Answer MET Question 7

Question: Why it is important to maintain high efficiency of operation? And low values of voltages regulation for power transformer?

Answer: Commercial efficiency of a transformer is given by;

$\displaystyle \small \mathrm{\eta = \frac{Output\ in\ watts}{Input\ in\ watts}\times 100 }$

However this does not reflect the actual condition as the load varies throughout the day for a distribution transformer.

All day efficiency  is given by;

$\displaystyle \small \mathrm{\eta = \frac{Output\ in\ KWH}{Input\ in\ KWH}\times 100\ for\ 24\ hours}$

With a higher efficiency of operation of a transformer the losses will be minimum.

The losses are the direct capital loss for the power supplier.

Maximum efficiency of the transformer is achieved when copper loss is equal to iron loss and it is at 58% of full-load.

Voltage regulation is the ratio of change in secondary terminal voltage from no-load to full-load with the no-load voltage. The drop in voltage takes place due to internal resistance and leakage resistance of the transformer winding.

$\displaystyle \small \mathrm{reg = \frac{V_1 - V'_2}{V_1}\times 100}$

A good power transformer should exhibit a regulation percentage of  less than 3%.

As the load increases on secondary side of a transformer the voltage drops. A good transformer should keep its volatage as constant as possible under all condition of load.