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Universal Motor, Advantages, Disadvantages, Applications, Working

Posted on by Rajasri Mundrathi

Hello guys, welcome back to my blog. In this article, I will discuss universal motor, the advantages of universal motor, the disadvantages of universal motor, applications, working of the universal motor, etc.

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Universal Motor

The direction of rotation of a DC machine depends upon the field current and the polarities of the armature current. A motor designed to operate on both AC and DC supply is called a universal motor. This unique feature makes them preferable for many types of special applications.

Universal motors are designed for voltages ranging from 32 to 250 volts and frequencies ranging from zero to 60 Hertz. High resistance brushes which are made of carbon are used to limit the circulating current.

Construction Of Universal Motor

A universal motor is specially constructed and operates on both supplies. It is also called an AC series motor. When the motor connected to a DC power source, they work just like a DC motor with the help of commutator rings a unidirectional current is always made to flow through the left and right sides of the coil.

The torque action is always unidirectional and the rotor of this universal motor continues to rotate when the same motor is connected to an AC power source.

Working Of Universal Motor

Working Of Universal Motor

As the field coil and rotor coils are connected in series the same phase of electricity passes through the field coil and rotor coils. Always it is obvious that in this case the electricity flowing through the left and right part of the coil is never unidirectional but along with the change in the direction of this current. 

The direction of the magnetic flux also changes as the same electricity flow through field and rotor coils. This simple trick will make sure that the torque action is always unidirectional. Irrespective of the speed of the rotor and frequency of electricity, the torque action is always in the same direction, as a result, the rotor will continue to rotate even under an AC power source.

Principle Of operation

When this motor is fed with a DC power source, then it works as a DC series motor. Current flows through the windings of the conductor and produces an electromagnetic field, then the conductors experience a mechanical force. This direction of force is determined by Fleming’s left-hand rule.

When the universal motor is fed with an AC power supply, a unidirectional torque is developed. This is because armature winding and field windings are connected in series and they are in phase with each other.

The starting torque is relatively very high and having the high-speed capability, the power rating is significantly smaller than other motors. The speed load characteristics of universal motors are similar to DC series motors.

The speed is low at full load conditions and very high at no-load conditions. When the motor is running from an ac source, the commutation will be much poorer than with a DC source. This spark significantly shortens brush life.

Advantages Of Universal Motor

  1. Universal motors are less costly due to their simple construction and no requirement for permanent magnets.
  2. Universal motors provide good torque at low speeds.
  3. They can rotate at high speed due to the connection of armature windings and field windings in series.
  4. Due to its small size and less weight of the universal motor, it is most preferable in many applications.
  5. Eddy current losses are reduced due to the presence of an electromagnetic field and heating is avoided.
  6. Universal motors require low power input to run the motor.
  7. These motors have the capability to run at any given availability speed.

Disadvantages Of Universal Motor

  1. Universal motors produce relatively higher noise and this noise increases with the speed of the motor.
  2. There are high chances of vibrations and these vibrations may damage the motor.
  3. There is no possibility to run the motor in opposite direction.
  4. These motors caused overheating.
  5. Universal motors require frequent maintenance due to brushes and commutators wear out very quickly.

Applications Of Universal Motor

  1. Universal motors are used for many domestic appliances such as vacuum cleaners, sewing machines, etc.
  2. These motors with high ratings are used in blenders, portable drills, etc.
  3. Universal motors are used in polishers and kitchen appliances.
  4. These motors are used in electric shavers.
  5. Grinder

I hope this article may help you all a lot. Thank you for reading.

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Rajasri Mundrathi

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