Current transformer fault analysis

September 29, 2023

The Current Transformer is composed of a closed core and a winding according to the principle of electromagnetic induction. When the current transformer is in operation, its secondary circuit is always closed, so the impedance of the series coil of the measuring instrument and the protection circuit is small, and the working state of the current transformer is close to the short circuit. Once a current transformer fails, it will cause serious damage. To find a CT secondary open circuit fault, you can check and judge from the following phenomena:

The loop meter indicates an abnormality, which is generally reduced or zero. The open circuit of the current loop used for the meter will make the three-phase ammeter indication inconsistent, the power meter indication decrease, and the meter speed slow or not.

The CT body has no noise, uneven vibration, severe heat generation, smoke, etc. Of course, these phenomena are not obvious when the load is small.

In the event of a misoperation or refusal of the relay, this condition can be detected and handled during a false trip or a step-by-step trip.

Electricity meters, relays, etc. are burnt out. The burnout of the relay with the power meter and the meter, the transmitter of the remote device, and the protection device not only makes the CT open twice, but also causes the PT to be short-circuited twice.

CT secondary circuit terminals, component wire ends have discharge and sparking.

It is found that the CT secondary open circuit must first distinguish which group of current loop faults, open phase differences, whether there is any impact on protection, report scheduling, and remove the protection that may be misplaced.

Try to short-circuit the CT twice with a good short-circuit on the nearest test terminal as soon as possible, and then check the open-circuit point.

If a spark is found during the short circuit, the short circuit should be valid. The fault point should be in the loop below the short contact point and can be further searched. If there is no spark when shorted, the short circuit may be invalid. The fault point may be in the loop before the short contact point. The short contact point can be changed forward point by point, and the range check can be narrowed.

Terminals and components that are prone to failure should be checked within the scope of the fault. For the detected faults, the protection that can be handled by itself, immediately after the processing and the exit.

Minimize the primary load current. If the CT is seriously damaged, the load should be transferred and the power should be cut off.

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