1. Introduction Because secondary regulations cannot provide a detailed description of circuit breaker operation and control, designers have been able to rely more on their subjective thinking in this area. Different local customs and different designers have led to diverse practices, resulting in the implementation of some imperfect wiring designs in engineering projects. This issue has become even more prominent in recent years with the continuous application of new control methods and new circuit breaker equipment. This article analyzes and discusses this issue encountered in engineering design practice. 2. Closing Circuit Wiring The analysis uses the trip and closing wiring diagrams of a representative operating box and mechanism box as examples, as shown in Figures 1 and 2 respectively. In Figure 2, S8 is the remote-to-local switching switch, which is closed in the remote position; S1LA is the circuit breaker auxiliary contact; Y1A is the closing coil; K75LA is the anti-pumping relay; K10 is the operation interlocking contact, which is closed when the circuit breaker is in normal operation; and Y3A is the trip coil. [img=332,271]http://www.cechinamag.com/images/Article/05b1bf0a-f3ba-481a-a212-11fce7c6e6bd/231.jpg[/img] [img=327,148]http://www.cechinamag.com/images/Article/05b1bf0a-f3ba-481a-a212-11fce7c6e6bd/232.jpg[/img] 2.1 Closing Wiring Method 1: Connect the starting terminal and closing command terminal of the trip position relay in the control box together on the protection panel and connect them to the closing command terminal of the mechanism box via a cable. The problem with this wiring method is that after the closing operation is completed, the local anti-pumping relay in the mechanism box remains active, cutting off the closing circuit and preventing a second closing operation. It may also cause the trip position relay to start simultaneously. The analysis is as follows: In the first scenario, after the control box issues a closing command, energizing the closing coil Y1A of the mechanism box and closing the circuit breaker, the closing command activates the anti-pumping relay K75LA via the normally open contact of S1LA. After the command disappears, the anti-pumping relay K75LA forms a holding circuit with the coils of the trip position relays 1-3TWJa through relevant contacts. The reason for this anomaly is that the return voltage of the anti-pumping relay K75LA is very low. The anti-pumping relay K75LA is an intermediate relay. Regarding DC intermediate relays, the product manual lists the parameter that the return voltage should not be less than 5% of the rated UN voltage. Considering the dispersion of the return characteristics, it basically does not return when the voltage is greater than 15% UN. In the series circuit formed by 1-3TWJa and K75LA, as long as the voltage division of K75LA reaches 5% UN, it may not return after starting; when the voltage division reaches 15% UN, it basically does not return. Most engineering examples show that the coil resistance values ​​of the two relays are not much different, and the voltage division of the anti-pumping relays meets the condition of not returning. Figures 1 and 2 are selected from an engineering project using 110V DC voltage. The resistance of the 1-3TWJa coil is 5KΩ, K75LA is 1.9KΩ, and the voltage division of K75LA is 27%UN. The second case will only occur when the voltage division of the trip position relay reaches the starting value, which is not common. Since the above abnormality will occur in wiring method 1, this wiring should not be used. 2.2 Closing circuit wiring method 2 This wiring method is based on the first wiring method, unwinding the coil wiring of the anti-pump relay K75LA and canceling the anti-pump function of the circuit breaker mechanism box. There are two reasons for using this wiring method: (1) This can eliminate the abnormal phenomenon that occurs in wiring method 1; (2) The operating box also has an anti-pump device. However, further analysis reveals that this method will cause major safety hazards. First, the anti-pump function of the operating box can only cut off the closing command from the operating box. When operating locally, it does not work, and the anti-pump function is lost during local operation. Secondly, if the closing command terminal of the circuit breaker mechanism box becomes positively energized due to a fault during the closing operation, a tripping event will occur if the operation or protection trips. Due to local operation and other control requirements, the positive power supply terminal must be led to the mechanism box. This positive power supply terminal may be metallically short-circuited to the closing command terminal via the changeover handle, terminals, etc. When this happens during the circuit breaker's closing operation, the closing command is isolated by the normally closed auxiliary contact of the circuit breaker and cannot act on the closing coil. However, the mechanism's anti-pumping function is disabled, and the closing circuit is in a closing preparation state. Once the circuit breaker trips due to a system or primary equipment fault, the closing command will immediately close after energizing the closing coil via the auxiliary contact, resulting in a serious consequence of the switch tripping and failing to cut off the fault. If the circuit breaker mechanism box has an anti-pumping function, the anti-pumping relay will activate and cut off the closing circuit in the above situation, and the circuit breaker will not perform any form of closing operation after tripping. Furthermore, there is no signal indication for this type of secondary device fault. Due to the existence of the above two problems, this wiring method should not be used. 2.3 Closing Circuit Wiring Method 3: The closing command terminal and the trip relay starting circuit of the operating box are separately led to the mechanism box from the operating box and the protection panel. The trip relay starting circuit is connected in series with the normally closed auxiliary contact of the circuit breaker and then connected in parallel with the closing command terminal from the operating box to the closing starting terminal of the mechanism box. This wiring method retains the anti-pumping function of both the operating box and the mechanism box, and eliminates the problems that occur in wiring methods 1 and 2. Furthermore, the integrity of the closing circuit can be monitored by the control circuit disconnection signal, which is essential for circuit breakers that are constantly in hot standby mode. This wiring method is a relatively complete closing circuit wiring method. 