High Voltage Bushings: Condenser Vs. Non-Condenser

Transformer bushings are essential components that enable electrical conductors to safely pass through grounded barriers, such as transformer tanks. The main difference between the two types is how they handle electrical stress.

Non-condenser bushings:

Non-condenser bushings, also known as solid insulation bushings, that use thick, bulk insulation materials instead of a fancy "capacitance grading" system to insulate electricity.

They have a simple structure: a conductor surrounded by materials such as porcelain, oil or air. Lacking a controlled capacitive system and manage stress through conductor shape and insulator properties. Their main advantage is a simple, robust construction that is cost-effective for low and medium-voltage applications(up to 36 kV).

Condenser bushings

Condenser (capacitive) bushings are designed for higher voltages( 72.5 kV and above).  

Compared to solid insulation bushings, condenser bushings have a relatively complex construction. They have a special core in the middle that's "capacitance-graded". This means it's designed to spread out voltage evenly. Their core innovation is the inclusion of conductive layers (often metal foil) embedded within the main insulation, —typically high-grade paper impregnated with resin or oil.

These layers are concentrically arranged, creating a series of capacitors between the conductor and the grounded flange. This structure creates a controlled, uniform voltage gradient along the length of the bushing, effectively minimizing dangerous concentrations of electrical stress. This allows for a more compact, efficient, and reliable design at extremely high voltages.

Types of condenser bushings:

Condenser bushings are mainly divided into different types based on their main insulation system.

1.  Oil-impregnated paper (OIP): This is a traditional and highly reliable type of insulation where paper is impregnated with insulating oil. It is known for its excellent dielectric properties, but a sealed system is required.

2.  Resin-impregnated paper (RIP): This is a modern dry-type bushing. Layers of paper are impregnated with epoxy resin under vacuum and heat to form a solid, monolithic unit. RIP bushings are maintenance-free and non-leaking, and are now the dominant technology for new apparatus.

3. Gas-Insulated Condenser Bushings: Filled with sulfur hexafluoride (SF₆) gas. Smaller and good for indoor equipment.

In summary, while non-condenser bushings are adequate for lower voltages, complex capacitor designs are essential for ensuring the safety, stability, and extended service life of high-voltage networks.