Reliability Standards-TPL-007-1

TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

A. Introduction
1.

Title:
Transmission System Planned Performance for Geomagnetic
Disturbance Events

2.

Number:

3.

Purpose:
Establish requirements for Transmission system planned performance
during geomagnetic disturbance (GMD) events.

4.

Applicability:

TPL-007-1

4.1. Functional Entities:
4.1.1 Planning Coordinator with a planning area that includes a Facility or
Facilities specified in 4.2;
4.1.2 Transmission Planner with a planning area that includes a Facility or
Facilities specified in 4.2;
4.1.3 Transmission Owner who owns a Facility or Facilities specified in 4.2;
4.1.4 Generator Owner who owns a Facility or Facilities specified in 4.2.
4.2. Facilities:
4.2.1 Facilities that include power transformer(s) with a high side, wyegrounded winding with terminal voltage greater than 200 kV.
5.

Background:
During a GMD event, geomagnetically-induced currents (GIC) may cause transformer
hot-spot heating or damage, loss of Reactive Power sources, increased Reactive Power
demand, and Misoperation(s), the combination of which may result in voltage collapse
and blackout.

6.

Effective Date:
See Implementation Plan for TPL-007-1

B. Requirements and Measures
R1.

Each Planning Coordinator, in conjunction with its Transmission Planner(s), shall identify
the individual and joint responsibilities of the Planning Coordinator and Transmission
Planner(s) in the Planning Coordinator’s planning area for maintaining models and
performing the study or studies needed to complete GMD Vulnerability Assessment(s).
[Violation Risk Factor: Lower] [Time Horizon: Long-term Planning]

M1. Each Planning Coordinator, in conjunction with its Transmission Planners, shall provide
documentation on roles and responsibilities, such as meeting minutes, agreements,
copies of procedures or protocols in effect between entities or between departments of
a vertically integrated system, or email correspondence that identifies an agreement
has been reached on individual and joint responsibilities for maintaining models and
performing the study or studies needed to complete GMD Vulnerability Assessment(s),
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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

in accordance with Requirement R1.
R2.

Each responsible entity, as determined in Requirement R1, shall maintain System
models and GIC System models of the responsible entity’s planning area for performing
the study or studies needed to complete GMD Vulnerability Assessment(s). [Violation
Risk Factor: High] [Time Horizon: Long-term Planning]

M2. Each responsible entity, as determined in Requirement R1, shall have evidence in either
electronic or hard copy format that it is maintaining System models and GIC System
models of the responsible entity’s planning area for performing the study or studies
needed to complete GMD Vulnerability Assessment(s).
R3.

Each responsible entity, as determined in Requirement R1, shall have criteria for
acceptable System steady state voltage performance for its System during the
benchmark GMD event described in Attachment 1. [Violation Risk Factor: Medium]
[Time Horizon: Long-term Planning]

M3. Each responsible entity, as determined in Requirement R1, shall have evidence, such as
electronic or hard copies of the criteria for acceptable System steady state voltage
performance for its System in accordance with Requirement R3.
R4.

Each responsible entity, as determined in Requirement R1, shall complete a GMD
Vulnerability Assessment of the Near-Term Transmission Planning Horizon once every
60 calendar months. This GMD Vulnerability Assessment shall use a study or studies
based on models identified in Requirement R2, document assumptions, and document
summarized results of the steady state analysis. [Violation Risk Factor: High] [Time
Horizon: Long-term Planning]
4.1. The study or studies shall include the following conditions:
4.1.1. System On-Peak Load for at least one year within the Near-Term
Transmission Planning Horizon; and
4.1.2. System Off-Peak Load for at least one year within the Near-Term
Transmission Planning Horizon.
4.2. The study or studies shall be conducted based on the benchmark GMD event
described in Attachment 1 to determine whether the System meets the
performance requirements in Table 1.
4.3. The GMD Vulnerability Assessment shall be provided within 90 calendar days of
completion to the responsible entity’s Reliability Coordinator, adjacent Planning
Coordinators, adjacent Transmission Planners, and to any functional entity that
submits a written request and has a reliability-related need.
4.3.1. If a recipient of the GMD Vulnerability Assessment provides
documented comments on the results, the responsible entity shall
provide a documented response to that recipient within 90 calendar
days of receipt of those comments.

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

M4. Each responsible entity, as determined in Requirement R1, shall have dated evidence
such as electronic or hard copies of its GMD Vulnerability Assessment meeting all of the
requirements in Requirement R4. Each responsible entity, as determined in
Requirement R1, shall also provide evidence, such as email records, web postings with
an electronic notice of posting, or postal receipts showing recipient and date, that it has
distributed its GMD Vulnerability Assessment within 90 calendar days of completion to
its Reliability Coordinator, adjacent Planning Coordinator(s), adjacent Transmission
Planner(s), and to any functional entity who has submitted a written request and has a
reliability-related need as specified in Requirement R4. Each responsible entity, as
determined in Requirement R1, shall also provide evidence, such as email notices or
postal receipts showing recipient and date, that it has provided a documented response
to comments received on its GMD Vulnerability Assessment within 90 calendar days of
receipt of those comments in accordance with Requirement R4.
R5.