2.4 Closing Circuit Wiring Method 4: The closing command terminal and the trip relay starting circuit of the operating box are separately led to the mechanism box from the operating box and the protection panel, which is the same as wiring method 3. However, the trip relay starting circuit is connected in series with the normally closed auxiliary contact of the circuit breaker and then connected to the negative power supply terminal, which is different from wiring method 3. This wiring method eliminates the problems associated with wiring methods 1 and 2, but its limitation is that it cannot monitor the integrity of the closing circuit. Many projects use this wiring method because closing failures generally do not lead to system safety accidents; therefore, existing wiring methods can be temporarily left uncorrected. 3. Other Wiring-Related Issues 3.1 Trip Circuit Wiring Method For trip circuits I and II, one wiring method separates the closing relay start-up and trip command circuits at the terminals of the operating box and protection panel, connecting them to the mechanism box. Since the integrity of the trip circuit is monitored by the disconnection signal formed by the closing relay connection point, a cable break in this wiring method cannot cause the closing relay to lose power, and a signal cannot be issued in time. This may result in the switch refusing to trip after a primary equipment failure. This wiring method should not be used. The correct wiring method is to connect the closing relay start-up terminal and the trip command terminal on the protection panel and then lead the cable to the trip command terminal in the mechanism box. 3.2 Circuit Breaker Control Disconnection Signal The control circuit disconnection signal is formed by connecting the normally closed contacts of the trip relay and the close relay in series. A well-designed wiring system allows this signal to monitor the integrity of the trip circuit during circuit breaker closing operation, enabling monitoring of the entire trip circuit, such as broken operating cables, broken trip coils, unmet interlocking conditions, and incorrect positions of remote/local switching switches. In hot standby mode, it monitors the integrity of the closing circuit and simultaneously monitors the integrity of the two sets of operating power supplies, making it one of the most important signals. [b]3.3 Independence of Trip I and II Interlocking Circuits[/b] In actual engineering, many switch manufacturers provide trip I and II interlocking contacts that lack independence. For example, a pair of trip interlocking contacts may be converted into two pairs via recirculation to interlock trip I and II respectively. Since the recirculation relay is connected to the power supply of operating I, when the power supply to the operating I circuit fails, trip II will also fail to operate due to the inability to interlock. Therefore, circuit breaker manufacturers must provide two independent pairs of contacts for each interlocking quantity for tripping circuits I and II. [b]3.4 Wiring of the anti-pumping contact in the mechanism box[/b] The anti-pumping contact in the mechanism box should be between the closing coil and the negative terminal of the power supply. This way, when the positive terminal of the closing coil becomes positively energized due to a fault, the anti-pumping contact can also disconnect the closing coil circuit to prevent tripping. [b]3.5 The small operating power switch on the mechanism box should be retained[/b] Currently, many projects have eliminated the fuses or automatic air switches and other protective devices in the operating circuit of the circuit breaker mechanism box, retaining only the small power switch from the protection panel to the operating box. While this makes the operating power supply clear and simple, it eliminates the convenient and quick means of disconnecting the power supply locally in the mechanism box, creating safety hazards for local equipment commissioning. In fact, there is nothing wrong with retaining the local operating power switch. One reason for canceling the local power switch was the concern that it would be inconvenient to detect local power failure if the local power switch tripped. This problem does not actually exist. Analysis of the control circuit disconnection signal formed by the normally closed contacts of the trip relay TWJ and the closing relay HWJ shows that the local operating power failure can be detected by this signal. Another reason is that it is considered cumbersome to obtain the operating power from the mechanism box through a series connection between the small power switch in the operating box and the small power switch on the mechanism box. However, this has no substantial impact on the circuit breaker tripping and closing operations. Moreover, the switch can be disconnected to stop operation during local commissioning, increasing the safety of the commissioning work. [b]4. Summary[/b] Circuit breaker operation control is the final link in the entire control process of protection and automation. It is the execution link and has a significant impact on the safe operation of the power grid. This aspect requires more attention from protection management agencies at all levels, and also requires continuous efforts and communication from professionals of relevant parties such as protection manufacturers, circuit breaker manufacturers, design institutes, construction and operation units to further improve it.