power factor calculator

Hm. An exe file from an unknown source to aid in calculating the trivial. Should I be wary?

Bill

Yes. And for more than the obvious reasons.

I've taken a peek at the (JavaScript) source code of a few popular on-line calculators and discovered some nasty errors and quite a few just based on poor rules of thumb. If I'm doing some calculations that I'm going to sign, I want some assurance that the damned things work right.

Besides, this one won't run on my system.

If you have nothing good to say, please be silent. Before you open your big mouth visit my site!!

Why should we? Because *you* say so?

You seem to just be trolling for web hits and have contributed little.

daestrom

I wrote a little BASIC program that produce a .DXF file that, when printed out, made a nomogram for power factor calculation - I'd based it on one that I'd seen used for operators to calculate the power factor of an arc furnace given the megatwatt and megavar readings. I'll have to hunt that down, now in this era of Java I could make it a bit more user-friendly ( having to print the .DXF through Autocad was a bit of a drawback, but much easier than trying to do all the pixel-twiddling myself).

Does anyone use nomograms any more?

A different Bill than the above...

As a Mac user, I really do not know what a .DXF file is. What does this program do? Given only megawatt and megavar is there more to PF than

PF = megawatt/sqrt(megawatt^2 + megavar^2) ?

With calculators and Excel available, I find little need for nomograms. But I do appreciate the elegance of nomograms.

The first Bill

DXF = Drawing eXchange Format is a generic data structure for CAD applications.

No, or yes.

The above assumes only fundamental components (60 Hz) of current and voltages. Re-written, it is:

PF = Watts / ( Vrms * Irms )

The trouble arises when the Irms and/or Vrms values contain harmonics of the 60 Hz fundamental. The calculated PF is no longer the same. Using the wrong figure can get you into trouble when sizing capacitor banks for VAR correction, for example.

nomograms. But

.DXF files are an Autocad thing (Autocad is computer-aided drafting software that used to have Mac versions a long time ago) but they were convenient for me at the time as a way to produce a printed graph.

Agreed, even a calculator or slide rule makes the nomogram unncessary but it was interesting to work out how to produce it. My motivation at the time was that we'd upgraded the power transformer for one arc furnace and the old nomograms that were included in the original operating and maintenance manuals didn't cover the new power levels.

There can be a lot more to power factor, depending on the wave shapes - harmonics give a whole lot of complications.

An alternative Bill

>

I can understand why someone doing this all day might find some program with zillions of inputs into a spread sheet handy. There was no mention of harmonics. For the run of the mill guy, like me, who hardly worries about power factor, I would be content understanding what is going on and spending a bit of time doing a custom calculation. That is often much simpler than trying to remember how to use a program, a spreadsheet, or even a nomogram that is complicated.

I don't even want to know what might be involved in calculating power factor using a nomograph when harmonics are present. How do you even go about determining what power correcting capacitor is required when harmonics are present when you really need a filter? Sometimes trying to save effort of that nature is really not effective.

Bill

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Oh well, many have written complex calculators- I have one in VB(5) that is an extension of an HP11C calculator, without the programming and stats but able to handle the normal complex number math as well as complex trig and hyperbolics, etc (handy for T lines) - as well as up to 4 simultaneous (complex) equations. With help files as well and non-crash, (mostly- tried to catch all the possibilities with a slightly better record than microsoft) error handling. It was a fun thing, done, in the absence of anything better to do, to get something that was better than what is generally available for one's one purposes. - Sometimes it appears that an increase in calculating power is absorbed by an increase in the complexity of the problem tackled. There is also the perception that the numbers put in are not only correct , but correct to the n'th decimal place, and the output numbers must be correct to the last digit shown on the display.

Note: I am not going back to a slide rule, log tables, or large, laboriously drawn circle diagrams. However, with a slide rule, you had to estimate so that you had a good idea of the magnitude of the result. If you got 5432.672341 where you estimated 2, a question naturally arose in one's mind- "Oh shit - I boobed!:"

Isn't that the truth. Twenty years ago, we were calculating real-time training simulations using some very abbreviated mathematics. Truly complex things were simplified down to first and second order polynomials. Now, the computing power is so much higher, all sorts of spare time to do more in real-time. And those 'perfectly acceptable' simplifications are no longer 'acceptable' and we find ourselves doing a lot higher calculus and matrix algebra in real-time.

Kind of like 'junk'. No matter how big the garage, attic, or basement storage, the amount of 'junk' you have will grow to fill it.

Yes, I remember with the slide-rule you had to have an 'idea' of what the answer should be. Like figuring the decimal place at least. My kids had to learn 'estimating' in school and didn't understand why, since they also use a calculator in class.

But then I look at one of their homework problems, and without a calculator I'm able to say, "This answer couldn't possibly be right." They check, and

9 out of 10, they start erasing and wonder how their dad is so smart ;-) But I just did a little 'one and a half significant digit math' in my head is all.

daestrom

But with either your general purpose calculator or your slide rule, you are responsible for supplying (and understanding) the formula being used, its shortcomings and limitations on the scope of its use.

If you just use a spreadsheet or other program without understanding the model upon which it is based, you could be asking for trouble.

Right on!

I have seen the results of this. In academic situations, problems can be set to separate the "plug in and crank" students from the thinking students before they get to the stage where they can do harm. In industry, it helps to have a friend and mentor, such that I had, who, when presented with an opinion from a brash young knowitall (myself) would politely ask "Why?" - genuinely wanting to know. That simple question can be initially devastating but very useful in furthering one's understanding.

Paul- you are generally quiet but when you "speak", you are typically right on target. --

Don Kelly @shawcross.ca remove the X to answer