Measuring Power Factor - Errors???

[nigeld]

In the process of measuring power factor, I wish to use a C.T. and a P.T., how do I determine the errors that these devices will introduce to the signals I am trying to measure?

What are accepted methods of measuring PF? How do I minimise these errors?

Nigel.

 

[jbartos]

Suggestion:
CTs and PTs have their errors determined by the standards to which manufacturers manufacture them. Standards vary.
PF can be measured by a voltmeter, ammeter and wattmeter.
The worst case PF Error is given by the additions or meter errors in terms of meter accuracies. The error may be minimized by more accurate meters.

 

[DougMSOE]

Would suggest that when using PT and CT that you keep the burden on the PT & CT as light as possible. You may want to look at the calibration curve for these devices. You will get a very good idea of how much and in what direction the errors will go.
If harmonics are in the circuit you may want to use digital filtering once you have collected the raw data.

 

[jbartos]

Suggestion:
Total Power Factor will include effects of harmonics
Displacement Power Factor will include fundamental waveforms of voltage, current, and power only.

 

[busbar]

ANSI C12.11-compliant instrument transformers are shipped with individual ratio- and angle-correction records. Some multifunction meters allow for software modification using correction/compensation values, and an assortment of power-factor displays.

 

[nigeld]

Regarding Standards, ie ANSI and IEEE, where do i go to find the documents? Are there any links to sites that have these available, or must they be ordered and purchased?

Thankyou all for your quick and helpful responses!

Regards, nigel.

 

[busbar]

A fair number of electrical standards are available for purchase as PDFs with online ordering features. It takes a little getting used to, but there’s standards.ieee.org, shop.ieee.org, ansi.org and a vendor global.ihs.com

Typing ANSI C12.11 description in to a google search field will return a description of the standard.

 

[Marke]

How about connecting a load of known power factor, i.e. a resistive load and see what readings you get. You could also make a measurement with a purely capacitive load. Pure inductance is dificult to achieve.
You need to use a supply that is very clean and undistorted for the capacitive measurement.

Best regards,

Mark Empson

http://www.lmphotonics.com