Star and Delta Connection Difference in Motors

Try it and see. If the motors stalls and/or burns up, then untry it. Your numbers are wrong, and any possible power savings will be small. (In star, it will be vP and iP rather than vL and iL.

please go through this and expecting ur reply

Good to Know: Where Cos Φ = Power factor = the phase angle between Phase Voltage and Phase Current and not between Line current and line voltage.We know that the values of Phase Current and Phase Voltage in Star Connection;I_L = I_PHV_PH = V_L /√3 ….. (From V_L = √3 V_PH)
Putting these values in power eq……. (1)
P = 3 x (V_L/√3) x I_L x CosФ …….…. (V_PH = V_L /√3)
P = √3 x√3 x (V_L/√3) x I_L x CosФ ….… {3 = √3x√3}
P = √3 x V_L x I_L x CosФHence proved;Power in Star Connection,P = 3 x V_{PH x} I_PH x CosФ orP = √3 x V_L x I_L x CosФ

The word <...ur...> has no meaning in the English language.

The Star/Delta starter is probably the most commonly used reduced voltage starter, but in a large number of applications, the performance achieved is less than ideal, and in some cases, the damage and interference is much worse than that caused by a Direct On Line starter.

The Star/Delta starter requires a six terminal motor that is delta connected at the supply voltage. The Star Delta starter employs three contactors to initially start the motor in a star connection, then after a period of time, to reconnect the motor to the supply in a delta connection.

While in the star connection, the voltage across each winding is reduced by a factor of (1 /.'/'3) [1 divided by root three].

This results in a start-current reduction to (1 /.'/'3) [1 divided by root three] of the DOL start current and a start torque reduction to one third of the DOL start torque.

If there is insufficient torque available while connected in star, the motor can only accelerate to a partial speed compared to the full speed it would reach if connected in delta. When the timer operates (set normally from 5-10 seconds), the motor is disconnected from the supply and then reconnected in delta, resulting in full line voltage running currents and torque.

The transition from star connection to delta connection requires that the current flow through the motor is interrupted. This is termed "Open Transition Switching" and with an induction motor operating at a partial speed compared to full load speed, there is a large current and torque transient produced at the poi, unless proper protection methods are used, can cause severe damage to the supply service's infrastructire and to other connected equipment.

If there is insufficient torque produced by the motor when running in star, there is no way to accelerate the load to full speed without switching to delta and causing those severe current and torque transients.

These must be allowed-for in the design of the motor and its starting system if they are to have an economic useful life. Update: Electronic motor-control systems, which offer soft-starts in DELTA configuration, are now replacing the use of manual or semi-automatic star-delta starters.

Technical explanation

When the windings of a 3-phase motor are connected in STAR: the voltage applied to each winding is reduced to only (1 /.'/'3) [1 divided by root three] of the voltage applied to the winding when it is connected directly across two incoming power service lines in DELTA. the current per winding is reduced to only (1 /.'/'3) [1 divided by root three] of the normal running current taken when it is connected in DELTA. so, because of the Power Law V [in volts] x I [in amps] = P [in watts], the total output power when the motor is connected in STAR is: PS = [VL x (1/.'/'3)] x [ID x (1/.'/'3)] = PD x (1/3) [one third of the power in DELTA] where: VL is the line-to-line voltage of the incoming 3-phase power service ID is the line current drawn in DELTA PS is the total power the motor can produce when running in STAR PD is the total power it can produce when running in DELTA.

a further disadvantage when the motor is connected in STAR is that its total output torque is only 1/3 of the total torque it can produce when running in DELTA.

taken from answers.com

Dear brich,

Thanks for your valuable time spent, briefly

1) the power consumption will be same irrespective of whether it is connected in star or delta.

2) since the flux will be reduced by applying rt3 times reduced voltage in the windings, hence the torque also. as result we cant save energy by running the motor in star, because it will not cause any change in power consumption. only the torque will be reduced.

pls. correct me if im wrong

thanks

I'm not sure why you are asking, you seem to know all the answers!

I don't think AP#1 is asking about star-delta starting. I think he means connecting and running a motor in star or delta. Perhaps he will confirm.

I think you are right.

He appears to have convinced himself that with the same mechanical load, running at the same speed, on the same motor, that he will save power running in Star!!!

But I could be wrong.

So do not please ask me why? I haven't a clue myself how he thinks that.....

