In recent years, with the widespread application of microcomputer relay protection technology in high-voltage power supply and distribution systems, the reliability, selectivity, sensitivity, and speed of protection have been improved. Whenever it is a comprehensive automation station, the circuit breaker opening and closing control circuit is equipped with an opening and closing maintenance circuit to ensure the normal operation of the high-voltage system. If the current in the circuit of the opening and closing coils cannot be cut off normally, it will cause long-term electrification of the opening and closing coils, resulting in the burning of the components and closing lines. In severe cases, the burning of the opening and closing coils on the operating board can not only damage the circuit breaker, but also potentially cause more serious consequences, such as production shutdown, power outage, fire, etc. Therefore, it is necessary to replace the opening and closing coils of the high-voltage circuit breaker to ensure the stability and reliability of the power system.

However, due to the wide variety of types of opening and closing coils for high-voltage circuit breakers (as shown in Figure 1), and many models that have been discontinued, as well as the fact that the installation positions of most circuit breaker opening and closing coils are concealed (as shown in Figure 2), it is inconvenient to replace them, and the existing logistics are slow, it is necessary to improve the control circuit of high-voltage circuit breakers.

Figure 1, Types of Closing Coils Figure 2, Installation Position of Closing Coils This article combines the phenomenon of circuit breaker opening and closing coil burning during power system operation, and based on in-depth research on the secondary circuit control methods of high-voltage circuit breakers at home and abroad, adopts the method of adding time relays, replacing the opening and closing coils with delay relays, to ensure the reliable and stable operation of the power system in a timely manner.

The reasons for the burning of the opening and closing coils and operating boards of high-voltage circuit breakers are both indirect and direct reasons


Design reasons
At present, the opening and closing coils of circuit breakers are designed for short-term electrification. It seems that in order to ensure reliable operation of the circuit breaker, whether manual or protective operation, there is a self holding circuit in series in the control circuit. Once the opening and closing command is issued, the control circuit is in a holding state until the auxiliary contact switch caused by the switch action can disconnect the control circuit. If the circuit breaker fails to operate for some reason or the auxiliary contacts are not properly switched in place, it will also cause the control circuit to be electrified for a long time. This situation will continue until the opening and closing coils are burned out, and in severe cases, the protection device plug-in and operation board will be burned out.

Human factors
For the control circuit of old-fashioned circuit breakers, if the auxiliary contact of the circuit breaker is not connected in series, and the operator closes the circuit breaker before the mechanism stores energy or the energy storage is completed, it will cause the opening and closing coils to burn out. But currently, the control circuit of the new circuit breaker has energy storage auxiliary contacts in series, so even if the operator lacks experience and misoperates, the opening and closing coils will not be burned.

Direct cause
The auxiliary contact action of the circuit breaker is incorrect
The operating circuit of most spring mechanisms is connected in series with auxiliary contacts of circuit breakers. If the switching of auxiliary contacts is not correct after the circuit breaker is activated, it will cause the operating circuit to be electrified for a long time until the coil is burned out. In severe cases, it will be connected in series with the burning protection device and operating board. For some spring mechanisms, the operating circuit does not have auxiliary contacts. Especially in the closing circuit, after the circuit breaker is closed, the closing pulse is continuously triggered. If the relay protection opens at this time, due to the presence of the closing command, the circuit breaker will reclose after opening. If this fault is a permanent fault, the protection will act again to trip the switch.

This circuit breaker will close and open multiple times, which will exacerbate the damage to the circuit breaker and cause the accident to escalate.

Internal issues with circuit breakers and operating mechanisms

When the circuit breaker operates normally in the external circuit, if there are internal defects in its body and operating mechanism, such as poor installation of auxiliary switches, improper matching of iron core top rods and connecting rods, and low voltage in the control circuit, it can also cause the circuit breaker to not operate correctly, resulting in the above consequences.[Kailong Electrics]