Before we go for comparing both types of Circuit breaker, just see pictures of both i.e. live tank and dead tank SF6 circuit breaker. How these breakers looks from outside.
Now first talk about live tank circuit breaker.
see above image, The top part of the breaker is interrupter means breaking unit ..the unit in which moving and fixed contacts are placed.
This top part is made up of porcelain or polymer and as this top part keeps circuit breaker current carrying contacts, these contacts remain closed during normal operation and opens when circuit breaker tripped on account of fault in the circuit or manually breaker is opened.
As this top portion or we can say, top tank carry High voltage contacts of breaker, so this type of breaker is called Live tank circuit breaker.
Now come to dead tank circuit breaker,
See above picture of dead tank circuit breaker, here, for smplicity, only one phase of the breaker is shown.
The breaker or interrupter unit i.e. fixed and moving contacts, arc quenching medium (SF6 gas) etc. is placed inside a metal tank. This metal tank is earthed so this type of breaker is called dead tank or earthed tank circuit breaker.
You can also see in the pic, there are circular shaped or toroidal current transforms inside the bushing. The dead tank circuit breaker comes with ot without these Current transformers . These CTs can be used as protection CTs.
Kindly note that vaccum circuit breaker also comes in live tank and dead tank design.
Use, advantages and disadvantages of live tank and dead tank circuit breaker
- Live tank circuit breakers is filled with very much less SF6 gas as compared to dead tank circuit breaker. Dead tank circuit breaker require too much sf6 gas as compared to live tank circuit breaker as the interrupter are in a large metal chamber so to provide necessary insulation. As SF6 gas is green house gas(gas causes global warming). Live tank design is so environment friendly.
- Dead tank circuit breaker, there are chances of fault between interrupter contacts and metal tank so require current transformers in the bushing to provide fast acting protection in case of fault within circuit breaker.
- Dead tank circuit breaker is less prone to earthquakes as compared to live tank.