normal ampere ratings are the same as the ones used to determine the
emergency ampere ratings.
2.3.4.2 Continuous Conductor Ampere Ratings
The Summer Continuous Conductor Ampere Rating and the Winter
Continuous Conductor Ampere Rating are based on the Maximum
26
Allowable Normal Operating Temperature and wind conditions
determined by the New Transmission Proposal Applicant but not more
favorable7 than a wind speed of 2.0 feet per second striking the
conductor perpendicularly. The Maximum Allowable Normal
Operating Temperature is the lesser of the Maximum Conductor Sag
Temperature and the conductor temperature that will result in a loss of
tensile strength of not more than 10% over a 40 year lifespan for the
Transmission Circuit if the conductor is continuously exposed to this
temperature. When the Maximum Allowable Normal Operating
Temperature is equal to the Maximum Conductor Sag Temperature,
there is no need to calculate the continuous conductor ampere ratings
since the conductor sag ratings will be worst case and thus the normal
and emergency ampere ratings will be equal to the conductor sag
ampere ratings. When the Maximum Allowable Normal Operating
Temperature is lower than the Maximum Conductor Sag Temperature,
then the continuous conductor ampere ratings should be calculated and
the lesser of the continuous conductor ampere ratings or the conductor
sag ampere ratings become the normal ampere ratings
The Summer Continuous Conductor Ampere Rating is calculated
based on the following parameters:
o Maximum Allowable Normal Operating Temperature
o Ambient Temperature of 40C (104 F)
o Wind conditions not more favorable than a wind speed of 2.0
feet per second striking the conductor perpendicularly
The Winter Continuous Conductor Ampere Rating is calculated based
on the following parameters:
o Maximum Allowable Normal Operating Temperature
o Ambient Temperature of 10C (50 F)
o Wind conditions not more favorable than a wind speed of 2.0
feet per second striking the conductor perpendicularly
2.3.5
Calculation of Actual Transmission Circuit Normal Thermal
MVA Ratings
The actual Transmission Circuit normal thermal MVA ratings shall be
calculated by New Transmission Proposal Applicant using the
following formulae:
7
The phrase “not more favorable than” means that the wind conditions used by the New Transmission Proposal
Applicant to determine the continuous conductor ampere rating, if different than a wind speed of 2.0 feet per
second and a wind direction angle of 90 degrees with respect to the conductor direction, must not yield a higher
convective heat loss than would be calculated if a wind speed of 2.0 feet per second and a wind direction angle of
90 degrees were used with all other variables being the same.
27
SNTMVA = (NOKV * SNAR * 31/2) / 1000
(9)
where
SNTMVA = Summer Normal Thermal MVA Rating
SNAR = Summer Normal Ampere Rating
WNTMVA = (NOKV * WNAR * 31/2) / 1000
(10)
where
WNTMVA = Winter Normal Thermal MVA Rating
WNAR = Winter Normal Ampere Rating
2.3.6
Calculation of Actual Transmission Circuit Normal MVA Ratings
The actual Transmission Circuit normal MVA ratings shall be
calculated by New Transmission Proposal Applicant using the
following formulae:
SNMVA = Minimum {SNTMVA, VSLR}
(11)
where
SNMVA = Summer Normal MVA Rating
VSLR = Voltage & Stability Loadability Rating determined by
MISO and specified in the Transmission Proposal
Request
WNMVA = Minimum {WNTMVA, VSLR}
(12)
where
WNMVA = Winter Normal MVA Rating
2.3.7
Transmission Line Design Standards
As stated in the tariff, each New Transmission Line Facility must be
designed and constructed to satisfy all relevant federal, state, and
local laws, regulations, industry standards, Good Utility Practice, and
building codes including the National Electric Safety Code in effect at
the time the New Transmission Line Facility is place into service. All
28
New Transmission Lines Facilities must be designed and constructed
to meet or exceed the requirements within the National Electric
Safety Code applicable to Grade B construction. With regard to
weather assumptions, all New Transmission Line Facilities must be
designed to meet all weather assumptions applicable to all regions, as
defined and stated in the National Electric Safety Code, in which the
New Transmission Line Facility will be located. All New
Transmission Line Facilities must be designed and constructed to
satisfy all clearance requirements specified within the National
Electric Safety Code for load levels within the minimum specified
load ratings.
29
3.0 New Substation Facilities
3.1 Transmission Proposal Request Specifications
Listed below are the minimum Transmission Proposal Request specifications for
New Substation Facilities which will be included in all Transmission Proposal
Requests and additional Transmission Proposal Request specifications for New
Substation Facilities which may be included in some Transmission Proposal
Requests depending on specific circumstances.
3.1.1
Minimum Transmission Proposal Request Specifications
The Transmission Proposal Request (TPR) shall always specify the
following requirements for each New Substation Facility:

Bus-branch planning one-line diagram showing all Transmission
System Buses, Transmission Circuit terminals, Generation Element
terminals, Transmission Transformers, Series Compensation Devices,
Shunt Compensation Devices, HVDC Converters, and loads.

Transmission System Bus voltage characteristics and nominal
operating kV.

Transmission Transformer size, impedance, and phase shift
requirements.

Series Compensation Device minimum normal and emergency load
ratings, impedance range requirements, and bypass requirements.

Shunt Compensation Device size requirements

Circuit Breaker Assembly minimum load ratings and circuit breaker
interrupting ratings for each acceptable bus configuration alternative
specified in the TPR.

Transmission Physical Bus minimum normal and emergency load
ratings for acceptable bus configuration alternatives that contain one or
more Transmission Physical Buses.

Minimum protection system redundancy, speed, and other
requirements for protection schemes that do not interface with
incumbent Transmission Owners (e.g., bus protection, transformer
protection, etc.)
30
3.1.2

High level protection system requirements for protection schemes that
will interface with incumbent Transmission Owner schemes (e.g., line
protection, etc.).

Breaker failure protection system requirements
Additional Transmission Proposal Request Specifications
A Transmission Proposal Request (TPR) may specify the following
additional information for each New Substation Facility when determined
appropriate based on specific circumstances:

List of acceptable bus configurations and/or position assignment
constraints for each Transmission System Bus.

