Hollow insulators – find manufacturers and suppliers

Hollow insulators are usually cylindrical, internally hollow bodies made of insulating material - typically ceramic, silicone or composite materials.

They are designed to meet mechanical and electrical requirements in high-voltage systems. The cavity makes it possible to integrate or feed through electrical equipment such as circuit breakers, instrument transformers and bushings inside, while at the same time ensuring electrical insulation from the environment.

Below you will find an overview of the structure and materials, the mode of operation and the use of hollow insulators, as well as an overview of their advantages and an overview of the challenges and requirements they face:

Structure and materials of hollow insulators:

Hollow insulators usually consist of:

1. Insulating body: Made of porcelain, epoxy resin or silicone composite materials (GRP).
2. Outer ribs (shields): Increase the creepage distance to the surroundings, prevent leakage currents and improve weather resistance.
3. Flanges at the ends: Made of metal, for attachment to other system components and for electrical connection.
4. Interior (cavity): Air or gas-filled, possibly fitted with technical components e.g. vacuum interrupters, transducers or sensors.

Modern hollow insulators are often manufactured as so-called composite hollow insulators, in which a glass fiber-reinforced structure is combined with a weatherproof silicone cover.

How hollow insulators work:

The central task of a hollow insulator is to provide electrical insulation between a live internal conductor or device and the earthed environment. It acts like a protective sheath and ensures that no flashovers or leakage currents occur.

The outer rib structure extends the creepage distance and improves the dielectric strength in the event of soiling and moisture, e.g. rain, dust or industrial fumes. The interior protects sensitive installations from environmental influences, allows pressure relief and can contribute to increasing the internal dielectric strength in the case of gas-filled versions, e.g. SF₆.

Use of hollow insulators:

Hollow insulators can be found almost everywhere in high-voltage installations, both outdoors and indoors. Their use is always necessary when a cavity for integrated technology or bushings is required in addition to the insulation. Typical areas of application are

1. Feedthroughs:
In high-voltage transformers or switchgear.
For feeding conductor connections through earthed enclosure walls.
Ensuring insulation between the inner conductor and earth potential.

2. Instrument transformers and sensors:
Integration of voltage or current transformers inside.
Protection of sensitive components from environmental influences.
Improving the compact design.

3. Switchgear housing, e.g. vacuum circuit-breaker:
The insulator shell encloses the switch mechanism.
Insulates the moving contact parts from the housing.
Protection against atmospheric interference.

4. Gas-insulated switchgear (GIS):
Used as part of the gas-tight enclosure often with SF₆.
Integration in complex modular systems.
Very high insulation requirements in a small space.

5. Pressure relief and protection functions:
In explosion-protected areas or with internal arcing.
The cavity allows targeted pressure dissipation through designated openings.

Advantages of hollow insulators:

• Weight reduction compared to solid insulators with comparable mechanical stability.
• Interior space for integration of electrical components or conductors.
• Low maintenance and often more durable than open-mounted systems.
• Better dielectric strength due to controlled internal insulation.
• Higher mechanical load capacity with simultaneous electrical insulation.

Challenges and requirements for hollow insulators:

Hollow insulators are subject to very high requirements in terms of:

• Mechanical strength: Especially under wind load, short-circuit forces or seismic effects.
• Electrical insulation strength: Even under extreme environmental conditions (lightning, dirt, moisture).
• Tightness: Especially for gas-insulated devices (SF₆ tightness required for decades)
• Partial discharge-free: No impermissible electrical discharges inside.
• Durability and UV resistance: Particularly important in outdoor applications.

Hollow insulators are indispensable components of modern high-voltage infrastructure. Their ability to safely insulate high voltages while protecting and integrating electrical components makes them versatile - from transformers to switchgear. Their design requires precise engineering know-how, particularly with regard to material selection, tightness, electrical field distribution and mechanical resilience. In energy technology, they are a key component for safe and compact high-voltage solutions.

Below is an overview of the most important points that should be considered when purchasing hollow insulators:

When purchasing hollow insulators - whether for high-voltage switchgear, transformers or gas-insulated systems - it is not just about selecting a suitable product, but also about the long-term safety, functionality and cost-effectiveness of the system. The decision influences aspects such as operational safety, maintenance costs, service life and regulatory compliance. A well-founded selection is therefore essential.

