The low-voltage bushing is a key insulating and supporting component on the low-voltage side of the transformer. It is used to connect the low-voltage winding of the transformer with external terminal equipment and realize electrical insulation, mechanical fixation, and current conduction functions. The following is an explanation of its definition, structure, function, characteristics, etc.:
Definition and Use
The low-voltage bushing is an insulating device on the low-voltage side of the transformer. It is used to connect the low-voltage winding with external equipment (such as busbars, switch cabinets, etc.), and it also performs insulation and mechanical support functions. Its core functions include
Electrical insulation: prevent the low-voltage winding from short-circuiting with the transformer casing;
Mechanical fixation: support the low-voltage lead to avoid vibration or stress damage;
Current conduction: lead the low-voltage current to the external circuit through the conductive rod.
Structure and materials
Low-voltage bushings are usually composed of conductive rods, insulating bushings, flanges, seals, and other parts. The material selection takes into account both insulation performance and mechanical strength.
Insulating bushings: mostly made of ceramic or epoxy resin composite materials, with high insulation strength and arc resistance;
Conductive rods: generally made of cold-rolled plates or tin-plated plates; tinning on the surface can improve conductivity and prevent oxidation.
Seals: made of rubber or silicone to ensure the sealing between the bushing and the transformer tank.
Core function analysis
Electrical insulation function
Low-voltage bushings need to withstand the power frequency voltage and transient overvoltage during transformer operation, and their insulation design must meet the following requirements:
Insulation level: usually needs to withstand a 1-3 kV power frequency withstand voltage test;
Creep distance: according to the voltage level and environmental conditions, the creepage distance on the bushing surface must meet the standard (such as IEC 60137).
Mechanical support and current conduction
Support function: The bushing needs to bear the weight of the low-voltage lead and the stress caused by thermal expansion and contraction.
Current carrying capacity: The cross-sectional area of the conductive rod needs to be designed according to the rated current of the transformer (for example, the current on the low-voltage side of a 1000 kVA transformer is about 1443 A, and a conductive rod with sufficient cross-sectional area needs to be matched).
Environmental adaptability
Moisture-proof and anti-fouling: Bushings installed outdoors need to have hydrophobicity and anti-fouling flashover capabilities.
Weather resistance: The material needs to withstand ultraviolet rays, ozone, and temperature changes.
Technical characteristics
Rated voltage: Usually 0.4-1 kV, matching the voltage on the low-voltage side of the transformer;
Rated current: Determined by the capacity of the transformer, such as the low-voltage bushing of an 800 kVA transformer needing to carry about 1155 A current;
Mechanical strength: Need to withstand the electric force during a short circuit (for example, the three-phase short-circuit current may reach tens of kiloamperes).
Application scenarios
Low-voltage bushings are widely used in the low-voltage side of oil-immersed transformers, dry-type transformers, and special transformers (such as rectifier transformers) and are commonly found in:
Power system: transformer low-voltage side outgoing lines in substations and distribution stations;
Industrial field: distribution transformers in metallurgy, the chemical industry, and other industries;
New energy field: box-type transformers in wind power and photovoltaic power stations.