Transmission Transformer no-load and/or load tap changing
requirements

Transmission Transformer winding connection requirements.
3.2 Methods for Determining Minimum Design Requirements of New Substation
Facilities
3.2.1
Minimum Transmission Physical Bus Load Ratings
3.2.1.1 Straight Buses
For straight buses, the load ratings for Transmission Physical
Buses will be based on i) the minimum ratings associated with
each Transmission Element, Generation Element, and
transmission load that connects directly to the Transmission
Physical Bus and ii) an allowance for substation expansion.
The formulae below will be used to determine the minimum
emergency and normal ampere ratings applicable to the
Transmission Physical Bus if it is a straight bus:
TPBEAR = 1.25 * {EAR(i) } / 2
i
where
TPBEAR = Transmission Physical Bus Emergency
Ampere Rating
31
(13)
i = Index of ultimately planned Transmission Elements,
Generation Elements, and transmission loads
connecting directly to the Transmission Physical
Bus
EAR(i) = Emergency Ampere Rating for Transmission
Element, Generation Element, or
transmission load i
TPBNAR = 1.25 * {NAR(i) } / 2
i
(14)
where
TPBNAR = Transmission Physical Bus Normal
Ampere Rating
NAR(i) = Normal Ampere Rating for Transmission
Element, Generation Element, or
transmission load i
In the formulae above, the ratings of each of the connecting
element are summed and then divided by two (2) to represent
the theoretical maximum amount of flow that could pass
through the worst-case section of the bus for any possible
position assignment. The 125% factor is also applied to allow
for future substation expansion above and beyond the ultimate
plan for the substation.
For example, assume a straight bus terminates three 230 kV
circuits, each of which have a Summer Emergency Ampere
Rating of 1,200 A and a Summer Normal Ampere Rating of
900 A. The emergency and normal ampere ratings of the bus
would be calculated as follows:
TPBEAR = 1.25 * (3*1200A) / 2 = 2,250 A
TPBNAR = 1.25 * (3*900A) / 2 = 1,688 A
3.2.1.2 Double Buses
For double bus configurations (i.e., breaker-and-a-half, doublebus / double-breaker, or a combination of the two, etc.), the
load ratings for Transmission Physical Buses will be based on
i) the minimum ratings associated with each Transmission
Element, Generation element, and transmission load connected
32
within the bus configuration and ii) an allowance for substation
expansion. .
The formulae below will be used to determine the minimum
emergency and normal ampere ratings applicable to the
Transmission Physical Bus if it is one of the two Transmission
Physical Buses in a double-bus configuration:
TPBEAR = 1.25 * {EAR(i) } / 4
i
(15)
where
TPBEAR = Transmission Physical Bus Emergency Ampere
Rating
i = Index of ultimately planned Transmission Elements,
Generation Elements, and transmission loads connecting
within the double-bus configuration associated with the
Transmission Physical Bus
EAR(i) = Emergency Ampere Rating for Transmission
Element, Generation Element, or transmission load i
TPBNAR = 1.25 * {NAR(i) } / 4
i
(16)
where
TPBNAR = Transmission Physical Bus Normal Ampere
Rating
NAR(i) = Normal Ampere Rating for Transmission Element,
Generation Element, or transmission load i
In the formulae above, the ratings of each element are summed
and then divided by four (4) to represent the theoretical
maximum amount of flow that could pass through the worstcase section of either Transmission Physical Bus assuming a
50/50 split8 in total flows between the two Transmission
Physical Buses. The 125% factor is used to allow for future
8
While a 50/50 split in flows is not worst case, it is also not best case for breaker-and-a-half bus configurations
since some of the flows through the substation will not go through either Transmission Physical Bus if adjacent
positions in a three-break string have flows in opposite directions. Furthermore, it is expected that position
assignment constraints will be specified in the TRP to offset any concerns of assuming a 50/50 flow split between
Transmission Physical Buses.
33
substation expansion above and beyond the ultimate plan for
the substation as well as help account for situations where flow
split between Transmission Physical Buses is something other
than 50/50.
For example, assume a five position breaker-and-a-half bus
terminated four 345 kV circuits, each of which had a Summer
Emergency Ampere Rating of 3,000 A and a Summer Normal
Ampere Rating of 2500 A, and the 345 kV winding terminal of
a Transmission Transformer with a maximum nameplate rating
of 700 MVA (1,172A @ 345 kV). The emergency and normal
ampere ratings of the bus would be calculated as follows:
TPBEAR
= 1.25 * ((4*3000A) + 1172A) / 4 = 4,117 A
TPBNAR
= 1.25 * ((4*2500A) + 1172A) / 4 = 3,492 A
3.2.2
Minimum Circuit Breaker Assembly Load Ratings
Minimum Circuit Breaker Assembly load ratings shall apply to all circuit
breakers within the ring bus configurations and double-bus configurations
as well as bus-tie breakers connecting two or more straight buses.
Minimum Circuit Breaker Assembly load ratings do not apply to non-bustie breakers connecting Transmission Elements or Generation Elements to
straight buses since these circuit breakers would be considered Substation
Terminal Equipment for the connecting Transmission Element or
Generation Elements.
3.2.2.1 Ring Bus Configuration
If a ring bus configuration is included in the Transmission Proposal as
an acceptable bus configuration option for a specific Transmission
System Bus within a specific New Substation Facility, then the default
minimum rating for all Circuit Breaker Assemblies within the ring bus
will be set equal to the industry standard Terminal Equipment Rating
Class ampere rating that is closest to, but not less than, the highest
minimum emergency rating associated with any Generation Element
or Transmission Element connected to the ring bus regardless of
whether or not the Circuit Breaker Assembly is adjacent to the element
with the highest minimum emergency rating. For example, if a 345
kV ring bus connects to three Transmission Circuits, each with a
minimum Summer Emergency Ampere Rating of 1,792 MVA (3,000
A), and one Transmission Transformer winding terminal with a
maximum nameplate rating of 2,250 MVA (3,766 A at 345 kV), then
34
each Circuit Breaker Assembly within the ring bus must be rated at
4,000 amperes, which is the Terminal Equipment Rating Class just
above 3,766 A.
MISO reserves the right, on a case-by-case basis, to provide position
assignment constraints and/or higher minimum Circuit Breaker
Assembly ratings if analysis performed within the top-down planning
process determines such additional constraints are appropriate.
3.2.2.2 Breaker-and-a-Half Bus Configurations
If a breaker-and-a-half bus configuration is included in the
Transmission Proposal Request as an acceptable bus configuration
option for a specific Transmission System Bus within a specific New
Substation Facility, then the default minimum rating for all Circuit
Breaker Assemblies within a single three-breaker string between two
main buses must be set equal to the industry standard Terminal
Equipment Rating Class ampere rating that is closest to, but not less
than, the highest minimum emergency rating associated with either of
the two Generation Elements and/or Transmission Elements
connected to the breaker string regardless of whether or not the Circuit
Breaker Assembly is adjacent to the element with the highest
minimum emergency rating. For example, if a three-breaker string in
a 500 kV breaker-and-a-half bus terminates a Transmission Circuit
with a minimum Summer Emergency Ampere Rating of 2,598 MVA
(3,000 A) and a Generation Element with a nameplate rating of 850
MVA (982 A @ 500 kV), then each Circuit Breaker Assembly within
the three-break string must be rated at 3,000 amperes.
MISO reserves the right, on a case-by-case basis, to provide position
assignment constraints and/or higher minimum Circuit Breaker
Assembly ratings if analysis performed within the top-down planning
process determines such additional constraints are appropriate.
3.2.2.3 Double-Bus / Double Breaker Bus Configurations
If a double-bus / double-breaker bus configuration is included in the
Transmission Proposal Request as an acceptable bus configuration
