Electric Motor Winding Insulation

There are four insulation classes in use namely.

Electric motor winding insulation.

All four classes identify the allowable temperature rise from an ambient temperature of 40 c 104 f. After a motor is rewound the windings must be further insulated with resin or varnish. The electrical insulation system is sometimes referred to as insulation class or thermal classification the different classes are defined by nema underwriters laboratories ul and iec. Nema motor insulation classes describes the ability of motor insulation in the windings to handle heat.

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. Standard motor capabilities established by the national electrical manufacturers association nema and expressed in the mg i standard part 30 indicate that standard nema type b motors can withstand 1000 v peak at a minimum rise time of 2 μs 500 v μs. 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 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.

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. The electrical insulation system for wires used in generators electric motors transformers and other wire wound electrical components is divided into different classes by temperature and temperature rise. Dip and bake epoxy varnishing trickle varnishing vacuum pressure impregnation and. 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.

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. Most repair shops will use a megger or a ground insulation tester. A b f and h. This insulation protects the windings from contamination shorting electrically and also make the windings more mechanically rigid.

If the value returned is. The megger will help to detect areas of deteriorating insulation where the windings may soon short. 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. The highest voltage is normally seen by the first turn of the winding.