Transformer including voltage transformer and current transformer voltage transformer is a kind of voltage changer, have voltage transformation and isolate the twofold effect, it will be high pressure loop or low voltage circuit of high voltage to low voltage (100 v), supply the meter and relay protection device to realize measurement, metering, protection, and so on. Current transformer is a kind of current commutation device, a current transformation and isolation of twofold effect, it will be high voltage circuit or high current low voltage circuit into a low voltage low current (5 a) for general, supply meter and relay protection device to realize measurement, metering, protection, and so on. Actual measurement, in order to better match with full scale, there are 5 a the following the current transform for large current transformer (5 a).