P12x/EN T/Eb6 - Schneider - error

P12x/EN AP/Eb6Page 42/78Application GuideMiCOM P120/P121/P122/P12318. SELECTIVE SCHEME LOGIC (P122 & P123 ONLY)The following figure describes the use of non-cascade protection schemes using the startcontacts from downstream relays to block operation of upstream relays.In the case of Selective Overcurrent Logic (SOL), the start contacts are used to increase thetime delays of upstream relays, instead of blocking them. This provides an alternativeapproach to achieving a non-cascade type of overcurrent scheme. It may be more familiar tosome utilities than the blocked overcurrent arrangement.ABCP0024ENaFIGURE 13: TYPICAL SCHEME LOGICThe SOL function temporarily increase the time delay settings of the second and third stagesof phase overcurrent, derived and measured earth fault and sensitive earth fault protectionelements. This logic is initiated by energising the appropriate logic input (Log Sel1 or LogSel2) as selected in AUTOMAT.CRTL/INPUTS menu.To allow time for a start contact to initiate a change of setting, the time settings of the secondand third stages should include a nominal delay. Guidelines for minimum time settings areidentical to those given for blocked overcurrent schemes.The tSel1 and tSel2 timers can be independently set from 0 to 150 s.