• First of all, it must be precisely defined for which operating voltage and application the insulator is intended. Hollow insulators are manufactured for medium-voltage ranges, e.g. 12-36 kV, high-voltage ranges up to 245 kV and extra-high voltage ranges > 420 kV.
• The insulator must match the electrical system voltage and the insulation concept of the entire system.
• Depending on the location, e.g. switchgear, bushing, transformer housing or outdoor installation, different insulator shapes and technologies may be required.
• A hollow insulator must be able to withstand mechanical forces such as wind load, dead weight and short-circuit forces as well as electrical requirements such as lightning impulse voltages, continuous operating voltage and switching overvoltages. Important points are
• Design in accordance with national and international standards, e.g. IEC 62155, IEC 62231.
• Sufficient creepage distance (depending on environmental pollution class).
• Mechanical strength: Bending, pressure and torsional strength.
• Protection against partial discharges at operating voltage.
• Compatibility with pressure load with SF₆ or vacuum filling.
• The type of material influences behavior, weight, maintenance requirements and service life. There is usually a choice:
• Porcelain: Robust, proven, heavy, but more brittle against mechanical stress.
• Composite materials (GRP + silicone coating): Lightweight, shatterproof, UV-resistant, self-cleaning, ideal for modern outdoor installations.
• Epoxy resin: Frequently used in indoor systems and compact GIS systems, with limited thermal requirements.
• The choice depends heavily on the location, climatic stress and maintenance concept.
• Absolute tightness is crucial for hollow insulators with gas filling, e.g. SF₆, dry air or integrated switchgear:
• Durable sealing systems e.g. O-ring, bonded joints, metal seals.
• Check for leakage rates e.g. SF₆ ≤ 0.5 % per year.
• Condensate prevention in the interior.
• Possibility of pressure relief in the event of a fault, e.g. electric arc.
• Accessibility to the interior equipment, e.g. maintenance and sensors, also plays a role.
• Hollow insulators must be able to withstand extreme conditions, especially in outdoor installations:
• UV and ozone resistant surfaces.
• Resistance to temperature fluctuations and frost.
• Resistance to soiling: e.g. hydrophobic surfaces with silicone.
• Suitability for specific environments: Industry, coast, desert, mountains.
• Longer creepage distances or coated surfaces are required in the case of extreme soiling.
• The insulator must be mechanically and electrically compatible with other components such as flanges, housings or electrical conductors:
• Standardized flange dimensions or customer-specific fits.
• Hole pattern and mounting options.
• Alignment and feed-through cross-section for conductors.
• Integration into existing systems or assemblies.
• Dimensional clarity before purchasing prevents subsequent conversion costs or downtimes.
• A high-quality hollow insulator should have a service life of at least 30 years. The following must be taken into account:
• Ageing resistance of the materials, e.g. no embrittlement or cracking.
• Weather-resistant screen structure.
• Proven long-term experience with comparable products.
• Manufacturer information on test cycles and service life forecasts.
• Even if hollow insulators are generally low-maintenance, their design should allow for regular visual inspections, measurements and cleaning if necessary.
• The insulator should be tested and certified in accordance with standards. Important standards include
• IEC 62231 Composite hollow insulators.
• IEC 62155 Hollow insulators for electrical equipment.
• ANSI, IEEE for international applications.
• The manufacturer should be able to provide full test reports on electrical, mechanical, thermal and climatic resistance.
• Choosing an experienced and reliable manufacturer is critical.

Purchasing hollow insulators requires technical understanding, forward planning and a holistic view of the operating conditions. The ideal solution is not necessarily the cheapest, but the one that works reliably for decades, requires little maintenance and fits into the overall system without any problems. Close cooperation with the manufacturer and, if necessary, the system planning department is essential to ensure a perfect fit, safety and investment protection.

Hollow insulators can be purchased from various suppliers. You will find comprehensive information on manufacturers and suppliers of Hollow insulators around the world on Exportpages.