Bus operation refers to the power supply and power failure of the bus, and the rearrangement of equipment on the bus between two buses. Bus is the confluence of equipment, with many connecting elements and heavy workload. Whether it is the normal spring and autumn maintenance work or the bus reversing work after the accident, full preparations must be made before the operation, and other changes such as operation mode should be paid attention to during the operation. Bus switching operation is a very frequent and complicated operation for substation, with a little carelessness. Misoperation accidents will occur. 1 Danger point of normal bus switching operation 1. 1 General principles of normal bus switching operation. The bus coupler circuit breaker must be closed first, and the control fuse must be removed to ensure that the bus disconnector can meet the requirements of equipotential operation when it is turned on and off. In the process of closing and pulling the bus disconnector, if a big spark may occur, the bus disconnector closest to the bus coupler circuit breaker should be closed first; The operation sequence of switches is reversed; When operating the bus disconnector, minimize the potential difference. Before opening the bus coupler circuit breaker, the ammeter of the bus coupler circuit breaker should indicate zero; At the same time, the auxiliary contact and position indicator of bus disconnector should be switched normally. Equipment "leakage", or reverse charging of the secondary side of bus voltage transformer, resulting in accidents. In the process of bus phase inversion, if the bus differential protection is not damaged, it should generally be put into operation. At the same time, the closing of non-selective switch of busbar differential protection and the switching of low-voltage blocking busbar differential protection linking piece should be considered. If the bus coupler circuit breaker cannot be used for some reason, the bus coupler disconnector must be used to close the no-load bus, and the secondary side of the bus voltage transformer should be disconnected first to prevent the fuse of the bus voltage transformer from fusing or the automatic switch from tripping. 1.2 analysis of dangerous points and control measures in operation When the bus phase is reversed, after closing the bus coupler circuit breaker, due to technical failure or negligence, I forgot to install the fuse of the bus coupler DC control circuit. Under normal circumstances, the operation can go smoothly to the end. However, in case of misoperation, protective action or DC two-point grounding during operation, the bus coupler circuit breaker will be disconnected at this time, and the voltages of the two buses are not equal. At this point, closing the first group of bus disconnectors or pulling down the last group of bus disconnectors is essentially to connect or disconnect two groups of bus system circuits with bus disconnectors. Loop voltage difference? 8? The effective value of 5U is equal to the actual difference between the supply voltages of two buses, which can reach hundreds or thousands of volts. When the bus circuit breaker is disconnected, due to the large current in the closing circuit and the large voltage difference in the opening circuit, the bus disconnector often cannot be opened, resulting in a short circuit of the bus. Control measures: Bus-coupling operation is a typical operation, which must be held by a duty officer with high technical level, rich experience, skilled business and care before operation. In addition to charging with the bus coupler circuit breaker, the operating power supply of the bus coupler circuit breaker should be turned on when the bus trips, so as to prevent the bus coupler circuit breaker from accidentally tripping, resulting in the event of pulling the disconnector with load. In the field operation procedure, it should be carried out according to the following steps: ① Close the bus coupler circuit breaker; (2) Remove the fuse of DC control circuit of bus coupler circuit breaker; (3) Check whether the bus coupler circuit breaker is closed. These three items are important safety technical measures necessary to realize the equipotential operation of the inverted bus, and should be written into the regulations so that the personnel on duty can master them skillfully and make no mistakes during operation. When the bus phase is reversed, the accident of pulling the disconnector with load occurs at the wrong interval, or when the bus coupler circuit breaker is pulled before the bus phase is reversed, it is not determined or checked again that all the equipment on the running bus has been reversed, and the ammeter of the bus coupler circuit breaker is not checked to indicate zero, so the bus coupler circuit breaker is pulled. If the equipment leaks electricity, it will cause a power outage. Control measures: Strictly regulate the switching operation system, strictly implement the switching system, operate only after the equipment is correct, and do not miss or jump items during operation. After each operation, check whether it is in good condition, tick "√" on the first operation, carefully review after the operation, and then proceed to the next operation. Electrical, electromagnetic and mechanical locking devices are installed between the disconnector, grounding switch and circuit breaker to prevent misoperation. When closing, if the locking device fails or the isolating switch and grounding switch cannot operate normally, the position and state of the corresponding circuit breaker and isolating switch must be checked in strict accordance with the locking requirements, and the locking can be lifted only after