residential generators

[mikelp]

Re: residential generators

Originally posted by dillon3c:
I'm a bit confused..
Why would you need to feed a 15 KW generator @ a residence,w/ parallel 300kcmils..

It's actually a commercial installation and the parallel 300MCM feeders are from the utility. They are parallel 4/0 feeders from a 100KW generator (not a 15KW). I realize that the topic of the thread was simply residential generators; however the topic was discussing whether or not an "optional standby" generator could be "undersized". That is the crack that my post falls into.....I really don't feel that I have taken over the idea that began the post as we are dealing with the specific topic outlined in the very first entry.

[ September 15, 2005, 10:47 AM: Message edited by: mikelp ]

 

[engy]

Re: residential generators

"...chosen to install a 100KW 3 phase generator with a maximum output of 364A..."

At what power factor do you get 364A? 0.8?
I get 346A with 100kW and 0.8pf?
What is the power factor of the facility?

How long are you pulling the 321A?
Briefly, or commonly around that value during the day?

Is this 24x7 facility manned 24 hrs/day? (not all are)

May still be OK, but you will want, and maybe have, load monitoring with provisions to manually or automatically shed non-essential load. The degree to which you monitor/shed load should be in line with how critical the load actually is?

 

[mikelp]

Re: residential generators

Originally posted by engy:
"...chosen to install a 100KW 3 phase generator with a maximum output of 364A..."

At what power factor do you get 364A? 0.8?
I get 346A with 100kW and 0.8pf?
What is the power factor of the facility?

How long are you pulling the 321A?
Briefly, or commonly around that value during the day?

Is this 24x7 facility manned 24 hrs/day? (not all are)

May still be OK, but you will want, and maybe have, load monitoring with provisions to manually or automatically shed non-essential load. The degree to which you monitor/shed load should be in line with how critical the load actually is?

You have a valid point and the truth is that most of the load is applied between the hours of 8 AM and 5 PM. 100KW generator is a standard model size, but the alternator that is supplied with the unit and its nameplate rating is actually 105KW at .8 PF thereby leading to the calculation discrepancy that you have pointed out.

Based on your comment on the load of the facility over the hours of a 24 hour period, I have re-opened my spreadsheet of data and anylized only the operating hours of 8 to 5 over the seven day period.

My sample rate was once a minute over a 5 minute integration period, over seven days. I have removed all data taken between the hours of 17:00 and 08:00 over the seven day period. Analyzing the left over data,
Here are my results:

Phase A
Max Amps:286
Average maximum amps:183
Average Amps:163
Average KW:18.6
Maximum Average KW:31.9
Average PF:0.9

Phase B
Max Amps:277
Average maximum amps:179
Average Amps:160
Average KW:17.6
Maximum Average KW:30.6
Average PF:0.9

Phase C
Max Amps:321
Average maximum amps:165
Average Amps:145.4
Average KW:17
Maximum Average KW:30.4
Average PF: 0.9


As you can see by the results, although there are some relativley high amperage maximums, the average KW usage was sampled every minute and recorded in 5 minute integrals over the same time periods. The high amps occured very briefly over the operating hours.

It is my intention to reinstall the data logging equipment at this site again for a period no less than 30 days, obtaining results at 15 minute intervals per the optional load calcultion described in 220.87 in the 2005 NEC (formerly 220.35 of the 2002)

I will repost with results for those who are interested after that time. Thanks for all comments from interested parties. They are appreciated.