INDUCTION MOTOR TESTING

INDUCTION MOTOR TESTINGBY K.Selvam

What are the various types of TestsInsulation Test 500V / 5000V MeggerResistance Test Multimeter / Micro Ohm MeterNo Load TestBlocked Rotor TestLoad Test / Heat Run TestVibration measurementNoise measurementCalculation Copper Loss, Iron Loss & efficiency by drawing Circle diagram from the above test.Insulation TestThe 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 moisture fully.Do & Don'ts while meggeringDisconnect 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. As far as it is to be kept in air.

At least one minute time the voltage should be applied to the motor.After meggering dont 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, assemble the motor then check the IR value.How Test is to be Carried Out?Motor Terminal BoxW2U2V2W1V1U1

U1U2 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 MotorClamp 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 Winding to winding. Connect both megger probes between U1V1, V1W1,Resistance TestThis 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?

W2U2V2W1V1U1Motor Terminal BoxMeasure the resistance between U1 & U2Measure the resistance between V1 & V2Measure the resistance between W1 & W2Compare the Values. It should be almost equal

No Load TestBalanced 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 TestThe 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 JEC37DC MotorAC Generator6600 V 50Hz 7.5 MVAVCB VCB AC Motor6600 V 50Hz 1500 KWDC MotorAC Generator1100 V 40Hz 7.5 MVAVCB 3 winding Transformer

Vibration MeasurementNoise measurementRTD Resistance measurementWinding Temperature Measurement

All these things are to be doneBased on the above test and values Circle diagram is to be drawn and All losses & Efficiency is to be calculated.