The transformer is a sensor in the power system for obtaining electrical once-in-a-loop information from secondary equipment such as measuring instrument and relay protection. The transformer converts high voltage, high current proportionally into low voltage (100, 100/) and small current (5, 1A), which is side-by-side in a system, secondary side-on measuring instrument and relay protection, etc. In order to ensure the safety of the staff when touching the measuring instrument and relay, each secondary winding of the transformer must have a reliable ground to prevent damage to the insulation between windings and the long-term high voltage of the secondary part. Transformers include current transformers and voltage transformers, mainly electromagnetic.