Types of Bushings in Transformers

Transformers are essential components of the electrical power distribution system, responsible for stepping up or stepping down voltage levels for efficient energy transfer. While many components contribute to a transformer’s functionality, one crucial element is often overlooked – the bushing. Bushings play a pivotal role in the overall performance and safety of transformers. In this post, we will discuss into the various types of bushings used in transformers, their functions, advantages, and applications.

1. What are Bushings in Transformers?

Bushings in transformers are insulated components that serve as connectors between the transformer windings and the external power system. They enable the safe transfer of high voltage currents from the internal to the external circuits without causing electrical breakdown or loss. Bushings also prevent oil leakage and provide mechanical support to the winding structures.

2. Types of Bushings

Oil-Impregnated Paper Bushings

Oil-impregnated paper bushings are one of the earliest and most commonly used types of bushings in transformers. They consist of layers of high-grade insulating paper impregnated with insulating oil, which enhances their dielectric strength. These bushings are suitable for low to medium voltage applications and are known for their reliability and cost-effectiveness.

Resin-Impregnated Paper (RIP) Bushings

Resin-impregnated paper (RIP) bushings are an advancement over oil-impregnated paper bushings. They have multiple layers of crepe paper impregnated with epoxy resin, providing better mechanical strength and higher resistance to environmental factors such as moisture and contaminants. RIP bushings are widely used in medium to high voltage transformers and offer enhanced performance and longer service life.

Capacitor Bushings

Capacitor bushings, also known as condenser bushings, are specifically designed to control the electric field around the bushing and prevent corona discharge. They consist of a series of capacitor plates, and the dielectric material between these plates plays a vital role in ensuring uniform voltage distribution. Capacitor bushings are commonly used in high voltage and extra-high voltage transformers and are ideal for applications where corona discharge needs to be minimized.

Resin Bonded Paper (RBP) Bushings

Resin bonded paper (RBP) bushings are a more modern variant of bushings that offer improved dielectric strength and mechanical properties. They are manufactured by impregnating high-quality paper with epoxy resin under vacuum conditions. RBP bushings provide excellent resistance to partial discharges, making them suitable for high voltage and extra-high voltage transformers.

Gas Insulated Bushings

Gas insulated bushings are a special type of bushing that utilizes SF6 gas as an insulating medium. These bushings have a compact design and are often used in gas-insulated transformers (GIS) where space is limited. The SF6 gas provides superior insulation properties, high dielectric strength, and excellent arc-quenching capabilities, ensuring safe and reliable operation.

Advantages and Disadvantages of Different Bushing Types


– Oil-Impregnated Paper Bushings:

  – Cost-effective and reliable for low to medium voltage transformers.

  – Good resistance to short-circuits and overloads.

– Resin-Impregnated Paper (RIP) Bushings:

  – Improved mechanical strength and moisture resistance.

  – Longer service life and reduced maintenance requirements.

– Capacitor Bushings:

  – Minimization of corona discharge and radio interference.

  – Suitable for high voltage applications.

– Resin Bonded Paper (RBP) Bushings:

  – Excellent resistance to partial discharges.

  – Ideal for high voltage and extra-high voltage transformers.

– Gas Insulated Bushings:

  – Compact design, suitable for gas-insulated transformers.

  – High dielectric strength and arc-quenching capabilities.


– Oil-Impregnated Paper Bushings:

  – Prone to oil leaks, which can be environmentally hazardous.

  – Limited suitability for high voltage applications.

– Resin-Impregnated Paper (RIP) Bushings:

  – More expensive compared to oil-impregnated paper bushings.

  – Requires careful installation to avoid damage during handling.

– Capacitor Bushings:

  – Higher manufacturing complexity.

  – Sensitive to changes in the dielectric material.

– Resin Bonded Paper (RBP) Bushings:

  – Initial manufacturing costs can be higher than traditional paper bushings.

  – Requires expertise in handling epoxy resins.

– Gas Insulated Bushings:

  – High initial investment due to gas-insulated transformer technology.

  – SF6 gas has environmental concerns, as it is a greenhouse gas.

Applications of Different Bushing Types

– Oil-Impregnated Paper Bushings: Distribution transformers, smaller power transformers.

– Resin-Impregnated Paper (RIP) Bushings: Medium and large power transformers, generator transformers.

– Capacitor Bushings: High voltage and extra-high voltage transformers, power capacitors.

– Resin Bonded Paper (RBP) Bushings: High voltage and extra-high voltage transformers, special applications.

– Gas Insulated Bushings: Gas-insulated transformers, high voltage and extra-high voltage applications in confined spaces.

Bushings are an indispensable component in transformers that facilitate the safe and efficient transfer of electrical energy. Each type of bushing offers specific advantages and is suitable for different voltage ranges and applications. From traditional oil-impregnated paper bushings to modern gas-insulated bushings, the choice of the right type depends on the specific requirements of the transformer and the operating conditions.

Understanding the characteristics, advantages, and limitations of various bushing types empowers transformer manufacturers and power system engineers to make informed decisions, ensuring reliable and effective electrical power transmission across the grid. By paying due attention to this critical component, we can enhance the performance, safety, and longevity of transformers, ultimately contributing to the stability and efficiency of the entire power distribution system.

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