Electric Motor Winding Testing

Ac motor winding resistance test.

Electric motor winding testing.

All values obtained from winding dc resistance test. The megger will help to detect areas of deteriorating insulation where the windings may soon short. Most repair shops will use a megger or a ground insulation tester. If there is any reading on any of these then the motor is bad do not use it.

You may find that when it runs ungrounded that the casing becomes live at up to supply voltage. Check that the correct voltage is applied to the motor. Record initial and corrected values on motor testing record sheet. To check the condition of the armature windings the armature will probably have to be removed from the motor.

Technicians should perform a series of tests on an electric motor during routine preventive maintenance or before replacing it. However while the meg ohm test has a valid role to play it is simply not capable of detecting all the likely faults within a motor s winding. We ll start with a quick review of why testing is important followed by a discussion of rotor bar hipot surge and motor winding resistance as well as a discussion of vibration analysis. With a multimeter set to low ohms usually 200 test between each winding terminal and the metal casing of the motor.

Since there are three terminals. Power supply test for single phase motors the expected voltage is about 230v or 208v depending whether you are using the uk or america voltage system. The reading ohms for each winding should be the same or almost identical. Often it is required to test the winding of the 3 phase windings with the aid of a multimeter or ohmmeter to determine whether the motor is still good or burnt or shorted.

For phase to phase terminals u to v v to w w to u test the motor winding resistance or ohm reading using a multimeter or ohmmeter. Usace testing procedure cont 11 winding dc resistance test follow usace procedure three sets of results total a to b phase b to c phase c to a phase correct values to 40 c using the formula in step 8. If the winding s insulation wears away near the motor s case the bare wire winding shorts to ground. Know that the three steps have identical or almost identical windings.

Test electric motor windings when a bad motor winding cannot be found by a physical inspection many times an ohmmeter may show that there is a defective winding. This includes testing the motor for grounded windings. If windings are shorted together the electro magnetic fields cannot be created for that coil causing the motor to run erratically or fail all together. The most common failure mode of a 3 phase ac motor is burnt winding or shorted winding leading to the damage of the motor.