# Formula question

11349 Views 89 Replies 29 Participants Last post by  Lz_69
I have a question. Looking in my Ugly's Book for relevant, three-phase formulas, I found one for calculating amperes when "KW" (kilowatts) is known. The formula has KW X 1000 being divided by the product of voltage, power factor, and 1.73.

If the power is already KW, why is KW multiplied by 1000?:001_huh:
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You are converting Kw to watts.
That won't work. If I multiply kilowatts by 1000, I'm converting it to megawatts. To convert KW to watts, the KW would be divided by 1000.

If you have an Ugly's, why don't you see if that formula is written that way? Mine is a 2002 edition.
like john said, you are coverting to watts so you can get amps (not ka)

3kw = 3000w = 3kw x 1000
Actually, when you divide power in KW by the product of voltage, power factor, and 1.73, you get amps times ten to the third power, or "kiloamps."

If power in KW (power times 10 to the third power) is multiplied by 1 times ten to the third power (1000) the result is power in megawatts or power times ten to the sixth power. Amps solved in this way will be wrong by a factor of 1000.

I think the problem is because the power in watts is expressed as kilowatts in the formula.
Amps = Watts/(Volts * 1.73 * pF)

if we know that we have 15kW load for the sake of the exercise a motor to calculate the amps we need to know 2 other pieces of info 1. the line voltage and 2. the power factor.

Notice the formula solves for amps not kiloamps.

The formula then has watts as the unit of measurement for power not kilowatts.

So to change kW into watts we multiply by 1000 ie 15kW is the same as 15000W this is the figure we need to plug into our formula.

BTW waco

in another post that is now closed you answered a question about whether or not a low voltage would effect the kW rating of an installation and you answered yes. I disagree the motors in the installation would draw more amps to compensate but the power they deliever and hence use wouldn't change.

ie for a single phase 120V motor to deliever 1kW

A = kW x 1000 / (V x pf)
= 1 x 1000 / 120 x 1 (pf not important for this example so assume 1)
= 1000 / 120
= ~8.3A

the same motor at 100V
A = kW x 1000 / (V x pf)
= 1 x 1000 / 100 x 1 (pf not important for this example so assume 1)
= 1000 / 100
= 10A

The power measured going into the installation is unchanged. Of course the motor would be technicly overloaded and this may cause other problems.

The other thing is the lights and other resistive loads would actually use less power.
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When working with "kilo" anything, the result of the operation will also be "kilo." "Kilo" is just another way of saying ten to the third power. If you multiply "kilowatts" by 1000, you get "megawatts." No way around that.

As for the other, motors aren't the same as straight resistant loads. Motors that cannot reach their design rotation suffer losses as the phase difference between voltage and current increases. Thus, such motors generate wattage which doesn't translate to torque.

I think the point was that wattage is not a suitable measure for anything regarding motors unless they are able to operate at their design parameters.
the point is though you are not multipling the kilowatts by 1000 giving you megawatts you are multiply the NUMBER of kilowatts by 1000 thus giving you watts.

As for your point about motors I did say in my post that an overloaded motor would cause other problems.

In fact I would argue that an overloaded motor has a better power factor than an underloaded one.

It is unlikely that that a motor designed for 120V running at 107V would not run at full speed. The likely scenario is that the motor would be drawing too much current to meet the load requirements.
When working with "kilo" anything, the result of the operation will also be "kilo." "Kilo" is just another way of saying ten to the third power. If you multiply "kilowatts" by 1000, you get "megawatts." No way around that.
Since you are multiplying kilowatts by 1,000 you are getting a larger number in return, which is watts.

100,000 watts = 100 kilowatts = 0.1 megawatts
0.1 (1,000) = 100
100 (1,000) = 100,000
I have a question. Looking in my Ugly's Book for relevant, three-phase formulas, I found one for calculating amperes when "KW" (kilowatts) is known. The formula has KW X 1000 being divided by the product of voltage, power factor, and 1.73.

If the power is already KW, why is KW multiplied by 1000?:001_huh:
Kilowatts x 1000 = watts. Period. It is not megawatts. 1000 kW is a megawatt.
But 1 kW times 1000 = 1000 W.
And 1000 kW times 1000 = 1,000,000 W

InPhase277
I have a question. Looking in my Ugly's Book for relevant, three-phase formulas, I found one for calculating amperes when "KW" (kilowatts) is known. The formula has KW X 1000 being divided by the product of voltage, power factor, and 1.73.

