Relay protection can be classified in the following four ways:

1. Classified by protection objects: power line protection and main equipment protection (such as generators, transformers, bus bars, reactors, capacitors, etc.).

2. Classified by protection function: short-circuit fault protection and abnormal operation protection. The former can be divided into main protection, backup protection and auxiliary protection. The latter can be divided into overload protection, demagnetization protection, out-of-step protection, low-frequency protection and non-protection, and full-phase operation protection.

3. Classify the signal quantity through protection device comparison and operation processing: there are analog protection and digital protection, organic electric type, rectifier type, transistor type and integrated circuit type (operational amplifier) protection devices, which directly reflect the continuous analog input The signal belongs to analog protection, and uses microprocessor and microcomputer protection devices. After sampling and converting analog quantity into analog/digital quantity, it reflects the digital protection of discrete digital quantity.

4. Classified according to the principle of protection: overcurrent protection, low voltage protection, overvoltage protection, power direction protection, distance protection, differential protection, longitudinal protection, gas protection, etc.

5. Abnormality: If the relay protection device is found to be abnormal or malfunctioning, in addition to strengthening monitoring. It should also return its outlet presser foot to the protective device that may cause misoperation. Then contact the relay protection personnel for processing.

In any of the following abnormal situations, you should exit in time:

1. Bus differential protection

When sending the "bus-bar difference AC disconnect" and "bus-bar difference DC voltage disappear" signals. When the unbalanced current of the busbar is not zero, the busbar switch series has no special bypass busbar, instead of line operation and reverse operation.

2. High frequency protection

When the DC power supply disappears; the periodic channel test parameters do not meet the requirements. When the equipment fails or the channel abnormal signal cannot be returned, the side bus switch operation process.

3. Distance protection

When the adopted PT fails or the three-phase voltage circuit is disconnected, under normal circumstances, the auxiliary magnetic current is too large and too small. When the load current exceeds the corresponding part of the protection allowable current.

4. Microcomputer protection

When the main alarm light is on and one of the four protections (high frequency, distance, zero sequence, comprehensive weighing) is turned on, the corresponding protection is exited. If two failures occur, the equipment should be removed from all protections and the lights of all signal alarm plug-ins will not light up. If the power indicator is off, it means that the DC has disappeared. After the DC power is restored, exit the outlet pressure plate and put it back in. If the CPU is normal, it means that the communication circuit between the protection and the interface CPU is abnormal, and the CPU patrol switch processing is exited. If the signal does not return, it means that the CPU has a fatal fault, exit the protection outlet pressure plate and disconnect the patrol check switch for processing.

5. Gas protection

Refueling, filtering or replacing silica gel during operation of the transformer; after maintenance input, the underground oil pump or oil cooler (radiator) drains the oil, it is necessary to open the valve or drain plug of the breathing system or clean the humidifier.