Final answer:
The energy meter is expected to make 368 revolutions when connected to a 40A, 230V, and 0.4 power factor load for an hour. If it actually makes 360 revolutions, the percentage error in meter reading is 2.17%.
Step-by-step explanation:
The number of revolutions made by the energy meter when connected to a load can be calculated using the formula:
E (energy in kWh) = VIcos(φ)t/1000
where V is the voltage in volts, I is the current in amps, φ is the phase angle corresponding to the power factor (pf), and t is the time in hours.
The power factor cos(φ) is given by pf = 0.4.
E = 230V × 40A × 0.4 × 1h / 1000
= 3.68 kWh
To find the number of expected revolutions (R), we multiply the energy consumed (E) by the revolutions per unit of energy (r), which is 100 revolutions/kWh in this case.
R = E × r
R = 3.68 kWh × 100 rev/kWh
R = 368 revolutions
To calculate the percentage error between expected and actual revolutions:
Percentage Error = |Actual Revolutions - Expected Revolutions| / Expected Revolutions × 100%
Percentage Error = |360 - 368| / 368 × 100%
Percentage Error = 2.17%
Therefore, the meter makes 368 expected revolutions, but if it actually makes 360 revolutions, the percentage error is 2.17%.