At least in the data-centers I helped manage the inverters were in-line running 100% duty-cycle, meaning frequency sync is not required as there is no bypass. The servers never see the raw commercial power. Data-centers in the US are indeed 3-phase. FWIW the big Cats did have controllers that would maintain sync even when commercial power was gone but we did not need it. There wasn't even a way to physically merge commercial and generator power. ATS inputs and outputs were a binary choice.

I know what you mean though, the generators I worked with in the military had a manual frequency sync that required slowly turning a dial and watching light bulbs that got brighter with frequency offset. Very old equipment for Mystic Star, post-WWII era equipment. 50's to 90's

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dylan604 3 days ago | parent | next [-]

In the facilities I have been in (not managed), they were all in-line as you describe as well. Mains power is dirty. Having a data center without line condition on mains would be insane.

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Bender 3 days ago | parent [-]

Mains power is dirty. Having a data center without line condition on mains would be insane.

Agreed. Even my home computer and networking equipment is 100% in-line with inverters and never see commercial power. PG&E in California got me into this habit with all the Planned Safety Power Shutoffs, wildfires, surges from really old transformers and unplanned outages. Now each of my tiny indoor rings of power have 200 to 800 amp-hour capacity each and over-sized inverters. I put the whole-house inverter plans on hold for now.

	▲	dylan604 2 days ago \| parent [-]
		way back when, I worked for a VHS dubbing facility where we had a voltage meter with an alarm set to warn when voltage would drop below a certain rate, but I don't remember the exact value. At that point, the VCRs would glitch and the recordings would be bad but the dip would be momentary and not enough to force the machines to stop like a full outage. When the alarm sounded, we stop all of the decks and re-rack the room and restart all of them. Without the alarm, it was impossible to catch these without 100% QC of a tape. That is when I groked how much worse a dip can be than a spike. Some equipment will start to pull harder when the voltage drops which kills more power supplies than spikes. Surge protectors are great for the spikes, but line conditioners or battery backups are the only protection from the dips. Management decided that the fully time battery conditioned expense was not worth it, so we were constantly running with some set of equipment down because of a dead power supply

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jimmygrapes 3 days ago | parent | prev [-]

Manually syncing several of the MEP012 generators was always far more stressful to me than any physical dangers!

	▲	Bender 2 days ago \| parent [-]
		I bet. I never messed with the trailer or skid mounted generators. It sounds like you were also USAF. At least modern day noise cancelling headphones are much better. Guessing you probably have tinnitus from working on them. At least I think that is partially where mine came from.