When the primary current of the current transformer changes within a certain range, it is generally specified as 10～120%I1N, the secondary current should change proportionally, and the primary and secondary voltages (or currents) should be in the same phase. However, due to the internal impedance, excitation current, and loss of the transformer, the ratio and phase errors are called ratio differences and angular differences, respectively. The ratio difference is the ratio of the difference between the magnitude of the converted secondary current and the primary current to the latter, that is, fI is the ratio difference of the current transformer. When KNI2>I1, the ratio difference is positive, otherwise it is negative. For current transformers without compensation measures, the ratio difference is negative and the angle difference is positive. Both the absolute value and the angle difference of the ratio difference decrease with the increase of current. Using compensation methods can reduce the error of the transformer. It is generally compensated by winding additional windings or adding additional iron cores on the transformer, and connecting corresponding resistance, inductance, and capacitance components.