single phase electric motors

We have all come across a single-phase motor as it is widely used in homes and workspaces. These motors’ simple build-up, affordability, and dependability are significant reasons for their popularity.

Simply put, a single-phase motor is an electrically-powered rotary machine used to convert electric energy into mechanical energy.

Single-phase motors work on the same principle as 3 phase motors; however, there is a slight difference. Unlike a 3 phase motor, a single-phase motor runs on only one phase. A single-phase motor works on an oscillating magnetic field rather than a rotating magnetic field.

Let us look at different types of single-phase electric motors. 

Split phase motor

It implements an auxiliary winding outside the stator coil to provide the initial phase difference needed for rotation. The starting winding must be shut off once the motor has reached full speed (around 75% of rated speed).

Two-value capacitor motor

These motors use capacitance instead of resistance to shift the starter phase. Once the motor is set at a particular speed, preferably around 75% to 80% of full speed, a centrifugal switch disconnects and restarts the capacitor.

Permanent split capacitor motor

This motor has a series of permanent capacitors with the starting winding. They do not have any centrifugal switch. As a result, these motors are comparatively more reliable than other single-phase motors. 

Shaded-pole motor

This motor is more simplistic than other single-phase motors, as it does not require any extra starter circuits or switches. This causes an unequal distribution of inductive forces across the rotor and causes it to rotate.

Working of a single-phase motor 

A motor is operated based on the torque produced by it. Be it AC or DC motors. They use two fluxes that deliver the required torque. Like other AC motors, single phase electric motors have stators and rotors but operate very differently.

The 120-degree phase separation between 3 AC currents moving through stator windings generates a rotational motion in three-phase motors. Even so, the magnetic field is produced only by a single-phase “pulses” between two motor poles as there’s only one AC generating two potential strong magnetic states (the Current seems to have two sinusoidal peaks, in which the magnetic field lines are equal in magnitude but opposite in alignment, or “up-down”). This comes close to a spinning field, but not quite. So, for the rotor to move, these motors should be given a specific “shove” or feel a force “out-of-phase” with the stator phase. 

If the rotor is not already moving, the pulsating, “up-down” magnetic field will not affect it since their up-down magnetic forces reject each other precisely. Motor starters go around this problem by introducing an out effect (auxiliary windings, capacitors, etc.) that simulates a spinning magnetic field to start the motor.

Wrapping it up:

A single-phase induction motor is much more cost-efficient than other motors. It is used only in the case of low-power applications like pumps, compressors, small fans, etc. The role of these motors is similar in each product. Still, before purchasing any electronic device, you must look for the type of motor used. 

By Manali