BAL-004-WECC-4

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BAL-004-WECC-4 ─ Automatic Time Error Correction
WECC-0147 Att. C-1 Clean as Proposed with Non-Sub NERC Change

A. Introduction
1. Title:

Automatic Time Error Correction

2. Number:

BAL-004-WECC-4

3. Purpose:

To maintain Western Interconnection (WI) frequency, and ensure that time
error accumulation via Primary Inadvertent Interchange (PII) payback is
conducted in a manner that does not result in a negative impact on
reliability.

4. Applicability:
4.1. Functional Entities:
4.1.1.

Balancing Authorities operating synchronously within the WI

5. Effective Date: The first day of the second quarter following regulatory approval.
6. Background:
Pre-2000 (prior to mandatory Standards), the Western Electricity Coordinating Council
(WECC) operated using the Minimum Operating Reliability Criteria (MORC). Per MORC
Section D. Time Control, Control Areas were required to assist in maintaining frequency
at or near 60.0 Hz, as prescribed in the Western System Coordinating Council (WSCC) 1
Procedure for Time Error Control (PTEC). Various versions of the PTEC predate 1980.
In February 2003, the WECC Automatic Time Error Correction (ATEC) Procedure
(Procedure) became effective for all Balancing Authorities in the WI. The original intent
of the Procedure was to minimize the number of manual Time Error Corrections in the
WI. 2
In June 2007, the Procedure was translated into BAL-STD-004-1, Time Error Correction,
followed by BAL-004-WECC-1 through 3, Time Error Correction. 3 BAL-004-WECC-1
required Balancing Authorities within the WI to maintain Interconnection frequency
within a predefined frequency profile, and to ensure that Time Error Corrections would
not result in a negative impact on Interconnection reliability.
In September 2009, in response to Federal Energy Regulatory Commission (FERC) Order
723, WECC received Standard Authorization Request (SAR) WECC-0068 requesting
modification of BAL-004-WECC-1. Modifications were effective April 1, 2014, creating
BAL-004-WECC-2. BAL-004-WECC-2 introduced two performance metrics: 1) in
Requirement R1, a 150% metric, and 2) in Requirement R2, a 90-day metric. Neither of
these metrics are supported by technical studies. They were included in BAL-004-WECCWECC began in 1967 as the Western Systems Coordinating Council (WSCC), a group of 40 power systems
with a common goal of providing reliable power to the public whom they served. WECC was founded
March 22, 1994.
2
The Procedure provided for cost assignment and equitable payback of Inadvertent Interchange, not
otherwise addressed in BAL-004-4, Time Error Correction.
3
See Version History Table.
1

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2 as a compromise during drafting.
In May 2018, FERC approved minor revisions to BAL-004-WECC-2 as part of WECC SAR
WECC-0124, effective October 1, 2018, creating BAL-004-WECC-3. 4
In 2023, this Standard was reviewed as part of the WECC SAR WECC-0147. The drafting
team noted: 1) Version 3, Requirement R5 migrated from the pre-2000 MORC without
initial or subsequent technical support, and 2) R5 addresses capabilities of Automatic
Generator Control (AGC) found in no other Standard, without mandating its use or
stating how that capability interfaces with ATEC. R5 is retained herein until it can be
properly addressed per a NERC Standard Authorization Request.
7. Standard-Only Definition:
7.1

Interchange Software:

This Standard uses the Standard-Only term “Interchange Software” to mean:
The single electronic confirmation tool identified by the Western Electricity
Coordinating Council (WECC), or its successor, to be used by all Balancing Authorities
throughout the Western Interconnection (WI), that serves as the primary means for
confirmation and creation of the final record of Scheduled Net Interchange (NIS 5) and
Actual Net Interchange (NIA 6), during all periods when the Interchange Software is
available.
7.2. ATEC:
This Standard uses the term “ATEC” as defined in the WECC Regional Definitions
section of the NERC Glossary of Terms Used in Reliability Standards.

FERC Docket No. RD18-2-000. Effective Date October 1, 2018.
Previously called Net Scheduled Interchange
6
Previously called Net Actual Interchange
4
5

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B. Requirements and Measures

