rockman7892
Electrical
- Apr 7, 2008
- 1,161
I'm in the process of determining size of 480V diesel genset for an industrial site to replace existing temporary units. I'm evaluating size based on both metering data captured via a portable power meter for site at service entrance as well through load calculation in order to evaluate both for gen sizing. The facility is a gas pumping facility which consists of general lighting, heat trace, and motor loads, to switch between utility and gen with loads connected to a common MCC. The motor loading cosists of several small 1.5 and 10hp motors as well as (2) 50hp motors as largest motors.
I have understanding of the load calculation process in accounting for all motor and non-motor loads in kW and then accounting for "starting load" of largest motor to arrive at generator size. For starting load of largest motors i've used 2.5-3x motor kW or what default values software provided. I've used Kohler's gen sizing program (similar to CAT's) to check sizing calcs.
At one point a portable power meter was setup at service entrance of facility for a short period of time to try to capture actual facility loading while operations mimic'd normal full load conditions at the time. I'm trying to determine how to best use that measured data in conjunction with load calculations to come up with generator size.
Obviously as expected the actual metering data is less than that derived by calculation. In looking at the metering data the maximum sustained current (not a spike that would represent motor starting or transient) is approximately 618A on a single phase corresponding to approximately 513kVA assuming balanced load. Unfortunately I cant seem to be able to identify the pf in the meter at this time of measurement (since it was taken of current trend) so will have to make an assumption to determine kW. Assuming a .8pf gives a measured kw value of 410kW (note: metering was not performed long enough for meter to capture max avg power based on 10min window)
In comparison when preforming gen calc using hand calcs or more specifically generator software I arrive at a running kW=675.2 and kVA=775.5. This includes a max starting kw=107 from starting of 50hp motor when all other load is running. The kw rating from calculation is approx. 275kW larger than measured value and likely has a bunch of conservativeness built into it so looking for good engineering judgement on how to evaluate both methods to arrive at optimal gen set size.
Does anyone have sound approach for using measured power for deterring gen set sizes backed up by calculations like I have in this case?
I have understanding of the load calculation process in accounting for all motor and non-motor loads in kW and then accounting for "starting load" of largest motor to arrive at generator size. For starting load of largest motors i've used 2.5-3x motor kW or what default values software provided. I've used Kohler's gen sizing program (similar to CAT's) to check sizing calcs.
At one point a portable power meter was setup at service entrance of facility for a short period of time to try to capture actual facility loading while operations mimic'd normal full load conditions at the time. I'm trying to determine how to best use that measured data in conjunction with load calculations to come up with generator size.
Obviously as expected the actual metering data is less than that derived by calculation. In looking at the metering data the maximum sustained current (not a spike that would represent motor starting or transient) is approximately 618A on a single phase corresponding to approximately 513kVA assuming balanced load. Unfortunately I cant seem to be able to identify the pf in the meter at this time of measurement (since it was taken of current trend) so will have to make an assumption to determine kW. Assuming a .8pf gives a measured kw value of 410kW (note: metering was not performed long enough for meter to capture max avg power based on 10min window)
In comparison when preforming gen calc using hand calcs or more specifically generator software I arrive at a running kW=675.2 and kVA=775.5. This includes a max starting kw=107 from starting of 50hp motor when all other load is running. The kw rating from calculation is approx. 275kW larger than measured value and likely has a bunch of conservativeness built into it so looking for good engineering judgement on how to evaluate both methods to arrive at optimal gen set size.
Does anyone have sound approach for using measured power for deterring gen set sizes backed up by calculations like I have in this case?