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NPCC Agenda Item # 9 RC Mtg. 09/10/02

NPCC Agenda Item # 9 RC Mtg. 09/10/02. 2002 Underfrequency Load Shedding Assessment. UFLS Assessment. Last Assessment in 1991 (JWG-2) Present Assessment initiated in January 2001 by TFSS to assess adequacy of both the NPCC UFLS program as prescribed, and as implemented

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NPCC Agenda Item # 9 RC Mtg. 09/10/02

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  1. NPCC Agenda Item # 9 RC Mtg. 09/10/02 2002 Underfrequency Load Shedding Assessment

  2. UFLS Assessment • Last Assessment in 1991 (JWG-2) • Present Assessment initiated in January 2001 by TFSS • to assess adequacy of both the NPCC UFLS program as prescribed, and as implemented • Study conducted by the SS-38 Working Group on Inter-Area Dynamic Analysis

  3. NPCC UFLS Program – Objective • Return the system frequency to • 58.5 Hz within 10 s • 59.5 Hz within 30 s • For a generation deficiency of up to 25% of the system load

  4. NPCC UFLS Program -- Requirements • Shed 10% of load at 59.3 Hz • Shed 15% of load at 58.8 Hz • Load shedding by threshold type relays with a definite time delay not to exceed 0.75 s • Load shedding based on rate of frequency decay is permissible if the UFLS program objectives are met

  5. Issues Addressed in this Assessment • Voltage control following load rejection • Off-nominal frequency characteristics of nuclear and combined cycle generating plants • System-wide governing response • Ability to utilize additional load shedding to compensate for non-conforming generators

  6. Methodology • Islanding scenarios simulated in each Area • Generation deficiencies tested up to 25% • Sensitivity analysis for: • Load modeling • Governor response

  7. Preliminary Findings • Adequacy of the UFLS program as prescribed is affected by • System inertia • Overvoltage protection • Governor response

  8. Preliminary Findings • Adequacy of the UFLS program as implemented is affected by • UFLS relay time delay • Amount of load armed • Number of load shedding stages • Amount of non-conforming generation

  9. Preliminary Findings • The UFLS program as prescribed is inadequate in two Areas

  10. Potential Recommendations • SS-38 is presently investigating the following potential recommendations: • Modification to the UFLS relay time delay • Limitations on compensatory load shedding • Further investigation of methods to protect against off-nominal frequency operation

  11. Status • A “Draft for Comment” report was discussed by TFSS at their July 18 – 19 meeting • Input has been sought from TFSP regarding the ability of members to modify the UFLS relay time delay • A revised Draft report will be discussed by TFSS at their September 17 – 18 meeting • A final report will be prepared for the RCC with a target date of November 2002

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