Dear Anonymous Poster,

Here is a copy of a post of mine that I made over in Electriciantalk.com. I include it here for your edification :

Testing out a new switchboard setup today, this for an irrigation project that I have been working on. 8 x pumps, each driven via VSDs from the PLC that I am doing the coding for.
I had, with help from one of our electricians, set up 3 VSDs wired up to the PLC inputs and outputs, with socket outlets wired to the VSD outputs to connect some motors. Electrician had wired up cords/plugs to some suitable small motors that had been hiding under a workbench in the workshop. I carefully entered a pile of settings into the drives to match the motors and the controls that we are using. No problem.
On starting two of the motors, they seemed to spin up OK. So back into the office to look back into the PLC and see if the speed feedback from the drives was coming through. Looking good, when I noticed the unmistakeable smell of kentucky fried motor windings wafting back into the office...oh darn.
Turns out that the one thing I hadn't checked (thought the electrician had done this) was that the motors, 400V star/240V delta types, were in fact wired for star. Not so, both were connected in delta and both are well fried by the 400V that I was feeding them. Fortunately, they were both of near-zero value. It would have been a different story if I had done this to a $60K pump motor I am sure. Lesson learned.

Can I have the address of the near 0 value motor supplier please? Is the VLD of the same value?

Now that the motors are gone they will not need the VLD's. So chances are they are near 0 value for now!

A near-zero value motor is one which is well past its use-by date but which is nevertheless still lying around under one of the benches in the workshop. If you do much motor work you would probably have the odd one lying around your own workshop. They still go, but you wouldn't want to inflict them on a customer and are really only good for testing and the like.

The motors that I fried went out with the scrap metal last week, but I attach a photo of another near-zero value motor. Can you spot its obvious problem? And no, I did not inflict this on it!

Considered that the discoloration could be dust, I think it is not burnt. (unless you forgot to scrap it too)

The picture can have some optical deviations but my 2 cents are a bent shaft or a missing base.

It isn't burnt, this one is being used in testing.

The picture is taken from above, the base is underneath.

Looks like a slightly bent shaft to me!

WOW!!

I have luckily never seen such damage.......did a building fall on it?

I must admit I don't know at this point.

I will ask the gents who loaned it to us when I next see them.

The shaft is wilted, for one thing.

I think that motor is somewhere around 55 years old or more, and that sort of thing is to be expected.

They sell little blue pills for that now however. God bless the chemists...

Just curious, Was your overload protection on the VSD set correctly. If you had multiple motors per VSD, each should have its own protection.

Just one motor per VSD, and most of the protections deactivated. Hardly seemed worth the trouble, the motors were all just spinning unloaded and if Bigears (me) had kept his wits about him, they would still be spinning.

You can check that easily:

needed is on Ampere (clamp) meter and a pressure meter and velocity or air volume

1. connect in delta

2. connect in star

difference in current can be used to calculate your power savings (in money from the pocket)

difference in air volume gives you the air losses

efficiency can be calculated by comparation. A VFD can be of help to you.

Just what do you expect? If you save the power in continuous operation you most likely do less work. If you need torque you will have to provide it.

So far I know and I am not an electrician Star Delta is used for start up operations. But you are talking continuous operation. Make sure your motor curve and your load match in the sweet spot. Run it in Delta.

Remove 50% of the blades from your 2.5kw exhaust fan. You will then have 50% of the original load on your motor.

The motor outputs whatever power the fan needs, even if that is less than the motor rated power. The electric power input is also lower. The could be a slight loss of efficiency as the motor is working at less than design, but it's not worth worrying about.

You should connect the motor (star or delta) the way it says on the nameplate. Motors usually have a tolerance on voltage +/- 10%. The speed does not change appreciably within that voltage range, so the fan power is constant, and the amps varies inversely with supply volts.

If your motor is (say) 230 volt Δ, 400 volt star, you might think from the above that if you connect it in Δ to 400 volt, the current, compared with 230 volt Δ, would be down by 1/√3, but that is way outside the voltage tolerance and the motor would not like it, though if the actual power is well below rated it might last a while. But it would be a waste of time anyway because it's the power hence cost that you want to minimise, not the current.

Spam sucks.

So do spammers.

Reported.

The idea of star-delta starting is to limit the inrush current. Motors thus started will spin up gently and then accelerate to full speed after the timed delay.

I use a small 20 HP circular saw and without S-D starting it jerks, the whole bench vibrates, and its nasty and noisy. With S-D starting, its completely smooth.

Having said that, S-D is more complicated to implement. Its really necessary when you have a machine with significant load or friction on start-up. Our saw has a lot of inertia, and so connecting directly to Delta allows the full line Voltage across the coils with NO back EMF to limit the inrush. That is the point. If you want your system to last, and you have any significant starting load or mass to rotate up to speed, choose S-D.

But unless I'm mistaken and he comes back to say so, AP#1 isn't asking about motor starting.

The power consumption is a function of the LOAD's torque-speed characteristic curve, which cannot be seen from here.

While reading your signature, it struck me that maybe you don't know the "Lumberjack Song" from Monty Python team? If not, here is a link:-

LumberJack Song - Monty Python

GA

You got that pretty much backward.