option for a specific Transmission System Bus within a specific New
Substation Facility, then the default minimum rating for the two
Circuit Breaker Assemblies that terminate a single Transmission
Element or Generation Element must be set equal to the industry
standard Terminal Equipment Rating Class ampere rating that is
closest to, but not less than, the minimum emergency rating associated
with the Generation Element or Transmission Element being
terminated. For example, if two Circuit Breaker Assemblies in a 765
35
kV double-bus / double-breaker bus configuration terminate a
Transmission Circuit with a minimum Summer Emergency Ampere
Rating of 3,975 MVA (4,000 A), then each Circuit Breaker Assembly
terminating the Transmission Circuit must be rated at 4,000 amperes.
If that same bus configuration also terminates a Transmission
Transformer with a nameplate rating of 2,250 MVA (1,698 A @ 765
kV), then each Circuit Breaker Assembly terminating the
Transmission Transformer 765 kV winding terminal must be rated at
3,000 amperes, which is the next highest industry standard Terminal
Equipment Rating Class ampere rating.
3.2.3
Minimum Transmission Circuit Substation Terminal Equipment
Ampere Ratings
For substation terminals at New Substation Facilities that terminate
Transmission Circuits associated with a New Transmission Line Facility,
the Transmission Proposal Request will specify minimum Substation
Terminal Equipment Ampere Ratings equal to the industry standard
Terminal Equipment Rating Class ampere rating that is closest to, but not
less than, the minimum Summer Emergency Ampere Rating specified in
the Transmission Proposal Request for the Transmission Circuit associated
with the New Transmission Line Facility. For substation terminals at New
Substation Facilities that terminate Transmission Circuits associated with
existing transmission line facilities (e.g., an existing Transmission Circuit
is cut into a New Substation Facility at the midpoint creating two new
Transmission Circuits, but no New Transmission Line Facility is specified
in the Transmission Proposal Request other than the taps), the
Transmission Proposal Request will specify minimum Substation
Terminal Equipment Ampere Ratings equal to the industry standard
Terminal Equipment Rating Class ampere rating that is closest to, but not
less than, the maximum ampere rating of the existing Transmission Circuit
as defined by the incumbent Transmission Owner. For substation
terminals at New Substation Facilities that terminate Transmission
Circuits that represent a combination of existing transmission line
facilities and New Transmission Line Facilities (e.g., a new Transmission
Circuit is created by building a 30 mile New Transmission Facility and
then installing another 30 miles of conductor on the spare positions of an
existing transmission line facility, etc.), the Transmission Proposal
Request will specify minimum Substation Terminal Equipment Ampere
Ratings equal to the industry standard Terminal Equipment Rating Class
ampere rating that is closest to, but not less than, the greater of the
maximum ampere rating of the portion of the Transmission Circuit
installed as an upgrade to existing transmission facilities as defined by the
incumbent Transmission Owner and the minimum Summer Emergency
Ampere Rating specified in the Transmission Proposal Request for the
New Transmission Line Facility. It is expected that these two ratings will
36
be equivalent. In all cases, MISO will specify the minimum Substation
Terminal Equipment Ampere Rating in the Transmission Proposal
Request for all Transmission Circuit terminals located at a New Substation
Facility.
3.2.4
Minimum Generation Element Substation Terminal Equipment
Ampere Ratings
All Substation Terminal Equipment associated with a Generation Element
at a New Transmission Substation must have an ampere rating greater than
or equal to the lesser of the maximum nameplate rating (expressed in
amperes at the transmission interconnection voltage level) of all
generators associated with the Generation Element or the maximum
nameplate rating (expressed in amperes at the transmission
interconnection voltage level) of all generator step-up (GSU) transformers.
For example, if a combined cycle generating units has a total of three 100
MW generators (two gas turbine driven and one steam turbine driven) and
each generator has a maximum nameplate MVA of 120 MVA, the total
generator MVA would be 360 MVA. If the generators connect to a 345
kV bus via three 112 MVA GSU transformers, then the total GSU MVA
would be 336 MVA. The minimum Substation Terminal Equipment
Ampere Rating of the substation terminal would be equal to the industry
standard Terminal Equipment Rating Class ampere rating that is closed to,
but not less than, the maximum nameplate rating of the 345 kV GSU
windings, expressed in amperes. The 345 kV GSU ampere ratings would
be calculated as follows:
GSU HS Ampere Rating
= (336 MVA * 1000) / (345 kV * 31/2 ) = 562 A
Therefore, the minimum Substation Terminal Equipment Ampere Rating
would be specified as 2,000 A.
3.2.5
Transmission Transformer Size and Impedance Requirements
When a New Substation Facility contains one or more proposed
Transmission Transformers, it is first necessary to determine the optimal
range of transformer impedances that will best optimize the flow impacts
of the new transformer in terms of congestion benefit and future
robustness. For a given location, when a proposed Transmission
Transformer is specified with a higher series impedance magnitude, there
is less congestion relief on parallel facilities, but also less loading impact
on series facilities (including the proposed Transmission Transformer
itself). When a proposed Transmission Transformer is specified to have a
lower series impedance magnitude, there is more congestion relief on
37
parallel facilities, but also more loading impact on series facilities.
Therefore, the process of specifying transformer size and impedance
requirements is to first find the best range of impedance magnitudes to
give ample congestion relief on parallel facilities without introducing
significant congestion on series facilities. To do this, the top-down
planning process will test multiple transformer impedances within the
production cost models and power flow models to find the “sweet spot”
that provides the greatest overall benefits. Once the right range of
impedances has been determined, the next step is to determine the size of
the Transmission Transformer (or set of parallel Transmission
Transformers) that will feasibly provide this impedance. In addition, the
Transmission Transformer must be sized to provide the necessary capacity
plus a margin for growth. Typical impedance ranges for Transmission
Transformers are in the 5% to 10% range at an MVA base equal to the
ONAN rating of the transformer. To avoid specialized transformers that
may also need specialized spares, MISO will constrain available
Transmission Transformer options to the impedance range above to
determine suitable candidates for a Transmission Transformer. Finally,
cost considerations and size requirements will be considered to select the
best overall combination of size and impedance for the Transmission
Transformer, and these parameters will specified in the Transmission
Proposal Request.
Example. A solution idea has been submitted to the top-down planning
process to install a New Substation Facility with a Transmission
Transformer to interconnect an existing east-west 345 kV line with both
circuits of an existing north-south double-circuit 161 kV line at the point
where the two transmission lines physically cross each other. A number
of potential transformer impedances are tested in the production cost
models and power flow models, and the best range of impedances for the
transformer is found to be in the 3.0% to 4.0% @ 100 MVA range (100
MVA is the base used in the power flow and production cost models).
Impedances below 3.0% begin to cause congestion on series elements on
the 161 kV system and impedances above 4.0% do not remove adequate
congestion on parallel elements on the 161 kV system. The highest
unconstrained9 contingent flows simulated for the transformer impedances
for various impedance levels are as follows:





