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Commentator

Join Date: Sep 2008
Location: India
Posts: 91

# Power saving in star connection

11/29/2008 10:57 AM

Dear friends,

How power is saved if we make motor connection from delta to star? One 400V,18.5 kw, 36 A,delta connected motor was taking 16 amps at load. After connecting in star it takes only 9 amps at the same load and working normal.

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Guru

Join Date: Sep 2006
Location: California, USA, where the Godless live next door to God.
Posts: 4666
#1

### Re: Power saving in star connection

11/30/2008 12:02 AM

See my response to your other post.

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Power-User

Join Date: Apr 2006
Location: Bangalore India
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#2

### Re: Power saving in star connection

12/01/2008 12:35 AM

here is an answer by nimmi on answers.com (in the year 2007) to your quistion I am just reproducing it for you.

If we change the connection from delta to star then power consumption will come down.
Because the rpm will come down by 8 to 10 due to low voltage.
Conversion icreases the slip.
we know the power is directly propotional to cube of the flow.
P1/P2= cube of(N1/N2) = cube of (Q1/Q2)
so flow will come down,thus rpm will come down so the power will come down.
So the motor is derated by 1/under root of 3
so phase current becomes equal to line amps, hence the power factor is improved by this conversion.
But mind it Sir! there are chances of burning of motor if the load on the motor is increased beyond 55 to 58%.
We changed it in few of our motors, first we identified the motors which were running at less than 50% load, & the conversion was done only in the motors running at less than 50% load to avoid the risk of burning of motors.

crm

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Commentator

Join Date: Sep 2008
Location: India
Posts: 91
#3
In reply to #2

### Re: Power saving in star connection

12/02/2008 9:16 AM

Dear crm,

The motor winding would burn out if current flow increases beyond the rated FLC current.

For example, one 18.5 kw motor was consuming 50% of rated power in delta. After connecting it in star it consumed only 30% of rated power. But for the real rated power in star (i.e. rated power in delta/1.732), it is 50%.

If the power consumption in delta is more than 58% (for example 65%) it would be going to reduce in star and the current flow through each winding would not be higher than the rated current. So it would not affect the winding

there are chances of burning of motor if the load on the motor is increased beyond 55 to 58%.

So above lines are correct or not?

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