Reliability Standard VAR-002-4.1

VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules

A. Introduction
1.

Title:

Generator Operation for Maintaining Network Voltage Schedules

2.

Number:

3.

Purpose: To ensure generators provide reactive support and voltage control, within generating
Facility capabilities, in order to protect equipment and maintain reliable operation of the
Interconnection.

4.

Applicability:

VAR-002-4.1

4.1. Generator Operator
4.2. Generator Owner
5.

Effective Dates
See Implementation Plan.

B. Requirements and Measures
R1. The Generator Operator shall operate each generator connected to the interconnected
transmission system in the automatic voltage control mode (with its automatic voltage regulator
(AVR) in service and controlling voltage) or in a different control mode as instructed by the
Transmission Operator unless: 1) the generator is exempted by the Transmission Operator, or 2)
the Generator Operator has notified the Transmission Operator of one of the following:
[Violation Risk Factor: Medium] [Time Horizon: Real-time Operations]
• That the generator is being operated in start-up,1 shutdown, 2 or testing mode pursuant to a
Real-time communication or a procedure that was previously provided to the Transmission
Operator; or
• That the generator is not being operated in automatic voltage control mode or in the control
mode that was instructed by the Transmission Operator for a reason other than start-up,
shutdown, or testing.
M1. The Generator Operator shall have evidence to show that it notified its associated Transmission
Operator any time it failed to operate a generator in the automatic voltage control mode or in a
different control mode as specified in Requirement R1. If a generator is being started up or shut
down with the automatic voltage control off, or is being tested, and no notification of the AVR
status is made to the Transmission Operator, the Generator Operator will have evidence that it
notified the Transmission Operator of its procedure for placing the unit into automatic voltage
control mode as required in Requirement R1. Such evidence may include, but is not limited to,
dated evidence of transmittal of the procedure such as an electronic message or a transmittal
letter with the procedure included or attached. If a generator is exempted, the Generator
Operator shall also have evidence that the generator is exempted from being in automatic
voltage control mode (with its AVR in service and controlling voltage).

1

Start-up is deemed to have ended when the generator is ramped up to its minimum continuously sustainable load and the
generator is prepared for continuous operation.
2
Shutdown is deemed to begin when the generator is ramped down to its minimum continuously sustainable load and the generator
is prepared to go offline.

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VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
R2. Unless exempted by the Transmission Operator, each Generator Operator shall maintain the
generator voltage or Reactive Power schedule 3 (within each generating Facility’s capabilities4)
provided by the Transmission Operator, or otherwise shall meet the conditions of notification
for deviations from the voltage or Reactive Power schedule provided by the Transmission
Operator. [Violation Risk Factor: Medium] [Time Horizon: Real-time Operations]
2.1. When a generator’s AVR is out of service or the generator does not have an AVR, the
Generator Operator shall use an alternative method to control the generator reactive
output to meet the voltage or Reactive Power schedule provided by the Transmission
Operator.
2.2. When instructed to modify voltage, the Generator Operator shall comply or provide an
explanation of why the schedule cannot be met.
2.3. Generator Operators that do not monitor the voltage at the location specified in their
voltage schedule shall have a methodology for converting the scheduled voltage specified
by the Transmission Operator to the voltage point being monitored by the Generator
Operator.
M2.

In order to identify when a generator is deviating from its schedule, the Generator Operator will
monitor voltage based on existing equipment at its Facility. The Generator Operator shall have
evidence to show that the generator maintained the voltage or Reactive Power schedule
provided by the Transmission Operator, or shall have evidence of meeting the conditions of
notification for deviations from the voltage or Reactive Power schedule provided by the
Transmission Operator.
Evidence may include, but is not limited to, operator logs, SCADA data, phone logs, and any other
notifications that would alert the Transmission Operator or otherwise demonstrate that the
Generator Operator complied with the Transmission Operator’s instructions for addressing
deviations from the voltage or Reactive Power schedule.
For Part 2.1, when a generator’s AVR is out of service or the generator does not have an AVR, a
Generator Operator shall have evidence to show an alternative method was used to control the
generator reactive output to meet the voltage or Reactive Power schedule provided by the
Transmission Operator.
For Part 2.2, the Generator Operator shall have evidence that it complied with the Transmission
Operator’s instructions to modify its voltage or provided an explanation to the Transmission
Operator of why the Generator Operator was unable to comply with the instruction. Evidence may
include, but is not limited to, operator logs, SCADA data, and phone logs.
For Part 2.3, for Generator Operators that do not monitor the voltage at the location specified on
the voltage schedule, the Generator Operator shall demonstrate the methodology for converting
the scheduled voltage specified by the Transmission Operator to the voltage point being monitored
by the Generator Operator.

