SVL requirement for short 66 kV cables inside susbtation

[Power0020]

I wonder if a single point bonded 66 kV cable connecting power transformer to GIS (about 90 m long) needs to be equipped with SVL?

I would ground the lead sheath towards the GIS side (where transients may originate) and leave the transformer side open, surge arrestors are already there on transformer 66 kV cable sealing end side.

The induced sheath voltage during faults never exceed 5 kV, but, i don't know if any code requires the SVL for transients? no switching transients are major on 66 kv and no lightning current is supposed to escape the surge arrestor within just 1.5 m of the sealing end.

any clue?

 

[RRaghunath]

The voltage rise in the sheath at the ungrounded end is the concern and deciding factor for SVL. Cable vendors do provide calculation for the same taking in to account 1phase-to ground fault current as well as the cable length. Why don't you review the subject with the vendor!
Prima facie, I agree a 90m cable should not require SVL.

Rompicherla Raghunath

 

[Power0020]

I did, the vendor showed that no voltages exceed allowable, 65 V during normal operation, 5 kV during faults (L-G, L-L-G).

But, what about other transients?

A properly sized SVL shouldn't conduct during faults, otherwise its energy capability will be too high, i.e. it is protecting the jacket from voltages exceeding its power frequency withstand or the like, a value of about 5 kV is considered ok by most codes and cable manufacturers.

the jacket BIL is somewhere around 50 kV, the job of SVL is to protect it, this is what I understand out of INMR article here:

http://www.inmr.com/sheath-voltage-limiters-protect-hv-power-cables/3/

 

[RRaghunath]

Switching and lightning surges matter for power conductors, I think. Do we need to consider transients here, I am not sure.
May be, since the sheath is part of 66kV substation earthing system, the surges that circulate in the earth grid may appear partly at the unearthed end of the sheath and may cause sparkover if not protected by SVL.

Rompicherla Raghunath