Each responsible entity, as determined in Requirement R1, shall provide GIC flow
information to be used for the transformer thermal impact assessment specified in
Requirement R6 to each Transmission Owner and Generator Owner that owns an
applicable Bulk Electric System (BES) power transformer in the planning area. The GIC
flow information shall include: [Violation Risk Factor: Medium] [Time Horizon: Longterm Planning]
5.1. The maximum effective GIC value for the worst case geoelectric field orientation
for the benchmark GMD event described in Attachment 1. This value shall be
provided to the Transmission Owner or Generator Owner that owns each
applicable BES power transformer in the planning area.
5.2. The effective GIC time series, GIC(t), calculated using the benchmark GMD event
described in Attachment 1 in response to a written request from the
Transmission Owner or Generator Owner that owns an applicable BES power
transformer in the planning area. GIC(t) shall be provided within 90 calendar
days of receipt of the written request and after determination of the maximum
effective GIC value in Part 5.1.

M5. Each responsible entity, as determined in Requirement R1, shall provide evidence, such
as email records, web postings with an electronic notice of posting, or postal receipts
showing recipient and date, that it has provided the maximum effective GIC value to
the Transmission Owner and Generator Owner that owns each applicable BES power
transformer in the planning area as specified in Requirement R5, Part 5.1. Each
responsible entity, as determined in Requirement R1, shall also provide evidence, such
as email records, web postings with an electronic notice of posting, or postal receipts
showing recipient and date, that it has provided GIC(t) in response to a written request
from the Transmission Owner or Generator Owner that owns an applicable BES power
transformer in the planning area.

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

R6.

Each Transmission Owner and Generator Owner shall conduct a thermal impact
assessment for its solely and jointly owned applicable BES power transformers where
the maximum effective GIC value provided in Requirement R5, Part 5.1, is 75 A per
phase or greater. The thermal impact assessment shall: [Violation Risk Factor: Medium]
[Time Horizon: Long-term Planning]
6.1. Be based on the effective GIC flow information provided in Requirement R5;
6.2. Document assumptions used in the analysis;
6.3. Describe suggested actions and supporting analysis to mitigate the impact of
GICs, if any; and
6.4. Be performed and provided to the responsible entities, as determined in
Requirement R1, within 24 calendar months of receiving GIC flow information
specified in Requirement R5, Part 5.1.

M6. Each Transmission Owner and Generator Owner shall have evidence such as electronic
or hard copies of its thermal impact assessment for all of its solely and jointly owned
applicable BES power transformers where the maximum effective GIC value provided in
Requirement R5, Part 5.1, is 75 A per phase or greater, and shall have evidence such as
email records, web postings with an electronic notice of posting, or postal receipts
showing recipient and date, that it has provided its thermal impact assessment to the
responsible entities as specified in Requirement R6.
R7.

Each responsible entity, as determined in Requirement R1, that concludes, through the
GMD Vulnerability Assessment conducted in Requirement R4, that their System does
not meet the performance requirements of Table 1 shall develop a Corrective Action
Plan addressing how the performance requirements will be met. The Corrective Action
Plan shall: [Violation Risk Factor: High] [Time Horizon: Long-term Planning]
7.1. List System deficiencies and the associated actions needed to achieve required
System performance. Examples of such actions include:


Installation, modification, retirement, or removal of Transmission and
generation Facilities and any associated equipment.



Installation, modification, or removal of Protection Systems or Special
Protection Systems.



Use of Operating Procedures, specifying how long they will be needed as
part of the Corrective Action Plan.



Use of Demand-Side Management, new technologies, or other initiatives.

7.2. Be reviewed in subsequent GMD Vulnerability Assessments until it is determined
that the System meets the performance requirements contained in Table 1.
7.3. Be provided within 90 calendar days of completion to the responsible entity’s
Reliability Coordinator, adjacent Planning Coordinator(s), adjacent Transmission
Planner(s), functional entities referenced in the Corrective Action Plan, and any
functional entity that submits a written request and has a reliability-related
need.
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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

