(A) Large kW rating
(B) High power factor
(C) Large kVA rating
(D) None of the above
Answer: (C) Large kVA rating
Explanation:
Power factor:
The overall power factor is defined as the cosine of the angle between the phase voltage and phase current.
In AC circuits, the power factor is also defined as the ratio of the real power flowing to the load to the apparent power in the circuit.
Hence power factor can be defined as watts to volt-amperes.
It is also defined as the ratio of resistance to the impedance of the circuit.
So that by increasing resistance, the power factor can be increased. But due to power losses practically it is not used.
Typically capacitor is used for power factor improvement purposes.
Disadvantages of low power factor:
Large kVA rating of the equipment
Greater conductor size
Large copper losses
Poor voltage regulation
The reduced handling capacity of the system
Cost of station and distribution equipment is more for a given load
Causes of low power factor:
Most of the AC motors are of induction type (1φ and 3φ induction motors) which have a low lagging power factor
These motors work at a power factor which is extremely small on light load (0.2 to 0.3) and rises to 0.8 or 0.9 at full load
Arc lamps, electric discharge lamps and industrial heating furnaces operate at a low lagging power factor
The load on the power system is varying; being high during morning and evening and low at other times
During low load period, the supply voltage is increased which increases the magnetisation current, this results in the decreased power factor
Low power factor can be avoided by:
Using synchronous motors instead of induction motors
Using high-speed induction motors to low-speed machines
Not operating induction motors at less than the rated output
By using the following equipment
Static capacitors
Synchronous condenser
Phase advancer
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