How is the yearly energy found?

Average load 250 kW x 4800 h = 1,200,000 kWh

How are the 5% losses accounted for on the HV side?

Demand and energy are divided by 0.95 because losses are metered on the HV side

Demand and energy are multiplied by 0.95

Asked 2/16
2079 Baisakh · 8 marks

HV vs LV supply tariff for a factory

Short answer

Annual energy 1,200,000 kWh, max demand 375 kVA. LV cost: demand Rs 270,000 + energy Rs 1,320,000 = Rs 1,590,000. HV cost includes 5% losses: demand 394.74 kVA, energy 1,263,158 kWh, plus equipment charge Rs 22,500, total Rs 1,522,500. Difference Rs 67,500; HV is cheaper.

A factory works for 16 hours a day for 300 days in a year. The following two systems of tariff are available: • High voltage supply at Rs. 1 per unit plus Rs. 50 per month per kVA of maximum demand. • Low voltage supply at Rs. 60 per month per kVA of maximum demand plus Rs. 1.1 per unit. The factory has an average load of 250 kW at 0.8 power factor and a maximum demand of 300 kW at the same power factor. The high voltage equipment costs Rs. 500 per kVA and losses can be taken as 5%. Interest and depreciation charges are 12%. Calculate the difference in the annual cost between the two systems.

Data: working hours = 16 × 300 = 4800 h/year; average load 250 kW; maximum demand 300 kW at 0.8 pf.

\begin{aligned} \text{Energy used} &= 250 \times 4800 = 1{,}200{,}000\ \text{kWh} \\ \text{Max demand} &= \frac{300}{0.8} = 375\ \text{kVA} \end{aligned}

Low voltage supply

\begin{aligned} \text{Demand charge} &= 60 \times 12 \times 375 = \text{Rs } 270{,}000 \\ \text{Energy charge} &= 1.1 \times 1{,}200{,}000 = \text{Rs } 1{,}320{,}000 \\ \text{Total} &= \text{Rs } 1{,}590{,}000 \end{aligned}

High voltage supply

With HV supply the consumer owns the transformer and switchgear, and their 5% losses are metered on the HV side. The HV equipment is rated for the factory's 375 kVA maximum demand.

\begin{aligned} \text{Max demand on HV side} &= \frac{375}{0.95} = 394.74\ \text{kVA} \\ \text{Energy on HV side} &= \frac{1{,}200{,}000}{0.95} = 1{,}263{,}158\ \text{kWh} \\ \text{Demand charge} &= 50 \times 12 \times 394.74 = \text{Rs } 236{,}842 \\ \text{Energy charge} &= 1 \times 1{,}263{,}158 = \text{Rs } 1{,}263{,}158 \\ \text{Cost of HV equipment} &= 500 \times 375 = \text{Rs } 187{,}500 \\ \text{Interest and depreciation} &= 0.12 \times 187{,}500 = \text{Rs } 22{,}500 \\ \text{Total} &= 236{,}842 + 1{,}263{,}158 + 22{,}500 = \text{Rs } 1{,}522{,}500 \end{aligned}

System	Annual cost (Rs)
Low voltage	1,590,000
High voltage	1,522,500

Answer: Difference in annual cost = Rs 67,500; the high voltage supply is cheaper.

(If the HV equipment is instead rated for 394.74 kVA, its annual charge is Rs 23,684 and the difference becomes Rs 66,316.)

✓ Answer checked by Claude Opus 5.5 (high effort)

MV vs LV supply tariff for a 2-shift factory · Utilization of Electrical Energy, chapter 6 · asked 2×
Optimum pf under two-part tariff (200 kW) · Industrial Power Distribution and Illumination, chapter 10
EVA; 10 days, 50 labour days at Rs 1000 · Project Engineering, chapter 4 · asked 2×

All Utilization of Electrical Energy chapter 6 questions →

HV vs LV supply tariff for a factory

Low voltage supply

High voltage supply

Related questions