Looking for a rule of thumb to design UPS protection network?
Uninterruptible power supplies is essential nowadays in both commercial and industrial buildings. However, short circuit protection is not that simple matter, at least I think, when using UPS.
Normally, when network is available, UPS goes to bypass mode during short circuit. When network is unavailable, UPS has to draw the current to supply short circuit from its battery. Typical short circuit feeding capability seems to be around two times nominal current. Usually UPS can feed short circuit about 0,3 seconds.
A larger UPS network has its own main switchboard, feeders and switchboard for final circuits. I would like to know how you take into account these limitations in design.
- What size of MCBs are you using in UPS switchboards?
- How about selectivity between breaker in final switchboard and main switchboard?
- Do you find current selectivity be enough?
If you take into consideration selectivity (energy) and short circuit during the batteryoperation it results in surprisingly low current level MCBs.
- Or do you reckon short circuit to happen during battery operation such a rare occasion that it is ignored?
Do any of the readers of this Engineering Blog have some rule of thumb to design UPS network protection ?
Use the comments area below, thanks