E-MOTOR: SLOT LINER INSULATION NKN TUBES FOR STATOR WINDING COPPER HAIRPINS
Politubes offers a “tailor made” range of electrical insulation NKN (Nomex/Kapton/Nomex) – NMN (Nomex/Mylar/Nomex) spiral wound tubing used to insulate stator slot liner of electric motors (eMotor) that are using copper hairpin winding.
Compared with the traditional copper wire winding, the hairpin winding guarantees better performance in terms of efficiency, power density, cost, noise reduction, and it conforms to the most recent eMobility technological developments especially for traction motors.
This advantage is clear as shown in the drawing below, that more copper conductors can be arranged in the stator slots due to the use of rectangular copper hairpin windings; this improves by far the slot fill factor.
Nomex/Kapton/Nomex (NKN) multilayers spiral tubing are thinner than traditional insulation methods. They are supplied without overlaps with thicknesses between 0,16 and 0,18 mm.
Reducing the thickness of slot insulator is crucial to improve motor efficiency and performance in terms of:
- Improving thermal conductivity and reducing thermal resistance
- Reducing the temperature of the copper hairpin hotspot
- By reducing the insulator volume, because of a reduced thickness and lack of overlaps, it means that the amount of copper inside the slot can be increased, improving motor performance
- Reducing phase resistance
Thermal management is of fundamental importance for motor reliability as it can influence its torque. Overheating can reduce efficiency of the motors, deteriorate components like permanent magnets and reducing strength of slot insulation. On the other hand, heat dissipation improvement can be also translated into positive impact of all vital matrix and motor life time.
NKN tubes are flexible, they can be inserted easily onto the copper hairpins and take the rectangular shape.
Nomex – Kapton – Nomex tubes are custom-designed and are suitable for both 400V and 800V E-motors.
For 800V motors we use special categories of Nomex and Kapton with very higher dielectric performance, 3X the thermal conductivity (heat dissipation ) and lifetime.
Over the years, some companies specializing in the automation production processes offer now fully automatic systems for inserting our tubes into slots.
When compared to traditional insulation methods (tapes to insulate wedges and slot wedges), spiral wound tubes offer some important advantages:
- Dielectric strenght up to 12 kV
- Integration UL system till 220°C
- Higher mechanical tensile strength
- Superior chemical resistance
- Excellent resin impregnation properties
- Increasing uniformity, thermal, dielectric and chemical insulation
- Higher production output because with one production step, motors producers obtain the insulation of the whole slot.
NKN tubes and endcaps are often used in the automotive industry also to provide the best insulation at splices, motor lead terminals and other components inside motors, ensuring uniformity of the whole insulation system.
For eMobility industries, Politubes also provides spiral wound tubing and ultrasonically welded endcaps made with a combination of Nomex and DuPont’s Mylar HS type heat shrink polyester.
(Nomex and Kapton are DuPont registered trademarks)