If the power is already KW, why is KW multiplied by 1000?:001_huh:
K or Kilo means 1,000
hence kilo=1000 x watts
Inphase277, you're flat wrong. One KW multiplied by 1000 is one MW. One KW divided by 1000 is one watt.

As I wrote, KW is another way of expressing thousands of watts. One KW is 1000 watts.

What do you think "kilo" means?
kilo

1870, shortening of kilogram. The prefix meaning "one thousand" was introduced in Fr. 1795, when the metric system was officially adopted there, from Gk. khilioi "thousand," of unknown origin.
Inphase277, you're flat wrong. One KW multiplied by 1000 is one MW. One KW divided by 1000 is one watt.

As I wrote, KW is another way of expressing thousands of watts. One KW is 1000 watts.

What do you think "kilo" means?
All these online conversion calculators say your wrong. :thumbsup:

http://www.unitconversion.org/power/megawatts-to-kilowatts-conversion.html

http://www.easyunitconverter.com/power-unit-conversion/power-unit-converter.aspx

http://www.smpspowersupply.com/powerunits.html

http://online.unitconverterpro.com/metric-conversion/convert-alpha/power.html
If you multiply "kilowatts" by 1000, you get "megawatts." No way around that
3Kw = 3000 watts...agreed?

10 Kw = 10,000 watts...yes?

so to convert 3 to 3000, do you multiply by 1000 or divide by 1000?

to convert 10 to 10,000, do you multiply by 1000 or divide by 1000?

You're talking equations, not actual values.

1 Megawatt = 1000 Kilowatts
1 Kilowatt = 1000 watts
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Inphase277, you're flat wrong. One KW multiplied by 1000 is one MW. One KW divided by 1000 is one watt.

As I wrote, KW is another way of expressing thousands of watts. One KW is 1000 watts.

What do you think "kilo" means?
Wrong.
1 kW = 1000 W = 1 x 1000 W
1000 kW x 1000 = 1,000,000 W = 1000 x 1000 W

You are either too dense to get this or so arrogant that you think everyone else is wrong when you have been told by not just the people on this forum, but also the Ugly's Book.

You take the number of KILOWATTS (which is 1) and multiply it by 1000 to obtain WATTS. 1 x 1000 = 1000. You are mistaken because you are starting with 1000 instead of 1. It is 1 kW, not 1000 kW.

In other words, if you state it as 1000 W, drop the multiplier. But if you state it as 1 kW, you need the multiplier to make watts.

InPhase277
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This has got to be about the most bizarre thing I ever read! Type in the number 1 in megawatts and instantly read 1000 for kilowatts. That means a megawatt is 1000 times more than a kilowatt which is 1000 times more than a watt and 1,000,000 times more than a milliwatt!

Working in powers of ten remains an essential aspect of working with and understanding the terms and measures used in electricity and electronics. Obviously, it is a subject which must not be taught much anymore.

So, whoever replied with multiple links to online conversions, maybe you ought to give them a try.
I don't know how else to explain it. If your too dense to get it, then so be it...YOU sir, are absolutely WRONG. Good day.

OK, one more try....

You are not trying to actually change the number. You are trying to CONVERT the number. You want the value to REMAIN THE SAME. If you have 1 (one) Kilowatt and you need watts, you don't want to change the VALUE of the Kilowatt, you just want to change the units. 1 Kilowatt = 1000 Watts and to convert FROM Kilowatts TO watts, you must MULTIPLY by 1000. That is an absolute, undenyable FACT.

Have you ever seen the commercial where the guy wants a color copy of a B&W printout...keeps saying "but if you put it on the color copier..." and at the end he says "is it me, or her?"

Well...it's YOU.

I hope "your" math has served you well, but somehow I doubt it. I pray for your customers if you apply your math to their home. I don't know any other way to explain it...without a big hammer...so now..good day, sir.
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:no:
I'm just glad I do not work for this guy, I'd have a nervous breakdown. I do feel sorry for the homeowners that come in contact with this guy.

I don't see how he can disagree with the number of people in the same field as him and the four links to conversion calculators I had linked ALL SAYING THE SAME THING.

EDIT: Okay last try: a watt is a watt. kilo is 1,000, kilowatt is 1,000 watts. Mega is 100,000, Megawatt is 100,000 watts. Multiply or divide to change between kilo, mega, giga and so on. This is middle school math, you should now this.
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