Types of Faults in Three Phase Induction Motor

In electrical machines, an induction motor is a type of alternating current (AC) motor which operates on the principle of electromagnetic induction. Induction motors are classified into two types depending on the power supply used; they are single-phase induction motors and three-phase induction motors. In this article, we will primarily focus on studying about three-phase induction motors and their faults.

One of the important points about three-phase induction motors is that they are very commonly used in a wide range of domestic, commercial, and industrial applications due their smaller size, low cost, and higher efficiency. Before going to discuss about the faults that occur in the three-phase induction motors, let us first understand their construction and working.

What is a Three-Phase Induction Motor?

A three-phase induction motor is a type of alternating current machine which operates on the principle of electromagnetic induction between the stator and rotor.

A three-phase induction motor consists of two main parts namely, a stator and a rotor. A stator is a stationary part that carries a three-phase winding made up of copper or aluminum conductors. A 3-phase alternating current supply is provided to this stator winding.

The rotor is a moving part of the induction motor that carries a short-circuited rotor winding. The rotor winding receives excitation from the stator winding through the electromagnetic induction. That is why it is called an induction motor.

Apart from stator and rotor, a three-phase induction motor consists of several other major components which are listed below −

• Motor frame

• Stator core

• Mechanical shaft

• Bearings

• End covers

• Cooling fan, etc.

Types of Three-Phase Induction Motor Faults

In a three-phase induction motor, the following two types of faults can occur −

• Electrical Faults

• Mechanical Faults

The electrical faults occur in the electrical components like stator and rotor windings of the induction motor. While the mechanical faults occur in the mechanical components like bearings, frames, etc. Let us discuss about different types of electrical and mechanical faults that occur in a three-phase induction motor.

Electrical Faults

Some of the common electrical faults that occur in a three-phase induction motor are explained below −

(1) Single Phasing Fault

When one of the three-phases of the supply is lost, the fault occur in that case is termed as single-phasing fault. Because of this fault, the three-phase induction motor will heat up or can burn. This is due to the fact that we need balanced three-phase supply for the normal operation of the three-phase induction motor.

(2) Overload Fault

When a load of more than rated capacity of the three-phase induction motor is connected at its shaft, then the overload fault occurs. Due to the overload fault, the motor starts vibrating heavily and could heat up or burn.

(3) Reverse Phase Sequencing Fault

In this fault, the phase sequence of the three-phase supply is changed. This fault occurs when the order of phases of the supply voltage is swapped. This fault causes change in the direction of the three-phase induction motor.

(4) Inter-Turn Short-Circuit Fault

When two turns of the motor windings short circuit with each other, then the fault is called the inter-turn short-circuit fault. This fault can cause burning of the complete winding or the coil of a specific phase.

(5) Under-Voltage or Over-Voltage Fault

When the three-phase supply voltage goes below a specific voltage limit, then the fault occurred is termed as under voltage fault. On the other hand, if the three-phase supply voltage goes above a certain limiting value, then the fault is called as an over-voltage fault.

Both of these faults cause heating and burning of the motor windings.

(6) Earth Fault

When one of the three phases comes in contact with body of the three-phase induction motor, a short-circuit between the phase and metal body of the motor occurs. This type of fault is called the earth fault.

In the condition of earth fault, the motor starts drawing very high current from the supply and heat up. Also, if a living being touches the motor’s body, that can get a heavy electric shock.

(7) Crawling Fault

It is a special type of fault that occurs in a three-phase induction motor. In this type of fault, the motor runs at 1/7th of its rated speed. This fault mainly occurs when the motor is fully loaded and supplied from a rated voltage supply. This fault affects the stability and efficiency of the motor.

Mechanical Faults

As mentioned above, the mechanical faults are those that occur in mechanical components and structure of the motor. Some of the common mechanical faults of three-phase induction motors are explained below −

(1) Damage of Bearings

In a three-phase induction motor, two bearings are provided on both ends of the rotor shaft. The purpose of these bearings is to provide a friction free rotation of the shaft.

A bearing consists of rotating balls sandwiched between two rings namely, inner ring and outer ring. A lubricant is applied to the balls of the bearings to further reduce the friction.

Sometimes, a physical damage occurs to the bearings that may cause jam of the motor shaft.

(2) Rotor Imbalance

Rotor imbalance is a type of mechanical fault that occurs in a three-phase induction motor due to non-uniform distribution of rotor mass. Due to this fault, some nonuniform forces act on the rotor when it rotates. These forces can damage the rotor and bearings, produce heavy vibrations and noise, etc.

(3) Misalignment of Rotor Shaft

This type of mechanical fault occurs due to improper installation of the shaft and bearings or thermal expansion of the shaft material. Due to shaft misalignment, motor can produce heavy vibrations and cause bearing wear.

(4) Failure of Cooling Fan

In a three-phase induction motor, a cooling fan is provided to dissipate the heat produced during operation of the motor. Sometimes, this cooling fan stops working due to which the motor start overheating. This fault can damage the windings or reduce the lifespan of the motor.

(5) Rotor Broken Bar Fault

This type of mechanical fault mainly occurs in squirrel cage rotors. In this fault, some of the rotor bars are damaged or cracked.

Conclusion

This is all about different types of electrical and mechanical faults that occur in an induction motor. These faults can cause different types of effects in the induction motors like heating, burning of coils, vibrations, noise, etc. It is ideal that the three-phase induction motor is periodically inspected for any of these faults to ensure their stable and efficient operation.

FAQs Related to Types of Faults in Induction Motors

The following are some commonly asked questions related to the types of faults in three-phase induction motors.

1. What are the faults in 3 phase motor winding?

The following are the main types of faults that occur in a 3-phase induction motor winding −

• Single-phased winding fault

• Phase to phase short circuit fault

• Interturn short circuit fault

• Earth fault

2. What is the common fault in motors?

The following are the major faults that commonly occur in induction motors −

• Open circuit of stator winding

• Short circuit of stator winding

• Broken rotor conductor or bar

• Cracked end ring of the rotor

• Irregularities in the air-gap

• Bearing failure

3. What are the two types of winding in the three-phase motor?

The following are the two main types of windings in a three-phase induction motor −

• Three-phase stator winding

• Short-circuit rotor winding

4. What are the main types of stator winding faults?

The following are the main types of stator winding faults −

• Open-circuit fault

• Inter-turn short circuit fault

• Coil-to-coil short circuit fault

• Phase-to-ground short circuit fault

• Phase-to-phase short circuit fault

5. What are the mechanical faults in induction motors?

Some major mechanical faults that occur in induction motors are listed below −

• Bearing failure

• Rotor imbalance fault

• Cracking of end rings

• Cooling fan faults

• Shaft misalignment

• Loss components