When using current transformers, the accuracy of measurement determined by the primary current amplitude error (contrast) and phase error (difference). In medium accuracy without the requirement of DC component of electric meter, the absolute value of these two is very low, but it can be compensated through the relevant correction circuit. DC component of current transformer is different, because the difference of its  phase difference is large and stable. The special characteristic of amplitude error is relatively small. There is an energy measurement error. The error changes with the primary current. If the phase difference don't compensate, it cannot be applied in high perceptual load.

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