BAL-004-WECC-02: Automatic Time Error Correction

Purpose
To maintain Interconnection frequency and to ensure that Time Error Corrections and Primary Inadvertent Interchange (PII) payback are effectively conducted in a manner that does not adversely affect the reliability of the Interconnection.

Applicability
Functional Entities: Balancing Authorities that operate synchronously in the Western Interconnection.

Effective Date
On the first day of the second quarter, after applicable regulatory approval has been received (or the Reliability Standard otherwise becomes effective the first day of the fourth quarter following NERC Board adoption where regulatory approval is not required).

Requirements and Measures
R1. Following the conclusion of each month each Balancing Authority shall verify that the absolute value of its Accumulated Primary Inadvertent Interchange (PIIaccum) for both the monthly On-Peak period and the monthly Off-Peak period are each individually less than or equal to:

1.1. For load-serving Balancing Authorities, 150% of the previous calendar year’s integrated hourly Peak Demand,

1.2. For generation-only Balancing Authorities, 150% of the previous calendar year’s integrated hourly peak generation.

[Violation Risk Factor Medium:] [Time Horizon: Operations Assessment]

M1. Forms of acceptable evidence of compliance with Requirement R1 include but are not limited to any one of the following:

• Data, screen shots from the WECC Interchange Tool (WIT),

• Data, screen shots from the internal Balancing Authority tool, or

• Production of data from any other databases, spreadsheets, displays.

R2. Each Balancing Authority shall, upon discovery of an error in the calculation of PIIhourly, recalculate within 90 days, the value of PIIhourly and adjust the PIIaccum from the time of the error. [Violation Risk Factor: Medium] [Time Horizon: Operations Assessment]

M2. Forms of acceptable evidence of compliance with Requirement R2 include but are not limited to any one of the following:

•Data, screen shots from the WIT,

• Data, screen shots from the internal Balancing Authority tool, or

• Production of data from any other databases, spreadsheets, displays.

R3. Each Balancing Authority shall keep its Automatic Time Error Correction (ATEC) in service, with an allowable exception period of less than or equal to an accumulated 24 hours per calendar quarter for ATEC to be out of service. [Violation Risk Factor: Medium] [Time Horizon: Same-day Operations]

M3. Forms of acceptable evidence of compliance with Requirement R3 may include, but are not limited to:

•Dated archived files,

• Historical data

• Other data that demonstrates the ATEC was out of service for less than 24 hours per calendar quarter.

R4. Each Balancing Authority shall compute the following by 50 minutes after each hour:

4.1. PIIhourly,

4.2. PIIaccum,

4.3. Automatic Time Error Correction term (IATEC).

[Violation Risk Factor: Medium] [Time Horizon: Operations Assessment]

M4. Forms of acceptable evidence of compliance with Requirement R4 include but are not limited to any one of the following:

•Data, screen shots from the WECC Interchange Tool that demonstrate compliance,

• Data, screen shots from internal Balancing Authority tool that demonstrate compliance, or

• Data from any other databases, spreadsheets, displays that demonstrate compliance.

R5. Each Balancing Authority shall be able to change its Automatic Generation Control operating mode between Flat Frequency (for blackout restoration); Flat Tie Line (for loss of frequency telemetry); Tie Line Bias; and Tie Line Bias plus Time Error Control (used in ATEC mode), to correspond to current operating conditions. [Violation Risk Factor: Medium] [Time Horizon: Real-Time Operations]

M5. Forms of acceptable evidence of compliance with Requirement R5 include but are not limited to any one of the following:

• Screen shots from Energy Management System,

• Demonstration using an off-line system.

R6. Each Balancing Authority shall recalculate the PIIhourly and PIIaccum for the On-Peak and Off-Peak periods whenever adjustments are made to hourly Inadvertent Interchange or ∆TE. [Violation Risk Factor: Medium] [Time Horizon: Operations Assessment]

M6. Forms of acceptable evidence of compliance with Requirement R6 include but are not limited to any one of the following:

• Data, screen shots from the WECC Interchange Tool that demonstrate compliance,

• Data, screen shots from an internal Balancing Authority tool that demonstrate compliance with, or

• Data from any other databases, spreadsheets, displays that demonstrate compliance.

