Interchange Distribution Calculator (IDC)
User’s Manual
Version 0
Mark up for PFV Project, v2, 11/08/2012 (Included comments from Nelson/Mohamad, and preliminary
comments from Yasser)
Mark up for PFV Project, v3, 11/16/2012 (Included comments from Yasser on a number of topics)
Mark up for PFV Project, v4, 12/03/2012 (Included comments/questions from Nelson and Yasser)
Mark up for PFV Project, v5, 12/06/2012 (Revised comments on Coordinated Flowgates)
Mark up for PFV Project, v6, 12/14/2012 (Some minor edits relative to the use of the term markets, and
other miscellaneous changes)
Mark up for PFV Project, v7, 12/21/2012 (Some minor edits based on team conference call of
12/20/2012
Mark up for PFV Project, v8, 01/17/2013 (Incorporated comments from Tom Mallinger and discussed
with the team)
Mark up for PFV Project, v9, 1/22/2013 (Incorporated comments from Yasser on GTL calculation)
Mark up for PFV Project, v10, 1/24/2013 (Incorporated comments from Nelson/Mohamad on Dynamic
Schedule, Exceedances, DC Line, and Phase Shifter.)
Mark up for PFV Project, v11, 2/1/2013 (Final – Included comments from IDCWG Review)
Mark up for PFV Project, v12, 2/13/13, (based on discussion at February BPS meeting, clarifications
added to the tables within the subpriority section)
Interchange Distribution Calculator (IDC) User’s Manual
Table of Contents
1.0
Record of Revisions ............................................................................................................. 4
2.0
General Information ............................................................................................................. 5
2.1
NERC Reliability Standards............................................................................................. 5
2.2
IDC Provider and 24x7 Technical Support ...................................................................... 5
3.0
Transmission Loading Relief Levels ................................................................................... 5
3.1
TLR Levels ....................................................................................................................... 6
3.2
TLR Level 6 ..................................................................................................................... 7
3.3
TLR Matrix .................................................................................................................... 10
3.4
TLR Sub-Priorities ......................................................................................................... 11
3.5
TLR Reallocation ........................................................................................................... 13
4.0
IDC Factors ........................................................................................................................ 14
4.1
Introduction .................................................................................................................... 14
4.2
Transmission Distribution Factor (TDF)........................................................................ 14
4.3
Generation Shift Factor (GSF) ....................................................................................... 14
4.4
Load Shift Factor (LSF) ................................................................................................. 15
4.5
Generation-to-Load Distribution Factor (GLDF) .......................................................... 15
4.6
How are GSF, TDF, LSF, and GLDF Calculated in the IDC? ...................................... 16
4.7
Generation Ownership Factors ....................................................................................... 17
4.8
Line Outage Distribution Factor (LODF) ...................................................................... 17
4.9
PTDF & OTDF Flowgates ............................................................................................. 17
5.0
Parallel Flow Calculation Procedure ................................................................................. 17
5.1
Introduction .................................................................................................................... 18
5.2
Basic Principles .............................................................................................................. 18
5.3
Calculation Method ........................................................................................................ 18
5.4
Calculation Procedure .................................................................................................... 18
5.5
Sample Calculation ........................................................................................................ 18
6.0
Flowgate Administration ................................................................................................... 18
6.1
General ........................................................................................................................... 18
6.2
Guidelines for Permanent Flowgates ............................................................................. 21
6.3
Guidelines for Temporary Flowgates ............................................................................. 21
6.4
Guidelines for Informational Flowgates ........................................................................ 21
6.5
IDCWG Flowgate Review ............................................................................................. 21
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Interchange Distribution Calculator (IDC) User’s Manual
6.6
7.0
Flowgate Administration ................................................................................................ 23
Market Guidelines for the IDC .......................................................................................... 24
7.1
General ........................................................................................................................... 24
7.2
Market Data Inputs ......................................................................................................... 24
7.3
Market Impacts on Flowgates ........................................................................................ 26
7.4
Market TDF Calculations ............................................................................................... 26
7.5
Tag Mapping to Marginal Zones .................................................................................... 27
7.6
Marginal Zone Participation Factors .............................................................................. 27
7.7
Market Pseudo Balancing Areas .................................................................................... 28
7.8
Market Flows.................................................................................................................. 28
7.9
TLR Notifications .......................................................................................................... 29
7.10
Market Relief Responsibility ...................................................................................... 29
7.11
Firm Re-dispatch Credits ............................................................................................ 31
7.12
Market Tag Dump Data .............................................................................................. 32
8.0
Phase Shifters in the IDC ................................................................................................... 32
8.1
Setup and Use of Phase Shifters in IDC ......................................................................... 32
8.2
Modeling Requirements for Phase Shifters .................................................................... 33
8.3
Submittal of e-tags over Phase Shifters.......................................................................... 33
8.4
IDC Use of Phase Shifters in Regulate Mode ................................................................ 33
8.5
IDC Use of Phase Shifters in Non-Regulate Mode ........................................................ 34
8.6
IDC Use of Phase Shifters in Bypass Mode ................................................................... 34
9.0
DC Ties in the IDC ............................................................................................................ 35
9.1
Modeling Requirements for DC Ties ............................................................................. 35
9.2
Submittal of e-tags over DC Ties ................................................................................... 35
9.3
DC Ties IDC Responsibility .......................................................................................... 35
10.0 NERC Tag Dump ............................................................................................................... 36
10.1
NERC Tag Dump Data Format .................................................................................. 36
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Interchange Distribution Calculator (IDC) User’s Manual
1.0
Record of Revisions
Revision
Number
0
Date
Effective
2/27/2012
Description
Created from a collection of existing documents
Page 4 of 37
Interchange Distribution Calculator (IDC) User’s Manual
2.0
General Information
2.1
NERC Reliability Standards
The purpose statement of NERC Reliability Standard IRO-006-5 states that, “To ensure
coordinated action between Interconnections when implementing Interconnection-wide
transmission loading relief procedures to prevent or manage potential or actual SOL and IROL
exceedances to maintain reliability of the bulk electric system.” This coordinated action, for the
Eastern Interconnection, is obtained through the Interchange Distribution Calculator (IDC).
The Transmission Loading Relief Procedure used by the Reliability Coordinators in the Eastern
Interconnection is described in NERC Reliability Standard IRO-006-EAST-1.
2.2
IDC Provider and 24x7 Technical Support
The IDC program is provided to the Eastern Interconnection by OATI. NERC administers
user access.
OATI provides 24x7 support of the IDC system. During normal business hours, the OATI help
desk will be available to answer calls and provide basic system support. During off-hours all
calls to the help desk will be directed to the OATI answering service where calls will be
followed up and trouble tickets will be escalated to the appropriate line of support. Please contact
a NERC System Administrator for assistance in registration matters.
Email: [email protected]
Phone: 763-201-2010
FAX: 763-553-2813
3.0
Transmission Loading Relief Levels
The Interchange Distribution Calculator (IDC) uses TLR levels to define the severity of the
loading on the transmission system as well as actions that will be taken by the IDC to relieve the
overloading. TLRs are issued in levels from 0-6. TLR levels 3 and 5 are also sub-divided as a or
b. These subdivisions define the timing for the start of the TLR.
The NERC Transmission Loading Relief (TLR) procedure utilizes a Pro-Rata curtailment
method for all of the TLR Levels that require MW curtailment. For the Curtailment/Reallocation
calculations during TLR Level 3a and 5a, Non-Firm Priority transactions (1NS through 6NN)
and Firm Priority transactions (7F and 7FN) are assigned sub-priorities within each individual
priority bucket in order to make the curtailment of Non-Firm transactions more efficient. When
the transactions have been assigned to their Service Priority Bucket each tag is then analyzed a
second time to give them a Sub-Priority within their associated Service Priority bucket such that
when it is time to curtail in this bucket the MWs are curtailed utilizing these priorities.
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Interchange Distribution Calculator (IDC) User’s Manual
PFV Project:
(GTL and Market Flow) The IDC will perform all Generation-to-Load (GTL) calculations and
identify the components of these impacts that are firm and non-firm in order for these
calculations to be consistent and transparent across the Eastern Interconnection. These
calculations will replace Market Flow calculations provided by PJM, MISO and SPP, as well as
the Network and Native Load (NNL) impacts calculated by the IDC and used by all other
Balancing Authorities in the Eastern Interconnection.
(Non-Firm and Firm GTL) In order to comparably treat Point-to-Point (PTP) transactions and
Network Integration (NI) and Native Load (NL) service transactions, the NI/NL components are
no longer assumed as having firm transmission service. Instead, each generator providing for the
load in its host area will be assigned non-firm and firm service components, according to the
transmission services granted to the generator to provide for its load. This NI/NL component,
