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 MOTORSĀ
DC Motors
2. Parallel motors
3. Compound motors
4. Self-excited motors
5. Permanent Magnet DC Motors (PMDC)
SPECIAL MOTORS
2. Brushless DC motor
3. Hysteresis engine
4. Reluctance motor
5. Universal motor
AC Motors
2. Synchronous motor
DC SERIES ELECTRIC MOTORSĀ
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.
DC SHUNT ELECTRIC MOTORSĀ
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.
DC COMPOUND ELECTRIC MOTORS
Specifications of both series and shunt motors are observed in compound type motors and this goes under two following categories:
Ā 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.
WHAT ABOUT AC OR AC MOTORS?
The most common dynamos used in industry and home are AC induction motors.
TYPEES OF AC ELECTRIC MOTORSĀ
Synchronous AC Electric Motors
Asynchronous AC Electric Motors
SYNCHRONOUS AC ELECTRIC MOTORSĀ
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
- No sensitivity to voltage fluctuations
- High efficiency
- Suitable and adjustable power factor
- Direct working with high voltage levels
DISADVANTAGES OF SYNCHRONOUS ELECTRIC MOTORS
- The speed of the motor is constant and cannot be adjusted for higher or lower speeds
- The motor cannot withstand additional load
- 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
- The motor requires an initial starter device that could be an auxiliary motor
ASYNCHRONOUS AC ELECTRIC MOTORS
Squirrel cage
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
- It has replaced other motors in multiple industries due to its reasonable price and design simplicity
- The rotation speed of this alternator is almost constant at different loads
- Changing the load does not stop this type of electric motor
- It has a better power factor than slip ring motors
DISADVANTAGES OF SQUIRREL CAGE ASYNCHRONOUS ELECTRIC MOTORS
- When working with less work, its power factor decreases
- 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
- Squirrel cage asynchronous electric motors are sensitive to voltage changes and if the voltage drops, the current will increase accordingly
- It has low torque
- 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 WINDINGĀ
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
- The generated heat occurs outside the starter
- This alternator has the ability to start in a row and under load
- The starting current of the electric motor is adjustable
- Rotor winding electric motors have maximum torque at the moment of start
AC INDUCTION MOTORSĀ
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 MOTORSĀ
Single-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 ā 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.
