What is Power Factor?
The cosine of the angle between voltage and current is known as the power factor. The phase difference between voltage and current is zero, ideally in an AC circuit. But there exists some phase difference between the two, practically.
Power factor is basically the measure of how efficiently the received power is used in an electrical system. The power supplied to the electrical system is efficiently used and is indicated by a high-power factor. A system that doesn’t efficiently consume the received electric supply has a low power factor, and this results in losses. In DC circuits, there is no power factor included due to zero frequency. But, the value of the power factor always fluctuates between 0 and 1 in AC circuits.
Types of Power
Real Power – The power supplied to the equipment that performs suitable and productive work is known as real power.
Reactive Power – The power essential for equipment such as motors and transformers to generate magnetic fields allowing actual work to be done, is known as reactive power.
Apparent Power – Apparent power is the vector sum of real power and reactive power.
Power Factor Correction
The following methods are used for the power factor correction:
- Power factor correction technique using capacitors
- Power factor correction technique using a synchronous condenser
Important Questions on Power Factor
1) What is the power factor?
The cosine of the angle between voltage and current is known as the power factor. The power factor is basically the measure of how efficiently the received power is used in the electrical system.
2) What will happen to the overall power for a power system having induction motor loads and a synchronous motor, which is overexcited, is also attached to it?
a) Overall power factor improves
b) Overall power factor degrades
c) Overall power factor becomes upf
d) Overall power factor remains same
Correct Option: (a)
Explanation: The Overall power factor improves because the synchronous motor that is overexcited performs as a source of lagging reactive power.
3) In an AC circuit, how many types of power can be defined?
a) 1
b) 2
c) 5
d) 3
Correct Option: (d)
Explanation: We can define three types of power in an AC circuit: average power, apparent power and instantaneous power. A circuit component generates or disintegrates power according to the equation: P = IV, where I denote the current through the component and V denotes the voltage across it.
4) Which among the following is the power factor in a pure capacitive or inductive circuit?
a) -1
b) Infinity
c) 1
d) Zero
Correct Option: (d)
Explanation: A pure inductive circuit is a circuit which contains only inductance, and a pure capacitive circuit is a circuit containing only a pure capacitor. Hence, the current is lagging by 90 degrees from the voltage in a pure inductive circuit or a pure capacitive circuit. And as we know, the cosine of the angle between the voltage and the current is the power factor. Therefore:
Φ = π/2 = Power factor (cosπ/2) =0
5) How is the power factor measured?
The cosine of the phase difference between voltage and current is known as the power factor, and therefore, using the following formula, the power factor is measured.
Power Factor = cosɸ,
where ɸ denotes the phase difference between the current phasor and voltage.
6) The unit of power factor is Watts.
a) True
b) False
Correct Option: (b)
Explanation: The above statement is false because, as per the definition, the power factor is the ratio of the resistance to the impedance of an AC circuit. So, both are resistance quantities which means that the ratio between them will be 1, and therefore, the power factor is a unitless quantity.
7) What are the causes of the low power factor?
The following are causes of low power factor:
- The existence of harmonic current in the system.
- Inappropriate wiring leads to a three-phase imbalance.
- The voltage increases when the system is loaded lightly, and this eventually increases the magnetization current demand of the machine.
- If the current drawn by inductive loads is lagging, this results in a poor power factor.
8) In the case of ____ circuits, the power factor is called the leading power factor.
a) LR
b) LC
c) RLC
d) RC
Correct Option: (d)
Explanation: In the case of RC circuits, the power factor is called the leading power factor and not in the case of any other circuits like RLC, LR or LC.
8) Which among the following is the power factor in a pure resistive circuit?
a) 1
b) -2
c) Zero
d) Infinity
Correct Option: (a)
Explanation: In an AC circuit, a circuit that includes only a pure resistance is known as a pure resistive AC Circuit. The power factor is one for a purely resistive circuit because the reactive power is equal to zero, that is,
Φ = 0 ➔ Power factor (cos 0) =1
9) What is the low power factor correction?
A method of improving the power factor, and consequently, improving the power quality, is known as low power correction. Using a capacitor bank and synchronous condenser, the low power factor can be corrected.
10) The power factor is the ratio of ________.
a) Average power to the apparent power
b) Apparent power to the reactive power
c) Reactive power to the average power
d) Apparent power to the average power
Correct Option: (a)
Explanation: The ratio of average power to the apparent power is known as the power factor. To get true power in the circuit, the factor with which the volt-amperes are to be multiplied is known as the power factor. Power factor = average power/ apparent power.
|
Related Articles |
Suggested Videos
Stay tuned to BYJU’S and Fall in Love with Learning!
