This discussion is locked.

You cannot post a reply to this discussion. If you have a question start a new discussion

Transformer protection

Hi all,

I am working on the LV side of a scheme with a private HV transformer (>1MVA) and have been told by the HV contractor that since it is fed / protected by a fuse switch, it is not appropriate to make use of the transformer overtemp / tank pressure / oil level relay to disconnect at HV, reason being that it can't break a fault and that's what the fuse is for. I do get the principle that RMU switches are not fault-breaking devices and you shouldn't, for example, use an external overcurrent relay on the HV terminals to operate one, but should these functions not be considered to prevent the fault developing sufficiently to fire the fuses in the first place? For example if the oil level alarm triggers via SCADA, or the oil temp trip triggers despite LV load shedding, is there really time to wander up to site and manually operate?

Also I would have thought that you'd be pretty unlucky for the fault to strike at precisely the same time as the transformer relay, even if both happen in a single event, due to thermal inertia etc?

Please correct me before I make a fool of myself questioning it in public!

Ultimately it's not our scope but we'll be picking up the multicore wiring one way or the other; also for future reference.

TIA,

Jam

Parents

0 Jam over 3 years ago

Thanks OMS, I agree with what you've said (and it's definitely not a TLF arrangement) ... But what then is the point of the transformer protection relay (e.g. RIS2) that they / the HV consultant have specified in this situation if it's not to remove the transformer before said sacrifice? Is it really just for alarms?

To clarify I wasn't intending to wire up the trip contacts to the LV breaker (though overtemp alarm will shed load); my question was whether they really can't operate the HV. The comment from the HV contractor was a surprise as I've seen quite a number of sites with that exact arrangement.

(I am assuming that there is is a facility to open the switch disconnector remotely, e.g. for E/stop)

The upshot is likely to be that I'll be bringing out the contacts to a marshalling box and sending a multicore from there to the RMU "for future use", picking up anything not claimed by the HV contractor for SCADA alarms.

Jam
Cancel
Vote Up 0 Vote Down

Cancel

Reply

0 Jam over 3 years ago

Thanks OMS, I agree with what you've said (and it's definitely not a TLF arrangement) ... But what then is the point of the transformer protection relay (e.g. RIS2) that they / the HV consultant have specified in this situation if it's not to remove the transformer before said sacrifice? Is it really just for alarms?

To clarify I wasn't intending to wire up the trip contacts to the LV breaker (though overtemp alarm will shed load); my question was whether they really can't operate the HV. The comment from the HV contractor was a surprise as I've seen quite a number of sites with that exact arrangement.

(I am assuming that there is is a facility to open the switch disconnector remotely, e.g. for E/stop)

The upshot is likely to be that I'll be bringing out the contacts to a marshalling box and sending a multicore from there to the RMU "for future use", picking up anything not claimed by the HV contractor for SCADA alarms.

Jam
Cancel
Vote Up 0 Vote Down

Cancel

Children

No Data

Transformer protection

Join us to get the best from IET EngX.

Community Rules & Guidelines