Baoding Jikai Power Equipment Co., Ltd.
DC Composite Suspension Insulators for UHVDC Transmission
As countries continue to expand long-distance power transmission networks, high-voltage direct-current technology is becoming increasingly important for connecting generation resources with major load centers. These projects require insulation equipment capable of operating under high electrical stress, heavy mechanical loads and demanding outdoor conditions.
The DC composite suspension insulator is designed for direct-current transmission lines, including high-voltage and ultra-high-voltage systems from ±400kV to ±1100kV. By combining a silicone rubber housing, an acid-resistant ECR fiberglass core and hot-dip galvanized steel fittings, this type of insulator provides electrical insulation and mechanical support for overhead DC transmission conductors.
Why DC Transmission Requires Specialized Insulators
Direct-current transmission lines operate differently from conventional alternating-current systems. Continuous DC voltage can influence surface charge accumulation, pollution behavior, electric field distribution and corona performance.
For this reason, insulators used in HVDC and UHVDC projects must be selected according to more than the nominal voltage level. Engineers generally evaluate:
- DC system voltage
- Specified mechanical load
- Routine tensile test load
- Nominal structure height
- Creepage distance
- Wet DC withstand voltage
- Lightning impulse withstand voltage
- Switching impulse withstand voltage
- Visible corona voltage
- Local pollution and environmental conditions
The final insulator configuration must coordinate electrical insulation performance with the mechanical loading and installation arrangement of the transmission tower.
Voltage Classes from ±400kV to ±1100kV
The available FXBZ series covers several DC transmission voltage classes, including:
- ±400kV
- ±500kV
- ±660kV
- ±800kV
- ±1100kV
This wide range allows the insulator structure to be selected according to the electrical requirements of both HVDC and UHVDC transmission projects.
The supplied product data includes specified mechanical load ratings from 120kN to 1000kN. Available configurations also provide different structure heights, creepage distances and connection dimensions.
Representative Technical Ranges
The following table summarizes representative values from the supplied technical information. Final values depend on the selected model and project configuration.
| DC Voltage Class | Structure Height Range | Creepage Distance Range | Mechanical Load Options | Visible Corona Voltage |
|---|---|---|---|---|
| ±400kV | 8000mm | 28030mm | 160kN, 210kN, 300kN | ≥750kV |
| ±500kV | 6290–6800mm | 20500–22800mm | 120kN–420kN | ≥650kV |
| ±660kV | 8500–9200mm | 33400–38400mm | 160kN–420kN | ≥750kV |
| ±800kV | Approximately 5790–12000mm | 36300–45430mm | 160kN–550kN | ≥900kV |
| ±1100kV | 12300–16600mm | 47355–63910mm | 160kN–1000kN | ≥1235kV |
These values demonstrate how the structure becomes longer and the creepage distance increases as the required DC voltage and insulation level rise.
Long Creepage Distance Supports Outdoor Insulation
Creepage distance is the shortest path along the insulator surface between conductive components. It is an important parameter for outdoor insulation, especially where dust, salt, industrial pollution or moisture may accumulate.
The supplied DC composite suspension insulator range provides creepage distances from approximately 20500mm for selected ±500kV configurations to more than 63000mm for selected ±1100kV models.
The required creepage distance should be determined according to the DC voltage, local pollution severity, altitude, environmental conditions and project insulation-coordination requirements.
HTV Silicone Rubber Improves Pollution Performance
The sheds and housing are manufactured from high-temperature vulcanized silicone rubber. According to the supplied product information, the material can reach an HC1 hydrophobicity level.
Hydrophobicity helps prevent water from forming a continuous conductive film across the insulator surface. Instead, water tends to remain in separate droplets, supporting insulation performance under wet conditions.
Silicone rubber also provides hydrophobicity-transfer characteristics. Even after pollution accumulates on the surface, the material can help the contamination layer retain water-repellent behavior.
According to the supplied product data, the pollution flashover voltage of composite insulators can be two to three times that of porcelain insulators under corresponding conditions. Actual performance should be confirmed through the final model data and required project tests.
Reduced Cleaning Requirements in Polluted Areas
DC transmission lines may cross deserts, coastal regions, industrial zones, agricultural areas and mountainous terrain. In some locations, regular cleaning of long insulator strings can be difficult and expensive.
The hydrophobic silicone rubber surface helps the insulator maintain pollution resistance after contamination accumulates. This makes composite suspension insulators particularly suitable for lines where routine access and cleaning are difficult.
Although the product is designed to reduce cleaning requirements, utilities should still carry out inspections according to the operating conditions and maintenance plan of the transmission line.
Lightweight Design Simplifies Transportation and Installation
The supplied information states that composite insulators weigh approximately one-seventh to one-tenth as much as corresponding porcelain insulators.
This weight reduction can provide important advantages for HVDC projects:
- Lower transportation difficulty for long insulator units
- Easier handling at tower construction sites
- Reduced installation equipment requirements
- Faster replacement during emergency maintenance
- Improved suitability for remote and mountainous transmission routes
These advantages become increasingly important for ultra-high-voltage insulators with large structure heights and long creepage distances.
