Overview of Project Reliability-Based Control Dynamic Transfer Capability Task Force January 31, 2011

Project Reliability-Based Control Presentation Scope a)Reliability-Based Control Standard Purpose Statements b)Purpose Statement A and the Field Trial of the Balancing Authority ACE Limit c)Purpose Statement B and C and the introduction of transmission-related ACE Bounds d)History of WECC Frequency Performance under R-BC e)Tools Development f)Discussion

Project Reliability-Based Control Purpose Statements A) To maintain Interconnection frequency within predefined frequency limits under all conditions (i.e., normal and abnormal), to manage frequency-related issues such as frequency oscillations, instability, and unplanned tripping of load, generation or transmission, that adversely impact the reliability of the Interconnection. B) To support corrective action by the BA when its excessive Area Control Error, as determined by this standard, may be contributing to or causing other action to be taken to correct a System Operating Limit (SOL) problem.

Project Reliability-Based Control Purpose Statements C) To prevent Interconnection frequency excursions of short- duration attributed to the ramping of Interchange Transactions. D) To support timely congestion relief by requiring the Balancing Authority with an inappropriate ACE to employ corrective load/generation management within a defined timeframe when participating in transmission loading relief procedures.

Reliability-Based Control defines a method of relating frequency and ACE limits. This relationship is based on outage statistics and relay settings, and is intended to avoid activation of frequency sensitive relays. Under the proposed standard, BAs may incur violations when their ACE exceeds a variable frequency-based ACE limit continuously for longer than a time limit (T v ) specified by the standard. Thirty consecutive clock- minutes is the criteria being used in the Field Trial in the Eastern, Western and Texas Interconnections. Project Reliability-Based Control

Frequency (Hz) -Y*Bias = ACE ( MW ) CPM Limit BAAL Low Y= FTL Low FRL Low FAL Low Frequency Bias Line Western Interconnection Frequency Limits, BAAL and CPM Similar curves in upper-right quadrant not shown Reliability-Based Control Standard Proof-of-Concept Field Trial Frequency Relay Limit (FRL) - if exceeded, will result in tripping of frequency-related relays Frequency Abnormal Limit (FAL) - cannot be exceeded w/out exposing interconnection to unacceptable level of risk (greater than a one in ten-year probability of unwarranted load shed relay activity) Frequency Trigger Limit (FTL) – can operate for limited time before risk to Interconnection is unacceptable.

Reliability-Based Control Standard Proof-of-Concept Field Trial The targeted research indicated that the wide bounds associated with setting the FTL at Hz for the WECC might not allow for sufficient operation to maintain the targeted RMS: “For the Interconnection one-minute average frequency error to meet the targeted RMS, e 1, frequency cannot wander at levels much beyond 3 to 4 times of e 1 away from scheduled frequency for more than a few hours per year. To help return frequency to its schedule when it is abnormally deviated and help meet the targeted frequency profile, it would be beneficial to limit FTL low and FTL high for each Interconnection to a setting in the range of 3 to 4 times of its e 1 away from scheduled frequency, particularly FTL low for WECC's and FTL high for all Interconnections.”

FTL Standard Limits in Western Interconnection FTL as reflected in the targeted research

FTL Standard Limits in Western Interconnection FTL adjusted to three times epsilon1 Limits applicable at three times epsilon1

FTL Standard Limits in Western Interconnection FTL as reflected in the targeted research

FTL Standard Limits in Western Interconnection FTL adjusted to three times epsilon1 Limits applicable at three times epsilon1

Purpose Statement B: To support corrective action by the BA when its excessive Area Control Error, as determined by this standard, may be contributing to or causing action to be taken to correct a SOL problem. Project Reliability-Based Control

Purpose Statement B: To support corrective action by the BA when its excessive Area Control Error, as determined by this standard, may be contributing to or causing action to be taken to correct an SOL or IROL problem.

