Overhead transmission lines crossing and local earthing effect 1

[Mr zezo]

There's a 11 kv overhead transmission lines passing under 66 kv overhead transmission lines .What's the best way to get rid of the induced emf while working on the 11kv lines, should the portable local earthing protect us and how? Note that, the 11 kv in that case acting like a transformer secondary( 66kv is the primary and air is the core) and it is an ungrounded system , and the local earthing meaning shorts the 3 wires and connecting them to ground.
What should happen if I use only one local earthing and if I use 2 local earthing one before working area and one after working area?

 

[sushilksk]

Other way to think it like a capacitor, 11kV conductor being one plate and 66kV conductor being second plate, air being used as di-electric.

Using 2 local earthing is better and reliable.

 

[stevenal]

Bracket grounding can cause circulating current and a voltage rise at the work site. Single point grounding avoids this hazard.
why-single-point-grounding-works

 

[jghrist]

The earthing is for safety, in case the 11 kV line you are working on gets contacted by an energized line (like the 66 kV line). The emf is not a safety or health hazard. Grounding before and after the work area provides better safety from inadvertent contact because fault current has two ways to flow, reducing the chance that a fatal amount of fault current flows through you to ground.

 

[stevenal]

I disagree with jghrist. Induced voltages and currents do kill. Even when the shock itself is less than hazardous, the resulting fall might be. In the case of contact between the two lines, by providing two grounds, you are likely putting a worker in the path of the ground fault current. Equipotential grounding is what you want, accomplished by grounding at a single point.
Osha
Hubbell
thread238-357883

 

[jghrist]

Induced voltages and currents are not the same as emf (electromagnetic fields).

 

[sushilksk]

Local earthing should be at the point of working. Even if you use two local earthing, distance between these two should be very low (say <3m). There will not be any circulating current. In one practical case, when working at 11kV line, worker pulled conductor of 11kV line with a jerk. It started oscillations and touched another 11kV line which was crossing over it at 90 deg in the middle of span. Everybody was safe as proper earthing was used.


In this case, even if single earthing is used, worker will be in the path of the ground fault current. Correct me if I am wrong.

 

[stevenal]

Since Mr zero spoke of "induced emf", I took the initialism to refer to electro-motive force (voltage).