also called Generation-to-Load (GTL), will have non-firm and firm amounts that are subject to
curtailment.
(2 Tier Curtailment) In order to incent TSPs to enter into Coordination Agreements that honor
external constraints when providing transmission service (PTP, Network and Native), a two tier
curtailment approach is being implemented. TSPs that do not enter into Coordination
Agreements will have their firm transactions curtailed first in a TLR 5 (First-to-Curtail). Firm
curtailments for TSPs that do have Coordination Agreements will be implemented after the
completion of curtailments for TSPs without Coordination Agreements (Last-to-Curtail).
(Sub-priorities) To avoid shifting of relief obligations to tags and other BAs in future hours if a
BA fails to meet its current hour firm obligation, any shortfall in meeting its current hour firm
relief obligation will be assigned the lowest sub-priority in the 7FN bucket (S4) which means
that these transactions will be the first to be curtailed for any 7FN curtailments in the hour
beyond next hour. Firm sub-priorities will be established for both tags and GTL flows.
(Sub-priorities) To avoid shifting of relief obligations to tags and other BAs in future hours if a
BA fails to meet its current hour non-firm relief obligation, any shortfall in meeting its current
hour non-firm relief obligation will be assigned the lowest sub-priority in the non-firm priority of
the relief obligation bucket (S4) which means that these transactions will be the first to be
curtailed for any non-firm curtailments in the hour beyond next hour.
(Excess Relief) Any excess relief provided in the previous hour will be accounted for by
reloading all curtailments for the effective TLR hour before starting the curtailment process to
provide additional relief.
[PFV Project: Market Flows and coordinated flowgates are eliminated with PFV.]
3.1
TLR Levels
The listed system condition examples are intended to assist the Reliability Coordinator in
determining what level of TLR to call. The Reliability Coordinator has the discretion to
choose any of these levels regardless of the examples listed, provided the Reliability
Coordinator has reliability reasons to take such action. TLR levels are neither required nor
expected to be issued in numerical order of level.
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Interchange Distribution Calculator (IDC) User’s Manual
Level
TLR-1
TLR-2
TLR-3a
TLR-3b
TLR-4
TLR-5a
TLR-5b
TLR-6
TLR-0
3.2
Examples of Possible System Conditions
At least one Transmission Facility is expected to approach or exceed its SOL or IROL within 8 hours
At least one Transmission Facility is approaching or is at its SOL or IROL
 Analysis shows that holding new and decreasing non-firm Interchange Transactions and energy
flows for the next hour can prevent exceeding this SOL or IROL.
At least one Transmission Facility is expected to exceed its SOL or IROL within the next hour.
 Analysis shows that full or partial curtailment or reallocation 1 of non-firm Interchange
Transactions and energy flows can prevent exceeding this SOL and IROL.
 At least one Transmission Facility is exceeding its SOL or IROL, or
 At least one Transmission Facility is expected to exceed its SOL or IROL within the current hour.
o Analysis shows that full or partial curtailment or reallocation 2 of non-firm Interchange
Transactions and energy flows can prevent exceeding this SOL and IROL.
At least one Transmission Facility is expected to exceed its SOL or IROL.
 Analysis shows that full curtailment of non-firm Interchange Transactions and energy flows or
reconfiguration of the transmission system can prevent exceeding this SOL and IROL.
At least one Transmission Facility is expected to exceed its SOL or IROL within the next hour.
 Analysis shows that the following actions can prevent exceeding this SOL and IROL:
o Full curtailment of non-firm Interchange Transactions and energy flows, and
o Reconfiguration of the transmission system, if possible, and
o Full or partial curtailment or reallocation3 of firm Interchange Transactions and energy
flows.
 At least one Transmission Facility is exceeding its SOL or IROL, or
 At least one Transmission Facility is expected to exceed its SOL or IROL within the current hour.
 Analysis shows that the following actions can prevent exceeding this SOL and IROL:
o Full curtailment of non-firm Interchange Transactions and energy flows, and
o Reconfiguration of the transmission system, if possible, and
o Full or partial curtailment or reallocation4 of firm Interchange Transactions and energy
flows.
 At least one Transmission Facility is exceeding its SOL or IROL, or
 At least one Transmission Facility is expected to exceed its SOL or IROL upon the removal from
service of a generating unit or another transmission facility.
No transmission facilities are expected to approach or exceed their SOL or IROL within 8 hours and the
Interconnection-wide transmission loading relief procedure may be terminated.
TLR Level 6
This section describes the functionality that currently exists and options that the reliability
coordinator has when declaring TLR Level 6. This will help ensure the correct action is taken for
the given event.
IDC Treatment of TLR Level 6
When a reliability coordinator issues a TLR Level 6 on a flowgate in the IDC the application will
search the non-firm and firm e-tags that are in the IDC database for those that affect the flowgate
“Reallocation” is a term defined within the NAESB TLR Standards.
“Reallocation” is a term defined within the NAESB TLR Standards.
3
“Reallocation” is a term defined within the NAESB TLR Standards.
4
“Reallocation” is a term defined within the NAESB TLR Standards.
1
2
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Interchange Distribution Calculator (IDC) User’s Manual
greater than or equal to 5%. It will create two sets of e-tags from this list for the reliability
coordinator to curtail:
1.
If the Interchange Transaction and Intra-BA PTP e-tags have an active MW amount in
the current hour it will be curtailed to zero MW.
2.
If the Interchange Transaction and Intra-BA PTP e-tags are planned to start the next hour
it will not be allowed to start and will be curtailed to zero for the next hour
3.
Dynamic Schedule e-tags will be accounted for as part of the GTL Flowgate impact
calculation based on the real time Dynamic interchange flow uploads by the different
entities (see the Dynamic Schedule section under 7.8 below for details).
.
Once this report is created and displayed as the congestion management report, the reliability
coordinator will then have three options to move forward with the TLR Level 6:
1.
2.
3.
Confirm the curtailment list that contains the non-firm and firm complete
curtailments for the current and next hour.
1.1.
This will alert the other reliability coordinators that a TLR Level 6 has been
declared and that there are curtailments that need to be acknowledged for
implementation.
1.2.
Once the sinking reliability coordinators acknowledge the curtailments, the IDC
will send a reliability cap of zero MW to the balancing authorities on the e-tags
for curtailment implementation.
Exclude some or all of the e-tag curtailments from the IDC congestion management
report before declaring a TLR Level 6.
2.1.
This can be done by the issuing reliability coordinator using the “Reissue/Exclude” option in the congestion management report.
2.2.
This will give the issuing reliability coordinator the option of selecting those
transactions they wish to exclude from the TLR issuance.
2.3.
Once the appropriate e-tags are selected the reliability coordinator will re-issue
the TLR and the list of excluded e-tags will appear on the congestion management
report but will not be in the curtailed state. The reliability coordinator will then
have to confirm the TLR to send the TLR Level 6 notification to the other
reliability coordinators.
2.4.
Any e-tags that were not chosen for exclusion will be sent out to the other
reliability coordinators for acknowledgement and curtailment.
2.5.
This option allows the reliability coordinator to declare a TLR Level 6 without
implementing e-tag curtailments.
Disregard some or all of the e-tag curtailments from the congestion management
report while acknowledging the curtailments of a TLR Level 6.
3.1.
The sinking reliability coordinator can only do this for each e-tag curtailment after
they receive a TLR Level 6 congestion management report from the issuing
reliability coordinator.
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Interchange Distribution Calculator (IDC) User’s Manual
3.2.
The sinking reliability coordinator will select the “Disregard” option for the e-tags
they wish not to curtail. This is done in the IDC Acknowledgement screen.
3.3.
When the “Disregard” option is chosen and the “Acknowledgement” button
selected the IDC will update the congestion management report to identify to all
reliability coordinators that the sinking reliability coordinator has disregarded the
curtailment and does not plan on implementing it.
3.4.
This will prompt the issuing reliability coordinator to initiate a conversation with
the sinking reliability coordinator for further clarification on why the suggested
curtailment will not take place.
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Interchange Distribution Calculator (IDC) User’s Manual
Firm
Non-firm
TLR Description
3.3
TLR Matrix [PFV Project: Market flows are replaced by GTL flows and NNL is no longer relevant]
TLR Matrix
Purpose and intent of
TLR Level
TLR Level 0
TLR termination and
Interchange Transaction
restoration and
notification
TLR Level 1
Notification of
potential SOL or IROL
violation
TLR Level 2
Hold transfers at
present levels to
prevent SOL or IROL
violations
TLR Level 3a
Reallocation of
transmission service by
curtailing non-firm
transactions and
allowing firm to flow
The transmission
system is secure. One
or more transmission
facilities are expected
to approach, or are
approaching, or are at
their SOL or IROL.
TLR Level 3b
Curtail non-firm
transactions to mitigate
SOL or IROL violation
TLR Level 4
Gives operators time to
reconfigure the
transmission system to
mitigate an SOL or
IROL violation
One or more
Transmission Facilities
are above their SOL or
IROL, or such
operation is imminent
and it is expected that
facilities will exceed
their reliability limit
unless corrective action
is taken.
TLR Level 5a
Reallocation of transmission
service by curtailing firm
transactions and allowing
higher priority firm to flow
TRL Level 5b
Curtail firm transactions to
mitigate SOL or IROL
violation
TLR Level 6
Implement emergency
procedures
Conditions that may
warrant calling this
level of TLR
The Reliability Coordinator
initiating the TLR Procedure
shall notify all Reliability
Coordinators within the
Interconnection via the
RCIS when the SOL or
IROL violations are
mitigated and the system is
in a reliable state, allowing
Interchange Transactions to
be reestablished at its
discretion. Those with the
highest transmission
priorities shall be
reestablished first if
possible.
The transmission
system is secure. The
RC foresees a
transmission or
generation contingency
or other operating
problem within its
Reliability Area that
could cause one or
more transmission
facilities to approach or
exceed their SOL or
IROL.
The transmission
system is secure. One
or more transmission
facilities are expected
to approach, or are
approaching, or are at
their SOL or IROL.
The TLR level 2 is a
transient state, which
requires a quick
decision to proceed to
higher TLR levels to be
implemented according
to their transmission
priority levels.
The transmission system is secure.
One or more transmission
facilities are at their SOL or
IROL. All Interchange
Transactions using Non-firm
Point-to-Point Transmission
Service that are at or above the
Curtailment Threshold have been
curtailed. The Transmission
Provider has been requested to
begin an Interchange Transaction
using previously arranged Firm
Transmission Service that would
result in a SOL or IROL violation.
No further transmission
reconfiguration is possible or
effective.
One or more Transmission
Facilities are operating above
their SOL or IROL, or such
operation is imminent, or one or
more Transmission Facilities
will exceed their SOL or IROL
upon the removal from service
of a generating unit or another
transmission facility. All
Interchange Transactions using
Non-firm Point-to-Point
Transmission Service that are at
or above the Curtailment
Threshold have been curtailed.
No further transmission
reconfiguration is possible or
effective.
One or more
Transmission Facilities
are above their SOL or
IROL. One or more
Transmission Facilities
will exceed their SOL