7.3.1. If a recipient of the Corrective Action Plan provides documented
comments on the results, the responsible entity shall provide a
documented response to that recipient within 90 calendar days of receipt
of those comments.
M7. Each responsible entity, as determined in Requirement R1, that concludes, through the
GMD Vulnerability Assessment conducted in Requirement R4, that the responsible
entity’s System does not meet the performance requirements of Table 1 shall have
evidence such as electronic or hard copies of its Corrective Action Plan, as specified in
Requirement R7. Each responsible entity, as determined in Requirement R1, shall also
provide evidence, such as email records, web postings with an electronic notice of
posting, or postal receipts showing recipient and date, that it has distributed its
Corrective Action Plan or relevant information, if any, within 90 calendar days of its
completion to its Reliability Coordinator, adjacent Planning Coordinator(s), adjacent
Transmission Planner(s), a functional entity referenced in the Corrective Action Plan,
and any functional entity that submits a written request and has a reliability-related
need, as specified in Requirement R7. Each responsible entity, as determined in
Requirement R1, shall also provide evidence, such as email notices or postal receipts
showing recipient and date, that it has provided a documented response to comments
received on its Corrective Action Plan within 90 calendar days of receipt of those
comments, in accordance with Requirement R7.

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events
Table 1 –Steady State Planning Events
Steady State:
a. Voltage collapse, Cascading and uncontrolled islanding shall not occur.
b.

Generation loss is acceptable as a consequence of the planning event.

c.

Planned System adjustments such as Transmission configuration changes and re-dispatch of generation are allowed if such adjustments
are executable within the time duration applicable to the Facility Ratings.

Category

GMD
GMD Event
with Outages

Initial Condition

1. System as may be
postured in response to
space weather
information1, and then
2. GMD event2

Event

Interruption of
Firm Transmission
Service Allowed

Load Loss Allowed

Yes3

Yes3

Reactive Power compensation devices and
other Transmission Facilities removed as a
result of Protection System operation or
Misoperation due to harmonics during the
GMD event

Table 1 – Steady State Performance Footnotes
1.

The System condition for GMD planning may include adjustments to posture the System that are executable in response to space weather
information.

2.

The GMD conditions for the planning event are described in Attachment 1 (Benchmark GMD Event).

3. Load loss as a result of manual or automatic Load shedding (e.g. UVLS) and/or curtailment of Firm Transmission Service may be used to meet
BES performance requirements during studied GMD conditions. The likelihood and magnitude of Load loss or curtailment of Firm
Transmission Service should be minimized.

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

Attachment 1
Calculating Geoelectric Fields for the Benchmark GMD Event
The benchmark GMD event1 defines the geoelectric field values used to compute GIC flows that
are needed to conduct a GMD Vulnerability Assessment. It is composed of the following
elements: (1) a reference peak geoelectric field amplitude of 8 V/km derived from statistical
analysis of historical magnetometer data; (2) scaling factors to account for local geomagnetic
latitude; (3) scaling factors to account for local earth conductivity; and (4) a reference
geomagnetic field time series or waveshape to facilitate time-domain analysis of GMD impact
on equipment.
The regional geoelectric field peak amplitude used in GMD Vulnerability Assessment, E peak, can
be obtained from the reference geoelectric field value of 8 V/km using the following relationship
Epeak = 8 × 𝛼 × 𝛽 (V/km)

(1)

where α is the scaling factor to account for local geomagnetic latitude, and β is a scaling factor
to account for the local earth conductivity structure.
Scaling the Geomagnetic Field
The benchmark GMD event is defined for geomagnetic latitude of 60 and it must be scaled to
account for regional differences based on geomagnetic latitude. Table 2 provides a scaling
factor correlating peak geoelectric field to geomagnetic latitude. Alternatively, the scaling
factor  is computed with the empirical expression
  0.001  e ( 0.115L )

(2)

where L is the geomagnetic latitude in degrees and 0.1 ≤ α ≤ 1
For large planning areas that cover more than one scaling factor from Table 2, the GMD
Vulnerability Assessment should be based on a peak geoelectric field that is:
 calculated by using the most conservative (largest) value for α; or
 calculated assuming a non-uniform or piecewise uniform geomagnetic field.

1

The benchmark GMD event description is available on the Project 2013-03 Geomagnetic Disturbance Mitigation project
page:http://www.nerc.com/pa/Stand/Pages/Project-2013-03-Geomagnetic-Disturbance-Mitigation.aspx

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

Table 2 Geomagnetic Field Scaling Factors
Geomagnetic Latitude
Scaling Factor1
(Degrees)
()
≤ 40
45
50
54
56
57
58
59
≥ 60

0.10
0.2
0.3
0.5
0.6
0.7
0.8
0.9
1.0

Scaling the Geoelectric Field
The benchmark GMD event is defined for the reference Quebec earth model described in Table
4. The peak geoelectric field, Epeak, used in a GMD Vulnerability Assessment may be obtained by
either


Calculating the geoelectric field for the ground conductivity in the planning area and
the reference geomagnetic field time series scaled according to geomagnetic latitude,
using a procedure such as the plane wave method described in the NERC GMD Task
Force GIC Application Guide;2 or
Using the earth conductivity scaling factor β from Table 3 that correlates to the ground
conductivity map in Figure 1 or Figure 2. Along with the scaling factor  from equation
(2) or Table 2, β is applied to the reference geoelectric field using equation (1) to obtain
the regional geoelectric field peak amplitude Epeak to be used in GMD Vulnerability
Assessment. When a ground conductivity model is not available, the planning entity
should use the largest β factor of adjacent physiographic regions or a technically
justified value.



