Question

What is a Tera-Tera system in a power system network mean and how does it operate? How does current flow from one earth electrode in a house to the electrode earth of the substation? like how does it take that path, if there is no connection between them; other than the fact they are both buried underground.

Answer 1

I will explain the Tera Tera system later ,but First I will explain how current flows from our house to Substation if there is no connection between them other than them buried to earth.

Actually Earth can be used as a return (Even water bodies can be used as return(used in transnational HVDC)).

Another example is the traction system.Current returns via Rails and Earth.

Earth is INFINITE SOURCE OF ELECTRONS OR CHRAGED PARTICLES...once a low resistive path is ensured to it then there is no problem in flow of current.

Imagine a water filled in a tub. You insert a pump that pumps water.One end of the pipe is connected to water in tub(bottom end) ,top end of pipe is connected to bottom of pump.Now There is a pipe that comes out from the top of the pump.Now if you connect back the pipe coming out of pump to the tub...then we have a system where water is being pumped out and back to the tub again.If you try to track the path taken by water in the tub,you won't be able to track its path...you can only track its path in the pipe above.But you can't track its path in the tub,but you are sure that water is coming out and back into the tub.

Similarly A generator is kind of Electron pump(Charge pump) it is sucking out charges at Substation end..flows in wires..then through a load returns to earth...Flows through earth and the returns to Substation...but it is very hard to track the actual path.But it DOES flow back via EARTH.(However mind boggling it seems.In Australia SWER system is used for this purpose alone.Only 1 wire is used for supplying and Earth is used as return).(Search Earthing system in Wikipedia,there you will see two types of earthing..Protective and Functional earthing.Normally we use protective earthing.But Functional earthing means earth used for carrying load current.)

Now About Tera Tera system.

TT system is used for protection purposes and not to carry load current under normal operation.

Normally in transmission we use 3 wires(R Y B of three different phases).At distribution Substation we add another wire called as neutral wire.If load is balanced there would be no current in the neutral wire...but this is almost never the case as single phase loads are used by consumers.So to supply single phase fro distribution transformer we have 3 phases and a neutral wire.All of these wires are connected to a common point (Star connection) and then that point is grounded to earth.

Many earthing schemes use this neutral wire in some sort or other for protective earthing.BUT IN TERA TERA THIS NEUTRAL WIRE IS NOT USED FOR PROTECTIVE PURPOSE.(only for load purpose it is used).

In TERA TERA SYSTEM WE CONNECT THE EXPOSED METTALIC PARTS WHICH ARE CONDUCTIVE TO EARTH.And then we use Residual Current devices in this path for tripping.

So in TERA TERA we use MOTHER EARTH FOR CARRYING THE FAULT OR RESIDUAL CURRENT.