Power Factor Correction Design Question

[tmillard]

I did some searching on the forum this morning regarding power factor and have a design question.

We just recently a new high school and construction was completed last year. The school just had the electrical contractor that did the job monitor the power for a week. It turns out the power factor is around .74. (No swells, sags, etc.) They have several large chillers with induction motors so my guess is that these are the main contributors to the problem.

I know that you can specify the chillers to come with power factor correction. Would it be better to do that or provide correction for the whole building, right at the main service? If so, how would you best determine what size cap bank would you need for a whole building?

Thanks...

Tom Millard

 

[petersonra]

I am inclined towards adding PFC capacitors right at the motors. It is simpler. Schools rarely have qualified people around a lot to take care of some expensive and complicated system that might give them slightly better performance.

 

[RayS]

I'd try for correction at the loads, as it will correct PF all the way to the load. Also will automatically switch amount of correction as required if installed on load side of starters, but make sure it is not downstream of any drives.

 

[kingpb]

Better determine if the chillers, or other motors in question operate off a VFD, if so, you will need to rethink your caps at the motors.

 

[sceepe]

Measure the power factor of your chillers first. The mechanical guys in my office swear that their large 3 phase chillers have higher power factors. We have had schools that had 2-3 ton heat pumps in each room. These types of mechanical sytems actually had lower power factors than the central chiller systems.

Also if the power factor of these two big loads was the problem, wouldn't you see a change when they were not running?