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#1
09-27-2007, 07:23 PM
 Unregistered Guest Posts: n/a
Amps To Kilowatts

How Do You Determine Kilowatts From Amps? I Have 288 Amps How Do You Determine How Many Kilowatts That Is?
#2
09-28-2007, 11:00 AM
 thesmartfisherman.com A Kind Apex Predator Join Date: Sep 2006 Location: Florida Posts: 232 Rep Power: 8
Re: Amps To Kilowatts

What Voltage are you assuming?

The conversion of Amps to Watts is governed by the equation

Watts = Amps x Volts

For example 1 amp * 110 volts = 110 watts

In your case I will assume 110 volts so:

288 * 110v = 31,680 volts

or

31.68 Kilowatts
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#3
10-02-2007, 01:17 AM
 Unregistered Guest Posts: n/a
Re: Amps To Kilowatts

You made an error in the reply that makes it confusing
288A * 110V = 31,680 Watt

but 288A on a 110V grid is unlikely; I would expect it is 480V in a three phase grid; that makes it even more difficult :-)
#4
10-02-2007, 10:57 AM
 thesmartfisherman.com A Kind Apex Predator Join Date: Sep 2006 Location: Florida Posts: 232 Rep Power: 8
Re: Amps To Kilowatts

Quote:
 Originally Posted by Unregistered You made an error in the reply that makes it confusing 288A * 110V = 31,680 Watt but 288A on a 110V grid is unlikely; I would expect it is 480V in a three phase grid; that makes it even more difficult :-)
That was just an example of the arithmetic.
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#5
11-21-2007, 05:55 AM
 Unregistered Guest Posts: n/a
Re: Amps To Kilowatts

Quote:
 Originally Posted by Unregistered How Do You Determine Kilowatts From Amps? I Have 400 Amps How Do You Determine How Many Kilowatts That Is?
at 3phase 208volts

I Have 400 Amps How Do You Determine How Many Kilowatts That Is? at 3phase 208volts
#6
11-20-2008, 04:16 PM
 Unregistered111 Guest Posts: n/a
Re: Amps To Kilowatts

400amps @ 3p208

400*(3*208)=249,600w

249,600/1000=249.6
#7
04-10-2009, 03:55 AM
 mohamed Guest Posts: n/a
Kilowatts to amps

i hav motor for machine 380 v /3 phas /30 kw i whant know how many amps this motor ned
#8
04-10-2009, 05:14 AM
 JohnS Moderator Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,438 Rep Power: 19
Re: Kilowatts to amps

Quote:
 Originally Posted by mohamed i hav motor for machine 380 v /3 phas /30 kw i whant know how many amps this motor ned
The question is whether the 380 V is measured line to neutral or line to line. If it is line to line, then it is only 219 V line to neutral.

I will assume it is line to neutral
30 kW/380 V = 78.9 A
That is the sum of the three phase currents, each phase is 26.3 A, assuming the load is balanced.
(It may need higher current during starting.)

Edit: It is actually more likely that it is 219 V line to neutral and 380 line to line.
30 kW/219 V = 137 A, 45.7 A in each phase (assuming balanced load)

Last edited by JohnS; 04-10-2009 at 06:34 AM.
#9
04-13-2009, 06:39 AM
 MJWorner Guest Posts: n/a
Re: Kilowatts to amps

Quote:
 Originally Posted by JohnS The question is whether the 380 V is measured line to neutral or line to line. If it is line to line, then it is only 219 V line to neutral. I will assume it is line to neutral 30 kW/380 V = 78.9 A That is the sum of the three phase currents, each phase is 26.3 A, assuming the load is balanced. (It may need higher current during starting.) Edit: It is actually more likely that it is 219 V line to neutral and 380 line to line. 30 kW/219 V = 137 A, 45.7 A in each phase (assuming balanced load)
A three phase induction motor would be running phase to phase (no neutral required). The calculation is: 30,000W/380V/1.73 (sqrt of 3) or45.58028441
Amps. That being said, overcurrent protection will have to be sized to carry momentary starting load of about 250%. This could be even higher in an application with large inertial loading. The calculation is assuming 100% efficiency as well, so you need to know if 30kW is the size of the motor or the consumption under load and divide the current figure by efficiency.

Note that the square root of the phasing is used as actual voltage (an hence current) in a three phase circuit is 120 electrical degrees apart so the actual currents peak 1/150 of a second apart in 50 Hz or 1/180 of a second at 60 Hz.

Motor name plate data should indicate FLA (full load amps) and LRA (locked rotor amps). Local code requirements or good engineering practice will dictate wire size and overcurrent protection.

Sounds like you are looking at wire in the #6 AWG range (~15 sq mm) with an increase in size of (~5 sq mm) for each 30m increase in length.

Of course that's looking at it from half a world away.

Last edited by MJWorner; 04-13-2009 at 06:59 AM.
#10
04-13-2009, 06:59 AM
 MJWorner Guest Posts: n/a
Re: Amps To Kilowatts

Quote:
 Originally Posted by Unregistered111 400amps @ 3p208 400*(3*208)=249,600w 249,600/1000=249.6
That should be 400A x sq rt 3 (1.73) x 208V = 144,106.63 W or 144.1 kW.

You have to take the square root of the phases because they don't peak simultaneously but sequentially 1/180 of a second apart.

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