What is an AC Motor : Types, Working & Its Applications

We know that the main function of an electric motor is to convert the energy from electrical to mechanical. There are different types of electric motors available in the market like ac motor and dc motor where its classification can be done based on different parameters like type of power source, output motion type, construction & application. These motors operate through the interaction among the magnetic field of the motor & the flow of current within the winding of a wire to produce force in the torque form that is applied on the shaft of the motor.

These motors can be power-driven through AC (alternating current) sources or DC (direct current) sources, where ac sources are inverters, power grids, generators, and dc sources are rectifiers, batteries. Electric motors are more efficient as compared to other prime movers utilized in transportation, industry & the ICE (internal combustion engine). This article discusses an overview of one of the types of electric motor like AC motor and its working.

What is an AC Motor?

An electric motor like an AC motor works with an alternating current to generate mechanical energy through magnetism blended with AC. The AC motor structure includes coils to generate a rotary magnetic field within an attached rotor toward an output shaft so that a second magnetic field can be generated.

These motors have been used for several years by designers and engineers to apply in different applications. These motors are very helpful in generating stable torque equal to the rated speed. These motors are very simple to handle & can be configured at a less cost.

AC Motor Working Principle

The basic working principle of an AC Motor mainly depends on magnetism. The basic AC Motor includes a wire coil & two permanent magnets nearby a shaft. Once an alternating current is supplied to the wire coil, then it turns into an electromagnet that produces a magnetic field. This motor includes two essential parts like stator and rotor. This stator includes a wire loop, a solid metal axle, freely moving metal parts that conduct electricity, a coil, a squirrel cage, etc.

In the stator of an AC motor, we can transmit the power toward the external coils to make up the stationary part like the stator. The coils of wire can be activated in pairs, in series to generate a magnetic field that turns approximately the exterior of the ac motor.

The rotor is balanced within the magnetic field which is changing constantly because of the rotation thus, based on the electromagnetism law; the magnetic field can generate an electric current within the rotor.

If the conductor used in this is a wire or a ring, then current supplies in a loop around it, or if the conductor is a solid metal piece simply, then eddy current will flow around it. The current induced can generate its magnetic field & based on another electromagnetism law, the rotary magnetic field will rotate also. Once the magnets interact, then the coil of wires & shaft will start to turn the motor.

AC Motor Construction

In an AC motor, there are two essential parts like stator (stationary part) and rotor (rotating part). Apart from these, there are some other parts which are discussed below.

Stator

The stator in the ac motor is an inactive part and the main function of this is to transmit a rotary magnetic field for interacting through the rotor.

Stator Core

The stator core in the motor is designed with laminations or thin metal sheets which are mainly used to decrease energy loss.

Stator Windings

Stator windings in the motor will load together to form a hollow cylinder. The stator core coils slots for the insulated wires are protected. Once the ac motor which is assembled is in process, the connection of stator windings can be done toward a power source. Every coils group with the steel core will turn into an electromagnet once the current supply is provided.

Rotor

The rotating part in the motor is the rotor and it is an essential part that is connected to the shaft. In an AC motor, the most common type of rotor used is the squirrel cage rotor. It is a cylindrical shape that is made through stacking slight steel laminations.

Shaft

The rotor assembly can be formed by pressing onto a steel shaft which expands outside of the motor casing to let the connection to an outside system broadcast the rotating power.

Bearings

Bearings are placed on the shaft of the motor to give support to the rotor & allow rotating. Some types of motors utilize a fan by placing it on the shaft of the rotor to cool down the motor once the shaft is revolving.

In the ac motor, bearings are used to hold the shaft within the place. Here, bearings will reduce the friction of the shaft that is connected toward the casing so that motor efficiency can be enhanced.

Enclosure

The enclosure in the motor includes a yoke or frame & two end brackets. The stator is located within the frame and the rotor is arranged within the stator through a small air gap that separates it from the stator. There is no straight physical link between the rotor & the stator.

The enclosure within the motor guards the inside parts against ecological elements & water. This part includes two end brackets as well as a frame.

AC Motor Speed Control

The applications of AC motors involve mostly in industrial areas wherever these motors are required to control heavy-duty machines. In power plants wherever timeliness & accuracy are very essential for the operation, then AC motors have to be controlled. So, a variety of techniques may be used for controlling ac motor frequency & speed.

There are several techniques to control the AC motor speed like altering the number of poles within extremely small increments, altering the motor’s slip & altering the AC signal’s frequency.
From the above techniques, altering the poles is not used regularly as it is not efficient for frequent control.

Another technique like altering the rotor slip of the motor is mostly used once the AC motor is designed mainly for high slip. So by using this technique, this motor should be equivalent to the electric load. So when the power is changed then load speed will be changed. In addition, this load must include extensive inertial components.

The most frequently used technique for controlling the speed of an AC motor is altering the frequency of the motor. By using this technique, AC motor drives with variable speed are utilized to change the motor speed which is known as VFD (variable frequency drives), ASD (adjustable speed drives), or AC inverters.

A six-step inverter, PWN, or vector flux is used to adjust the AC frequency. A variable voltage inverter or six-step inverter mainly changes the power from AC to DC & after that, it switches to reproduce a sine wave. By using the PWM technique, DC voltage is changed quickly to equivalent “area under the curve.”

