A 50 Hz, 25 kVA 7200/240 V transformer has the following equivalent circuit para

Question

A 50 Hz, 25 kVA 7200/240 V transformer has the following equivalent circuit parameters:

Primary resistance = 15?, Secondary resistance = 0.02 ?

Primary leakage reactance = 140?, Secondary leakage reactance = 0.15?,

Magnetising reactance = 30 k?, Core loss resistance = 200 k?

(a) The transformer is connected to two loads in parallel. The first load is 10 kW at 0.707

power factor lagging and the second load is 15kVA with a power factor of 0.8 lagging.

Find the percentage regulation and power efficiency for the transformer with the two

loads connected in parallel.

(b) If a capacitor is connected in parallel with the loads, the power factor of the combined

load can be improved to 0.95 lagging power factor. What is the value of the capacitor in

Farad? Under this condition, calculate the percentage regulation and power efficiency for

the transformer with the capacitor connected.

(c) Repeat part (a) and (b) with each load operating at 50% of the original loads, with other

parameters remaining constant.

(d) Prepare a table comparing the efficiency and regulation for part a, b and c. Comment on

the results.

Explanation / Answer

a) the power efficency is 87.15%

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