The answer to the residual current transformer rated current

April 07, 2021

The answer to the residual Current Transformer rated current

First, the residual current transformer rated current must meet the load rated current needs, such as the rated current of 250A or more.

Second, if the design residual current action threshold is 30mA, you must output the corresponding action current or signal twice when the current transformer has 30mA residual current at a time.

General current transformer can not do, large current measurement of small primary current. How to solve both the need to meet the needs of a rated current, but also to meet the 30mA? We can tell "milk brother"; the core of the main residual current transformer is an amorphous material. With high permeability, low coercivity, high saturation, small hysteresis loss, small remanence, the initial stage of magnetization on the leakage current is very sensitive. At the same time resistance to large current impact.

So when a 30mA residual current appears, the second can immediately feel its existence. Then when the residual current is equal to the rated current, the magnetic induction intensity of the transformer core is rapidly saturated, and the secondary current no longer increases. And its hysteresis loss, small remanence, to ensure the normal work of the transformer. But also need to ensure that the line short circuit fault, the dynamic thermal stability of the transformer. We summarize the working characteristics of the residual current transformer is small current-sensitive, high current saturation.

Third, some people think that the remaining current transformer will only appear 30mA residual current, the possibility of large current, and the rated current does not matter. This is obviously not in line with the actual situation. In a power supply system, 30mA is a commonly used residual current threshold, the residual current may well be the rated load current, or even the system fault current. Therefore, the residual current transformer can not tolerate these currents. Residual current protection, is the sky, passive water, without the wood.

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