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Transformer classification and use
Dec 07, 2017


Transformer (Transformer) is a kind of static motor, it can convert one form of voltage power to another form of voltage power.

First, the classification and use of transformers

Power transformers: Transformers used to transmit and distribute power in power systems.

Question 1 why long-distance transmission must use high-voltage power transmission?

Electric furnace transformer (special),

Electric furnace (such as steel furnace) power supply.

Welding transformers (special),

Electric welding machine.


Rectifier transformer (special):

Power the DC locomotive.

Experimental transformers (transformers).

Instrument transformer.

Control Transformer: used in electronic circuits.

Second, the working principle of the transformer

(1) Schematic

A core: to provide a closed path of flux.

Two windings: primary winding (primary) N1, secondary winding (secondary) N2. The company is located in:

(2) working principle

When a winding connected to the AC voltage, there is excitation current i0 exist, the current in the core can produce an alternating main flux Φ.

Ф induces potentials e1 and e2 in the two windings, respectively

e1 = -N1 dФ / dt e2 = -N2 dФ / dt

If omitted winding resistance and leakage voltage drop, then the ratio of the above two formulas:

U1 / U2≈ (-e1) / (-e2) = N1 / N2

U1 / U2 ≈ (-e1) / (-e2) = N1 / N2 = k, k is defined as the transformation ratio of the transformer. That is: U1 / U2 = N1 / N2 From this formula can be seen, if the fixed U1, as long as change the turns ratio can achieve the purpose of changing the voltage, namely:

If N2> N1, the step-up transformer (step-up transformer);

If N2 <N1, the step-down transformer (step-down transformer).