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DFCCIL Junior Executive Electrical 2018 Official Paper

Option 2 : 800

__Concept:__

- The number of revolutions made by the energy meter per kilowatt-hour is known as the meter constant of an energy meter.
- Unit of meter constant is revolution per kilowatt-hour (rev / kWh)
- It is constant for a particular energy meter.

Meter constant (K) = No. of revolution by meter / Energy consumed (E)

E (in kWh) = voltage x current x cos ϕ × time x 10-3 = Load × time x 10-3

Where, cos ϕ = power factor

__Calculation:__

Load power = 450 W, time = 100 sec, Number of revolutions = 10

Energy supplied in 100 seconds \(= 450 \times \frac{{100}}{{3600}} \times {10^{ - 3}} = 12.5 \times {10^{ - 3}}\;kWh\)

Number of revolutions in 100 seconds = 10

Meter constant = number of revolutions / kWh

Meter constant \( = \frac{10}{{12.5 \times {{10}^{ - 3}}}} = 800\;rev/kWh\)