The earth models used to calculate Table 3 for the United States were obtained from publicly
available information published on the U. S. Geological Survey website.3 The models used to
calculate Table 3 for Canada were obtained from Natural Resources Canada (NRCan) and reflect
the average structure for large regions. A planner can also use specific earth model(s) with
documented justification and the reference geomagnetic field time series to calculate the β
factor(s) as follows:
𝛽 = 𝐸/8
(3)

2 Available at the NERC GMD Task Force project page: http://www.nerc.com/comm/PC/Pages/GeomagneticDisturbance-Task-Force-(GMDTF)-2013.aspx
3

Available at http://geomag.usgs.gov/conductivity/

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

where E is the absolute value of peak geoelectric in V/km obtained from the technically justified
earth model and the reference geomagnetic field time series.
For large planning areas that span more than one β scaling factor, the most conservative (largest)
value for β may be used in determining the peak geoelectric field to obtain conservative results.
Alternatively, a planner could perform analysis using a non-uniform or piecewise uniform
geoelectric field.

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

FL-1

Figure 1: Physiographic Regions of the Continental United States4

Figure 2: Physiographic Regions of Canada

4

Additional map detail is available at the U.S. Geological Survey (http://geomag.usgs.gov/)

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events
Table 3  Geoelectric Field Scaling Factors
USGS
Scaling Factor
Earth model
()
AK1A
AK1B
AP1
AP2
BR1
CL1
CO1
CP1
CP2
FL1
CS1
IP1
IP2
IP3
IP4
NE1
PB1
PB2
PT1
SL1
SU1
BOU
FBK
PRU
BC
PRAIRIES
SHIELD
ATLANTIC

0.56
0.56
0.33
0.82
0.22
0.76
0.27
0.81
0.95
0.74
0.41
0.94
0.28
0.93
0.41
0.81
0.62
0.46
1.17
0.53
0.93
0.28
0.56
0.21
0.67
0.96
1.0
0.79

Table 4  Reference Earth Model (Quebec)
Layer Thickness (km)

Resistivity (Ω-m)

15

20,000

10

200

125

1,000

200

100

∞

3

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

Reference Geomagnetic Field Time Series or Waveshape5
The geomagnetic field measurement record of the March 13-14 1989 GMD event, measured at
NRCan’s Ottawa geomagnetic observatory is the basis for the reference geomagnetic field
waveshape to be used to calculate the GIC time series, GIC(t), required for transformer thermal
impact assessment.
The geomagnetic latitude of the Ottawa geomagnetic observatory is 55; therefore, the
amplitude of the geomagnetic field measurement data were scaled up to the 60 reference
geomagnetic latitude (see Figure 3) such that the resulting peak geoelectric field amplitude
computed using the reference earth model was 8 V/km (see Figures 4 and 5). Sampling rate for
the geomagnetic field waveshape is 10 seconds.6 To use this geoelectric field time series when a
different earth model is applicable, it should be scaled with the appropriate conductivity scaling
factor .

Figure 3: Benchmark Geomagnetic Field Waveshape. Red Bn (Northward), Blue Be (Eastward)
5

Refer to the Benchmark GMD Event Description for details on the determination of the reference geomagnetic
field waveshape: http://www.nerc.com/pa/Stand/Pages/Project-2013-03-Geomagnetic-DisturbanceMitigation.aspx
6

The data file of the benchmark geomagnetic field waveshape is available on the NERC GMD Task Force project
page: http://www.nerc.com/comm/PC/Pages/Geomagnetic-Disturbance-Task-Force-(GMDTF)-2013.aspx

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

Figure 4: Benchmark Geoelectric Field Waveshape - EE (Eastward)

Figure 5: Benchmark Geoelectric Field Waveshape – EN (Northward)

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

C. Compliance

1. Compliance Monitoring Process
1.1.

Compliance Enforcement Authority
As defined in the NERC Rules of Procedure, “Compliance Enforcement Authority”
means NERC or the Regional Entity in their respective roles of monitoring and
enforcing compliance with the NERC Reliability Standards

1.2.

