3 ms·

Large customers pay not by wattage but by… I’m spacing on the word but essentially how much their power draw fucks up the sine waves for voltage and current in

Large customers pay not by wattage but by… I’m spacing on the word but essentially how much their power draw fucks up the sine waves for voltage and current in the power grid. I imagine common power rail systems in hyperscaler equipment helps a bit with this, but for sure switching PSUS chop up the input voltage and smooth it out. And that leads to very strange power draws.

murderfs 2y ago
You're probably thinking of power factor, which is usually not a big deal for datacenters. All of your power supplies are going to have active PFC, and anything behind a double conversion UPS is going to get PFC from the UPS. The biggest contributors are probably going to be the fans in the air conditioning units.
- Animats 2y ago
  This isn't about power factor. That's a current vs. voltage thing within one cycle. It's about demand side ramp rate - how fast load can go up and down. Ramp rate has been a generation side thing for a century. Every morning, load increases from the pre-dawn low, and which generators can ramp up output at what speed matters. Ramp rate is usually measured in megawatts/minute. Big thermal plants, atomic and coal, have the lowest ramp rates, a few percent per minute. Ramp rate demand side, though, is a new thing. There are discussions about it [1] but it's not currently something that's a parameter in electric energy bills. [1] https://www.aceee.org/files/proceedings/2012/data/papers/0193-000178.pdf https://www.aceee.org/files/proceedings/2012/data/papers/019...
  - hinkley 2y ago
    For factories it’s both, but if by “this” you mean the article, I agree. Bursty traffic is the problem they’re most trying to solve. It’s akin (but other side of the coin) to when NAS hardware learned to stagger drive spool up during power on to avoid brownouts. Startup current on spinning platters is ridiculous. You have to do something to buffer, and you can do it on the supply or demand side. Or for large problems, both.
quickthrowman 2y ago
You’re thinking of power factor. My utility will force companies to use power factor correction equipment (a capacitor bank) if their power factor is too low. The data center issue is not related to power factor.
oakwhiz 2y ago
Power factor, but most power supplies have a good amount of power factor correction on them now, and datacenters can have PFC as an independent system and/or inside some types/modes of UPSes. Oddly enough the capacitive power factor of power supplies cancels out with some of the inductive loads of supporting mechanical equipment.

murderfs 2y ago

You're probably thinking of power factor, which is usually not a big deal for datacenters. All of your power supplies are going to have active PFC, and anything behind a double conversion UPS is going to get PFC from the UPS. The biggest contributors are probably going to be the fans in the air conditioning units.

Animats 2y ago
This isn't about power factor. That's a current vs. voltage thing within one cycle. It's about demand side ramp rate - how fast load can go up and down. Ramp rate has been a generation side thing for a century. Every morning, load increases from the pre-dawn low, and which generators can ramp up output at what speed matters. Ramp rate is usually measured in megawatts/minute. Big thermal plants, atomic and coal, have the lowest ramp rates, a few percent per minute. Ramp rate demand side, though, is a new thing. There are discussions about it [1] but it's not currently something that's a parameter in electric energy bills. [1] https://www.aceee.org/files/proceedings/2012/data/papers/0193-000178.pdf https://www.aceee.org/files/proceedings/2012/data/papers/019...
- hinkley 2y ago
  For factories it’s both, but if by “this” you mean the article, I agree. Bursty traffic is the problem they’re most trying to solve. It’s akin (but other side of the coin) to when NAS hardware learned to stagger drive spool up during power on to avoid brownouts. Startup current on spinning platters is ridiculous. You have to do something to buffer, and you can do it on the supply or demand side. Or for large problems, both.

quickthrowman 2y ago

You’re thinking of power factor. My utility will force companies to use power factor correction equipment (a capacitor bank) if their power factor is too low. The data center issue is not related to power factor.

oakwhiz 2y ago

Power factor, but most power supplies have a good amount of power factor correction on them now, and datacenters can have PFC as an independent system and/or inside some types/modes of UPSes. Oddly enough the capacitive power factor of power supplies cancels out with some of the inductive loads of supporting mechanical equipment.