A workshop operates three identical induction heating units, each rated at 2 kW, 240 V, 50 Hz with a power factor of 0.85 lagging. The units are connected in parallel to a three‑phase 415 V, 50 Hz supply. The electricity tariff is: first 500 kWh at ₦15 kWh⁻¹, next 500 kWh at ₦12 kWh⁻¹, thereafter ₦10 kWh⁻¹. The units run 6 hours per day, 5 days a week.

(a) Calculate the weekly energy cost if the supply is billed on apparent energy (kVAh) using the given power factor.
(b) If a power‑factor correction bank improves the overall PF to 0.95, recalculate the weekly energy cost.
(c) Determine the weekly saving obtained by the correction.

Question

A workshop operates three identical induction heating units, each rated at 2 kW, 240 V, 50 Hz with a power factor of 0.85 lagging. The units are connected in parallel to a three‑phase 415 V, 50 Hz supply. The electricity tariff is: first 500 kWh at ₦15 kWh⁻¹, next 500 kWh at ₦12 kWh⁻¹, thereafter ₦10 kWh⁻¹. The units run 6 hours per day, 5 days a week.

(a) Calculate the weekly energy cost if the supply is billed on apparent energy (kVAh) using the given power factor.
(b) If a power‑factor correction bank improves the overall PF to 0.95, recalculate the weekly energy cost.
(c) Determine the weekly saving obtained by the correction.

Accepted Answer

Without correction ₦3176.47; with correction ₦2842.11; weekly saving ₦334.36

City Guilds Model Questions Vol1 2024 Engineering Question 10

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