GUIDELINES FOR UTILIZATION OF FREQUENCY AND TIME ERROR DEVICES AND CALIBRATING TIE LINE SIGNAL

Transcription

1 Document name Category Document date March 11, 2003 Adopted/approved by GUIDELINES FOR UTILIZATION OF FREQUENCY AND TIME ERROR DEVICES AND CALIBRATING TIE LINE SIGNAL ( ) Regional Reliability Standard ( ) Regional Criteria ( ) Policy (x) Guideline ( ) Report or other ( ) Charter Board of Directors Date adopted/approved December 5, 2003 Custodian (entity responsible for maintenance and upkeep) Stored/filed Previous name/number (if any) Status Control Work Group Physical location: Web URL: (x) in effect ( ) usable, minor formatting/editing required ( ) modification needed ( ) superseded by ( ) other ( ) obsolete/archived)

2 WECC Guideline: UTILIZATION OF FREQUENCY AND TIME ERROR DEVICES AND CALIBRATING TIE LINE SIGNALS Date: March 11, 2003 These guidelines should be considered by Member Systems to provide acceptable interconnected system operation. The guidelines provide information for frequency, time error, and tie line control devices. The recommendations are intended to promote uniformity of control within the Western Electricity Coordinating Council (WECC) interconnected system without placing an undue burden on the Member Systems. If a Member System's present equipment does not meet these criteria, then an orderly replacement effort is expected. Specific values rather than general terms are provided below regarding accuracy, maintenance intervals, and availability. The intent is to provide better information for system managers in justifying and specifying the devices required for acceptable interconnected system operation. The values for accuracy were selected on the basis of recommendations made by the WECC Control Work Group. Within the recommended accuracy, the control errors for a WECC system with a bias of 300 or less will be approximately 1 percent of the bias for both time and frequency error. For systems with a bias greater than 300, the control errors should be 0.5 percent or better of the bias for both time and frequency error. Tie line telemetering error shall be 0.5% or better of the full scale of the tie line telemetry. Improved measurements for control and monitoring have material benefits. However, the direct value of control measurement improvement is difficult to quantify. A direct benefit of more accurate control is less inadvertent interchange. Improved monitoring accuracy greatly simplifies post-disturbance analysis. In general, the Control Work Group regards adequate control and monitoring facilities to be essential to meet the overall benefits of interconnected system operation. I. Time and Frequency Error Devices Low-cost, accurate time error and frequency devices are available and WECC Member Systems are encouraged to use such devices as described below: A. Time Error Devices -2-

3 1. Time error devices should have an internal oscillator drift of no more than 50 milliseconds per day. While operating on an internal oscillator the system's reference time will then not drift more than this amount between daily time error checks sent out by the WECC time error monitor. 2. The availability of time error control should be better than 99 percent when tie-line bias and automatic time error correction mode is being used in AGC. 3. The maximum error in conversion from the standard time to the time error in the control algorithm should not be greater than 50 milliseconds. 4. The time error device should be equipped with an easy means of resetting the time error by the dispatcher. 5. Periodic tests should be made to ensure drift and conversion accuracy of the time error used for control. These tests should be performed at least once a year or more frequently if required to ensure accuracy. 6. Suggested minimum sample rate is to use at least the same scan cycle as the generation control algorithm for interchange data acquisition. B. Frequency Devices 1. Use of dual scale frequency equipment is desirable. A narrow-band scale with high accuracy and resolution is recommended for control; a wide-band scale should be used for system disturbance monitoring. The narrow-band range is approximately Hz to Hz. The wide-band range is selected based on the control area's expected frequency deviation should it become separated from the remainder of the system. For example, 55.0 Hz to 65.0 Hz. 2. At least one alternate system frequency source for use during loss of the normal control center source is desirable. The alternate source should be from the main portion of the power system and be readily available for control input. A means should be provided to monitor the availability of the alternate source. 3. The frequency equipment accuracy times the frequency bias should be less than 2 MW. Telemetering accuracy criteria should apply for an alternate frequency source. For control purposes, if a control area's frequency bias setting is less than 150 MW/0.1Hz, the minimum accuracy for frequency deviation output equipment should be at least 0.01 Hz, including any final conversions for computing. Control areas with large bias settings should have an accuracy value of at least Hz. 4. Frequency devices for control should have the same availability as the system's generation control equipment. -3-

