If Broken or Loose Grounding of Link Box

Please break your message into brief parts. Use CR4 "1,2,3.." list

1. 132 kV cable has four joints.
2. Each joint is in a link box.
3. 3 km length between each joint.
   

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Question not clear, at present. Question part ends with ?

sir if spluice joint area broken due to excavation or loose grounding in link box what will problem create

irfan

I think you mean to write (using the 1--2--3-- button at top of CR4 message box):-

If :-

1. Area around a cable joint is broken-up by excavation, or

2. Grounding inside a link box is lose.

- what problems will be created. If I am right, following are my answers to 1 and 2. I am not a High Voltage specialist, but some general facts apply.

1. Sharp stones can be pressed onto cable causing damage. When local ground has sharp stones, it is necessary to fill excavation with fine material close to cable to protect cable. Ground thrown in loose will not conduct heat and cool cable as well as normal ground. It needs to be "compacted" mechanically to restore normal state. Early failure of cable or shortened life will be caused when correct filling is not done.

2. "In" or "inside" a box grounding or earthing is not the word. Bonding, meaning "joining together" electrically is what is important. The voltage drop along a cable, during a short circuit is considerable. Especially when the cable is long and the electrical source is strong, a very large voltage can appear along a cable if there is a short circuit at its end. The cable metal sheath is the main return path to to the generator. When the box is locally earthed, there could be a dangerous voltage between box and cable, if they were not bonded together. When there is a link in a box, to give access for testing, then bonding between the sheaths of cables entering it would be vital to carry ground fault current currents.

3. Perhaps you mean boxes in which all 3 phases are brought together and the sheath bonding joins the 3 sheaths together? In this case the currents between the sheaths may not be small in normal operation and a loose connection could overheat or spark. Sometimes, due to errors in design, particularly long runs, the circulating currents are excessive and overheating occurs, causing failure of the cable at the box.

I hope this helps, Irfan.