Troubleshooting of the secondary open circuit of Electrical Current Transformer

(1) The indication of the loop instrument is abnormal, which is generally reduced or zero. The open circuit of the current loop used to measure the meter will cause the indication of the three-phase ammeter to be inconsistent, the indication of the power meter will decrease, and the speed of the meter will be slow or not rotating. If there is sometimes no indication from the meter, it may be in a semi-open state (poor contact).

(2) Whether the CT body has noise, uneven vibration, severe heating, smoke, etc. Of course, these phenomena are not obvious when the load is small.

(3) The terminals of the CT secondary circuit and the wire ends of the components are discharged or sparked.

(4) The relay protection has misoperation or refusal. This situation can be found and dealt with in the accidental trip or over-level trip.

(5) The watt-hour meter, relay, etc. smoke and burn out. However, if there are reactive power meters and watt-hour meters, transmitters of remote control devices, and relays of protection devices burn out, not only will the CT secondary open circuit, but also the PT secondary short circuit. The above are just some basic clues to check the secondary open circuit of CT. In fact, in normal operation, the primary load is not large, the secondary does not work, and it is not the open circuit of the current circuit for measurement, the secondary open circuit fault of CT is not easy to find. We need to explore and accumulate experience in actual work. Check and handle the CT secondary open circuit fault, and try to reduce the primary load current to reduce the voltage of the secondary circuit. Pay attention to safety during operation, stand on the insulating mat, wear insulating gloves, and use well-insulated tools.

(1) When the secondary CT is found to be open, it is necessary to distinguish which group of current loops are faulty, the difference of the open circuit, and whether it affects the protection, report to the dispatch, and remove the protection that may malfunction.

(2) Try to reduce the primary load current. If the CT is severely damaged, the load should be transferred and the power should be cut off.

(3) As soon as possible, try to use good short wires on the nearby test terminal to short-circuit the CT secondary according to the drawing, and then check and deal with the open circuit point.

(4) If sparks are found during the short-circuit, the short-circuit should be effective, and the fault point should be in the circuit below the short-circuit point, which can be further searched. If there is no spark during the short-circuit, the short-circuit may be invalid, and the fault point may be in the circuit before the short-circuit point. The short-circuit point can be changed point by point to reduce the scope of inspection.

(5) Within the fault range, check the terminals and components that are prone to faults. For faults that are checked out, they can be handled by themselves, such as loosening of external components such as wiring terminals, poor contact, etc., immediately deal with it and put in the withdrawn protection. If the open circuit point is on the wiring terminal of the CT body, the power supply should be cut off. If you can't deal with it by yourself (such as inside the relay) or you can't find out the fault by yourself, you should first short-circuit the CT twice before reporting to the superior.