Permanent connection of motors in star configuration!

[ConfusednClueless]

Could somebody please help?

In the current climate of energy saving I have been asked why we do not permanently connect our motors in star instead of star/delta?

For the life of me I cannot figure out why we would ever want to but can't seem to put it into words well enough for the people asking the question. Can anybody provide a good explaination as to why this would / wouldn't be a good idea please?

We're talking about 3 phase (415V) 50Hz induction motors ranging in size from 0.75kW up to 90kW and numerous different applications including DOL, Star-delta, soft start and VSD.

Thanks

 

[rbulsara]

Have them expalin to you why or how connecting them in star would save energy? The you will think about it.

 

[ozmosis]

If all your motors on your site are all running with loads <33%, then it might be feasible but I guess not. If this were the case then the question would not be 'can we re-connect in star?' but 'can we switch them off?'.
It's a question rather like "let's switch all the lights off and save energy" only to realise you can't see anything.
As rbulsara says, think about it.

 

[jraef]

Sounds as though someone fell for the same trap as those who buy "energy savers" capacitor systems for motors. They think that if the current goes down, they save energy.

ConfusednClueless,
In case you are not following what the others have said, here is what we mean. They (those asking the question) are not thinking about the work being performed by the motor. In Star, not only will the current go down to 33% of normal but the torque as well, meaning the motors will be capable of performing less work. If the load doesn't change and it required more than 33% torque to do the work required (highly probably), then the motors will stall. So the work will not be performed at all. Where is the energy savings in that? If that is the goal, then just turn them off!

If on the other hand, the loads ARE only requiring less than 33% torque (however doubtful this is), you have a different situation. Why are they running at all, or why not just cycle them on and off under more loaded conditions, or why not use smaller motors, or why not invest in Variable Frequency Drives? In other words, if the motors can operate with that much less torque, someone has done a very poor job of engineering your system and just connecting the motors in Star is not going to help you much.

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[rbulsara]

The motor will consume power as it is necessary to drive the load. A 40kW of load is a 40kW of load, it does not matter how the motor is connceted. Get the hint?

In fact changing winding configurations of existing motors presents many other issues which not only not save any energy, but will cause you other grief.

Changing starting methods also do not save you energy.

Only way to save power is to reduce the load. Someways of reducing the load are more efficient than others, but that is a different subject.

 

[petronila]

Dear All,

All you sayd is true. But I think the ConfusednClueless question may have another significance,For some "electricians" the right motor connection is not the rated, is thouse drain less no load current, if we have an electric motor rated delta connection and is delta connected at rated voltage will drain the right no load current. But if this motor is connected in Wye will drain less, This situation could make believe the motor will run with less current and can be associated with more efficiency, maybe ConfusednClueless was talking with some of this "electricians". In some cases the wrong connecteed Motor is oversized or the load is very light and the motor can runs in Wye with out burn inmediatelly.

Regards

Petronila

 

[aolalde]

Electric motors must be connected per the nameplate's motor manufacturer instructions. A wye start-delta run motor will be burnout by stalling if it is left wye connected with full load.