Pilot Protection Relaying uses a communications channel (pilot channel) to provide coordination between the line protection relays. The relaying system is an advanced alternative to Step Distance Relaying which requires no communication and therefore manual coordination between relays.
Communications assisted methods are unique in that they effectively eliminate the non-detection zones (NDZ) found in many local methods used for islanding detection. As a result, local protection elements may be set less sensitively, reducing false operations during system disturbances.
Power system islanding occurs when distributed generation becomes isolated from the power system grid and continues to provide power to the portion of the grid it remains connected to. Islanding can occur through the operation of switching devices such as breakers, disconnects or reclosers. Utilities can also experience islanding with system faults, switching operations, environmental causes and equipment failure. For example, a fault causing a recloser to open and lockout causes the generator to become islanded from the source station.