Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
In AC Dynamic braking of induction motor. Three lead connection obtained by
A) disconnecting the one phase from the source
B) disconnected phase leaving it open
C) By connecting the disconnected phase with another phase with line
D) None of these
By connecting the disconnected phase with another phase with line
In AC dynamic braking (also known as single-phase braking) of a three-phase induction motor, the stator is disconnected from the three-phase AC supply and connected across a single-phase AC source. A three-lead connection is established by disconnecting one phase from the supply line and joining that disconnected phase terminal to another phase terminal already connected to the line.
In AC dynamic braking (also known as single-phase braking) of a three-phase induction motor, the stator is disconnected from the three-phase AC supply and connected across a single-phase AC source. A three-lead connection is established by disconnecting one phase from the supply line and joining that disconnected phase terminal to another phase terminal already connected to the line.
TbтАЛ=TfтАЛтИТTbтА▓тАЛ тАФ Net braking torque generated under single-phase AC dynamic braking
sbтАЛ=2тИТs тАФ Slip corresponding to the backward rotating magnetic field
When a single-phase AC voltage is applied across the stator winding using a three-lead connection, it produces two equal and oppositely rotating magnetic fields as per the double revolving field theory. As the rotor rotates, the reverse-rotating component produces a strong backward braking torque. Since the net torque acts opposite to the direction of motion, it rapidly decelerates the motor to a standstill without reversing its direction.
AC dynamic braking is achieved by feeding single-phase AC supply to the stator of a 3-phase induction motor.
A two-lead connection leaves one phase completely open, whereas a three-lead connection connects the open phase terminal to another line terminal to utilize all three stator windings.
The three-lead connection reduces winding impedance, allowing higher current and producing significantly higher braking torque than a two-lead setup.
Utilizes existing AC supply without requiring a separate DC excitation source.
Higher braking torque compared to two-lead single-phase dynamic braking configuration.
Braking torque drops to zero as the motor speed approaches zero, preventing complete holding lock.
Causes higher stator heating compared to DC dynamic braking.
Braking of induction motors in crane hoists and machine tools.
Quick deceleration of industrial drives where separate DC power supply is unavailable.
Option A (disconnecting one phase) only describes removing 3-phase power, but does not specify making the jumper connection for a three-lead terminal.
Option B (leaving disconnected phase open) describes a two-lead connection rather than a three-lead connection.
C is correct тАФ In AC dynamic braking, a three-lead connection is obtained by joining the disconnected phase terminal directly to another phase connected to the single-phase AC line.
Remember: DC dynamic braking produces zero torque at standstill and requires a DC source, while Plugging provides high braking torque down to zero speed but risks motor reversal if not disconnected via a speed-sensing switch.