LV generator protection - engineering site - Schneider Electric

In shortA Generator Set has specificoverload and short-circuit withstandcharacteristics as a result of thehigh generator reactances.This has the followingconsequences:b for protection of people andequipment, specific circuit-breakersettings providing both protection ofthe installation set and coordinationwith the downstreamprotection devices.b for proper operation on duty of themonitoring functions preventingmalfunctions and ensuring alarmmanagement if necessary in eventof:v non-linear loads (harmonics)v loads with a high energisingcurrent (motors, LV/LV transformers,etc.)v parallel-connection of GeneratorSetsv operation in prolonged overloadconditions (Standby Set).Standards specify the specificpower available according to thetype of application of a GeneratorSet - production, transfer, standby.E79476EE79364EProtection and Monitoringof a LV Generator Set3.1. Generator protectionThe following diagram shows the electrical sizing parameters of a Generator Set.Pn, Un and In are, respectively, the power of the thermal motor, the rated voltageand the rated current of the generator.ThermalmotorFigure 12: Block diagram of a Generator Set.Nota 1: Also remember that Generator Set sizing is optimised, i.e. that Pn isnormally around one third of normal installed power.3.1.1. Overload protectionThe generator protection curve must be analysed.Figure 13: Example of an overload curve T=f(I).OverloadsStandards and requirements of applications can also stipulate specific overloadconditions:For example:I / Int1.1 > 1 h1.5 30 sThe setting possibilities of the overload protection devices (or Long TimeDelay) will closely follow these requirements.Note on overloadsb for economic reasons, the thermal motor of a Replacement Set may be strictlysized for its nominal power. If there is an active power overload, the diesel motorwill stall. The active power balance of the priority loads must take this into accountb a production Set must be able to withstand operating overloads:v one hour overloadv one hour overload every 12 hours (Prime Power).(see chapter 3.5 “The installation standards”)16