I'll throw something out here that's worth considering too - DCs are actually *too large* to be made part of under frequency load shed schemes and the like because dumping one via the methods at the utility's disposal (open breakers) creates too large a step change on the system
Do DCs connect to the medium voltage distribution system like a large industrial load would?
Perhaps smaller DCs? Everything in the MW class very quickly starts needing pretty large transmission (with appropriate step down infrastructure) and as the OP alluded to.. the other things needed to deal with potentially large step changes in supply/loss.
Most of them are directly transmission connected these days
Can you describe exactly how that works and what it means in more detail? What voltage do they get the connection at? What kind of poles and wires?
That depends heavily on the utility and the region. What I've seen is a (usually) short line from a 230 or 345kV substation to a step-down transformer right outside the datacenter which goes into their various feeders. Typical transmission class construction up to their transformer.
Doesn't ERCOT require for their large demand users to flexible in order to meet demand spikes on their grid?
I don't work in ERCOT so, unfortunately I can't speak to that. Their rules are different than the rest of the country, but I think I heard about something like that - that's not quite the same thing I'm talking about, mind, load shed is generally automated.
Does the utility or the data center operator own and operate the transformer? Where's the meter?
JFC a meter at 345kV !
standalone meter CT/VT combo usually at the point of interconnection on the high side of the transformer. The transformer is normally customer owned in my experience but it could be owned by the distribution company, all depends on agreements
Some utilities want to and require that they own and operate that unit, but not all.
Holy shit, that's more than I thought
Exactly this in all the facilities I’ve visited. They really really don’t want to put the HV stuff *in* the DC for a lot of good reasons. The 11/33kV room is OK internally though before stepping down to the 415V to the floor which eventually becomes the 230V (in Australia) at the rack level.
That room is a very complicated (contractual) grey area in a DC. 😃
I don’t exactly know what this means. Yes, they are (for large commercial facilities) in the ones I’ve seen but the utility still builds and owns the infrastructure that steps the voltage down from HV to LV (33/11kV). Even when this is “embedded” into the DC structure. If you have examples?
That isn’t quite (completely) true. DCs are often much more flexible because of the nature of their construction (multiple data halls is just one example) and in some scenarios can drop some of their load.. (When given an economic reason to do so).
There is not to my knowledge at present a mechanism to force a DC to ramp down in controlled fashion at utility command quickly enough without creating that massive step, but I think there's going to need to be