or IROL upon the
removal from service of
a generating unit or
another transmission
facility.
Effect on current
hour, non-firm tags
Reloads previously
curtailed tags
Reloads previously
curtailed tags
Prevents all tags with
TDF > 5% from
starting or increasing
N/A
Curtails all tags with
TDF > 5%
N/A
Curtails tags with TDF > 5%
Curtails tags with TDF
> 5%
Curtails all GTL flow
with TDF > 0%
N/A
Curtails all GTL flow with
TDF > 0%
Curtails all GTL flow
with TDF > 0%
Curtails all tags with
TDF > 5%
Curtails tags with TDF > 5%
Curtails tags with TDF > 5%
Curtails tags with TDF
> 5%
Curtails all GTL flow
with TDF > 5%
Curtails GTL flow with TDF >
5%
Curtails all GTL flow with
TDF > 0%
Curtails all GTL flow
with TDF > 0%
N/A
Curtails/reallocates tags
with TDF > 5% until
relief request is met
Curtails/reallocates
GTL flow with TDF >
5% until relief request
is met
N/A
Curtails tags with TDF
> 5% until relief
request is met. No
reallocation
Curtails GTL flow with
TDF > 0% until relief
request is met. No
reallocation
Curtails/reallocates tags
with TDF > 5% until
relief request is met
Curtails/reallocates
GTL flow with TDF >
5% until relief request
is met
N/A
Effect on current
hour, non-firm GTL
flow
Reloads previously
curtailed GTL flow
Reloads previously
curtailed GTL flow
Prevents all GTLflow
with TDF > 0% from
starting or increasing
N/A
Effect on next hour,
non-firm tags
Reloads previously
curtailed tags
Reloads previously
curtailed tags
Effect on next hour,
non-firm GTL flow
Reloads previously
curtailed GTL flow
Reloads previously
curtailed GTL flow
Prevents all tags with
TDF > 5% from
starting or increasing
Prevents all GTL flow
with TDF > 5% from
starting or increasing
Effect on current
hour, firm tags
Effect on current
hour, firm GTLflow
Reloads previously
curtailed tags
Reloads previously
curtailed GTL flow
Reloads previously
curtailed tags
Reloads previously
curtailed GTL flow
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Curtails tags with TDF > 5%
until relief request is met
Curtails GTL flow with TDF
> 5% until relief request is
met
Curtails all tags with
TDF > 5%
Curtails all GTL flow
with TDF > 5%
Effect on next hour,
firm tags
Reloads previously
curtailed tags
Reloads previously
curtailed tags
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
Curtails tags with TDF > 5%
until relief request is met
Curtails all tags with
TDF > 5%
N/A
N/A
N/A
N/A
Curtails GTL flow with TDF >
5% until relief request is met
Prevents all firm tags with
TDF > 5% from starting or
increasing
Prevents all firm GTL flow
with TDF > 5% from starting
or increasing
Effect on next hour,
firm GTL flow
Reloads previously
curtailed GTL flow
Reloads previously
curtailed GTL flow
N/A
N/A
N/A
N/A
One or more transmission
facilities are operating
above their SOL or IROL,
or such operation is
imminent and it is
expected that facilities
will exceed their
reliability limit unless
corrective action is taken,
or one or more
Transmission Facilities
will exceed their SOL or
IROL upon the removal
from service of a
generating unit or another
transmission facility.
Page 10 of 37
Curtails all GTL flow
with TDF > 5%
Interchange Distribution Calculator (IDC) User’s Manual
3.4
TLR Sub-Priorities
Transactions in a Non-Firm Priority bucket are given an additional Sub-Priority. The table below
gives more details for each Sub-Priority.
S1 – Current Hour Active MWs
S2 – (Current Hour Scheduled MWs) – (Current Hour Active MWs)
S3 – (Next Hour Scheduled MWs) – (Current Hour Scheduled MWs)
S4 – New Tagged MWs
PFV Project:
Priority
S1
Purpose
To allow a flowing tagged transaction to
maintain or reduce its current MW amount in
accordance with its energy profile.
S2
To allow a flowing tagged transaction that has
been curtailed or halted by TLR to reload to
the lesser of its current-hour MW amount or
next-hour schedule in accordance with its
energy profile.
To allow a flowing tagged transaction to
increase from its current-hour schedule to its
next-hour schedule in accordance with its
energy profile.
To allow a tagged transaction that had never
started and was submitted to the Tag
Authority after the TLR (level 2 or higher) has
been declared to begin flowing (i.e., the
Interchange Transaction never had an active
MW and was submitted to the IDC after the
first TLR Action of the TLR Event had been
declared.)
S3
S4
Explanation and Conditions
The MW amount is the lowest between currently
flowing MW amount and the next-hour schedule.
The currently flowing MW amount is determined by
the e-tag Energy Profile and Adjust tables. If the
calculated amount is negative, zero is used instead.
The tagged transaction MW amount used is
determined through the e-tag Energy Profile and
Adjust tables. If the calculated amount is negative,
zero is used instead.
The MW amounts used in this sub-priority are
determined by the e-tag Energy Profile table. If the
calculated amount is negative, zero is used instead.
The tagged transaction would not be allowed to start
until all other tagged transactions submitted prior to
the TLR with the same priority have been
(re)loaded. The MW amount used in the sub-priority
is the next-hour schedule determined by the e-tag
Energy Profile table.
PFV Project:
(Subpriorities) There will be no unconstrained GTL flow and no next-hour prediction of GTL
flow. Therefore, S2 and S3 will be 0 MW.
Non-Firm GTL Flow Sub-Priority assignments are similar to those used for tagged transactions.
S1 – Current Hour GTL Flow MWs – Less the shortfalls or plus the exceedances from
previous relief obligations (S4)
S2 –
S3 –
S4 – Shortfalls (positive) or exceedances (negative) from previous hours’ relief obligations
Priority
S1
S2
S3
Purpose
To allow GTL Flow to maintain or reduce
its current MW amount.
N/A
N/A
Explanation and Conditions
Contains the current GTL flow contributions less the
shortfalls or plus the exceedances from previous relief
obligations (to S4).
N/A
N/A
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Interchange Distribution Calculator (IDC) User’s Manual
S4
To avoid shifting of relief obligations to
tags and other BAs in future hours
Contains the relief obligation shortfalls or
exceedances from 2 hours earlier
PFV Project:
Firm Tagged Transactions and Generation-to-Load (GTL) Impacts
(Subpriorities) Tagged transactions in a Firm Priority bucket are given a Sub-Priority. The table
below gives more details for each Sub-Priority.
S1 – Current Hour Active MWs
S2 – (Current Hour Scheduled MWs) – (Current Hour Active MWs)
S3 – (Next Hour Scheduled MWs) – (Current Hour Scheduled MWs)
S4 – New Tagged MWs with a classification of First-to-Curtail or Last-to-Curtail
Priority
S1
Purpose
To allow a flowing tagged transaction to
maintain or reduce its current MW amount in
accordance with its energy profile.
S2
To allow a flowing tagged transaction that has
been curtailed or halted by TLR to reload to
the lesser of its current-hour MW amount or
next-hour schedule in accordance with its
energy profile.
To allow a flowing tagged transaction to
increase from its current-hour schedule to its
next-hour schedule in accordance with its
energy profile.
To allow a tagged transaction that had never
started and was submitted to the Tag
Authority after the TLR (level 2 or higher) has
been declared to begin flowing (i.e., the
tagged transaction never had an active MW
and was submitted to the IDC after the first
TLR Action of the TLR Event had been
declared.)
S3
S4
Explanation and Conditions
The MW amount is the lowest between currently
flowing MW amount and the next-hour schedule.
The currently flowing MW amount is determined by
the e-tag Energy Profile and Adjust tables. If the
calculated amount is negative, zero is used instead.
The tagged transaction MW amount used is
determined through the e-tag Energy Profile and
Adjust tables. If the calculated amount is negative,
zero is used instead.
The MW amounts used in this sub-priority are
determined by the e-tag Energy Profile table. If the
calculated amount is negative, zero is used instead.
The tagged transaction would not be allowed to start
until all other Interchange Transactions submitted
prior to the TLR with the same priority have been
(re)loaded. The MW amount used in the sub-priority
is the next-hour schedule determined by the e-tag
Energy Profile table. These tags are classified as
First-to-Curtail and Last-to-Curtail.
There will be no unconstrained GTL flow and no next-hour prediction of GTL flow. Therefore,
S2 and S3 will be 0 MW.
Firm GTL Flow Sub-Priority assignments are similar to those used for tagged transactions.
S1 – Current Hour GTL Flow MWs – Less the shortfalls or plus the exceedances from
previous relief obligations (S4)
S2 –
S3 –
S4 – Shortfalls (positive) or exceedances (negative) from previous hours relief obligations
Priority
S1
S2
Purpose
To allow GTL Flow to maintain or reduce
its current MW amount.
N/A
Explanation and Conditions
Contains the current GTL flow contributions less the
shortfalls or plus the exceedances from previous relief
obligations (to S4)
N/A
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Interchange Distribution Calculator (IDC) User’s Manual
S3
S4
N/A.
To avoid shifting of relief obligations to
tags and other BAs in future hours
N/A
Contains the relief obligation shortfalls or
exceedances from 2 hours earlier, classified as Firstto-Curtail or Last-to-Curtail.
During TLR 3, the tag impacts and GTL flow impacts in S4 will be cut first on a proportional
basis, followed by the S3, S2, and S1 tag impacts and GTL flow impacts respectively. During
TLR 5, the sequencing is the same, with the First-to-Curtail classification being cut before the
Last-to-Curtail classification in each subpriority priority
3.5
TLR Reallocation
When a TLR Level 3B or 5B is called, the IDC processes tags and GTL flow for the current
hour. However, the processing for the TLR Level 3B or 5B does not stop with the current hour.
The TLR 3B or 5B also initiates a second pass of processing at XX:25 to make adjustments for
the next hour. When a TLR Level 3B or 5B is called, the IDC in effect performs a TLR 3B or 5B
for the current hour and a TLR 3A or 5A for the next hour respectively.
When an RC requests a TLR 3B or 5B calculation for the current hour, the IDC will set up the
next hour calculation (second pass) to perform reallocation identical to a TLR 3A or 5A, where
the desired flow on the flowgate will be equal to the current flow on the flowgate at the time the
TLR 3B or 5B issuance subtracted by the amount of relief the RC has requested.
When a TLR 3B or 5B is issued on or after XX:25, the IDC will perform the current and next
hour calculations simultaneously, and will present the RC with a Congestion Management
Report that includes both the current and next hour solutions.
When a TLR 3B or 5B is issued prior to XX:25, the IDC will perform the current hour
calculations immediately, and only perform the next hour reallocation calculations identical to a
TLR 3A at XX:25. The issuing RC will not be required to confirm the next hour calculations,
and alarms will be sent to all impacted RCs if there are tags that need to be acknowledged.
If the RC desires to change the TLR level or modify the amount of relief after XX:25, the RC
will re-issue the TLR at the desired level and for the relief desired using the normal TLR reissuing process. The Congestion Management Report will be modified to provide the next hour
information using the new inputs.
PFV Project:
(Reload) During any TLR issuance, re-issuance or reallocation, IDC will be changed such that it
allows the Reliability Coordinator to set a max flow Target for reload for each flowgate. This
will enable the operator to determine how much GTL to increase during the next TLR run for the
flowgate. During every TLR run, IDC calculates the GTL next hour, the next hour Tagged
impacts for all flowgates. To determine the amount of allowable GTL next hour, the Reliability
Coordinator will communicate to the IDC the capacity on the flowgate that is projected to be
unused next hour based on the next hour information. This projected unused capacity will be
allocated to the GTL for all entities on a pro-rata basis based on current GTL in all priority
buckets combined (>5%).
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Interchange Distribution Calculator (IDC) User’s Manual
4.0
IDC Factors
4.1
Introduction
The IDC calculates several factors that are used in the transmission loading relief process.
These factors are:
 TDF – Transmission Distribution Factor
 GSF – Generation Shift Factor
 LSF – Load Shift Factor
 GLDF – Generation-to-Load Distribution Factor
 LODF – Line Outage Distribution Factor
 PTDF & OTDF Flowgates
4.2
Transmission Distribution Factor (TDF)



