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
If starting winding of a single-phase induction motor not connected during starting?
Damage the starting winding
Damage the running winding
nothing will happen
the motor operates with a lower speed
Damage the running winding
Quick Summary: A single-phase induction motor is not self-starting because it produces a pulsating magnetic field rather than a rotating one. If the starting winding is not connected, the rotor remains stationary, and the running (main) winding draws a massive stalled-rotor current, which causes the winding insulation to overheat and potentially burn out.
A single-phase induction motor is not self-starting because it produces a pulsating magnetic field rather than a rotating one. If the starting winding is not connected, the rotor remains stationary, and the running (main) winding draws a massive stalled-rotor current, which causes the winding insulation to overheat and potentially burn out.
Ist≈(5−7)×Irated — Stalled rotor current magnitude
Tstart=0 — Starting torque without auxiliary winding
In a single-phase induction motor, the torque T=0 at standstill. To initiate rotation, the starting winding creates a phase-shifted auxiliary magnetic field. Without this, the motor behaves like a transformer with a short-circuited secondary, drawing high currents (5 to 7 times the rated current) continuously, leading to thermal failure of the main winding.
Single-phase motors are not inherently self-starting.
A stationary rotor acts as a transformer secondary short-circuited at standstill.
Excessive current causes I2R heating, which exceeds the thermal rating of the main winding.
Centrifugal switches are commonly used to disconnect the starting winding after reaching 75-80% of rated speed.
Simplicity in construction
Low maintenance cost for household appliances
Not self-starting without auxiliary circuits
High starting current leads to voltage dips
Fans
Refrigerators
Washing machines
Option A is incorrect because the starting winding is disconnected; it cannot be damaged by a current that doesn't flow through it.
Option D is incorrect because the motor will not reach any speed; it will remain at zero RPM (stalled).
B is correct — If the starting winding is not connected, the motor remains at a standstill, causing the running winding to draw excessive current and overheat.
Always remember that in electrical machines, 'stall' condition is synonymous with maximum current draw, which is the most common cause of winding failure due to excessive heat.