Correct Answer - Option 2 : 0.95 lagging
Power Factor:
- The overall power factor is defined as the cosine of the angle between the voltage and 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 also be defined as the ratio of watts to volt-amperes.
- It is also defined as the ratio of resistance to the impedance of the circuit.
- The capacitor is used for power factor improvement.
Disadvantages of Low Power Factor:
1. Large kVA rating of the equipment:
The electrical machinery (e.g., alternators, transformers, switchgear) is always rated in kVA and it is given as,
\(kVA = \frac{{kW}}{{cos\phi }}\)
It is clear that the kVA rating of the equipment is inversely proportional to the power factor. The smaller the power factor, the larger is the kVA rating.
Therefore, at a low power factor, the kVA rating of the equipment has to be made more, making the equipment larger and expensive.
2. Greater conductor size:
To transmit or distribute a fixed amount of power at constant voltage, the conductor will have to carry more current at a low power factor. This necessitates a large conductor size.
3. Large copper losses:
The large current at low power factor causes more I2R losses in all the
elements of the supply system. This results in poor efficiency.
4. Poor voltage regulation:
The large current at a low lagging power factor causes greater voltage drops in alternators, transformers, transmission lines, and distributors. This results in the decreased voltage available at the supply end, thus impairing the performance of utilization devices. In order to keep the receiving end voltage within permissible limits, extra equipment (i.e., voltage regulators) is required.
5. Reduced handling capacity of system:
The lagging power factor reduces the handling capacity of all the elements of the system. It is because the reactive component of current prevents the full utilization of installed capacity.
Conclusion:
From the above concept, it is clear that 0.95 lagging is the most economical power factor out of these options.