verification. When the voltage circuit of relay protection and automatic device needs to be switched to another voltage transformer due to the equipment switching to another bus or the voltage transformer on the bus, there may be two dangerous points at this time: ① the voltage loss caused by poor contact of the voltage circuit, the relay protection and automatic device will malfunction, the voltage transformer will charge the dead bus twice, and the fuse of the voltage circuit will blow, resulting in the misoperation of relay protection. (2) When the auxiliary contacts of the bus disconnector are not closed and connected at the same time, the voltage transformer on the running bus will charge the voltage transformer on the power-off bus through the secondary grid connection point after the bus is pulled open by the reverse bus operation. At this time, the power failure bus and voltage transformer will become the load of voltage transformer on the running bus, and it will also cause the fuse on the secondary side of two bus voltage transformers to blow or the automatic switch to trip. If the auxiliary contacts of the bus disconnector are disconnected at the same time, the protection, instrumentation and automation of the equipment will be enabled. Control measures: After the bus disconnector is operated, it is necessary to carefully check not only the actual indicating position of the disconnector, but also the contact condition of the auxiliary contact of the disconnector and whether the auxiliary contact indicator light on the protection device indicates normal. If any abnormality is found, remedial measures should be taken in time to prevent problems. Do not think that the position of the disconnector is in the actual state and ignore the situation of the secondary auxiliary contact during operation. The auxiliary contacts of some disconnectors often fail because of their poor operating environment and low reliability, which affects the reliability of the switch circuit. In order to improve the feasibility of automatic switching, on the one hand, we should choose good quality auxiliary contacts of disconnector and strengthen regular maintenance; On the other hand, it is necessary to improve the maintenance quality and ensure that the auxiliary contacts are flexible, convertible and have good contact. When operating the disconnector, due to the long running time of the equipment, the supporting insulator is broken. Control measures: make accident prediction before bus tripping operation to prevent abnormal operation. For the disconnector operated at a distance, it is not allowed to operate manually on the spot under live condition, so as to avoid losing electrical locking or asymmetrical disconnection caused by split-phase operation, which will affect the normal operation of relay protection. Try to use the buttons in the remote control operation box, and it is forbidden to stand under the isolating switch during operation to avoid accidents. For the local manual disconnector, the operator should pay attention to the standing position. When closing, it should be quick and decisive, but there should be no impact at the end of closing. Even if it is closed by grounding or short circuit, it should not be opened again. The switch should be slow and cautious, especially when the static contacts are separated. If arc light is found, it should be shut down quickly, stop running and find out the reason. When the no-load bus is charged, the inductive voltage transformer and the switching capacitor form a series resonance. Control measures: When charging an empty bus with an inductive voltage transformer, in order to avoid series resonance between the parallel capacitance between the contacts of the circuit breaker and the inductive reactance of the voltage transformer, the isolating switch of the voltage transformer should be turned off or an appropriate resistor should be connected in parallel (in series) in the secondary circuit of the voltage transformer before the bus stops sending power. 2 Danger points and control measures of bus-reversing operation in case of accident Many power plants (substations) reverse the bus when dealing with faults, mistakenly use conventional methods to operate, and close two bus disconnectors at the same time, resulting in artificial short circuit of buses in operation and expanding the accident. Therefore, when it is necessary to dump the equipment on a bus to a normal bus after a bus fault, the operation must follow the principle of "pull before closing", that is, pull the disconnector on the faulty bus first, and then close the disconnector on the operating bus. 3 Precautions: No matter whether the bus is connected reversely in case of accident or in case of normal maintenance, the personnel on duty should consider the best closing sequence of disconnectors, that is, the bus disconnector closest to the bus coupler circuit breaker should be closed first; When the switch is pulled, the operation sequence is reversed. Because the closer to the bus circuit breaker, the smaller the voltage difference, and vice versa. If the operator ignores the concept of voltage difference and operates the bus disconnector far away from the bus circuit breaker first, then the first set of bus disconnector contacts closed or the last set of bus disconnectors opened will generate small sparks. Although this small spark can be extinguished by itself, it will not cause short circuit, but it is easy to burn the contact and working face of bus disconnector. In particular, the indoor bus disconnector driven by worm gear has slow contact opening and closing speed and long spark action time, which should be paid special attention to.