Medium voltage cable join

[MANUEL MARTINEZ]

I?m been asked to extend a 400 KCM, 23 KV, 100%BIL, EPR, line 450 meters with a 500 KCM, 23 KV, 133% BIL, EPR cable. I want to know if any restriction exist to join different insulation calbes Thanks

 

[big john]

I?m been asked to extend a 400 KCM, 23 KV, 100%BIL, EPR, line 450 meters with a 500 KCM, 23 KV, 133% BIL, EPR cable. I want to know if any restriction exist to join different insulation calbes Thanks

Short answer: If you have protection that will trip out any fault in less than 60 seconds then there is no concern.

Long answer: The insulation level is based on how long the cable can tolerate an applied overvoltage.

Medium-voltage cables are classified by system. A 23kV cable does not mean that you can put any voltage on that cable as long as it doesn't exceed 23,000 volts-to-ground. These cables are designed based on the L-G rating of a 23kV system, and this is where the insulation level comes in:

If you have a 100% rated cable then it is only designed for 13.2kV and in the event of a ground-fault will tolerate full L-L voltage applied across it only for 60 seconds or less. If your system is solidly grounded, it's very likely that a fault will clear quickly then this isn't a problem and will work fine.

If your system is ungrounded, where conditions of maintenance mean that a ground fault would be discovered and quickly addressed, then 133% insulation would work. This means that the cable is designed to tolerate full 23kV L-L voltage for up to 60 minutes.

If your system is ungrounded where you expect faults may run for periods greater than an hour, then you get 173% rated insulation which is designed to handle full L-L system voltage indefinitely.

 

[Julius Right]

You are right, big john, of course. See UL 1072 Table 13.1 or IEC 60502-2 4.1 Rated voltages. [Also EPRI EL-5036-V4 and ICEA S-68-516 and so on].
However the existing cable is 100% rated insulation and the
new extension is 133% that means ?better?. We don?t know if the supply voltage is 23 kV indeed. May be less?
In my opinion, the only problem is to find a suitable joint-including the splice.I think Raychem [TE now] could help to find one.

 

[MANUEL MARTINEZ]

Thanks

Thanks

Thanks for your answers, I wonder if parallels cables must have same insulation, a join of cables may have the same? I rather prefer to use the same cable it is already installed, any argument to convince my client.

 

[GoldDigger]

Thanks for your answers, I wonder if parallels cables must have same insulation, a join of cables may have the same? I rather prefer to use the same cable it is already installed, any argument to convince my client.

Since there is only one current path, there is no reason that all parts be identical.
If you needed to pull a new cable in parallel for more current you could not have one which is all new spec cable and the other which is spliced from two types.

 

[lightning97531]

te splice

te splice

You are right, big john, of course. See UL 1072 Table 13.1 or IEC 60502-2 4.1 Rated voltages. [Also EPRI EL-5036-V4 and ICEA S-68-516 and so on].
However the existing cable is 100% rated insulation and the
new extension is 133% that means ?better?. We don?t know if the supply voltage is 23 kV indeed. May be less?
In my opinion, the only problem is to find a suitable joint-including the splice.I think Raychem [TE now] could help to find one.

Te makes a splice that connects anything from 350 to 750 mcm and works on 15 to 35 of cable.