Iron loss of a transformer can be measured by:

Question

Question

This question was previously asked in

ALP CBT 2 Electrician Official Paper (Held On: 23 Jan 2019 Shift 3)

Answer 1

Iron losses of transformer are measured by conducting open circuit test. During open circuit test transformer works at very low power factor.

The low power factor wattmeter is the instrument that measures lower values of power factor accurately.

Hence low pf wattmeter is used to measure iron losses of transformer.

Note:

Open circuit test:

It is done by keeping one of the windings open (without load, usually high voltage winding is open) and applying rated voltage to other winding (usually low voltage winding because it is easier to apply rated voltage).
The current drawn from this terminal is the no-load current at low power factor corresponding to core loss component. Since the no-load current is very small it doesn’t contribute to the copper loss. Core loss is calculated by multiplying the applied voltage and no-load current.
As the secondary side is open, the entire coil will be purely inductive in nature. So, the power will be lagging due to inductive property of the circuit. So LPF (Low Power Factor) Wattmeter is used in open circuit test of transformer.

It is used to find

Short circuit test:

It is done by shorting one of the winding terminals (usually low voltage terminal) and applying a small voltage across the other winding terminals (high voltage terminal because the current in HV terminal will be less and easy to handle) and using a wattmeter to measure the power dissipated in the LV terminal. Wattmeter will indicate the full load copper loss.
In short circuit test the secondary winding of transformer is short circuited. As secondary side is short circuited the entire coil will be purely resistive in nature. So, the power factor will be High or unity.

Short circuit test is done to find