Electric Motor Winding Insulation

The correct insulation of the winding of a motor is determined by both the temperature rise in the motor and the temperature of the ambient air.

Electric motor winding insulation.

This insulation protects the windings from contamination shorting electrically and also make the windings more mechanically rigid. The main component for electric motor is a stator what is stator basically stators are wound with insulated windings made from cooper wire the insulation materials for winding of stator such as polyester poly vinyl formal polyurethane etc. If a motor is subjected to an ambient temperature higher than 40 o c it must normally be de rated or a higher insulation class of material used. There are four types of varnishing methods that we will describe below.

Nema motor insulation classes describes the ability of motor insulation in the windings to handle heat. If the value returned is. A if the insulation resistance of a new cleaned or repaired motor that has been stored for some time is less then 10 mω the reason might be that the windings are humid and. All four classes identify the allowable temperature rise from an ambient temperature of 40 c 104 f.

The main purpose of insulation is to protect the windings in the slots of the stator lamination and layer between winding. The megger will help to detect areas of deteriorating insulation where the windings may soon short. Classes b and f are the most common in many applications. There are four insulation classes in use namely.

Dip and bake epoxy varnishing trickle varnishing vacuum pressure impregnation and. A b f and h. If the motor is not put into operation immediately upon arrival it is important to protect it against external factors like moisture high temperature and impurities in order to avoid damage to the insulation before the motor is put into operation after a long period of storage you have to measure the winding insulation resistance. Most repair shops will use a megger or a ground insulation tester.

When a bad motor winding cannot be found by a physical inspection many times an ohmmeter may show that there is a defective winding. After a motor is rewound the windings must be further insulated with resin or varnish. Regular checks of motor insulation resistance the key to prolonging the life of any electrical device is periodic checks maintenance the insulation resistance of stored and active motors should be checked regularly. Winding insulation test primarily for non submersible type pump motors prep determine testing voltages determine minimum acceptable resistance at 40 c short all three phases together at terminals use a multimeter to measure resistance between the leads and grounded motor frame.