In recent years, our bureau has successively introduced several types of circuit breakers manufactured abroad or by domestic joint ventures, including products from AEG, ABB, Alstom, Toshiba (Japan), and Siemens. These circuit breakers all have anti-pumping circuits in their operating mechanisms, making them relatively safe and reliable. However, except for circuit breakers manufactured by Siemens, other products will generate parasitic loops when used with protection devices. [b]1 Causes of Parasitic Loops and Modification Methods[/b] 1.1 Causes of Parasitic Loops The 110 kV Camel Substation, which has been put into operation by our bureau, uses AEG products for its 110 kV circuit breakers and NARI Group Corporation's LFP series protection devices. The circuit breaker control principle diagram is shown in Figure 1. Before commissioning, during the integrated electrical primary and secondary linkage test, an abnormal phenomenon occurred where the green light would also illuminate after the circuit breaker was closed. The investigation revealed a parasitic circuit. When the circuit breaker was closed in the control room, S3 was switched to the remote position, and its contacts 1 and 2, as well as contacts 5 and 6, were connected. The closing command was then triggered. After the circuit breaker was closed, contacts 43 and 44 of S1 were closed, and the green light LD was lit through these contacts and the coil of the K11 anti-pumping relay. [img=420,261]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/zjdl/2002-3/63-1.jpg[/img] －S3—Local/Remote Switch; －S4—Local Closing Button; －S5—Local Trip Button; －S1—Circuit Breaker Auxiliary Contact; －S2—Spring Energy Storage Contact; －K14—Pneumatic Interlocking Contact; －Y1—Trip Coil; －Y4—Closing Coil; －K11—Anti-Pump Relay 1.2 Original Improvement Method How to eliminate this parasitic circuit? Two simple solutions were considered. Method 1: Retain the TBJ anti-pump circuit in the protection device, disconnect the coil of the anti-pump relay-K11 in the circuit breaker operating mechanism, and short-circuit its contacts 11 and 12 connected in series in the closing circuit, as shown in Figure 2. [img=600,220]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/zjdl/2002-3/64-1.jpg[/img] Method 2: The green light LD and the anti-pumping relay TWJ coil are connected to the negative power supply through the auxiliary normally closed contact of the circuit breaker, as shown in Figure 3. [img=600,228]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/zjdl/2002-3/64-2.jpg[/img] As far as we know, many brother units often use these two solutions when encountering this type of problem. [b]2 Comparison of the two anti-pumping functions and problems after modification[/b] 2.1 Anti-pumping function of TBJ in the protection device. A careful analysis shows that the anti-pumping function of TBJ in the protection device is different from that in the circuit breaker mechanism. As is well known, the TBJ anti-pumping principle in the protection device is that when contacts 5 and 8 of the control switch KK or contact HJ are closed, the circuit breaker closes. If the circuit breaker closes to a faulty line, the protection device activates, contact TJ closes, the circuit breaker trips, the TBJ current coil is activated, and contact TBJI closes for self-holding. At this time, if control switch KK fails to reset, or its contacts 5 and 8 are stuck, or contact HJ is stuck, even if the closing pulse is not eliminated, the TBJ voltage coil can self-hold, and the normally closed contact TBJV disconnects the closing coil circuit, preventing the circuit breaker from closing again. The circuit breaker and other electrical components will not be subjected to short-circuit current again. Only after the closing pulse is released and the TBJ voltage coil is de-energized will the wiring return to its original state. Therefore, the TBJ anti-pumping principle in the protection device only activates after the protection device has activated; it is a current-activated, voltage-self-holding "series anti-pumping" mechanism. 2.2 Anti-pumping function of K11 in the circuit breaker operating mechanism: The anti-pumping function of K11 in the circuit breaker operating mechanism is as follows: After the closing pulse is issued, the circuit breaker closing shaft rotates. If, due to a mechanism-related reason, the closing shaft does not stop at the closed position, the mechanism will return to the open state. At this time, if contacts 5 and 8 of KK are stuck or for other reasons, the closing pulse is not canceled (because the protection is not activated, the TBJI in the protection device is not started, and the normally closed contact of TBJV is still in the closed state), the anti-pumping relay K11 is energized and self-holding. The normally closed contact of K11 disconnects the closing coil circuit, preventing the circuit breaker mechanism from operating a second time until the closing pulse is canceled and the self-holding circuit of the K11 relay is released. It is a voltage-activated and self-holding "parallel anti-pumping". Therefore, the anti-pumping function in the mechanism can ensure that even if the mechanism itself fails and the closing pulse is not canceled, the circuit breaker can only close once. Regardless of success or failure, the circuit breaker closing coil will not be energized a second time. This is mainly determined by the circuit breaker structure. The main contact travel of a circuit breaker is generally small; for example, the main contact travel of a 10-35kV vacuum circuit breaker is only 8-10 mm. It cannot withstand continuous closing impacts; otherwise, the vacuum coil is easily damaged. When the first closing attempt fails, it cannot be closed immediately; a second operation is only permitted after adjusting the mechanism. If the anti-pumping circuit within the mechanism is removed, it will affect the safe operation of the circuit breaker. 2.3 Problems with the Original Two Modification Methods The first method, while eliminating the parasitic circuit, sacrifices the anti-pumping function within the circuit breaker's operating mechanism, which is unreasonable. The second method, while also eliminating the parasitic circuit, also loses the function of monitoring the closing circuit, which is somewhat of a trade-off. Some professionals believe that not monitoring the closing circuit is not a major problem, especially for imported circuit breakers; as long as the wiring is correct, the probability of the closing coil breaking is very small. Regarding this viewpoint, the "Electrical Design Manual for Power Engineering" compiled by the Northwest Electric Power Design Institute of the former Ministry of Energy specifies the principle: "In order to ensure the reliability of the control circuit and prevent the circuit breaker from failing to operate due to vibration causing terminal wiring to come loose or auxiliary contacts to malfunction, thus expanding the accident, it is recommended to still install power supply and trip/close circuit integrity monitoring." Therefore, the author believes that this solution, which sacrifices the monitoring of the integrity of the closing circuit, is not very reasonable. [b]3 New Solution[/b] In summary, the anti-pumping function in the circuit breaker mechanism and the anti-pumping function of the TBJ in the protection device are two completely different concepts. The former is mainly an effective measure to ensure the safe operation of the circuit breaker itself, while the latter is an effective measure to prevent electrical components from being repeatedly impacted by short-circuit currents and expanding the fault when the system fails. The two anti-pumping functions are complementary and indispensable. In addition, according to the secondary circuit design specifications, the integrity of the circuit breaker's trip/close circuit should be monitored to ensure the safety of electrical equipment during operation. Regarding the causes of the above parasitic circuits, the author believes that Siemens' circuit breaker operating mechanism circuit design is relatively mature and worth recommending. The specific method involves first connecting the normally closed contact of a mechanism anti-pumping relay – K11 and the normally closed auxiliary contact – S1 of the circuit breaker in series in the coil circuit of the green light LD and the trip position relay TWJ, and then connecting them to the closing circuit, as shown in Figure 4. This solution avoids the parasitic circuits mentioned above, thus preventing the abnormal phenomenon of the green light illuminating after the circuit breaker closes. Both anti-pumping circuits still function, and the integrity of the closing circuit is monitored, fully meeting the requirements of the circuit breaker manufacturer and the power system. [img=492,211]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/zjdl/2002-3/65-1.jpg[/img]