R1. Each Balancing Authority shall use the Interchange Software as the sole source of data
to calculate its ATEC. [Violation Risk Factor: Severe] [Time Horizon: Operations
Assessment]
M1. Each Balancing Authority will have evidence that it used the Interchange Software as
the sole source of data to calculate its ATEC, as required in Requirement R1.
Evidence may include, but is not limited to production of a corporate attestation or
operating procedure indicating use of the Interchange Software as the sole source for
calculating ATEC.
R2. Each Balancing Authority shall operate its system such that, the month-end absolute
value of its On-Peak and Off-Peak, accumulated Primary Inadvertent Interchange
(PIIaccum), as calculated by the Interchange Software, are each individually less than or
equal to 150% of the previous calendar year’s integrated hourly peak demand where
peak demand is total load plus total exports. [Violation Risk Factor Medium:] [Time
Horizon: Operations Assessment]
2.1. For new Balancing Authorities, the peak demand will be the maximum hourly
integrated peak demand as it increases during the first year of operation.
M2. Each Balancing Authority will have evidence that it operated its system such that the
month-end absolute value of its On-Peak and Off-Peak, accumulated Primary
Inadvertent Interchange (PIIaccum), as calculated by the Interchange Software, are
each individually less than or equal to 150% of the previous calendar year’s integrated
hourly peak demand where peak demand is total load plus total exports, average load
in those hours, as calculated by the Interchange Software, per Requirement R2, or per
the exception allowed in R2.1.
R3. Each Balancing Authority shall, upon discovery of an error in its On-Peak or Off-Peak
Inadvertent Interchange calculation, recalculate and correct the Inadvertent
Interchange values within 90 days from the time the error is discovered. [Violation
Risk Factor: Medium] [Time Horizon: Operations Assessment]
M3. Each Balancing Authority discovering an error in its On-Peak or Off-Peak Inadvertent
Interchange calculation will have evidence that it recalculated and corrected the
Inadvertent Interchange values, within 90 days from the time the error is discovered,
as required in Requirement R3.
Evidence may include, but is not limited to:
•

Screen shots from the Interchange Software;

•

Screen shots from the Balancing Authority’s internal software functions such as
internal databases, spreadsheets, and displays;

•

Dated archive files; and

•

Historic data.

R4. Each Balancing Authority shall keep ATEC in service, with an allowable exception
period of less than or equal to an accumulated 24 hours per calendar quarter for
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ATEC to be out of service. This period is separate from any period during which the
Interchange Software was unavailable. [Violation Risk Factor: Medium] [Time
Horizon: Same-day Operations]
M4. Each Balancing Authority will have evidence that it kept ATEC in service as
required in Requirement R4, subject to the allowable exceptions provided.
Evidence may include, but is not limited to:
•

Screen shots from the Interchange Software;

•

Screen shots from the Balancing Authority’s internal software functions such as
internal databases, spreadsheets, and displays;

•

Dated archive files; and

•

Historical data.

R5. Each Balancing Authority shall be able to change its Automatic Generation Control
(AGC) operating mode to correspond to current operating conditions. [Violation
Risk Factor: Medium] [Time Horizon: Real-Time Operations]
M5. Each Balancing Authority will have evidence that its AGC is able to change operating
modes to correspond to current operating conditions, as required in R5.
Evidence may include, but is not limited to:
•

Screen shots from Energy Management System; and

•

Demonstration using an off-line system.

R6. Each Balancing Authority shall upload hourly Actual Net Interchange (NIA) to the
Interchange Software no later than 50 minutes after each hour. [Violation Risk
Factor: Medium] [Time Horizon: Operations Assessment]
M6. Each Balancing Authority will have evidence that it uploaded hourly Actual Net
Interchange (NIA) to the Interchange Software no later than 50 minutes after each
hour, as required in Requirement R6.
Evidence may include, but is not limited to:
•

Screen shots from the Interchange Software;

•

Screen shots from the Balancing Authority’s internal software functions such
as internal databases, spreadsheets, and displays;

•

Dated archive files; and

•

Historical data.

R7. Each Balancing Authority making a month-end adjustment shall input that value as part
of its Actual Net Interchange (NIA). [Violation Risk Factor: Medium] [Time Horizon:
Operations Assessment]
M7. Each Balancing Authority making a month-end adjustment will have evidence that
it input that value as part of its Actual Net Interchange (NIA), as required in
Requirement R7.
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R8. Each Balancing Authority making a month-end adjustment shall ensure that value
is added to its accumulated Primary Inadvertent Interchange. [Violation Risk
Factor: Medium] [Time Horizon: Operations Assessment]
M8. Each Balancing Authority making a month-end adjustment will have evidence that
the value was added to its accumulated Primary Inadvertent Interchange, as
required in Requirement R8.

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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 period(s) 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 applicable entity 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.
•

1.3

Each Balancing Authority in the WI shall keep the following records for the
preceding calendar year (January – December) plus the current calendar year:
•

Its values for PIIhourly, PIIaccum (On-Peak and Off-Peak), ∆TE, and any
month-end adjustments.

•

Documentation illustrating any period(s) during which the Balancing
Authority operated without ATEC, including the reason ATEC was not in
operation.

Compliance Monitoring and Enforcement Program: As defined in the NERC Rules
of Procedure, “Compliance Monitoring and Enforcement Program” 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.

