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Topic Title: Load schedule for a delta connected motor
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Created On: 28 March 2013 09:25 PM
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 28 March 2013 09:25 PM
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MAXMIRA

Posts: 78
Joined: 25 January 2011

Hi all,
Can anyone help me I have been given a load schedule for a 35kw delta connected motor. The load schedule shows the 35kw spread across the three phases I.e. 11.66kw per phase. I think this is incorrect as I would put it as 35kw per phase. Can anyone tell me which is the correct method and possibly back it up with some maths. Your help would be much appreciated.
Maxmira
 28 March 2013 09:29 PM
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slittle

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I'd take it as 35 kw spread across the phases.

It's been too longer week to do the maths for me, I'll let someone else have a crack at it.


Stu
 28 March 2013 10:07 PM
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chunk522

Posts: 126
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It wouldnt be 35kw per phase, As Stu said you spread it across the 3 phase If memory serves me the calc is
Power / sqr3 x v x PF
Its a big motor though that is are you sure its not 3.5kw
 28 March 2013 10:40 PM
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slittle

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I've got 40kw floating pumps, it's not that big but it wouldn't start dol


Stu
 28 March 2013 10:54 PM
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chunk522

Posts: 126
Joined: 12 December 2010

Originally posted by: slittle

I've got 40kw floating pumps, it's not that big but it wouldn't start dol





Stu


LOL agreed
 29 March 2013 08:28 AM
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Jaymack

Posts: 4639
Joined: 07 April 2004

Originally posted by: chunk522
Originally posted by: slittle
I've got 40kw floating pumps, it's not that big but it wouldn't start dol [IMG][/IMG]
Stu

LOL agreed

Check with the supplier if you can't assess this yourself. A 40kW DOL motor is not a lot at 400V, but it depends on the capacity and protection of the supply to start such a motor, whilst maintaining an adequate starting torque and without an excessive voltage drop on the particular motor ...... and the whole installation. A maximum of 160 to 200kW DOL, is common in industry before using a higher voltage; but then they're usually designed for a stiffer supply.

Regards
 29 March 2013 08:48 AM
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Jaymack

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Originally posted by: MAXMIRA
Can anyone tell me which is the correct method and possibly back it up with some maths.

The motor input power = 1.73 × Volts (Line) × Amps (Line) × P.F.
The motor output power is the nameplate power = ditto ................ × Efficiency.

Regards
 29 March 2013 04:44 PM
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slittle

Posts: 3515
Joined: 22 November 2007

Originally posted by: Jaymack

Originally posted by: chunk522

Originally posted by: slittle

I've got 40kw floating pumps, it's not that big but it wouldn't start dol [IMG][/IMG]

Stu


LOL agreed


Check with the supplier if you can't assess this yourself. A 40kW DOL motor is not a lot at 400V, but it depends on the capacity and protection of the supply to start such a motor, whilst maintaining an adequate starting torque and without an excessive voltage drop on the particular motor ...... and the whole installation. A maximum of 160 to 200kW DOL, is common in industry before using a higher voltage; but then they're usually designed for a stiffer supply.



Regards


Perhaps I should have added "on a 100 amp supply, 600 metres from the cutout it doesn't want to start DOL".... We've got several star delta and three new ones on softstarts


Stu
 29 March 2013 10:57 PM
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Vidas

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