High-voltage insulation covers all measures, materials and components that safely separate electrical voltages in the high-voltage range from conductive or touchable components. The aim is to reliably prevent electrical breakdowns, surface leakage currents and partial discharges.
Simply put: high-voltage insulation ensures that electrical energy stays where it should work and does not jump across to persons, components or housings.
In electrical engineering, e-mobility, transformer and mechanical engineering, high-voltage insulation is safety-critical. Faulty design leads not only to failures but also poses a significant risk to people and a considerable fire risk.
What is considered high voltage?
The term high voltage is defined depending on the standard:
- Low voltage: up to 1,000 V AC or 1,500 V DC
- High voltage: above these limits
In practice, however, the term is often used at lower voltages, particularly:
- Automotive HV systems: from 60 V DC
- Industry and energy technology: several kV up to more than 100 kV
For insulation design, not only the rated voltage counts, but also overvoltages, pulse loads and ambient conditions.
Fundamentals of high-voltage insulation
High-voltage insulation must take several physical effects into account:
- Electrical breakdown: exceeding the dielectric strength of the material.
- Surface leakage current: current flow along the surface of an insulating material.
- Partial discharges: local discharges in air inclusions or defects that lead to long-term destruction.
- Electric field strength: local field enhancements at edges, tips or transitions.
This results in three central design principles:
- Sufficient material thickness
- Defined creepage and clearance distances
- Field-optimised geometries without sharp edges
Materials for high-voltage insulation
Material selection is critical and depends on voltage, temperature, environment and service life. Typical materials are:
- Aramid paper (Nomex): high voltage and temperature resistance, very good ageing resistance. Standard in motors, transformers and generators.
- Polyimide films (Kapton): very high dielectric strength, temperature stable up to class H and beyond. Property values and manufacturers of the material class are covered under polyimide.
- Mica products (mica, mica composite, mica tape): excellent partial discharge and dielectric strength. Indispensable at very high voltages.
- Polyester films (PET, e.g. Mylar, HOSTAPHAN): economical, good electrical properties, limited temperature stability.
- Glass-fibre-reinforced laminates (GFRP, FR4): mechanically stable, suitable for load-bearing insulation parts.
- Potting compounds and impregnating resins: reduce air content, improve field distribution and long-term stability.
Structure of high-voltage insulation systems
High-voltage insulation is almost always systemic in structure and consists of several levels:
- Primary insulation: direct separation of live parts.
- Secondary insulation: additional barrier if the primary insulation fails.
- Groundwall insulation: separation from earthed components.
- Surface insulation: ensuring sufficient creepage distances.
In electrical machines, multilayer composites of films, papers, tapes and resin systems are used.
High-voltage insulation in practice
Electric motors and generators
- Slot insulation, form coil and field coil insulation
- Banding with mica tapes
- VPI or trickle impregnation to suppress partial discharges
E-mobility
- High-voltage batteries
- Inverters and power electronics
- Cables, connectors and busbars
Transformers
- Layer and main insulation
- Pressboard, aramid paper, oil or resin systems
Industry and energy technology
- High-voltage switchgear
- Power capacitors
- Test and measurement systems
Standards and requirements
Central standards in the high-voltage insulation environment are:
- IEC 60085: insulation material classes
- IEC 60216: thermal ageing
- IEC 60664: insulation coordination, creepage and clearance distances
- IEC 60034: electrical machines
- ISO 6469: high-voltage safety in vehicles
- DIN ISO 2768: dimensional and form tolerances for insulation parts
These standards define minimum distances, test voltages and safety margins.
Benefits of correctly designed high-voltage insulation
- High operational reliability
- Prevention of breakdowns and partial discharges
- Long service life of machines and equipment
- Compliance with legal and regulatory requirements
- Protection of people and equipment
GOBA Takeaway
High-voltage insulation is not a single component but a safety-critical overall system. Its quality determines the reliability, service life and safety of electrical systems. In electric motors, transformers and e-mobility applications, high-quality materials such as aramid paper, polyimide films or mica products are indispensable. Standards-compliant design with controlled field distributions, sufficient creepage distances and tested insulation systems is the foundation for safe high-voltage operation.
