What Is The Main Function Of Bushing in High Voltage Equipment?

In high voltage equipment, bushing is key part connecting internal high voltage conductor to external circuit. Its core functions can be summarized in the following aspects, combining with the particularity high-pressure environment to explain in detail:
1.Electrical insulation: isolating high voltage to prevent malfunction.
Challenges in high voltage environments: Internal conductors of high voltage devices (e.g. transformers, circuit breakers, GIS) have extremely high voltage (usually ≥110kV). If the conductor penetrates directly through the shell of the device or connects to the external circuit, it is easy to cause arc discharge or insulation breakdown, causing damage or even explosion of the device.
Bushing function:
Main insulation function: The bushing adopts high voltage material (such as oil-paper capacitor insulation, SF6 gas insulation, epoxy resin insulation, etc.) to form multi-layer insulation barrier to withstand the high voltage difference between conductor and casing.
Electric field uniformization: The capacitor bushing adopts a built-in capacitor screen structure, so that the electric field is evenly distributed along the axial direction of conductor and breakdown caused by the concentration of local electric field is avoided.
Creep distance control: The the bushing surface adopts the umbrella skirt or corrugated structure, increases the creeping distance of the surface and prevents flashes in rain, snow and dirty environment.
2.Mechanical support and fixation: ensuring conductor stability
Features of high voltage equipment: high current and magnetic field of internal conductors may cause vibration or displacement during operation.
Casing function:
Rigid support: The casing flange equipment bushing connection is tight, fixed conductor position, prevent wire from vibrating or mechanical stress and loose or bad contact.
Short circuit resistance: In the event of a short circuit failure, the casing needs to withstand a large amount of conductor electricity to avoid conductor deformation or casing rupture.
3. Environmental distancing: Inside protective equipment
High pressure equipment protection requirements: external moisture, dust, chemical gas, etc. must be prevented from intruding into the interior, to prevent aging insulation or corrosion of metal parts.
Casing function:
Sealing design: The connection between the housing and the housing of the equipment is sealed or welding process to ensure an IP protection level (e.g. IP67) against the entry of liquid or solid foreign bodies.
Weather-resistant materials: silicone rubber or composite insulation materials used in the outer shell to protect the environment from UV rays, ozone and extreme temperatures.
4. Voltage level adaptation and conversion
Complexity of high voltage systems: Voltage levels may vary between different devices (e.g. connection between transformer high voltage sides and transmission line).
Role of bushing:
Voltage matching: The rated voltage of the bushing must be consistent with the system voltage to ensure insulation safety margin.
Interface transition: The bushing provides standardized interfaces (e.g. flanges and threads) to simplify installation and reduce contact resistance when the device is connected to cables and buss.
V. Heat dissipation and temperature rise control
Heat problems in high voltage equipment: When a conductor passes through a large current, heat is generated. If the heat dissipation poorly, it can cause insulation to age faster.
Role of bushing:
conduction design: Some bushings uses materials with good thermal conductivity,such as metal flanges, to assist conductors heat dissipation.
Ventilation structure: Some oil-soaked shafts transfer heat to the outside of the equipment through oil circulation or natural convection.
6. Monitoring and diagnostic functions (smart bushings)
The development trend of modern high voltage equipment: It is necessary to monitor the condition of equipment in real time to improve the operation reliability.
Bushing function:
Built-in sensors: Some smart bushings integrate temperature, partial discharge and capacitance sensors and transmit data to the monitoring system via fiber or wireless.
Fault warning: Through the analysis of sensor data, we can detect the potential problems of insulation degradation and overheating in advance, and avoid sudden failure.
Examples of typical application scenario examples
Transformer high-voltage bushing:
Connect the high voltage winding of the transformer to the transmission line and withstand the highest voltage of the system.
Adopting the structure of oil paper capacitor, including insulating oil, porcelain sleeve or silicone rubber shed.
GIS (gas insulated switchgear) bushing:
Conductors are encased in SF6 gas, and the bushing acts as a transition interface between the gas and the outside air.
It is necessary to satisfy both gas sealing performance and the heat preservation performance.
Converter transformer valve side bushing:
Used for HVDC transmission, can withstand complex DC field and harmonic superposition.
special insulating materials and structural design are used to prevent the accumulation of space charges under DC electromagnetic field.
Comparison with low low-voltage bushing
Low pressure Low-voltage bushing characteristics
Insulation requires high voltage and uniform electric field to prevent partial discharge. insulation thickness is relatively thin and the focus is on preventing leakages and short circuits.
Complex structure (e.g. capacitor screen, multilayer insulation, sealing structure) Simple (single-layer insulation, basic sealing)
High material cost (ceramics, SF6 gas, special resins) low (epoxy resin, common silicone rubber)
Security risk failure can lead to explosions and large power outages usually limited to local equipment damage
High-voltage bushing is a "small but critical" component of high-pressure equipment. Its design needs to take into account electrical, mechanical, thermal and environmental factors in order to ensure long-term safe operation of the equipment in extreme conditions.