Step down Transformer is to refer to the input end of the higher voltage, converted to the output of a relatively low ideal voltage, so as to achieve the purpose of step-down transformers. The step down transformer is a very important equipment in the electric transformer system, its normal operation is not only related to its safety, the reliable power of the user, but also directly affects the stability of the electric system.

In the electric system, the step down transformer is one of the most important electrical parts, and the relay protection device is an important guarantee for the normal operation of the electric system. With the continuous development of the society, the rapid economic progress, the continuous improvement of living standards, people's demand for electric power has gradually improved, which puts forward higher requirements for the relay protection of step down transformers. For the design of relay protection, we should briefly design the relay protection from its protection principle, specific relay protection measures for transformer faults, and the importance of relay protection these several aspects.         The basic principle is the principle of electromagnetic induction. Formula for principle Description: E-- Effective value of inductive potential f-- Frequency N-- The maximum value of the main flux of the turn is due to its differences from the number of winding to the number of the secondary winding, and the magnitude of the inductance E1 and E2 are also different. When the internal resistance pressure drop, the voltage size is different.

When the transformer two sides no-load, one side only passes through the main magnetic flux current, this current is called the magnetizing current.