LV generator protection - engineering site - Schneider Electric

The Schneiderprotection solution4.2.2. The monitoring functions4.2.1.1. Current unbalanceb application:the acceptable values for current negative phase sequence components areapproximately:v 15 % for generatorsv 20 % for motorsAs current unbalance effects are thermal and thus slow, the tripping threshold forthis protection must be configured according to the thermal time constant of theequipment (a few minutes).It can be used as an alarm to allow better distribution of single-phase loads.E88009EI meanFigure 26.b principle:the function compares a current unbalance to the threshold previously set by theuser. The current unbalance Dl is the value as a % of the difference, E max,between maximum current and mean current, lmean.Imean = (I1+I2+I3)/3.Emax = max (Ii) - Imean.∆I = Emax/Imean.The activation and de-activation thresholds, configured by the user, are a % ofImean:∆l = 5 % represents a relatively small unbalance (l1 = 4000 A, l2 = 3800 A, l3 =3600 A).∆l = 90 % represents a strongly unbalanced power supply (l1 = 4000 A, l2 = 1200A, l3 = 1120 A).Example 1: I1 = 4000 A, I2 = 2000 A, I3 = 3300 A.Imean = 3100 A.Emax = I2 - Imoy.∆I = Emax/Imean, ∆I = 35 %.Nota : calculation of current (or voltage) unbalance in HV distribution is normallyused: Iunbal(%) = 100 x (Iinverse)/(Idirect)Micrologic calculates current unbalance as per the formula:Iunbal(%) = 100 x (lmax)/(lmean)Both calculation modes yield similar results.b current unbalance setting:setting range setting step accuracyactivation 5 à 60 % of Imean 1 % -10 % to 0 %thresholdactivation 1 to 40 s 1 s -20 % to 0 %time delayde-activation -5 % to 0 % of 1 % -10 % to 0 %thresholdactivation thresholdde-activation 10 to 360 s 1 s -20 % to 0 %time delay32