Electric Motor Types

Electric Motor Types
Squirrel cage induction motor

Electrical motors are commonly used in almost all industries. Motor types are usually divided in two major types according to the power source type, AC and DC motors.

AC electrical motors

This type of motors is used in a variety of applications starting from domestic to large factories and oil and gas fields. This type are working on AC power source.

AC motor types

AC motors are induction and synchronous, while induction motors are two types, single and three phase induction motors.

AC induction motors are the most used types of motors in almost all industries. And could be divided in two, single phase and three phases induction motor.

Three phase induction motor

Three phase induction motor is well known as self starting motor, as it needs no capacitor to start. While single phase type needs this start capacitor. Three phase type also draws less current than single phase motor of the same power rating. As shown in the below example.

Example:

10hp three phase motor working on 400V power source, and 0.95 power factor then the current will be I = P /(1.73*V*pf) = 11.6 A

While 10 hp single phase motor working on 110V power source, and pf = 0.85. Then its current I = p/(V*pf) = 79.78A

This example shows that if you have a mechanical load of 10 hp, So its much better to drive it with 3 phase motor. Now, you may ask the following important question:

Why 3 phase motor if better? while the load still the same 10 hp, and it will draw the same amount of electrical energy! You are right. The consumed power is the same in both cases.

But the current is not the same which means the protection and control accessories (such as circuit breakers, relays, and contactors) as well as the power cable, will be designed at lower current rating and then it will cost less.

I have written a detailed article about three phase induction motor you can find it here.

Single phase Induction motor

 A Single phase Induction motor is a type of motor having single phase winding. The winding is mounted over the stator. While the cage winding is placed on the rotor.

When the single phase power supply connects to the winding of the stator. It produces a pulsating magnetic field. Now the rotor of the is rotated by some other source. Because when we connect supply, the rotor does not self start. It will need special starting means.

Once the rotor starts rotation by some auxiliary source while the stator connects with Power Supply, the single phase induction motor starts rotation.

Parameters of Single phase Induction motor

phase induction motor consists of stator and rotor.The construction of this type of motor is just like squirrel’s cage three-phase induction motors.  We will explain each part briefly.

Stator

As clear from its name stator is the static part of the induction motor. In a 1 phase Induction motor, the number of windings in the stator are two.

To reduce the eddy current losses the stator of this type of motor has laminated stamping.

Similarly, to reduce the hysteresis losses the stamping is made of silicon steel. Once we connect a single phase power supply to the stator windings, the magnetic field produces.

Rotor

The rotor is the rotating part of the induction motor. It connects load via shaft.The rotor of a single-phase induction motor is cylindrical, and its periphery has slots.

The rotor consists of bars made of aluminum, copper, or brass. The copper or aluminum bars are also called rotor conductors. These bars are mounted  over the perimeter of the rotor.

The rotor conductors are also called end rings. These rings are made of aluminum or copper. No brushes or slip rings exist in a single-phase induction motor.

working principle

In Single-phase Induction motor, when we apply AC power to windings of the stator. It produces flux called Main Flux. In the same time rotor conductor links with main flux.

During this process, the EMF is induced. Once the rotor circuit closes, the current flows in a rotor. The rotor current produces rotor flux. Now two main flux and rotor flux produces torque. And the motor starts rotating.

Due to initial resistance, the motor rotates at slightly less speed than the synchronous speed. The formula for the synchronous speed is

speed formula
speed formula

Where

  • F is the frequency of Supply Voltage
  • P  denotes the number of poles  of Motor

DC electrical motors

DC Motor is a type of electrical motors which uses direct current as a source of electrical power and converts the power into mechanical energy.

Working principle of DC Motor

The DC motor works on the principle of the magnetic field. When the Electric field and magnetic field interact, the torque produces.

Or, simply when a current-carrying conductor is placed in a magnetic field it produces a mechanical force on the conductor. The working principle of DC motor are also the same.

The next step is to find the direction of rotation. We use Fleming’s Left-hand rule to find the direction. The speed of the DC motor depends upon the emf. The formula for generated emf is.

emf
emf

Where

  • P is the Numbers of poles
  • φ is flux per pole
  • Z is the Numbers of conductors
  • N is the speed of the DC motor
  • A is the Numbers of parallel paths

Types of DC Motors

Nowadays DC motors are commonly used. It has different applications. Based on different applications DC motors are divided into four main types. i.e. permanent magnet, series, shunt, and compound DC motors.

We will discuss each type of motor in detail.

Permanent Magnet DC Motors

In this type of DC motor, a permanent magnet is used for creating flux. The main usage of this type of motors is low horsepower applications, like windshield wipers, Blowers, and washers.

Besides this, in other applications where speed control is not necessary, this type of motors is the best choice. These types of motors provide enough speed regulation and starting torque.

