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Home > News & Articles > Universal Motor: Construction, Application, Characteristics, Types and Working
Updated on 03rd April, 2023 , 6 min read
A universal motor is a type of motor that can operate on both AC (Alternating Current) and DC (Direct Current); this motor is therefore called a Universal Motor. The electric motor, which is a mechanism capable of turning electrical energy into mechanical energy, was created by Michael Faraday and Henry Joseph. The motor generates a rotational motion by utilizing the magnetic fields generated by the rotor and stator. Universal motors can even run on all frequencies, making them widely adaptable.
Universal Motor can work with nearly the same features on both an AC and a DC power source. It is referred to as 'Universal' because of its ability to work at all power levels.
Most universal motors are designed to run at rates of up to 3500 RPM. These motors operate faster on a DC source than they do on an AC supply of the same voltage. This is owing to the reactance voltage loss, which exists only in AC and not in DC.
The construction of a universal motor is relatively simple and consists of two main parts: the stator and the rotor.
The stator is the stationary part of the motor and is made up of a series of electromagnets. These electromagnets are typically arranged in a circular pattern around the inside of the motor housing. The number of electromagnets can vary depending on the size and power rating of the motor. The stator is usually made of laminated steel to reduce eddy current losses.
The rotor is the rotating part of the motor and is typically made up of a series of conducting bars that are arranged in a cylindrical shape. These bars are usually made of copper or aluminium and are connected by two end rings that complete the circuit. The rotor is mounted on a shaft that is supported by bearings and is free to rotate within the stator.
The rotor and stator are connected by a set of brushes that contact the commutator. The commutator is a segmented ring that is mounted on the rotor shaft and is connected to the rotor bars. As the rotor spins, the brushes contact different segments of the commutator, which changes the direction of the current flow through the rotor windings.
When a universal motor is supplied with a DC power source, it operates similarly to a DC series motor with brushes. The current flows from the field coils on the stator to the commutator through the brushes and reaches the armature coils or rotor winding. Each segment of the commutator conducts current in the same direction, which produces an electromagnetic flux. As a result of the magnetic field around it, the current-carrying armature conductor experiences a mechanical force or torque, causing the rotor to spin. The motor operates with high efficiency in this configuration.
On the other hand, when the universal motor is subjected to an AC power source, the current flows in different directions in the opposite coils. To address this, a series connection is used, which causes the polarity change and magnetic flux in the winding to reverse simultaneously. As a result of the unidirectional magnetic field and torque action, the rotor rotates in the same direction despite the alternating current. However, the efficiency of the motor is much lower when using AC power.
Connecting a DC series motor to an AC power source results in significant losses due to eddy currents and a fluctuating magnetic field. Therefore, to prevent this, the stator windings and armature are laminated. To change the direction of the motor's rotation, either the stator or the rotor winding connections need to be reversed.
The two types of Universal Motor are:
This motor has concentrated poles and is used for appliances that require minimal power. High resistance brushes are used in the motor's construction to enhance commutation.
A distributed field winding is used in this form of motor. The compensating winding is an additional winding in addition to the main field winding. When the motor is supplied with alternating current, the additional winding reduces the high voltage reactance in the armature caused by the alternating flux. It is found in high-powered equipment.
The compensating winding is incorporated into the pole faces and linked to the armature in sequence. The compensating windings magnetic field cancels out the armature's cross-magnetic flow.
Overall, the versatility, efficiency, and ease of control of universal motors make them an excellent choice for various industrial, commercial, and domestic applications.
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