P12x/EN T/Eb6 - Schneider - error

P12x/EN AP/Eb6Page 16/78Application GuideMiCOM P120/P121/P122/P1234. BUSBAR PROTECTION ON RADIAL SYSTEMSThe use of non-directional overcurrent relays to protect a busbar is based on the followinghypotheses:- The network is a radial system,- The incoming and outgoing feeders are clearly defined, the incomers being alwaysconsidered as suppliers of energy and feeders as loads.Under these circumstances, the busbar is effectively protected using the interlockingprinciple (Figure 2).IncomerI>/t>I>>/t>>I>>>/t>>>TripBack tripBlock short time overcurrentBusbarFeeder 1 Feeder 2 Feeder nI>/inst.I>>/t>>I>/inst.I>>/t>>I>/inst.I>>/t>>P0023ENaFIGURE 2: BLOCKED OVERCURRENT FOR BUSBAR PROTECTIONThe instantaneous overcurrent signals of the feeders protection are grouped together andwired to the « Blocking logic » logic input of the relay protecting the incomer. The blockingfunction is programmed to inhibit either the first or first two thresholds. The third I>>>threshold picks up at a high value (>10 In) with a short time delay (>>). As this third threshold is not blocked by the blocking logic of relaysprotecting the incomers, the trip order is sent in less than 60 ms and the busbar is deenergised.