3.0%:
3.25%:
3.5%:
3.75%:
4.0%
279 MW
248 MW
223 MW
179 MW
168 MW
9
The transformer impedance flow is unconstrained, but the rest of the system is constrained to fully test the
economic benefits of the various transformer impedances
38
To ensure adequate capacity under a robust set of futures, it is decided that
the minimum Transmission Transformer size to be pursued is a 300 MVA
unit. The best economic performance resulted when a transformer
impedance of 3.5% @ 100 MVA was simulated. Upon inspection of
Tables 3A through 3N and targeting an impedance of 3.5% @ 100 MVA,
the following possible Transmission Transformer options are available:




180/240/300 MVA with Z = 6.25% @ 180 MVA (Table 3N)
201.6/268.8/336 MVA with Z = 7.0% @ 201.6 MVA (Table 3M)
240/320/400 MVA with Z = 8.5% @ 240 MVA (Table 3L)
268.8/358.4/448 MVA with Z = 9.5% @ 268.8 MVA (Table 3K)
Other potential options would include paralleling two smaller units (e.g.,
two 168 MVA units, etc.) or adding a larger unit with a smaller nameplate
impedance and then adding a series reactor to optimize flows, but these
options were not investigated due to the higher cost. Considering
impedance requirements, capacity requirements, and costs, the 336 MVA
transformer with a nameplate impedance of 7.0% @ 201.6 MVA is
selected as the best overall option. This transformer size and impedance
would be specified in the Transmission Proposal Request, with industry
standard impedance tolerances equal to +/- 7.5% of the specified
impedance (i.e., which equates to a range of approximately 6.5% to 7.5%
@ 201.6 MVA)
3.2.6
Bus Configuration and Position Assignment Constraints
MISO may specify bus configuration and/or position assignment
constraints in the Transmission Proposal Request to ensure a reliable and
robust system that provides operational flexibility. Table 4A, 4B, and 4C
in Attachment A provides a guideline that will be used in determining
acceptable bus configuration for specific Transmission System Buses
contained within proposed New Substation Facilities. This guideline
reflects the following guiding principles which will also drive bus
configuration specifications and position assignment constraints outlined
in a Transmission Proposal Request:

Straight buses will not be permitted for EHV voltage levels

The maximum number of Transmission Circuits that can be
terminated on a single-zone straight bus is two.

The maximum number of Transmission Circuits that can be
terminated on a double-zone straight bus is four, two on each side
of the tie-breaker.
39

The maximum number of Generation Elements and/or
Transmission Elements that can be terminated on a single-zone
straight bus is three, of which not more than two can be
Transmission Circuits.

The maximum number of Generation Elements and/or
Transmission Elements that can be terminated on a double-zone
straight bus is six, three on each side of the tie-breaker.

Ring buses will not be permitted to terminate more than four
Transmission Circuits

Ring buses will not be permitted to terminate more than six
Generation Elements and Transmission Elements, of which not
more than four can be Transmission Circuits

When two parallel Transmission Transformers are connected to the
same ring bus, they must not be terminated on adjacent positions
unless the ring bus has only three (3) total positions.

When two Generation Elements are connected to the same ring
bus, they must not be terminated on adjacent positions, unless the
ring bus only has (3) three total positions.

When two parallel Transmission Circuits are connected to the
same ring bus, they must not be terminated on adjacent positions,
unless the ring bus only has three (3) total positions.

Double bus-configurations include pure breaker-and-a-half, pure
double-bus / double-breaker, and a combination of the two.

A pure breaker-and-a-half bus must have an even number of
positions with a minimum of 6 (six).

A breaker-and-a-half bus cannot have fewer than five (5) positions,
one of which is a double-breaker position, otherwise it is a ring bus
with open positions.

When two parallel Transmission Transformers are connected to a
breaker-and-a-half bus, they must not share a common circuit
breaker (i.e., terminate on adjacent positions on the same breaker
string).

When two Generation Elements are connected to the same breakerand-a-half bus, they must not share a common circuit breaker.
40