A proposed solution would be to “cap” ACE in the form of a dynamic limit applicable to either positive or negative ACE based upon the transmission constraint being mitigated. Purpose Statement BPurpose Statement B: To support corrective action by the BA when its excessive Area Control Error, as determined by this standard, may be contributing to or causing action to be taken to correct an SOL or IROL problem.

Purpose Statement C: To prevent Interconnection frequency excursions of short-duration attributed to the ramping of Interchange Transactions. Over the course of reviewing frequency data from the Field Trial, the RBC SDT found that the predominant source of frequency excursions exceeding the Frequency Trigger Limit (FTL) of Hz in the Eastern Interconnection was attributed to the inability of resources to adequately ramp to match the implementation of Interchange Transactions or coincident actions within the Interconnection. Such coincident actions would include implementation of pumped storage, on/off peak transition, load changes, intermittent resources and generation status changes. Imbalance across such short-duration excursions is not adequately addressed in the current CPS2 or the BAAL implemented under the Field Trial. The largest deviations have brought the Eastern Interconnection frequency to levels where the Interconnection is at greater risk of a coincident event causing under-frequency load shedding. The above factors were explained in the approved SAR, however, the purpose statement was not revised to reflect inclusion of these additional sources of short-duration frequency excursions. Early in he development, the RBC SDT proposed that the Purpose Statement C be revised to: “To prevent Interconnection frequency excursions of short-duration attributed to the ramping of Interchange Transactions or coincident actions within the Interconnection.” Future work in this area should include the proposed change to Purpose Statement C. Project Reliability-Based Control

History of WECC Frequency Perfomance Under R-BC

Targeted Frequency Bounds Epsilon 1 and 10 The targeted frequency bounds, epsilon 1 ( ∈ 1 ) and epsilon 10 ( ∈ 10 ), are based on historic measured frequency error. These bounds, typically in millihertz (mHz), embody the targeted frequency characteristics used for developing the Control Performance Standard. Each Interconnection is assigned its own frequency bounds. The Targeted Frequency Bound for an Interconnection is computed as follows: 1.The NERC Resources Subcommittee (RS) defines a desired frequency profile. 2.The NERC RS collects frequency data from designated providers within each Interconnection. The frequency bounds are the RMS of the one- and ten-clock-minute averages of the frequency error (deviation) from schedule. These values are derived from data samples over a given year. The NERC RS calculates and then sets the targeted frequency bounds, ∈ 1 and ∈ 10, to recognize the desired performance profile of frequency for each Interconnection. In WECC, ∈ 1 =22.8 and ∈ 10 =7.3.

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Project Reliability-Based Control Tools Development

FTL 9/08/2005 5:03 EST 8 minutes

This area indicates that the problem was spread across multiple RC regions The ACE-Frequency Monitoring Tool used by some Reliability Coordinators has the capability to identify the RC regions impacting frequency and “drill down” to the performance of the BAs within the RC region.

Balancing Authorities under the Field Trial have developed tools to monitor compliance to BAAL. This tool pulls in data from a “PI” data system and displays the BAAL boundaries along with clock-minute ACE plotted against clock-minute Actual Frequency, in addition to displaying the number of consecutive clock-minutes that ACE is outside the applicable BAAL bound. Tools Development

This tool pulls in data from a “PI” data system and displays CPS1 (dark line) and an adjusted CPS1 calculation for time-error corrections (yellow). When scheduled frequency equals 60 Hz, both curves are the same and exceeding the BAAL is equivalent to a CPS1 compliance of approximately %. The counter at the bottom displays the number of consecutive clock-minutes the adjusted CPS1 is worse than %. (Based upon FTL at Hz and Hz.) Tools Development

Balancing Authority ACE Limit Proof-of-Concept Field Trial Eastern Interconnection Field Trial Participation Participation reflects approximately 67% of the projected 2010 peak load for the Eastern Interconnection

Balancing Authority ACE Limit Proof-of-Concept Field Trial Western Interconnection Field Trial Participation Participation reflects approximately xx% of the projected 2010 peak load for the Western Interconnection

Project Reliability-Based Control Discussion Special thanks to Doug Hils