Star delta winding selection for motors 1

[arbil]

What is the basis for selection of star/delta winding for motors ? If we chage the connection of an existing star motor to delta or vice versa , what will be the impact ?

 

[EddyWirbelstrom]

If each end of the motor phase windings are brought out, then the windings can be connected in star during start and when the motor has accelerated it can be quickly switched to delta.

Advantages
Star connected motor phase voltage is 1 / ?3 of supply voltage, therefore motor phase starting current is 1 / ?3 times that when connected delta. The motor line starting current is therefore 1/3 times that when connected delta.

Disadvantages
Star connected motor starting torque is 1/3 that of delta connected motor.

 

[jraef]

That is only true for single voltage Star-Delta wound motors.

In dual voltage IEC motors, the Star windings are generally for connection to the higher voltage, the Delta windings are for connection to a lower voltage, specifically a voltage that is lower by a factor of 1.732 (?3). So for instance, 380 / 220V or 415 / 240V. Of this type, there are two sub-groups: dual voltage only, and dual voltage Star-Delta start, which has 12 leads.

Neither version intended to be operated in any other manner. Some people make claims that connecting them in the opposite pattern will save energy, but while technically true, they leave out the fact that doing so can have serious ramifications regarding the motor and load profile, most of which will lead to the early demise of the motor.






"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Most smaller size NEMA motors are wye. I am not sure about the larger sizes. 9 lead NEMA motors have internal connections that are nor easily changed. If it is a delta motor it must stay a delta motor, and a wye motor must stay a wye motor. A 12 lead motor may be changed between wye and delta but there are voltage, torque and utilization efficiency issues.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[loganath4880]

Normally large capacity motors will have star winding to have a differential protcection for its windings to minimize the effect of fault.

Mr,Mnewman already explained that delta conneted winding of same motor will produce more torque than star connected winding. A six lead motor can be connected in either way, subject to aqueuate cooling options done by the manufacturer

 

[waross]

A six lead motor can be connected in either way, subject to aqueuate cooling options done by the manufacturer

If a six lead motor rated 240/415 volts is connected delta at 415 volts, the iron will saturate and no amount of "cooling options" will be adequate to remove the excess heat before the motor fails due to burn out.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Marke]

Although many motors in Europe can be wired in delta or in star, there is only one correct connection for a given voltage.
If the motor is designed to be connected in delta at line voltage, connection in star at that line voltage considerably reduces the effective rating of that motor.(Down to 1 third rating)
If the motor is designed to be connected in star at line voltage, connection in delta at line voltage will overflux the iron and the motor will fail.

Best regards,

Mark Empson
L M Photonics Ltd

 

[waross]

Hello Mark. It's always a pleasure to see you dropping in.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[arbil]

Thanks Marke , that was exactly what I wanted to know ,i.e. if the motor is designed to operate at delta , and we change the connection to star (and vice versa), how will the motor behave .
As per your post , we can rule out the possibility of changing star designed motor to delta.But we can change a delta designed motor to star connection ,with reduced output.

 

[1000V]

Hi, found this thread through the search option. Wondering if I could tag a quesion on. We run a large agitator (for pulping paper) off a 132kW motor. We start the motor with a soft start unit. Sometimes, when the paper is too thick the soft start will not allow the motor to start as the current is too high. This will lead to a whole day of draining the pulper out, washing through with a fire hose etc etc.
I was wondering, at a time like this when the operator has made the pulper too thick if we could rewire the motor in Star? It is delta connected at 420V feed. Would this at least get the motor turning so more water can be added and maybe pumped out. The pump inlet is behind and extraction plate and will not pump unless the Agitator is running.

Will rewiring the motor cause damage. This probably seems like a stupid question to most coming from an elect tech.

Thanks for your time.

 

[Lectron]

Hi Folks Hey 1000V has your company considered WYE START AND DELTA RUN

 

[ScottyUK]

If the soft start can not get the motor running then it is unlikely that starting the motor in star will bring any benefit, but you will get all the downsides of a star-delta arrangement.

A variable speed drive would allow you to develop full torque from standstill but will be fairly pricey at that size, in the order of £6k or so for the bare drive.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[Marke]

Hi 1000V

If you wire the motor in star, you will get one third of the full voltage torque out of the motor. This is probably less than the torque being developed by the motor with the soft starter unless the start current is very restricted.

Can you give an indication of the type of soft start profile being used (i.e. current limit, voltage ramp etc) and what the maximum current that the soft starter is allowing is. This will give us a better idea what is actually happening and then perhaps we can help from there.

ScottyUK

A variable speed drive would allow you to develop full torque from standstill

Not necessarily true. Many VFDs struggle to produce full torque at zero shaft speed due to insufficient flux in the iron.
Closed loop vector will do this and the DTC drives will also do this, but most sensorless vector drives only reach full torque etc at frequencies between 3Hz and 10Hz depending on the design. A bigger drive does not help.

Best regards,

Mark Empson
L M Photonics Ltd

 

[Lectron]

I was wondering 1000v if you can do full across the line starting (as a bypass around your existing controller) using a standard motor starter and a jog button

 

[ScottyUK]

Hi Marke,

Laziness on my part for not being more specific; yes, I agree with you.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[1000V]

Hi, thanks for your replies. I realise it is a silly question so thanks for being so good. Apparently the soft start was installed to prevent tripping of the package sub because the peak inrush is huge. Since it appears that the package Sub ACB feeds critical plant they decided on the soft start. It would probably be better to look at distribution alternatives and diversity in order to start the motor DOL. Maybe look at a smaller pulley on the motor shaft. Would anyone agree?

It's hard suggesting that there maybe a better way than their recent 10k project!

P.S The softstart is an ABB type. I noticed whilst quickly scanning through the parameters that their is a kick start option and an initial start voltage. Is anyone familiar with these?