3.2.7
When two parallel Transmission Circuits are connected to the
same breaker-and-a-half bus, they must not be share a common
circuit breaker.
Minimum Circuit Breaker Interrupting Ratings
Minimum interrupting ratings for circuit breakers will be determined by
MISO during the reliability analysis component of the top-down planning
process. MISO will specify minimum interrupting ratings based on the
industry standard symmetrical interrupting rating that is closest to, but not
less than, 125% of the maximum fault exposure for a specific circuit
breaker. The industry standard interrupting ratings MISO will used are
listed in Table 5 of Attachment A. The 125% factor allows for growth of
the system (both in terms of new Generation Elements and new
Transmission Elements) that will likely push the bus fault current levels
up over time. The maximum fault exposure for a specific circuit breaker
will be determined as the greater of the maximum calculated symmetrical
fault current that flows through the circuit breaker given a short-circuit
fault on either of the two terminals of the circuit breaker. Calculation of
this fault current assumes i) all Generation Elements are in service10, all
Transmission Elements are in their normal configuration (for most
Transmission Elements, this means in service), and iii) if the short-circuit
fault is being simulated within a protective zone that is supplied by more
than one circuit breaker, all other circuit breakers supplying that protective
zone are open. The short-circuit fault type with the highest current
magnitude will be used, which is generally the three-phase bolted fault,
but can sometimes be a bolted fault phase-to-ground fault depending on
the relative magnitudes of the Thevenin equivalent positive sequence and
zero sequence bus impedances at the fault location. Several examples may
help to clarify the type of analysis that MISO will perform to determine
circuit breaker interrupting capability requirements.
Example 1. A single 230 kV circuit breaker protects a 230 kV capacitor
bank and associated bus work and is supplied by a straight bus. The
maximum bus fault current at the circuit breaker terminals is 21,934 A.
Because there is only one circuit breaker supplying the capacitor bank, the
maximum bus fault current at the circuit breaker terminals represents the
maximum fault exposure of the circuit breaker. That is, the capacitor bank
contributes no fault current to the short-circuit fault, thus for a fault on the
capacitor-side of the circuit breaker, the circuit breaker will be exposed to
a fault current magnitude equal to the maximum bus fault current and for a
fault on the bus-side of the circuit breaker, the circuit breaker will carry no
fault current. The lower bound for the minimum symmetrical interrupting
rating of the circuit breaker is 125% of 21,934 A or 27,418 A. Therefore,
10
The worst case assumption that all generation is in service is a standard assumption used in short-circuit studies
including breaker duty studies.
41
a circuit breaker with a minimum interrupting rating of 31.5 kA will be
specified in the Transmission Proposal Request.
Example 2. A 500 kV circuit breaker is located in a four-position 500 kV
ring bus between two Transmission Circuits that terminate on the ring bus
designated as Circuit A and Circuit B. The maximum bus fault current at
the ring bus is 34,583 A. However, neither of these circuit breakers will
ever be exposed to this fault current level regardless of which terminals of
the circuit breaker are faulted since there are parallel paths to the fault that
do not flow through the circuit breaker. The worst case scenario for a
fault on Circuit A is to assume all other circuit breaker supplying Circuit
A are open. This includes the other circuit breaker at the substation that
connects to Circuit A and all remote circuit breakers that connect to
Circuit A. This scenario is representative of a scenario where the circuit
breaker in question is slightly slower than the other circuit breakers or the
other circuit breaker happen to be open for maintenance or other reasons.
While the total fault current is reduced for this scenario, the fault current
flow through the circuit breaker represents 100% of this reduced fault
current and is higher than what it would be with the circuit breakers
closed.11 Assume under this scenario that the fault current through the
circuit breaker is equal to 28,345 A (based on the output of a bus/branch
short-circuit fault study program where the opposite terminal is opened
and the new bus fault current magnitude corresponds to the fault current
that would flow through the circuit breaker in question with all other
Circuit A circuit breakers open). If the 125% factor is applied to this fault
current, the tentative lower bound for the minimum required interrupting
rating becomes 125% of 28,345 A or 35, 432A. This is a tentative lower
bound because it is also necessary to check the scenario where the shortcircuit fault occurs on the Circuit B terminals of the circuit breaker. If the
same process is applied for a short-circuit fault on Circuit B and the
resulting fault current is simulated to be 29,667 A, the 125% factor must
be applied to this fault current level (since it is greater than the Circuit A
fault current level) to determine the final lower bound for the required
minimum interrupting rating. The lower bound for the minimum
interrupting rating is determined to be 37,084A, and thus a minimum
interrupting rating of 40 kA is specified in the Transmission Proposal
Request.
Example 3. A 345 kV circuit breaker within a six-position 345 kV
breaker-and-a-half bus scheme is located between one of the Transmission
Physical Buses and one of the Transmission Circuits that terminate at the
bus. The maximum bus fault current at the circuit breaker terminals is
35,932 A. It can be reasoned that the worst case fault will be a fault on the
11
The notion that the maximum fault current through a line circuit breaker occurs when the remote terminal is
open is a fully accepted principle in the industry and can easily be proven using two-bus equivalent short-circuit
models. The same method is used for circuit breakers protecting Transmission Transformer windings.
42
bus-side terminals of the circuit breaker with all other circuit breakers
supplying the bus in an open position. The reason is because opening the
other circuit breakers connected to the bus does not alter the bus/branch
topology of the system (all elements are still connected through the other
Transmission Physical Bus). Therefore, a bus fault with all other bus
breakers open will still result in a fault current magnitude through the
circuit breaker equal to the maximum bus fault current, or 35,932 A. It is
thus not necessary to investigate a line-side terminal fault on the circuit
breaker, as this fault current will be less than the maximum available fault
current at the bus, even with all of the other circuit breakers supplying the
faulted Transmission Circuit in an open position. The 125% factor is then
applied to the maximum bus fault current of 35,932 A to yield a lower
bound on the minimum interrupting rating equal to 44,915 A. The
resulting minimum interrupting rating for this circuit breaker, and all other
circuit breakers at the substation that connect directly to one of the
Transmission Physical Buses, is 50 kA.
3.2.8
System Protection Requirements
For any New Substation Facility included in the scope of an Open
Transmission Project, the following minimum system protection,
metering, and control design standards apply.
3.2.8.1 System Protection Requirements for Facilities that
Interconnect to Existing Incumbent Transmission Owners
For Transmission Circuits and other facilities with protective
zones that are shared with existing incumbent Transmission
Owners (i.e., facilities that represent ties between existing
substations owned by incumbent Transmission Owners and
New Substation Facilities, etc.), the incumbent Transmission
Owner will determine the design requirements for system
protection, metering, and controls that are specific to that
facility. Specifically, the incumbent Transmission Owner will
specify the following data to be included in the Transmission
Proposal Request:

System protection redundancy requirements (e.g.,
instrument transformers, protective relays, auxiliary
relays and DC trip circuitry, communications, battery
systems, etc.)

Type of system protection scheme(s) to be used (e.g.,
DCB, DCUB, POTT, PUTT, phase comparison, line
differential, etc.).
43

Type of communications channel used in protection
systems (e.g., power line carrier, fiber optic,
microwave, etc.)

Characteristics of communications signals used in
Transmission Circuit protection systems (e.g., type of
modulation, frequencies, etc.)

Characteristics of transfer trip signals used for breaker
failure protection.

