Transformer Bushing Insulator

What Are Transformer Bushings?

A transformer bushing provides a controlled insulated path for live conductors through grounded metal, performing three core functions:

• Electrical insulation – prevents leakage between energized conductors and grounded parts
• Mechanical support – holds conductors rigid under mechanical forces
• Sealing – prevents moisture ingress and oil leakage

Bushings are used on both the high-voltage and low-voltage sides of transformers, and their reliability directly influences transformer safety and lifespan.

2. Types of Transformer Bushings

Transformer bushings are categorized by insulation type and voltage level:

 Porcelain Bushings

• Made of glazed ceramic

• Good mechanical and dielectric strength

• Up to ~245 kV

• Excellent weathering resistance

• Common in outdoor substations and distribution transformers

 Resin-Impregnated Paper (RIP) Bushings

• Paper layers impregnated with epoxy resin

• Dry, oil-free design

• Up to ~800 kV

• Non-flammable and partial-discharge resistant

• Compact and lightweight

 Oil-Impregnated Paper (OIP) Bushings

• Paper insulation impregnated with transformer oil

• Excellent dielectric and heat dissipation

• Up to ~1200 kV

• Proven long-term performance but requires oil monitoring

 Polymer/Composite Bushings

• Silicone rubber or epoxy composite insulation

• Lightweight with hydrophobic surfaces

• Good against contamination and tracking

• Often used in coastal or polluted outdoor environments

3. Materials & Construction

Bushings are engineered from combinations of:

• Core conductor – copper or aluminum for high conductivity

• Insulating body – porcelain, silicone rubber, epoxy resin, or gas/oil systems

• Capacitance grading layers – distribute electric fields uniformly

• Seals & flange assemblies – ensure leak-proof mounting to transformer tanks

These elements work together to balance electrical and mechanical performance, reducing corona and partial discharges at high voltages.

4. Electrical & Mechanical Performance Parameters

Important performance specifications include:

Optimizing these measures ensures bushings endure decades under electrical, thermal, and environmental stress.

5. Testing & Quality Standards

Bushings must pass rigorous international tests, including:

Electrical Tests:

• Power frequency withstand

• Lightning impulse

• Partial discharge

• Capacitance & tan-delta

Mechanical Tests:

• Cantilever load

• Thermal cycling

• Sealing & leakage

Relevant standards:

• IEC 60137 – High-voltage bushings

• IEEE C57.19 – Bushing design & performance

• ANSI C29 – Insulator & bushing performance benchmarks

Zetwerk’s facilities comply with these standards, ensuring quality for utility and industrial applications.

6. Key Applications

Transformer bushings are vital in:

• Power transformers (110–800 kV)

• Distribution transformers

• Switchgear & circuit breakers

• Generators & reactors

• Renewable energy step-up transformers

With renewable systems and harsher operating conditions, advanced insulation designs are increasingly important.