Power Factor

[CLHaines]

How can one tell if the "power factor" of a building has been altered/corrected to a better value. Is there any tell tell signs without the owner or anyone else being present to ask. Finally, wat is likely to be the power factor of an electric heater with simple resistance?

 

[dpc]

Power factor of a resistance heater = 1.

The only way to determine the power factor is to measure it with an appropriate meter. Most modern electronic power meters can display power factor.

 

[Marmite]

The tell tale sign would be the presence of power factor correction capacitors in the switchroom(s). Power factor of a resistive heater is unity.
Regards
Marmite

 

[waross]

A poor power factor means that the site operating with a lagging phase angle. The the phase angle may be reduced and the power factor improved by the installation of capacitors.
The more capacitors, the more correction. It is not good to over correct.
I check the KWHr meter if it is electronic. Divide the HW by the KVA to get power factor. I almost always ask the owner to show me the power bills.
If the property is not subject to a penalty for a low power factor there may be a simple meter that doesn't show KVA and the power bill will not show any power factor information.
This is a job for someone who is familiar with power factor calculations. Most KWHr meters do not show power factor directly but supply enough information to calculate it.
There is so much variation in the characteristics of modern digital KWHr meters that it may be beyond the scope of this forum to train you as a power factor expert.
Oh by the way, your heater will have a power factor of 100% but it will improve the power factor of a system slightly when connected.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[CLHaines]

Thank you all for your help.
I thought the best way to find out the PF would be through bills as suggested above but most utility companies don't have this info. The main objective during the survey is to establish if the PF is <0.9 or between "0.9 and 0.95" or >0.95 and nothing further
I guess there is no simple answer although I do like the idea of being able to calculate the PF by dividing the HW by the KVA. I'll have to try this out..

 

[rovineye]

Do you mean KW vice HW Bill?

 

[waross]

Typically a power bill will show Kilo Watt Hours and Kilo Volt Amp Hours. Dividing the Kilo Watt Hours by the Kilo Volt Amp Hours gives the average power factor for the month.
Some bills also show the PF. As I have mentioned, if the service is not subject to PF penalties this information will not be shown. If the service is not subject to power factor penalties the meter will probably not be recording these values.
If you can connect a power factor correction capacitor temporarily you can measure the power factor with a clip-on ammeter.
Connect the capacitor to the service. Measure the incoming current just ahead of the capacitor connection, the load current just past the capacitor connection, and the capacitor current.
You can use the law of cosines to determine the power factor or scale it on a drafting table.
1 Lay off a vertical line.
2 Lay off a scale representation of the capacitor current on the upper end of the vertical line.
3 From the upper end of the capacitor current draw an arc scaled to the load current.
4 From the lower end of the capacitor current draw an arc scaled to the line current.
5 From the intersection of the arcs draw a horizontal line to intersect the vertical line. This is the "base".
6 Divide the hypotenuse (load current) into the base. This will be the power factor.
It's probably a lot easier to just rent a power factor meter for a day.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[CLHaines]

Thank you for all your help. You guys are just brilliant

 

[rovineye]

Thanks Bill. *
Got you now. Being shipboard I don't get power bills, nor have any kind of hour meters. Just fuel bills!

It is all pretty easy for me, as I always have KW and KVA meters, and usually pf meters. I only care about pf when doing testing when a pf is specified, and when checking to see that I am within the generator capability curve at various conditions.

One question. Is the penalty usually determined by the pf over the average of say a month, vice some sort of worst case scenario?

 

[itsmoked]

rovineye; There's no standard on PF penalties. They're all over the place. Some very lenient some harshly punitive.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

The most punitive charge for as little as 1% off unity, leading or lagging, on a real time basis.
The most lenient penalties read KWHrs and KVARHrs every month and calculate the average, and charge for KVARHrs in excess of 90% power factor. Many of these may be corrected by the installation of a small capacitor bank that stays online 24/7.
If a plant runs equipment with a poor power factor 168 hours a month and the capacitors are online 744 hours per month, it doesn't take much to correct the KVARHrs to a 90% average.
Some meters will allow a leading power factor which really rolls back the KVARHrs. Other meters will not run backward but the KVARHs still add up.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[fangas]

There's no standard on PF penalties. They're all over the place. Some very lenient some harshly punitive.

I'll say. I was in LA a number of years back. Same company, 2 plants in 2 neighboring cities (A short block apart) , 2 different municapality electric providers, 2 "incredibly" different rate structures.
Usage, Demand, & PF.

However, if you figured the bill from 1 plant against the structure of the other, they the bottom line came out almost a wash.

Guess it all depends on the mood and creativity of the people writing it.

Ed

 

[oldfieldguy]

With the present availability of simple and inexpensive metering devices such as the products like the GE PQM, etc., if I was worrying about power factor on a regular basis, I'd look into having one installed.

Of course, these metering features are built into many modern protective devices, too. This might be incentive to change out a set of old but functional electromechanical relays.

If I wanted a one-time or short-time picture, I'd call the local electrical testing company and get them to install a recorder for a while. A competent service company can give you a real-time snapshot or a trend over time for your study.



old field guy