11kV/400V TX with no LV protection

mapj1 said:

To re-assure yourself, you only need to check, what is the upstream protection for the TX.

... and possibly whether there is an intertrip, where necessary, to prevent on-going energization from EM induction.

Yes, but if it is that sort of scheme there will be signalling between sets of breakers, some more remote and the local ones to ensure the correct intertripping sequence-
And then it can get get very complex as those who know far more than me about the HV side mutter darkly about the merits of staggered thresholds for permissive versus direct tripping (*),  And then, at least in the UK , there will be some catch-all that still disconnects eventually even if the inter-trip telemetry fails

In any case, all of this will come out in the wash of inquiring about the primary side protection. If you get an answer you do not understand and there is no clarification forthcoming, then come back and we will see what we can do to help de-mystify it.

Mike.

PS (It is an aside but a permissive intertrip is a sort of voting system where the trip only fires if there is both a  command to trip from the other end of the line and also a local overload at some level,  Direct intertrip is easier to understand but less flexible - if the remote command comes in to trip, then it will always trip - even if the fault is somewhere else)

I agree with those above regarding how it should work, ie that protection provided via the upstream HV protection should suffice (and indeed is necessary to protect the LV windings), and a short section of LV tail would be expected to be covered by operation at HV. However I would note that the OP has suggested the LV tails are ~30m long, which is a little longer than usual (but by no means problematic) and going between buildings suggests not in a "no fault zone", and furthermore the implication is that selection of the cable is within their scope to select. One ought therefore to consider whether the HV fuse/relay provides sufficient cover at LV through to the first piece of LV protection, and whether the cable will withstand the fault.

It is also worth noting that some HV protection does not operate on low overcurrents; for example HV transformer fuses are sometimes specified as backup rather than full range protection (to avoid inadvertent operation on LV faults) while self-powered relays such as the common Schneider VIP range require a certain current through the CTs to power up the relay. Hopefully this will have been considered by the HV designer in the selection but one shouldn't assume and if you have a long run to the first piece of LV protection you ought to check you have enough current to operate the HV at the far end of the cable. In most cases it will be fine.