Evidence Retention
The following evidence retention periods identify the period of time an entity is
required to retain specific evidence to demonstrate compliance. For instances
where the evidence retention period specified below is shorter than the time
since the last audit, the CEA may ask an entity to provide other evidence to show
that it was compliant for the full time period since the last audit.
The Planning Coordinator, Transmission Planner, Transmission Owner, and
Generator Owner shall keep data or evidence to show compliance as identified
below unless directed by its Compliance Enforcement Authority to retain specific
evidence for a longer period of time as part of an investigation:
For Requirements R1, R2, R3, R5, and R6, each responsible entity shall retain
documentation as evidence for five years.
For Requirement R4, each responsible entity shall retain documentation of the
current GMD Vulnerability Assessment and the preceding GMD Vulnerability
Assessment.
For Requirement R7, each responsible entity shall retain documentation as
evidence for five years or until all actions in the Corrective Action Plan are
completed, whichever is later.
If a Planning Coordinator, Transmission Planner, Transmission Owner, or
Generator Owner is found non-compliant it shall keep information related to the
non-compliance until mitigation is complete and approved or for the time
specified above, whichever is longer.
The Compliance Enforcement Authority shall keep the last audit records and all
requested and submitted subsequent audit records.

1.3.

Compliance Monitoring and Assessment Processes:
Compliance Audits
Self-Certifications
Spot Checking
Compliance Investigations
Self-Reporting
Complaints

1.4.

Additional Compliance Information

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None

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Table of Compliance Elements
R#

Time
Horizon

VRF

Violation Severity Levels
Lower VSL

Moderate VSL

High VSL

Severe VSL

R1

Long-term
Planning

Lower

N/A

N/A

N/A

The Planning
Coordinator, in
conjunction with its
Transmission
Planner(s), failed to
determine and
identify individual or
joint responsibilities of
the Planning
Coordinator and
Transmission
Planner(s) in the
Planning
Coordinator’s
planning area for
maintaining models
and performing the
study or studies
needed to complete
GMD Vulnerability
Assessment(s).

R2

Long-term
Planning

High

N/A

N/A

The responsible entity
did not maintain
either System models
or GIC System models
of the responsible

The responsible entity
did not maintain both
System models and
GIC System models of
the responsible

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

entity’s planning area
for performing the
study or studies
needed to complete
GMD Vulnerability
Assessment(s).
R3

Long-term
Planning

Medium N/A

N/A

N/A

R4

Long-term
Planning

High

The responsible
entity's completed
GMD Vulnerability
Assessment failed to
satisfy one of
elements listed in
Requirement R4, Parts
4.1 through 4.3;

The responsible
entity's completed
GMD Vulnerability
Assessment failed to
satisfy two of the
elements listed in
Requirement R4, Parts
4.1 through 4.3;
OR
The responsible entity
completed a GMD
Vulnerability
Assessment, but it

The responsible entity
completed a GMD
Vulnerability
Assessment, but it
was more than 60
calendar months and
less than or equal to
64 calendar months
since the last GMD
Vulnerability
Assessment.

OR
The responsible entity
completed a GMD
Vulnerability
Assessment, but it

entity’s planning area
for performing the
study or studies
needed to complete
GMD Vulnerability
Assessment(s).
The responsible entity
did not have criteria
for acceptable System
steady state voltage
performance for its
System during the
benchmark GMD
event described in
Attachment 1 as
required.
The responsible
entity's completed
GMD Vulnerability
Assessment failed to
satisfy three of the
elements listed in
Requirement R4, Parts
4.1 through 4.3;
OR
The responsible entity
completed a GMD
Vulnerability
Assessment, but it

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

R5

Long-term
Planning

Medium The responsible entity
provided the effective
GIC time series, GIC(t),
in response to written
request, but did so
more than 90 calendar
days and less than or
equal to 100 calendar
days after receipt of a
written request.

was more than 64
calendar months and
less than or equal to
68 calendar months
since the last GMD
Vulnerability
Assessment.

was more than 68
calendar months and
less than or equal to
72 calendar months
since the last GMD
Vulnerability
Assessment.

was more than 72
calendar months since
the last GMD
Vulnerability
Assessment;

The responsible entity
provided the effective
GIC time series, GIC(t),
in response to written
request, but did so
more than 100
calendar days and less
than or equal to 110
calendar days after
receipt of a written
request.

The responsible entity
provided the effective
GIC time series, GIC(t),
in response to written
request, but did so
more than 110
calendar days after
receipt of a written
request.

The responsible entity
did not provide the
maximum effective
GIC value to the
Transmission Owner
and Generator Owner
that owns each
applicable BES power
transformer in the
planning area;
OR
The responsible entity
did not provide the
effective GIC time
series, GIC(t), upon
written request.

OR
The responsible entity
does not have a
completed GMD
Vulnerability
Assessment.

