Difference between Dead Tank and Live Tank CT



Current Transformers are classified as Dead Tank Type and Live Tank Type CTs based on their construction. The term Dead and Live has their own meaning from the view point of potential of Secondary Windings and Core.


Dead Tank itself means that the potential of the Tank of CT is at earth potential i.e. zero as shown in the figure below.



The classification of CT i.e. whether Dead Tank or Live Tank comes from whether the Core and Secondary Winding of CT is located in Dead Tank or Live Tank of CT. If the Core and Secondary Winding is located in Dead Tank, then it is Dead Tank type CT while in case the Core and Secondary Winding is located in Live Tank portion then it is Live Tank type CT. Figure below depicts the Dead Tank type and Live Tank type CT.

Dead Tank type CT:


Observe that the Core and Secondary Winding is located in Dead Tank portion and hence it is Dead Tank type CT.

Live Tank type CT:



Carefully observe that Core and Secondary Winding is located in the Live Tank portion.

Now the question arises which type of CT shall be used and what are their advantages and disadvantages?

Basically the use of a particular type of CT depends on the requirement but these days mostly Live Tank CT is used. The advantages and disadvantage will be clear while comparing both types of CT.

Difference between Live Tank and Dead Tank type CT:

Sr. No.
Live Tank CT
Dead Tank CT
1)     
In live tank CT, the core with the secondary winding is housed in the top tank which is LIVE.(AT HIGH VOLTAGE)
In dead tank CT, the core and secondary winding is housed in the bottom tank which is earthed or DEAD.
2)     
In Live Tank, the core and secondary winding is insulated against the high voltage and housed in the top live tank.
In Dead Tank CT, the primary winding is brought down to the bottom tank and it is insulated from the earthed tank and cores.
3)     
In Live Tank CT, we insulate the core and secondary winding.
In Dead Tank CT, we insulate the primary winding.
4)     
Only after application of pre-defined insulation on secondary, primary is wound. Application of insulation over wound cores is easy.
It is practically difficult to apply the pre-defined insulation over the primary because the primary needs to pass through the wound cores.
5)     
Insulation is robust and reliable.
Insulation is not robust.
6)     
Primary winding is of shortest possible length and its natural shape offers high strength against the short time current dynamic forces.
The primary has to pass through the porcelain insulator and the larger length of the primary conductor produces maximum mechanical force during short time dynamic current which might damage the insulation.
7)     
Heat generated during short time thermal current is the minimum as primary copper volume is minimum and the heat dissipation is fast as the primary copper is directly in contact with transformer oil.
Heat generated during short time thermal current is maximum. Copper volume is maximum and the heat dissipation is slow as the heat need to conduct through the major insulation which is normally a bad conductor of heat.
8)     
The transformer is compact and economical.
The transformer is bulky and costly.
9)     
Primary winding is uniformly distributed around Core, Hence CT is truly low reactance type, which has inherent better transient performance.
-
10)  
As the length of Primary inside the CT is less (so resistance will be less), the heat produced in the primary will be less.
As the length of Primary is more (so resistance will be more) compared to Live Tank type CT, the heating will be more.

Thank you!

Comments

Post a Comment

Popular posts from this blog

Concept of Subtransient, Transient & Steady State

Image
The concept of Subtransient, Transient and Steady State arises in case of fault in an Alternator. Let us assume a sudden short circuit in three phase of alternator. The fault current will flow in all the three phases of alternator and its waveform will be as shown in figure below. When the alternator is short-circuited, the currents in all the three-phases rise rapidly to a high value of about 10 to 18 times of full load current, during the first quarter cycle. The flux crossing the air gap is large during a first couple of cycles. The reactance during these first two or three cycle is least and the short circuit current is high. This reactance is called subtransient reactance and is denoted by X". The first few cycles come under sub-transient state. After a first few cycles, the decrement in the r.m.s. value of short circuit current is less rapid than the decrements during the first few cycles. This state is called the Transient  State and the reactance in th
Read more

Open Circuit and Short Circuit Characteristics of Synchronous Machine

Image
Open Circuit Test and Short Circuit Test are performed on a Synchronous Machine to find out the parameters of Synchronous Machine and hence to have an idea of their performance.  Open Circuit Test of Synchronous Machine is also called No Load, Saturation or Magnetizing Characteristics for the reason which will be clear after going through the post. For getting the Open Circuit Characteristics of Synchronous Machine, the alternator is first driven at its rated speed and the open terminal voltage i.e. voltage across the armature terminal is noted by varying the field current. Thus Open Circuit Characteristic or OCC is basically the plot between the armature terminal voltage E f versus field current I f while keeping the speed of rotor at rated value. It shall be noted that for OCC, the final value of E f shall be 125% of the rated voltage. Figure below shows the connection diagram for performing the Open Circuit Test of Alternator. As clear from the figure above
Read more

Restricted Earth Fault Protection of Transformer

Image
Restricted Earth Fault (REF) protection is basically a Differential Protection. The only difference in between the Differential Protection and REF Protection is that, latter protection is more sensitive as compared to the former protection scheme. In earlier posts we have already discussed Differential Protection of Transformer and various characteristics of Differential Protection. In this post we will focus on Restricted earth Fault protection. Also Read, Transformer Differential Protection Percentage Differential Protection - Slope in Differential Protection Harmonic Restraining in Differential Protection For the sake of understanding REF Protection, we take a Transformer of configuration DYn i.e. HV side of Transformer is Delta connected while the LV side is Start connected and neutral is grounded solidly. As shown in figure above, there are a total of four Current Transformers (CTs), three CTs connected in each phase i.e. R, Y and B and one CT connected in neutral. The secondary o
Read more