Transfer Distribution Factors (TDF’s) represent the impactof an Interchange Transaction
on a given flowgate.
TDF is the measure of responsiveness or change in electrical loading on system facilities
due to a change in electric power transfer from one area to another expressed in per cent
(up to 100%) of the change in power transfer.
TDFs address the question, “What portion of a power transfer shows up on flowgate X?”
How is TDF used in the IDC?




4.3
TDFs are used to determine which Interchange Transactions are eligible for TLR
curtailment in the IDC.
Only those Interchange Transactions with a TDF of 5% or greater are subject to TLR
Curtailments.
If a tag indicates a TDF of 8.3% on flowgate X, this means that 8.3% of the transfer
amount on that tag flows on flowgate X.
Use the following formula to calculate the MW impact on a flowgate for a particular
Interchange Transaction:
MW impact = (Interchange transaction MW) x (TDF)
Generation Shift Factor (GSF)



Generation Shift Factors (GSF) describe a generator’s impact on a flowgate
The Generation Shift Factors (GSF) represent the change in flow on a flowgate due to an
incremental injection at a generator bus, and a corresponding withdrawal at the swing bus
IDC disregards losses ⇒ the principles of superposition apply.
o GSF between any two generators is the difference between the generators’GSF to
the swing bus
GSFk→m= GSFk→swing – GSFm→swing
How is the GSF used in the IDC?
 GSFs are the most basic IDC calculation used in TDF calculations (all TLR levels) and
GLDF calculations (TLR level 5)
Page 14 of 37
Interchange Distribution Calculator (IDC) User’s Manual



4.4
GSFs on the Flowgate GSF display in the IDC indicate which generators contribute to or
relieve congestion on a selected flowgate.
If a generator indicates a GSF of 15.2% on flowgate X, this means that 15.2% of the
generator’s output flows on flowgate X, provided the injection is withdrawn at the swing
bus
Use the following formula to calculate the MW impact on a flowgate for a particular
generator:
MW impact = (Gen MW) x (GSF)
Load Shift Factor (LSF)
Load Shift Factors (LSF) describe how changes in system loading impacts a flowgate.
How is the LSF used in the IDC?
 LSFs are used to calculate GLDFs, which are used to determine GTL obligations.
 LSFs are shown along with GSFs on the GLDF displays in the IDC.
 The LSFs alone are not used by the IDC –the LSF is a component of the Generation-toLoad Distribution Factor (GLDF)
4.5
Generation-to-Load Distribution Factor (GLDF)


Generation-to-Load Distribution Factors (GLDF) describe a generator’s impact on a
flowgate while serving load in that generator’s Balancing Authority Area
A GLDF is the difference between GSF and an LSF and determines the total impact of a
generator serving its native Balancing Authority load on an identified transmission
facility or monitored flowgate.
The GTL process allows for non-firm and firm of Network Integration (NI) and Native Load
(NL) services to be treated comparably with non-firm and firmPoint-to-Point (PTP) Transactions
during TLR events. The Interchange Distribution Calculator (IDC) assists the Reliability
Coordinator (RC) in allocating appropriate relief of all PTP transactions and GTL impactsin
order to ensure comparable curtailment.[PFV Project: NNL is replaced by GTL for all PTP
transactions.]
How is GLDF used in the IDC?
 GLDFs are used to determine the GTL of Balancing Authorities where generators in the
BA serve the native and network load of the BA.
 The GTL calculation forms the basis for determining a BA relief obligation in a TLR.
 Only those generators with a GLDF of 5% or greater are used in calculating the GTL
relief obligation.
 GLDFs are shown in the Flowgate GLDF display and the CA GLDF display in the IDC.
 In the Flowgate GLDF display the user selects a flowgate and is shown a list of
generators that contribute to flow as a byproduct of serving their own Balancing
Authority Area load (i.e., the GTL impact).
 In the CA GLDF display, the user is shown a listing of flowgates that are impacted by
generators serving their own Balancing Authority Area load. From this list, the user can
drill down and view the generator contribution to flow.
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Interchange Distribution Calculator (IDC) User’s Manual

The GLDF is calculated according to the following formula:
GLDF = GSF -LSF
[PFV Project: NNL is replaced by GTL in the process.]
4.6
How are GSF, TDF, LSF, and GLDF Calculated in the IDC?







All factors (GSF, TDF, LSF) are calculated from a master shift factor matrix of each bus
and each flowgate.
This matrix is calculated by simulating an incremental injection in every bus
(individually, one at a time) and a corresponding withdrawal at the swing bus. The term
is loosely called GSF even though it is calculated for every bus, regardless of being
attached to a generator.
The Balancing Authority’s TDFs are calculated as the weighted sum of the GSFs in a
Balancing Authority Area for every in-service generator –the weighting factors are the
generators’ MBASE in the PSSE base case model, adjusted for de-ration as provided via
the SDX
TDF = Σ( GSF x MBASE x DE-RATION ) / Σ( MBASE x DE-RATION )
The Balancing Authority’s LSFs are calculated as the weighted sum of the GSFs in a
Balancing Authority Area for every connected load bus as defined in the PSSE base case
–the weighting factors are the load MW amount on the buses.
LSF = SUM( GSF x LOAD ) / SUM( LOAD )
The TDF between two Balancing Authority Areas is the difference between the TDFs of
the Balancing Authority Areas (principle of superposition):
TDFBA1 –BA2= TDFBA1–TDFBA2
The TDF of a tag is the TDF between the source and sink Control Areas
TDFTag= TDFSourceBA–SinkBA= TDFSourceBA–TDFSinkBA
Tag path:
o Every tag has a defined path:
Source BA –TP1–TP2–…–TPn–Sink BA
o The TDF of a tag is the sum of the TDFs of every segment on a tag –which is
equivalent to the TDF between the source and sink BA:
Segment 1:TDFSourceBA–TP1= TDFSourceBA–TDFTP1
Segment 2:TDFTP1–TP2= TDFTP1–TDFTP2
Last Segment:TDFTPn–SinkBA= TDFTPn–TDFSinkBA
TDFTag = TDFSourceBA – TDFTP1 + TDFTP1 – TDFTP2 + TDFTP2 – TDFTP3 + …+
TDFTPn –TDFSinkBA = TDFSourceBA – TDFSinkBA
 Special case –segmented tag, or tags through controlled devices (phase shifters and
DC ties):
o 100% of the tag scheduled MW flows through the controlled device
o TDF of tag is the sum of the TDF between the Source BA and the entry point
to the controlled device, and the TDF between the exit point of the controlled
device and the sink BA.
o Example:
 Tag 1 – segmented through DC/phase shifter: TDFTag1= TDFBA1 –P1 +
TDFP2–TDFBA2
 Tag 2 – AC tag between BA-1 and BA-2: TDFTag2 = TDFBA1 –TDFBA2
 TDFTag1 ≠ TDFTag2
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Interchange Distribution Calculator (IDC) User’s Manual

Special case diagram –segmented tag, or tags through controlled devices (phase
shifters and DC ties):
DC Tie/Phase
Shifter
Shiftershifter
BA-1
BA-2
Tag 1
Tag 2
4.7
Generation Ownership Factors
The IDC Generation Ownership Factor gives the Reliability Coordinator a mechanism for
designating ownership where a unit has owners in multiple Balancing Areas. Each generator in
the IDC model can be divided by percentage ownership. The total ownership for each generator
in the IDC must equal 100%.
4.8
Line Outage Distribution Factor (LODF)



4.9
Line Outage Distribution Factor (LODF) represents the percentage of flow on a
contingent facility that will flow on the monitored elements, if the contingent facility is
outaged–Contingency Analysis
Post-Contingency Flow on Monitored Element = Pre-Contingency Flow on Monitored
Element + (Pre-Contingency Flow on Contingent Element)*LODF
LODFs are not used in IDC TLR calculations – they are only used in assisting the RCs in
filling the TLR NERC Report.
PTDF & OTDF Flowgates




