Oil-Air Condenser Bushing
Introduction to Condenser Bushings
The condenser bushing relies upon a central rod enclosed in oil impregnated paper layers. Between each layer are concentrically arranged conductive foils. Condenser bushings are typically utilised for 25kV to 52kV applications. The condenser shown above is for a fluid insulated transformer, the lower end would connect to the transformer windings (oil side) whilst the upper end connects to incoming/outgoing circuit (air side).
The purpose of the conductive foils (usually aluminium or conductive ink) is to equalise the capacitance between the layers. This is achieved by varying the length of the conductive foils (sometimes referred to as 'equalisation plates') depending upon the paper diameter; the diameter grows with each paper layer applied.
The central conductor may be copper bolt with terminal connections at each end, or, a thick walled tube (larger current capacity). It is necessary to us a thick walled tube not just to increase the current carrying capacity, but also to reduce the skin effect.
The bushing's unique shape and construction is designed to withstand strong adverse weather conditions. A spring inside the condenser body maintains a pressure between the gaskets and sealing surfaces; this prevents the leakage of insulating oil.