How to deal with secondary circuit failure of current transformer?

   Since only a very small impedance is allow in the secondary circuit of the current transformer, it is close to a short-circuit state under normal working conditions, with extremely small sound, and is generally consider silent. Current transformer failures are often accompanied by sound or other phenomena. If the core through-hole screw is not clamp tightly, the silicon steel sheet will loosen and the alternating magnetic flux in the core will change. As the alternating magnetic flux in the core changes, the vibration amplitude of the silicon steel sheet increases and a buzzing sound is emitt. This sound does not change with the load and will last for a long time. When the load is light or no load, some ends of the silicon steel sheet that leave the stack will oscillate, causing a certain buzzing sound. This sound is sometimes absent and sometimes disappears, and disappears with the increase of line load.

When the secondary circuit is open and the current is 0, the impedance is infinite, and the secondary winding generates a very high electromotive force, with a peak value of several thousand volts. Because the secondary circuit is in a closed circuit state when the current transformer is operating normally, the magnetic flux generated by the secondary side magnetic potential demagnetizes the magnetic flux generated on the primary side. When the secondary side is open, the demagnetizing magnetic flux disappears, causing the magnetic flux in the core to increase and be in a serious saturation state. This is the change of magnetic flux over time, and the waveform is a flat-top wave. Since the induced electromotive force of the secondary winding is proportional to the change of magnetic flux, it is obvious that the core may overheat and burn out the current transformer. Due to the increase in magnetic flux density and the non-sinusoidal nature of magnetic flux, the silicon steel sheet oscillates unevenly, thus making a loud noise.

When the secondary side of the current transformer is open, the on-duty personnel should wear insulating shoes and insulating gloves, short-circuit the test terminals of the secondary circuit of the fault current transformer on the distribution cabinet, and inspect and handle it. If the above measures are ineffective, it is believe that there may be a fault inside the current transformer, and it should be stop from use. If the current transformer may cause the protection device to operate, the relevant protection device should be stop.

When the secondary winding or circuit of the current transformer is short-circuit, the indication of the energy meter, power meter, etc. can be zero or reduce, and the relay protection device may also malfunction or not operate. If the operating on-duty personnel fail to discover it in time and still add load according to normal conditions, it will cause the equipment to be damage by overload that is not allow. After this kind of fault occurs, the load should be kept unchanged, the protective device that may malfunction should be disabled, and the maintenance personnel should be notified to eliminate it quickly.

If smoke or fire is found inside the current transformer, it should be cut off with a circuit breaker and the fire should be extinguish with sand or a fire extinguisher.

How to deal with secondary circuit failure of current transformer?

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