5.0
PTDF – Power Transfer Distribution Factor.
o PTDF Flowgates are Flowgates that do not consider contingencies during
curtailment evaluation. With PTDF Flowgates the monitored branches alone are
considered during curtailment evaluation.
OTDF – Outage Transfer Distribution Factor.
o OTDF Flowgates are Flowgates that take into account a predefined contingency
during curtailment evaluation. With OTDF Flowgates the monitored branches are
considered with a specific facility removed from service during curtailment
evaluation.
A Flowgate can exist as a PTDF Flowgate or an OTDF Flowgate.
A Flowgate defaults to a PTDF Flowgate unless OTDF branch data is specified in the
Flowgate creation process.
Parallel Flow Calculation Procedure [PFV Project:Existing
process is replaced with GTL calculation process—see 7.0 below]
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Interchange Distribution Calculator (IDC) User’s Manual
6.0
Flowgate Administration
6.1
General
Purpose
The Flowgate Administration Reference Document explains how RELIABILITY
COORDINATORS can add, modify, and remove flowgates from the Interchange Distribution
Calculator (IDC). The procedures that follow in this document:
 Ensure that the Reliability Coordinators have the flowgate data they need to manage
system reliability.
 Ensure that market participants receive timely information about flowgate changes they
need to assess impacts on Interchange Transactions.
 Address administrative authorities, criteria, and processes for:
o Adding and deleting “permanent” Reliability Flowgates.
o Modifying Reliability Flowgates in the Book of Flowgates.
o Defining “temporary” Reliability Flowgates
o Expiring “temporary” Reliability Flowgates
o Adding “temporary” Reliability Flowgates to the Book of Flowgates
o Modifying Informational Flowgates
Terms
Flowgate. A single transmission element, or group of transmission elements, intended to model
MW flow impact relating to transmission limitations and transmission service usage. Within the
IDC, Transfer Distribution Factors (see PTDFs and OTDFs as defined below) are calculated to
approximate MW flow impact on the flowgate caused by point-to-point transfers.
Flowgate Categories:
Temporary Flowgate: A flowgate created by a RELIABILITY COORDINATOR within the
IDC to monitor or mitigate a Constraint for which a PERMANENT FLOWGATE has not
been identified. TEMPORARY FLOWGATES expire either at the time of the next model
update, by default, or on the End Date and Time entered in the IDC, not to exceed ninety
days, by the RELIABILITY COORDINATOR who created the TEMPORARY
FLOWGATE.
Permanent Flowgate: A flowgate approved by the Reliability Coordinator Working Group
and listed in the Book of Flowgates. PERMANENT FLOWGATES remain in the IDC unless
removed from the Book of Flowgates and deleted from the IDC.
Flowgate Types: A flowgate may be classified as one or more of the following types.
Informational Flowgate Type: A flowgate the RELIABILITY COORDINATOR can
establish for monitoring purposes only. An INFORMATIONAL FLOWGATE does not
qualify for Transmission Loading Relief (TLR) usage and should be reviewed periodically.
Page 18 of 37
Interchange Distribution Calculator (IDC) User’s Manual
Reliability PTDF Flowgate Type: A RELIABILITY PTDF FLOWGATE is represented by
the PTDF of its defined transmission element(s). The defined transmission element(s) can be
the monitored element(s) or the contingent element(s). This type of flowgate qualifies for
TLR usage under NERC reliability standard IRO-006, “Reliability Coordination –
Transmission Loading Relief.”
Reliability OTDF Flowgate Type: A RELIABILITY OTDF FLOWGATE is another type
of reliability flowgate. It is represented by the OTDF on the Monitored Element(s) with the
simulated outage of the critical contingency. This type of flowgate also qualifies for TLR
usage under NERC reliability standard IRO-006.
Benchmark Flowgate Type: A Benchmark Flowgate is a type identified by the IDCWG for
internal use by the Interchange Distribution Calculator (IDC) as a quality assurance measure.
It is used in monitoring differences in calculated Transfer Distribution Factors (TDFs) by the
IDC. A separate column in the Book of Flowgate (Flowgates page) identifies Benchmark
Flowgates.
Responsibilities and Authorities
The Operating Reliability Subcommittee (ORS) is responsible for:

The ORS has final approval for the basic set of flowgates taking into account
recommendations from the IDCWG.

Reviewing and authorizing all changes to the Book of Flowgates at each of its regularly
scheduled meetings.

Resolving disputes resulting from the implementation of Section B, “Guidelines for
Permanent Flowgates,” or Section C, “Flowgate Administration,” in this reference
document.
Individual Reliability Coordinators are responsible for:

The responsible RELIABILITY COORDINATOR or its IDCWG representative
authorizes changes to PERMANENT FLOWGATES through submittal to the IDCWG.

Authorizing and modeling TEMPORARY FLOWGATES within the IDC.

Recommending conversion of TEMPORARY FLOWGATES to PERMANENT
FLOWGATES.

Reviewing and updating periodically its PERMANENT and INFORMATIONAL
FLOWGATES.

Authorizing the removal of PERMANENT and INFORMATIONAL FLOWGATES.

Determine the need for TEMPORARY FLOWGATES along with the Transmission
Providers they represent. TEMPORARY FLOWGATES can be created directly within
the IDC and may become available for potential TLR use within 20 minutes to one hour
after they are entered into the IDC. TEMPORARY FLOWGATES can be deleted at any
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Interchange Distribution Calculator (IDC) User’s Manual
time and expire on the End Date and Time, not to exceed ninety days, entered in the IDC
by the RELIABILITY COORDINATOR who created the TEMPORARY FLOWGATE.
If no End Date and Time is entered for the TEMPORARY FLOWGATE, it will expire
when the IDC base case is updated.

Establish an INFORMATIONAL FLOWGATE to help monitor power flows over certain
interfaces.
The Interchange Distribution Calculator Working Group (IDCWG) is responsible for:

Performing the on-going function of administering the Book of Flowgates under the
direction of the IDCWG. Administration includes but is not limited to the following:
1. Tracking the relationship between TEMPORARY FLOWGATES and PERMANENT
FLOWGATES.
2. Reviewing flowgate data, including the transmission element(s), which define
PERMANENT FLOWGATES.
3. Reviewing flowgate data, including the transmission element(s), which define
TEMPORARY FLOWGATES used for TLR greater than TLR Level 1.

Authorizing Book of Flowgate changes that can be unanimously agreed upon. If the
IDCWG cannot unanimously agree, or if they see reasons for ORS discussions, then the
IDCWG will forward the flowgate review to the ORS with its recommendations.

Provide semi-annual updates to the ORS on Book of Flowgates changes highlighting key
changes in PERMANENT FLOWGATES.

Modeling the basic set of permanent Book of Flowgates changes as approved by ORS.

Maintaining records showing when flowgate changes were made and being the “owner”
of the Book of Flowgates.

Developing a posted flowgate review process for evaluating flowgates.
The NERC staff is responsible for:

Posting the basic set of flowgates on the NERC web site, and posting IDC messages
regarding flowgate changes and TEMPORARY FLOWGATE additions. IDC message
posting is expected to be an automated process.
The IDC Service Provider is responsible for:

Model the flowgate changes after their approval.

Communicate information regarding TEMPORARY FLOWGATE additions,
modifications, or deletions to RELIABILITY COORDINATORS. Whenever a flowgate
is added, deleted, or changed the IDC service provider will send a message to the
IDCWG with a copy to a NERC listserver. NERC staff will publicly post the message on
the NERC crc.nerc.com web page. Permanent Book of Flowgates changes will be posted
separately.
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Interchange Distribution Calculator (IDC) User’s Manual
6.2
Guidelines for Permanent Flowgates
A PERMANENT FLOWGATE must meet at least one of the following five requirements to be
in the Book of Flowgates:
1. A TLR has been called on the flowgate at least once during the past two years.
2. A TLR greater than TLR Level 1 has been called on the TEMPORARY FLOWGATE at
least once during the past two years and the TEMPORARY FLOWGATE was created
multiple times during the past two years.
3. The flow on the flowgate has exceeded a reasonably high percentage (i.e. 90%) of its
applicable rating or INTERCONNECTED RELIABILITY OPERATING LIMIT (IROL)
at least once during the past three years.
4. The flow on the flowgate is expected to exceed a reasonably high percentage (i.e. 90%)
of its applicable rating or IROL in the coming year.
5. The IDCWG or ORS has determined that the flowgate should remain in the Book of
Flowgates, or the RELIABILITY COORDINATOR recommends and presents the
rationale to the ORS that a flowgate be included or retained in the Book of Flowgates.
PERMANENT FLOWGATES will not be removed from the Book of Flowgates or the IDC
database unless requested by the responsible RELIABILITY COORDINATOR.
6.3
Guidelines for Temporary Flowgates
1. TEMPORARY FLOWGATES will expire either at the time of the next model update, by
default, or on the End Date and Time entered in the IDC, not to exceed ninety days, by
the RELIABILITY COORDINATOR who created the TEMPORARY FLOWGATE.
IDC base cases are normally updated on a monthly basis. The IDC model updating
process schedule will be posted on the NERC web site as it becomes known.
2. TEMPORARY FLOWGATES, which are used for TLR greater than Level 1, should go
through a IDCWG review. Individual RELIABILITY COORDINATORS may
recommend converting a TEMPORARY FLOWGATE into a PERMANENT
FLOWGATE by following Step 3 in the PERMANENT FLOWGATES section above.
6.4
Guidelines for Informational Flowgates
1. INFORMATIONAL FLOWGATES are included in the Book of Flowgates (BoF) that is
posted on the NERC web site.
2. INFORMATIONAL FLOWGATES may be converted to Reliability Flowgates by going
through the formal recommendation process.
6.5
IDCWG Flowgate Review
RELIABILITY COORDINATORS may request the IDCWG to review and revise the list of
PERMANENT FLOWGATES in accordance with the guidelines detailed in Section B. A
standardized approach should be used for reviewing all flowgates. The Book of Flowgates will
Page 21 of 37
Interchange Distribution Calculator (IDC) User’s Manual
be kept up to date so that it is consistent with the latest IDC base case. The IDCWG will
generally not review TEMPORARY FLOWGATES unless:

They are used for a TLR greater than Level 1.

A flowgate is repeatedly created as a Temporary Flowgate.