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Violation Severity Levels
R#

Violation Severity Levels
Lower VSL

Moderate VSL

High VSL

Severe VSL

R1.

NA

NA

NA

The Balancing Authority
failed to use the Interchange
Software as the sole source
to calculate ATEC.

R2.

Following the conclusion of
each month each Balancing
Authority’s absolute value of
PIIaccum for either the OnPeak period or Off-Peak
period exceeded 150%, but
was less than or equal to
160% of the previous
calendar year’s peak
demand or peak generation
for generation-only
Balancing Authorities.

Following the conclusion of
each month each Balancing
Authority’s absolute value of
PIIaccum for either the OnPeak period or Off-Peak
period exceeded 160%, but
was less than or equal to
170% of the previous
calendar year’s peak demand
or peak generation for
generation-only Balancing
Authorities.

Following the conclusion of
each month each Balancing
Authority’s absolute value of
PIIaccum for either the OnPeak period or Off-Peak
period exceeded 170%, but
was less than or equal to
180% of the previous
calendar year’s peak
demand or peak generation
for generation-only
Balancing Authorities.

Following the conclusion of
each month each Balancing
Authority’s absolute value of
PIIaccum for either the OnPeak period or Off-Peak
period exceeded 180% of the
previous calendar year’s
peak demand or peak
generation for generationonly Balancing Authorities.

R3.

The Balancing Authority did
not recalculate PIIhourly and
adjust the PIIaccum within
90 days of the discovery of
the error; but made the
required recalculations and
adjustments within 120
days.

The Balancing Authority did
not recalculate PIIhourly and
adjust the PIIaccum within
120 days of the discovery of
the error; but made the
required recalculations and
adjustments within 150 days.

The Balancing Authority did
not recalculate PIIhourly and
adjust the PIIaccum within
150 days of the discovery of
the error; but made the
required recalculations and
adjustments within 180
days.

The Balancing Authority did
not recalculate PIIhourly and
adjust PIIaccum within 180
days of the discovery of the
error.

R4.

The Balancing Authority
operated during a calendar

The Balancing Authority
operated during a calendar

The Balancing Authority
operated during a calendar

The Balancing Authority
operated during a calendar
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quarter without ATEC in
quarter without ATEC in
service for more than an
service for more than an
accumulated 24 hours, but
accumulated 72 hours, but
less than or equal to 72
less than or equal to 120
hours.
hours.

quarter without ATEC in
service for more than an
accumulated 120 hours, but
less than or equal to 168
hours.

quarter without ATEC in
service for more than an
accumulated 168 hours.

R5.

N/A

N/A

N/A

The Balancing Authority is
not able to change its AGC
operating mode to
correspond to current
operating conditions.

R6.

The Balancing Authority
failed to upload hourly
Actual Net Interchange to
the Interchange Software no
later than 50 minutes after
each hour, but uploaded the
required data in less than or
equal to two hours.

The Balancing Authority
failed to upload hourly
Actual Net Interchange to
the Interchange Software no
later than 50 minutes after
each hour, but uploaded the
required data in less than or
equal to four hours.

The Balancing Authority
failed to upload hourly
Actual Net Interchange to
the Interchange Software no
later than 50 minutes after
each hour, but uploaded the
required data in less than or
equal to six hours.

The Balancing Authority
failed to upload hourly
Actual Net Interchange to
the Interchange Software no
later than 50 minutes after
each hour, but uploaded the
required data in more than
six hours.

R7.

NA

NA

NA

The Balancing Authority
making a month-end
adjustment failed to input
that value as part of its Net
Actual Interchange.

R8.

NA

NA

NA

The Balancing Authority
making a month-end
adjustment failed to add that
value to its accumulated
Primary Inadvertent
Interchange.

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D. Regional Variances
None.

E. Associated Documents
None.

Version History
Version
1
1
1

Date
February 4, 2003
October 17, 2006
February 6, 2007

1

February 6, 2007

1

February 6, 2007

1

February 6, 2007

1

June 19, 2007

2
2

December 19, 2012
October 16, 2013

Action

Effective Date.
Created Standard from Procedure.
Changed the Standard Version from 0 to
1 in the Version History Table.
The upper limit bounds to the amount of
Automatic Time Error Correction term
was inadvertently omitted during the
Standard Translation. The bound was
added to the requirement R1.4.
The statement “The Time Monitor may
declare offsets in 0.001-second
increments” was moved from TEoffset to
TDadj and offsets was corrected to
adjustments.
The reference to seconds was deleted
from the TE offset term.
The standard number BAL-STD-004-1
was changed to BAL-004-WECC-01 to be
consistent with the NERC Regional
Reliability Standard Numbering
Convention.
Adopted by NERC Board of Trustees.
A FERC Letter Order was issued on
October 16, 2013, approving BAL-004WECC-02. This standard will become
enforceable on April 1, 2014.

