Class 2 (2nd Engineer) MET 📅 Oct 2025

Exam Question

(a) Why is it important to maintain high efficiency of operation and low values of voltage regulation for power transformers (6)

(b) 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 0.01 Ω respectively and the curresponding leakage reactances are 1.1Ω and 0.035Ω respectively. The supply voltage is 2200V. Calculate (10)

(i) The equivalent impedance referred to the primary circuit

(ii) The voltage regulation and secondary terminal voltage for full load having a power factor of 0.8 lagging and 0.8 leading

Reference Answer

(a) Transformers with high efficiency minimize energy losses (copper losses due to winding resistance and iron losses due to core magnetization). This translates directly to lower operating costs and reduced environmental impact due to less wasted energy. High-efficiency transformers typically achieve 95.5% efficiency for 5 kVA units and up to 97.5% for units up to 1 MVA.
Lower energy losses mean less heat is generated within the transformer. This reduces the risk of overheating, extending the lifespan of the equipment and preventing potential fire hazards. Overheating can damage the insulation and reduce the lifespan of the transformer. Lower operating temperatures contribute to enhanced reliability and a longer operational life for the transformer.
Low voltage regulation ensures that the output voltage remains relatively constant even under varying load conditions. This stability is essential for the stable operation of equipment connected to the transformer. Voltage fluctuations can lead to wear and tear on connected equipment. Maintaining a constant voltage extends the lifespan of the equipment.

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