ELECTRIC MOTORS

Electric motors convert electrical energy into mechanical motion. Each rotating electric motor consists of two moving parts and an actuator. The moving part is also called rotor and the fixed part that is chiefly inside the motor is also called stator.

TYPES OF ELECTRIC MOTORS 

icon-dc

DC Motors

1. Series motors
2. Parallel motors
3. Compound motors
4. Self-excited motors
5. Permanent Magnet DC Motors (PMDC)
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SPECIAL MOTORS

1. Stepper motor
2. Brushless DC motor
3. Hysteresis engine
4. Reluctance motor
5. Universal motor
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AC Motors

1. Induction motor
2. Synchronous motor

DC SERIES ELECTRIC MOTORS 

DC series motors have high starting torque and hence are used in industries that require high starting torque, such as cranes, hydraulic lifts, impact presses and elevators. This type of dynamo is also used in city locomotives (metro and tram), which is called as traction motor.

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DC SHUNT ELECTRIC MOTORS 

Shunt or parallel DC motors have a maximum torque at nominal speed. Therefore, industrial fans and blowers are other applications of these motors. These types of motors should not be launched under heavy load because their armature current rises too high this damages the motor.

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DC COMPOUND ELECTRIC MOTORS

Specifications of both series and shunt motors are observed in compound type motors and this goes under two following categories:

 1) EXTRA COMPOUND DC ELECTRIC MOTORS:

This type of motors is used in cases where the characteristics of the series motors are necessary, but when removing the load, the motor does not get out of control and its speed does not go too high.

2) DEFECTIVE COMPOUND DC ELECTRIC MOTORS:

This type of motors is used at loads less than nominal loads and in cases where almost constant speeds are required. These motors are commonly used in laboratories to provide a constant speed.

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WHAT ABOUT AC OR AC MOTORS?

The most common dynamos used in industry and home are AC induction motors.

ADVANTAGES OF USING AC ELECTRIC MOTORS
  1. Simple and robust design
  2. Reasonable price
  3. Low maintenance cost
  4. Easy and full connection to a power supply
TYPEES OF AC ELECTRIC MOTORS 
icon-Synchronous-AC-Electric-Motors

Synchronous AC Electric Motors

icon-Asynchronous-AC-Electric-Motors

Asynchronous AC Electric Motors

SYNCHRONOUS AC ELECTRIC MOTORS 

In synchronous dynamos, the rotor and stator are wound. When the stators are connected to the power supply, a rotating field is created in the motor that rotates at a synchronous speed. The rotor is also wound, which is powered by a DC source. By connecting the DC current to the rotor, the rotor begins to rotate with the rotating field of the stator. To start a synchronous electric motor, it firstly rotates at a synchronous speed after disconnecting the primary actuator.

ADVANTAGES OF SYNCHRONOUS ELECTRIC MOTORS

  1. No sensitivity to voltage fluctuations
  2. High efficiency
  3. Suitable and adjustable power factor
  4. Direct working with high voltage levels
DISADVANTAGES OF SYNCHRONOUS ELECTRIC MOTORS
  1. The speed of the motor is constant and cannot be adjusted for higher or lower speeds
  2. The motor cannot withstand additional load
  3. In addition to alternating current for the stator winding, constant current is also required for the poles of the motor, so the price of this electric motors compared to its similar cases is higher
  4. The motor requires an initial starter device that could be an auxiliary motor

ASYNCHRONOUS AC ELECTRIC MOTORS

Squirrel-cage

Squirrel cage

Slip-Ring

Slip Ring

The rotor of squirrel cage motor is cylindrical in shape, in which aluminum or copper rods are placed inside iron or steel grooves, which are made in two ways, the first type is composed of round rods and the second type is rectangular rods, or it is formed as two connected or separated circles. The rotor rods of the electric motor are designed diagonally so that the stator fields on the rotor create a kind of overlap and this prevents vibration or locking at the start moment.

ADVANTAGES OF SQUIRREL CAGE ASYNCHRONOUS ELECTRIC MOTORS
  1. It has replaced other motors in multiple industries due to its reasonable price and design simplicity
  2. The rotation speed of this alternator is almost constant at different loads
  3. Changing the load does not stop this type of electric motor
  4. It has a better power factor than slip ring motors
DISADVANTAGES OF SQUIRREL CAGE ASYNCHRONOUS ELECTRIC MOTORS
  1. When working with less work, its power factor decreases
  2. It is impossible to change the speed of this electric motor by voltage reduction method and it requires a device (AC Drive) to do this
  3. Squirrel cage asynchronous electric motors are sensitive to voltage changes and if the voltage drops, the current will increase accordingly
  4. It has low torque
  5. When starting this motor, they receive a lot of current from the network, about 3 to 7 times the nominal current

ASYNCHRONOUS AC ELECTRIC MOTORS ROTOR WINDING 

The problem with squirrel rack motors is the low resistance of its rotor. The rotor rods are shorted by a loop at the beginning and also the end of the connection. At the moment of start, when the rotor is not magnetic, this attracts a large flux (electric field lines that pass through the surface perpendicular to the path called the electric flux) to magnetize and this increases the current of the electric motor, therefore in the start moment a lot of current from network is taken and the starting torque decreases. To solve this problem, rotor winding electric motors were designed and built, which largely eliminated this defect.