3

The voltage or Reactive Power schedule is a target value with a tolerance band or a voltage or Reactive Power range communicated
by the Transmission Operator to the Generator Operator.
4
Generating Facility capability may be established by test or other means, and may not be sufficient at times to pull the system
voltage within the schedule tolerance band. Also, when a generator is operating in manual control, Reactive Power capability may
change based on stability considerations.

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VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
R3.
Each Generator Operator shall notify its associated Transmission Operator of a status change on
the AVR, power system stabilizer, or alternative voltage controlling device within 30 minutes of
the change. If the status has been restored within 30 minutes of such change, then the Generator
Operator is not required to notify the Transmission Operator of the status change. [Violation Risk
Factor: Medium] [Time Horizon: Real-time Operations]
M3.

The Generator Operator shall have evidence it notified its associated Transmission Operator
within 30 minutes of any status change identified in Requirement R3. If the status has been
restored within the first 30 minutes, no notification is necessary.

R4.

Each Generator Operator shall notify its associated Transmission Operator within 30 minutes of
becoming aware of a change in reactive capability due to factors other than a status change
described in Requirement R3. If the capability has been restored within 30 minutes of the
Generator Operator becoming aware of such change, then the Generator Operator is not
required to notify the Transmission Operator of the change in reactive capability. [Violation Risk
Factor: Medium] [Time Horizon: Real-time Operations]
•

Reporting of status or capability changes as stated in Requirement R4 is not applicable to
the individual generating units of dispersed power producing resources identified through
Inclusion I4 of the Bulk Electric System definition.

M4.

The Generator Operator shall have evidence it notified its associated Transmission Operator
within 30 minutes of becoming aware of a change in reactive capability in accordance with
Requirement R4. If the capability has been restored within the first 30 minutes, no notification is
necessary.

R5.

The Generator Owner shall provide the following to its associated Transmission Operator and
Transmission Planner within 30 calendar days of a request. [Violation Risk Factor: Lower]
[Time Horizon: Real-time Operations]
5.1. For generator step-up and auxiliary transformers5 with primary voltages equal to or
greater than the generator terminal voltage:

M5.

5.1.1.

Tap settings.

5.1.2.

Available fixed tap ranges.

5.1.3.

Impedance data.

The Generator Owner shall have evidence it provided its associated Transmission Operator and
Transmission Planner with information on its step-up and auxiliary transformers as required in
Requirement R5, Part 5.1.1 through Part 5.1.3 within 30 calendar days.

5

For dispersed power producing resources identified through Inclusion I4 of the Bulk Electric System definition, this requirement
applies only to those transformers that have at least one winding at a voltage of 100 kV or above.

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VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
R6.
After consultation with the Transmission Operator regarding necessary step-up transformer tap
changes, the Generator Owner shall ensure that transformer tap positions are changed
according to the specifications provided by the Transmission Operator, unless such action would
violate safety, an equipment rating, a regulatory requirement, or a statutory requirement.
[Violation Risk Factor: Lower] [Time Horizon: Real-time Operations]
6.1. If the Generator Owner cannot comply with the Transmission Operator’s specifications, the
Generator Owner shall notify the Transmission Operator and shall provide the technical
justification.
M6.

The Generator Owner shall have evidence that its step-up transformer taps were modified per
the Transmission Operator’s documentation in accordance with Requirement R6. The Generator
Owner shall have evidence that it notified its associated Transmission Operator when it could
not comply with the Transmission Operator’s step-up transformer tap specifications in
accordance with Requirement R6, Part 6.1.

4

VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules

C. Compliance
1.

Compliance Monitoring Process:
1.1. Compliance Enforcement Authority:
As defined in the NERC Rules of Procedure, “Compliance Enforcement Authority”
refers to 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 Compliance Enforcement Authority may ask an entity to provide other
evidence to show that it was compliant for the full time period since the last audit.
The Generator Owner shall keep its latest version of documentation on its step-up
and auxiliary transformers. The Generator Operator shall maintain all other evidence
for the current and previous calendar year.
The Compliance Monitor shall retain any audit data for three years.
1.3. Compliance Monitoring and Assessment Processes:
“Compliance Monitoring and Assessment Processes” refers to the identification of
the processes that will be used to evaluate data or information for the purpose of
assessing performance or outcomes with the associated reliability standard.
1.4. Additional Compliance Information:
None.

