Electric Motor Winding Insulation

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.

Electric motor winding insulation.

A b f and h. The main purpose of insulation is to protect the windings in the slots of the stator lamination and layer between winding. Nema motor insulation classes describes the ability of motor insulation in the windings to handle heat. Dip and bake epoxy varnishing trickle varnishing vacuum pressure impregnation and.

If the value returned is. 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. The megger will help to detect areas of deteriorating insulation where the windings may soon short. There are four types of varnishing methods that we will describe below.

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. Electrical insulating material product categories electrical insulating material coated cloth products 26 insulating compounds 23 insulation paper and film 193 rigid laminate 44 sleeving tubing 190 standoff insulators 22 surge rope 12 varnish resin 462 wedges 80. 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. Classes b and f are the most common in many applications.

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. This insulation protects the windings from contamination shorting electrically and also make the windings more mechanically rigid. After a motor is rewound the windings must be further insulated with resin or varnish. 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.

All four classes identify the allowable temperature rise from an ambient temperature of 40 c 104 f. 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. There are four insulation classes in use namely. When a bad motor winding cannot be found by a physical inspection many times an ohmmeter may show that there is a defective winding.