The future of electric motor insulation: epoxy impregnation and encapsulation for 800-volt architectures
As the electric vehicle industry moves to 800-volt architectures, e-motors will be expected to be able to carry higher currents without overheating, so motor designers will need to take advantage of the latest insulation technologies.
Secondary insulation, which fills the voids between the stator and rotor coils, provides several essential benefits in electric motor designs. It lowers operating temperature, helps to reduce mechanical stress, and protects windings from contaminants. As the automotive industry demands ever-higher performance from e-motors, the role of secondary insulation is becoming even more critical.
In a recent webinar, Huntsman Technical Sales Manager Florian Gnaedinger explained how secondary insulation materials will play a crucial role in enabling and facilitating new electric mobility technologies, such as 800 V and ESM magnetless rotor designs.
Motor designers face several challenges that are specific to automotive applications. Secondary insulation must be suitable for mass production, must enable short cycle times, and must meet exacting safety standards. Automotive traction motors must function reliably in very tough environments, and insulation materials may be expected to maintain performance at temperatures ranging from -40° to 180° C.
Meeting these challenges requires resin systems that offer optimal viscosity and reactivity. Secondary insulation materials are also expected to deliver mechanical benefits, so they must exhibit good adhesion to the primary insulation, and non-conductive reinforcing fillers must deliver a void-free matrix to improve mechanical performance.
There are two main processes used to provide secondary insulation: impregnation, which uses unfilled resins; and encapsulation, which uses filled resins.
Secondary insulation applications in electric motors include stator impregnation and three types of encapsulation: stator potting, end-turn potting, and rotor potting. Each of these requires a specific type of resin system, with a thermal conductivity and a glass transition temperature (Tg) that’s optimized for the specific application, as well as for the manufacturing process that will be used.
Huntsman offers a wide range of resin systems, and our experts work closely with customers to select the ideal product for each particular component and manufacturing process.
Resin systems for impregnation
For stator impregnation, an unfilled resin system with comparatively low thermal conductivity is recommended. ARALDITE™ CY 38500 is a 1k mono-component resin that features easy handling and processing, fast impregnation and cure time. It is free of solvents, VOCs and CMRs. It combines high Tg with excellent mechanical properties.
In his webinar, Gnaedinger presents the results of a 3-point bending test performed on a copper coil, with and without impregnation. The impregnated coil shows far higher tensile strength, less elongation at break, and far higher E-modulus, even after 300 cycles between -40° and 180° C.
Resin systems for encapsulation
Encapsulation technology can greatly improve the efficiency and durability of electric motors, and is also used for electronic devices such as batteries, inverters, voltage converters, electronic control units, wire harnesses, sensors and switches.
Specific advantages of encapsulation include optimized heat transfer to cooling elements, which can increase power density. Processing is done under vacuum, which produces excellent, void-free insulation. Encapsulation also delivers noise damping and complete protection against chemicals and other contaminants.
For stator potting, filled resins are used to deliver higher levels of thermal conductivity, up to an optimal level of 1.1 to 1.2 W/m.K (watt per meter-kelvin). It’s possible to increase thermal conductivity beyond this level, but this delivers fewer benefits, and the increased viscosity leads to processing challenges.
For end-turn potting, a resin with a high level of fillers, and a correspondingly high thermal conductivity, is optimal.
Resin systems with very high glass transition temperature provide addition mechanical benefits, and are appropriate for rotor potting.
Huntsman’s resin systems for encapsulation are also free of solvents, VOCs and CMRs. Processing and curing times are comparable to those of impregnation processes. Viscosity and thermal conductivity are adaptable, depending on the needs of a particular component and manufacturing process.
Huntsman’s encapsulants deliver superior crack resistance. Gnaedinger presents the results of a series of tests in which materials were exposed to cycles of extreme heat and cold (from 23° to -50° C) in order to trigger cracking. ARALDITE™ CW 30407/ARADUR™ HW 30408 remained crack-free, demonstrating that this is the preferred choice for parts that will be subjected to extremely cold temperatures.
A trusted partner
Selecting an optimal resin system is a complex process, and manufacturers need to work closely with resin system suppliers, beginning in the early stages of product planning. Huntsman is a leading global supplier to the automotive industry, with a broad and deep base of knowledge and a team of experts who constantly work with customers to implement the most up-to-date technologies.
Our products are supported by our ISO-certified testing labs, as well as by sophisticated computer simulation capabilities that help customers develop new products and processes quickly and cost-effectively. However, the most important driver of our product development is our ongoing interaction with our customers, which begins in the early phases of their projects.
All our resin systems are designed based on two-way feedback between Huntsman and our customers. For example, as Mr. Gnaedinger explains, the specification of 1.2 W/m.K as the optimal thermal conductivity for stator potting is the result of detailed discussions with different customers, and multiple iterations of the real-world production process.