Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
The single-phase induction motor is alway operate at ______________ power factor.
Lagging
Leading
Unity
90 degree lagging
Lagging
Quick Summary: A single-phase induction motor always operates at a lagging power factor because it is an inductive load. The presence of stator windings, which are essentially inductors, results in a phase lag between the applied voltage and the current drawn by the motor.
A single-phase induction motor always operates at a lagging power factor because it is an inductive load. The presence of stator windings, which are essentially inductors, results in a phase lag between the applied voltage and the current drawn by the motor.
PF=cos(ϕ) — Definition of power factor
Z=R+jXL — Impedance of the inductive winding where XL=2πfL
The motor draws magnetizing current to create the rotating magnetic field necessary for torque production. This magnetizing current is inductive in nature, meaning it lags the supply voltage by nearly 90°. Since the stator coil possesses both resistance and significant inductive reactance, the net current vector always lags the terminal voltage vector, resulting in a lagging power factor that is typically low, especially at light loads.
Induction motors consume reactive power to sustain their magnetic fields.
The power factor is lowest at no-load conditions due to the dominance of magnetizing current.
Inductive reactance (XL) causes current (I) to lag voltage (V).
Capacitors are often used in parallel with these motors to improve (increase) the lagging power factor.
Simple and robust construction
Lower maintenance requirements
Inherently low power factor
Requires auxiliary winding for starting
Domestic appliances like fans and washing machines
Small pumps and compressors
The power factor of a single-phase induction motor is typically in the range of 0.6 to 0.8 lagging under full-load conditions.
Option B (Leading) is incorrect because the motor does not contain capacitive elements that could cause a leading phase shift.
Option C (Unity) is only possible if the motor is operated in a specific configuration with heavy shunt capacitance, which is not the default case.
A is correct — Single-phase induction motors are inherently inductive loads, which forces the current to lag behind the voltage.
Always remember: whenever you see 'Induction' in a motor or transformer name, expect a lagging power factor due to the excitation current requirement.