Insulation Test

Carryout the steps detailed on section Insulation resistance. When steadily reducing insulation resistance (IR) values are observed, even though they may be above the minimum acceptable levels, they are an indication that the moisture level in the insulation is increasing due to absorption o ambient moisture. ALL SPECTRUM SERIES and Flame Proof motors have winding with class F insulation as standard. Using proven materials of non-hygroscopic nature. They are given a varnish impregnation process, and the highest grade of class F thermosetting resin varnish. All motors leave the factory only if the IR value is practically infinite. The presence of moisture in the insulation can, therefore, come about only on account of cracks or damage suffered by the insulation or the varnished surfaces. If such be the case, arrange to dry out the machine as detailed in section Drying out and to give an alkyd resin varnish dip and brake treatment to the windings. This is motors owing to the large volume may be poured over the exposed winding a number of times until a fair degree of impregnation is achieved. Then bake the windings at about 140oC for 8 to 10 hours depending on size in a circulation air oven; this temperature must NOT be exceeded.