Following tests are carried out on the transformer to check weather it is good or bad.
- Winding resistance test : This test is carried out to reveal any open circuited windings. It is carried out by using ohmmeter or multimeter. The winding resistance should be within the tolerance limits of specified value at specified temperature. If it is zero or infinity, then that winding is supposed to be short circuited or open circuited respectively. This transformer is not good transformer.
- Insulation resistance test : This test is done between windings, core and shield by user insulation tester. The insulation resistance of each winding to all other windings, core and frame connected together must be greater than 10 MΩ at room temperature.
A very high resistance (infinity) indicates that the corresponding winding is open circuited and it is faulty. If it shows a very low resistance, then the corresponding winding is short circuited and it is faulty. Otherwise, it is good.
Transformers