10 sec requirement

Status
Not open for further replies.
ATSman

ATSman

ATSman
Location
San Francisco Bay Area
Occupation
Electrical Engineer/ Electrical Testing & Controls
Can someone site the origin of the Calif code requirement for the EPSS to deliver power to a health care facility within 10 seconds after a power failure?
Thanks
 
If NFPA 99 is part of California's codes, look at 4.4.1.1.11

Roger
 
I'm curious about the rational for the time. Ten seconds seems quite arbitrary, like it was plucked out of the air. I don't mind if it's arbitrary, but I'd like know that if it's not backed up by some research or other requirement. (Kinda like the 25 ohm ground rule....)
 
zbang said:
I'm curious about the rational for the time. Ten seconds seems quite arbitrary, like it was plucked out of the air. I don't mind if it's arbitrary, but I'd like know that if it's not backed up by some research or other requirement. (Kinda like the 25 ohm ground rule....)
Click to expand...
It probably has a lot to do with how long it takes a genset to start and transfer under full load . I have witnessed many of these tests and usually 7 secs is enough time. Have a snickers with those extra 3 seconds.
 
quogueelectric said:
It probably has a lot to do with how long it takes a genset to start and transfer under full load . I have witnessed many of these tests and usually 7 secs is enough time. Have a snickers with those extra 3 seconds.
Click to expand...

I've seen many of generators fireup and transfer somewhere between 5 to 7 sec.
 
I've also heard that the 10 seconds was for generator start up and transfer. I'm sure ideally we'd all like instant emergency light but if Code required that then generators would not be able to provide emergency light because motors are not ideal and they do need some time to start. It seems that the larger motors start getting close to that 10 second line. I'm talking in the 300kW range.
 
I have seen few new generators of any size that can't get going in under ten.

If it is having trouble you should check the start delay and transfer delay times at the ATS to see if that is burning up to much time.

With an emergency generator I keep the start delay very short, like 1 second, at worse that will result in a unneeded start up. But I set the start up voltage pretty low so short sags do not initiate a start up.
 
Transfer Time

Transfer Time

Actually, this is a closed transition ATS. The customer does his tests from the processor test pad which is a hot-bus-hot-bus test. I explained that during an actual outage (dead-bus-hot-bus test) there is no synchronizing time added to the xfer & it will switch in 4-5 sec once generator comes up to proper V & F. They do not want to open the breaker to do there testing and this is way over the head of the AHJ who is on their butt.
The reason for the long synchronizing time is that the utility frequency varies from 59.98HZ to 60.03HZ and the 1000KW generator varies from 60.13HZ to 60.19HZ. Because of this the xfer time can exceed 10 sec or it will not transfer at all after the 1 min time out.
Has anyone seen utility frequency vary this much? This is in San Francisco, not exactly the boondocks.
 
Tony,
That frequency range does not appear to be abnormal. I have a GridWise grid monitor screen saver and it would not be uncommon to find the frequency moving in that range. The monitoring point is for the Western interconnect and is connected in Richland, WA at the Pacific Northwest National Laboratory. You can download the screen saver here. I understand that frequency disturbances move though the complete grid at about 1/3 the speed of light, but are attenuated as you move away from the source of the disturbance.
That being said, I agree with you assessment that this will not be an issue under power failure conditions as there would be no attempt to sync with nonexistent utility power and the 10 second rule only applies when the generator is picking up the load after a power loss.
 
Last edited:
quogueelectric said:
It probably has a lot to do with how long it takes a genset to start and transfer under full load . I have witnessed many of these tests and usually 7 secs is enough time. Have a snickers with those extra 3 seconds.
Click to expand...

3 seconds used to be the standard utility recloser delay. Since deregulation that standard went by the wayside and multiple recloser practices exist.
 
weressl said:
3 seconds used to be the standard utility recloser delay. Since deregulation that standard went by the wayside and multiple recloser practices exist.
Click to expand...
I guess it depends north or south winter or summer the original post was for a hospital or some sort of health care facility (hospital) however I clearly remember listening to switchyard operators tell thier horror stories of the switch I had to open in the snowstorm/freezing rain with a hand crank because the automated system failed. The sheer terror in thier face describing the load arcing as they were hand cranking a switch open was priceless. Tell me just one more time. Awesome power.
 
Status
Not open for further replies.
Top