Emergency frequency load shedding scheme

Abstract

A load shedding system and method for controlling imbalances in a power system includes a signal generator adapted to generate a signal representative of a local system, and a modifying circuit adapted to adjust set frequencies. The system also includes a processing circuit adapted to process data received from the signal generator and modifying circuit and set load shedding priorities for the local system based on the processed data.

What is claimed is: 
     
         1 . A method of pre-empting a frequency decline, comprising the steps of:
 (a) continuously monitoring voltage of a local system over a set time interval;   (b) estimating a rate of change of frequency with time from voltage measurements taken during the time interval; and   (c) using the rate of change of frequency with time to determine a frequency load shedding point.   
     
     
         2 . The method according to  claim 1 , further including the step of deriving a frequency signal indicative of the local system. 
     
     
         3 . The method according to  claim 1 , further including the step of determining a magnitude of power carried by the local system. 
     
     
         4 . The method according to  claim 1 , further including the step of determining a change of power with frequency. 
     
     
         5 . The method according to  claim 1 , further including the step of setting load shedding priorities for the local system. 
     
     
         6 . A method of pre-empting a frequency decline, comprising the steps of:
 (a) continuously monitoring voltage and current of a feeder;   (b) estimating a rate of change of frequency with time from voltage and current measurements taken during a set time interval;   (c) estimating a rate of change of power with frequency;   (d) using the rate of change of frequency to determine a frequency load shedding point; and   (e) using the rate of change of power with frequency to set load shedding priorities.   
     
     
         7 . The method according to  claim 6 , further including the step of deriving a frequency signal indicative of the local system. 
     
     
         8 . The method according to  claim 6 , further including the step of determining a magnitude of power carried by the local system. 
     
     
         9 . The method according to  claim 6 , further including the step of comparing the rate of change of frequency with time to a load shedding constant. 
     
     
         10 . The method according to  claim 9 , wherein if the rate of change of frequency with time is more negative than the load shedding constant, load shedding occurs at higher frequencies. 
     
     
         11 . The method according to  claim 9 , wherein if the rate of change of frequency with time is less negative than the load shedding constant, load shedding occurs at predetermined frequencies. 
     
     
         12 . The method according to  claim 6 , further including the step of communicating load shedding priorities to relays and breakers. 
     
     
         13 . The method according to  claim 6 , wherein the more negative the rate of change of power with frequency is the higher the load shedding priority is for a feeder.