Basic Electronics and Electrical Engineering: Chapter 5: Induction Motors
Capacitor Start Induction Motor
Construction, Working Principle, Circuit Diagram, Characteristics, Applications
The capacitor‒start motor is identical to a split‒phase motor except that the starting winding has as many turns as the main winding.
CAPACITOR
START INDUCTION MOTORS
The capacitor‒start
motor is identical to a split‒phase motor except that the starting winding has
as many turns as the main winding. Moreover, a capacitor C is connected in
series with the starting winding as shown in Fig. 5.29 (i). The value of
capacitor is so choosen that IS leads Im by about 80°
(i.e., α=80°) which is considerably greater than 25° found in split‒phase motor
[Ref Fig. 5.29 (ii)]. Consequently, starting torque (TS = kImIs
sin α) is much more than that of a split‒phase motor. Again, the starting
winding is opened by the centrifugal switch when the motor attains about 75% of
synchronous speed. The motor then operates as a single‒phase induction motor
and continues to accelerate till it reaches the normal speed.
Characteristics of Capacitor start Induction motor
The characteristics of
capacitor start induction motors are
1. Although starting
characteristics of a capacitor‒start motor are better than those of a split‒phase
motor, both machines possess the same running characteristics because the main
windings are identical.
2. The phase angle
between the two currents is about 80° compared to about 25° in split‒phase
motor. Consequently, for the same starting torque, the current in the starting
winding is only about half that in a split‒phase motor. Therefore, the starting
winding is only about half that in a split‒phase motor. Therefore, the starting
winding of a capacitor‒start motor heats up less quickly and is well suited for
applications involving either frequent or prolonged starting periods.
Applications of Capacitor start Induction motor
Capacitor‒start motors
are used where high starting torque is required and where the starting period
may be long. e.g., to drive
• Compressors
• Large fans
• Pumps
• High inertia loads
The power rating of
such motors lies between 120W and 7.5 kW.
Basic Electronics and Electrical Engineering: Chapter 5: Induction Motors : Tag: Basic Engineering : Construction, Working Principle, Circuit Diagram, Characteristics, Applications - Capacitor Start Induction Motor
Basic Electronics and Electrical Engineering: Chapter 5: Induction Motors
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