Electric Motor Winding Insulation

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.

Electric motor winding insulation. 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. 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. Nema motor insulation classes describes the ability of motor insulation in the windings to handle heat.

The megger will help to detect areas of deteriorating insulation where the windings may soon short. 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 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.

Classes b and f are the most common in many applications. The main purpose of insulation is to protect the windings in the slots of the stator lamination and layer between winding. 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.

After a motor is rewound the windings must be further insulated with resin or varnish. Dip and bake epoxy varnishing trickle varnishing vacuum pressure impregnation and. When a bad motor winding cannot be found by a physical inspection many times an ohmmeter may show that there is a defective winding. 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. This insulation protects the windings from contamination shorting electrically and also make the windings more mechanically rigid. 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. A b f and h.