Electric Motor Winding Insulation

After a motor is rewound the windings must be further insulated with resin or varnish.

Electric motor winding insulation.

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. 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. If the value returned is.

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. The difference between the average winding temperature and any hot spot is limited and it is usual to allow a 10 o c margin for class b and f insulation and a 15 o c margin for class h. There are four types of varnishing methods that we will describe below.

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. 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. Dip and bake epoxy varnishing trickle varnishing vacuum pressure impregnation and. Classes b and f are the most common in many applications.

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. 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. There are four insulation classes in use namely. This insulation protects the windings from contamination shorting electrically and also make the windings more mechanically rigid.

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. Considering the ambient temperature and hot spot allowance gives the maximum temperature rise within which the motor must be designed to operate 105 o c. Nema motor insulation classes describes the ability of motor insulation in the windings to handle heat. A b f and h.