Question

The disc of an energy meter makes 600 revolutions per unit of energy. When a 1000 watt load is connected, the disc rotates at 10.2 r.p.s if the load is on for 12 hours, how many units are recorded as error ? 

Answer 1

Since load power is one kWh, energy actually consumed is 

= 1 × 12 = 12 kWh 

Total number of revolutions made by the disc during the period of 12 hours 

= 10.2 × 60 × 12 = 7,344 

since 600 revolutions record one kWh, energy recorded by the meter is 

= 7,344/600 = 12.24 kWh 

Hence, 0.24 unit is recorded extra.