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Single Phase Motors Characteristics
There are various types of single phase motor. Depending upon their construction and operation, they are having different characteristics. Let us discuss characteristics of each single phase motor one-by-one.
Characteristics of Split-Phase Induction Motor
The single phase split-phase induction motor has following characteristics −
The starting torque of split phase induction motor is 1.5 to 2 times of the rated fullload torque and the starting current is 6 to 8 times of the full load current.
The cost of split phase induction motors is very low, due to which these are very popular in the market.
The starting winding of split phase induction motor is made of fine wire, thus the current density is very high and the winding heats up quickly. Therefore, this type of single phase motor is suitable where starting period is small.
These motors are used in applications where moderate starting torque is required and where starting period is small.
The power rating of such motors lie between 60W to 250W.
Characteristics of Capacitor-Start Motor
The capacitor start motor has better starting characteristics than that of split phase motor.
The phase angle between starting winding current and main winding current is about 80°. Therefore, the starting winding of a capacitor start motor heats up less quickly and therefore, is well suited for applications involving prolonged starting period.
The capacitor start motors are used in the applications where high starting torque is required and where the starting period may be long.
The power rating of capacitor start motors lie between 120W and 750W.
Characteristics of Capacitor-Start and Capacitor-Run Motor
In case of capacitor-start and capacitor-run motor, the starting winding and the capacitor can be designed for perfect two-phase operation at any load. Thus, this motor produces a constant torque.
Because of constant torque, the capacitor-start and capacitor-run motor is vibration free.
Characteristics of Shaded-Pole Motor
The principle characteristics of shaded-pole motor is the extremely simple construction and absence of centrifugal switch.
These motors are suitable only for low power applications because of their very low starting torque, efficiency and power factor.
These motors are available in power ratings upto about 30W.
Characteristics of AC series Motor (or Universal Motor)
The AC series motor or universal motor has following characteristics −
The speed of universal motor increases with a decrease in load, i.e. has high speed at no-load.
The universal motor has a high starting torque.
At full load, the power factor of universal motor is about 90%. However, at the start and overload, the power factor is relatively lower.
Characteristics of Single-Phase Repulsion Motor
The single-phase repulsion motor has a high starting torque and a high speed at noload.
At any given load, the speed developed by the repulsion motor depends upon the position of the brushes.
The single-phase repulsion motor draws a low starting current as compared to other single phase motors.
Characteristics of Repulsion-Start Induction-Run Motor
The starting torque of repulsion-start induction-run motor is about 2.5 to 4.5 times of the full-load torque.
The starting current is about 3.75 times of the full-load current.
Because of their high staring torque, these motors are used to drive devices like pump, compressors etc.
These motor posed a serious problem of maintenance of centrifugal switch, commutator and brushes.
Characteristics of Repulsion-Induction Motor
The no-load speed of repulsion induction motor is slightly above the synchronous speed because of the effect of repulsion winding.
The full-load speed of repulsion induction motor is slightly less than the synchronous speed just like in an induction motor.
These motors have about 6% speed regulation.
The starting current is about 3 to 4 times of the full-load current.
The starting torque is about 2.25 to 3 times of the full-load torque and may be lower for large motors.
This type of motor is suitable for applications which requires a high starting torque and a constant running speed.
These motors are available in power ratings from 0.25 to 0.5 h.p.
Characteristics of Reluctance Motor
The reluctance motors have poor power factor, torque and efficiency.
The high inertia loads cannot be accelerated to synchronous speed by these motors.
These motors have weak pull-in and pull-out torque.
These motors are cheaper than other types of single phase motors.
The reluctance motors are used in constant-speed applications.
Characteristics of Hysteresis Motor
The hysteresis motors have uniform torque from standstill to synchronous speed. Therefore, they can synchronise any load which it can accelerate without affected by its inertia.
A hysteresis motor is quiet and produces smooth rotation, because of the absence of teeth on the rotor or salient poles or windings.
In the hysteresis motor, the rotor takes the same number of poles as the stator field. Therefore, by changing the number of stator poles through pole-changing connections, a set of synchronous speeds can be obtained.
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