Minimum Design Requirements
Task Team
Hypothetical Illustrative Examples
April 23, 2015
Purpose and Objective
• Purpose of Examples
– Developed pursuant to stakeholder requests, the purpose of
these examples is to illustrate the revised proposals regarding
the methods to be used to determine minimum load ratings and
maximum impedances for New Transmission Line Facilities that
are competitively bid via Open Transmission Projects
• Objective of Examples
– The objective of the examples is to assist stakeholders in
understanding the current proposals so that they may develop
and submit comments on the current proposal by May 15th.
MISO will discuss the comments, responses, and proposed
modifications to the proposals with stakeholders during the June
8th Minimum Design Requirements Task Team conference call
2
Summary of Examples
•
•
The examples are based on methodologies originally proposed in
October 2014 and revised in March 2015. The presentations
documenting these proposals are attached and/or posted with this
document.
In developing the examples, it became apparent that some
additional scenarios should be explored, including
– Methodologies to address congestion predominant in the winter where
the winter emergency rating is the critical factor.
– Situations where using standard incumbent TO ratings may not be
adequate to address the congestion in the most optimal manner.
3
Hypothetical Example 1
Hypothetical Example 1A
Transmission Line Minimum Rating Calculation
• Assumptions
– A new 345 kV transmission line is to be constructed between two
existing substations owned by the same incumbent Transmission
Owner
– The incumbent Transmission Owner has an established standard
summer emergency rating of 1,792 MVA for all new 345 kV
transmission lines with 3,000 A terminal equipment being the limiting
factor
– MISO determines the direct distance between the two substations is
approximately 22 miles.
5
Hypothetical Example 1A
Transmission Line Minimum Rating Calculation
• Determination of minimum summer emergency conductor
ampere ratings for the transmission line:
– The incumbent’s standard summer emergency ratings of
1,792 MVA for 345 kV transmission lines translated into a
minimum summer emergency conductor ampere rating of
3,000 A.
– The TPR will therefore establish the minimum summer
emergency conductor ampere rating as 3,000 A.
6
Hypothetical Example 1A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 1: Determine minimum emergency thermal rating
for the transmission line as follows:
Minimum Emergency Thermal MVA Rating
= 345 kV * 3,000 A * 31/2 / 1000 = 1,792 MVA
Note: The minimum emergency thermal MVA rating requirement
applies to all seasons
7
Hypothetical Example 1A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 2: Estimate the route length.
• The direct route length is determined to be 22 miles
• Upon a high level review of the area, MISO staff determines a
small town is in the direct path of the line, and estimates an
adjusted route length of 26 miles is appropriate.
– Step 3: Apply 20% adder to route mileage estimate to
determine the maximum mileage estimate.
• Maximum mileage estimate = 26 miles * 1.2 = 31.2 miles
• Maximum mileage estimate rounded up to 32 miles.
8
Hypothetical Example 1A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 4: Determine voltage and stability loadability rating.
Since the maximum mileage estimate is less than 50 miles, no
voltage and stability loadabiltiy rating will be determined.
– Step 5: Determine minimum emergency ratings for the
transmission line:
• Since the maximum mileage estimate for the transmission line
route is less than 50 miles, the minimum emergency ratings for
the transmission line are set equal to the minimum emergency
thermal rating of the line.
• Minimum Emergency MVA Ratings = 1,792 MVA
9
Hypothetical Example 1A
Transmission Line Minimum Rating Calculation
• Determination of the minimum normal MVA ratings for the
transmission line.
– The minimum normal MVA ratings for the transmission
line are set at 75% of the minimum emergency MVA
ratings as follows:
• Minimum Normal MVA Ratings = 0.75 * 1,792 MVA = 1,344 MVA
• Determination of the minimum SIL ratings for the
transmission line.
– Since the maximum mileage estimate is less than 50 miles, no
minimum SIL ratings are specified for the transmission line.
10
Hypothetical Example 1B
Transmission Line Maximum Impedance Calculation
• Step 1 – Determine Default Maximum Impedance
– Since the line is less than 50 miles in length, no default
maximum impedance is specified.
