Types of Faults and Condition Monitoring Methods of Induction Motors

Types of Faults and Condition Monitoring Methods of Induction Motors

Maheswari M. (Malla Reddy Engineering College, India) and Gunasekharan S (Malla Reddy Engineering College, India)
DOI: 10.4018/978-1-5225-6989-3.ch007

Abstract

Induction motors are the electromechanical devices used to convert electrical energy into mechanical energy and work under the principle of mutual inductance. They have stator and rotor as two major parts. They run at constant speed when the supply voltage and frequency are constant and are suited for constant speed drives. They have rugged construction but working environment causes different faults. As per IEEE and EPRI study on induction motor faults, bearing fault and stator faults are 46% and 36%, respectively. The broad categories of the fault are stator winding fault, broken rotor fault, rotor mass unbalance fault, bowed rotor faults, single phasing fault, bearing fault, and crawling. Unbalanced stator voltage and current, oscillations in torque, drop in efficiency and torque, overheating and unwarranted vibration are the effects of these faults. Undetected faults cause complete failure of motor and it is costly in terms of lost production time, maintenance cost, and wasted raw materials.
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Introduction

Induction motors are the electro mechanical device used to convert electrical energy into mechanical energy. It works under the principle of mutual inductance such as transformer. So it is also called as Induction motor. It is also known as rotating transformer because of its similar operating principle. The invention of induction motor made most of the industrial operations as automatic process. An induction motor consists of magnetic circuits interlinking two electrical circuits placed in two main parts of the machine. The major two parts of induction motor are stator and rotor as shown in Figure 1. The stationary part of the motor is called as stator and the rotating part is known as rotor. The transmission of power takes place from one part to other through electromagnetic induction principle. In general, stator and rotor consists of two circuit namely electric circuit and magnetic circuit as discussed by Sen (1989). The electric circuit is made up of insulated copper or aluminium which is used to carry the current . The circuit made up of laminated magnetic materials used to carry magnetic flux is known as magnetic circuit is shown in Figure 2.

Figure 1.

Cross Section View of Induction Motor

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Figure 2.

Magnetic Circuit of Induction Motor

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Construction

The major parts of induction motor are stator and rotor. Stator is the stationary part and rotating part is called as rotor. The parts of induction motor are

  • 1.

    Stator

  • 2.

    Rotor

  • 3.

    End Flanges

  • 4.

    Bearings

  • 5.

    Shaft

  • 6.

    Cooling Fan

  • 7.

    Terminal Box

Let us see the structure and functions of each part in detail.

Stator

Stator is a stationary part of the motor and it consists of (a) Outer cylindrical frame (b) Magnetic path and (c) Set of insulated electrical windings as shown in Figure 3.

Outer Cylindrical Frame

Cylindrical frame is made up of cast iron or sheet steel or cast aluminium alloy. It has feet for foot mounting of the motor or a flange for mounting of the motor.

Magnetic Path

It consists of a set of slotted high grade alloy steel laminations which is supported by the stator frame. Magnetic path is laminated to reduce the eddy current loss and heating.

Set of Insulated Electrical Windings

The stator has three sets of coils one for each phase and are separated by 120° for a three phase. These windings are placed inside the slots of the laminated magnetic path.

Figure 3.

Stator of an Induction Motor

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