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HI all, Thank you for all the responses. I have limited access to my computer today (and yesterday) but I look forward to reading and digesting all comments. Just to clarify a few things, the renewable system was designed and built for two reasons. One is obviously for reduction in energy...

HI, I work on renewable energy microgrids for commercial and industrial. Typically this includes solar panels and battery storage. I am exploring adding a renewable microgrid to an existing building which has a diesel generator backup. There is an ATS that switches to diesel during a grid...

Well let me clear a few things up. The idea (to use batteries) has already been decided by the main contractor, and we have been hired to design the backup system. @itsmoked These are fairly large batteries. 240KWH of capacity, enough to keep the elevator on for 3 to 4+ hours on a full charge...

@ScottyUK Thanks for the input. I'm sort of not in the loop on the business decisions for not having a diesel genset. My job is to design the renewable backup system and make sure it works! But I agree, a diesel would make more sense given the emergency load panel consists mainly of electric...

Thanks Brian, This is helpful. This is early stage of design and so I'm just trying to find out any potential show stoppers now. (I also know nothing about elevator control systems) This is a new construction building so it looks like I need to sync up with the elevator installers and team up...

Hi all, I am designing a system that will provide backup power (batteries) to an elevator in the event of a grid outage. I have 150KW of total power at my disposal to power the load. The renewable inverters cannot handle in-rush that will go beyond 150KW without faulting out. The elevator...

Thanks Keith and Bill for your insights and help on the matter. Bill, Are you saying that replacing the wye/delta with a wye/wye would solve the problem? (The new wye on the 480V side being only 3 wire). Noted that the replacement transformer should not be a 3 legged core. I will look into...

Transformer NOT connected: A-B 213.0V A-C 214.5V B-C 214.1V Transformer Connected: A-B 213.5V A-C 214.5V B-C 214.5V Currents measured at main utility breaker while transformer is connected A: 62.8A B: 63.0A C: 45.2A N: Not Measured Couldn't get current readings with transformer disconnected...

Thanks Waross, I will do this today. I do know that the phases are imbalanced in terms of current, I can report a snapshot of loads in a bit. I will check phase to phase voltages with transformer connected vs disconnected and report back soon.

@xnuke, Your three bullet point assumption are spot on, except that the transformer is grounded. What I meant in my original post was that the neutral feeding into the 208 Wye side is not bonded to the ground inside the transformer ( HPS tech support asked me to check for this, and I have...

David, We need Wye on the 208 side so we can output power to the building in a grid outage. Are you saying a Wye/Wye transformer would work fine to connect PV and battery, and just leave neutral disconnected on the 480 PV/battery side? This would get rid of this grounding bank phenomena...

@David, Assuming this is the case, what are the dangers of connecting the system if these unbalanced phases are pushing current through the transformer?

I have not done this, but it is on my list, and a great suggestion. The problem is that it is City owned building with emergency response personnel. It takes 2-3 weeks to get permission to shut power. So it might be some time before I can do it.

That's correct. 480 side is PV and battery. Point of grid connection is 208V. Really I think the whole 480V side can be ignored (i could be wrong) since the issue occurs even when the 480 side is disconnected.

Hi All, I'm working on a small microgrid system that is interconnected to the main grid of a medium size building (Average load of building is about 15KW). The PV in 30KW and battery is about 115KWH. It is an AC coupled system at 480Vac fed to a transformer which steps down to 3 phase 208Vac...