Power factor without current flow?

[zbang]

As I understand it, power factor as a quantity can not exist when there is no current flow and thus no e/i phase angle difference to measure. In that case and assuming that reporting not-a-number (NaN) is not possible, does it make more sense to report PF as 0.0 or 1.0? My view is to assume the angle difference is 0 deg and report cos(0)=1. For many real-world systems*, it seems that 1.0 is more sensible so trends/calculations/graphs don't have huge excursions to zero.

*where the budget doesn't allow for $5k logging devices and which are likely to have a PF from around 1.0 to maybe 0.7 lagging

Why? The monitoring device I'm using reports a PF of 0.0 when no current flows (I'm not sure how it reports leading PF since I haven't set up a test for that yet, and it's not much of a concern right now).

 

[LarryFine]

I don't see how a power factor can exist without current, so it can't be claimed to be 1 or 0 or anything at all.

 

[winnie]

I agree that power factor is meaningless when current is zero.

If the system doesn't have a clear way to express 'this number is meaningless' then IMHO it probably makes sense to keep reporting the last meaningful value...but both 0 and 1 are equally (in)valid.

Whatever is accepting these values for further interpretation needs to recognize that when current == 0 the PF number should be ignored.

 

[MyCleveland]

Just a lack of error handling in your device. No current in circuit should show a NULL value...nothing to report...instead of zero.

 

[zbang]

Yep, it's a cheap device and I "fixed" the value to null in my own software (it was easier than remembering the previous one). That doesn't answer my question- if there must be a number, which makes more sense?

(Some graphing software doesn't deal well with datasets containing null values, nor do some popular spreadsheets when calculating averages/min/max/etc.)

 

[LarryFine]

Just a lack of error handling in your device. No current in circuit should show a NULL value...nothing to report...instead of zero.

Well, since there cannot be a zero PF, perhaps that is an appropriate number to display

 

[wwhitney]

Say you have a power factor 1 device that is turning on and off, and you look at graphs over time of I, V, and PF. Do you want to see the PF graph as a straight line, or do you want to see it as a step function showing when the device is turned on and off?

Cheers, Wayne

 

[wwhitney]

Well, since there cannot be a zero PF, perhaps that is an appropriate number to display

Sure, there can be PF 0, it just means that current and voltage are 90 degrees out of phase, and no net energy is occurring over one cycle.

Cheers, Wayne

 

[petersonra]

N/A

 

[ramsy]

That doesn't answer my question- if there must be a number, which makes more sense?

Table 9, Note 2 provides an impedance formula for use with Power Factors other than 0.85 default, used for all NEC table values.

Point-to-point short circuit analysis must also set PF=85%, where NEC Tbl. 9 impedances are converted 1/(Z per foot) to "C" table results, published in IEEE Std. 241–1990 (IEEE recommended practice for commercial building power systems).

 

[Besoeker3]

Unless the power factor is disconnected there will be current even if the PF is just quadrature..