DNO maintenance on 11KV line

LED Lighting · Sep 25, 2016

Something that's always confused me and never been explained to me is when the DNO work on a 11KV line they clamp the 3 phases togeather and spike to ground. Then further down the line they do the same.
This creates an alternative path for the electric to travel (through the ground) making the section in between the 2 connections safe to work on.

Can anyone explain how this works please and also why they don't have a big BANG or flash when connecting?????

Thanks in advance

mhar · Sep 25, 2016

Part of my youngest's job is issuing permits to work on the 11kV network.
The line is first made dead by central control and the earthing that you see describe is the 'belt and braces'.
Once everything is made safe a permit to work can be issued.
Flashes and bangs do happen during faults or when breakers are closed on a fault. If an animal comes into contact with two phases a breaker will operate, however the cause of the fault is likely no longer there and howver many teams are sent to search for the cause of the fault, they will not find it. Therefore they sometimes close breakers on a fault to see if it is still there or to clear (vapourise!) it. Apparently manually closing a breaker on a fault can be a bit nerve-wracking

LED Lighting · Sep 25, 2016

I came across this first when working on a solar Farm. The way they explained it to me then was like the supply from the farm is still live as they could not isolate it. That's what really confused me.
They also said the stake to earth at that point and the other one down the line creates an alternative path for the electric flow.
As an electrician this really confused me as you would at least expect a flash (arc) on connection and a breaker would operate.

mhar · Sep 25, 2016

The earthing is the belt and braces on an already proven dead line. The breakers / isolators have already been opened in order to de-energise the section

Pete999 · Sep 25, 2016

The earthing of a HV line, is done at both ends of the cable,switch to OFF at both subs then switch to EARTH at both subs, thus proving the cable is dead and earthed. There may be confusion regarding spiking the cable, this operation actually drives a chisel through the cable at the point where the joint is to be made.

seltechpc · Sep 25, 2016

The circuit is isolated and earthed at the substation ends to make it 'dead'. Permits are issued and portable earths are issued to the Linesmen to apply either side of the place of work. This is to ensure that any pick up induced voltage is drained to earth either side of the point of work. They are also issued with field earths to apply at the point of work to further insure the point of work is 'dead'. Earths are always applied to the solid earth first before applying to the line. I have seen someone killed when it was done the other way around.
These portable earths are purely to drain induced voltages from the line, these voltages can be in the order of several kV even when the line is earthed at both ends. Even higher on EHV circuits.

As Pete stated spiking is to ensure a cable is dead before cutting it to joint or remove, it destroys the cable at that point but is better than putting a hacksaw through a live cable because you cannot test the conductors or see the remote ends.