Layer insulation is a central insulation measure in electrical machines. It separates the individual winding layers of a coil or winding package from one another and therefore prevents short circuits, partial discharges and thermal overloads.
In simple terms: layer insulation is the “partition wall” between two wire layers, so that current does not jump from one winding level to the next.
In electric motors, generators and transformers, it is essential for ensuring the required dielectric withstand strength and service life of the machine.
Structure and function of layer insulation
In windings with multiple wire layers, whether round wire, flat wire or formed coils, an insulation layer is placed between the individual layers.
- Basic principle: each winding layer is electrically separated from the next.
- Purpose: avoidance of electrical breakdowns, uniform voltage distribution, mechanical protection during the winding process.
- Additional function: improvement of impregnability and thermal stability.
Particularly in high-voltage and large machines, layer insulation can be built up in multiple layers, sometimes with mica tape or resin systems, to ensure partial discharge resistance.
Materials for layer insulation
Material selection depends on voltage, temperature class and mechanical stress:
- Aramid paper (Nomex): high thermal and electrical strength, standard in modern machines.
- Polyester films (HOSTAPHAN, Mylar): good electrical properties, cost-effective, mechanically robust.
- Polyimide films (Kapton): for high-temperature applications up to 220 °C.
- DMD laminate (polyester fleece, polyester film, polyester fleece): good dielectric strength, mechanical stability and impregnability.
- NMN laminate (Nomex, PET, Nomex): better temperature resistance than DMD, proven for class F and H.
- Mica products (mica tape, Mica Composite (Mikanit)): indispensable at high voltage, extremely high dielectric strength.
- Glass fabric: mechanical reinforcement, in combination with resins.
Typical insulation classes: B (130 °C), F (155 °C), H (180 °C), C (above 220 °C).
Manufacturing and processing
- Inserting films or cut parts: before or during winding.
- Taping: with mica or glass tapes around each layer.
- Impregnation: via trickle process, dipping or VPI (Vacuum Pressure Impregnation).
- Curing: thermal or chemical, to solidify resin and insulation.
- Quality assurance: dimensional inspection, visual checks, electrical tests.
Manufacturing requires high precision: unclean edges or folds can cause field enhancements and promote partial discharges.
Requirements for layer insulation
- Electrical requirements: high dielectric strength, partial discharge resistance, sufficient creepage distances.
- Thermal requirements: resistance according to the insulation class, ageing stability under continuous load.
- Mechanical requirements: resistance to pressure during winding, vibration resistance in operation.
- Chemical requirements: resin compatibility, resistance to oils and solvents.
- Manufacturing requirements: good stampability, flexibility and defined minimum bend radii.
Applications
- Electric motors: layer insulation in stator and rotor windings.
- Generators: interlayers in field and armature coils, often multilayered.
- Transformers: separation between winding layers in medium- and high-voltage applications.
- Rail drives and large machines: heavily loaded coils with multilayered layer insulation (mica and glass tapes).
- E-mobility: hairpin windings require specialised insulation films for high voltage stresses.
Advantages and challenges
Advantages
- Increased dielectric withstand strength.
- Extended service life of coils and windings.
- Flexible material choice for different temperature classes.
- Good impregnability in resin systems.
Challenges
- Compliance with minimum bend radii for thin films.
- Avoidance of folds, edge cracks and air bubbles.
- Ensuring resin penetration.
- Material selection depending on voltage level and standards.
GOBA Takeaway
Layer insulation is an inconspicuous but indispensable detail in electric motors, generators and transformers. It determines dielectric withstand strength, ageing resistance and operational reliability of the machine. With materials such as Nomex, DMD, Kapton or mica tape, a wide range of requirements from standard to high-performance applications can be covered. Those who master material selection, manufacturing and testing processes ensure durable and reliable machines.