Change Tracking
New
Errata
Errata
Errata

Errata

Errata
Errata

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Version
3

Date
December 6, 2017

Action
Approved by the WECC Board of
Directors.

3

February 8, 2018

Adopted by the NERC Board of
Trustees.

3

May 30, 2018

FERC Order issued approving BAL-004WECC-3. Docket No. RD18-2-000. Effective
Date October 1, 2018.

4

March 13, 2024

WECC Board of Directors Approved

Change Tracking

Five-year review. The
project: 1) relocates the
Background section to
the preamble of the
Guidance section, 2)
adds On-Peak and OffPeak parameters in
Requirement R1/M1, 3)
addresses WECC
Interchange Tool
software successors
throughout, 4)
conforms the
document to current
drafting conventions
(R1/M1, R4/M4), and 5)
addresses nonsubstantive syntax and
template concerns.

This project: 1) expands
the existing Background
section, 2) creates a
Standard-specific
definition (Interchange
Software); 3) creates a
requirement to use the
Interchange Software;
4) addresses treatment
of Balancing Authorities
that do not have a full
year of operating data;
5) consolidates and
clarifies requirements;
and 6) updates the
document to NERC's
newest templates.

Standard Attachments
Not used.

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G. Rationale
Nomenclature Update
To conform to NERC’s definitional approach, the legacy term Net Actual Interchange (NAI) was
replaced with Actual Net Interchange (NIA). Net Scheduled Interchange (NSI) was replaced
with Scheduled Net Interchange (NIS). The legacy terms and the updated terms are
synonymous.
Requirement R1:
The goal of Requirement R1 is to ensure a consistent ATEC calculation within the WI.
Because ATEC is an automatic process, allowing inconsistent calculation of ATEC will cause
imbalance in accumulations.
Requirement R2:
The goal of Requirement R2 is to limit the amount of PIIaccum that a Balancing Authority can
have at the end of each month.
To reach the goal, each Balancing Authority should ensure that the absolute value of its
PIIaccum for both the on-peak period and the off-peak period each individually does not
exceed 150% of the previous year’s Peak Demand for load-serving Balancing Authorities, and
150% of the previous year’s peak generation for generation-only Balancing Authorities. The
Balancing Authority is required to keep each PIIaccum period within the limit. For example,
the Balancing Authorities actions may include:
•

Identifying and correcting the source of any metering or accounting error(s) and
recalculating the hourly Primary Inadvertent Interchange (PIIhourly) and the PIIaccum
from the time of the error;

•

Validating the implementation of ATEC; or

•

Setting Lmax equal to L10.until the PIIaccum is below the limit in Requirement R1.

This approach is required because PIIaccum may grow from month-end adjustments and
metering errors, even with the inclusion of IATEC in the ACE equation.
Requirement R3:
The goal of Requirement R3 is to promote: 1) the timely correction of errors in the calculation
of PII and PIIaccum, and 2) the accurate, fair, and timely payback of accumulated PII balances.
When a Balancing Authority finds an error in the calculation of its PII, the Balancing Authority
needs time to correct the error and recalculate PII and PIIaccum.
Hourly adjustments to hourly Inadvertent Interchange (II) require a recalculation of the
corresponding hourly PII value, the corresponding PIIaccum, and all subsequent PIIaccum for
every hour up to the current hour.

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The drafting team selected 90 days as a reasonable amount of time to correct an error and
recalculate PII and PIIaccum, since recalculation of PII and PIIaccum is not a real-time
operations reliability issue. As PII hourly is corrected, then PIIaccum should be recalculated.
Requirement R4:
The goal of Requirement R4 is to promote fair and timely payback of PIIaccum balances by
ensuring that ATEC remains in service whenever possible.
When a Balancing Authority is not participating in ATEC, payback of PIIaccum is delayed.
The limit of 24 hours per quarter discourages a Balancing Authority from withdrawing ATEC
participation, for example, for economic gain during selected hours. If the limits were
increased to 60 hours, a Balancing Authority could technically withdraw ATEC participation
for one hour from Monday to Friday.
Requirement R5:
A review of NERC Standards conducted by the Version 4 drafting team concluded that this
Requirement is best located in a Standard focused on Automatic Generator Control (AGC).
However, until an AGC-specific Standard is drafted, the Requirement should not be retired.
The goal of Requirement R5 is to ensure that AGC has the ability to respond to varying
operating conditions.
Requirement R6:
Not used.
Requirement R7:
Not used.
Requirement R8:
Not used.

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