By considering these AC motor speed control techniques, we can operate a power plant where AC motors are utilized to power fans, pumps, etc. These applications need preciseness to maintain an operation running efficiently. The simple technique is to install consistent AC drives which are mainly designed to control the motor speed precisely.

These methods are available with different control settings so that one can simply discover speed controls to meet the requirements of your application. The main benefits of ac motor speed controls are the operating of machines can be controlled smoothly, acceleration control, production rates can be adjusted, savings of energy, etc.

Types of AC Motor

AC motor is classified into two types like synchronous motor and induction motor.

Synchronous Motor

The main function of a synchronous motor is to change the AC electrical energy into mechanical energy. As the name suggests, this kind of motor works simply at a synchronous speed.

The synchronous motor working principle is, once the power supply is provided to the synchronous motor, and then a rotating field can be formed. So this field seeks to drag the rotor through it, although could not perform due to the inactivity of the rotor. Therefore no starting torque can be generated. So basically this is not a self-starting motor.

Induction Motor

The induction motor is also known as an asynchronous motor. The function of this motor is to change the AC power into mechanical power through electromagnetic induction. This type of motor is simply categorized into two types like the single-phase & the three-phase.

An induction motor working principle is, the armature winding in this motor works like both the windings like armature & field. Once the connection of stator windings can be done with an AC supply, then flux can be generated within the air gap. Here the flux will rotate at a set speed that is known as synchronous speed. So the voltages can be induced through the rotary flux within the stator & rotor windings.

If the circuit of the rotor is closed, then-current supplies throughout the rotor winding & responds through the rotary flux to generate a torque. In the stable condition, the rotor revolves at a very close speed of synchronous speed.

Again induction motor is available in two types like single-phase induction & three-phase induction motor.

Single Phase Induction Motor

Generally, the construction of a single-phase induction motor is similar to a 3- phase motor. The arrangement of AC windings can be done on the stationary part like the stator whereas the short-circuited conductors are arranged within a rotating part like the rotor. The main difference between these two is, there is simply a single-phase supply toward the stator.

If we consider the motor diagram, an ac supply is provided to the winding of the stator, and then a pulsating flux density will be generated, which will connect the rotor circuits. In the rotor circuits, the induced voltage will cause a current to supply, generating a flux density to resist change within the stator flux connected to the circuit.

In the motor, both the flux densities of both the stationary and rotating parts will operate within the y-direction, This easy qualitative analysis specifies an issue, the supplies with a single-phase will generate pulsating fields instead of rotary fields because pulsating fields do not generate torque.

Three Phase Induction Motor

The three-phase induction motors are extensively used for generating mechanical energy within the applications of industries. In industrial areas, most of the motors used are three-phase induction. So as compared to other motors, this motor is the most essential one.

This is one kind of ac motor that works through a three-phase supply as evaluated to the 1- phase induction motor wherever 1-phase supply is required to activate it. The three-phase supply will generate an electromagnetic field within the stator winding which leads to producing the torque within the winding of the rotor of the motor including the magnetic field.

Advantages & Disadvantages

The advantages of ac motor include the following.

• Design is easy & simple
• The power factor is good
• Inexpensive
• An AC source can be directly connected to this motor
• Good power to weight ratio
• Maintenance is less

The disadvantages of ac motor include the following.

• The starting torque of this motor is very less
• At low speeds, it won’t operate
• Poor positioning control
• Limited speed through the frequency supply

There are some problems t could arise like eddy current loss is high, less power factor, sparking within the brushes and there is a chance for an increase within armature & field winding reactance drop.

Applications

The applications of ac motor include the following.

• They are appropriate for projects wherever constant motion & permanent speed are not necessary.
• They are not appropriate for applications that need very fewer speeds.
• These motors are a very good choice for applications that need high performance & torque o/p.
• These motors are used in power tools, clocks, disk drives, fans, blowers, pumps, compressors, conveyors, audio turntables, home appliances, washing machines & industrial areas.

How to Select an AC Motor?

Some factors should be considered while choosing an AC motor

• We have to know the requirements of power; the ac motor should not run across their load as it could be injured
• We have to give a suitable cooling mechanism as the motor could produce a lot of heat
• To avoid breakdowns, we have to offer a dry & clean area for the ac motor
• The motor parts could exhaust, so we should change it by checking the parts
• There is a chance to enter the dirt into the motor while supplying the cooling we should be careful for this, and then we should block the air gap & the cooling ducts. Checking of insulation should be done once in a while to avoid the damage of insulation by applying low test voltage. Need to verify the bearings & rotors of the ac motor to give lubrication toward the motor’s bearing.
• Based on the starting torque, the motor should be selected
• We should consider the starting torque
• Efficiency & pull out torque is a significant factor
• Power factor must be considered

Thus, this is all about an overview of an AC motor, types & it’s working. These motors are used to convert the energy from electrical to mechanical otherwise torque through AC from a generator or power grid. These motors are used in a wide range of applications due to flexibility, efficiency, longevity, availability & quite an operation. AC motors which are used for general purposes also called induction motors which utilize a rotary magnetic field for producing torque for machine tools & powering conveyors. HVAC AC motors are mainly used in blowers, fans, heaters, compressors & air conditioners. In the assembly of a pump, ac motors are used to move an impeller & also used in pump systems for moving water & other fluids. Here is a question for you, what is a DC motor?