3 phase motor power consuption formula

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Anonymous Poster	3 phase motor power consuption formula 08/08/2008 6:32 AM
	what is the formula to calculate load of three phase motor if I have reading of amp. per phase.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#1 Re: 3 phase motor power consuption formula 08/08/2008 8:33 AM
	The electrical load is the product of the current, the voltage and the power factor. The mechanical load is the product of the torque and the angular velocity. The ratio of these two is the efficiency. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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Jeff Millar Member Join Date: Aug 2008 Posts: 6	#4 In reply to #1 Re: 3 phase motor power consuption formula 08/11/2008 11:45 PM
	Good answer. Can you clarify the following please : LV Motor, rated at 7.5 KW, 415 V, 3 ph, 50 Hz. Shaft KW = 7.5 KW ? Load factor given as : 75 % ( 0.75 ) Given pf = 0.73 Eff. =0.85 What is the Continuous rated load ? How to calculate the Absorbed power of this Continuous rated load ? I think : Motor Shaft kw = Motor rated kw. Absorbed Power ( kw ) = Rated load x Load factor/ efficiency Equals 7.5 x 0.75 / 0.85 = 6.61 kw rated continuous load. Is this the correct Load Study procedure using the IEC ? or what should the following be : Continuous rated load KW = LOAD FACTOR = Absorbed power / Rated load ? ( I think not ) Thank you
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V.I.Abraham Guru Join Date: May 2007 Location: Pune , India Posts: 875 Good Answers: 42	#2 Re: 3 phase motor power consuption formula 08/08/2008 9:14 AM
	Hi Guest, In addition to per phase amp , you must also know the operating voltage of the motor and weather the motor is star/ delta connected and power factor to calculate the electrical power consumed by the motor . It is not necessary that all the power consumed is transferred to useful load (by load if you meant by that). For calculating the useful power you must know the inefficiency of the mechanical systems.
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martin-electrical Associate Join Date: Jul 2007 Posts: 41	#3 Re: 3 phase motor power consuption formula 08/10/2008 1:56 PM
	Lets see : Assume you know the Horsepower Example 5 HP 1HP =746W 5HP=3745W Assuming Y connection 208v W=3(IxI R) 3745 dived by 3= (42x42)R 1248/ 1764=Resistance , and W=SqRoot of3xExIx cosO w already known, E known, I known . plugging in numbers 1.732 x 208 x 42 x cosO= 3745 have fun
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Fangas Participant Join Date: Sep 2008 Posts: 2	#5 Re: 3 phase motor power consuption formula 09/18/2008 4:26 PM
	I X E X 1.73 = VA (Apparent Power) kVA X Power Factor = W (Real Power) W / 746 = Hp Be aware. P.F. will change depending upon the load. Nameplate P.F. is a full load value. And both the Watt & Horsepower values will not be real shaft output values. Various losses within the motor will not be reflected
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