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VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
Table of Compliance Elements
R#

R1

Time
Horizon

Real-time
Operations

Violation Severity Levels
VRF

Lower VSL

Medium

N/A

Moderate VSL

N/A

High VSL

N/A

Severe VSL
Unless exempted, the
Generator Operator did not
operate each generator
connected to the
interconnected
transmission system in the
automatic voltage control
mode or in a different
control mode as instructed
by the Transmission
Operator, and failed to
provide the required
notifications to
Transmission Operator as
identified in Requirement
R1.

6

VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
R#

R2

Time
Horizon

Real-time
Operations

Violation Severity Levels
VRF

Lower VSL

Medium

N/A

Moderate VSL

N/A

High VSL

The Generator
Operator did not
have a conversion
methodology when it
monitors voltage at a
location different
from the schedule
provided by the
Transmission
Operator.

Severe VSL
The Generator Operator did
not maintain the voltage or
Reactive Power schedule as
instructed by the
Transmission Operator and
did not make the necessary
notifications required by
the Transmission Operator.
OR
The Generator Operator
did not have an operating
AVR, and the responsible
entity did not use an
alternative method for
controlling voltage.
OR
The Generator Operator did
not modify voltage when
directed, and the responsible
entity did not provide any
explanation.

R3

Real-time
Operations

Medium

N/A

N/A

N/A

The Generator Operator
did not make the required
notification within 30
minutes of the status
change.
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VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
R#

R4

R5

Time
Horizon

Real-time
Operations

Real-time
Operations

Violation Severity Levels
VRF

Lower VSL

Medium

Lower

N/A

N/A

Moderate VSL

High VSL

N/A

N/A

N/A

The Generator Owner
failed to provide its
associated
Transmission
Operator and
Transmission Planner
one of the types of
data specified in
Requirement R5 Parts
5.1.1, 5.1.2, and 5.1.3.

Severe VSL
The Generator Operator
did not make the required
notification within 30
minutes of becoming
aware of the capability
change.

The Generator Owner failed
to provide to its associated
Transmission Operator and
Transmission Planner two or
more of the types of data
specified in Requirement R5
Parts 5.1.1, 5.1.2, and 5.1.3.

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VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
R#

Time
Horizon

Violation Severity Levels
VRF

Lower VSL

Moderate VSL

High VSL

Severe VSL
The Generator Owner did
not ensure the tap
changes were made
according the
Transmission Operator’s
specifications.

R6

Real-time
Operations

OR
Lower

N/A

N/A

N/A

The Generator Owner
failed to perform the tap
changes, and the
Generator Owner did not
provide technical
justification for why it
could not comply with the
Transmission Operator
specifications.

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VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
D. Regional Variances

None.
E. Interpretations

None.
F. Associated Documents

None.
Version History
Version

Date

Action
Added “(R2)” to the end of levels on
non-compliance 2.1.2, 2.2.2, 2.3.2,
and2.4.3.

Change Tracking

1

5/1/2006

July 5, 2006

1a

12/19/2007

Added Appendix 1 – Interpretation of
R1 and R2 approved by BOT on August
1, 2007

1a

1/16/2007

In Section A.2., Added “a” to end of
standard number. Section F: added
“1.”; and added date.

Errata

1.1a

10/29/2008

BOT adopted errata changes; updated
version number to “1.1a”

Errata

1.1b

3/3/2009

Added Appendix 2 – Interpretation of
VAR-002-1.1a approved by BOT on
February 10, 2009

Revised

2b

4/16/2013

Revised R1 to address an
Interpretation Request. Also added
previously approved VRFs, Time
Horizons and VSLs. Revised R2 to
address consistency issue with VAR001-2, R4.
FERC Order issued approving VAR002-2b.

Revised

3

5/5/2014

Revised under Project 2013-04 to
address outstanding Order 693
directives.

Revised

3

5/7/2014

Adopted by NERC Board of Trustees

3

8/1/2014

Approved by FERC in docket RD14-11000

4

8/27/2014

Revised under Project 2014-01 to
clarify applicability of Requirements to

Revised

Revised
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VAR-002-4.1 — Generator Operation for Maintaining Network Voltage Schedules
BES dispersed power producing
resources.
4

11/13/2014

Adopted by NERC Board of Trustees

4

5/29/2015

FERC Letter Order in Docket No. RD153-000 approving VAR-002-4

4.1

June 14, 2017

4.1
4.1

Project 2016-EPR-02 errata
recommendations

Errata

August 10, 2017

Adopted by the NERC Board of
Trustees

Errata

September 26,
2017

FERC Letter Order issued approving
VAR-002-4.1 RD17-7-000

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VAR-002-4.1 Application Guidelines

