PROTECTIVE RELAY CLASSIFICATION

According to functional categories

1. Protective relays, monitoring relays, reclosing relays, regulating relays, Auxiliary relays, synchronizing relays
2. According to input quantity, operating principle and performance characteristic.

Inputs: Current, Voltage, Power, Frequency, Pressure, Temperature, Flow, and vibration.

Operating principle: 

Current balance, Percentage, Multi restraint, product, Solid state, Static, Microprocessor, Electromechanical, Thermal Performance characteristics: Distance, Directional over-current, Inverse time, Definite time, Under-voltage, Over-voltage, Ground or phase, High or low speed, phase comparison, Directional comparison

1. According to the method of connection to the power circuit Primary relays. Secondary relays connected through C.Ts and P.Ts.
2. According to the method of action Direct-acting relays Indirect-acting relays, those operate through auxiliary relays.
3. According to the degree of importance Main relays Supplementary relays such as signal relays, time relays, contact multiplier relays.
4. According to time of action Quick relays: operate in 4-40ms. Ordinary relays: operate in 40-200ms.
5. According to type of contacts Relays with normally-open contacts Relays with normally closed contacts.

Relay performance is generally classified, as (1) correct, (2) no conclusion,

(3) incorrect. Incorrect operation may be either failure to trip or false tripping, the cause of it may be poor application, incorrect setting, personnel error, or equipment malfunction.