We are planning to replace generator. There is 800A main service and highest reading was 480amp per phase. This reading includes chiller load that was running during measurement. We were informed that 200kw generator was previously recommended to provide power to entire building. According to my calculation the 200kw natural gas generator will not have sufficient capacity since LRC of chiller needs to be taken under consideration. I?m looking into propose lager generator that would handle chiller load but of course would impact someone else recommendation. Let me know your opinion? Thanks
generator sizing
- Thread starter necnyc
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What is the LRC and FLa of the chiller?
mayanees
Senior Member
- Location
- Westminster, MD
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- Electrical Engineer and Master Electrician
gen sizing considerations...
gen sizing considerations...
In addition to all of the typical considerations used in generator selection, also look at equipment rating breakpoints.
I'm not sure of your voltage, but for purpose of discussion, starting with:
480Volt system:
Your 200kW genset equates to 300 amps at 0.8 pf, which at 115% cabling gives 345 amps. That fits under a 400 amp switchboard breaker. But it could be increased to a 225kW genset and still utilize the 400 amp frame at the switchgear, so that's an easily rationalized increase from 200 to 225.
(225kw/0.8/1.732/480V) * 1.15 = 389 amps)
208Volt system:
Your 200kW genset at 208V equates to 694 amps at 0.8 pf, which at 115% cabling gives 798 amps. That's full building backup at that level, since it's an 800 amp board, so there's no obvious level to increase to. If it's a 208 Volt system, the driving consideration will be the (largest motor) chiller starting inrush, which might have you installing 800 amp overcurrent protection on a larger genset.
There have been significant improvements to the available starting current from a given generator - largely attributed to electronic governor response. You may find that there's a particular 225kW genset with ample starting kVA and not need to go past that size.
What is the system voltage, and how large is the chiller?
John M
gen sizing considerations...
In addition to all of the typical considerations used in generator selection, also look at equipment rating breakpoints.
I'm not sure of your voltage, but for purpose of discussion, starting with:
480Volt system:
Your 200kW genset equates to 300 amps at 0.8 pf, which at 115% cabling gives 345 amps. That fits under a 400 amp switchboard breaker. But it could be increased to a 225kW genset and still utilize the 400 amp frame at the switchgear, so that's an easily rationalized increase from 200 to 225.
(225kw/0.8/1.732/480V) * 1.15 = 389 amps)
208Volt system:
Your 200kW genset at 208V equates to 694 amps at 0.8 pf, which at 115% cabling gives 798 amps. That's full building backup at that level, since it's an 800 amp board, so there's no obvious level to increase to. If it's a 208 Volt system, the driving consideration will be the (largest motor) chiller starting inrush, which might have you installing 800 amp overcurrent protection on a larger genset.
There have been significant improvements to the available starting current from a given generator - largely attributed to electronic governor response. You may find that there's a particular 225kW genset with ample starting kVA and not need to go past that size.
What is the system voltage, and how large is the chiller?
John M
generator sizing
Thanks Bob and John for reply. The system voltage is 208V. Measurements were performed by building?s staff. I was informed that there is "75 ton" chiller, but I?m going there next week to review chiller and proposed space by building since there is potential issue with required clearance. I will let you know chiller FLA when I come back from site visit.
Thanks
Thanks Bob and John for reply. The system voltage is 208V. Measurements were performed by building?s staff. I was informed that there is "75 ton" chiller, but I?m going there next week to review chiller and proposed space by building since there is potential issue with required clearance. I will let you know chiller FLA when I come back from site visit.
Thanks
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