Guidelines and Technical Basis
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 R1:

This requirement has been maintained due to the importance of running a unit with its automatic
voltage regulator (AVR) in service and in either voltage controlling mode or the mode instructed by
the TOP. However, the requirement has been modified to allow for testing, and the measure has
been updated to include some of the evidence that can be used for compliance purposes.
Rationale for R2:

Requirement R2 details how a Generator Operator (GOP) operates its generator(s) to provide
voltage support and when the GOP is expected to notify the Transmission Operator (TOP). In an
effort to remove prescriptive notification requirements for the entire continent, the VAR-002-3
standard drafting team (SDT) opted to allow each TOP to determine the notification requirements
for each of its respective GOPs based on system requirements. Additionally, a new Part 2.3 has
been added to detail that each GOP may monitor voltage by using its existing facility equipment.
Conversion Methodology: There are many ways to convert the voltage schedule from one voltage
level to another. Some entities may choose to develop voltage regulation curves for their
transformers; others may choose to do a straight ratio conversion; others may choose an entirely
different methodology. All of these methods have technical challenges, but the studies performed
by the TOP, which consider N-1 and credible N-2 contingencies, should compensate for the error
introduced by these methodologies, and the TOP possesses the authority to direct the GOP to
modify its output if its performance is not satisfactory. During a significant system event, such as a
voltage collapse, even a generation unit in automatic voltage control that controls based on the
low-side of the generator step-up transformer should see the event on the low-side of the
generator step-up transformer and respond accordingly.
Voltage Schedule Tolerances: The bandwidth that accompanies the voltage target in a voltage
schedule should reflect the anticipated fluctuation in voltage at the GOP’s Facility during normal
operations and be based on the TOP’s assessment of N‐1 and credible N‐2 system contingencies.
The voltage schedule’s bandwidth should not be confused with the control dead‐band that is
programmed into a GOP’s AVR control system, which should be adjusting the AVR prior to
reaching either end of the voltage schedule’s bandwidth.
Rationale for R3:

This requirement has been modified to limit the notifications required when an AVR goes out of
service and quickly comes back in service. Notifications of this type of status change provide little
to no benefit to reliability. Thirty (30) minutes have been built into the requirement to allow a GOP
time to resolve an issue before having to notify the TOP of a status change. The requirement has
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VAR-002-4.1 Application Guidelines
also been amended to remove the sub-requirement to provide an estimate for the expected
duration of the status change.
Rationale for R4:

This requirement has been bifurcated from the prior version VAR-002-2b Requirement R3. This
requirement allows GOPs to report reactive capability changes after they are made aware of the
change. The current standard requires notification as soon as the change occurs, but many GOPs
are not aware of a reactive capability change until it has taken place.
Rationale for Exclusion in R4:

VAR-002 addresses control and management of reactive resources and provides voltage control
where it has an impact on the BES. For dispersed power producing resources as identified in
Inclusion I4, Requirement R4 should not apply at the individual generator level due to the unique
characteristics and small scale of individual dispersed power producing resources. In addition,
other standards such as proposed TOP-003 require the Generator Operator to provide Real-time
data as directed by the TOP.
Rationale for R5:

This requirement and corresponding measure have been maintained due to the importance of
having accurate tap settings. If the tap setting is not properly set, then the VARs available from
that unit can be affected. The prior version of VAR-002-2b, Requirement R4.1.4 (the +/- voltage
range with step-change in % for load-tap changing transformers) has been removed. The
percentage information was not needed because the tap settings, ranges and impedance are
required. Those inputs can be used to calculate the step-change percentage if needed.
Rationale for Exclusion in R5:

The Transmission Operator and Transmission Planner only need to review tap settings, available
fixed tap ranges, impedance data and the +/- voltage range with step-change in % for load-tap
changing transformers on main generator step-up unit transformers which connect dispersed
power producing resources identified through Inclusion I4 of the Bulk Electric System definition to
their transmission system. The dispersed power producing resources individual generator
transformers are not intended, designed or installed to improve voltage performance at the point
of interconnection. In addition, the dispersed power producing resources individual generator
transformers have traditionally been excluded from Requirement R4 and R5 of VAR- 002-2b
(similar requirements are R5 and R6 for VAR-002-3), as they are not used to improve voltage
performance at the point of interconnection.
Rationale for R6:

This requirement and corresponding measure have been maintained due to the importance of
having accurate tap settings. If the tap setting is not properly set, then the VARs available from
that unit can be affected.
16