5 REASONS that damages Induction Motor

Electric Motor is the most reliable Electrical Machine which play a very important role in industry.

NOTE- In this post, 'motor' word used for Induction motors only.

Both 1single phase & 3phase induction motors are useful but 3 phase motors are preferred over single phase, Because :

1Single phase motors are bulky in size as compare with 3phase motor of same rating.
1Single phase motor need capacitor for starting on the other hand 3phase motor don't need any type of auxiliary accessory for starting.
Cable for 1phase is thicker in size as compare with cable required for 3phase motor of same rating.
Since distribution system is 3phase, if we install 1phase motors it becomes difficult to balance the load on all the 3phases.

NOW, Back to the topic !

5 REASONS THAT DAMAGES INDUCTION MOTOR

Winding is the softest part of motor. Motor get damaged when any harm occurs to the winding. Winding get damaged due to the following 5 reasons.

Overload
Wrong & loose connections
Material ingression
Single phasing
Over Voltage & Under Voltage

Next, We are going to discuss how these reasons damages the motor. We will also discuss the preventive remedies for this.

Windings of damaged Induction Motors

1. OVERLOAD

One major reason of motor damage is 'OVERLOAD'

Overload generally means 'more than the capacity'. Load output at motor shaft becomes higher than rated value. At this point of overload; torque becomes higher & speed becomes lower. High torque results in high current which damages the motor's winding.

Overload for short interval don't harm the motor instantly. Damage occurs to the motor when overload occurred many times OR overload occurred for long period of time.

Reasons of Overload

*Due to Bearing faults

Rotor of motor rotates freely with the help of bearings on both deriving end & non-deriving end. When one of the bearing get damaged, it overloads the motor.

*Due to mechanical faults

Several types of mechanical faults put excessive load on motor like tight belt pulley arrangement, broken bearing on load side, lack of oil or grease.

*Due to excess load burden

Load at motor's shaft output; should be lower than the rated value. Excess load creates overload on motor.

REMEDY

Thermal overload relay of proper rating should be installed for overload protection.

2. LOOSE OR WRONG CONNECTIONS

Damage due to loose connections

"Every single connection must be tight at any cost. 1 Loose connection can damage the whole system. Loose connection is like a crime in Electrical!"

Similar the case with the motor, terminal connections must be tight at rated torque. Loose connections creates sparking.

Loose connection Sparking at terminal plate create carbon between the leads. Current don't flow properly, some time it conducts or some time not. This creates the situation of 1single phasing. At this stage, motor don't burn instantly, it takes some time to get damaged.
Loose connection sparking also creates high temperature around the periphery. This high temperature burns the motor leads after that leads get broken or earthed with motor body.

Damage due to wrong connections

Motor connections 'star or delta' must be according to the rated parameters which are printed on motor's name plate.

Connect the motor in Delta connection only when it is prescribed on name plate. If by chance we connect the star configure motor in delta, it will burn the motor as explained below.

Three phase motor has 3 set of coils, each set internally is individual not connected with other coil sets.(when all the six leads are out).

Each set has 2 leads therefor 3 sets have total 6 leads.

When connection in star each set gets voltage of phase-Neutral.(single phase)

When connection in Delta each set gets voltage of phase1-phase 2. (Double phase)

If set is capable of handle single phase voltage (Star connection) & we are connecting the motor in Delta, it burns the motor.

Connections 'star or delta' should be made in correct way.

Star & Delta connection diagrams are explained below:

STAR & DELTA CONNECTIONS

As explained above, there are total 3 sets.

u+u1, v+v1, w+w1.

Each set is individual not connected with each other internally.

STAR Connections

For STAR Connections, Short one sided 3 leads with each other. This short junction is 'Neutral'.

The basic requirement for star connection is 'Single phase (phase-Neutral) supply appear across one set.

DELTA Connections

For Delta Connections, Connect the leads of one particular set with another set. The basic requirement for Delta connection is '2 phases must be given to each set' so that double phase appears across the one set.

REMEDY for Wrong OR Loose connections

1.Make a habit of double check. We are humans, chances of error are always there from our side. Always try to inspect the connection 2times at least.

2.Before connections always read the name plate first.

3. MATERIAL INGRESSION

Motors are solid, tough & powerful Electrical machines. They are made to pull the load But winding inside the motor is; softest part. Winding should be clean at any cost.

Any type of material like iron dust, moisture, water droplets & chemicals can easily damage the winding if they get enter inside the motor. Material ingression deteriorate the insulation of motor winding which results winding get short circuited or earthed.

REMEDY

1.Motor area must be clean & dry. It should be super protected from iron dust, rain & harsh weather conditions.

2. Install the motor with Ingress protection according to surrounding environment.

3. Connection box cover must be tight perfectly,

4. SINGLE PHASING

Single phasing is the phenomenon at which motor runs on 2 phases rather than 3. At this stage, Motor consumes excessive current & produces humming noise. Motor rotates slower than the rated speed OR In some cases it produces humming noise with no rotation.

Single phasing is most dangerous situation for motor, it burns the motor more rapid than other reasons of damage.

Reasons of Single phasing

•Single phasing occur when one of the fuse got blown out.

•When contactor's 1 point get oxidized or damaged.

•When one of the terminal connection is loose or broken.

REMEDY

1.By Using MPCB(Motor Protection Circuit Breaker) or thermal overload relay; we can protect the motor from 1single phasing.

2. BY using supply monitoring device. This device continuously monitors all the 3 phases, it operates when any of the phase is missing. This device makes the system complex & costlier that's why It is not appropriate using the device on small rating motors.

We can use this device on high rating motors OR we can use this device on main distribution panel where multiple motors are connected.

(If you want to know about supply monitoring device you can go through our post of Supply monitoring Device .)

5. OVER-VOLTAGE & UNDER-VOLTAGE

Electric Motors are designed to work at particular voltage range beyond these range motors don't work precisely. It works efficiently at rated voltage, It works more efficiently when voltage is stable.

Voltage fluctuation harm the motor if fluctuation is wide. Both Over voltages & Under Voltages are harmful for the motor which damage the motor due to different reasons.

--Over Voltage links with Insulation- Higher the Voltage heavier the Insulation !

High Voltage produces excess Electric stress between the coils; this stress can deteriorate the insulation of the winding.

--Under Voltage links with high current- Current becomes higher when voltage is lower !

This current can goes beyond the rated value & increase the motor temperature. At this stage Motor rotates slower & don't work precisely.

REMEDY

1.Voltage stabilizer should be install to eliminate the voltage fluctuation.

2. Over voltage, Under Voltage protection device should be install to monitor the power supply.

This is all about the reasons that damages the motor. Hope! You like the post. If you have any doubt, suggestion or query please do comments.