The power current transformer consists of a closed core and a winding, which has a small number of turns on the primary side and is strung in the line of current to be measured. The number of turns on the secondary side winding is relatively large, and is connected in series in the measuring instrument and the protection circuit. When the power current transformer is working, its secondary side circuit is always closed, so the impedance of the series coil of the measuring instrument and the protection circuit is small. The operating state of the power current transformer is close to a short circuit.
There are many types of power current transformer. According to the application, they can be divided into power current transformer for protection and power current transformer for protection. The former is for settlement of electricity costs; the latter is for current speed protection, overcurrent protection, overload protection, etc. Power current transformer for different applications have different precisions.
For example, the accuracy of the power current transformer for calibration is 0.1S. The error is 0.1%; the accuracy of the power current transformer for measurement is 0.2S 0.5, the error is 0.2% and 0.5%; the accuracy of the power current transformer of the measuring level is 0.5, 1.0, 2.0, etc.; the accuracy of the power current transformer for protection is 10P10, 10P20, 5P10, 5P20, etc. In some special occasions, there are more accurate power current transformer, which are 0.005 grade, 0.05 grade, etc., and are used less frequently.