The circuit breaker wiring error caused the operation and control power supply air switches to trip simultaneously during the closing process

Linhuai Substation of Bengbu Power Supply Company is an old substation with a history of 40 years. In May 2011, it carried out the last comprehensive automation transformation of the interval - the comprehensive automation transformation of the 1# main transformer protection.

On the third day of the renovation work, the 10kV 01 circuit breaker on the low-voltage side of the main transformer was verified for opening and closing and signal verification. When the operating power supply or the measurement and control power supply (motion signal and measuring device power supply) of the 01 circuit breaker was supplied separately, there was no crosstalk between the operating circuit and the signal circuit. However, during the actual closing operation of the 01 circuit breaker, the protective screen 01 operating power supply air switch and the 1# main transformer measurement and control power supply air switch were tripped at the same time, but the 01 circuit breaker had been successfully closed; the opening was normal after the power was supplied again; the above process was repeated and the fault still existed. When the operating power supply of the protective screen was supplied separately but the measurement and control power supply was not supplied, the opening and closing were normal. Because the original 01 circuit breaker "spring no energy storage" signal was not used, the newly equipped wiring used this signal during this comprehensive automation renovation, which caused this phenomenon. It shows that the closing circuit was caused by the instantaneous short circuit of the contact point caused by the spring no energy storage (when the circuit breaker releases energy during the closing process), which caused the operating power supply air switch and the 1# main transformer measurement and control power supply air switch to trip at the same time.

Based on the above judgment, we disconnected the power supply of each circuit and shook the insulation of the spring energy-stored contacts in the protection closing circuit and the spring non-energy-stored contacts in the remote signal circuit. The result was good. We further checked the secondary wiring of the 01 circuit breaker and found that there was an error. The details are as follows:

The incorrect wiring is as follows (original wiring):

HQ—closing coil; TQ—tripping coil; DL—circuit breaker auxiliary contact; CK—spring energy storage contact

The wiring after correction is as shown below (correct wiring):

Figure 2

Based on the above fault phenomenon, we analyze as follows:

1. The circuit breaker opened and closed normally before the comprehensive automation transformation, but the above phenomenon occurred after the transformation. This is due to the connection of the newly connected "spring without energy storage" contact.

2. The circuit breaker is open normally and the separate operating power supply is open and closed normally. Only the air switch trips at the moment of closing, which means that the switch fails during the process of spring energy release at the moment of closing.

3. The spring contact of the closing circuit and the contact of the signaling circuit use a normally open contact and a normally closed contact in the same section of the travel contact. During the closing process of the circuit breaker, the spring contact of the closing circuit and the spring contact of the signal circuit are instantly adhered due to the rapid release of the spring energy. At the same time, due to the incorrect connection method of the circuit breaker wiring as shown in the figure above, the negative power supply of the circuit breaker operation is short-circuited to the positive power supply of the remote signal.

4. After correcting the wiring, even if the above adhesion occurs, short circuit is not allowed due to the existence of closing coil HQ. The specific contact points are as shown in the figure below:

Spring energy storage contact diagram:

Spring contact installation diagram:

Figure 4

After the wiring is corrected as shown in the figure above, the circuit breaker opens and closes normally. At the same time, it also exposes the irregularity of the wiring of the circuit breaker manufacturer, reminding the protection personnel to be careful and careful when constructing the secondary circuit to prevent accidents or potential accidents.