Rated voltage of lightning Arresters
Rated voltage of lightning Arresters
(OP)
When LAs are used on the delta tertiary of transformers 110% rated voltage arresters are used, being ungrounded system.So in a 33 kV tertiary, 45 kV LAs are used to get 36 kV continuous power frequency voltage withstand performance. If a delta/star transformer is fed from a star/star (132/33 kV) feeding transformer (with secondary star neutral solidly grounded or low impedance earthed through an NGR) what should be the rating of 33 kV LAs to be used with delta/star transformer? In that case, are phase to phase arresters necessary in addition to phase to ground LAs?






RE: Rated voltage of lightning Arresters
Lightning stresses your insulation to ground, so I'm not sure what benefit line to line arresters would provide.
RE: Rated voltage of lightning Arresters
RE: Rated voltage of lightning Arresters
RE: Rated voltage of lightning Arresters
If you have distributed generation on the star side of the 33 kV delta wye transformer, then you have to consider the possibility of backfeed from an ungrounded source and will need a phase to phase rated arrester.
RE: Rated voltage of lightning Arresters
When power flow is from unearthed Y to delta, why you consider higher voltage rating for arresters? Still the 33 kV side neutral remains earthed.
RE: Rated voltage of lightning Arresters
For the backfeed case, once the feeder circuit breaker operates, assuming a single-line-to-ground fault, one corner of the delta winding will be grounded and the other two phases will be at phase-to-phase potential.
RE: Rated voltage of lightning Arresters
In the event of a ground fault, the unfaulted phase voltage will be raised up to the phase-to-phase voltage as shown in the Coefficient of Grounding (COG =1.73). See the info below for detail info in this matter
RE: Rated voltage of lightning Arresters
This really has nothing to do with whether or not the load prior to the fault is a backfeed condition. Forward feed would be the same.