The most commonly used in the power system is the three phase transformer winding. It is more economic, less area, more convenient for maintenance and management to use a three phase transformer winding to connect three power transmission systems of different voltages than using two ordinary transformers. The three phase three winding transformer is often to use the connection method of Y-Y-△, namely that both original and secondary winding use Y connection method, and the third winding uses △. △ method itself is a closed loop which permits third harmonic current of the same phase to pass, so that third harmonic current does not appear in the original and secondary winding of the Y connect method. In that way, it also provides a neutral point for both the original and the secondary side. In the long distance transmission system, the third winding can also connect with a synchronous condenser to improve the power factor of line.
The capacity of the three phase transformer winding is the largest capacity among the three winding.
Multi-winding transformers are often used in electronic equipment, such as power transformer. 1 and 1┡ are two same original winding. They can be connected in series or in parallel to match two different supply voltages. 2、3、4、4┡ are secondary winding which can output different voltages to meet different needs. It can also guarantee the isolation requirement of each circuit.
Formula is as follows :
The capacity of three phase transformer winding is the largest capacity in the three winding.