Type of automatic reclosing system and characteristics
(e.g., number of shots, reclosing times, high-speed
reclosing capability, conditions for reclosing, etc.).
3.2.8.2 System Protection Requirements for Facilities that do not
Interconnect Directly with Existing Substations owned by
Incumbent Transmission Owners
For facilities with protective zones that are not shared with
incumbent Transmission Owners or Generation Owners (i.e.,
facilities entirely within a New Substation Facility or facilities
that interconnect two New Substation Facilities, etc.), the
following minimum design standards for system protection,
metering, and control shall apply:

Substation Buses
Substation buses include straight buses and each of the
buses associated with a double-bus configuration.
Buses shall be protected by high speed differential
(87) protective relaying systems that will initiate
tripping (where “initiate tripping” is defined as the
pickup of the first protective relay element that
initiates tripping) within 2 cycles or less for shortcircuit faults located within the bus protective zones.
Bus protection systems must contain two redundant
protection schemes including redundant current
transformers, redundant DC sources (a battery and
battery charger are not considered a redundant DC
source), redundant protective relays, redundant
auxiliary and/or lockout relays, and redundant DC trip
circuitry (including redundant trip coils on each circuit
breaker or circuit breaker pole). Bus protection relays
should trip lockout (86) relays and shall not initiate
automatic reclosing on any circuit breaker. Lockout
44
relays should hold trip signals on each circuit breaker
protecting the bus and open closing circuits on each
circuit breaker protecting the bus. Bus protective
relays should initiate breaker failure for all circuit
breakers tripped. If the highest bus fault current for
which any one circuit breaker could be exposed is
determined to be 90% or greater of the knee-point
current in any CT saturation curve, a high-impedance
bus differential relay scheme shall be used.

Transmission Transformers
Transmission transformers include autotransformers
and multi-winding power transformers (both
individual three-phase units and banks of three singlephase units) where at least two terminals connect to
transmission level voltages (where transmission level
is defined as 100 kV and above). Transmission
transformers shall be protected by both sudden
pressure relays (63) and high speed differential (87)
protective relaying systems. There should be no
intentional delay (definite time or inverse time)
associated with the differential protective relay
elements. Transmission Transformer protection
systems must contain two redundant protection
schemes including redundant current transformers,
redundant DC sources (battery and battery charger are
not considered a redundant DC source), redundant
protective relays (including redundant 87 and
redundant 63 relays), redundant auxiliary and/or
lockout relays, and redundant DC trip circuitry
(including redundant trip coils on each circuit breaker
or circuit breaker pole). For transformer banks
comprised of single-phase transformer units,
independent 63 relays must be installed on each
transformer unit. Transmission transformer protective
relays (87 and 63) should trip lockout (86) relays and
shall not initiate automatic reclosing on any circuit
breaker. The primary 87 and 63 relay elements should
trip the primary lockout and the secondary 87 and 63
relay elements should trip the secondary lockout. It is
permissible for all relay elements to trip all lockouts
so long as a single point-of-failure is not introduced
into the protection system. Lockout relays should
hold trip signals on each circuit breaker protecting the
transformer and open closing circuits on each circuit
45
breaker protecting the transformer. Transformer
protective relays should initiate breaker failure for all
circuit breakers tripped.

Shunt Reactors and Capacitors
Shunt reactors and capacitors (including Static VAR
Compensators) shall be protected by high speed
protective relaying systems with no intentional delay.
Shunt reactor and capacitor protective zones must
contain two redundant protection schemes including
redundant current transformers, redundant DC sources
(battery and battery charger are not considered
redundant), redundant protective relays, redundant
auxiliary and/or lockout relays, and redundant DC trip
circuitry (including redundant trip coils on the circuit
breaker). Shunt reactor and capacitor protective relays
shall trip lockout (86) relays and shall not initiate
automatic reclosing on the circuit breaker. Lockout
relays shall hold the trip signal and open the closing
circuit on the circuit breaker or circuit switcher
protecting the shunt reactor or capacitor bank. Shunt
reactor and capacitor bank protective relays should
initiate breaker failure for the circuit breaker or circuit
switcher protecting the shunt reactor or capacitor
bank.

Series Reactors and Capacitors
Minimum system protection requirements for series
reactors and series capacitors shall be determined on a
case-by-case basis and included in the applicable
Transmission Proposal Request. At a minimum,
completely redundant protection systems will be
required if these elements are not already in the
protective zone of another elements (e.g.,
Transmission Circuit, Transmission Transformer,
etc.).

Phase Angle Regulating and Voltage Regulating
Transformers
Minimum system protection requirements for phase
shifting transformer and voltage regulating
transformers shall be determined on a case-by-case
basis and included in the applicable Transmission
46
Proposal Request. At a minimum, completely
redundant protection systems will be required if these
elements are not already in the protective zone of
another elements (e.g., Transmission Circuit,
Transmission Transformer, etc.)

HVDC Transmission Circuits and Converters
Minimum system protection requirements for HVDC
Transmission Circuits and associated converter
equipment shall be determined on a case-by-case basis
and included in the applicable Transmission Proposal
Request. At a minimum, completely redundant
protection systems will be required for these elements.

