1.
Prove that in case of a single phase transformer emf
per turn is constant. Also draw the phasor diagram at leading, lagging and unity
power factor.

2.
Develop the equivalent circuit of transformer referred
to (i) primary side (ii) secondary side.

3.
Explain why the rating of a transformer is specified in
terms of kVA and why do we prefer to conduct Open Circuit Test on LV side and
Short Circuit Test on HV side?. What is voltage regulation?

4.
A 50 kVA, 4400/220 V transformer has R

_{1}= 3.45 Ω, R_{2}= 0.009 Ω. The values of reactances are X_{1}= 5.2 Ω and X_{2}= 0.015 Ω. Calculate for the transformer equivalent resistance and reactance (i) referred to the primary side (ii) referred to the secondary side.(iii) also calculate total copper losses first using individual resistances of the two windings and then using equivalent resistances as referred to each side. (Ans.:- (i) 7.05 Ω, 11.2 Ω (ii) 0.0176 Ω, 0.028 Ω, (iii) 910.4 W
5.
Following results were obtained on a 100 kVA, 11000/220
V single phase transformer:

(i) O.C. Test (LV side) 220 V, 45 A, 2000 W

(ii) S.C. Test (HV side) 500 V, 9.09 A, 3000 W

Determine
equivalent circuit parameters of the transformer referred to low voltage side.

(Ans.:- R

_{LV}= 0.0145 Ω, X_{LV}= 0.0165 Ω, Z_{LV}= 0.175 + j0.45 = 0.483 & 68.80^{0})
6.
The following
results were obtained on a 50 KVA, 2400/120 V single phase transformer

Short
circuit test (HV side) : 810 W, 20.83 A, 92 V

Open
circuit test (LV side) : 396W, 9.365 A, 120 V

Calculate (i)
the equivalent circuit parameters, (ii) efficiency at full load, 0.8 power
factor lagging. (ii) Efficiency at half of the full load, 0.82 power factor
lagging. (Ans.:- Ro=24.2, Xo=4.992, Z02=55, R02=36.3, X02=41.31, 97.07%)

7.
A 100 kVA transformer has 400 turns on the primary and
80 turns on the secondary. The primary and secondary resistances are 0.3 Ω and
0.1 Ω respectively and the corresponding reactances are 1.1 Ω and 0.035 Ω
respectively. The supply voltage is 2200 V. Calculate the voltage regulation
and secondary terminal voltage for full – load having a p.f. of (i) 0.8 lagging
(ii) 0.8 leading. (Ans.:- (i) 3.36%, 425.2V (ii) -1.54%, 446.8V)

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