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pratyasha5
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Join Date: Jan 2009
Posts: 12

Full Load Current

02/03/2009 4:59 AM

how to calculate full load current for 500 kw motor if this load is fed from 33/6.9 transformer.?
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sb
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Join Date: Mar 2007
Posts: 2550
Good Answers: 103
#1

Re: full load calculation

02/03/2009 7:16 AM

Power= √3VI CosΦ

You know P, V, powerfactor, you have to calculate I

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Current Maarey
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Join Date: Aug 2008
Location: East
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#2
In reply to #1

Re: full load calculation

02/03/2009 8:20 AM

Your response is perfect for such a question. A GA from my side.

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hersona
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Join Date: Jul 2008
Posts: 3
#3

Re: Full Load Current

02/04/2009 1:53 AM

my question to you my friend is, what voltage(x) is being fed to the motor?

500kw / 6.9v = Full Load Amps or 72.463a

then make the adjustment for the power factor
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sb
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#4
In reply to #3

Re: Full Load Current

02/04/2009 3:02 AM

You are right, never mentioned it is a 3Φ motor, just assumed by the rating - but can be anything -

Any way doesn't really matters,your answer is correct but it is

500Kw/6.9Kv

Ks do matter (especially if they remove from my pay packet as it usually happens when they recover taxes in the end of year)

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pratyasha5
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#5

Re: Full Load Current

02/04/2009 3:31 AM

then can you tell me the value of breaker needed for this purpose?
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hersona
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Join Date: Jul 2008
Posts: 3
#6
In reply to #5

Re: Full Load Current

02/04/2009 11:58 AM

Well my friend thank god for this web site! If im correct this motor is connected to a motor starter right. Then your overload protection will be 90A my friend, and the circuit breaker will be 110A CB.

I need work!!! LOL!
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sb
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#7
In reply to #6

Re: Full Load Current

02/04/2009 12:24 PM

just a bit correction, 500KW motor is likely to be 3Φ and then the currents change

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pratyasha5
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Posts: 12
#8
In reply to #7

Re: Full Load Current

02/05/2009 3:59 AM

Full load as told by my friend is 72.3 Amps. So the overload protection must be less or equal to 72.3 Amps.

It must be 70 % of the total full load current.????
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sb
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#9
In reply to #8

Re: Full Load Current

02/05/2009 5:05 AM

So that the motor trips as soon as it starts ?

It is clear that unfortunately so, you are getting your homework done by us.

Please go back and study back the basics of fault protection systems and do your work yourself.

Please as yould be engineers do not get your basics from the net. Get clarifications certainly, that also when you have some serious doubts.

As on now what ever you and your classmate ( a guess) have written are part of pre-final engineering syllabus if not earlier.

I could give you the solution but I don't feel I should. After the previous post - you have confirmed, despite several posts, that it is a single phase 500KW Motor.

This total thread smells of a collapsing projectwork

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pratyasha5
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Posts: 12
#10
In reply to #9

Re: Full Load Current

02/05/2009 7:38 AM

no its not project work. Its a small qu`estion in my mind. But thanks 4 all the assistance
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#12
In reply to #8

Re: Full Load Current

02/06/2009 6:15 PM

your wrong>
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sb
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Posts: 2550
Good Answers: 103
#11

Re: Full Load Current

02/05/2009 8:03 AM

Assuming you are right, and not one of the subject, the overload setting of the Motor is between 115 to 125% of the rated current. This (115 or 125) depends upon the duty factor etc

You can google it and a few sites that are quite useful are

www.mikeholt.com/mojonewsarchive/EC-HTML/HTML/Motor_Calculations_-_Part_1~20030303.htm

or you can refer to NFPA

www.nfpa.org/assets/files//PDF/necdigest/CodeIssues071305.pdf

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