Measuring Power Factor with STD tools

I have an AEMC Model 3910 analyzer that measures amps, volts, kw and pf.

Is has been replaced by the model shown at this site

http://www.tequipment.net/AEMC8230.html

you need to be able to measure the phase angle between the voltage & current. The simplest way is to use a power factor meter. Here is a global source list for analog and digital pf meters.

Also, most digital power meters will provide power factor in addition to kw, kva, kvar, volts & amps. I prefer Electro Industries, but many others are available.

Electromechanical power factor meters have been around for decades. For a brief description of how they work, see http://www.tpub.com/content/doe/h1011v4/css/h1011v4_96.htm.

If you are talking about single phase power, the KW and KVA will always be equal.

If you are talking about three-phase power:

If you know the Kilowatts, voltage and the current you can determine the Power Factor. The Kilowatts and KVA are equal at Unity Power Factor.

At a KW, take the voltage control and dip the current meter, this is Unity Power Factor. Current flow is minimum at unity power factor. This is a good way to check all your metering on a new start-up.

Then make a right angle graph with a 45 degree line, the KW is one leg, the current is another and they relate at the 45 degree line if your voltage is dipped at each KW setting to get minimum current. Years ago I carried these graphs for 4.16KV and 2.4KV but they are in deep storage, the square root of 3 drops out of the equations at Unity power factor as I recall.

To determine the current at non-unity power factor, take the current at unity and divide by the desired power factor (i.e. 0.8) to get close, for a specific KW the voltage must be adjusted to change the KVA or Power Factor.

CAUTION on Leading Power Factor as the Generator can "skip poles" or "loose synchronism" if you go too far away from unity. This will cause severe mechanical vibrations and likely damage to the generator and trip protective relays, usually starting with over current at high loads.

"If you are talking about single phase power, the KW and KVA will always be equal."

Are you saying that reactive power doesn't exist in a single-phase circuit? That makes no sense! Any inductance or capacitance in any AC circuit (single- or three-phase) requires reactive power, which is part of the KVA, but not part of the KW.