Impregnation of electrcal machines with solventless resins

In the past, solvents containing impregnation systems were in vogue, e.g. phenoloic‐alkyd, isophthalic polyester, silicone, etc. for electrical machines. The disadvantages of solvent borne impregnants are a higher dissipation factor (at elevated temperatures) and water absorption, etc., due to the presence of air voids formed during the curing process. The phenomenon has been controlled with the present day use of solvent/ess systems, e.g. polyester, polyesterimide, epoxy and silicone resins. Solvent/ess polyester resins are now indigenously available along with their additives such as: inhibitor, catalyst and reactive diluent, etc. Modern methods of impregnation for electrical machines in BHEL include: (a) Dip impregnation by rotational method (b) V P I process The methods include storing the catalysed resin in cool storage, warming for impregnation, and final impregnation under vacuum and pressure, and curing in an oven. A monitoring system has also been standardised for the impregnation resin to keep its viscosity and gelling time within the specified tolerances by the addition of an appropriate amount of inhibitor and reactive diluent. Proper monitoring keeps the tank life of the system indefinitely long and its properties within limits.