What is the power ratio between power in Star and Delta circuit?

Editorial / Best Answer

KaranSorout  

  • Member Since Jul-2006 | Jul 13th, 2006


The power ratio between Star to Delta is 1:3

Explanation:

 

Lets suppose Vs be the supply voltage per phase.

So the line voltage of the supply will be 3Vs.

Now assume any type of load; for simplicity Im assuming it a only resistive load.

And let it be R per phase.

 

For Delta connected load:

 

Calculation for per phase power; PD= I2R

 

Where I load current (per phase)

And,

I = 3Vs/R       {as line voltage of the supply is directly applied to the phase of the delta load}

So,

            Pd = (3Vs/R )2R = 3Vs2/R  watts per phase.

For 3 phases:

            P3D = 3Pd = 3*3Vs2/R = 9Vs2/R watts.

 

Now for Star connected load:

 

PS = I2R = (Vs/R)2R = Vs2/R watts

For 3 phases: P3S = 3PS = 3 Vs2/R watts

 

Conclusion:

P3S / P3D  =  3Vs2/R / 9Vs2/R = 1/3

It may be better concluded by drowing figures. If any variations, can connect to me through karan.sorout@gmail.com  

Showing Answers 1 - 34 of 34 Answers

SASI KUMAR.A

  • Jul 6th, 2006
 

The Power Ratio between STAR and DELTA is  1:3

KaranSorout

  • Jul 13th, 2006
 

The power ratio between Star to Delta is 1:3

Explanation:

 

Let?s suppose Vs be the supply voltage per phase.

So the line voltage of the supply will be ?3Vs.

Now assume any type of load; for simplicity I?m assuming it a only resistive load.

And let it be ?R? per phase.

 

For Delta connected load:

 

Calculation for per phase power; PD= I2R

 

Where I ? load current (per phase)

And,

I = ?3Vs/R       {as line voltage of the supply is directly applied to the phase of the delta load}

So,

            Pd = (?3Vs/R )2R = 3Vs2/R  watts per phase.

For 3 phases:

            P3D = 3Pd = 3*3Vs2/R = 9Vs2/R watts.

 

Now for Star connected load:

 

PS = I2R = (Vs/R)2R = Vs2/R watts

For 3 phases: P3S = 3PS = 3 Vs2/R watts

 

Conclusion:

P3S / P3D  =  3Vs2/R / 9Vs2/R = 1/3

It may be better concluded by drowing figures. If any variations, can connect to me through karan.sorout@gmail.com  

sibani

  • Jul 31st, 2006
 

1:2

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andyarok

  • Apr 11th, 2008
 

Wow guys what happened? Never give wrong info guys. Total Power remains the same.

Irrespective of the type of  connection  Power  remains same.  Imagine  that  u loose  1/3  of the  power  for  every  Y-delta  T.F. Dont Joke pa.

If u need explanation then will reply


jeet29

  • Jul 6th, 2009
 

Power for a circuit will always be same despite of it is connected in star or delta ...because star or delta
are the only connection types which connect your equipments with the power
sources.  The only things which have a difference or the ratio is voltage
and current in star or delta connected system.

In Star,
line voltage=1.732*phase voltage
line current=phase current

For Delta,
line voltage=phase voltage
line current=1.732*phase current

GeeK_Percy

  • Oct 3rd, 2009
 

It is 1

Suppose v= line voltage applied
                             i=line current

For star connected resistances
      power= 3*(v/1.732)*i=1.732*v*i

For delta
    power=3*v*(i/1.732)=1.732*v*i


Both are same

saginala13

  • Jun 19th, 2010
 

WE KNOW THREE PHASE POWER P=ROOT3VICOSPI in any circuit, whether it is sta or delta.... and one we have to remeber is for an type of load current i or P.F indvidualy change but the product icos(pi) wil not change.

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the power in both the connections are equal  because

in star line currents=phase currents
           line voltages=1.732*phase voltages
so power(P)=3VI=1.732*vline*iline
in delta line voltages=phase voltages
             line currents=1.732*phase currents
so power(P)=3VI=1.732*vline*iline

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Mudigal Prakash

  • Aug 4th, 2011
 

Power remains same and is 1:1, only Line and Phase currents and Voltages change. Because Power = 3*Phase Voltage *Phase current* Power factor. For star connection : phase Voltage = Line voltage / root 3, Phase current = line current, whereas in Delta connection phase voltage = line voltage, phase current = line current/root 3.

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shruti

  • Nov 24th, 2014
 

power ratio remains the same irrespective of the connection.
if power ratio would change why would we use a star delta starter or a star delta or delta star transformer.
so guys, power ratio is 1 for star and delta circuits...

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AK ROUT

  • Mar 31st, 2015
 

1:3 .do not confuse with as in case of a transformer where power remains same.Here due to change in load configuration power changes.

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aditya kashyap

  • Apr 26th, 2015
 

There are 2 perspectives of seeing this problem

1.In case of a transformer, where the power going from primary side to secondary side is same. Therefore in its case power remains same.Note that transformer does not consume power, it just transforms it with a few losses.

2.If a star connected load(say of R in each phase) is connected across a  3 phase supply, Power=(√3)(V line)(I line) then I line=(V line÷((√3)(R))), hence P=(V line^2÷R)

Now when same load is connected as delta, P=(√3)(V line)(I line). Here I line=√3(V line÷R) hence power=3(V line^2÷R)=3P.Therefore power consumed in delta is 3times that in star.

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D.BASHEER AHMAD

  • Sep 5th, 2015
 

STAR CONNECTION
Vph=Vline/1.732
Iph=Iline
POWER =3*Vph*Iph*PF (OR) 1.732*Vline*Iline*PF
Line Current = Phase Current


DELTA CONNECTION
Vph=Vline
Iph=Iline/1.732
POWER =3*Vph*Iph*PF (OR) 1.732*Vline*Iline*PF
Line Voltage = Phase Voltage


We can connect in any way of the connection, the Power remains same. There is difference in Voltage and Current

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Girish R Pillai

  • Sep 6th, 2015
 

Sorry, This answer is wrong because the question is for the same load.

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Girish R Pillai

  • Oct 16th, 2015
 

Its 1:3 if the supply source and load are same. But the equation for power , P = √3. VL x IL x cos phi is the same, values changing.

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Aritra Rakshit

  • Mar 23rd, 2016
 

Load is not same. Because if you connect same impedance in star and again in delta. Equivalent impedance will change per line.

For Delta:
z=z1||(z2+z3)

For Star:
z=z1+z2

so, ultimately power ratio remains unity.

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Pankaj sawale

  • Jan 3rd, 2017
 

The explanation must be 9Vs^2/R/27Vs^2/R and then it become 1/3

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Anil Suwalka

  • May 30th, 2017
 

1:1

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Pragya

  • Jul 22nd, 2017
 

1:1

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sandeep kumar

  • Sep 15th, 2017
 

How much rating motor we use for star and delta connection?

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Anbumozhi R

  • Dec 3rd, 2017
 

Power is Same. Whether it is star to Delta conversion or Delta to star conversion. Power is 1:1

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RUP KAMAL KUTUM

  • Feb 2nd, 2018
 

Well first you assumed voltage per phase as Vs and Line voltage as sqrt(3) x Vs: Which is for star connection. Then, you assumed the same thing for Delta Connection(where line and phase voltages are the same) which is what went wrong here. Power consumed always remains the same irrespective of Star or Delta connection. There is a book I am reading that does the same mistake of 1st saying that Star and Delta load always consumes the same power then showing an example saying P-delta is 3 times P-star, which is wrong,

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