A request is made to convert a Temporary Flowgate to a Permanent Flowgate.
INFORMATIONAL FLOWGATES are not to be used for TLR. The review for
INFORMATIONAL FLOWGATES may differ from that of a Reliability Flowgate. IDCWG
review of Reliability Flowgates for thermal purposes may differ from the review of Reliability
Flowgates used for voltage or dynamic stability purposes.
Flowgate review may require the responsible RELIABILITY COORDINATOR to provide
additional flowgate detail as determined by the IDCWG.
Page 22 of 37
Interchange Distribution Calculator (IDC) User’s Manual
6.6
Flowgate Administration
The Flowgate Administration process is shown in the flowchart below.
IDCWG or
RC review
BoF
By
Reliability
Coordinator
Need to
create or
modify
Temporary
FG created
in IDC
Permanent
FG created
in IDC
Inform IDCWG
by IDCWG FG
process
IDCWG
Review
IDCWG
Approve?
By
IDCWG
Yes
No
RC provides
additional
information
ORS
Review
Inform ORS
ORS
Approve?
No
Yes
● Update
BoF and
post
● IDCWG records revision
● Notify IDC provider
● Notify RC via IDC
Page 23 of 37
ORS:
● Reviews changes to BoF
● Resolves disputes
Interchange Distribution Calculator (IDC) User’s Manual
7.0
GTL Guidelines for the IDC
7.1
General
The IDC software was created as a tool to allow a Reliability Coordinator to utilize the NERC
TLR procedure to receive relief on a congested Flowgate. This relief is assigned by evaluating
the submitted real time point-to-point e-tag transactions and Balancing Area generation to load
calculated by GTL engine based on real time data inputted to the IDC by the Market Entities.
GTL calculates a Gen-To-Load Impact for each identified Balancing Authority in the IDC
Model.[PFV Project: GTL calculation process replaces the Market Flow calculation process.]
7.2
GTL Data Inputs
[PFV Project: GTL calculation process replaces the Market Flow calculation process.]
[PFV Project: Market service priorities are eliminated in PFV.]Marginal Zone Data
Marginal Zone data is submitted to the IDC to provide a refined representation of the
generation dispatch serving interchange inside the market area. The Market Operator is
responsible for supplying three pieces of information to the IDC regarding Marginal Zones.
 Marginal Zone model representation
 Generator Mobility Factors
 Marginal Zone Participation Factors
Marginal Zone Modeling
The NERC Interchange Distribution Calculator Working Group (IDCWG) has been
charged with monitoring the creation of the Marginal Zones for the IDC base case model.
The group has identified a series of parameters and criteria to determine is a Marginal
Zone size is appropriate in nature or need to be adjusted.
In the IDC PSS/E base case a Marginal Zone is defined as a reasonably sized group of
generators that have similar Flowgate impacts. The Marginal Zone size should be
manageable and consistent within reasonable parameters and computational tools, not too
big or too small.
Generator Mobility Factors
This data will indicate on a per-generator basis the anticipated availability of a generator
to participate in the interchange of the Marginal Zone. It is used to help calculate the TDF
for each of the Marginal Zones.
Marginal Zone Participation Factors
This data is used to help calculate the TDFs for the market area. This data describes how
much each defined zone in the market area is contributing to serving exports/sinking
imports.
[PFV Project: Coordinated Flowgate process is eliminated in PFV.] [PFV Project:
Coordinated Flowgate process is eliminated in PFV.]Marginal Zone Generator Data
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Interchange Distribution Calculator (IDC) User’s Manual
Two sets of data will be provided to support the IDC distribution factor calculation.
Individual Generator Mobility Factor (GMF)
This data will indicate on a per-generator basis the anticipated availability of a generator
to participate in interchange in the Marginal Zone. This data will be provided to the IDC
no less than once an hour.
Marginal Zone Participation Factors
This data will describe how much each defined zone within the market area is
contributing to serving exports/sinking imports. This data will be provided to the IDC at
least every 15 minutes but not more often than every 5 minutes.
Load and Interchange Data
Control Zone Daily Forecast Load
This data will be distributed through the IDC Tag Dump for the market areas. Reliability
Coordinators will use this data to perform contingency analysis studies for the next day.
This data will be provided to the IDC once a day.
Control Zone Next Day Hourly Forecast Load
This data will be distributed through the IDC Tag Dump for the market areas. Reliability
Coordinators will use this data to perform contingency analysis studies for the next day.
This data will be provided to the IDC once a day at 12:00 CST. This data will be updated
as more accurate data is available for the next day.
Control Zone Current Day Hourly Forecast Load
This data will be distributed through the IDC Tag Dump for the market areas. Reliability
Coordinators will use this data to perform contingency analysis studies.
Control Zone Current and Next Hour Forecast Load
This data will be distributed through the IDC Tag Dump for the market areas. Reliability
Coordinators will use this data to perform contingency analysis studies. This data will be
provided to the IDC once every hour.
[PFV Project: This data is no longer needed in PFV.] [PFV Project: This
data is no longer needed in PFV.] [PFV Project: This data is no longer
needed in PFV.] [PFV Project: This data is no longer needed in
PFV.]7.3 Generation-To- Load (GTL) [PFV Project: the following is
the new GTL calculation methodology]
Balancing Authorities can be identified in the models and the registry such that the IDC
recognizes zonal structures and calculates GTL flow within the footprint appropriately. Like all
other entities, these BAs will provide the IDC the data via SDX needed to make such calculation.
The GTL calculation for zonal structure BAs will be comprised of two components, GTLNative
and GTLTransfer. The GTLNative is a representation of the flow within the zone, while the
GTLTransfer is a representation of the interchange between the zones. Both components are
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subject to curtailment in an appropriate TLR Level. The GTL Native component would represent
what IDC identified as NNL in current IDC methodology.
Transmission Service Priorities
Transmission service is classified into non-firm and firm priorities with the potential for
multiple non-firm priorities, based on the generator priority to serve its load. These generator
priorities are provided via e-Tags (intra-BA tags where only the transmission priorities are
utilized; that is, the energy profiles are ignored and the actual generation output is used
instead), or via the SDX through the so-called Generator Prioritization method.
Load and Interchange Data
Control Zone Daily Forecast Load
This data will be distributed by the IDC through the IDC Tag Dump for the market areas.
Reliability Coordinators will use this data to perform contingency analysis studies for the
next day. This data will be provided to the IDC once a day.
Control Zone Next Day Hourly Forecast Load
This data will be distributed by the IDC through the IDC Tag Dump for the market areas.
Reliability Coordinators will use this data to perform contingency analysis studies for the
next day. This data will be provided to the IDC once a day at 12:00 CST. This data will
be updated as more accurate data is available for the next day.
Control Zone Current Day Hourly Forecast Load
This data will be distributed by the IDC through the IDC Tag Dump for the market areas.
Reliability Coordinators will use this data to perform contingency analysis studies.
Control Zone Current and Next Hour Forecast Load
This data will be distributed by the IDC through the IDC Tag Dump for the market areas.
Reliability Coordinators will use this data to perform contingency analysis studies. This
data will be provided to the IDC once every hour.
7.3
[PFV Project: Coordinated flowgate process is eliminated with PFV. GTL is
calculated for every flowgate in the Book of Flowgates.] 7.4 Market
TDF
Calculations
The IDC uses real-time Marginal Zone Participation Factors and Generation Mobility Factors to
calculate two separate TDF values for each Market Area. One is based on the Import capabilities
of the area and the other will be based on the export capabilities of the area. The TDFs are used
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to identify the impacts of the transactions Sourcing or Sinking in the Market Area, and to provide
a more detailed representation of the generating units that are affected by the curtailment of
tagged transactions.
The Market Operator will provide the Marginal Zone Weighting Factors and the Generation
Mobility Factors to the IDC every 15 minutes. The IDC will update the TDF matrices associated
with the Market Areas when it receives updated factors; thus providing and more accurate
representation of the market response to TLR actions. Balancing Areas that are not part of a
market will not provide this additional real-time data to the IDC.
7.5
Tag Mapping to Marginal Zones
The Marginal Zone concept is used in order to more accurately identify the set of generators
whose schedules change in response to point-to-point curtailments. The Market Operator will
provide the IDC with sets of export and import Marginal Zone weighting factors. The Export
factors will be utilized to assess the impact of transaction that source in the market area. The
Import factors will be utilized to assess the impact of transaction that sink in the market area.
These weighting factors will be used by the IDC to weight and scale the Market’s zonal TDFs
and calculates the Market TDF.
It is possible that a transaction can appear to be skewed by these calculations. If all of the
marginal import generation and all of the marginal export generation is located in a single
Marginal Zone, the IDC will treat the tag as transferring energy inside of a Control Zone. This
tag will have a 0% effect on all flowgates and never be curtailed. To address this situation, the
tags that model energy transfers in this way use the historical Balancing Area TDFs.
7.6
Marginal Zone Participation Factors
While individual generator dispatch is not specifically provided, the relative dispatch of the
Marginal Zones results in a finer granularity of impact calculations for the market area.
For the IDC to properly account for tagged transactions, a Market Operator needs to send data
describing the locations of the marginal generators that are either supplying generation to exports
or are having energy replaced by imports.
The Market Operator is required to define a set of zones that can each be easily aggregated into a
common distribution factor that is representative of the zone. This information must be shared
and coordinated with the Interchange Distribution Calculator. The Market Operator must then
send the IDC the participation factors for those zones (percentages that indicate on a real-time
basis how those zones are providing or would provide marginal megawatts). Two sets of data are
required:
 An Import set, which indicates the next marginal units to supply replacement energy
should the import transactions be curtailed.
 An Export set, which indicates the last marginal units used to supply the energy exported
to other areas.
These Marginal Zone sets are used to determine more granular Transfer Distribution Factors in
the IDC for use in analyzing Imports and Exports. Essentially, imports are replacing energy that
would have been generated by the next marginal units while exports are being served by the last
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marginal units. The Market Operator determines these marginal units by developing three
different dispatch solutions based on forecast load, an optimistic (reduced) load, and a
pessimistic (inflated) load. These solutions are then compared to identify the changes in dispatch
that signal which units are marginal units. By comparing these numbers, it can be determined
which Marginal Zones will move to accommodate changes in load. These numbers can then be
abstracted into the percentage each zone will contribute to the movement. By utilizing these
abstract percentages, changes in imports and exports can be assigned to source and sink from
various zones as appropriate.
Marginal Zone Definition
Marginal Zones are determined through the collaboration of a Market Operator and the
NERC Interchange Distribution Calculator Working Group (IDCWG). Marginal Zones
should be comprised of generators that have electrically similar characteristics from a
distribution factor point of view.
Participation Factor Calculation
Raw Marginal Zone Participation Factors are determined relatively simply. The Market will
examine the constraints and pricing and/or cost information for the footprint and determine
the percentage of generation output in each zone that represents the next marginal megawatts
and the last marginal megawatts. These will establish, for imports and exports, a set of
participation factors that, when summed, will equal 100%.
7.7
Pseudo Balancing Areas
Certain schedules may always come from a specific generator. To the extent that these sources
are known, the BA may elect to request that these sources be modeled as Pseudo Balancing
Areas. For each of these Pseudo Balancing Areas, a specific TDF will be generated to ensure
transaction impact is modeled appropriately. Pseudo Balancing Areas must be approved by the
NERC ORS before implementation.
7.8
GTL Calculation Process
[PFV Project: The Market Flow calculation process is eliminated in PFV.]PFV Project:
The IDC GTL engine receives the real time output and transactions associated with a BA
footprint; this is done via WebSDX data submission. Based on this input, IDC GTL calculates
the impact of a given BA or Market Entity on all defined flowgates in the IDC. IDC will
calculate GTL for every BA represented is the model. IDC splits GTL into two components;
GTLNative which represents the output of generation within a Control Zone of BA serving load
within the same Control Zones. Whereas the GTLTransfer represents any exports or imports taking
place between Control Zones defined within a BA. Hence, if a BA doesn’t model multiple
Control Zones within the model, the GTLTransfer will be zero and consequently treating all
generation output serving load within all of the BA as GTLNative.
Generally, the current Market Entities that currently report Market Flow to the IDC are expected
to have both GTLNative and GTLTransfer components representing their GTL (formerly known as
Market Flow). GTLNative, the impact of all generators within a historical Balancing Authority
residing within the Market Entity serving the load within the historical BA, each of which would
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be represented as Control Zone within the Market Entity in the GTL process. GTLTransfer
component of such configuration (multiple Control Zones within a BA) is calculated by
allocating the excess generation in each of the exporting Control Zones to help serve the load in
those Control Zones with less generation than load. The GTLTransfer is not limited to Market
Entities; however, it is rather dependent on how a BA models its area in the IDC model. If a BA
doesn’t model multiple Control Zones within the model, the GTLTransfer will be zero. All impacts
are calculated at 0% and 5% threshold levels for each flowgate defined for each flowgate defined
in the Book of Flowgates.
Dynamic Schedules
Specific Dynamic Schedule exports will be tagged with a specific source. To prevent double
counting, if a unit is associated with a Dynamic Schedule, its output will be reduced by that
amount before estimating its GTL effect. [PFV Project: Entities may upload real time
Dynamic interchange flow to IDC GTL.] The real time information would be used by the IDC
GTL to calculate impact of the transaction on all flowgates. If no such information is provided to
IDC GTL, then the schedule MW from E-Tag will be used as the schedule MW for the dynamic
transaction.
Tagged Export
All Tagged exports are processed using either the Marginal Zone concept or using the given
Source/Sink on tagged transaction. Entities that will be using the Marginal Zone approach will
provide IDC GTL with the information needed to evaluate allocate the transaction appropriately
to each zone.
For GTL purposes, all tagged exports are used to scale the generation output of specific resource
if transaction as tagged from the resource, or Control Zone if transaction is tagged to the specific
location, or the entire BA fleet if the transaction sources from the entire BA. The scaling is
necessary for the purpose of determining the participation of a resource of fleet of resources in
the injection of GTL.
Tagged Import
All Tagged imports are processed using either the Marginal Zone concept or using the given
Source/Sink on tagged transaction. Entities that will be using the Marginal Zone approach will
provide IDC GTL with the information needed to allocate the transaction appropriately to each
zone within the BA.
For GTL pruposes, all tagged imports are used to scale the load of a given Control Zone or the
entire BA depending on the granularity of the Sink on the tagged schedule. The scaling of the
load is necessary to reduce the amount of load that IDC GTL must use as BA served load, which
is served by native generation or using other BA generation.
7.10 BA Relief Responsibility
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[PFV Project: GTL calculation process replaces the Market Flow calculation process.]
[PFV Project: GTL calculation process replaces the Market Flow calculation process.]
PFV Project:
BA Relief Responsibility