In rotor winding electric motors, instead of a rod in the rotor, the rotor is wound and the ends of these windings are connected to sliding loops that are themselves driven out of the motor by brushes. By placing resistance banks (starter) in the way of these windings, the resistance of the rotor can be increased or decreased and the motor current can be changed as desired.

ADVANTAGES OF ASYNCHRONOUS ROTOR WINDING AC ELECTRIC MOTORS
  1. The generated heat occurs outside the starter
  2. This alternator has the ability to start in a row and under load
  3. The starting current of the electric motor is adjustable
  4. Rotor winding electric motors have maximum torque at the moment of start

AC INDUCTION MOTORS 

AC Induction motors, as most electric motors, have a fixed outer part called a stator and a rotor that rotates inside it. Electric motors use a rotating magnetic field virtually to drive their rotors. The three-phase AC induction motor is the only type in which the rotating magnetic field is naturally generated by the stator due to its feeder nature. DC motors, on the other hand, require an electrical or mechanical device to produce this rotating field. To start a single-phase AC induction motor, an external electrical device is required to produce this rotating magnetic field. Inside each AC motor are two series of magnetic magnets.

TYPES OF INDUCTION ELECTRIC MOTORS 

icon-Single-phase-induction-motors

Single-phase induction motors

Three-phase-induction-motors

Three-phase induction motors

Induction electric motors are usually divided according to the number of stator windings.

HOW TO READ THE LICENSES PLATE OF AN ELECTRIC MOTOR?

On electric motors, a plate is installed by the factory, on which all the information of the motor is brought for start-up, and if the announced items are not observed properly, the motor burns or its useful life is reduced.

No The motor model specified by the manufacturer
Type Engine name, by having the motor name and referring to the manufacturer, more information about the motor could be found
AMPS The maximum virtual current the motor needs to operate
V The operating voltage of the electric motors, no more or less voltage should be applied to the windings of the motor. If there is an asterisk (Y) or a triangle, the voltage is used in the same connection (the operating voltage of the motor above is 415 volts in star mode)
HERTZ Specifies the operating frequency of the motor, the operating frequency of the motor is usually 50 or 60 Hz
Note The speed of electric motors is related to the frequency, so an electric motor that is at a frequency of 50 Hz, for example 1500 rpm, the same electric motor at a frequency of 60 Hz is no longer 1500 rpm
DATE Specifies the date of manufacture
R.P.M Indicates the speed of the electric motor in one minute on the output shaft
KW Indicates the electric motor power
Note If the V amount on the electric motors was 380/220, this means that this should be in a triangle mode in the 110 V power network that is used in some countries and in countries that have a voltage of 220 V (voltage between one phase and null), it should be closed like a star.
IP indicates the protection of the electric motor against dust, according to:
P.H types of protections according to the standard DIN 40050
P00 Open without protection against contact with foreign objects and water, the motor must be kept indoors
P10 Protected from hand contact and large foreign objects – Protected against water, the motor can operate in the open space and under rain
P11 Protected from hand contact and large foreign objects, waterproof
P20 Protected against contact with fingers and medium weight objects without water protection, suitable cover must be provided for the motor
P21 Safe against contact with fingers and medium weight objects, waterproof
P22 Protected against contact of fingers and objects of medium weight, protected against water discharge vertically or obliquely at an angle of more than 30 degrees to the horizon
P30 Protected against contact with tools, lightweight foreign objects, etc., without protection against water
P31 Protected against contact with tools, lightweight foreign objects, etc., waterproof
P32 Protected against contact with tools, lightweight foreign objects, etc., P\protected against vertical or inclined water discharge at an angle of more than 30 degrees to the horizon
P40 and above Protected against all external factors

There may be other useful information on the motors, the user can find out by referring to the product catalog.

1) Input voltage

2) Input current

3) Output torque

and speed

4) The degree of protection indicated by IP

5) Power factor

6) Frame size

7) Installation environment condition

8) Insulation class

9) Efficiency

ENVIRONMENTAL CONDITIONS FOR ELECTRIC MOTORS INSTALLATION
Usually, a series of conditions must be considered regarding the installation environment of the electric motor in order to maximize the life of different parts of the 3-phase motor, such as insulation between windings, bearings, grease used in bearings, and so on. The most important of these conditions are related to temperature, humidity, vibration and altitude at the installation site. The rated power and current of electric motors are usually designed for a maximum temperature of 40 ° C and an altitude of 1000 meters above sea level). If the ambient temperature and altitude conditions exceed these amounts, an electric motor must be less than the nominal amount under load. Quantities and coefficients must be applied according to the manufacturer’s instructions. For example, for a specific manufacturer in the catalog, a table like the one below is given:

The efficiency of the electric motor indicates what percentage of the input power is transferred to the useful work and useful mechanical power (on the shaft) and how much of it is wasted as heat.

The IEC 60034-30-1:2014 standard defines four categories for the manufacture of electric motors in terms of efficiency. These categories with the IE code, which stands for International Efficiency, are as follows:

  • IE1 Standard Efficiency
  • IE2 High Efficiency
  • IE3 Premium Efficiency
  • IE4 Super Premium Efficiency

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