Transformer Theory and Application

PARTS OF A TRANSFORMER

 There are three basic parts of a transformer:

  1. an iron core which serves as a magnetic conductor,
  2. a primary winding or coil of wire and
  3. a secondary winding or coil of wire.

The primary is usually referred to as the input; the secondary as the output.

PRINCIPLE OF OPERATION

An alternating current applied to the primary winding induces a alternating magnetic flux in the iron core. Most of this flux stays with in the core and only a small percentage of it travels through the air. The alternating magnetic flux in the iron core then links the turns of the secondary windings inducing a voltage. This all follows from Faraday's law of induction. This explains why the primary has a voltage, and the secondary has a voltage, yet there is no interconnection between them.

WHY WE USE TRANSFORMERS

TO DISTRIBUTE POWER AT HIGH VOLTAGE.

It is more cost effective to distribute power at higher voltages since power dissipation (loss) in a resistive load is given by the square of the current times the resistance of the wire. It is best to use the lowest possible current and thus the largest potential difference (voltage). A typical transformer will take in input of 480 or 600 volts and step the voltage down to 240 volts for some motors, or 120 volts for other applications like consumer products, lights, etc.. The overall result is better voltage regulation, minimized line loss and reduced wiring costs.

TO ELIMINATE DOUBLE WIRING.

For maximum safety, 120 volt lighting and control circuits may be obtained from 240, 480, or 600 volt power circuits by installing transformers at the most convenient location to the load. This eliminates separate circuits and independent metering for power and often results in substantial savings.

TO INSULATE CIRCUITS.

Installing transformers provides a means of subdividing circuits to accommodate independent demand. Connecting to a 3 phase, 480 volt circuit a transformer can provide

  1. 120/240 volt 3 wire single phase load:
  2. 120 volt single phase load:
  3. 240 volt single phase load.
Transformers permit grounding of each low voltage circuit.