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EmSAT Achieve Exam  >  EmSAT Achieve Questions  >  For a 20 - kVA transformer, the iron and copp... Start Learning for Free
For a 20 - kVA transformer, the iron and copper losses at full load are 300 W and 250 W, respectively. What is the transformer efficiency under full load at unity power factor?
  • a)
    48.66%
  • b)
    98.76%
  • c)
    98.52%
  • d)
    97.32%
Correct answer is option 'D'. Can you explain this answer?
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Verified Answer
For a 20 - kVA transformer, the iron and copper losses at full load ar...
Given:
kVA rating (kva) = 20
Iron loss (iron_loss) = 300 W
Copper loss (copper_loss) = 250 W
Calculations:
Total Losses:
total_loss = iron_loss + copper_loss
total_loss = 300 W + 250 W
total_loss = 550 W
Apparent Power Output (Sout):
We are considering full load, so Sout is equal to the kVA rating converted to VA.
Sout_va = kva * 1000 (conversion factor from kVA to VA)
Sout_va = 20 kVA * 1000 VA/kVA
Sout_va = 20000 VA
Output Power (Pout):
At unity power factor (unity PF), all the apparent power is transferred as real power (Pout).
Pout_w = Sout_va (since PF = 1)
Pout_w = 20000 VA
Efficiency:
efficiency = (Pout_w / (Pout_w + total_loss)) * 100
efficiency = (20000 W / (20000 W + 550 W)) * 100
Result:
efficiency ≈ 97.32%
Therefore, the efficiency of the 20 kVA transformer at full load and unity power factor is approximately 97.32%.
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Most Upvoted Answer
For a 20 - kVA transformer, the iron and copper losses at full load ar...
Calculation of Transformer Efficiency:

Given Data:
- Transformer rating = 20 kVA
- Iron losses = 300 W
- Copper losses = 250 W
- Power factor = 1 (Unity)

Formula for Efficiency:
- Efficiency = Output Power / Input Power

Calculations:
- Input Power = Output Power + Total Losses
- Output Power = Transformer rating = 20 kVA = 20,000 VA
- Total Losses = Iron Losses + Copper Losses = 300 W + 250 W = 550 W
- Input Power = 20,000 VA + 550 W = 20,550 W

Efficiency Calculation:
- Efficiency = Output Power / Input Power
- Efficiency = 20,000 VA / 20,550 W
- Efficiency = 0.9758 or 97.58%
Therefore, the transformer efficiency under full load at unity power factor is 97.58%, which is closest to option 'D' (97.32%).
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For a 20 - kVA transformer, the iron and copper losses at full load are 300 W and 250 W, respectively. What is the transformer efficiency under full load at unity power factor?a)48.66%b)98.76%c)98.52%d)97.32%Correct answer is option 'D'. Can you explain this answer?
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For a 20 - kVA transformer, the iron and copper losses at full load are 300 W and 250 W, respectively. What is the transformer efficiency under full load at unity power factor?a)48.66%b)98.76%c)98.52%d)97.32%Correct answer is option 'D'. Can you explain this answer? for EmSAT Achieve 2025 is part of EmSAT Achieve preparation. The Question and answers have been prepared according to the EmSAT Achieve exam syllabus. Information about For a 20 - kVA transformer, the iron and copper losses at full load are 300 W and 250 W, respectively. What is the transformer efficiency under full load at unity power factor?a)48.66%b)98.76%c)98.52%d)97.32%Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for EmSAT Achieve 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for For a 20 - kVA transformer, the iron and copper losses at full load are 300 W and 250 W, respectively. What is the transformer efficiency under full load at unity power factor?a)48.66%b)98.76%c)98.52%d)97.32%Correct answer is option 'D'. Can you explain this answer?.
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