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

Phase failure relays (pfr)

Is it standard practise to fit pfr's to the breaker side of an MCCB, rather than the supply side in a motor control panel which has a standby generator connected, in case of mains failure ?

  • It may be. Usually a single phase is lost if there are fuses,  rather than breakers, as breakers are ganged - while one fuse may fail before the other two, leaving motors unsure which way to rotate,  which is where the protection comes in.

     Therefore the detection needs to go anywhere after the last place that a single phase isolation  like that  may credibly occur, and before the load that actually cares if it does not get all three phases at once.  Nearer the load makes it easier to maintain, and keeps the fault levels that have to be interrupted to a lower level, as well as covering for single phase faults at all points further upstream.

    The standby supply may make the fault tree harder to follow, but as I'm sure that will change over on all 3 phases together, the end result is the same as if there was one supply,

    Mike.

     

  • PFR.pdf

    The busbars are fed either from the generator or mains supply, never both.

    To me, the pfr will indicate “mains available” when the generator is supplying the site ?

    The naming could probably cahnge to power available ?

  • Looking at that drawing and feeling slightly dense, what exactly is the load that must be  disconnected if one phase fails, and how is that achieved ?

    I presume the fault you  are guarding against with the phase fail tester is the loss of only one of  fuses F1/F2/F3  is that correct 

    Is everything after that point ganged MCB or similar 3 or 4 pole switching?

    Mike.