• Step 2 – Determine Economic Maximum Impedance
– Assume the economic study process did not determine that a
maximum impedance limit was necessary to ensure delivery of
simulated economic benefits.
• Step 3 – Determine Maximum Impedance
– No maximum impedance is specified since no maximum
impedance is determined from steps 1 and 2.
11
Hypothetical Example 1
Transmission Line Min Rating and Max Impedance
• Summary of results:
–
–
–
–
–
–
–
Minimum Summer Emergency Conductor Ampere Rating = 3,000 A
Minimum Summer Emergency MVA Rating = 1,792 MVA
Minimum Winter Emergency MVA Rating = 1,792 MVA
Minimum Summer Normal MVA Rating = 1,344 MVA
Minimum Winter Normal MVA Ratings = 1,344 MVA
Minimum Surge Impedance Loading = None Specified
Maximum Positive Sequence Line Impedance = None Specified
12
Hypothetical Example 2
Hypothetical Example 2A
Transmission Line Minimum Rating Calculation
• Assumptions
– A new 500 kV transmission line is to be constructed between two
existing substations owned by two different incumbent Transmission
Owners – Incumbent A and Incumbent B
– Incumbent A has an established standard summer emergency
conductor rating of 2,895 A to be used for all new 500 kV
transmission lines
– Incumbent B has no standard ratings for 500 kV transmission line
facilities.
– MISO determines the direct distance between the two substations is
approximately 45 miles.
14
Hypothetical Example 2A
Transmission Line Minimum Rating Calculation
• Determination of minimum summer emergency conductor
ampere ratings for the transmission line:
– Currently Proposed Method: Since Incumbent B does not have a
standard load rating for 500 kV transmission lines, MISO would
model ratings of 1,800 A and 2,700 A to determine which rating
performs best from an economic standpoint (e.g., B/C standpoint,
etc.). Assuming 1,800 A performed the best, the minimum summer
emergency conductor ampere rating would be set at 1,800 A.
Note: The 1,800 A and 2,700 A ratings are based on 90% of the
respective 2000 A and 3000 A industry standard terminal equipment
rating classes for 500 kV per the current proposal.
15
Hypothetical Example 2A
Transmission Line Minimum Rating Calculation
• Determination of minimum summer emergency conductor
ampere ratings for the transmission line:
– Alternative Method Discussed during PSC Meeting: Since
Incumbent B does not have a standard load rating for 500 kV
transmission lines, MISO will select the greater of the standard rating
maintained by Incumbent A (2,895 A) and the rating choice made
under the current proposal based on rating sensitivity analysis in the
economic studies. Since the Incumbent A standard rating exceeds
both the choices available in the rating sensitivity analysis, there is
no need to conduct such analyses under the alternative method for
this specific example. Therefore, the minimum summer emergency
conductor ampere rating would be set at 2,895 A.
16
Hypothetical Example 2A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 1: Determine minimum emergency thermal rating
for the transmission line as follows:
• Current Proposal:
Minimum Emergency Thermal MVA Rating
= 500 kV * 1,800 A * 31/2 / 1000 = 1,559 MVA
• Alternative Proposal:
Minimum Emergency Thermal MVA Rating
= 500 kV * 2,895 A * 31/2 / 1000 = 2,507 MVA
Note: The minimum emergency thermal MVA rating requirement
applies to all seasons
17
Hypothetical Example 2A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 2: Estimate the route length.
• The direct route length is determined to be 44miles
• Upon a high level review of the area, MISO staff determines a
direct path line route is feasible, and makes no adjustments to
the estimated route length of 44 miles.
– Step 3: Apply 20% adder to route mileage estimate to
determine the maximum mileage estimate.
• Maximum mileage estimate = 44 miles * 1.2 = 52.8 miles
• Maximum mileage estimate rounded up to 53 miles.
18
Hypothetical Example 2A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 4: Determine voltage and stability loadability rating.
