The figure below shows the most common electric motor. These are categorized based on the input supply, construction, and operation mechanism, and are described further below.
1 DC Motor
Direct current motor, as the name implies, uses a direct current indirect / direct-unidirectional. DC motors are used in special applications where high torque or acceleration over a broad speed range.
DC motor which has three main components:
DC motors
The polar terrain.
Simply put, the interaction of two magnetic fields causes the rotation of the DC motor. DC motor has a stationary field poles and armature that moves in the space between the bearing field poles. A simple DC motor has two field poles: a north pole and a south pole. Magnetic lines of force extend across the opening between the poles from north to south. For motors larger or more complex contained one or more electromagnets. Electromagnet receives electricity from outside resources as the field structure.
Dinamo.
When the current goes through the armature, it becomes an electromagnet. Cylindrical dynamo, connected to the countershaft to drive the load. For the case of a small DC motor, the armature rotates in a magnetic field formed by the poles, to the north and south magnetic poles change locations. If this is the case, the current is reversed to transform north poles and south dynamo.
ƒCommutator.
This component is mainly found in the DC motor. Its purpose is to reverse the direction of the electric current in the armature. The commutator also aids in the transmission of current between the armature and resources.
Advantages Of DC Motor
The main advantage is the DC motor speed control, which does not affect the quality of power supply. It can be controlled by adjusting:
ƒTegangan dynamo - increasing the armature voltage will increase the speed
ƒArus field - reducing the field current will increase the speed.
DC motors are available in many sizes, but its use is generally limited to a few low speed, low power use to moderate such as machine tools and rolling mills because of problems with mechanical commutation at a larger size. Also, they are restricted only for use in areas that are clean and not dangerous because the risk of sparking at the brushes. DC motors are also relatively expensive compared to AC motors.
calculation
The relationship between speed, field flux and armature voltage is shown in the following equation:
where:
E = electromagnetic force that developed the dynamo terminals (volts)
Φ = flux field is directly proportional to the field current
N = speed in RPM (revolutions per minute) T = electromagnetic torque
Ia = armature current
K = constant equation
Characteristics of DC Shunt Motor
Characteristics of DC shunt motor
Here on a shunt motor speed (ETE, 1997):
The speed is practically constant independent of load (up to a certain torque as speed decreases, see Figure above) and therefore suitable for commercial use with a low initial load, such as machine tools.
Speed can be controlled by means of inserting resistance in series with the armature arrangement (reduced speed) or by inserting resistance in the flow field (velocity increases).
2 Motor AC
Alternating current motor uses an electric current that reverses direction on a regular basis at regular intervals. The electric motor has two basic electrical parts: a "stator" and "rotor" as shown in Fig. The stator is the stationary electrical component. The rotor is the rotating electrical component to rotate the motor shaft.
The main advantage of DC motors over AC is that the speed of an AC motor is more difficult to control. To overcome this disadvantage, AC motors can be equipped with variable frequency drives to control the speed increase reduced power. Induction motor is a motor that is most popular in the industry because of its reliability and easier maintenance. AC induction motors are inexpensive (half or less than the price of a DC motor) and also provide power to weight ratio is quite high (about twice the DC motor).
Synchronous Motor
Synchronous motors are AC motors, working at a steady pace on the frequency of the system. These motors require direct current (DC) for the generation of power and has a low starting torque, and therefore synchronous motor suitable for use beginning with the low load, such as air compressors, motors and generators frequency changes. Synchronous motors are able to improve the power factor of the system, so it is often used in systems that use a lot of electricity.
Synchronous Motor
The main components of Synchronous Motor:
Rotor. The main difference between synchronous motor and the induction motor is that the rotor of the synchronous motor at the same speed as the rotating magnetic field. This is possible because the magnetic field of the rotor is no longer induced. The rotor has permanent magnets or DC-excited currents, which are forced to lock in a certain position when confronted with another magnetic field.
ƒStator. The stator generates a rotating magnetic field which is proportional to the frequency supplied.
This motor rotates at synchronous speed, which is given by the following equation (Parekh, 2003):
where:
f = frequency of the supply frequency
P = number of poles
Induction Motor
Induction motors are the most common motors used in various industrial equipment. Its popularity is due to their simple design, cheap and easy to come by, and can be directly connected to an AC power source
Induction motor has two main electrical components:
Rotor induction motor using two types of rotor:
- Squirrel cage rotor consists of thick conductive rods embedded in slots parallel plots. These bars are short-circuited at both ends by means of short-circuiting rings.
- A wound rotor has three-phase windings, double-layer and distributed.
Created around a circle of stator poles. Three phase digulungi wire on the inside and the other end connected to a small ring that is mounted on the rod as the brush is attached to it.
ƒ
Stator. The stator is made of a number of stampings with slots to carry three-phase windings. It is wound for a definite number of poles. Windings are geometrically spaced 120 degrees.
Induction Motor
Classification of Induction Motors
Induction motors can be classified into two main groups (Parekh, 2003):
Single-phase induction ƒMotor. This motor has only one stator winding, operating with single-phase power supply, has a squirrel cage rotor, and requires a tool to turn the bike. So far this bike is the most common type of motor used in household appliances, such as wind fan, washing machine and clothes dryer, and for the use of up to 3 to 4 Hp.
ƒMotor three-phase induction. Rotating magnetic field produced by a balanced three-phase supply. These motors have high power capabilities, can have a squirrel cage or wound rotor (although 90% have a squirrel cage rotor); and self-starting. It is estimated that approximately 70% of the motor industry uses this type, for example, pumps, compressors, conveyor belts, power lines and grinder. Available in sizes 1/3 to hundreds of horsepower.
Induction Motor Speed
Induction motor works as follows. Electricity is supplied to the stator, which generates a magnetic field. The magnetic field is moving at synchronous speed around the rotor. Rotor current generates a second magnetic field, which is trying to fight the stator magnetic field, which causes the rotor to rotate.
However, in practice, the motor never runs at synchronous speed but the "base rate" is lower. The difference between these two speeds due to "slip / shear" which increases with increasing load. Slip only occurs in an induction motor. To avoid slip ring can be mounted a slide / slip ring, and the motor is called "slip ring motors / slip ring motors".
The following equation can be used to calculate the percentage of slip / friction (Parekh, 2003):
where:
Ns = synchronous speed in RPM
Nb = base speed in RPM
The relationship between load, speed and torque
Figure below shows the torque-speed curve of three-phase AC induction motor with a fixed current. When the motor (Parekh, 2003):
Start ƒ- flame lit there is apparently a high initial currents and low torque ("pull-up torque").
ƒ- Achieve 80% full speed, the torque is at the highest level ("pull-out torque") and the current begins to drop.
- At full speed, or synchronous speed, torque and stator current down to zero.
Torque-Speed Curve AC Induction Motors
