Under-Frequency Load Shedding (UFLS)

The UFLS Program performance assessments include, but are not limited to the following practices:

  1. Are performed at least once every five years for each identified island
  2. Are based on the most recent UFLS Program data that is collected annually from the Distribution Providers connected to the ATC system
  3. Are based on the most recent under-frequency and over-frequency settings provided by Generation Owners connected to the ATC system, otherwise the setting limits given in the NERC PRC-025 Reliability Standard are assumed to apply
  4. Consider generation-load imbalance scenarios up to 25 percent within the identified island [per the NERC PRC-006 Reliability Standard]
  5. Use the Equivalent Inertia method for the frequency performance evaluation
  6. Use the assumptions of aggregate inertia range of 3.3 to 4.7, generator governor droop range from 12 to 18 percent, and load damping range of 1.0 to 2.0 percentĀ in the Equivalent Inertia simulations
  7. Use the PSSE Dynamic Module method for the volts per hertz evaluation
  8. Use complex load modeling in the PSSE Dynamic Module simulations.

The Capacitor Bank Coordination assessments include, but are not limited to the following practices:

  1. Are performed at least once every five years for each identified island.
  2. Are based on the most recent UFLS Program data that is collected annually from the Distribution Providers connected to the ATC system.
  3. Are based on the most recent under-frequency and over-frequency settings provided by Generation Owners connected to the ATC system, otherwise the setting limits given in the NERC PRC-025 Reliability Standard are assumed to apply.
  4. Are based on the most recent over-voltage and under-frequency settings of shunt reactive power devices that are provided by ATC System Protection.
  5. Consider generation-load imbalance scenarios up to 25 percent within the identified island [per the NERC PRC-006 Reliability Standard].
  6. Use the PSSE Dynamic Module method for the voltage response evaluation.
  7. Use complex load modeling in the PSSE Dynamic Module simulations.