Underground Distribution loops - Arrester placement
Underground Distribution loops - Arrester placement
(OP)
In reference to URD (underground distribution) loops, we currently install arresters at the "open point" of the loop for our 35kV lines. However currently we do not do so for our 12kV lines. Would it be recommended to do so, and if so, why?






RE: Underground Distribution loops - Arrester placement
If you look at the clamping level of 9 or 10 kV arresters, even if you double that value it will provide sufficient protectice margin. At 35 kV its a different story which is why the open point arrester is used.
RE: Underground Distribution loops - Arrester placement
Can you expand a bit and/or point me to some additional resources? I will likely need to provide recommendation to a director for this within a week or so and would like to have a firm understanding on what I am recommending.
RE: Underground Distribution loops - Arrester placement
RE: Underground Distribution loops - Arrester placement
I've found that we don't use them currently, due to the fact the doubled wave magnitude ends up being around 60kV, and the transformer BILs are 95kV (for the 12kV system). Therefore the transformers should be protected without the use of an open point arrester.
However, I spoke with some companies who suggest that there's more to it than just BIL, and that the cable itself could suffer degradation from even 60kV (deficiencies in the cable could be exploited over time; not in one incident, but over time they could end up failing). However I can not locate any data to verify this. Thoughts?
RE: Underground Distribution loops - Arrester placement
RE: Underground Distribution loops - Arrester placement
Cable has a similar withstand to surges. It can tolerate many smaller surges and have negligible effect on its performance, but it is still degrading slightly. If you get one or two high magnitude surges, it may fail the cable.
Hopkinson of GE published a paper on this in the 1980s. I think Mashikian and one of his grad students did another paper on it a little later, maybe the early 1990s.
RE: Underground Distribution loops - Arrester placement
Having a tough time coming up with a decision on this matter. It's one thing to recommend we start using them; it's another thing to have to be able to actually justify that decision.
RE: Underground Distribution loops - Arrester placement
RE: Underground Distribution loops - Arrester placement
RE: Underground Distribution loops - Arrester placement
I have no data, but I don't believe it's very high. I'm more aware failures at the riser pole arresters, which are exposed to the weather. Point taken, though; arresters cause as well as prevent outages. An arrester failure is quickly addressed, though. Cable failures are not.
atlbraves49,
Yes. Remember risk equals impact times probability. Even low probability events can have high risk if the impact is high enough; and UG cable failures are high impact.