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

R6

Long-term
Planning

Medium The responsible entity
failed to conduct a
thermal impact
assessment for 5% or
less or one of its solely
owned and jointly
owned applicable BES
power transformers
(whichever is greater)
where the maximum
effective GIC value
provided in
Requirement R5, Part
5.1, is 75 A or greater
per phase;
OR
The responsible entity
conducted a thermal
impact assessment for
its solely owned and
jointly owned
applicable BES power
transformers where
the maximum
effective GIC value
provided in
Requirement R5, Part
5.1, is 75 A or greater
per phase but did so
more than 24 calendar
months and less than

The responsible entity
failed to conduct a
thermal impact
assessment for more
than 5% up to (and
including) 10% or two
of its solely owned
and jointly owned
applicable BES power
transformers
(whichever is greater)
where the maximum
effective GIC value
provided in
Requirement R5, Part
5.1, is 75 A or greater
per phase;
OR
The responsible entity
conducted a thermal
impact assessment for
its solely owned and
jointly owned
applicable BES power
transformers where
the maximum
effective GIC value
provided in
Requirement R5, Part
5.1, is 75 A or greater
per phase but did so

The responsible entity
failed to conduct a
thermal impact
assessment for more
than 10% up to (and
including) 15% or
three of its solely
owned and jointly
owned applicable BES
power transformers
(whichever is greater)
where the maximum
effective GIC value
provided in
Requirement R5, Part
5.1, is 75 A or greater
per phase;
OR
The responsible entity
conducted a thermal
impact assessment for
its solely owned and
jointly owned
applicable BES power
transformers where
the maximum
effective GIC value
provided in
Requirement R5, Part
5.1, is 75 A or greater
per phase but did so

The responsible entity
failed to conduct a
thermal impact
assessment for more
than 15% or more
than three of its solely
owned and jointly
owned applicable BES
power transformers
(whichever is greater)
where the maximum
effective GIC value
provided in
Requirement R5, Part
5.1, is 75 A or greater
per phase;
OR
The responsible entity
conducted a thermal
impact assessment for
its solely owned and
jointly owned
applicable BES power
transformers where
the maximum
effective GIC value
provided in
Requirement R5, Part
5.1, is 75 A or greater
per phase but did so
more than 30 calendar

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

R7

Long-term
Planning

High

or equal to 26
calendar months of
receiving GIC flow
information specified
in Requirement R5,
Part 5.1.

more than 26 calendar
months and less than
or equal to 28
calendar months of
receiving GIC flow
information specified
in Requirement R5,
Part 5.1;
OR
The responsible entity
failed to include one
of the required
elements as listed in
Requirement R6, Parts
6.1 through 6.3.

more than 28 calendar
months and less than
or equal to 30
calendar months of
receiving GIC flow
information specified
in Requirement R5,
Part 5.1;
OR
The responsible entity
failed to include two
of the required
elements as listed in
Requirement R6, Parts
6.1 through 6.3.

months of receiving
GIC flow information
specified in
Requirement R5, Part
5.1;
OR
The responsible entity
failed to include three
of the required
elements as listed in
Requirement R6, Parts
6.1 through 6.3.

N/A

The responsible
entity's Corrective
Action Plan failed to
comply with one of
the elements in
Requirement R7, Parts
7.1 through 7.3.

The responsible
entity's Corrective
Action Plan failed to
comply with two of
the elements in
Requirement R7, Parts
7.1 through 7.3.

The responsible
entity's Corrective
Action Plan failed to
comply with all three
of the elements in
Requirement R7, Parts
7.1 through 7.3;
OR
The responsible entity
did not have a
Corrective Action Plan
as required by
Requirement R7.

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TPL-007-1 — Transmission System Planned Performance for Geomagnetic Disturbance Events

D. Regional Variances
None.
E. Interpretations
None.
F. Associated Documents
None.

Version History
Version

Date

1

December 17, 2014

Action

Change Tracking

Adopted by the NERC Board of Trustees

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Application Guidelines
Guidelines and Technical Basis
Benchmark GMD Event (Attachment 1)
The benchmark GMD event defines the geoelectric field values used to compute GIC flows that
are needed to conduct a GMD Vulnerability Assessment. A white paper that includes the event
description, analysis, and example calculations is available on the Project 2013-03 Geomagnetic
Disturbance Mitigation project page:
http://www.nerc.com/pa/Stand/Pages/Project-2013-03-Geomagnetic-DisturbanceMitigation.aspx
Requirement R2
A GMD Vulnerability Assessment requires a GIC System model, which is a dc representation of
the System, to calculate GIC flow. In a GMD Vulnerability Assessment, GIC simulations are used
to determine transformer Reactive Power absorption and transformer thermal response.
Details for developing the GIC System model are provided in the NERC GMD Task Force guide:
Application Guide for Computing Geomagnetically-Induced Current in the Bulk Power System.
The guide is available at:
http://www.nerc.com/comm/PC/Geomagnetic%20Disturbance%20Task%20Force%20GMDTF%
202013/GIC%20Application%20Guide%202013_approved.pdf
Underground pipe-type cables present a special modeling situation in that the steel pipe that
encloses the power conductors significantly reduces the geoelectric field induced into the
conductors themselves, while they remain a path for GIC. Solid dielectric cables that are not
enclosed by a steel pipe will not experience a reduction in the induced geoelectric field. A
planning entity should account for special modeling situations in the GIC system model, if
applicable.
Requirement R4
The GMD Planning Guide developed by the NERC GMD Task Force provides technical
information on GMD-specific considerations for planning studies. It is available at:
http://www.nerc.com/comm/PC/Geomagnetic%20Disturbance%20Task%20Force%20GMDTF%
202013/GMD%20Planning%20Guide_approved.pdf
The diagram below provides an overall view of the GMD Vulnerability Assessment process:

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Application Guidelines
Requirement R5
The transformer thermal impact assessment specified in Requirement R6 is based on GIC
information for the Benchmark GMD Event. This GIC information is determined by the planning
entity through simulation of the GIC System model and must be provided to the entity
responsible for conducting the thermal impact assessment. GIC information should be provided
in accordance with Requirement R5 each time the GMD Vulnerability Assessment is performed
since, by definition, the GMD Vulnerability Assessment includes a documented evaluation of
susceptibility to localized equipment damage due to GMD.
The maximum effective GIC value provided in Part 5.1 is used for transformer thermal impact
assessment. Only those transformers that experience an effective GIC value of 75 A or greater
per phase require evaluation in Requirement R6.
GIC(t) provided in Part 5.2 is used to convert the steady-state GIC flows to time-series GIC data
for transformer thermal impact assessment. This information may be needed by one or more of
the methods for performing a thermal impact assessment. Additional information is in the
following section and the thermal impact assessment white paper.
The peak GIC value of 75 Amps per phase has been shown through thermal modeling to be a
conservative threshold below which the risk of exceeding known temperature limits established
by technical organizations is low.
Requirement R6
The thermal impact assessment of a power transformer may be based on manufacturerprovided GIC capability curves, thermal response simulation, thermal impact screening, or
other technically justified means. Approaches for conducting the assessment are presented in
the Transformer Thermal Impact Assessment white paper posted on the project page.
http://www.nerc.com/pa/Stand/Pages/Project-2013-03-Geomagnetic-DisturbanceMitigation.aspx
Transformers are exempt from the thermal impact assessment requirement if the effective GIC
value for the transformer is less than 75 A per phase, as determined by a GIC analysis of the
System. Justification for this criterion is provided in the Screening Criterion for Transformer
Thermal Impact Assessment white paper posted on the project page. A documented design
specification exceeding this value is also a justifiable threshold criterion that exempts a
transformer from Requirement R6.
The threshold criteria and transformer thermal impact must be evaluated on the basis of
effective GIC. Refer to the white papers for additional information.
Requirement R7
Technical considerations for GMD mitigation planning, including operating and equipment
strategies, are available in Chapter 5 of the GMD Planning Guide. Additional information is
available in the 2012 Special Reliability Assessment Interim Report: Effects of Geomagnetic
Disturbances on the Bulk-Power System:
http://www.nerc.com/pa/RAPA/ra/Reliability%20Assessments%20DL/2012GMD.pdf

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Application Guidelines
Rationale:
During development of this standard, text boxes were embedded within the standard to explain
the rationale for various parts of the standard. Upon BOT approval, the text from the rationale
text boxes was moved to this section.
Rationale for Applicability:
Instrumentation transformers and station service transformers do not have significant impact
on geomagnetically-induced current (GIC) flows; therefore, these transformers are not included
in the applicability for this standard.
Terminal voltage describes line-to-line voltage.
Rationale for R1:
In some areas, planning entities may determine that the most effective approach to conduct a
GMD Vulnerability Assessment is through a regional planning organization. No requirement in
the standard is intended to prohibit a collaborative approach where roles and responsibilities
are determined by a planning organization made up of one or more Planning Coordinator(s).
Rationale for R2:
A GMD Vulnerability Assessment requires a GIC System model to calculate GIC flow which is
used to determine transformer Reactive Power absorption and transformer thermal response.
Guidance for developing the GIC System model is provided in the GIC Application Guide
developed by the NERC GMD Task Force and available at:
http://www.nerc.com/comm/PC/Geomagnetic%20Disturbance%20Task%20Force%20GMDTF%
202013/GIC%20Application%20Guide%202013_approved.pdf
The System model specified in Requirement R2 is used in conducting steady state power flow
analysis that accounts for the Reactive Power absorption of power transformer(s) due to GIC in
the System.
The GIC System model includes all power transformer(s) with a high side, wye-grounded
winding with terminal voltage greater than 200 kV. The model is used to calculate GIC flow in
the network.
The projected System condition for GMD planning may include adjustments to the System that
are executable in response to space weather information. These adjustments could include, for
example, recalling or postponing maintenance outages.
The Violation Risk Factor (VRF) for Requirement R2 is changed from Medium to High. This
change is for consistency with the VRF for approved standard TPL-001-4 Requirement R1, which
is proposed for revision in the NERC filing dated August 29, 2014 (RM12-1-000). NERC
guidelines require consistency among Reliability Standards.
Rationale for R3:
Requirement R3 allows a responsible entity the flexibility to determine the System steady state
voltage criteria for System steady state performance in Table 1. Steady state voltage limits are
an example of System steady state performance criteria.