4 5. Frequency devices should be tested for accuracy with laboratory-quality measurement devices at least once a year or more frequently if required to ensure accuracy. 6. Frequency devices should respond to rapid changes at a rate of at least 1 Hz/sec. 7. Sample rates of frequency devices should be at least as fast as the generation control data acquisition rate. For disturbance monitoring, sampling up to 20 scans/sec is helpful. An alternative is to sample at least twice the frequency as the frequency of the information you are trying to capture (this is called the Shannon frequency). 8. Digital monitoring and retention of system frequency during a disturbance is recommended for systems with generation capacity greater than 500 MW to augment chart recorder record keeping. The range, accuracy, and sampling rate should be consistent with recommendations 1-7. A hardcopy as well as an electronic copy of the report should be provided upon request to enable postdisturbance frequency analysis. 9. Reasonably priced frequency transducers are available from several manufacturers, which provide at least 0.02% of center frequency accuracy (± Hz for 60 Hz). Most of these transducers utilize a nominal 120 VAC input with a millivolt or milliampere analog output which can be used to drive a strip chart recorder or an A/D converter. More sophisticated transducers with accuracy s up to Hz are available for larger control areas to meet the requirement of section I.B.3 and to provide greater control accuracy. II. Calibrating Tie Line Signals Tie line data from each point of interconnection should consist of a common accurate MWh energy reading and MW power flow signal to each control center. Continuous use of this data for control and accounting and for monitoring data accuracy by both parties to the interconnection is recommended. A. MW Telemetering 1. Digital control center computers easily integrate the telemetered MW power flow signal over an MWh energy measurement period. Automatic comparison of the integrated MW signal with the hourly accounting MWh reading is a proven method of monitoring the accuracy of the control data. This method should be used as much as possible by Member Systems. Telemetering found to be out of calibration should be corrected as soon as possible. 2. Systems that do not use digital computers for tie line data acquisition are encouraged to locate persistent errors by other methods, such as analog chart recorder analysis to compare tie line MW telemetering with MWh readings. -4-

5 3. Systems that are party to a tie line should use common metering and telemetering equipment associated with the tie line. With this arrangement, errors will cause bilateral inadvertent interchange between the parties and not affect other systems. Where deviations from the above occur, procedures for error checking must be established. 4. The accuracy of analog tie line MW telemetering is expected to be within 0.5 percent full scale, when the hourly integrated value is compared to MWh energy accounting. Overall accuracy of tie line telemetering signals from measurement and transmission and conversion to the control algorithm should be adjusted to 0.5 percent full scale when errors exceeding 1 percent full scale accuracy are detected. 5. If integrated MW values are not used to monitor tie line telemetering accuracy, the tie line telemetering devices should be tested and calibrated at least annually or as required to maintain accuracy for control. More frequent calibration is required if state-of-the-art, solid-state devices are not used. 6. Digital tie line MW telemetering equipment, which has greater accuracy than analog equipment is available and should meet or exceed the requirements specified in II.A.4. Use of digital equipment should be considered for new or replacement telemetering, particularly for high capacity tie lines. Accurate metering inputs remain a requirement. 7. It is recommended that high capacity tie lines have redundant MW telemetering communications to assure continuous availability. Redundant metering, in addition to telemetering, is desirable for the more critical high capacity tie lines. 8. Sampling rates should equal the generation control data acquisition rate. For disturbance monitoring, sampling rates as high as 20 scans/sec are useful. An alternative is to sample at a minimum Shannon frequency of the telemetered data. B. MWh Readings For Hourly Accounting 1. To ensure accurate MWh energy accounting readings, all control area tie line meters shall receive a single end-of-hour freeze signal. In addition, the single end-of-hour freeze signal shall be backed up by an automatic separate signal within five seconds of the primary freeze. Most kilowatt-hour remotes can be modified to block a secondary freeze signal within a specified time window. End-of-hour freeze signals should be triggered by a timing system or computer clock synchronized to the standard time receiver. 2. If two sets of meters are used, one reading must be considered primary and this reading used by both parties. The reading from the second set can be used for backup and comparison. -5-

6 3. Accounting MWh number corrections because of missing data or transmission errors should be corrected promptly and mutually by both parties in accordance with NERC Operating Manual. Approving Committee, Entity or Person Date Board of Directors December 5, 2003 Operating Committee October 30, 2003 Technical Operations Subcommittee September 15, 2003 Control Work Group - Drafted March 11,