Q4
(a) Why is it important to maintain high efficiency of operation? And low values of voltages regulation for power transformers?
(6)
(b) A shunt motor supplied at 230 V runs at 900 rpm. When the armature current is 30 A, the resistance of the armature circuit is 0.4 Ω. Calculate the resistance required in series with the armature circuit to reduce the speed to 500 rpm. Assume that the armature current is 25 Amps.
(10)
Reference Answer
### Part (a): Transformer Efficiency and Voltage Regulation **(i) Importance of High Efficiency of Operation (3 Marks)** High efficiency in a power transformer is of paramount importance for operational, economic, and safety reasons. Efficiency (η) is defined as the ratio of output power to input power. $$ \eta = \frac{\text{Output Power (P}_{out})}{\text{Input Power (P}_{in})} \times 100\% $$
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