Difference between Live tank and dead tank current transformer


Before we start, lets go back to CT basics, what a CT does , obviously a 2000/1 amp delivers 1 amp at secondary when 2000 amp is flowing or 0.5 amp when 1000 amp is flowing through the primary or line .

How this CT does that ? A CT generally have two terminals when you will look at it. CT is connected in the line through these terminals.

When CT is connected in the circuit or line ..its primary winding carries the line current.

Generally Primary winding of a CT is made to pass through a core called secondary core and a winding over secondary core called secondary winding generated the desired ampere.

Live tank means a metallic tank which is live means at voltage and dead tank means a metallic tank which is dead no potential or earthed.

A cross sectional diagram of both live tank and dead tank current transformer (CT) is shown below.

Dead and live tank ct
Cross section of the dead tank and live tank CT( image Credit: ABB)

Just see dead tank CT for a minute. In dead tank CT, primary winding usually a soild conductor comes down from top to bottom and again goes up from bottom to up, passing through a core i.e. secondary core at the bottom and there is a secondary winding over this core.

In live tank CT shown above, the solid primary conductor does not come down from top, it remains at the top but the secondary core is placed at the top. Primary conductor passes through secondary core at the top. Secondary winding is placed on the secondary core at the top. From the top, secondary wires comes down from top to CT terminal box.

In live tank CT, Secondary core is placed in the top live tank so is the name “live”.

In dead tank type, secondary core is placed in the bottom tank which is earthed.

So what are their advantages over one another. Each one has their pros and cons.

Pros and cons of both type of CT :

  • As the secondary core is placed at top in live tank CT. Its center of gravity is upper side so becomes difficult to handle during installation.
  • In the live tank CT , cost of supporting structure is reduced.
  • In the dead tank CT , heat from secondary winding is dissipated through oil while in live tank, heat is dissipated through main insulation which lowers the age of insulation.
  • In dead tank CT, weight of secondary core is freely resting on supports while in live tank type, weight of the core is take by insulation.

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