Current transformer is widely used in our work and life. Its function is mainly to convert the primary current with large value into the secondary current with small value through a certain transformation ratio. It has the functions of protection, measurement and so on. In daily life, it is easy to have open circuit fault of current transformer, so it is very important to know how to deal with it.
First, what is the secondary open circuit fault? If the secondary open circuit occurs, all the primary current will be used for excitation to seriously saturate the iron core. At the same time, the alternating magnetic flux will induce a very high voltage on the secondary coil, with a peak value of thousands of volts or even tens of thousands of volts. Obviously, such a high voltage acting on the secondary coil and secondary circuit will have disastrous consequences for personal safety and equipment safety, and the insulation of the coil will be burned out due to overheating. Therefore, the regulation stipulates that open circuit is strictly prohibited during the operation of current transformer. So in case of secondary open circuit fault, how should we check and deal with it?
Judge whether there is a secondary open circuit fault through the following points1. Whether the indication of loop instrument is abnormal, which is generally displayed as lower or zero. The current circuit of the measuring meter is open. In case of slow or no rotation of the meter. If there is no indication from the meter sometimes, it indicates that the current transformer may be in a semi open circuit state (poor contact). We should be vigilant.2. Whether the current transformer body has noise, whether the vibration is uniform, and whether there are serious heating, smoking and other phenomena. Of course, these phenomena are not obvious when the load is small.
3. Check whether the secondary circuit terminal and element wire head of current transformer are discharged and ignited.4. Misoperation or refusal of relay protection. This situation can be found and handled in case of false tripping or skip tripping. The watt hour meter, relay, etc. are burnt out by smoke. The secondary open circuit of current transformer will be caused by the burnout of reactive power meter and watt hour meter, transmitter of telecontrol device and relay of protection device.Next, how to deal with the secondary open circuit fault
1. If the secondary open circuit of current transformer is found, first distinguish which group of current circuit the fault belongs to, the phase of the open circuit and whether it has an impact on the protection, report to the dispatcher and remove the protection that may misoperate.2. Try to reduce the primary load current. If the current transformer is seriously damaged, transfer the load and cut off the power for inspection and treatment. If the state-owned bypass is used, the bypass power supply can be used to ensure the power supply.2. Try to short-circuit the current transformer for the second time on the nearest test terminal, and then check and deal with the open circuit point. During the short-circuit, the special short-circuit wiring for short-circuit shall be used. The short-circuit shall be proper and reliable, and the winding of fuse or general conductor is prohibited. According to the drawing.
3. Pay attention to the phenomenon of short-circuit. If there is spark during short-circuit, the short-circuit is effective. The fault point is in the circuit below the short-circuit contact, which can be further found. If there is no spark during short-circuit, the short-circuit may be invalid. The fault point may be in the circuit before the short contact. The short contact can be changed forward point by point to narrow the range to clarify the open point
5. Within the fault range, check the terminals and components prone to failure, and check that there are parts of the circuit that have been touched during operation. For the faults detected, those that can be handled by themselves can be handled immediately, and then the exited protection can be put into operation. If the open circuit point is on the wiring terminal of the transformer body, the power shall be cut off for treatment. In case of failure that cannot be handled or found out by yourself, report to the superior and send professional maintenance personnel to check and deal with it. At this time, the current transformer shall be short circuited for the second time, or the load shall be transferred and the power shall be cut off.
Obviously, how to deal with the open circuit problem of current transformer not only involves basic composition knowledge, but also needs to understand the causes of faults and have professional maintenance experience
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