For 100Kw generator, what will be minimum/ maximum loadfor its safe operation.
The maximum load will be given by the exhaust temperature, regardless of the nameplate rating. There is a maximum steady state temperature, which can be exceeded for short periods, say, 10 to 20 %, given by the engine mfr. The minimum load for an engine which runs at constant speed, i.e., a power generator, is about 50%. Below that it starts to shake dangerously. . .
For most generators there is no minimum load, as it can even be zero loaded. For the maximum load you will need to look at the manufacturers specifications. Do you have the make and model of the generator?