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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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_______________ is preferred for automatic drives.
Squirrel cage induction motor
Synchronous motors
Ward-Leonard controlled D.C. motors
Any of these
Ward-Leonard controlled D.C. motors
Quick Summary: Ward-Leonard controlled D.C. motors are preferred for automatic drives because they provide smooth, precise, and stepless speed control over a wide range in both directions. This system is essential for applications requiring rapid acceleration, deceleration, and frequent speed adjustments.
Ward-Leonard controlled D.C. motors are preferred for automatic drives because they provide smooth, precise, and stepless speed control over a wide range in both directions. This system is essential for applications requiring rapid acceleration, deceleration, and frequent speed adjustments.
N=kΦV−IaRa — Speed equation of a DC motor
Eb=kΦω — Back EMF relationship
The system utilizes a motor-generator (M-G) set where the output voltage of a DC generator is varied by adjusting its field current. This variable voltage is fed to the armature of the main DC motor, allowing control of motor speed according to the relation N∝ΦEb. By controlling both the field and the armature voltage, the system achieves flexible four-quadrant operation.
Provides precise speed control over a very wide range.
Supports regeneration and rapid braking.
Commonly used in elevators, hoists, and steel rolling mills.
Allows smooth acceleration from zero to full speed.
Stepless speed control
Wide range of speed
Excellent speed regulation
Easy reversal of rotation
Low overall efficiency due to M-G set
High capital cost
Large floor space requirement
High maintenance due to three rotating machines
Steel rolling mills
Colliery winders
Large electric excavators
Elevators
The system is historically significant for heavy industrial drives requiring precision.
Squirrel cage motors (Option A) are typically constant-speed machines.
Synchronous motors (Option B) are used for constant speed and power factor correction.
C is correct — Ward-Leonard controlled D.C. motors are specifically preferred for automatic drives due to their ability to provide smooth, precise, and wide-range speed control.
When comparing drive types for automatic control, always look for the option that offers the highest range of speed flexibility and direction reversal capabilities.