Breaker Failure Protection
Each Transmission Circuit breaker must contain a
breaker failure relay that will trip all electrically
adjacent sources when a trip signal is sent to the
circuit breaker and the circuit breaker fails to open and
interrupt the fault after a predetermined time.
Electrically adjacent sources are defined as electrically
adjacent circuit breakers within the substation as well
as generators and/or remote terminals if the circuit
breaker protects a Generation Element and/or a
Transmission Circuit respectively.
Breaker failure shall be initiated on the circuit breaker
if a trip signal to the circuit breaker is sent by a
protective relay element, auxiliary relay, lockout relay,
or remote transfer trip signal. Breaker failure shall not
be initiated for breaker trip signals generated by the
breaker control switch (01), from the SCADA system,
or from the circuit breaker manual trip switch located
on the circuit breaker. When breaker failure is
initiated, a breaker failure timer will be started. When
the breaker failure timer times out, breaker failure
tripping may be initiated depending on conditions
described below. The breaker failure timer must be
set within the range specified in the Transmission
Proposal Request, but in no case greater than 12 cycles
or less than 3 cycles.
Breaker failure relays must contain an overcurrent
fault detector (50) that measures the current flow
47
through the circuit breaker and must be set to detect all
bolted short-circuit faults for which the circuit breaker
provides primary protection. It is permissible to
assume all other circuit breakers (both local and
remote) providing primary protection for a specific
fault have opened when determining if a breaker
failure relay overcurrent fault detector has adequate
reach to all remote terminals. The overcurrent fault
detector setting must be set, in primary amperes, equal
to or greater than the continuous rating of the circuit
breaker unless such setting will not provide acceptable
reach, in which case the setting should be as close as
possible to the continuous current rating of the circuit
breaker (where “as close as possible” is defined as the
setting that provides the minimum required reach).
Pickup of the overcurrent fault detector shall not be a
requirement to initiate breaker failure for terminals
with multiple circuit breakers (i.e., ring bus and
double bus configurations), but instead will be used to
enable breaker failure tripping when appropriate as
further described below.
For faults that require a specific circuit breaker to trip
in order to clear the fault, breaker failure initiation
occurs when a relay element sends a trip signal to the
circuit breaker and a timer is started. When the timer
expires, if the overcurrent fault detector associated
with the breaker failure relay is picked up, then
breaker failure tripping shall occur. Breaker failure
tripping shall be made via a dedicated breaker failure
lockout relay (86) for the circuit breaker in question.
The lockout relay will hold a trip signal (which will
energize the trip coil when the 52A breaker auxiliary
contact is closed) and open the closing circuit on all
electrically adjacent circuit breakers at the substation.
Depending on the specifications supplied by
incumbent Transmission Owners who will be required
to trip remote circuit breakers in response to breaker
failure tripping for a specific circuit breaker, either the
breaker failure lockout relay or the breaker failure
relay will be required to send a transfer trip signal to
remote terminals that must open and clear the fault
and stop carrier transmission to those remote terminals
in the case where a directional comparison blocking
scheme is used to protect the Transmission Circuit.
48
For faults in protective zones that include transformers
and/or oil-filled reactors (generator protective zones,
Transmission Transformer protective zones, shunt
reactor zones, etc.), it is permissible to enable breaker
failure tripping if either the overcurrent fault detector
associated with the breaker failure relay is picked up
or a breaker auxiliary contact indicates the circuit
breaker is still closed (e.g., 52A contact is closed or
52B contact is open, etc.). This is allowed because it
is often not feasible for the breaker failure overcurrent
fault detector to detect small fault current magnitudes
associated with turn-to-turn internal transformer faults
that caused operation of differential or sudden
pressure relay elements, thus the overcurrent fault
detector could provide false indication that the fault
has been cleared. However, this practice shall not be
permitted for protective zones that do not include
transformers or oil-filled reactors (e.g., Transmission
Circuits, Transmission Physical Buses, etc.) since a
breaker auxiliary contact only indicates a mechanism
position and does not confirm that the fault current has
been interrupted.
Finally, it will be necessary for the New Transmission
Applicant to trip (and not initiate automatic reclosing
on) appropriate circuit breaker(s) protecting
Transmission Circuits or Generation Elements when
breaker failure transfer trip signals are received from
the remote end.
49
Attachment A
Attachment A contains a number of tables that are used by the procedures, policies, and
processes outlined in this document to determine minimum design requirements for New
Transmission Facilities associated with Open Transmission Projects.
TABLE 1
Industry Standard Terminal Equipment Rating Classes
69 kV
115 kV
138 kV
161 kV
230 kV
345 kV
500 kV
765 kV
1200 A
X
X
X
X
X
2000 A
X
X
X
X
X
X
X
3000 A
X
X
X
X
X
X
X
X
4000 A
5000 A
X
X
X
X
X
X
TABLE 2
Default Minimum Transmission Circuit Ampere Ratings
Nominal Operating
Emergency Ampere Rating
(kV)
(Amperes)
765
4,000
500
3,000
345
3,000
230
1,200
100-200
1,200
Below 100
1,200
50
TABLE 3A
Typical Impedance Ranges – 1350/1800/2250 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
0.37%
0.39%
0.41%
0.43%
0.44%
0.46%
0.48%
0.50%
0.52%
0.54%
0.56%
0.57%
0.59%
0.61%
0.63%
0.65%
0.67%
0.69%
0.70%
0.72%
0.74%
51
TABLE 3B
Typical Impedance Ranges – 900/1200/1500 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
0.56%
0.58%
0.61%
0.64%
0.67%
0.69%
0.72%
0.75%
0.78%
0.81%
0.83%
0.86%
0.89%
0.92%
0.94%
0.97%
1.00%
1.03%
1.06%
1.08%
1.11%
52
TABLE 3C
Typical Impedance Ranges – 720/960/1200 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
