Under frequency Element
Under frequency Element
(OP)
I've been reading this forum since I got out of school (about a year ago). I've learned alot from everyone here, hopefully I can start contributing as I become more competent in the power field, for now I have a question I would like advice on. Recently we had a main breaker trip on underfrequency (load shedding scheme) during an arcing feeder fault (before the feeder breaker could trip on time-overcurrent). The event report showed the frequency dropped to 58.5 Hz, so somehow the arcing fault "tricked" the relay into thinking the frequency had dropped. Is this caused by harmonics generated in the arcing fault? Would moving the PT inputs from the low side of the transformer (grounded wye) to the high side (delta) smooth out the waveform somehow and help the relay from being tricked again? The relay is an SEL 351.






RE: Under frequency Element
You may like to Check the relay literature and if it includes the element, check whether the same is set / enabled.
RE: Under frequency Element
RE: Under frequency Element
Thanks
RE: Under frequency Element
RE: Under frequency Element
RE: Under frequency Element
I am not saying, use UF as arc fault detection, but if there is a fault, it is better to trip then not.
RE: Under frequency Element