• Since the maximum mileage estimate is more than 50 miles and
the line is an EHV line, a voltage and stability loadabiltiy rating
will be determined.
• From the modified St. Clair curve, a line loadability of 3.0 * SIL
corresponds to a line length of 53 miles. Based on a 500 kV
minimum SIL of 910 MW, the voltage and stability loadability
rating (VASLR) of the line would be determined as:
VASLR = 3.0 * 910 MW = 2,730 MW
19
Hypothetical Example 2A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 5: Determine minimum emergency ratings for the
transmission line:
• Since the maximum mileage estimate for the transmission line
route is more than 50 miles and the line is an EHV line, the
minimum emergency ratings for the transmission line are set at
the lesser of the minimum emergency thermal ratings of the line
and the voltage and stability loadability rating of the line.
• Current Proposal:
– Minimum Emergency MVA Ratings = MIN{1559, 2730} = 1,559 MVA
• Alternative Proposal:
– Minimum Emergency MVA Ratings = MIN{2507, 2730} = 2,507 MVA
20
Hypothetical Example 2A
Transmission Line Minimum Rating Calculation
• Determination of the minimum normal MVA ratings for the
transmission line.
– The minimum normal MVA ratings for the transmission line are set at
75% of the minimum emergency MVA ratings as follows:
• Current Proposal
– Minimum Normal MVA Ratings = 0.75 * 1,559 MVA = 1,169 MVA
• Alternative Proposal
– Minimum Normal MVA Ratings = 0.75 * 2,507 MVA = 1,880 MVA
• Determination of the minimum SIL rating for the
transmission line.
– Since the maximum mileage estimate is more than 50 miles and the
line is an EHV line, the TPR will specify a minimum SIL rating of 910
MW per the current proposal.
21
Hypothetical Example 2B
Transmission Line Maximum Impedance Calculation
• Step 1 – Determine Default Maximum Impedance
–
Default Maximum Impedance = 0.65 per unit @ Line Rating MVA
–
Current Proposal:
• Default Maximum Impedance = 0.65 * 3452 / 1,559 = 49.6 
–
Alternative Proposal:
• Default Maximum Impedance = 0.65 * 3452 / 2,507 = 30.9 
• Step 2 – Determine Economic Maximum Impedance
– Assume the economic study process did not determine that a
maximum impedance limit was necessary to ensure delivery of
simulated economic benefits.
• Step 3 – Determine Maximum Impedance
– Maximum Impedances are set equal to the Default Maximum Impedances
22
Hypothetical Example 2
Transmission Line Min Rating and Max Impedance
•
Summary of results under current proposal:
–
–
–
–
–
–
–
•
Minimum Summer Emergency Conductor Ampere Rating = 1,800 A
Minimum Summer Emergency MVA Rating = 1,559 MVA
Minimum Winter Emergency MVA Rating = 1,559 MVA
Minimum Summer Normal MVA Rating = 1,169 MVA
Minimum Winter Normal MVA Rating = 1,169 MVA
Minimum Surge Impedance Loading = 910 MW
Maximum Positive Sequence Line Impedance = 49.6 
**Summary of results under alternative proposal:
–
–
–
–
–
–
–
Minimum Summer Emergency Conductor Ampere Rating = 2,895 A
Minimum Summer Emergency MVA Rating = 2,507 MVA
Minimum Winter Emergency MVA Rating = 2,507 MVA
Minimum Summer Normal MVA Rating = 1,880 MVA
Minimum Winter Normal MVA Rating = 1,880 MVA
Minimum Surge Impedance Loading = 910 MW
Maximum Positive Sequence Line Impedance = 30.9 
**NOTE: Approach preferred by MISO staff.
23
Hypothetical Example 3
Hypothetical Example 3A
Transmission Line Minimum Rating Calculation
• Assumptions
– A new 765 kV transmission line is to be constructed between two
existing substations owned by two different incumbent Transmission
Owners
– Neither incumbent Transmission Owner has standard load ratings for
765 kV facilities.
