Circuit breakers are available as live tank, dead tank, or grounded tank designs. Dead tank means interruption takes place in a grounded enclosure and current transformers are located on both sides of the break (interrupter contacts). Interrupter maintenance is at ground level and seismic withstand is improved versus live tank designs. Bushings (more accurately described as gas-filled weathersheds, because, unlike the condenser bushings found on bulk oil circuit breakers, gas breakers do not have true bushings) are used for line and load connections that permit installation of bushing current transformers for relaying and metering at a nominal cost. The dead tank breaker does require additional insulating oil or gas (i.e., more insulating oil or gas than just the amount required to perform successful interruption and to maintain adequate dielectric strength) to provide the insulation between the interrupter and the grounded tank enclosure.
Live tank means interruption takes place in an enclosure that is at line potential. Live tank circuit breakers consist of an interrupter chamber that is mounted on insulators and is at line potential. This approach allows a modular design as interrupters can be connected in series to operate at higher voltage levels. Operation of the contacts is usually through an insulated operating rod or rotation of a porcelain insulator assembly via an operating mechanism at ground level. This design minimizes the quantity of oil or gas required as no additional quantity is required for insulation of a grounded tank enclosure. The live tank design also readily adapts to the addition of pre-insertion resistors or grading capacitors when they are required. Seismic capability requires special consideration due to the high center of gravity of the live tank breaker design, and live tank circuit breakers require separate, structure mounted, free standing current transformers.
Grounded tank means interruption takes place in an enclosure that is partially at line potential and partially at ground potential. Although the grounded tank breaker’s current transformers are on the same side of the break (interrupter contacts) the grounded tank breaker relays just like a dead tank breaker. The grounded tank breaker design came about as a result of the installation of a live tank breaker interrupter into a dead tank breaker configuration.
The Outdoor Current Transformers may be Live Tank Design or Dead Tank Design. In the Live tank design, Active part (ie Core with secondary and Primary duly insulated) is in the top tank. Top Tank is live and secondary is insulated and taken to the bottom tank. In Dead Tank design, Active part is in bottom tank. The bottom tank is dead ( in ground Potential) and the primary is insulated and taken to the top tank for primary termination.