We all know about overhead transmission lines and underground cable for power transmission at high voltage.
ABB recently has successfully commissioned 1000 KV gas insulated transmission line(GIL) through a tunnel in a chineese river .The line is around 5 KM long.
Now Question in your mind?
What is this Gas insulated line and why world is turning towards GIL ?
First we try to explain you about gas insulated line?
First you try to find out the meaning from the world “gas insulated line “.
Think Think !!
Yes, this line has gas as the name suggests.. what type of gas ..guess ..yes , you are right ..it is SF6 but not completely SF6 its a blend of SF6(20 percent) while 80 percent is N2(Nitrogen).
Now guess the conductor being used in GIL … obviously it is aluminium.
See below how a GIL looks ?
This is 500 KV three phase AC line. It is laid in a tunnel.
GIL can also be installed overhead like this below.
Also GIL can be directly buried in ground.
Now you see installed GIL. But what is inside ..
Construction of GIL
So you see,
(i) A cylindrical aluminium conductor at the centre which will carry the current and transmit the power.
(ii)A outer aluminium enclosure for housing the central conductor and holds the insulators.
You have seen in overhead lines the induction problem ..a overhead charged line passing over a dead line , it induces voltage in dead line.
This is not in case of GIL ? How ? Read below ..
In GIL, when current flows through central conductor than due to voltage induced, an equal current flows in outer aluminium cylindrical section( enclosure) in opposite direction.
The magentic field generated by central conductor is cancelled by magentic field generated by enclosure. So GIL produces very little outside magentic field.
This is the biggest advantages of GIL.
Why GIL preferred? Advantages of GIL over conventional overhead transmission line and underground cables.
- Require less space
- Can be installed in tunnel, buried in ground or overhead on structures.
- Low power loss
- Heat dissipation in GIL is better than cable (When power is transferred than heat will generate but as the heat generats it should be dissipated to avoid insulation failure).
- Maintenance free
- Low electromagnetic field generation as already explained
- GIL can be used from 110 KV to to 1200 KV.
But GIL use is limited upto 70-80 Km due to technical reasons.