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Main types of Electric motors

Electric motors have evolved over the years and become more adaptable. They play a crucial role in most segments of every industry. The motors are classified into three major categories; DC motors, AC motors, and special purpose motors.

 

Types of DC Motors

 

Any motor operates on the basis of two components: the armature windings and field windings. The field windings create a static magnetic field while the armature coil looks like a piece of conductor that is always kept in the magnetic field.

 

Because of the magnetic field the armature experiences, it generates torque and rotates the motor shaft. The main classification of these motors is based on armature design and field windings connection. To put it differently, DC motors are based on how armature and field coil are connected to each other.

 

DC Series Motors

 

As the name suggests, the armature and field coils in this motor are connected in a series circuit. This means that the current flowing through the field and armature will be the same. Take an example of armature where current is 1a and field current is 1se. according to the Kirchhoff's current law, total current, in this case, will be 1 = 1a = 1se.

 

Now, check the diagram below. The field coil is carrying the entire armature’s current. Therefore, it should have less resistance. This is the reason it is made with several turns of thick copper wire.

 

 

 

 

 

DC Shunt Motors

 

DC Shunt Motors are designed with an armature and coin windings fitted in parallel connections. Shunt in electricity is used to mean parallel. These motors are very common today. Consider a situation where the armature current is 1a and the field current 1sh. Following the Kirchhoff current law, it would mean that the Total Current 1 = 1a = 1sh, (where sh is shunt field current). The field coil is fixed with full supply voltage. In order to withstand the voltage, the field coils have fine copper wires made of several turns.

 

 

 

DC Compound Motors

 

This motor is a hybrid of DC shunt and DC series models. The motor features both shunt and series fields. The shunt coil is made of few turns of fine thin copper wires for receiving full voltage at the input. Then, the field coils comprise of several turns of thick copper wires for lower resistance path. Indeed, the DC Compound Motor can be broken further into two: the long shunt compound motor and short shunt compound motor.

 

 

Permanent Magnet Motors (PMDC)

 

PMDC motors utilize permanent magnets to create field excitation. The magnets are fitted in a casing while other sections such as DC armature and commutators still remain. Because the field flux is fixed, the speed of PMDC is controlled by regulating the voltage of the armature. These motors are common in battery-operated applications such as trimmers and drills.

 

 

Types of AC Motors

 

Today, AC motors are more common than DC motors because they offer better speed regulation features. The differences are mainly in their operation and internal construction. Here are the main types of AC motors:

 

Synchronous Motors

 

This motor is operated using a 3-phase alternating power supply. The field current that is created by the starter section helps to rotate the motor in constant speed. The rotor has the same speed as that of the stator current.

 

Single Phase Induction Motors

 

This is another very common type of motor in many applications such as blowers and air conditioners. Here, the speed of the rotor is slower compared to that of the synchronous designs. It also depends on the load capacity. If the load capacity is more, the speed will go down.

 

Three Phase Induction Motors

 

These motors operate like the single phase models but differ slightly in that they have applied high voltage. For example, as opposed to single phase models that use 230 VAC power supply, they use 415 Volt supply. The motors are common in heavy applications like air compressors.

 

Special Purpose Motors

 

These motors are designed to perform specific actions. They include stepper motors and reluctance motors.

 

  • Stepper motors: In this motor, the complete rotation angle is broken into a number of steps such as 10 degrees X 18 steps. This implies that in a complete rotation, the rotor will move 18 times. Each time will be 10 degrees. The motors are common in robotics.
  • AC and DC Servomotors: These motors are used where fast response is required. The servomotors can be either DC or AC powered and are smaller compared to others. They are mainly used in robotics and radars.
  • Reluctance motors: This is a single-phase synchronous type of motor whose design closely resembles the induction motors. They help to provide smooth operations that need constant speed and are used in operations such as signal generators.
  • Linear induction motor: These motors offer linear scale movement as opposed to rotary. They use three-phase AC power and are preferred for heavy goods handling.

 

Conclusion

 

This post helps you to demystify the different types of motors so that you understand how they work and pick the right option. If you want more output from a motor, it is important to select the right one.