ECR Fiberglass Core Provides Mechanical Strength
The internal load-bearing component is an acid-resistant ECR fiberglass rod. It transfers mechanical tension between the two metal end fittings while maintaining electrical insulation.
According to the supplied product information, the ECR rod has passed a 7,200-hour test. The silicone rubber housing protects the fiberglass core from moisture, pollution and outdoor environmental exposure.
The product range includes specified mechanical loads of:
- 120kN
- 160kN
- 210kN
- 240kN
- 300kN
- 420kN
- 550kN
- 1000kN
The routine tensile test load shown in the supplied data is generally 50% of the specified mechanical load. For example, a 300kN model has a listed routine tensile test load of 150kN.
Galvanized Steel Fittings Support Outdoor Service
The end fittings are made from hot-dip galvanized steel. The supplied specification states that the zinc coating thickness is greater than 100μm.
The galvanized layer helps protect the steel components from corrosion caused by rain, humidity and outdoor pollution.
Different models provide connection dimensions for ball-socket or ring-ring arrangements. The required fitting type and connection mark should be confirmed according to the tower hardware and conductor installation design.
Electrical Withstand Performance by Voltage Class
The required withstand voltage rises as the DC transmission voltage increases. Representative values from the supplied data include:
| Voltage Class | Wet DC 1-Minute Withstand | Lightning Impulse Withstand | Wet Operating Impulse Withstand |
|---|---|---|---|
| ±400kV | ±750kV | +2800kV | +1800kV |
| ±500kV | +600kV | +2550kV | +1550kV |
| ±660kV | 750kV | 2800kV | 1800kV |
| ±800kV | +900kV | +3600kV | +1950kV |
| ±1100kV | +1150kV | +4500kV | +2200kV |
These figures should be used together with the complete model specification and approved insulation-coordination design.
Corona Performance in UHVDC Systems
Corona control is particularly important in high-voltage and ultra-high-voltage transmission. Excessive electric field concentration can cause corona discharge, energy loss, audible noise and radio interference.
The supplied data lists minimum visible corona voltage values ranging from at least 650kV for selected ±500kV models to at least 1235kV for the ±1100kV series.
The final corona performance depends on the complete insulator assembly, grading devices, fittings, installation position and system electric-field design.
How to Select a DC Composite Suspension Insulator
A suitable model should not be selected only by matching the system voltage. The complete line design must be evaluated.
Important selection factors include:
- DC system voltage and polarity
- Maximum conductor tension
- Specified mechanical load
- Required safety factor
- Structure height
- Creepage distance
- Pollution severity
- Altitude and environmental conditions
- Lightning and switching impulse levels
- Visible corona requirements
- Connection hardware and tower arrangement
Project buyers should provide the required voltage class, mechanical load, installation drawing, pollution level and connection arrangement before confirming the final model.
Customization for HVDC and UHVDC Projects
Different transmission projects may require different dimensions, mechanical ratings and installation structures. Available customization can include:
- Voltage level
- Specified mechanical load
- Creepage distance
- Nominal structure height
- Connection mark
- Structure design
- Installation requirements
The final product configuration should be based on the approved technical agreement and project drawings.
Supporting Long-Distance Power Transmission
HVDC and UHVDC systems make it possible to transmit large amounts of electricity over long distances. As these networks expand, insulation equipment must provide both reliable electrical performance and sufficient mechanical strength.
DC composite suspension insulators address these requirements through long creepage distances, high load ratings, hydrophobic silicone rubber housings and lightweight composite construction.
They are especially suitable for polluted, remote and difficult-to-maintain transmission corridors where transportation and regular cleaning may be challenging.
Conclusion
The DC composite suspension insulator is an important component in high-voltage and ultra-high-voltage direct-current transmission systems.
The supplied FXBZ series covers voltage classes from ±400kV to ±1100kV, with mechanical load ratings from 120kN to 1000kN and multiple structure height and creepage distance options.
Its HTV silicone rubber housing supports hydrophobicity and pollution resistance, while the acid-resistant ECR fiberglass core provides mechanical strength. Hot-dip galvanized steel fittings help protect the connection components during outdoor operation.
Final selection should be based on the DC voltage level, mechanical loading, creepage distance, pollution conditions, corona requirements and installation design of the transmission project.
Frequently Asked Questions
What voltage levels are available for DC composite suspension insulators?
The supplied product range includes models for ±400kV, ±500kV, ±660kV, ±800kV and ±1100kV DC transmission systems.
What mechanical load ratings are available?
The listed models provide specified mechanical load ratings from 120kN to 1000kN, depending on the selected voltage class and model.
Why is silicone rubber used for the housing?
HTV silicone rubber provides hydrophobicity, hydrophobicity transfer, pollution resistance, waterproof performance and outdoor aging resistance.
What material is used for the load-bearing core?
The internal core is manufactured from acid-resistant ECR fiberglass rod. According to the supplied product information, it has passed a 7,200-hour test.
Can the structure and creepage distance be customized?
Voltage level, mechanical load, creepage distance, structure design and installation requirements can be coordinated according to the project specification.