– MISO determines the direct distance between the two substations is
approximately 165 miles.
25
Hypothetical Example 3A
Transmission Line Minimum Rating Calculation
• Determination of minimum summer emergency conductor
ampere ratings for the transmission line:
– Since neither incumbent Transmission Owner has standard load
ratings for 765 kV transmission facilities, MISO would model ratings
of 2,700 A and 3,600 A to determine which rating performs best from
an economic standpoint (e.g., B/C standpoint, etc.). Assuming 2,700
A performed the best, the minimum summer emergency conductor
ampere rating would be set at 2,700 A.
Note: The 2,700 A and 3,600 A ratings are based on 90% of the
respective 3000 A and 4000 A industry standard terminal equipment
rating classes for 765 kV per the current proposal.
26
Hypothetical Example 3A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 1: Determine minimum emergency thermal rating
for the transmission line as follows:
Minimum Emergency Thermal MVA Rating
= 765 kV * 2,700 A * 31/2 / 1000 = 3,578 MVA
Note: The minimum emergency thermal MVA rating
requirement applies to all seasons
27
Hypothetical Example 3A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 2: Estimate the route length.
• The direct route length is determined to be 165 miles
• Upon a high level review of the area, MISO staff determines a
direct path line route runs through a wildlife refuge, a suburban
area, and a lake; and estimates that an adjusted route length of
180 miles is appropriate.
– Step 3: Apply 20% adder to route mileage estimate to
determine the maximum mileage estimate.
• Maximum mileage estimate = 180 miles * 1.2 = 216 miles
28
Hypothetical Example 3A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 4: Determine voltage and stability loadability rating.
• Since the maximum mileage estimate is more than 50 miles and
the line is an EHV line, a voltage and stability loadabiltiy rating
will be determined.
• From the modified St. Clair curve, a line loadability of 1.2 * SIL
corresponds to a line length of 216 miles. Based on a 765 kV
minimum SIL of 2,210 MW, the voltage and stability loadability
rating (VASLR) of the line would be determined as:
VASLR = 1.2 * 2,210 MW = 2,652 MW
29
Hypothetical Example 3A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 5: Determine minimum emergency ratings for the
transmission line:
• Since the maximum mileage estimate for the transmission line
route is more than 50 miles and the line is an EHV line, the
minimum emergency ratings for the transmission line are set at
the lesser of the minimum emergency thermal ratings of the line
and the voltage and stability loadability rating of the line.
• Minimum Emergency MVA Ratings
= MIN(2652, 3578) = 2,652 MVA
30
Hypothetical Example 3A
Transmission Line Minimum Rating Calculation
• Determination of the minimum normal MVA ratings for the
transmission line.
– The minimum normal MVA ratings for the transmission line are set at
75% of the minimum emergency MVA ratings as follows:
Minimum Normal MVA Ratings = 0.75 * 2,652 MVA = 1,989 MVA
• Determination of the minimum SIL rating for the
transmission line.
– Since the maximum mileage estimate is more than 50 miles and the
line is an EHV line, the TPR will specify a minimum SIL rating of
2,210 MW per the current proposal.
31
Hypothetical Example 3B
Transmission Line Maximum Impedance Calculation
• Step 1 – Determine Default Maximum Impedance
–
Default Maximum Impedance = 0.5 per unit @ Line Rating MVA
–
Default Maximum Impedance = 0.5 * 7652 / 2,652 = 110.3 
• Step 2 – Determine Economic Maximum Impedance
– Assume the economic study process determines that the maximum line
impedance should not exceed 90  to ensure acceptable performance from
an economic standpoint.
• Step 3 – Determine Maximum Impedance
– Maximum Impedances are set equal to the lesser of the two values
determined in Step 1 and 2.
