Induction Motor Testing

BY  K.Selvam 

What are the various types of Tests  Insulation Test – 500V / 5000V Megger  Resistance Test – Multimeter / Micro Ohm Meter  No Load Test  Blocked Rotor Test  Load Test / Heat Run Test  Vibration measurement  Noise measurement  Calculation Copper Loss, Iron Loss & efficiency

by drawing Circle diagram from the above test.

Insulation Test The insulation resistance, commonly known as IR value, is obtained by meggering the equipment using the megger. For LT motors 500V megger and for HT motors 2500V/5000V megger should be used for meggering. The Insulation value should be at least 20Mohm for LT motors and 2 Giga ohms HT motors. Comparison with the previous value will give the true condition of  the insulation. If value is less heat the motor to remove moisture and again megger it. 5 consecutive constant value for 5 hrs indicates that the winding has cleared its

Do & Don'ts while meggering •

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Disconnect the motor cable while meggering. Then only the exact IR value of the motor can be found out. The voltage applied through megger should not be more than 1.5 times of the rated voltage of the motor. The hand operated megger should be rotated at nominal speed. Not a very less speed. The wires between the motor terminals and the megger should not touch the metal parts.

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At least one minute time the voltage should be applied to the motor. After meggering don’t forget to discharge. Earth the all three motor terminals with a piece of wire for about 10 sec.

If the megger value is less Heat the motor using space heater or with Halogen bulbs. Still IR Value not improved then Dismantle the motor. Clean the stator with Insulation thinner. Reheat the motor. After IR Value improvement Apply the Insulation varnish,

How Test is to be Carried Out? Motor Terminal Box U1 V1 W1

W2

U2

V2

 U1 –U2 –

R Ph coil, V1-V2 – Y Ph coil, W1-W2 B ph Coil Connect the negative terminal of the megger to the Earth terminal of the Motor Clamp the Positive terminal to the winding one end. Apply the voltage from the megger for at least one minute. Note down the IR Value. Carry out the same for other winding Note down the IR Value. These IR values are between Phase to Earth. Discharge the winding charges. Now Conduct the test between

Resistance Test This Test is to be done to evaluate the winding

healthiness (ie ) Inter turn Short but not earthed. If there is any short circuit between turns to turns of the same winding, then the resistance value of that particular winding will vary with other winding. Megger test will not show this inter turn short. All the 3 phase winding resistance should be almost same. If there is a wide variation then there is a chance of Inter turn short.

How to do this test? Motor Terminal Box U1 V1 W1

W2

U2

V2

Measure the resistance between

U1 & U2 Measure the resistance between V1 & V2 Measure the resistance between W1 & W2 Compare the Values. It should be almost equal

No Load Test •

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Balanced voltages are applied to the stator terminals at the rated frequency with the rotor uncoupled from any mechanical load. Current, voltage and power are measured at the motor input. The losses in the no-load test are those due to core losses, winding losses, windage and friction.

Blocked Rotor Test •

The rotor is blocked to prevent rotation and balanced voltages are applied to the stator terminals at a voltage where the rated current is achieved. Current, voltage and power are measured at the motor input.

Load Test / Heat Run Test JEC37 DC Motor

DC Motor

AC Generator 6600 V 50Hz 7.5 MVA

AC Generator 1100 V 40Hz 7.5 MVA

VCB

3 winding Transformer

VCB

AC Motor 6600 V 50Hz

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Vibration Measurement

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Noise measurement

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RTD Resistance measurement

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Winding Temperature Measurement

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All these things are to be done

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Based on the above test and values Circle diagram is to be drawn and All losses & Efficiency is to be calculated.