How to calculate the efficiency of a transformer

When purchasing and installing the transformer, we must calculate the effective load of the transformer. At the rated power, the ratio of the output power of the transformer to the input power is called the efficiency of the transformer, namely: η=(P2÷P1) In the x100% formula, η is the efficiency of the transformer; P1 is the input power, and P2 is the output power.

When the output power P2 of the transformer is equal to the input power P1, the efficiency η is equal to 100%, and the transformer will not produce any loss. But in fact, there is no such transformer. The transformer always produces loss when transmitting electric energy, and this loss mainly includes copper loss and iron loss.

Copper loss refers to the loss caused by the resistance of the transformer coil. When the current flows through the coil resistance to generate heat, part of the electrical energy is converted into heat and is lost. Since the coil is generally wound by insulated copper wire, it is called copper loss.

The iron loss of the transformer includes two aspects: one is the hysteresis loss. When the alternating current passes through the transformer, the direction and size of the magnetic field lines passing through the silicon steel sheet of the transformer change accordingly, causing the internal molecules of the silicon steel sheet to rub against each other and release heat energy, thus losing Part of the electrical energy, this is the hysteresis loss. The other is eddy current loss. When the transformer is working, there are magnetic lines of force passing through the iron core, and induced current will be generated on the plane perpendicular to the magnetic lines of force. Since this current forms a closed loop by itself to form a circulating current and becomes a vortex, it is called vortex. The existence of eddy current makes the iron core heat up and consumes energy. This loss is called eddy current loss.

The efficiency of a transformer is closely related to the power level of the transformer. Generally, the greater the power, the smaller the loss and output power, and the higher the efficiency. Conversely, the lower the power, the lower the efficiency.