LV generator protection - engineering site - Schneider Electric

5.2. CommentsSource to protect Protection MonitoringMain sourceThe Long and Short Time Delay protection settings The monitoring functions mainly concernare of the Distribution type. Discrimination with verification of inrush power: this allows use, ifdownstream feeders is of the time type and total. necessary, of load shedding to cope with loadpeaks.Replacement sourceE88104The set is optimised with exact dimensioning.Setting of the LTD protection will follow the Set’sprotection curve and setting of the STD protectionwill be low (from 1.5 to 2.5 lg).The Set supplies priority feeders. As ourexample is an office building, these feeders areoften not linear. Due to the power ratio and highsubtransient impedances between the Set andthe Main source (transformer), voltage totalharmonic distortion (THDu) is often very highand greater than load withstand value (even fornon-sensitive loads).1. Installation of a Micrologic H ensurespermanent monitoring, if necessary, of therelevant harmonic pollution parameters.Safety sourceDiscrimination with downstream priority feedersmust allow for the low settings (in particular for theSTD).For feeders supplied by the UPS, discriminationmust be ensured with the downstream feeders (thisis because the UPS switches to mains 2 to performthe discrimination function).The Set must operate in all circumstances.The settings made will eliminate nuisance tripping.Discrimination must allow for these settings andchoose a downstream circuit distribution that willenable this.E88697l measurement and H spectrum vignettesE886982. Use of a UPS incorporating a harmonicsuppressionfilter is the ideal solution for using aGenerator Set/UPS combination with optimisedsizing and to bring upstream total harmonicdistortion down to a completely acceptable value.Fine network analysis in real time is not required.However, alarm transfer and storage arerecommended. If necessary, networkparameters (voltage, current, etc.) can bemeasured for analysis after the fault.E88103ESourceSafety andreplacement sourceGSNote 1: in the diagram on the previous page, theSafety Set and the Replacement Set are separate:this is advantageous only if the priority and safetyfeeders are physically separate. As explained inparagraph 1.3, the 2 functions are normally grouped.The following diagram gives an example of this:Non-priorityfeedersSafetyPriorityfeedersFigure 35.41