Coordinated frequency load shedding protection method using distributed electrical protection devices

A method for shedding load in response to an underfrequency event in an electrical power distribution network, wherein an AC power signal from a substation flows on a feeder or lateral electrical line through a plurality of switch-gear assemblies to a plurality of groups of loads provided among and between the switch-gear assemblies, each group of loads including a plurality of individual loads that may combine to be drawing power from the network or providing power to the network at any particular point in time, the method comprising:

• assigning a time delay value and a frequency set-point to each switch-gear assembly that are coordinated and calibrated relative to each other, where switch-gear assemblies that are farther downstream from the power source relative to the AC power signal flow will have shorter time delay values than other upstream switch-gear assemblies;
• monitoring a frequency of the AC power signal flowing on the electrical line at each switch-gear assembly;
• determining a direction of the AC power signal flow through each switch-gear assembly;
• determining that the underfrequency event is occurring if the frequency of the AC power signal falls below a predetermined minimum frequency;
• opening a first one of the switch-gear assemblies having a shortest time delay value in response to the underfrequency event so as to prevent at least one of the groups of loads from drawing power from the network;
• and
• preventing the first one of the switch-gear assemblies from opening in response to the underfrequency event if the direction of the AC power signal flow through the first one of the switch-gear assemblies indicates that the at least one of the groups of loads is providing power to the network.

A method for shedding load in response to an underfrequency event in an electrical power distribution network, wherein an AC power signal from a power source flow on at least one electrical line through a plurality of switch-gear assemblies to a plurality of groups of loads provided among and between the switch-gear assemblies, the method comprising:

• monitoring a frequency of the AC power signal flowing on the at least one electrical line at each switch-gear assembly;
• determining that the underfrequency event is occurring if the frequency of the AC power signal falls below a predetermined minimum frequency;
• and
• opening a first one of the switch-gear assemblies at a remote location relative to the power source in response to the underfrequency event so as to remove at least one of the groups of loads from the network.