Corona Resistant Winding Wires

In inverter driven motors, excessive surges and voltage peaks during speed variation, creates corona discharge in the stator windings, which induce extra thermal stress on the insulation, causing excessive thermal ageing there by weakening and even decomposing of the insulation, leading to premature failure of motors. Corona induced failure is a typical phenomenon. Mica based products are used in certain application where corona resistance is required. Mica is naturally occurring and is available easily. But it has it's own inherent weakness. It has poor flexibility and large area and as such, the space required is more for any mica based application.

This result by increasing the size of the motor, making it unusable where space constraints are there. More over it has poor adhesion to most of the resins. Improved dielectric materials having resistance to corona discharge-induced deterioration would therefore be highly necessary. M/s. Dupont has been manufacturing corona resistant Wire enamel under the brand name “Voltatex”.

Dual coated wire, with Polyesterimide as the base coat and Polyamideimide as the topcoat has been the most commonly used for applications up to thermal class 200. As discussed earlier, even these types of wires are susceptible to corona related failures. In order to overcome this deficiency, base coat is replaced with special corona resistant enamel.

• Basecoat of Corona resistant wire enamel class 200°C
• Top coat of Polyamide-imide (PAI) class 200°C +

We process Corona resistant wire in the range 3 mm to 0.63 mm. We can extend this range up to 0.3 mm by suitably modifying our machines. These corona resistant wires were tested for higher proof voltage and at elevated temperatures. There are certain guide lines about the voltage endurance test by RDSO. Our products conform to requirements of standards.

Further to this, the wire was impregnated with class vinyl toluene based class 200 impregnating varnish (resin) and tested for proof voltage at elevated temperatures. Test results were found satisfactory.