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 Topic Title: kw to amps, 3 phase calc Topic Summary: Created On: 04 December 2007 05:58 PM Status: Post and Reply Linear : Threading : Single : Branch
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 04 December 2007 05:58 PM steveth Posts: 26 Joined: 17 September 2007 just a quick one guys, forgotten how to do the calc to convert 3 phase kw to amps. i.e if a machine stated 25kw 3 phase, what would the current per phase being drawn be? cheers 04 December 2007 06:18 PM rocknroll Posts: 9083 Joined: 03 October 2005 (kW x 1000 / sqrt3 x UL x cos) IL = IP regards ------------------------- "Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"------------------------- Edited: 05 December 2007 at 08:13 AM by rocknroll 04 December 2007 08:44 PM Ricicle Posts: 872 Joined: 23 October 2006 Originally posted by: rocknroll Star (kW x 1000 / sqrt3 x UL x cos) IL = IP regards Not this old chestnut again If the machine is rated at 25kW the use the formula RnR posted, but this applies regardless of how the load is connected (star or delta). 25kW is 25kW ------------------------- Empty barrels make the most noise. 04 December 2007 09:11 PM DALEC Posts: 216 Joined: 04 November 2007 HI STEVETH , By my maths ( DOH !) I= 36 PER PHASE ..... regards dale ------------------------- master of puppets is pulling your strings--------------------------------------------http://www.elliselectricalservices.com 04 December 2007 09:23 PM Jaymack Posts: 5078 Joined: 07 April 2004 Originally posted by: Ricicle Originally posted by: rocknroll Star (kW x 1000 / sqrt3 x UL x cos) IL = IP Not this old chestnut again If the machine is rated at 25kW the use the formula RnR posted, but this applies regardless of how the load is connected (star or delta). 25kW is 25kW And we still can't get it right.........assuming the "machine" is a motor: - Power (Watts) = 1.73 × Line Volts × Line Amps × PF × Efficiency Jaymack 04 December 2007 09:32 PM Ricicle Posts: 872 Joined: 23 October 2006 Yeah and don't forget efficiency if it's a motor ------------------------- Empty barrels make the most noise. 04 December 2007 09:38 PM DALEC Posts: 216 Joined: 04 November 2007 whoops.... 63 amp per phase .... ( no cos or efficiency ) ------------------------- master of puppets is pulling your strings--------------------------------------------http://www.elliselectricalservices.com 04 December 2007 10:16 PM BigEddie Posts: 22 Joined: 20 April 2007 Dalec ,you were right first time at 36A . Use line volts @ 400V (If 415v = 34.8A) All O.K if you want it exact with PF and efficiency. As a rough guide you can't go far wrong with the old multiply by four and divide by three. It gives you an idea if your maths are not too good. 25000W x 4 /3 = 33.33A. 04 December 2007 10:16 PM Ricicle Posts: 872 Joined: 23 October 2006 Originally posted by: DALEC whoops.... 63 amp per phase .... ( no cos or efficiency ) You were closer the first time (but still not right) ------------------------- Empty barrels make the most noise. 04 December 2007 10:25 PM rocknroll Posts: 9083 Joined: 03 October 2005 Not this old chestnut again Okay for the students lets elaborate on the OP idea. A 25kW machine with a power factor of 0.9 amd am efficiency of 85%. What is the phase current? regards ------------------------- "Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"------------------------- 04 December 2007 10:30 PM extrasockets Posts: 392 Joined: 14 May 2006 HP = AMPS X VOLTS X EFF X 1.73 X PF/746 KW = AMPS X VOLTS X 1.73 X PF/1OOO I think... to many tonight EDIT and after reading the op again. KW X 1000 / 1.73 X VOLTS X PF Edited: 04 December 2007 at 10:33 PM by extrasockets 05 December 2007 09:49 PM Ricicle Posts: 872 Joined: 23 October 2006 Sorry couldn't resist 47.36Amps (@ 400V) ------------------------- Empty barrels make the most noise.
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