Working Principle of Transformer

In terms of long-distance transmission of electric energy, the AC system has been proven to be very effective. Through the transmission of high voltage, it is possible to transmit more electric energy through the power line with relatively low current and correspondingly lower loss. The AC power supply can increase or decrease the voltage with the assistance of the transformer, and the loss of the energy consumption of the transformer is very small.

For example, the transformer in our substation reduces the voltage from 380 to 220 or 110 kV. The distribution system operator then delivers power forward at this voltage level, and further reduces the voltage to the level required by the customer in stages.

Ⅰ. Transformer design:

The core of the transformer is an iron core made of laminated thin steel laminations. Each lamination is insulated from its adjacent laminations by a thin non-conductive insulating layer. The magnetic core forms a magnetic circuit. The transformer also includes at least two windings or "coils". These are wires wound on a steel core, and each coil has a different number of turns.

They convert the primary (input) voltage into a secondary (output) voltage proportional to the number of turns. In the case of a large transformer, the coil is immersed in a tank full of oil. This oil is installed in the transformer to insulate and cool the windings. The heat is dissipated through the heat sink or cooling system. The current is input through the bushing to ensure the insulation between the current connection and the transformer tank. The largest transformer currently in operation has an apparent power capacity of up to 600 megavolt-amperes (MVA) and a weight of up to 450 metric tons. 

Ⅱ. The working principle of the transformer:

Once current flows through the primary coil (with many windings), magnetic flux is generated in the magnetic core. This induces a voltage in the secondary coil. However, since this coil has fewer windings than the primary coil, the current flowing here is higher, but the voltage is lower. The product of current (I) and voltage (U) and the apparent power of the two coils are the same.

In other words, the decrease in current is the same factor as the increase in voltage. In a coil with more turns, the current is smaller and the voltage is higher; in a coil with fewer windings, the current is higher and the voltage is lower.