Suggestions for Ensuring the Accuracy of Relay Protection Operation and Improving the System
1. After learning the protection principles and secondary drawings, operating personnel should be familiar with the general operation of on-site protection devices, the handling of common signals, and the correct method of switching pressure plates in and out. They must strictly implement the "two tickets" and the protection operation regulations. Each time they switch in or out, they must strictly follow the division of equipment dispatching scope and obtain the consent of the dispatcher. To ensure the accuracy of protection switching, the names of each protection, pressure plates, time limits, circuit breakers tripped by the protection, and instructions for using the pressure plates are compiled into the operation regulations. Due to clear regulations and strict implementation, the time for duty personnel to consult protection diagrams is reduced, and errors in operation are avoided.
2. For protection operations under special circumstances, apart from those clearly specified in the regulations, operating personnel mainly master them through training and learning. It is required that stopping the DC power supply cannot replace stopping the protection; when using the bypass switch to replace a line, the protection settings must be adjusted to the same as those of the replaced line; for phase comparison bus differential protection, when the bus tie switch replaces a line, CT terminal switching must be performed. Special attention should be paid to the protection that initiates tripping of other switches, and the outlet pressure plate should be promptly withdrawn.
3. When abnormalities or defects are found in the operation of relay protection, in addition to strengthening monitoring, the outlet pressure plate of the protection that may cause maloperation should be withdrawn (for protections under dispatching jurisdiction, written permission must be obtained from the dispatcher before withdrawing the relevant protection), and then contact the relay protection personnel for handling. If any of the following abnormal conditions occur, they should be promptly withdrawn:
① When the bus differential protection sends out "bus differential AC circuit disconnection" or "bus differential DC voltage loss" signals; when the bus differential unbalanced current is not zero; during the operation of using the bus tie switch without a dedicated bypass bus to replace a line and during the restoration switching operation.
② When the high-frequency protection's DC power supply disappears; when the parameters of the periodic channel test do not meet the requirements; when the device fault or channel abnormal signal is issued and cannot be reset; during the operation of the bypass bus replacing the line switch.
③ When the PT used by the distance protection is out of operation or the three-phase voltage circuit is disconnected; when the magnetizing current is too large or too small under normal conditions; when the load current exceeds the corresponding section of the protection's allowable current.
④ When the total alarm light of the microcomputer protection is on, and at the same time one of the four protections (high-frequency, distance, zero-sequence, comprehensive reclosure or adaptive reclosure) alarm light is on, withdraw the corresponding protection; if two CPUs are faulty, all protections of the device should be withdrawn; if all signal lights of the alarm plug-in are not on, and the power indicator light is off, it indicates that the DC power has disappeared, and the outlet pressure plate should be withdrawn, and then re-engaged after restoring the DC power; if the total alarm light and the call light are on, and the print shows CPU×ERR signal, if the CPU is normal, it indicates that the communication loop between the protection and the interface CPU is abnormal, and the CPU inspection switch should be withdrawn for handling; if the signal cannot be reset, it indicates that the CPU has a fatal defect, and the protection outlet pressure plate should be withdrawn and the inspection switch should be disconnected for handling.
⑤ When the gas protection is used during oil filling, oil filtering, or silica gel replacement in transformer operation; when the submersible oil pump or oil cooler (radiator) is put into operation after oil drainage and maintenance; when it is necessary to open the vent valve or oil drain plug of the breathing system, or to clean the moisture absorber; when someone is working on the oil circuit of the on-load tap changer.
⑥ When the number of trip operations of the line switch due to faults exceeds the standard (generally, 110kV low-oil circuit breakers allow 5 times, 220kV low-oil circuit breakers allow 7 times; LW series 110kV SF6 circuit breakers allow 65 times, 220kV SF6 circuit breakers allow 50 times, 500kV SF6 circuit breakers allow 20 times; otherwise, the circuit breaker needs major overhaul); when the air pressure or oil pressure of the circuit breaker drops to a value that does not allow reclosure operation or has been locked.
