Deadbus Closing Standby Generator to Large Traffo Load
Deadbus Closing Standby Generator to Large Traffo Load
(OP)
I am looking into how to estimate if I can energise a large unloaded transformer load, about 50MVA made up of individual 1 to 4MVA units. When the mains fails all the LV loads will be shed throughout the factory.
So far I have been able to test with 16MVA with no problem. The remaining load is no available for test. The running load once energised was about 90kW, 140kVAr. The standby plant is made up of 2.5MVA units and I planned to use the first up.
I also tried enrgising one additiona 4MVA unit and it seemed to create a karger transient volatge dip. Why ?
Any ideas please.
So far I have been able to test with 16MVA with no problem. The remaining load is no available for test. The running load once energised was about 90kW, 140kVAr. The standby plant is made up of 2.5MVA units and I planned to use the first up.
I also tried enrgising one additiona 4MVA unit and it seemed to create a karger transient volatge dip. Why ?
Any ideas please.






RE: Deadbus Closing Standby Generator to Large Traffo Load
Beyond that, I'm not really clear on what your system looks like and what size generator you have.
RE: Deadbus Closing Standby Generator to Large Traffo Load
A rule of thumb for coordinating upstream overcurrent devices with transformer inrush is allow 12xFLC for 0.1 second and 25xFLC for 0.01 second. Would that be applicable in your case? You are probably well aware that transfomer inrush is of low PF and singificant second-harmonic current/DC offset...however short-lived, not the tidiest standby-genset load.
RE: Deadbus Closing Standby Generator to Large Traffo Load
I would think you can treat it as one large 50MVA transformer for a rough analysis. If there is significant impedance in the feeders to the transformers, this will be less accurate.
RE: Deadbus Closing Standby Generator to Large Traffo Load
The genset manufacturer said I should check the offload reactive lagging kvars is within the rating of the genset. It seems we have very good transformers with low losses and low running reactive loads i.e. only about 1% of the traffo ratings. I can generatye up to something like 1250 kVAR so this should not be a limitation.
What I am concerned is if I am missing something else that e.g. would cause an instability. I laso feel there should be some way to calculate this.
RE: Deadbus Closing Standby Generator to Large Traffo Load
RE: Deadbus Closing Standby Generator to Large Traffo Load
RE: Deadbus Closing Standby Generator to Large Traffo Load
RE: Deadbus Closing Standby Generator to Large Traffo Load