The development of induction motors took place by a French scientist named Francois. He was the person who formulated the presence of revolving magnetic fields which are called Arago’s rotations and this happened in the year 1824. Whereas during the period 1879, Walter Bailey exhibited the same principle through manually switching ON and OFF which is successfully called the initial primitive induction motor. And the first single-phase AC type of induction motor was developed by a Hungarian scientist where he employed a single-phase motor to enhance the invention. And this is how the development of induction motors took place. And now, this article is going to explain the split-phase induction motor, the theory behind the device, its advantages, and its uses.
What is Split Phase Induction Motor?
This device is also called a resistance start motor. The split-phase induction motor theory is explained as follows:
The device is mainly included with a stator and single-cage motor. The stator device consists of two windings which are auxiliary and main windings. In the construction of this device, it has a centrifugal switch which is present inside the motor, it has two shields acting as support for the rotor shaft. This switch has a series connection with the starting/auxiliary winding and this switch is used for the purpose of disconnecting auxiliary winding from the primary circuit.
This induction motor does not contain capacitance in the main circuit, the phase shift to the main current is attained through thin conductors where it leads to a high level of resistance to reactance ratio. By increasing the resistance value, the primary winding can be utilized while starting or else it leads to overheating. The device has minimal torque initially, because of the less phase angle between the two winding currents.
Here, the main winding holds the properties of less resistance and high inductive reactance whereas auxiliary winding is with high resistance value and less inductive reactance. The split-phase induction motor diagram is portrayed as below:
Because of the non-uniform rotating field, the current across both the windings is not similar. So, starting torque is minimal which is almost 1.5 – 2 times more than initial running torque.
Working of Split Phase Induction Motor
Initially, both the windings in the motor are in parallel connection and when the motor gets to 70 – 80% speed level of the synchronous speed, then the initial winding will get automatically disconnected from the main supply. When the rating of the motor is more than 100 watts, then for disconnecting the starting winding, a centrifugal switch is used. Similarly, when the rating of the motor is minimal, then for disconnecting the starting winding, a relay is used.
This relay is in series connection with the primary winding. Initially, there will be a huge amount of current flow in the circuit, and this makes the relay contact move to the closed position. In this way, the auxiliary winding is internal to the circuit and when the motor reaches to specified speed level, then the current flow in the relay tends to decrease so that the relay opens, and auxiliary winding will be disconnected from the power supply. This allows the motor to function only through the main winding.
The phasor diagram based on the working principle for this motor is shown below.
The current present in the main winding lags supply voltage by 900, whereas the current in starting winding is almost in the same phase as the line voltage. So, this tends to create a phase difference between the auxiliary and main windings. But the time phase difference is not in the order of 900 but in 300. This generated phase difference allows the magnetic field to start rotating.
Torque Speed Characteristics
In the below picture, ‘n0’ corresponds to the location where the functionality of the centrifugal switch starts to function. The initial torque of the split-phase induction motor is nearly 1.5 times more than the load torque. Whereas the maximum torque is almost 2.5 times more than the complete load torque when the synchronous speed is 75%. The motor’s initial torque is nearly 7 to 8 times high when compared with the entire load.
The directional path of the motor can be altered by overturning the line connection for either of the windings. But this overturning is possible only when the motor is in standstill condition.
- The initial torque of the motor is almost twice the value of full load torque
- The initial current value is 6 – 8 times more than the normal value
- When the load increases, the speed reduces by 5-7%. If this is not the case, the motor functions as constant speed motor
There are mainly five types of split-phase induction motor and those are:
- Shaded pole
- Permanent capacitor single phase
- Capacitor start & induction run
- Capacitor start & capacitor run
- Resistance start & induction run
Know more about Single Phase Induction Motor.
Advantages and Disadvantages
The advantages of split-phase induction motor are:
- The motor is not expensive and can be easily used in most the domestic applications
- The device can be modified once it wears out before reversing
- These motors are available in multiple frame sizes where this flexibility allows the device to be employed for multiple purposes
The disadvantages of split-phase induction motor are:
- As the motor’s starting torque is minimal, it is not used in the devices that operate above 1 KW
- These are only utilized where a high level of starting torque is required such as air compressors
- The device has a dependency on various resistance and inductance of the auxiliary winding
- When compared with three-phase motors, the split-phase induction motors have less efficiency and output while altering from electrical to functional
Applications of Split Phase Induction Motor
The application of the motor consists of various loads that are utilized for general functionality.
As because of exceptional initial torque and simple direction-reversal features, the device is implemented in lathe machinery, drilling equipment, washing machinery, woodworking equipment, belted type of fans, drill presses, burners those are of oil type, centrifugal pumps, compressors, AC’s, ground polishers, blow dryers, grinding machinery, heating kind of blowers those have belt-driven and used in conveyors consisting of tiny belt-driven, and several other minimal starting torque applications.
This motor is employed in conditions where the distribution of the three phases is not necessary.
This motor does not hold the ability to provide a high amount of initial torque, so that the load has to be very minimal, and also mechanical gain has to be used to stand as support for the motor to start
This is all about split phase motor. The article has explained the concepts of induction motor with split phase, its working principle, types, advantages and disadvantages, and applications. Also, know how the performance varies in each type of split-phase induction motor and their efficiencies?