Learning Unit One

 

At the end of this lesson you shall be able to

• Identify the features of an AC welding transformer
• Explain the working principle of an AC transformer
• Explain the care and maintenance of a welding transformer

AC Welding Transformer

This type of welding machine converts AC main supply into AC welding supply. Fig. 1 below illustrates.

AC main supply has high voltage-low current

AC welding supply has high current-low voltage

The welding machine is a step down transformer that reduces the main power supply 220-240 volts to a safe voltage.

Constructional features

It consists of an iron core made up of special alloy.  Two coils of wire are wound over he core without any interconnection between them.

One coil is called the primary winding and the second is called the secondary winding.  In terms of the number of turns, the primary coil has got more than the secondary side of the transformer. 

A current regulator is attached to the secondary output to adjust the current according to various sizes of electrodes.

Two welding cables are attached to the welding outputs terminals.  One is for the electrode holder and the other is for the work.  The transformer may air-cooled or oil-cooled.

Working Principle

The AC main supply 220-240 Volts is connected to the primary winding which produces the magnetic flux in the core. 

The magnetic flux affects the secondary winding and induces high current-low voltage welding supply

Care and Maintenance

• Transformer body must be properly earthen
• Transformer oil to be changed after recommended period
• Do not run machine continuously on its maximum capacity
• Switch off the main supply while cleaning internally and eternally
• Do not change current when welding is going on

Self Test Unit One                                                                 Marks Scored:         /20

Check your understanding by answering the following questions

1. AC welding machines are generally …………….. transformers.      (2 Marks)
2. The unit for measuring current is ………………….                          (2 Marks)
3. The cooling system of a welding transformer may be either:

a)                  …………………..

b)                  …………………..                                                                        (4 Marks)

4. Explain the term step down transformer as far as machines are concerned.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………                                                            (4 Marks)

5. What is the role of the current regulator?

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….                                                            (3 Marks)

6. List FIVE precautions regarding AC transformer.                             (5 marks)