Classes b and f are the most common in many applications.
Electric motor winding insulation.
There are four insulation classes in use namely.
All four classes identify the allowable temperature rise from an ambient temperature of 40 c 104 f.
Most repair shops will use a megger or a ground insulation tester.
After a motor is rewound the windings must be further insulated with resin or varnish.
If the value returned is.
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.
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 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.
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 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.
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.
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.
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.
This insulation protects the windings from contamination shorting electrically and also make the windings more mechanically rigid.
The main purpose of insulation is to protect the windings in the slots of the stator lamination and layer between winding.
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.
When a bad motor winding cannot be found by a physical inspection many times an ohmmeter may show that there is a defective winding.
Dip and bake epoxy varnishing trickle varnishing vacuum pressure impregnation and.
