Sepam - HV/MV Protection and control units (ENG) - Trinet

Phase overcurrentANSI code 50-51function n° F01X for phase overcurrentI1, I2, I3 1 ≤ X ≤ 6F02Y for phase overcurrentI1’, I2’, I3’ 1 ≤ Y ≤ 2Is is the vertical asymptote of the curve, and T is the operation time delay for 10 Is.The curve is defined according to the following equations:c standard inverse time SIT0.14 Tt = .(I/Is) 0.02 -1 2.97c very inverse time VIT or LTIOperationPhase overcurrent protection is three-pole.It picks up when one, two or three of the currentsreaches the set point. It is time-delayed.The time delay may be definite (definite DT) or IDMT(standard inverse SIT, very inverse VIT or LTI (1) ,extremely inverse EIT, ultra inverse time UIT).See curves in appendix.(1)The very inverse time VIT delay setting range may be usedto create LTI curves.Logic data K859 = 1 may be used to inhibit startup of the time delay.(regarding use, refer to “start-up of time delays”in appendix).Definite time protectionIs is the set point expressed in Amps,and T is the protection time delay.13.5t = .(I/Is)-1c extremely inverse time EITc ultra inverse time UITt =315. T(I/Is) 2.5 -1The function also takes into account current variations during the time delayinterval.For currents with a very large amplitude, the protection has a definite timecharacteristic:c if I > 20 Is, tripping time is the time that corresponds to 20 Is,c if I > 24 In, tripping time is the time that corresponds to 24 In.Block diagramT1.580 Tt = .(I/Is) 2 -1 0.808tI1I2I3I > Ist0F01X/2(F02Y/2)TK859F01X/1(F02Y/1)IsIDefinite time protection principle.IDMT protectionIDMT protection operates in accordance with the IEC60255-3 and BS 142 standards.tT11.2 10 20 I/IsIDMT protection principle.2/2 Protection functions