Electric Motor Winding Testing

If the winding s insulation wears away near the motor s case the bare wire winding shorts to ground.

Electric motor winding testing.

Check that the correct voltage is applied to the motor. This includes testing the motor for grounded windings. 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. Ac motor winding resistance test check the motor winding resistance or ohms reading with a multimeter.

The reading ohms for each winding should be the same or almost identical. 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. 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. Technicians should perform a series of tests on an electric motor during routine preventive maintenance or before replacing it.

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 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. All values obtained from winding dc resistance test.

To check the condition of the armature windings the armature will probably have to be removed from the motor. 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. Bearing problems may be the number one cause of electric motor failure but electrical faults are a close second. Most repair shops will use a megger or a ground insulation tester.

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. Since there are three terminals. If there is any reading on any of these then the motor is bad do not use it. The megger will help to detect areas of deteriorating insulation where the windings may soon short.

The meg ohm test has long been the tool of choice for most engineers and this simple test is often the only electrical test performed on a motor. Record initial and corrected values on motor testing record sheet. Know that the three steps have identical or almost identical windings. You may find that when it runs ungrounded that the casing becomes live at up to supply voltage.