The reason why the secondary winding of the Electrical Current Transformer cannot be opened

When the Electrical Current Transformer is running, the load is connected to the secondary side of the instrument or relay current coil, etc., and the impedance is very small, basically in a short circuit state. Therefore, due to the demagnetization of the magnetic flux generated by the secondary current and the magnetic flux generated by the primary current, the magnetic flux density in the core can be kept at a low level, usually less than 0.1T. Therefore, the secondary voltage of the Electrical Current Transformer is also very fast.

When the secondary winding is opened in operation, the current on the primary side remains unchanged, and the secondary current is equal to zero, and the demagnetization flux generated by the secondary current also disappears. In this way, all primary currents become excitation currents, and the special current of the Electrical Current Transformer is suddenly saturated. At this time, the magnetic flux density in the iron core can be as high as 1.8T or higher. As the core is severely saturated, the following consequences will occur.

(1) Due to the saturation of the magnetic flux, the secondary side of the Electrical Current Transformer will generate a high voltage of several thousand volts, and the waveform of the secondary magnetic flux becomes a flat-top wave, thereby generating an induced potential with a sharp wave from the secondary, and the secondary Insulation poses a threat and is dangerous to equipment and operators.

(2) Due to the sudden saturation of the iron core, the loss of the iron core increases, the heat increases severely, and the insulation may burn out.

(3) The iron core will be interrupted and the Electrical Current Transformer must be checked. The angle difference will increase and the measurement accuracy will be affected.

Therefore, the Electrical Current Transformer cannot be opened during operation.

In actual work, it is often found that no abnormal phenomena are found after the second opening of the Electrical Current Transformer. This is mainly because there is no load current in the primary circuit or the load is very light. At this time, the excitation current is small and the iron core is not saturated, so no abnormality occurs. During operation, if the Electrical Current Transformer is found to be turned on twice, the power should be cut off in time. When the load is not allowed to stop, the load current on the primary side should be reduced first, and then an insulated tool should be used for processing.