French term (edited): défaillance

I have to put a very low C/L here simply because it seems to me these terms are not being used correctly; this could simply be my own ignorance, or it could be that the writer got it slightly wrong — or there may be some special significance that escapes me.
SO, assuming it is intended to mean what I suppose it to and that the writer made a slight mistake, I would read this as "protections de ligne xxx ... et de défaillance..." which would mean 'line and fault protective devices' — note that even though we might think of them together, these are in fact two quite distinct functions, provided by different devices.

Note the common use of 'protective device' often necessary to translate 'protections' — another one of those cases where a noun 'missing' in FR has to be supplied in EN, since 'protection' in EN tends to be abstract and uncountable.

I'm sort of assuming that this 'P345' is in some way the name of the 'poste' that you have mentioned in another question, or similar?


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Note added at 1 heure (2017-09-05 16:34:04 GMT)
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Asker, that would make sense, inasmuch as some point needs to be defined as where the line begins and the substation ends; though I do have a suspicion that the P might still stand for Poste; the trouble is, in this specialist field, 'poste' is used for lots of different things, to the point that you can even have several different 'postes' within one 'poste' — confusing, NOT!

What puzzles me slightly is the 'au' — at the P345; this could be just a stray def. article as so often in FR (le point X); OR it might be indicative that there is some specific significance that could need to be addressed...

I think it is meant to be 'line protective devices at P345 AND fault protective devices' — the fact of having the 'at P345' in there makes it awkward to streamline it in EN as has been done in FR. Or of course 'devices providing line protection at P345 and [other!] devices providing fault protection'.
Once you're clear in your head as to the meaning, you can play around with the syntax to your heart's content...

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Note added at 6 heures (2017-09-05 21:00:20 GMT)
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It's important to appreciate that ALL the protective devices are inherently going to be 'electrical' ones; it is, however, important to differntiate between WHAT they are protecting or protecting against — and that is the distinction being made here: between protecting the line, and protecting against faults. Whence the slightly cumbersome wording.

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Note added at 6 heures (2017-09-05 21:10:53 GMT)
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Asker, since Eduardo has found the same 'P345', it looks as if it can't be a specific drawing reference as you thought, but something more specific to do with the lines; is there any connection with the 345 kV, which seems likely?

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Note added at 6 heures (2017-09-05 21:14:42 GMT)
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OK, so if you think the P345 is some model of protective device, than it makes more sence now: it is likely then to be 'line protection via P345 devices + fault protection (using the other devices listed, or possibly protecting against faults in those devices)

The fact that no specific equipment is specified for the 'défaillance' is exactly why 'fault' (= general) is better to use here than 'failure' (= in some specific element).