Series DC Motors

This type of motor is also called series wound motors. In this type of motors, the field winding is connected in series with the armature winding.

Series DC motor produces a large amount of starting torque. One of it limitation is that it cannot regulate speed. These are not fit for variable speed and If it is run with no load the coil can be damaged.

Shunt DC Motors

In this type, the field winding is connected in parallel (shunt) with the armature windings. If you need better speed regulations, this type of motor is the best choice. Shunt Motors offer better speed regulation.

Centrifugal Pumps, Weaving Machines, Lifts, Conveyor built, Lathe Machines, Fans have these types of motors.

Compound DC motor

Compound type is the combination of both series and Shunt DC motors.In this type of motors, the armature windings & field windings are connected in both shunt and series combinations.

Due to their combined characteristics, these types of motors offer good starting torque. Also, it is used in variable speed applications.

Let’s answer some important question about electric motors.

Why Is Single Phase Induction Motor Not Self-Starting?

It is not possible to self-start a single-phase induction motor. because induction motors powered by a single-phase supply produce pulsating magnetic field, not rotating. A conductor produces flux when a current flows through it. This flux has two components, each rotating in the opposite direction at the same speed (slip). This results in zero net flux, no induced current in the rotor conductors, and zero torque.

A single-phase induction motor features a squirrel-cage rotor and distributed stator windings. When its stator winding is fed from a single-phase supply, the flux (orfield) produced alternates along one space axis only.

In contrast to a two- or three-phase stator winding fed from a two- or three-phase supply, the flux is not synchronously rotating. As a result, we see that fluxes acting on a squirrel-cage rotor under alternate or pulsating conditions cannot produce rotation (only rotating fluxes can). Because of this, a single-phase motor cannot self-start.

Read my detailed article three vs single phase motor.

Which Type Of Motor Is Used In home appliances?

A permanent split capacitor (PSC) Motor, a single-phase alternating current (AC) motor, more precisely a split-phase induction motor, Is Used In Ceiling fans, Washing Machine, Refrigerators and Air Conditioner, in which the capacitor is permanently linked (as opposed to only being connected when starting.

There is a need for a mechanism to start the motor rotating when using the single-phase power supply found in residential appliances to drive a motor. A PSC motor can do this by using separate main and secondary windings where the main winding is connected directly to the power supply.

In contrast, the secondary windings are connected via a capacitor. The current flows through the primary winding first, then through the secondary winding with a slight delay caused by the capacitor.

A phase difference between the main and secondary winding current produces this change in the magnetic field, which alternates between the two windings and generates a torque that starts the motor rotation.

  • Lift Elevator uses 3 phase induction motors with VFD to control the speed smoothly, however, in the old days, DC motors were common to be used in Lift Elevator.
  • Conveyor Belts use 3 phase induction motor, geared motors or brushless DC motor depending on the speed, torque and operation periods.
  • Some home appliances uses universal motor, they are used in mixing grinders and power tools.

Why Is Induction Motor Called Asynchronous?

In simple Words, the stator and rotor do not revolve at the same speed, resulting in no rotor-stator synchronization. The actual speed of the motor is not equal to the synchronous speed. Due to this, an induction motor can be considered an asynchronous motor.

As the name implies, induction motors function on the induction of current in the rotor due to the stator’s changing flux. When a voltage is given to the induction motor’s stator, current flows through the winding, resulting in an induced current in the rotor owing to changing flux in the stator.

A trailing flux will be produced due to the current flow in the rotor, and the rotor will eventually rotate owing to the torque induced by these fluxes. Because rotor flux relies on stator flux, it will always lag behind the stator, so rotor speed will always be smaller than stator speed.

As a result of the lack of a separate excitation source for the rotor, the induction motor is referred to as an asynchronous motor. The induction of current in the rotor determines its movement. It is always lagging behind the stator; the rotor always rotates at less than synchronous speed.

Why Some Motors Have Brushes and Other Not Have Brushes?

Commutator of a universal motor
Sebastian Stabinger Paethon, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons

Motors with permanent magnets on the rotor don’t need a commutator or brushes. While motors with a coil on the rotor needs a commutator and brushes to feed the rotor coil and cause the current flow in the coil to alternate in direction.

Magnetic inductance is the phenomenon that allows a core wrapped in a coil of current-carrying wire to behave like a magnet in a brushed motor. When such a coil is wrapped around an armature and put in a permanent magnet’s field, the armature spins such that its poles line with the permanent field.

If the direction of the electrical current stays constant, the armature will cease rotating when its poles are as close to the opposing poles of the permanent field as feasible. However, if you can change the current direction just as the coil hits this equilibrium point, the coil will continue to spin. The commutator and brushes are in charge of this.

The commutator is separated into detached portions, and each section contacts the brushes in turn as the armature rotates. There are two brushes, each connecting to the battery’s opposing pole.

