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High Voltage Riddle No.4 - High voltage Dead tank & Live tank equipments
Please explain the difference between dead tank & live tank type CTs with relative merits/demerits and constructional difference.
Author : V.K. Nambiathiri - From: India
Thu, March 31st, 2011 - 15:39
Circuit breakers:

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.

Current transformer:

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.

Author : Hamid - From: Iran
Thu, April 7th, 2011 - 18:18
In 400kV substatons which type breaker $CTs , Dead or Live tank Type, preferred? 
Author : V.K.Nambiathiri - From: India
Sat, April 9th, 2011 - 09:02
Dead tank is more applicable. 
Author : Hamid - From: Iran
Wed, May 4th, 2011 - 18:13
Thanks a lot 
Author : V.K.Nambiathirt - From: India
Mon, July 11th, 2011 - 11:34
Dear Hamid

What is the advantage of live tank over dead tank...as we are using live tank ct in 800kv, 420kv,220kv,132kv..
what is the reason using live tank type...as u said that "Dead tank is more applicable"

Author : shozab kazmi - From: India
Wed, May 30th, 2012 - 15:42
describe us the details of live tank PT & how it works? 
Author : S.K.Deore
Mon, July 2nd, 2012 - 10:44
Dead Tank is more applicable because its cheaper. The manufacturing of bushing for power transformer can be used is this case and automatic wrapping of paper made it easy to manufacture (time and cost reduces) and available in plenty from many manufacturers. Installation is easier since the tank is far from live line.

Advantages of Live tank -->

a) Shorter primary conductor gives better rigidity and high short circuit current withstanding capability.

b) With uniformly distributed primary winding these CTs are with lower reactance -->provides inherent better transient performance.

c) Main source of heat - high current part is only in primary tank -- ensures less heating of bushing/core compared to dead tank type design. This ensures better thermal stability and less problem created through dissolved gas in insulating oil. In case something goes wrong - a well designed live tank CT wont explode only from top unlike the blast of insulator core of dead tank CTs' which can damage human life a well as the other substation equipments nearby.

Author : Saptarshi Chatterjee - From: India
Sat, February 15th, 2014 - 03:08
Dear V.K.Nambiathiri
in India we are following Live Tank Circuit Breakers from 132KV Level to 765KV level.
in case of 1200KV Dead tank Circuit breakers are adopting due seismic test pass.
in case of CTs either Live tank or dead tank both acceptable. but in case of 1200KV Dead Tank.
Further in 1200KV adopting Hybrid GIS system with inbuilt CT.
   Dear Saptarshi Chatterjee
Accepted the views given  
Author : Gopala Krishna Palepu - From: India
Tue, September 12th, 2017 - 16:24
Live tank CT are cheaper because the length of primary conductor is very less and the oil capacity is also less . Live tank CT is more susceptible to failure because  the secondary terminals ( multiple ) are to be routed from the tank top up to the bottom , where they are terminated .
In case of Live tank , the pressure relieving aperture is very close to the CT tank and the gas generated are released quickly reducing the chances of bursting .
The primary being shorter have lesser Resistance and hence less loss ( heat generation) giving specific advantages in cooling and overloading . 
Author : R K MOHAPATRA - From: India
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