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Right or wrong...I used the following: <5% VTHD <33% ITHD Anything above those #'s, I would look into filtering if operational/equipment issues were noticed, etc. I hadn't experienced any operational down-sides to those #'s, but your mileage may vary depending on your installation. Mike

If I'm not mistaken, if a UPS fails, it will want to transfer from the inverter/rectifier to its static bypass. Maybe this is why the time delay on your UV release didn't work. Mike

You'll most likely have to go through a service sales engineer and they can work it up for you. Mike

Is the UPS operating in "energy savings" mode rather than double conversion? I wonder if there is some issue w/ syncing as previously mentioned. If it is operating in D-C mode, then maybe an issue with the rectifier/inverter? Mike

I'll answer my own question in this thread: According to IEEE C62.92.2, separate neutral grounding reactors is considered an outdated method of gen grounding. So, we'll go with a grounding transformer w/ a resistor and deal with the existing equipment issues as needed. Mike

Thanks for the comments thus far: 1) We have no direct 15kV loads. We have about 60, Delta-Wye grounded transformers which are part of the electrical service entrance(s). We have both 480/277V and 208/120V secondaries. 2) We didn't consider a Wye-Delta grounding transformer, but doesn't mean...

All, I am the owner's rep for a project in design, which is to install two 2.1MW, 15kV class rotary UPSs (coupled with diesel engines for extended outages). Upon loss of utility, we obviously lose our ground reference. Two options: 1) Zig-zag w/ resistor (LRG). We would have to upgrade our...

We shouldn't forget motor contribution... Mike

Z spec?

Double check your electrode configurations as I am doubtful of a 4000A breaker having VCB (more likely HCB), but could be wrong. Also SWGR instead of PNL? Mike

If you are in the US..I believe the new building code requires some type of closed circuit camera to monitor the elevator in case of a passenger is stuck inside. Check the IBC. Mike

SKM is pretty good at modelling the CB characteristics for you if you send them the info. Mike

Not ideal, but is there a possibility of a series rating application at the panelboard? Mike

NFPA 497. Mike

I would say convention is to wire the disconnect such that when the switch is opened, the knife side of the switch is de-energized (switch base side is hot, knife side not). I'm not sure voltage separation/clearances can be maintained if the switch is opened as the knives will be energized so...

Try this: https://support.skm.com/KB/View/20316-modeling-3-winding-transformer Mike

Landed on always using the new door approach. Less time for connects in the field, etc. Mike PS I haven't had a negative experience with either option.

Perhaps this: https://us.rs-online.com/expert/industrial-control-panel-grounding-and-bonding/ Mike

Fault studies are complete, which precipitated the question. My inference is that only normal operation is considered, and failure modes are not. Mike

I maybe should ask: from a withstand perspective, would you include all the available fault current or just 1/2 as described? Thanks, Mike