For BAs that have chosen to tag non-firm intra-BA network service, the tag will be used
to establish the curtailment priority of the generator output provided via the SDX. As
such, a GTL calculation will be performed by the IDC and will be used to assign a relief
obligation to the BA. The IDC will not assign curtailment to these tags since their
impacts are being addressed in the relief obligation. However, the BA may elect to
modify the tag as they take steps to meet their relief obligation.

The IDC will no longer utilize unconstrained GTL flow. Unconstrained GTL flow is
supposed to represent a BAs impacts on a flowgate had they not redispatched their
system. There is no readily available mechanism to compute this value. In place of
unconstrained GTL flow, the current hour GTL flow that represents a redispatched
system will be utilized to assign relief obligations. This means that relief obligations
beyond the first hour will represent relief obligations that are incremental to those
accomplished in previous hours.

The IDC will no longer utilize a next-hour GTL for 3a and 5a TLR events. There is no
readily available mechanism to compute next-hour constrained GTL flow that represents
a redispatched system. In its place, the IDC will utilize the GTL calculated at 25 minutes
into the current hour for next hour relief obligations.
o Even for the first hour of the TLR event before the BA has responded to a relief
obligation assigned to them, the IDC will use the GTL calculated at 25 minutes
into the current hour for next hour relief obligations.

During TLR 3a and 3b, the IDC will use current hour non-firm forward GTL > 5% to
assign non-firm relief obligations. During TLR 5a and 5b, the IDC will use a
combination of current hour non-firm forward GTL > 5% to assign non-firm relief
obligations and current hour firm forward GTL > 5% to assign firm relief obligations.
Since the steps taken by the BA to meet their relief obligation could involve using
combinations of generators at or above 5% and below 5%, forward impacts and counterflow impacts, and generators with either firm and/or non-firm transmission service, a
credit for redispatch process will be used where the current hour GTL flows (both firm
and non-firm) will be adjusted to receive credit for steps taken from the issue time of the
TLR
The credit for redispatch (discussed below) will be determined by freezing the current net
GTL down to 0% for hour X flow at the issue time of the first hour relief obligation and
comparing this value with the current hour GTL flow calculated by the IDC at 15 minute
intervals in the current hour for next hour relief obligations. This frozen value will continue
to be used for all consecutive hours of relief obligation. If there is an hour when the GTL
flow of the BA is released, where no further GTL curtailments are needed relative to tag
curtailments in the same priority bucket and the full amount of GTL flows can be restored
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(the BA no longer needs to bind); the frozen value will be unfrozen. If there is a future hour
where there is a relief obligation, a new value for the GTL flow at the new issue time of the
relief obligation will be calculated and frozen.
7.11 Firm Re-dispatch Credits
PFV Project:
(Credit for Redispatch)
In the case where non-firm GTL impacts on a flowgate are greater than or equal to 5% reported
to the IDC on a flowgate that experiences congestion, the BAs with generator impacts greater
than or equal to 5% may be assigned a relief obligation during TLR 3 depending on the amount
of flowgate reduction requested and the priority assigned to a BA GTL MW. Meeting the relief
obligation may be demonstrated by adjusting generator output whose combined impact produces
the amount of the relief obligation.
Upon Relief obligation assignment to BA based on calculated non GTL within the BA, the
entity may choose to re-dispatch its generators to meet their relief obligation on a least cost basis
which may not result in the non-firm generators being curtailed. This triggers the need for
creating a mechanism to provide credit for the re-dispatch to avoid assigning further relief
obligation to this BA based on the non-firm flow that is still active since the BA provided the
relief using high priority flows.
Approaches for Meeting Relief Obligations
A BA may be assigned a GTL relief obligation during TLR due to GTL impacts in the IDC.
 The BA will meet its relief obligation using either those generators in priority buckets
assigned proportional curtailments by the IDC or any combination of generators
assigned or not assigned proportional curtailments by the IDC.

The IDC will identify a list of Inc generators and Dec generators within the BA to
assist them in meeting their relief obligation. The Inc and Dec generators will be
provided to the BA and its associated RC.A BA may use the Inc and Dec generators
to assist them for meeting their relief obligation or use a systematic economic
dispatch study to determine the most economical re-dispatch to meet the assigned
relief obligation.

