The electric motor winding is the functional heart of an electric motor. It consists of electrically conductive conductors arranged in a defined geometry to generate a magnetic field through current flow. This magnetic field interacts with the stator or rotor and thereby produces mechanical motion.
Put simply: without a winding there is no magnetic field, and without a magnetic field there is no rotational motion. The quality, design and insulation of the winding determine the efficiency, power density, acoustic behaviour and service life of the motor.
Electric motor windings are found in almost all electrical machines, from small drives and industrial and railway motors to traction drives in e-mobility.
Basic construction of an electric motor winding
Regardless of the motor type, a winding consists of several functional elements:
- Conductor: usually copper, less often aluminium, as round or flat wire.
- Turns: individual wire loops that together form a coil.
- Coils: defined groups of turns.
- Winding system: the entirety of all coils in the motor.
- Insulation: electrical separation between conductor, layers, slots and housing.
- Impregnation: resins or varnishes for mechanical fixing and electrical consolidation.
The winding is embedded in the stator or rotor, depending on the motor concept.
Types of winding
Different winding types are used depending on the design and application:
- Round-wire winding: classic design, flexibly deployable, easy to automate, common in standard motors.
- Flat-wire and rectangular-wire winding: higher copper fill factors, better heat dissipation, increasingly used in power-dense drives.
- Form-coil winding: preformed coils with high dimensional accuracy, ideal for series production and large machines.
- Hairpin winding: special form of flat-wire winding, widely used in e-mobility, high current densities.
- Single- and multi-layer windings: depending on voltage level and space requirements. Multi-layer windings require elaborate layer insulation.
Materials of the electric motor winding
Conductor materials
- Copper: high electrical conductivity, standard material.
- Aluminium: lighter and cheaper, lower conductivity, larger cross-sections required.
Insulation materials
- Wire enamels: primary insulation of each turn.
- Layer insulation: Nomex, DMD, NMN, polyester or polyimide films.
- Slot insulation: DMD, aramid paper, laminate composites.
- Phase insulation: separation of adjacent coil groups.
- High-voltage materials: mica, mica composite, mica tape.
Resins and varnishes
- Impregnating varnishes for standard motors.
- VPI resins for high-performance and large machines.
The material selection is based on the thermal class of insulation according to IEC 60085, typically B, F or H.
Manufacturing of the electric motor winding
- Wire preparation: selection, cutting, preforming where applicable.
- Winding: manual or automated, insertion into slots or forms.
- Applying insulation: slot, layer and phase insulation.
- Interconnection: connecting the coils into phases.
- Impregnation: dipping, trickle process or VPI.
- Curing: defined temperature profiles.
- Testing: electrical and mechanical tests.
Clean processing, adherence to minimum bending radii and crease-free insulation are decisive for quality.
Requirements for electric motor windings
- Electrical: dielectric strength, insulation resistance, low partial discharge.
- Thermal: endurance at nominal and overload temperatures.
- Mechanical: resistance to vibration and centrifugal force.
- Process-capable: reproducible manufacturing, easy to assemble.
- Service life: resistance to ageing, moisture and chemicals.
Especially in power-dense motors, the winding is often the limiting factor.
Applications
- Industrial drives: pumps, fans, conveyor technology.
- Household appliances: washing machines, vacuum cleaners, kitchen appliances.
- Automotive: e-motors, auxiliary units, fans.
- E-mobility: traction motors with hairpin or flat-wire windings.
- Generators and transformers: windings with increased insulation requirements.
Advantages and challenges
Advantages
- High efficiency with optimal winding design.
- Large design freedom through different winding types.
- Scalability from miniature to large machines.
Challenges
- Thermal load with increasing power density.
- High quality requirements for insulation and impregnation.
- Complex manufacturing of hairpin and high-voltage windings.
- Ageing through thermal cycles and vibration.
GOBA Takeaway
The electric motor winding is the central performance element of every electrical machine. Its design determines the efficiency, service life and reliability of the motor. Modern applications, especially in e-mobility, place ever higher demands on conductor geometry, insulation and manufacturing precision. Anyone who understands winding, insulation system and impregnation as an overall system and designs them cleanly creates the basis for powerful and long-lasting electric motors.