- 2075 Bhadra · 8 marks
Comparing two 750 kVA transformers
Short answer
Transformer B costs Rs 20,810 less and has lower iron and copper losses (70 W and 1655 W at full load). At 50% loading, annual energy saving is 4238 kWh (Rs 31,782). Second transformer is worth purchasing.
The 750 kVA transformer (iron loss 1500 W and copper loss 11500 W) is estimated to cost approximately Rs. 7,21,577/00. An equivalent transformer of another manufacture is quoted at Rs 7,00,767. The iron loss of the second transformer are 1430 W and copper loss are 9845 W. Is it worth considering the purchase of second transformer instead? Assume per unit cost of electricity be Rs. 7.5.
Given:
| Transformer | Cost (Rs) | Iron loss | Cu loss (full load) |
|---|---|---|---|
| A (750 kVA) | 7,21,577 | 1500 W | 11 500 W |
| B (750 kVA) | 7,00,767 | 1430 W | 9845 W |
Energy rate Rs 7.5/kWh. Assumption: the transformer is energised for the whole year (8760 h); copper loss depends on loading, so it is worked out for a typical average load of 50% and also for other loadings.
Saving in initial cost
Cost difference = 7,21,577 − 7,00,767 = Rs 20,810 (B cheaper)
Saving in losses with transformer B
Iron-loss difference = 1500 − 1430 = 70 W
Copper-loss difference = 11 500 − 9845 = 1655 W (at full load)
At 50% average load, Cu loss difference = 0.5² × 1655 = 413.75 W.
Energy saved/yr = (70 + 413.75) × 8760 / 1000
= 4237.7 kWh
Money saved/yr = 4237.7 × 7.5 = Rs 31,782
| Average load | Loss saving (W) | Rs saved/yr |
|---|---|---|
| Iron only (no load) | 70 | 4,599 |
| 50% | 483.75 | 31,782 |
| 75% | 1000.9 | 65,762 |
| 100% | 1725 | 1,13,333 |
Decision
Transformer B is both cheaper (by Rs 20,810) and has lower losses, so it saves money from the first day: there is no extra investment to pay back. Even at no load it saves Rs 4,599/yr, and at 50% load about Rs 31,782/yr. Over a 25-year life this is several lakh rupees.
Answer: Yes, the second transformer should be purchased (provided its quality, guarantee, impedance and after-sales service are equivalent).
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- kVAr and techno-economic analysis for 1000 kVA transformer · Industrial Power Distribution and Illumination, chapter 10
- PF improvement of 1020 kVA factory load · Industrial Power Distribution and Illumination, chapter 10 · asked 2×
- Energy and cost saving from lighting retrofit · Industrial Power Distribution and Illumination, chapter 10
- Optimum pf under two-part tariff (200 kW) · Industrial Power Distribution and Illumination, chapter 10
- Electronic ballast replacement savings with ToD tariff · Industrial Power Distribution and Illumination, chapter 10
- Transformer size for four blocks · Industrial Power Distribution and Illumination, chapter 4
- Equivalent impedance and copper loss of 50 kVA transformer · Electrical Machines I, chapter 2
- 50 kVA transformer: equivalent parameters, copper loss · Electrical Machines, chapter 2
- Iron loss and maximum efficiency of 20 kVA 220/2200 V transformer · Electrical Machines I, chapter 2 · asked 2×
- Iron loss and maximum efficiency of 20 kVA 250/2500 V transformer · Electrical Machines I, chapter 2 · asked 2×
All Industrial Power Distribution and Illumination chapter 10 questions →