• Active power: Measured in Watts (Normally shown as kW). Provides the "working" part of the power system. Produces heat, light, motion, etc.
• Reactive power: Measured as Volt-Ampere-reactive (Normally shown as kVAR). It only maintains the electromagnetic field and provides no 'working' part of the power system.
• Apparent power: Measured in Volt-Ampere (normally shown as kVA). Provides both working and non-working parts of the power system.
• The cosine ratio of the angle between the voltage and current in an AC circuit is known as power factor. It involves the relationship between the two types of power, working power and reactive power.
• Most loads (80%) in electrical distribution systems are inductive in nature and they have low power factor which is highly undesirable.
• Low power factor causes an increase in reactive current, resulting in additional losses of active power in all elements of power system.
• It is important to have power factor as close to unity as possible. Note that leading power factor is also undesirable for power systems.

Power factor for inductive circuit

If the circuit is inductive, the current lags behind the voltage by an angle $\theta$ and power factor is referred as lagging.

Power factor for capacitive circuit

If the circuit is capacitive, the current leads the voltage by an angle $\theta$ and power factor is referred as leading.

Causes of low power factor

• Most AC motors are of induction type (one phase and three phase)
• Arc lamps, electric discharge lamps, welding equipment and industrial heating furnace are operated at low power factor.
• Transformer draws a magnetizing current from the supply. If the transformer draws large amount of magnetizing current at light load, it causes low primary current power factor.

Solved Example: 9145-02

A supply system supplies the load 800 kW at power factor 0.8 leading. Calculate the reactive power. (UPRVUNL JE EE Oct 2021 Shift II)

A. 600 VAR

B. 1000 VAR

C. 600 kVAR

D. 1000 kVAR

Correct Answer: C

Solved Example: 9145-03

In an inductive circuit, if the active and reactive components of line current are equal, then its power factor is: (DSSSB JE EE Oct 2019)

A. 0.707 lagging

B. 0.5 lagging

C. 0.707 leading

D. Zero

Correct Answer: A

Solved Example: 9145-04

The power factor of a D.C. circuit is always: (URSC ISRO Technician B (Electronic Mechanic): Nov 2016)

A. Less than unity

B. Unity

C. Greater than unity

D. Zero

Correct Answer: B

Solved Example: 9145-05

A resistance of 8 $\Omega$, a capacitive reactance of 10 $\Omega$ and an inductive reactance of 4 $\Omega$ are connected to form a series RLC circuit. The impedance and power factor of the circuit will be: (ISRO (SDSC) Technician B (Electrical) April 2018)

A. 16.12 $\Omega$, 0.6 lagging

B. 10 $\Omega$, 0.8 leading

C. 10 $\Omega$, 0.8 lagging

D. 16.12 $\Omega$, 0.8 lagging

Correct Answer: B

Solved Example: 9145-06

The power factor of a circuit in which voltage and current waves are non-sinusoidal is defined as: (ESE Electrical 2015 Paper I)

A. It is the cosine of the angle of phase difference between the voltage and current waves

B. It is the cosine of the angle of phase difference between the two complex waves

C. It is the cosine of the angle of phase difference between two equivalent sine waves having respectively r.m.s. values equal to those of the voltage and current in the circuit

D. It is the sine of the angle of phase difference between the two complex waves

Correct Answer: C

Solved Example: 9145-07

Which of the following is TRUE for the power factor of an AC circuit? (UPRVUNL JE EE Oct 2021- Shift I)

A. Power factor is the ratio of apparent power to real power.

B. Power factor is the ratio of impendence to resistance.

C. Power factor has no unit.

D. Power factor is the sin value of phase angle between voltage and current.

Correct Answer: C

Solved Example: 9145-08

The reactive power component kVAR = ?? (PGCIL DT Electrical Aug 2021 NR III)

A. kW $\tan \phi$

B. kVA $\sin \phi$

C. kW $\cos \phi$

D. kW $\tan \phi$ OR kVA $\sin \phi$

Correct Answer: D

Solved Example: 9146-01

The power factor of a system on a 460 V, 3 Phase, 60 Hz, in which the ammeter indicates 100 amp and wattmeter reads 62 kW will be: (UPSSSC JE Electrical 2015 Paper II)

A. 0.95

B. 0.78

C. 0.65

D. 0.55

Correct Answer: B

Solved Example: 9146-02

A 200 V single phase AC source is connected to a load with an impedance of magnitude 10 $\Omega$ and phase angle +60 degrees. A capacitor is connected across the load and supplies 1000 VAR. The real power supplied by the source is: (DSSSB JE EE Nov 2019)

A. 2000 W

B. 4000 W

C. 1000 W

D. 3000 W

Correct Answer: A

Voltage Regulation is the measure of a circuit's ability to maintain a constant output voltage for changes in load condition or input voltage.

Types of voltage regulators

• Linear voltage regulator: They act like a voltage divider. They give a low output ripple voltage, response time is fast and low electromagnetic interference and less noise. However, their efficiency is low and they require large space, unless heat sink is provided and voltage above the input cannot be increased.
• Switching voltage regulator: A switching regulator with pulse width modulation, constant frequency, varying duty cycle, is efficient and easy to filter out noise.
  • Step up
  • Step down
  • Inverter voltage regulator

Solved Example: 9920-01

The A, B, C, D constant of a 220 kV line are : A = D = 0.94 $\angle$1$^\circ$, B = 130 $\angle$73$^\circ$, C = 0.001 $\angle$90$^\circ$. If the sending end voltage of the line for a given load delivered at nominal voltage is 240 kV, the % voltage regulation of the line is: (CIL MT Electrical 2017)

A. 5

B. 9

C. 16

D. 21

Correct Answer: C

Solved Example: 9920-02

In order to improve the voltage regulation of a supply system, wires used in wiring the system should have ______. (UPPCL JE Nov 2019)

A. High insulation resistance

B. More area of cross section

C. Less area of cross section

D. More specific resistance

Correct Answer: B

Solved Example: 9920-03

The voltage regulation of a shunt transmission line will be maximum when the value of $\tan \phi$ for lagging power factor is: (UPPSC AE Electrical Dec 2020)

A. Unity

B. Zero

C. $\dfrac{R}{X}$

D. $\dfrac{X}{R}$

Correct Answer: D

Solved Example: 9920-04

In a basic transmission line, the voltage at the receiving end without load is 660 V; and it is 420 V with full load. What is the percentage of voltage regulation? (ESE Electronics 2017)

A. 77%

B. 67%

C. 57%

D. 47%

Correct Answer: C