The relay protection is mainly the principle that the electrical volume (current, voltage, power, frequency, etc.) changes when the components in the power system occur short circuit or abnormal condition constitute the relay protection action. There are other physical quantities, such as the increase of a large number of gas and oil flow speed or the increase of oil pressure strength when the transformer tank fails. In most cases, no matter what kind of physical quantity is reflected, the relay protection device includes a measurement part (and a value adjustment part), a logical part, and an execution part.
①, the parameters in the operation of the power system (such as current, voltage, power factor Angle) are obviously different in the normal operation and the fault situation. The relay protection device is to use the changes of these parameters to judge the nature and scope of the power system fault on the basis of reflection and detection, and then make the corresponding reaction and treatment (such as warning signal or make the circuit breaker trip, etc.).

369-HI-R-M-0-0-0-E GE Relay protection device