5-24L90 Line Differential RelayGE Power Management5.3 SYSTEM SETUP 5 SETTINGS55.3 SYSTEM SETUP 5.3.1 AC INPUTSa) CURRENT BANKSPATH: SETTINGS ÖØ SYSTEM SETUP Ö AC INPUTS Ö CURRENT BANK X1‘X’ = F, M, or U. ‘F’, ‘M’, and ‘U’ are module slot position letters. See also the section INTRODUCTION TO AC SOURCES.Up to 6 banks of phase/ground CTs can be set.These settings are critical for all features that have settings dependent on current measurements. When the relay isordered, the CT module must be specified to include a standard or sensitive ground input. As the phase CTs are connectedin Wye (star), the calculated phasor sum of the three phase currents (IA + IB + IC = Neutral Current = 3Io) is used as theinput for the neutral overcurrent elements. In addition, a zero sequence (core balance) CT which senses current in all of thecircuit primary conductors, or a CT in a neutral grounding conductor may also be used. For this configuration, the groundCT primary rating must be entered. To detect low level ground fault currents, the sensitive ground input may be used. In thiscase, the sensitive ground CT primary rating must be entered. For more details on CT connections, refer to the HARD-WARE chapter.Enter the rated CT primary current values. For both 1000:5 and 1000:1 CTs, the entry would be 1000. For correct opera-tion, the CT secondary rating must match the setting (which must also correspond to the specific CT connections used).If CT inputs (banks of current) are to be summed as one source current, the following rule applies:EXAMPLE:SRC1 = F1 + F5 + U1WhereF1,F5, andU1 are banks of CTs with ratios of 500:1, 1000:1 and 800:1 respectively.1 pu is the highest primary current. In this case, 1000 is entered and the secondary current from the 500:1 and 800:1 ratioCTs will be adjusted to that which would be created by a 1000:1 CT before summation. If a protection element is set up toact on SRC1 currents, then PKP level of 1 pu will operate on 1000 A primary.The same rule will apply for sums of currents from CTs with different secondary taps (5 A and 1 A). CURRENT BANK X1PHASE CT X1PRIMARY: 1 ARange: 1 to 65000 A in steps of 1MESSAGE PHASE CT X1SECONDARY: 1 ARange: 1 A, 5 AMESSAGE GROUND CT X1PRIMARY: 1 ARange: 1 to 65000 A in steps of 1MESSAGE GROUND CT X1SECONDARY: 1 ARange: 1 A, 5 A