IDC will determine if the relief was provided in order to assign future hour relief
obligations. The net GTL flow will be evaluated at 15 minute intervals during the
hour from the start of the re-dispatch time to assess whether the relief obligation was
met during any of these four intervals. The output from the IDC’s evaluation will be
provided to the BA, its associated RC, and the RC issuing the relief request. As part
of the evaluation the IDC will update the Inc and Dec generators which will be
provided to the BA and its associated RC.
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
o If any of the intervals show the relief obligation has been exceeded, the largest
exceedence will affect the BA GTL in the hour beyond next hour.
Exceedences will be modeled in the IDC as reload credit prior to curtailing
transactions in subsequent hours.
o If all of the intervals show the relief obligation has not been met, the smallest
shortfall will affect the BA GTL sub-priorities in the hour beyond next hour as
documented in the Determination of Sub-priorities as discussed in section 3.4
– TLR Sub-Priorities of this document.
o Otherwise, (exactly met in one or more intervals and did not exceed in any of
the other intervals) there will be no impact on the sub-priorities in the hour
beyond next hour.
A credit for the re-dispatch that was accomplished from the start of the re-dispatch
time will be applied to the next hour relief obligation calculation by the IDC,
depending upon whether the BA met its relief obligation. The fact that generators
with lower priority transmission service were assigned a curtailments in previous
hours have not been reduced will not result in a double counting of the lower priority
GTL impacts.
7.12 Market Tag Dump Data
When a Balancing Area or Market Area expands, tags are eliminated between areas that have
become part of the same footprint. As a result, the Tag Dump data cannot be used to determine
interchange between these areas. Each entity that expands its Balancing Area or Market Area
boundary is responsible to provide a Net Interchange and Load value for the areas that are no
longer visible in the Tag Dump. These values will be uploaded to the IDC at least hourly to be
included in the Tag Dump.
8.0
Phase Shifters in the IDC
8.1
Setup and Use of Phase Shifters in IDC
This section describes how the settings selected for the phase shifters impact the modeling within
the IDC. The different settings will impact how the schedules are modeled and impacted by
TLRs. There are two scenarios possible to describe interfaces containing phase shifters. The first
scenario is that all tie lines on that interface contain phase shifters. The second scenario is that
there is a mix of phase shifters and normal AC tie lines. While some description is provided for
the second scenario, this would be a complex implementation and should be considered further
before implemented in the IDC.
Phase Shifters in the IDC can operate in one of three modes; Regulate, Non-Regulate, and
Bypass. The operating mode of the phase shifter defines how transactions scheduled across the
phase shifter are modeled in the IDC.
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8.2
Modeling Requirements for Phase Shifters
Specific modeling is required in the IDC to identify phase shifters. There is also a set of data that
is required to be entered in the Book of Flowgates (BoF) to support the IDC modeling. Pseudo
control areas are created on each side of each phase shifter, each with a generator, then one more
for the total on each side. The tag is broken up based on this layout.
When the correct POR/POD is selected the IDC knows to use this modeling. If the tag is not
submitted with the specific POR/POD identifying the phase shifter, that transaction will continue
to be modeled normally, flowing on the AC system not being modeled on the segments
representing the phase shifter. When the phase shifter is not regulating the submittal format on
the e-tag is irrelevant, the same result will occur whether the e-tag references the phase shifter or
not.
8.3
Submittal of e-tags over Phase Shifters
The manner in which a customer submits an e-tag over an interface that contains phase shifters
will determine how the TDF on the transaction is determined in the IDC. In order to accurately
capture the phase shifter path, there should be a specific POR/POD available to indicate that the
customer wants to flow energy over the phase shifters. If there are multiple phase shifters on an
interface, it is not expected that the customer could select which specific phase shifter would be
utilized for the flow.
If a customer submits an e-tag on a path that contains a phase shifter and does not select the
POR/POD associated with the phase shifter, the tag is assumed to flow over the AC network and
will be modeled as all other e-tags in the IDC.
If the customer submits an e-tag on a path that contains a phase shifter and does select the
POR/POD associated with the phase shifter, the IDC will know that the tag will flow over the
phase shifter and will break the tag into three segments prior to any internal calculation
processing for a TLR. If any of the segments of the tag are impacted by a TLR, the entire tag is
curtailed accordingly. The three segments are:
1) From the Source to the Phase Shifter
2) Across the Phase Shifter
3) From the Phase Shifter to the Sink
8.4
IDC Use of Phase Shifters in Regulate Mode
In Regulate Mode, the IDC models tags that can impact the phase shifter interface in two
different ways, depending on how the e-tags are created by the customer.
1. An e-tag not using the phase shifter POR/POD
 The IDC will see the phase shifter as an open circuit and will distribute 100% of
the flow across the rest of the network model.
2. An e-tag using the phase shifter POR/POD
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

The IDC will distribute the flow across the phase shifter. The percentage of flow
that will be directly modeled over the phase shifter is based on the selected
Distribution Factor. The Distribution Factor indicates what the percentage of the
submitted e-tag is targeted to flow on each separate phase shifter on the interface.
The sum of the distribution factors for an interface that is fully regulated by the
phase shifters should be 100%. Under this condition virtually no distribution from
these transactions will be seen on other flowgates. Their TDFs on other flowgates
become very close to zero. Under this condition these transactions will not be
subject to TLR curtailment by the IDC.
PFV Project:
When Phase Shifters operate in Regulate Mode, the flow across the phase shifter is controlled.
IDC receives from the RCs the flow on the phase shifter. By subtracting the tagged schedules
across the phase shifter, the remaining amount defines the network service flow across the phase
shifter. This remaining amount identifies the injection and withdrawal at the end buses of the
phase shifter. These end-buses are modeled in the IDC as pseudo-CAs, and IDC treats these
injections/withdrawals impacts through native/transfer components where the native component
is always zero.
8.5
IDC Use of Phase Shifters in Non-Regulate Mode
In Non-Regulate Mode, the Distribution Factors for the phase shifters do not apply. The IDC
calculates the TDFs based on the impedance of the current tap position. Note that the impedance
is lowest at neutral tap and increases as the taps move up or down away from neutral. When a
phase shifter is in non-regulate mode, all transactions are subject to all TLR curtailments. In this
case, even if the transaction is identified as flowing over the phase shifter POR/POD path, it is
subject to all TLR curtailments. The TDFs will accurately represent the current tap position.
Relatively speaking the impedance change from the various tap positions has a very small impact
on the distribution calculations. The results will be very close to those seen with the PAR model
removed from the IDC model.
8.6
IDC Use of Phase Shifters in Bypass Mode
Because SDX does not currently send the status of bypass disconnects, it is up to the user to
select this status in the IDC. With bypass selected, the model uses the impedance at the neutral
tap setting for the transformer. That means that the IDC ignores all of the following; the ISN tap
positions, the manual tap positions, and the SDX data for the transformer.
While the phase shifter is set to bypass mode in the IDC, an SDX branch outage of the phase
shifter will not take effect. The IDC model will still “see” the phase shifter as in service and on
bypass. If a user wants an SDX outage of the transformer to be reflected in the IDC, the phase
shifter should be left in non-regulate mode.
PFV Project:
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8.7
Phase Shifter Real Time Data Input
Each entity that operates a Phase Shifter may submit MW flow and the tap position of each
Phase Shifter. The submitting entity may submit the data for current time of future time based on
forecast flows and position of the equipment. IDC GTL will use the data to more accurately
determine the impact of the transactions flowing on the Phase Shifters. The Tap position data
will be used by IDC GTL to determine the appropriate impedance of this path and consequently
calculate a TDF that is more representative of real time operations. Any non-tagged flow
associated with the path maybe considered part of the an entity or set of entities’ GTL.
9.0
DC Lines in the IDC
9.1
Modeling Requirements for DC Lines
The methodology used in the IDC to model transactions that cross phase shifters is also utilized
to reflect transactions that flow on DC ties such that the TDF on the DC tie is zero. The DC tie
could be radial where only one end of the tie is located in the Eastern Interconnection or the DC
tie can be located fully within the Eastern Interconnection.
Specific modeling is required within the PSS/E model to represent the DC ties to allow this
methodology to be applied. A Change Order is required to establish the initial modeling process
for a new DC tie. Every subsequent PSS/E model build will include the required modifications
for all DC ties.
For a DC tie that has only one side in the Eastern Interconnection, the PSS/E model is modified
to contain a pseudo balancing area for the end of each DC tie that is not located in the Eastern
Interconnection. The ‘location’ of the source/sink for the DC ties are mapped within the IDC to
these pseudo balancing areas based on the data provided on the e-tag.
For a DC tie that is wholly in the Eastern Interconnection, the PSS/E model is modified to
contain two pseudo balancing areas, one to represent each end of the DC tie.
9.2
Submittal of e-tags over DC Lines
When an e-tag is submitted over a DC tie where there is defined mapping for that tie the
transaction is broken into segments similar to the process described for phase shifters. The TDF
for each segment is totaled to provide the overall TDF for that transaction.
If a transaction is impacted by a TLR, the user can view the TDF of the individual segments by
selecting the tag on the Congestion Management Report. This can also be viewed using the
Whole Transaction List.
9.3
DC Lines IDC Responsibility
When an e-tag is submitted over a DC tie line that leaves the Eastern Interconnection is impacted
by a TLR the RC located in the Eastern Interconnection will acknowledge the TLR. It is the RC
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located in the Eastern Interconnection responsibility to manage the TLR process for any DC tie
lines leaving the Interconnection.
PFV Project:
DC lines are modeled in the IDC similarly to Phase Shifters operating in Regulate Mode, where
the flow across the DC line is controlled. IDC receives from the RCs the flow on the DC lines.
By subtracting the tagged schedules across the DC line, the remaining amount defines the
network service flow across the DC line. This remaining amount identifies the injection and
withdrawal at the end buses (rectifier and inverter buses) of the DC line. These end-buses are
modeled in the IDC as pseudo-CAs, and IDC treats these injections/withdrawals impacts through
native/transfer components where the native component is always zero.
9.4
DC Ties Real Time Data Input
The Eastern Interconnection entity with whom the DC tie is connected may submit the real time
and forecasted flow of the DC Tie. Active Tagged transactions on DC Ties are considered for
current time and future time impacts. Any non-tagged DC Tie flow that maybe considered part
of an entity or set of entities’ GTL.
10.0 NERC Tag Dump
The IDC creates a text file each hour containing all of the e-tags in the IDC database. This file,
called the NERC Tag Dump, is posted to a NERC FTP site and is used by several reliability
entities in the Eastern Interconnection for system studies and reliability analysis.
10.1 NERC Tag Dump Data Format
The NERC Tag Dump uses the following format:
LINE 1
“TAG [TAG_NAME] START”
LINE 2
“TAG START DATE/TIME”, “TAG END DATE/TIME”, “SOURCE SC”, “SINK SC”, “SOURCE CA”,
“SINK CA”, “SOURCE”, “SINK”
LINE 3
“[TRANSMISSION]”, “TRANSMISSION START DATE/TIME”, “TRANSMISSION END DATE/TIME”,
“TP NAME”, “PRIORITY”, “TRANSMISSION PRODUCT”, “OASIS RESERVATION”, “MW”, “POR”,
“POD”,
There will be a separate line for each priority level of service.
LINE 4
“[ENERGY]”, “ENERGY START DATE/TIME”, “ENERGY END DATE/TIME”, “SCHEDULE MW”,
“ACTIVE MW”
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Interchange Distribution Calculator (IDC) User’s Manual
There will be a separate line for each change in the ENERGY Profile for each tag. This will include
curtailments that are done, etc.
LINE 5
“TAG [TAG_NAME] END”
LINE 6
“CONTROL ZONE [Control Zone Name] START”
The Control Zone Name will be validated against the current NERC BoF for accuracy. Each Control Zone
will have an assigned Reliability Coordinator that will be allowed to submit this data.
LINE 7
“LOAD/INTERCHANGE START DATE/TIME”, “LOAD INTERCHANGE END DATE/TIME”, “LOAD
MW”, “NET INTERCHANGE MW”
There will be a separate line for each hour identified
“LOAD MW” will be a positive value.
“NET INTERCHANGE MW” can be a positive or negative value
LINE 8
“CONTROL ZONE [Control Zone Name] END”
The Control Zone Name will be validated against the current BoF for accuracy. Each Control Zone will
have an assigned Reliability Coordinator that will be allowed to submit this data.
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