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Impregnating resins in the manufacture of motors and transformers, and criteria for their selection

21.10.2014
Electrical devices such as motors, generators, and transformers function on the basis of electromagnetic induction. The rotational or linear movement of such electrical rotary equipment is caused by electromagnetic fields, generated by electrical coils, and their mutual repulsion forces. The primary and secondary insulation completes the basic insulation of electrical equipment. By primary insulation is meant the first insulating layer applied directly to the electrical conductor. Primary insulating materials are varnishes – in the business of primary insulation mostly called wire enamels, the role of which is to provide electric strength of conductor. Requirements for insulating layer of winding wires are often contradictory: a thin insulating layer should be adverse to conditions, sufficiently resistant against mechanical, thermal and chemical influences, must have high electrical strength, low di-electric losses and dissipate heat well from the windings. After the period of rapid development of insulating materials in the second half of the last century, a development of production technologies (with reducing demand for energy) and improving of electrical conductors in terms of their reliability in winding is currently on the spotlight. Designers of new types of electrical devices emphasize reducing insulation thickness while maintaining the original properties of conductors under the current standards. Depending upon an interest in increasing thermal resistance classes of already existing insulation materials, there are introduced various elaborative combinations of existing types of insulation and by the application of new insulation materials, elements of nanotechnology are to be found. 
 
The production of winding wires in VUKI a.s. currently specializes in producing wires with rectangular cross section and special insulated wires in a low volume. As required of the quality system, all our products are manufactured according to the relevant technical standards, preferably under ISO and IEC. By strictly following these standards, we offer our customers original solutions based on their special requirements, among which mostly belong special sizes of isolation strips (even non-standard) with extremely large aspect ratios and extremely low increment of insulation or conductors with a combination of several types of insulation.


By secondary insulation, also referred to as impregnation, is meant the stage of electrically insulating an enamelled wire winding that follows the application of the primary insulation. It is a chemical process, when under the action of heat and impregnants we increase the mechanical stability of the electrical windings and protect the varnished wire during operation from mechanical damage, moisture and other environmental influences. Varnishes and impregnating resins, or generally called impregnants are liquids with different viscosity, which during the curing and crosslinking process generate additional electrical insulation layer on winding wire (of varnish insulation). The most commonly used are polyesterimide and polyester resins with reactive monomers, such as styrene, vinyl toluene, diallyl phthalate, acrylate, or combinations thereof. There are also so called monomer-free resins, without reactive monomer content, with a very low content of volatile substances, epoxy  resins, water soluble resin dispersions and alkyd varnishes containing organic solvent.

Impregnants produced in VUKI a.s. often achieve higher results than standard products in terms of mechanical strength at high temperature (150 °C, 180 °C) assessments in comparison with the parameters of European manufacturers, resulting in significantly contributing to increase motor performance, resistance to vibration, mechanical shock and reduce noise. VUKI a.s. manufacture incorporates the synthesis of resins - a huge advantage, as for production does not depend on changes in the assortment of resin suppliers. Most of VUKI a.s. impregnants are UL approved products for class F and H, or UL approved insulation system for class F and H.

The most efficient method of impregnation

Trickle method technology is considered to be the most economical impregnation system for production of electrical winding of rotors and stators. Individual components are positioned and fixed horizontally, whereby continuously rotate and pass through individual phases of impregnation process (preheating, trickling, crosslinking and cooling). Depending on the size of components and process requirements, speed of rotation, playing the most important role in achieving good penetration of windings, is electronically monitored during the whole process with particular emphasis on the trickle phase and crosslinking. Thanks to precise control of the impregnation process parameters (amount of impregnant, rotation speed, temperature and time) resin can be applied with utmost precision, using the principle of capillary action, ensuring maximum absorption and elimination of excess resin dripping from winding. Trickle impregnation method is an impregnation technology used for mass production of small motors being thermally stressed (washing machines, dryers, hand and kitchen tools and appliances, together with motors applied in automotive technology). Qualitative parameters of the method are: unique winding impregnation, adequate groove impenetrability of impregnant, uniform distribution, bubble and crack-free, minimum excess of resin, maximum winding filling, very high mechanical strength and high labour productivity.
 
Trickle method criteria must be accomplished and possessed by an individual impregnant as well, due to the fact that even a minimal change in its parameters is reflected in the quality of the whole impregnation process. Therefore, a close cooperation with the manufacturers of component suppliers of impregnants is essential. VUKI a.s. has gained a rich experience in providing trickle method technology and has specially developed products that meet the most demanding criteria of manufacturers of white goods and automotive industry components manufacturers. In its production program, VUKI a.s. has several top products within this category. We have been reflecting to constantly growing requirements on reducing losses in the manufacturing process, efficiency and ecology by a new range of products under the name 1K NAH/ ..., applying trickle method and containing very low in volatiles and being of a high strength.
 
VUKI a.s. offers ecological and low emission impregnants to be used in the process of dip impregnation. They are to be found under the name NAB/... and are cured at lower temperatures, releasing negligible amount of volatile matter. Their application in the market is getting more and more popular, especially in Western Europe because of their operational safety. Acrylic impregnants NAB/... represent zero risk of fire and explosion in operation, during transport and storage and compared to solvent varnishes have the advantage of lower consumption, shorter curing time and higher mechanical strength. They are suitable for isolation systems for temperature class H and can be used in electric motors, large and high-speed machines, transformers windings of thick-profile or circular-profile conductors. Moreover, we have achieved remarkable results applying dip impregnation with curing flow and UV light assistance.
 
Perfect properties are to be offered by our water soluble varnish Wasol 40, which has VUKI a.s. especially intended to use for impregnation of low and medium-voltage transformers and impregnation of stators for manufacturers of lawnmowers and household utensils. Among advantages of the impregnant belong: very good adhesion and flexibility, excellent mechanical reinforcement,  absolutely safe and convenient operation without the risk of explosion, unpleasant odors and impacts on human health. It can be diluted with demineralized water. Its pH, the main quality parameter, can be easily verified by a processor even without any laboratory background by a simple measurement using pH indicator. 
 
The company´s primary focus is to reach an absolute customer satisfaction  and maintain long-term business relationships based on technical support before, throughout and after a sole decision making to manufacture our impregnant. Unique proactive program of impregnant analysis for each customer at our expense is designed in order to capture and reflect any technology modification or requirement of our client throughout regular tests and adjustment of impregnant, both in production and in the repair sector.