LV generator protection - engineering site - Schneider Electric

The Schneiderprotection solutionThe activation and de-activation thresholds, configured by the user, are a % of Umax:∆U = 5 % represents a relatively small unbalance∆U = 90 % represents a strongly unbalanced power supplyExampleCase similar to a phase loss associated with unbalance on the other phases.U12 = 330 V, U23 = 390 V, U31 = 10 V.Umean = 243,3 V.Emax = U31 - Umean.∆U = Emax/Umean, ∆U = 96 %.b voltage unbalance setting:setting range setting step accuracyactivation 2 à 30 % of Umean 1 % -10 % to 0 %thresholdactivation 1 to 40 s 1 s -20 % to 0 %time delayde-activation 2 % of activation 1 % -10 % to 0 %threshold thresholdde-activation 10 to 360 s 1 s -20 % to 0 %time delay4.2.2.4. Overvoltage and undervoltageb application:the overvoltage and undervoltage protections can be used to:v check output voltage of a generatorv prevent transformer saturation (overvoltage)v switch from the Main to the Replacement sourcev prevent temperature rise on motor starting (undervoltage)Note: in actual fact, voltage drops and rises seriously affect the performance ofthe loads supplied (see motor characteristics table below).Voltage variation as a %Motor characteristics Un -10 % Un -5 % Un Un +5 % Un+10%Torque curve 0,81 0,90 1 1,10 1,21Slipping 1,23 1,11 1 0,91 0,83Nominal current 1,10 1,05 1 0,98 0,98Nominal efficiency 0,97 0,98 1 1,00 0,98Nominal power factor 1,03 1,02 1 0,97 0,94Starting current 0,90 0,95 1 1,05 1,10Nominal temp. rise 1,18 1,05 1 1 1,10Off-load P (Watt) 0,85 0,92 1 1,12 1,25b principle:the function is activated when one of the three phase-to-phase voltages (U12,U23, U31) is below (or above) the threshold set by the user for a time longer thanthe time delay. It is de-activated when the 3 phase-to-phase voltages move backabove (or below) the de-activation threshold for a time longer than the time delay.E88011EU max.U min.U12 U23 U31Figure 28.34