Reliability Standard VAR-002-3

VAR-002-3 — Generator Operation for Maintaining Network Voltage Schedules
A. Introduction
1.

Title:

Generator Operation for Maintaining Network Voltage Schedules

2.

Number:

VAR-002-3

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:
4.1. Generator Operator
4.2. Generator Owner

5.

Effective Dates
The standard shall become effective on the first day of the first calendar quarter after
the date that the standard is approved by an applicable governmental authority or as
otherwise provided for in a jurisdiction where approval by an applicable governmental
authority is required for a standard to go into effect. Where approval by an applicable
governmental authority is not required, VAR-002-3 shall become effective on the first
day of the first calendar quarter after the date the standard is adopted by the NERC
Board of Trustees or as otherwise provided for in that jurisdiction.

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VAR-002-3 — Generator Operation for Maintaining Network Voltage Schedules
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 Realtime 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).
R2.

Unless exempted by the Transmission Operator, each Generator Operator shall maintain the
generator voltage or Reactive Power schedule3 (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

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.
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-002-3 — Generator Operation for Maintaining Network Voltage Schedules
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.
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

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VAR-002-3 — Generator Operation for Maintaining Network Voltage Schedules
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]
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 transformers and auxiliary transformers with primary voltages equal
to or greater than the generator terminal voltage:
5.1.1.

Tap settings.

5.1.2.

Available fixed tap ranges.

5.1.3.

Impedance data.

M5. The Generator Owner shall have evidence it provided its associated Transmission Operator and
Transmission Planner with information on its step-up transformers and auxiliary transformers as
required in Requirement R5, Part 5.1.1 through Part 5.1.3 within 30 calendar days.
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.

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VAR-002-3 — 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-002-3 — Generator Operation for Maintaining Network Voltage Schedules
Table of Compliance Elements
R#

Time
Horizon

VRF

Violation Severity Levels
Lower VSL

R1

Real-time
Operations

Medium

R2

Real-time
Operations

Medium

Moderate VSL

High VSL

Severe VSL

N/A

N/A

N/A

N/A

N/A

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.

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.
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

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VAR-002-3 — Generator Operation for Maintaining Network Voltage Schedules

R#

Time
Horizon

VRF

Violation Severity Levels
Lower VSL

Moderate VSL

High VSL

N/A

N/A

N/A

Severe VSL
explanation.
The Generator Operator did not make
the required notification within 30
minutes of the status change.

R3

Real-time
Operations

Medium

R4

Real-time
Operations

Medium N/A

N/A

N/A

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

R5

Real-time
Operations

Lower

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.

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.

R6

Real-time
Operations

Lower

N/A

N/A

N/A

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

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VAR-002-3 — Generator Operation for Maintaining Network Voltage Schedules

R#

Time
Horizon

VRF

Violation Severity Levels
Lower VSL

Moderate VSL

High VSL

Severe VSL
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-002-3 — Generator Operation for Maintaining Network Voltage Schedules
D. Regional Variances

None.
E. Interpretations

None.
F. Associated Documents

None.

Version History

Version

Date

Action

Change Tracking

1

5/1/2006

Added “(R2)” to the end of levels on noncompliance 2.1.2, 2.2.2, 2.3.2, and 2.4.3.

July 5, 2006

1a

12/19/2007

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

Revised

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

8/16/2012

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
VAR-002-2b. Adopted by Board of
Trustees.

Revised

2b

4/16/2013

FERC Order issued approving VAR-002-2b

3

5/6/2014

Adopted by the NERC Board of Trustees

3

8/1/2014

FERC issued letter order approving
VAR-002-3

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Application Guidelines
Guidelines and Technical Basis
For technical basis for each requirement, please review the rationale provided for each
requirement.
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 VAR002-3 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.

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Application Guidelines
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 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 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 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.

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