0.69%
0.73%
0.76%
0.80%
0.83%
0.87%
0.90%
0.94%
0.97%
1.01%
1.04%
1.08%
1.11%
1.15%
1.18%
1.22%
1.25%
1.28%
1.32%
1.35%
1.39%
53
TABLE 3D
Typical Impedance Ranges – 504/672/840 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
0.99%
1.04%
1.09%
1.14%
1.19%
1.24%
1.29%
1.34%
1.39%
1.44%
1.49%
1.54%
1.59%
1.64%
1.69%
1.74%
1.79%
1.84%
1.88%
1.93%
1.98%
54
TABLE 3E
Typical Impedance Ranges – 450/600/750 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
1.11%
1.17%
1.22%
1.28%
1.33%
1.39%
1.44%
1.50%
1.56%
1.61%
1.67%
1.72%
1.78%
1.83%
1.89%
1.94%
2.00%
2.06%
2.11%
2.17%
2.22%
55
TABLE 3F
Typical Impedance Ranges – 420/560/700 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
1.19%
1.25%
1.31%
1.37%
1.43%
1.49%
1.55%
1.61%
1.67%
1.73%
1.79%
1.85%
1.90%
1.96%
2.02%
2.08%
2.14%
2.20%
2.26%
2.32%
2.38%
56
TABLE 3G
Typical Impedance Ranges – 403.2/537.6/672 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
1.24%
1.30%
1.36%
1.43%
1.49%
1.55%
1.61%
1.67%
1.74%
1.80%
1.86%
1.92%
1.98%
2.05%
2.11%
2.17%
2.23%
2.29%
2.36%
2.42%
2.48%
57
TABLE 3H
Typical Impedance Ranges – 360/480/600 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
1.39%
1.46%
1.53%
1.60%
1.67%
1.74%
1.81%
1.88%
1.94%
2.01%
2.08%
2.15%
2.22%
2.29%
2.36%
2.43%
2.50%
2.57%
2.64%
2.71%
2.78%
58
TABLE 3I
Typical Impedance Ranges – 336/448/560 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
1.49%
1.56%
1.64%
1.71%
1.79%
1.86%
1.93%
2.01%
2.08%
2.16%
2.23%
2.31%
2.38%
2.46%
2.53%
2.60%
2.68%
2.75%
2.83%
2.90%
2.98%
59
TABLE 3J
Typical Impedance Ranges – 300/400/500 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
1.67%
1.75%
1.83%
1.92%
2.00%
2.08%
2.17%
2.25%
2.33%
2.42%
2.50%
2.58%
2.67%
2.75%
2.83%
2.92%
3.00%
3.08%
3.17%
3.25%
3.33%
60
TABLE 3K
Typical Impedance Ranges – 268.8/358.4/448 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
1.86%
1.95%
2.05%
2.14%
2.23%
2.33%
2.42%
2.51%
2.60%
2.70%
2.79%
2.88%
2.98%
3.07%
3.16%
3.26%
3.35%
3.44%
3.53%
3.63%
3.72%
61
TABLE 3L
Typical Impedance Ranges – 240/320/400 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
2.08%
2.19%
2.29%
2.40%
2.50%
2.60%
2.71%
2.81%
2.92%
3.02%
3.13%
3.23%
3.33%
3.44%
3.54%
3.65%
3.75%
3.85%
3.96%
4.06%
4.17%
62
TABLE 3M
Typical Impedance Ranges – 201.6/268.8/336 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
2.48%
2.60%
2.73%
2.85%
2.98%
3.10%
3.22%
3.35%
3.47%
3.60%
3.72%
3.84%
3.97%
4.09%
4.22%
4.34%
4.46%
4.59%
4.71%
4.84%
4.96%
63
TABLE 3N
Typical Impedance Ranges – 180/240/300 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
2.78%
2.92%
3.06%
3.19%
3.33%
3.47%
3.61%
3.75%
3.89%
4.03%
4.17%
4.31%
4.44%
4.58%
4.72%
4.86%
5.00%
5.14%
5.28%
5.42%
5.56%
64
TABLE 3O
Typical Impedance Ranges – 134.4/179.2/224 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
3.72%
3.91%
4.09%
4.28%
4.46%
4.65%
4.84%
5.02%
5.21%
5.39%
5.58%
5.77%
5.95%
6.14%
6.32%
6.51%
6.70%
6.88%
7.07%
7.25%
7.44%
65
TABLE 3P
Typical Impedance Ranges – 120/160/200 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
4.17%
4.38%
4.58%
4.79%
5.00%
5.21%
5.42%
5.63%
5.83%
6.04%
6.25%
6.46%
6.67%
6.88%
7.08%
7.29%
7.50%
7.71%
7.92%
8.13%
8.33%
66
TABLE 3Q
Typical Impedance Ranges – 100.8/134.7/168 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
4.96%
5.21%
5.46%
5.70%
5.95%
6.20%
6.45%
6.70%
6.94%
7.19%
7.44%
7.69%
7.94%
8.18%
8.43%
8.68%
8.93%
9.18%
9.42%
9.67%
9.92%
67
TABLE 3R
Typical Impedance Ranges – 90/120/150 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
5.56%
5.83%
6.11%
6.39%
6.67%
6.94%
7.22%
7.50%
7.78%
8.06%
8.33%
8.61%
8.89%
9.17%
9.44%
9.72%
10.00%
10.28%
10.56%
10.83%
11.11%
68
TABLE 3S
Typical Impedance Ranges – 67.2/89.6/112 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
7.44%
7.81%
8.18%
8.56%
8.93%
9.30%
9.67%
10.04%
10.42%
10.79%
11.16%
11.53%
11.90%
12.28%
12.65%
13.02%
13.39%
13.76%
14.14%
14.51%
14.88%
69
TABLE 3T
Typical Impedance Ranges – 60/80/100 MVA Transformer
Transformer
Transformer
Nameplate
Impedance
Impedance
(% @ 100 MVA)
(% @ ONAN Base)
5.00%
5.25%
5.50%
5.75%
6.00%
6.25%
6.50%
6.75%
7.00%
7.25%
7.50%
7.75%
8.00%
8.25%
8.50%
8.75%
9.00%
9.25%
9.50%
9.75%
10.00%
8.33%
8.75%
9.17%
9.58%
10.00%
10.42%
10.83%
11.25%
11.67%
12.08%
12.50%
12.92%
13.33%
13.75%
14.17%
14.58%
15.00%
15.42%
15.83%
16.25%
16.67%
70
TABLE 4A
Bus Configuration Standards – Maximum Number of Total Positions
Nominal
Single-Zone Double-Zone
Pure
Pure
Operating
Straight
Straight
Ring
Double-Bus
Double-Bus
kV
Bus
Bus**
Bus
Breaker-and-a-Half Double-Breaker
100-199
3
6
6
Unlimited*
Unlimited*
230
3
6
6
Unlimited*
Unlimited*
345
Not Allowed Not Allowed
6
Unlimited*
Unlimited*
500
Not Allowed Not Allowed
6
Unlimited*
Unlimited*
765
Not Allowed Not Allowed
6
Unlimited*
Unlimited*
* NOTE: Limited by breaker duty requirements and/or critical infrastructure limitations.
** NOTE: Tie breaker does not count as a position and each of the two zones associated with a
double-zone straight bus must individually meet the requirements for a single-zone straight bus.
TABLE 4B
Bus Configuration Standards – Maximum Number of Transmission Circuit Positions
Nominal
Single-Zone Double-Zone
Pure
Pure
Operating
Straight
Straight
Ring
Double-Bus
Double-Bus
kV
Bus
Bus**
Bus
Breaker-and-a-Half Double-Breaker
100-199
2
4
4
Unlimited*
Unlimited*
230
2
4
4
Unlimited*
Unlimited*
345
Not Allowed Not Allowed
4
Unlimited*
Unlimited*
500
Not Allowed Not Allowed
4
Unlimited*
Unlimited*
765
Not Allowed Not Allowed
4
Unlimited*
Unlimited*
* NOTE: Limited by breaker duty requirements and/or critical infrastructure limitations.
** NOTE: Tie breaker does not count as a position and each of the two zones associated with a
double-zone straight bus must individually meet the requirements for a single-zone straight bus.
Nominal
Operating
kV
100-199
230
345
500
765
** NOTE:
TABLE 4C
Bus Configuration Standards – Minimum Number of Total Positions
Single-Zone Double-Zone
Pure
Pure
Straight
Straight
Ring
Double-Bus
Double-Bus
Bus
Bus**
Bus
Breaker-and-a-Half Double-Breaker
2
3
3
5
3
3
3
2
3
5
3
3
Not Allowed Not Allowed
5
3
3
Not Allowed Not Allowed
5
3
3
Not Allowed Not Allowed
5
Tie breaker does not count as a position.
71
TABLE 5
Industry Standard Circuit Breaker Interrupting Ratings
Nominal Operating
Industry Standard Interruption Ratings
(kV)
(kA)
765
40, 50, 63
500
31.5, 40, 50, 63
345
31.5, 40, 50, 63, 80
230
31.5, 40, 50, 63, 80
100-200
31.5, 40, 50, 63, 80
Below 100
31.5, 40, 50, 63
72