From the misoperation accident, talk about the contact line switching operation precautions. Pengtai Fang Luo Xiaochun feeder circuit breaker one phase undivided and caused the neutral point offset Ping Shaoxun connected the two power points of the contact line when performing the switching operation, due to the involvement of two A different unit has a problem with coordination. How to arrange the operating procedures to ensure the safety of the operation, this is the problem that the dispatcher should pay attention to when operating the order, but this is often not taken seriously by the dispatchers, leaving many security risks. This article combines a misoperation accident to talk about the switching operation of the tie line.
In the case of an accident, a dispatcher ordered this in the power-off operation of a tie line: firstly, the two substations were ordered to operate in the hot standby state, and after both sides reported the operation, they were ordered to operate to the inspection state and close the line. Grounding knives on both sides. However, during the second step of operation, one side of the circuit breaker is misaligned due to the DC grounding of the operating circuit, and the opposite duty officer is just in violation of the regulations, and the power is not verified before the grounding knife, which leads to the grounding of the live grounding. A vicious misoperation accident of the knife.
Exposure problems One of the main reasons for the accident was that the operator was not responsible and seriously violated the regulations, so that the power check was not performed before the grounding knife. For this, this article does not analyze too much. This article mainly gives some thoughts on the two other aspects of the accident.
(1) Unclear understanding of the operating procedures of the tie line In the process leading to the accident, the operation from the dispatcher to the operator for the tie line is divided into several steps, and the demarcation point between each step is There are countless states in mind. When there is work on the tie line or related equipment, it is necessary to install the grounding wire at the outlet end. The operation of the contact line from the running state to the repair state cannot be completed in one operation. Step-by-step operations must be ordered step by step. There should be a "cold standby" between the two steps.
As the demarcation point, the operation is first ordered to the cold standby state on both sides. After the reporting operation is completed on both sides, the operation is ordered to the maintenance state. The work of stopping the surface when the equipment is overhauled is a necessary condition for the subsequent work. This means that all aspects of the power supply must be completely disconnected before the grounding of the knives on the electrical equipment, and at least one obvious disconnection point in all aspects. Therefore, for the tie line, in addition to the front side must be operated to the cold standby state before the grounding knife, the opposite side of the possible incoming call must also operate to the cold standby state.
For the power failure operation of a double-return line, it should be operated in three steps. Before the above two-step operation, one step should be added. First, both sides of the double-circuit line common protection and automatic devices, such as lateral protection and current, are ordered. Balance protection, check another loop current reclosing, etc. After the two sides of the reporting operation are completed, follow the above steps to order the operation. If the operation is still performed in two steps, it is impossible to completely synchronize the operation on both sides. At this time, once the system is disturbed, it is possible to trip another return line on the side of the late operation to disengage the two systems.
(2) There is a lack of standardization in the management of the typical operation of the tie line switching operation. There is a great randomness in the operation mode. For example, a 35/10.5kV substation of the Bengbu Power Supply Bureau operates a 10kV grounding alarm when a 10kV feeder is operated. . At this time, the voltage of the 10kV bus to ground: 6A for phase A, 6850V for phase B, and 4400V for phase C. The on-duty personnel continue to operate other feeder circuit breakers (hot standby state), the grounding signal has not disappeared, and the relative ground voltage is biased. The shift value is even larger. After all the feeder circuit breakers were inspected, it was found that the C phase of a feeder circuit breaker was not broken.
The substation is a rural substation with 6 feeders of 10kV and a total length of 120km. In the ungrounded system of neutral point, the normal operation in the switching operation of this line, in addition to this operation mode, has long been used in various modes of operation. Coexistence: one side uses hot standby as the demarcation point and the other side uses cold standby as the demarcation point in two steps; both sides use cold standby as the demarcation point in two steps; one side uses cold standby as the demarcation point in two steps. The other side is in place, and so on. Different dispatchers have different orders at different times. Let's not say that there are hidden dangers in these operators. In the case of multiple operating modes, it means that the person in charge of the operation mistakenly believes that the operation does not matter, which makes them lose the correct operation. Some sensation, in this way, invisibly removed a security line of the operation of the switch.
3. Preventive measures From the perspective of standardized management of operations, whether it is a substation or a dispatching department, the most reasonable way should be selected for each typical operation as a unified norm for all parties, in dispatchers and substation duty personnel. A fixed pattern is formed in mind. In this way, on the one hand, it can be ensured in terms of methods, on the other hand, it can also enable relevant parties to achieve mutual supervision and mutual reminder. From this misoperation accident, it can be seen that the importance of rigorous operation style and standardized management of operations can be seen.
(Editing Xu Yulin), since the relative capacitances are basically equal, the phasor sum of the three relative capacitance currents is zero, and the potential of the main transformer neutral point is also zero.
When a circuit breaker with a feeder in the feeder is opened, one of the phases is not broken, and the device is in a hot standby state, the uninterrupted circuit breaker of the feeder is still connected to the busbar of the corresponding phase, thereby The distribution of the capacitance to the ground of the grid was changed, resulting in a shift of the neutral point to the ground potential.
After calculation, the neutral point potential shift is basically consistent with the actual phenomenon.
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