R7. Each Balancing Authority shall make the same adjustment to the PIIaccum as it did for any month-end meter reading adjustments to Inadvertent Interchange. [Violation Risk Factor: Medium] [Time Horizon: Operations Assessment]

M7. Forms of acceptable evidence of compliance with Requirement R7 include but are not limited to any one of the following:

• Data, screen shots from the WECC Interchange Tool that demonstrate compliance,

• Data, screen shots from an internal Balancing Authority tool that demonstrate compliance,

• Production of data from any other databases, spreadsheets, displays that demonstrate compliance.

R8. Each Balancing Authority shall payback Inadvertent Interchange using ATEC rather than bilateral and unilateral payback. [Violation Risk Factor: Medium] [Time Horizon: Operations Assessment]

M8. Forms of acceptable evidence of compliance with Requirement R8 include but are not limited to historical On-Peak and Off-Peak Inadvertent Interchange data, data from the WECC Interchange Tool, and ACE data.

Guidelines and Technical Basis

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.

Requirement R1:

Premise: Each Balancing Authority should ensure that the absolute value of its PIIaccum  for both the OnPeak 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 take action 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 PIIsccum  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.

Justification: PIIaccum may grow from month-end adjustments and metering errors, even with the inclusion of IATEC in the ACE equation.

Goal: To limit the amount of PIIaccum that a Balancing Authority can have at the end of each month.

Requirement R2:

Premise: 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 .

Justification: 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.

Goal: To promote the timely correction of errors in the calculation of PII and PIIaccum.

Requirement R3:

Premise: When a Balancing Authority is not participating in ATEC, payback of PIIaccum  is delayed.

Justification: 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.

Goal: To promote fair and timely payback of PIIaccum balances.

Requirement R4:

Premise: PIIhourly , PIIaccum , and IATEC  should be determined before the next scheduling hour begins.

Justification: To promote timely calculations 50 minutes was selected because it is before the next hour ramp begins and permits time to collect the data and resolve interchange metering values.

Goal: To promote the timely calculation of PIIhourly , PIIaccum , and IATEC.

Requirement R5:

Premise: The ACE equation, and hence the AGC mode, will contain any number of parameters based  on system operating conditions. Various AGC modes are identified corresponding to those operating conditions, as well as the specific sets of parameters included in the ACE equation.

Justification: Changing to the proper operating mode, corresponding to current operating conditions, affords proper movement of generating units in response to those conditions. The addition of the ATEC term results in an additional AGC mode and a different set of parameters. The inability to correctly calculate the ATEC term would dictate that AGC not be operated in the ATEC mode.

Goal: To set the AGC mode and calculate ACE in a manner that corresponds to the system operating conditions and to accommodate changes in those conditions.

Requirement R6:

Premise:  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.

Justification:  As PIIhourly is corrected, then PIIaccum should be recalculated.

Goal:  To promote accurate, fair and timely payback of accumulated PII balances.

Requirement R7:

Premise:  Month-end meter-reading adjustments are made, for example, when a Balancing Authority  performs monthly comparisons of recorded month-end Net Actual Interchange (NIA ) values derived from hourly Actual Interchange Telemetered Values against month-end Actual Interchange Register Meter readings.

Justification:  Month-end adjustments to IIaccum  are applied as 100% PIIaccum. 100% was chosen for simplicity to bilaterally assign PIIaccum to both Balancing Authorities, since the effect of this metering error on system frequency is not easily determined over the course of a month.

Goal:  To provide a mechanism by which corresponding month-end II adjustments can be applied to PIIaccum, when such adjustments cannot be attributed to any one particular hour or series of hours.

Requirement R8:

Premise:  ATEC includes automatic unilateral payback of Primary Inadvertent Interchange and  Secondary Inadvertent Interchange.

Justification:  Additional unilateral and bilateral exchanges disturb the balance and distribution between Primary Inadvertent Interchange and Secondary Inadvertent Interchange throughout the Interconnection; thereby stranding Secondary Inadvertent Interchange.

Goal:  To not strand Secondary Inadvertent Interchange.


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