Difference Between Single Phase and Three Phase Induction Motor

The induction motor is an AC motor that works on the grounds that electromagnetic induction recurs between the stator and the rotor of the motor. In this, the stator creates a rotating magnetic field while the rotor, which is the rotating part, follows this field. Induction motors are also known as asynchronous motors since the rotor rotates at a speed lesser than the synchronous speed of the stator’s created magnetic field. 

Induction motors can be for single-phase or three-phase AC supply systems. In a single-phase induction motor, the rotating magnetic field is not produced as in the case of three-phase induction motors because the currents supplied to the windings are of single-phase AC, which does not create a rotating field. Thus, the single-phase motors are always provided with some form of starting mechanism that will make them rotate. 

A three-phase supply, on the other hand, produces a rotating magnetic field with more efficiency than a single-phase supply. This is because each phase in the three-phase current is one-third of the total current. Hence, it results in producing a smooth and continuous rotating magnetic field. 

If one sums up the features of a single phase and three phase induction motor, the key difference is that the single phase motor is never self-starting while the three phase motor is self-starting. 

Read on to find out more about the difference as we compare single phase and three phase induction motors. 

Single-Phase Induction Motor

Single-phase induction motors are stater AC motors specifically built to be used with a single-phase power supply system. These motors are normally rated as low-power motors, so they can be used in homes and offices because the electric power from the poles is normally single phase. 

Single-phase induction motors, on the other hand, do not possess the ability to self-start like three-phase induction motors. To overcome this limitation, they seek an external starting mechanism like a capacitor-start method. By default, a single-phase AC power supply cannot generate a rotating magnetic field (RMF). Therefore, a capacitor is connected to produce a 90° phase shift in the auxiliary winding to produce an RMF required to start the motor. 

These motors are commonly known as capacitor start induction motors. Other types, depending on their starting structures, are split-phase induction motors, capacitive start and run motors and shaded pole induction motors. 

The RMF produced in a single-phase induction motor is less smooth if the motor uses an auxiliary winding and capacitive voltage for its creation. This may lead to operational vibrations, noise, and the shortening of the motor’s life span. It must also be noted that the Single-phase power supply is usually cheaper and less reliable than the three-phase power supply.

Three-Phase Induction Motor

A three-phase induction motor is mainly an AC induction motor that works on the electricity supply in three phases. It might be connected to the supply in either a star or delta connection, depending on the load needed. Usually, these motors are high-power motors that are used in industrial applications. 

The three phase induction motor performs well in creating a rotating magnetic field in the stator windings. This is made possible by the three sinusoidal currents that are present in the windings; they are displaced by 120 degrees. Such an arrangement results in the formation of a smooth, continuous RMF that results in improved performance as compared to single-phase motors that incorporate a capacitor-start. Three-phase power delivers a very smooth RMF that keeps motor vibrations and noise levels to a bare minimum. 

The three-phase power supply is highly reliable and cheaper than a single-phase power supply. The power supply is not fully dependent on one line because there is a fault, and at the same time, the current distribution is divided into several windings. This, in turn, minimises the losses at the copper level and improves the general efficiency. 

Three-phase induction motors are well equipped to handle a densely mechanical load, which is common in many industries. At a higher rating of power, they provide higher efficiency and performance compared to single-phase motors of a similar rating, giving better motor losses. Thus, they are less expensive in the long run, though they may be more expensive to buy initially. 

Three-phase induction motor stator and rotor construction are a little more complicated than that of single-phase types, and therefore, the manufacturing expenses are high. This is an added advantage because they offer better performance and are efficient when used in applications that require extra performance. 

Difference Between Single Phase and Three Phase Induction Motor

Below is a detailed table comparing a single phase and three phase induction motor. 

Read More - Induction Motor: Working Principles, Basics & Types Explained

To Sum Up

It is easier to restore the single phase from the three phases, and as a result, single phase induction motors are more reliable in comparison to three phase ones and are recommended for applications in which the load is not large, for example, home appliances and office devices. They are cheaper and less complex in their design, and their application is mostly recommended where power requirements are relatively low, and the devices are easy to service. 

In contrast, the three phases are designed to give better performance in applications that entail heavy loads like driven machinery and large industries. The full outline of three-phase motors lies in the capability of creating a smooth, continuous rotating magnetic field, which in turn enables high efficiency, low vibration, and reliable operating characteristics that become evident under the worst conditions. This makes them the best for industrial use since they provide performance and durability in the work setting. We hope this blog highlighting the difference between single phase and three phase induction motors has answered all your questions. You can buy both these motors from our eShop after you pick the most suitable one for your application- https://eshop.se.com/in/.

Frequently Asked Questions

Q1. How do the sizes of single phase and three phase motors compare?

Ans: Single-phase motors are typically larger for the same power rating due to the need to handle higher currents. Three-phase motors are more compact for equivalent power outputs.

Q2. How is the rotating magnetic field (RMF) generated in a single-phase induction motor?

Ans: In a single-phase induction motor, the RMF is generated using an auxiliary winding and a capacitor, which create a phase shift to produce a rotating magnetic field.

Q3. How is the RMF generated in a three-phase induction motor?

Ans: In a three-phase induction motor, the RMF is generated by the three-phase currents flowing through the stator windings, which are 120° apart, creating a smooth, continuous rotating field.