When we visit any electrical substation, generally, we see two types of Current Transformers. Some CTs have their tanks at the top, and some CTs have their tanks at the bottom.
Nowadays, Top Tank-type CTs are popular.
What is the basic difference between a Live tank & a Dead Tank type CT?
Live Tank-Type CT
1. In a Live tank type CT, the tank is at the top.
2. Also, this top tank is electrically connected to this conductor, and it is at the same potential as that of this conductor.
3. However, the Load current does not flow through this tank. Load current flows through the primary of the CT. This top tank is just charged at the same potential as that of the live conductor, by connecting a link between the conductor and the tank body. Hence it is called a live tank CT.
4. The core and secondary winding of the CT are accommodated in the top tank.
5. Insulation of the Secondary winding is designed for the potential difference between the secondary winding and the tank potential which is the same as that of the primary winding.
6. In this type of CT application of insulation is relatively easy, because the primary terminal of the CT which is nothing but the conductor, and the outer covering tank are at the same potential. Hence insulation is used only for CT core and secondary winding. Which is robust and can be standardized.
7. The primary winding is of the shortest possible length. Hence it has less resistance which in turn produces less heat.
8. Also, in this type, secondary terminals of the CT are run through porcelain insulator housing. This Saves a lot of copper and insulation compared to the dead tank CT.
9. CT is compact and economical.
10. However, due positioning of the tank at the top, the center of gravity of live tank-type CT is high. Which makes this type of CT mechanically less stable.
11. These types of CT are electrically more stable.
Dead Tank-Type CT
1. In a Dead tank type CT, the tank is at the bottom.
2. Also, this bottom tank is connected to the ground and is at zero potential.
3. Since the tank is at zero potential, it is called a dead tank CT.
4. The core and secondary winding of the CT are accommodated in the bottom tank.
5. Insulation of the Secondary winding is designed for the potential difference between the secondary winding and the zero potential of the tank.
6. In this type of CT application of the insulation is relatively complicated, and it is less robust comparatively.
7. The primary winding is run down and again brought up through the porcelain insulator housing. Which increases the length of the CT primary, which in turn increases primary winding resistance, consequently, heat and losses of the CT.
8. Also, in this type, the primary conductor of the CT is run through porcelain insulator housing, more copper and insulation are required comparatively.
9. CT is bulky and costly.
10. However, due positioning of the tank at the bottom, the center of gravity of live tank-type CT is low. Which makes this type of CT mechanically more stable.
11. These types of CT are electrically less stable.