The history of transformer bushings dates back to the early 20th century when electrical power systems were first developed. The earliest transformer bushings were made of porcelain and were designed to isolate high-voltage conductors from grounded objects. As power systems grew larger and more complex, the use of porcelain bushings became widespread during the 1920s and 1930s. What type of bushing does your transformer require? Refer to our bushing guide to explore various types and their applications.
What is a Transformer Bushing?
A transformer bushing is a necessary component that enables the flow of current into and out of a transformer. It provides an efficient path for electricity while isolating it from surrounding conductive materials. As an important part of high-voltage electrical systems, bushings offer reliable electrical insulation and mechanical support for conductors passing through the transformer tank. These bushings create an insulating barrier between high-voltage conductors and grounded metal components, ensuring the safe transmission of electricity from the transformer to external systems.
Working Principle of Electrical Bushings
Transformer bushings utilize internal insulating materials, such as oil, gas, or solid insulators, to isolate high-voltage conductors from grounded components. The structural design of bushings ensures uniform electric field distribution, thereby minimizing the risk of partial discharges. Additionally, bushings provide mechanical support, capable of withstanding the weight of conductors as well as external mechanical stresses from environmental factors such as wind or seismic activity.
Various Types of Transformer Bushings
Transformer bushings come in a wide range of designs and types, tailored to meet different application requirements. Below are some of the primary designs and types of transformer bushings:
Porcelain Bushings
Porcelain bushings are the oldest and most widely used type of transformer bushings. Built on high-quality porcelain material, these bushings feature a robust structure, enabling them to operate reliably under harsh environmental conditions. The excellent insulating properties of porcelain make these bushings particularly effective in applications requiring high-voltage insulation.
Additionally, porcelain bushings offer exceptional heat resistance, capable of withstanding extreme temperatures of up to 900°C. They are particularly suitable for outdoor environments that demand high voltage insulation and mechanical durability, such as in the installation and operation of transformers and circuit breakers. Their weather-resistant and anti-corrosion characteristics further enhance their versatility and reliability.
Oil-Insulated Bushings
Oil-insulated bushings are a type of transformer bushing that uses oil as the insulating medium, typically employing mineral oil or synthetic oil. These insulating oils provide excellent dielectric properties while also serving as an effective cooling agent, thereby enhancing the lifespan of the bushing.
Compared to traditional porcelain bushings, oil-insulated bushings feature a more compact design, reduced weight, and easier installation. They are capable of accommodating higher voltage levels.
Gas-Insulated Bushings
Gas-insulated bushings are an advanced type of bushing that uses sulfur hexafluoride (SF₆) gas as the insulating medium. SF₆ gas provides excellent electrical insulation, high dielectric strength, and low conductivity, allowing gas-insulated bushings to operate under high-voltage and ultra-high-voltage conditions. The use of SF₆ gas effectively reduces electric field intensity.
Gas-insulated bushings are particularly suited for applications requiring high insulation performance in complex power systems. Furthermore, gas-insulated bushings demonstrate strong adaptability to high-humidity or dust-laden environments, ensuring stable operation.
Resin-Based Bushings
Resin-Impregnated Paper (RIP) Bushings
RIP bushings are a type of dry bushing that uses resin-impregnated paper as a solid insulating material. Compared to traditional oil-insulated bushings, RIP bushings are more environmentally friendly and offer excellent insulation performance. They are well-suited for indoor applications and commonly used in switchgear and transformers.
Epoxy Resin Bushings
Epoxy resin bushings use epoxy resin as the insulating material, which provides resistance to moisture and chemical corrosion. These bushings are primarily designed for indoor environments and are particularly suitable for high-humidity or chemically aggressive conditions.
Resin-Cast Capacitive Bushings
Resin-cast capacitive bushings feature a core insulation structure made of alternating layers of insulating paper and aluminum foil, encapsulated in an external layer of cast epoxy resin to form solid insulation. These bushings are used in oil-gas hybrid systems, with the upper section designed for SF₆ gas insulation in GIS pipelines and the lower section immersed in transformer oil.
Capacitive Bushings
Capacitive bushings are constructed using a capacitive core formed by alternating layers of insulating paper and aluminum foil. This design ensures a uniform electric field distribution, thereby enhancing insulation performance.
High-Current Bushings for 40kV and Below
High-current bushings for voltages of 40kV and below are available in two structural types: rod-type and capacitive-type. Rod-type bushings are commonly used for the low-voltage windings of generator transformers, while capacitive bushings are suited for the low-voltage windings of large generator transformers. These bushings are tailored to meet the diverse requirements of medium- and low-voltage systems.
Oil-Impregnated Paper (OIP) Capacitive Bushings
OIP capacitive bushings are made with alternating layers of adhesive paper and aluminum foil, with the internal insulation filled with insulating oil. However, due to their susceptibility to aging and performance degradation, these bushings have been gradually phased out in modern applications, though they were widely used in early high-voltage equipment.
Hybrid Bushings
Hybrid bushings represent an innovative design that combines the advantages of oil-insulated and gas-insulated bushings. The lower section uses oil as the primary insulating medium, delivering excellent insulation and cooling performance, while the upper section employs sulfur hexafluoride (SF₆) gas as the insulating material to enhance electrical strength and overall performance.
The design of hybrid bushings not only significantly improves system safety and reliability but also reduces the risk associated with the failure of a single insulating medium. Hybrid bushings are particularly notable in ultra-high-voltage transmission systems.
Instrument Transformer Bushings
Instrument transformer bushings are high-performance bushings specifically designed for current transformers and voltage transformers. Typically made from porcelain or epoxy resin, these bushings provide stable electrical insulation for metering equipment while withstanding complex operating conditions, such as high voltages and mechanical stresses. They also prevent external moisture and other environmental factors from affecting the transformers.
Instrument transformer bushings are widely used in power generation, transmission, and distribution systems, ensuring the safety and accuracy of the entire power grid.
Final Thoughts
Transformer bushings are designed with a variety of materials and configurations to meet diverse application needs and operating conditions. Selecting the appropriate bushing requires careful consideration of factors such as voltage level, environmental conditions, mechanical stresses, and maintenance requirements to ensure the safety and efficiency of the power system.
With years of industry expertise, OUWEI boasts a team of professionals specializing in transformer technologies, dedicated to delivering quality solutions that adhere to stringent industry standards. Whether your requirements involve specific voltage ratings, dimensions, or unique environmental challenges, we offer customized products and services tailored to your needs. By partnering with OUWEI, you gain a trusted ally to help enhance the efficiency and performance of your electrical infrastructure.