This guarantees that the current flowing to the coils continually changes direction while the rotor rotates. This causes the magnetic field to reverse, allowing the rotor to continue spinning.

Brushless motors, like brush motors, use magnetic induction and have a rotor and a stator. The distinction is straightforward: the permanent magnet is positioned on the rotor rather than the stator, and the electromagnets are located on the stator.

The commutator and brushes are no longer required. The electromagnets are directly linked to the battery, and the polarity may be switched through a control circuit.

Do Ac Motors Have Brushes?

Depending on the type of motor, not all AC motors have brushes; the most common AC motor is the asynchronous squirrel rotor type, which does not require brushes since the rotor has short-circuited rings that enable current to flow owing to the magnetism generated in the rotor.

The synchronous motor is the second AC motor type, which uses brushes to put current through the rotor.

Basically, brushes operate by transporting current back and forth between the motor’s stationary and moving sections, therefore preventing motor damage. Instead of having an inherent element of the machine wear away due to this process, these are easily replaceable wear parts.

How To Tell If Motor Is Brushed Or Brushless?

Examine the motor; if it’s an open wound motor, which means you can see inside via air holes in the casing, you should be able to see a commutator if it has brushes.

carbon brushes
carbon brushes

A commutator is a ring of copper “teeth” affixed to the motor’s non-drive end and is where the brushes make contact with the rotor inside. If this is the case, you should also see an access port on either side of the commutator, which is used to remove the carbon brushes and replace them as they wear.

If the motor is sealed and has no external features, it is most likely an induction motor with no brushes. If it’s a single-phase motor with a huge “lump” on one side, it’s a capacitor, and the motor is another form of induction motor.

What Is The Most Power Full Electric Motor Type?

Three phase Induction motors are the most powerful motors available in the market. Occasionally, you will come across a huge synchronous motor, but induction motors are the workhorse when it comes to the world of big motors.

As it is cage type motors, you will need to be careful while you start them, and you should do this every time. We anticipate a voltage of somewhere in the range of 11Kv, and the insulation will be class F.

It is becoming clear that the commutator for motors will become increasingly large when the power of the motors is above 20MW.

When you have this sort of power, you’re probably pumping a lot of water or having a similar application, so you probably don’t need fine control of rotor speed, just loads of torque and power.

What Are The Types Of Starter Motors Used In Automobiles?

The most common starter motor used in automobiles is electric starter brushed motor. However, there are three types of starting motors used in automobiles.

Car starters were developed to replace the laborious methods of starting internal combustion engines widespread in nineteenth-century automobiles. Starter motors have progressed significantly since their inception in the early 1900s. Let’s have a look at starter motors quickly.

Electric Starter Motors

Electric starters are extensively utilized in gasoline and diesel engines. These starters are made from a magnet or a DC motor with a starter solenoid connected to the top.

When you turn on the ignition, DC power is given to a solenoid, which meshes the pinion with the flywheel’s starting ring gear. In recent years, many electric and magnetic starting versions have been employed.

Planetary Gear: 

A permanent magnet is used to link the pinion shaft and armature. Because of the direct connections, it can spin faster and provide greater torque.

Permanent Magnet Gear Reduction: 

Instead of a coil starter, it employs 4 to 6 magnets. The current is transmitted directly to the armature, which saves energy usage.

Offset Gear Reduction:

 This starter adds a gear train between the motor and the shaft. This allows it to create more cranking torque while being lightweight.

Pneumatic Starter

Pneumatic self-starters are commonly seen in big diesel and gasoline engines. It comprises a pressure tank, an air compressor, and a geared turbine. When the compressed air is released from the chamber, it spins the turbine and the flywheel’s gears.

Hydraulic Starter Motors

Hydraulic starter motors are used in diesel engines with 6 to 16 cylinders. These spark-free starting motors are regarded as safer than conventional varieties.

Pumps, valves, reservoirs, filters, and piston accumulators comprise the system. The motor is based on an axial piston motor design that can provide high torque regardless of temperature.

What Type Of Electric Motor Is Used In Gas Turbine?

We used electric starter motors and electric pre lubricating pumps to start the gas turbines. These are 3 phase ac induction motors also used as variable speed drives to make the gas turbines run smoothly.

A controlled starter system and a controlled fuel system are components of a starting system of a gas turbine. The regulated starting motor is accelerated along with an acceleration profile to a residence point.

Concurrently with the starting motor spinning up the gas turbine engine rotor, the fuel system controller instructs the pump motor to operate the fuel pump at a speed that fills the fuel line volumes and establishes appropriate pressure for fuel customization at light off.

Because the fuel pump motor and starter motor are regulated and coordinated independently, the starter motor keeps the gas turbine engine at the specified residence point until ignition happens.

The starting motor also delivers a regulated amount of aiding torque during gas turbine acceleration, reducing thermal transients and thereby increasing gas turbine engine operational life. 

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