3 ms·

The company that maintains my generators has a dummy load that is basically a large resistor bank and fan on a trailer. It seems like Amazon could just build so

by gnu8 9y ago

The company that maintains my generators has a dummy load that is basically a large resistor bank and fan on a trailer. It seems like Amazon could just build something like that on a larger scale to load the generators - short term they could even rent the dummy load trailers and hook them up in the parking lot, right? For a permanent solution, have logic to switch in the appropriate amount of resistance to maintain the minimum load required.

tgtweak 9y ago
There are, unfortunately, a lot of things between on and off when it comes to utility power. Over voltage, voltage drop (which can cause fuses to blow since amperage goes up), phase outage, phase imbalance, harmonic noise (causing ground/neutral feedback), micro outages (few cycles; <50ms). All of which can confuse systems such as a transfer switch, ups, generators or paralleling gear. Most downtime I've seen in datacenters has been due to irregular power, not power loss. Case in point. Dummy loads are good for testing but they are not typically variable - if you had 2.5mva generators and a 1mw dummy load you wouldn't be able to run more than 1mw of critical IT load. I'll say this is the first I've heard of not having enough load to start a generator. They will happily start up and idle.
- gnu8 9y ago
  I would say the automatic transfer switch should be configured conservatively and go to backup power at the first hint of instability. If irregular power is the usual cause of downtime then I would expect the ATS to cope with those conditions, or it gets replaced with one that will. Good point about the lack of variability. Not sure if the generators would take kindly to suddenly switching out a 1 mw dummy load to free capacity for real load. On the other hand, it's not like these engines have fixed RPM throttles, and they should be able to handle a wide range of loads, albeit not at peak efficiency. Something doesn't fully make sense about that story. Maybe the generators were sized for their ultimate planned capacity and thus way too much for their deployment at the time.
  - ADefenestrator 9y ago
    I thought large diesel generators generally did operate at a fixed speed in order to output 60Hz. I know inverter/generators are common these days for small gas gensets, but have the big diesel ones switched over as well?
cup-of-tea 9y ago
Can't you just have a smaller generator for low load? Literally wasting fuel so you can run a large generator for a low load should be criminal.
- gnu8 9y ago
  You might not realize how much fuel it takes just to maintain generators. They have to be exercised, load tested, overhauled, all on top of whatever time they spend providing backup power. Which is just as well, because an engine that sits without ever running won't operate when it is most needed, and the fuel can stagnate, or even attract water and grow algae.

by gnu8 9y ago

tgtweak 9y ago

There are, unfortunately, a lot of things between on and off when it comes to utility power. Over voltage, voltage drop (which can cause fuses to blow since amperage goes up), phase outage, phase imbalance, harmonic noise (causing ground/neutral feedback), micro outages (few cycles; <50ms). All of which can confuse systems such as a transfer switch, ups, generators or paralleling gear. Most downtime I've seen in datacenters has been due to irregular power, not power loss. Case in point. Dummy loads are good for testing but they are not typically variable - if you had 2.5mva generators and a 1mw dummy load you wouldn't be able to run more than 1mw of critical IT load. I'll say this is the first I've heard of not having enough load to start a generator. They will happily start up and idle.

gnu8 9y ago
I would say the automatic transfer switch should be configured conservatively and go to backup power at the first hint of instability. If irregular power is the usual cause of downtime then I would expect the ATS to cope with those conditions, or it gets replaced with one that will. Good point about the lack of variability. Not sure if the generators would take kindly to suddenly switching out a 1 mw dummy load to free capacity for real load. On the other hand, it's not like these engines have fixed RPM throttles, and they should be able to handle a wide range of loads, albeit not at peak efficiency. Something doesn't fully make sense about that story. Maybe the generators were sized for their ultimate planned capacity and thus way too much for their deployment at the time.
- ADefenestrator 9y ago
  I thought large diesel generators generally did operate at a fixed speed in order to output 60Hz. I know inverter/generators are common these days for small gas gensets, but have the big diesel ones switched over as well?

cup-of-tea 9y ago

Can't you just have a smaller generator for low load? Literally wasting fuel so you can run a large generator for a low load should be criminal.

gnu8 9y ago
You might not realize how much fuel it takes just to maintain generators. They have to be exercised, load tested, overhauled, all on top of whatever time they spend providing backup power. Which is just as well, because an engine that sits without ever running won't operate when it is most needed, and the fuel can stagnate, or even attract water and grow algae.