LV generator protection - engineering site - Schneider Electric

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4.2.2.2. Overcurrentb application:overcurrent protection is suitable for:v monitoring cyclic loads (prevent temperature rise of loads, etc.)v managing consumption (guard against overshoots).E88010EI consumedI sizingActivation1 hTa = activation time delayTd = de-activation time delayFigure 27: Consumption monitoring.This is used to calculate the mean value of consumed current. It can deliver aload shedding order to remain within the limits:v of the supplier’s contract - Main source -v or of delivered power - Replacement source.It provides thermal type protection for each phase and for the neutral (drytransformers).b principle:this function calculates the mean value of each current of the three phases andthe neutral over a time programmable between 5 minutes and one hour and overa sliding window refreshed every 15 seconds.b overcurrent settingsetting range setting step accuracyactivation 0.2 to 10 In 1 A ± 6.6 %thresholdactivation 1500 s 15 s -20 % to 0 %time delayde-activation 0.2 to 10 In of 1 A ± 6.6 %thresholdactivation thresholdde-activation 10 to 3000 s 15 s -20 % to 0 %time delay4.2.2.3. Voltage unbalanceb application:detection of voltage unbalance or loss.Voltage unbalance protection is more suitable to the installation as a whole,whereas current unbalance protection is more suitable for loads.This is because voltage unbalance will affect all the feeders of this installation,while current unbalance may vary according to its position in the installation.b principle:the function compares voltage unbalance to the threshold set beforehand by theuser.Voltage unbalance DU is the value as a % of the difference, E max, betweenmaximum voltage and the mean value of the phase-to-phase voltages, Umean.Umean = (U12 + U23 + U31)/3.Emax = max(Ui) - Umean.DU= Emax/Umean.33
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
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Page 4 and 5: In shortGenerator Sets (GS) are use
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LV generator protection - engineering site - Schneider Electric

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