– Maximum Impedance = MIN{110.3, 90} = 90 
32
Hypothetical Example 3
Transmission Line Min Ratings & Max Impedance
•
Summary of results under current proposal:
–
–
–
–
–
–
–
Minimum Summer Emergency Conductor Ampere Rating = 2,700 A
Minimum Summer Emergency MVA Rating = 2,652 MVA
Minimum Winter Emergency MVA Rating = 2,652 MVA
Minimum Summer Normal MVA Rating = 1,989 MVA
Minimum Winter Normal MVA Ratings = 1,989 MVA
Minimum Surge Impedance Loading = 2,210 MW
Maximum Line Impedance = 90.0 
33
Hypothetical Example 4
Hypothetical Example 4A
Transmission Line Minimum Rating Calculation
• Assumptions
– A new 230 kV transmission line is to be constructed between two
existing substations owned by a single incumbent Transmission
Owner
– The incumbent Transmission Owner has a standard conductor used
for new 230 kV transmission construction and uses a summer
emergency conductor ampere rating of 938 A.
– MISO determines the direct distance between the two substations is
approximately 68 miles.
35
Hypothetical Example 4A
Transmission Line Minimum Rating Calculation
• Determination of minimum summer emergency conductor
ampere ratings for the transmission line:
– Based on the summer emergency conductor ampere rating used by
the incumbent Transmission Owner, the TPR will specify a minimum
summer emergency conductor ampere rating of 938 A.
36
Hypothetical Example 4A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 1: Determine minimum emergency thermal rating
for the transmission line as follows:
Minimum Emergency Thermal MVA Rating
= 230 kV * 938 A * 31/2 / 1000 = 374 MVA
Note: The minimum emergency thermal MVA rating
requirement applies to all seasons
37
Hypothetical Example 4A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 2: Estimate the route length.
Since this is not an EHV line, MISO would not need to estimate a
route length, but could do so under special considerations if the
length of the proposed route was expected to be excessive for the
voltage level in question.
– Step 3: Apply 20% adder to route mileage estimate to
determine the maximum mileage estimate.
Not Applicable
38
Hypothetical Example 4A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 4: Determine voltage and stability loadability rating.
Since this is not an EHV line, MISO would not determine a voltage
and stability loadability rating for the line even though the length of
the expected route is above 50 miles.
39
Hypothetical Example 4A
Transmission Line Minimum Rating Calculation
• Determination of the minimum MVA ratings for the
transmission line.
– Step 5: Determine minimum emergency ratings for the
transmission line:
• Since the maximum mileage estimate for the transmission line
route is less than 50 miles, the minimum emergency ratings for
the transmission line are set equal to the minimum emergency
thermal rating of the line.
• Minimum Emergency MVA Ratings = 374 MVA
40
Hypothetical Example 4A
Transmission Line Minimum Rating Calculation
• Determination of the minimum normal MVA ratings for the
transmission line.
– The minimum normal MVA ratings for the transmission line are set at
75% of the minimum emergency MVA ratings as follows:
Minimum Normal MVA Ratings = 0.75 * 374 MVA = 281 MVA
• Determination of the minimum SIL rating for the
transmission line.
– Since this is not an EHV line, no minimum SIL ratings apply.
41
Hypothetical Example 4B
Transmission Line Maximum Impedance Calculation
• Step 1 – Determine Default Maximum Impedance
–
No default maximum impedances are determined for non-EHV lines.
• Step 2 – Determine Economic Maximum Impedance
– Assume the economic study process did not determine that a maximum
impedance limit was necessary to ensure delivery of simulated economic
benefits.
• Step 3 – Determine Maximum Impedance
– No maximum impedance is specified since no maximum impedance is
determined from steps 1 and 2.
42
Hypothetical Example 4
Transmission Line Min Ratings & Max Impedance
•
Summary of results under current proposal:
–
–
–
–
–
–
–
Minimum Summer Emergency Conductor Ampere Rating = 938 A
Minimum Summer Emergency MVA Rating = 374 MVA
Minimum Winter Emergency MVA Rating = 374 MVA
Minimum Summer Normal MVA Rating = 281 MVA
Minimum Winter Normal MVA Ratings = 281 MVA
Minimum Surge Impedance Loading = None Specified
Maximum Positive Sequence Line Impedance = None Specified
43