Power factor correction

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JdoubleU

Senior Member
One of our Dorm buildings has a power factor of 80 during the night and drops below 65 in the mornings. We think that the old ballast with the t12 may contribute to this issue. Does anyone know if changing these would make a big difference? Also, do you have any other Ideas on correcting this problem?
 

Electric-Light

Senior Member
One of our Dorm buildings has a power factor of 80 during the night and drops below 65 in the mornings. We think that the old ballast with the t12 may contribute to this issue. Does anyone know if changing these would make a big difference? Also, do you have any other Ideas on correcting this problem?

I don't think so. Ballasts used in commercial buildings are high power factor and they have a power factor of >0.90.

What are the harmonics? Whats the power factor on other buildings you're maintaining like? There are not many appliances in dorm rooms, but you can bet each occupant has their own computer.

I would guess rectifier front end loads. Computers and TV and I would guess that you have a very high odd harmonics. I'm sure the students leave their computer on 24/7 since they're not paying the power bill and I think that represents a significant portion of the power consumption. Power factor reduction caused by non linear loads can not be corrected with devices that apply corrective kVArs like capacitor banks or synchronous motors.

Given one or two computers per room with a PF of about 0.55 to 0.60, 200W/400VA per occupied room is a fairly good estimate of rectifier front end loads.

When they're back in their room and have their lights on and start using the laundry room, the high power factor ballasts and resistive clothes dryer increases the power factor, because the proportion of technology load relative to building demand is smaller.

What's the kVA demand at night vs morning?
What kind of read outs do you get during breaks when residents are away?

If you identify plug-in loads in rooms as the cause, I would work with the management to encourage residents to avoid leaving their computers on 24/7.
 
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USMC1302

Senior Member
Location
NW Indiana
Are you starting large loads, air handlers, etc via a building automation system? A P.F. of .8 will still earn a penalty from the POCO here. As suggested, take a good look at the loads and times, etc. We were able to get our P.F. up to .9+ and saved a chunk on utility bill.
 

brian john

Senior Member
Location
Leesburg, VA
Is the change in pf a short duration event or is it consistent.

Besides lighting what else is in the building (loads).

Are you penalized for a bad pf.
 

kwired

Electron manager
Location
NE Nebraska
what is the total load with low power factor vs total load vs higher PF?

You may have a case where the higher PF loads are not running and the majority of the load is low PF loads but the total KVA is lower.

I have a college age son, and I can say that from what I know of his typical routine the mornings are probably the time when less total KVA will be in use. Students are either sleeping or at class. HVAC is likely majority of load at this time.
 

Electric-Light

Senior Member
what is the total load with low power factor vs total load vs higher PF?

You may have a case where the higher PF loads are not running and the majority of the load is low PF loads but the total KVA is lower.

I have a college age son, and I can say that from what I know of his typical routine the mornings are probably the time when less total KVA will be in use. Students are either sleeping or at class. HVAC is likely majority of load at this time.

The time when students get to class and running the 40hp elevator at 20-30% load at nearly continuous duty cycle could affect the short time power factor.

We need to know the THD and if possible, percentage of each harmonics, so we can determine if its a line driven motor load or non-linear load though.

Personal computers and AV equipment have a power factor of about 0.5-0.6 caused by non-linear load. Most do not have any corrections at all. They must have a power factor correction under EN61000-3-2 for use in Europe. Units using the same power supply for shipment to Europe as well will have PFC.

Screw in CFLs and residential ballasts typically do not have PFC and they have 0.5-0.6

Commercial ballasts, VFDs have PFC.
 
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