Current transformers with “S” and without S both indicate the accuracy level of the measurement current transformer. Under the conditions of regular use, the error of the transformer is within the limit of the rule of this level. The commonly used levels for measurement in power engineering are 0.2, 0.5, 0.2S, 0.5S, etc. For example, the current transformer for 0.2 or 0.2S level measurement, the difference is that when the load is small, the 0.2S level is higher than the 0.2 level. Measurement accuracy. It is mainly used for places where the load variation range is relatively large, and some hours are almost empty. When the actual load current is less than 30% of the rated current, the combined error of the 0.2S class is significantly smaller than that of the 0.2 class current transformer. The accuracy of the transformer is well regulated at the time of manufacture. The commonly used accuracy is 0.1, 0.5, and 10P. Different loads use different accuracy. If the measurement requires accuracy, use 0.1 level. When a short circuit occurs, the current is very large, and the magnetic saturation of the transformer coil is considered, so the 10P level is generally selected for maintenance. The 0.5 level is selected for the measurement.

The one with S is a special current transformer, and the accuracy is high enough within the load range of 1%-120%. Generally, the error of measuring with 5 load points is less than the regular range, and without S is measuring with 4 load points. The error is less than the rule’s range. Class 0.2 and class 0.2S are for measuring current transformers. The difference is that at small loads, class 0.2S has higher measurement accuracy than class 0.2. It is mainly used for places where the load variation range is relatively large, and some hours are almost empty. When the actual load current is less than 30% of the rated current, the combined error of the 0.2S class is significantly smaller than that of the 0.2 class current transformer.