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The constant for a three phase, 3 element integrating wattmeter is 0.12 revolution of disc per kWh. If the meter is normally used with a potential transformer of ratio 22,000/110V and a current transformer of ratio 500/5A; find the error expressed as a percentage of the correct reading from the following test figures for the instrument only
Line voltage = 100 V; current = 5.25 A; power factor = 1
Time to complete 40 revolutions = 61s.
  • a)
    2.19% fast
  • b)
    1.66% fast
  • c)
    1.66% low
  • d)
    2.19% low
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
The constant for a three phase, 3 element integrating wattmeter is 0.1...
Actual energy consumed during the test period = √3 × ratio of P.T. × ratio of C.T. × VsIs cosϕ × t
 = 338.97 kWh 
Energy recorded by meter during the test period

 = −1.66% = 1.66% low
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Most Upvoted Answer
The constant for a three phase, 3 element integrating wattmeter is 0.1...
Error Calculation:

The error of the wattmeter can be calculated using the formula:

Error = [(Total revolutions - Correct revolutions) / Total revolutions] * 100

where Total revolutions is the number of revolutions indicated by the wattmeter and Correct revolutions is the actual number of revolutions.

Given:
Constant for the wattmeter = 0.12 revolution/kWh
Line voltage = 100 V
Current = 5.25 A
Power factor = 1
Time to complete 40 revolutions = 61s

Step 1: Calculate the actual power consumed in kWh.
Actual power = Line voltage * Current * Power factor * Time / 1000
Actual power = 100 V * 5.25 A * 1 * 61 s / 1000 = 323.25 Ws = 0.0898 kWh

Step 2: Calculate the correct number of revolutions.
Correct revolutions = Actual power / Constant for the wattmeter
Correct revolutions = 0.0898 kWh / 0.12 revolution/kWh = 0.7483 revolutions

Step 3: Calculate the total revolutions indicated by the wattmeter.
Total revolutions = 40 revolutions (given)

Step 4: Calculate the error.
Error = [(Total revolutions - Correct revolutions) / Total revolutions] * 100
Error = [(40 - 0.7483) / 40] * 100 = 1.853%

Error as a Percentage of Correct Reading:

Since the error is the percentage of the correct reading, the error is 1.853% low (since the indicated reading is lower than the correct reading).

Therefore, the correct answer is option C) 1.66% low.
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The constant for a three phase, 3 element integrating wattmeter is 0.12 revolution of disc per kWh. If the meter is normally used with a potential transformer of ratio 22,000/110V and a current transformer of ratio 500/5A; find the error expressed as a percentage of the correct reading from the following test figures for the instrument onlyLine voltage = 100 V; current = 5.25 A; power factor = 1Time to complete 40 revolutions = 61s.a)2.19% fastb)1.66% fastc)1.66% lowd)2.19% lowCorrect answer is option 'C'. Can you explain this answer?
Question Description
The constant for a three phase, 3 element integrating wattmeter is 0.12 revolution of disc per kWh. If the meter is normally used with a potential transformer of ratio 22,000/110V and a current transformer of ratio 500/5A; find the error expressed as a percentage of the correct reading from the following test figures for the instrument onlyLine voltage = 100 V; current = 5.25 A; power factor = 1Time to complete 40 revolutions = 61s.a)2.19% fastb)1.66% fastc)1.66% lowd)2.19% lowCorrect answer is option 'C'. Can you explain this answer? for Electrical Engineering (EE) 2024 is part of Electrical Engineering (EE) preparation. The Question and answers have been prepared according to the Electrical Engineering (EE) exam syllabus. Information about The constant for a three phase, 3 element integrating wattmeter is 0.12 revolution of disc per kWh. If the meter is normally used with a potential transformer of ratio 22,000/110V and a current transformer of ratio 500/5A; find the error expressed as a percentage of the correct reading from the following test figures for the instrument onlyLine voltage = 100 V; current = 5.25 A; power factor = 1Time to complete 40 revolutions = 61s.a)2.19% fastb)1.66% fastc)1.66% lowd)2.19% lowCorrect answer is option 'C'. Can you explain this answer? covers all topics & solutions for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for The constant for a three phase, 3 element integrating wattmeter is 0.12 revolution of disc per kWh. If the meter is normally used with a potential transformer of ratio 22,000/110V and a current transformer of ratio 500/5A; find the error expressed as a percentage of the correct reading from the following test figures for the instrument onlyLine voltage = 100 V; current = 5.25 A; power factor = 1Time to complete 40 revolutions = 61s.a)2.19% fastb)1.66% fastc)1.66% lowd)2.19% lowCorrect answer is option 'C'. Can you explain this answer?.
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