It is necessary to study the working characteristics of the zero-sequence current transformer, and confirm whether it can saturate and affect the correctness of the maintenance action when the external fault passes through a large current during maintenance. It can be tested. Let me briefly describe these measures.
Obviously, the direct experimental method is to bring a practical load on the secondary side, pass current from the primary side, and observe the secondary current to find the saturation point of the zero-sequence current transformer. However, the saturation point of the transformer may exceed 15-20 times the rated current. When the zero-sequence current transformer becomes relatively large, it will be difficult to stop the experiment on site.
In addition, the saturation point of the zero-sequence current transformer can also be measured through the volt-ampere characteristic experiment. As mentioned earlier, the saturation of the zero-sequence current transformer is due to the dead-core magnetic flux densely crossing the saturation current of the large generator. The experimental method of the volt-ampere characteristic is: the original side is opened, the current is passed in from the secondary side, and the voltage drop on the secondary side winding is measured. Due to the demagnetization of the original square flow of the zero-sequence current transformer, it is easy to saturate under the action of a small current. Therefore, the volt-ampere characteristic experiment does not need to add a large current, and it is easier in the field