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Application Guidelines
Rationale for R4:
The GMD Vulnerability Assessment includes steady state power flow analysis and the
supporting study or studies using the models specified in Requirement R2 that account for the
effects of GIC. Performance criteria are specified in Table 1.
At least one System On-Peak Load and at least one System Off-Peak Load must be examined in
the analysis.
Distribution of GMD Vulnerability Assessment results provides a means for sharing relevant
information with other entities responsible for planning reliability. Results of GIC studies may
affect neighboring systems and should be taken into account by planners.
The GMD Planning Guide developed by the NERC GMD Task Force provides technical
information on GMD-specific considerations for planning studies. It is available at:
http://www.nerc.com/comm/PC/Geomagnetic%20Disturbance%20Task%20Force%20GMDTF%
202013/GMD%20Planning%20Guide_approved.pdf
The provision of information in Requirement R4, Part 4.3, shall be subject to the legal and
regulatory obligations for the disclosure of confidential and/or sensitive information.
Rationale for R5:
This GIC information is necessary for determining the thermal impact of GIC on transformers in
the planning area and must be provided to entities responsible for performing the thermal
impact assessment so that they can accurately perform the assessment. GIC information should
be provided in accordance with Requirement R5 as part of the GMD Vulnerability Assessment
process since, by definition, the GMD Vulnerability Assessment includes documented
evaluation of susceptibility to localized equipment damage due to GMD.
The maximum effective GIC value provided in Part 5.1 is used for transformer thermal impact
assessment.
GIC(t) provided in Part 5.2 can alternatively be used to convert the steady-state GIC flows to
time-series GIC data for transformer thermal impact assessment. This information may be
needed by one or more of the methods for performing a thermal impact assessment. Additional
guidance is available in the Transformer Thermal Impact Assessment white paper:
http://www.nerc.com/pa/Stand/Pages/Project-2013-03-Geomagnetic-DisturbanceMitigation.aspx
A Transmission Owner or Generator Owner that desires GIC(t) may request it from the planning
entity. The planning entity shall provide GIC(t) upon request once GIC has been calculated, but
no later than 90 calendar days after receipt of a request from the owner and after completion
of Requirement R5, Part 5.1.
The provision of information in Requirement R5 shall be subject to the legal and regulatory
obligations for the disclosure of confidential and/or sensitive information.
Rationale for R6:
The transformer thermal impact screening criterion has been revised from 15 A per phase to 75
A per phase. Only those transformers that experience an effective GIC value of 75 A per phase

Page 25 of 26

Application Guidelines
or greater require evaluation in Requirement R6. The justification is provided in the Thermal
Screening Criterion white paper.
The thermal impact assessment may be based on manufacturer-provided GIC capability curves,
thermal response simulation, thermal impact screening, or other technically justified means.
The transformer thermal assessment will be repeated or reviewed using previous assessment
results each time the planning entity performs a GMD Vulnerability Assessment and provides
GIC information as specified in Requirement R5. Approaches for conducting the assessment are
presented in the Transformer Thermal Impact Assessment white paper posted on the project
page.
http://www.nerc.com/pa/Stand/Pages/Project-2013-03-Geomagnetic-DisturbanceMitigation.aspx
Thermal impact assessments are provided to the planning entity, as determined in Requirement
R1, so that identified issues can be included in the GMD Vulnerability Assessment (R4), and the
Corrective Action Plan (R7) as necessary.
Thermal impact assessments of non-BES transformers are not required because those
transformers do not have a wide-area effect on the reliability of the interconnected
Transmission system.
The provision of information in Requirement R6, Part 6.4, shall be subject to the legal and
regulatory obligations for the disclosure of confidential and/or sensitive information.
Rationale for R7:
Corrective Action Plans are defined in the NERC Glossary of Terms:
A list of actions and an associated timetable for implementation to remedy a specific
problem.
Corrective Action Plans must, subject to the vulnerabilities identified in the assessments,
contain strategies for protecting against the potential impact of the Benchmark GMD event,
based on factors such as the age, condition, technical specifications, system configuration, or
location of specific equipment. Chapter 5 of the NERC GMD Task Force GMD Planning Guide
provides a list of mitigating measures that may be appropriate to address an identified
performance issue.
The provision of information in Requirement R7, Part 7.3, shall be subject to the legal and
regulatory obligations for the disclosure of confidential and/or sensitive information.
Rationale for Table 3:
Table 3 has been revised to use the same ground model designation, FL1, as is being used by
USGS. The calculated scaling factor for FL1 is 0.74.

Page 26 of 26