Star, Y, delta, D, differences

[Biering]

I have a 1.1kW motor, 400V Star, Y, connection. I need more torque but I don’t have room for a bigger motor, so I was told that I could wire it in Delta, D, instead. But my question is, what consequences’ will this have? How much more power and torque will I get? And what will it “cost” in current? I only have 400V. What about the pull out torque, where will the maximum be? For instance in Y connection the maximum torque is at 0.6*1500rpm. Will this point also go up?
Thanks for your help!

 

[sslobodan]

Your motor will get 3 times more power but you should know can he withstand sqrt(3) larger voltage. In Europe its 230/400V and if you turn the motor that cant withstand 400V you will get pile of metal that is smoking, and will have to find new motor 400V - smaller in space. So my guess is that you need to find appropriate motor for you that is going in delta connection.

P.S. Delta to star (other way around) can be done without problem considering that U and I are sqrt(3) smaller

 

[Skogsgurra]

As Slobodan said. You can not do that. The iron will saturate and protection will trip. And, if you insist and bypasses protection, the motor will be destroyed.

There is a very real possibility to get more torque out of the motor, though. By using a frequency inverter, it is possible to run the motor close to its peak torque - at least for short times. So, if your problem is that the motor cannot start the load and 50 - 80 % more torque can do it, then a VFD is the answer. It has many other benefits as well. And units in that size are very economic, too.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[jraef]

Emphasis on the short time however. You cannot get more torque out of a motor continuously without overloading it. Torque is directly related to current, current is directly related to overload.

And whomever it was who suggested connecting the motor in Delta was a fool. Think about it, what he is telling you to do is to connect 400V to a 240V motor.

 

[waross]

Is it possible to change the gear ratio of your drive?
If you are able to change the gearing, then you may use a combination of a delta connection and a VFD to solve your problem.
First the gearing is changed to give you the required torque.
Then the connections are changed to delta to lower the voltage requirements of the motor.
Now the VFD may be used to increase the frequency and speed of the motor.
At the new, higher frequency, the motor will safely run on a higher voltage.
The key to this technique is maintaining the same or lower Volts per Hertz ratio to the motor windings.
If changing drive ratios is feasible, there are several gurus here who will talk you through the set up.
The optimum ratio change to match up with a star to delta conversion will be root 3. (1.73) Change at least 1.5:1 but not more than 2:1 for optimum.
Any change of less than 1.73:1 that gives you the required torque on the final drive is usable.
respectfully

 

[sreid]

Check the frame size of your motor. You may be able to find a higher HP motor in the same frame size.

 

[Biering]

Thank you very much for your comments.
I’m sorry that I didn’t mention it from the start, but I am going to use a frequency converter. You all talk about a sqr(3) ratio, will the “new” nominal speed for the motor then be 1.73*1500 rpm? Which equals around 87 Hz, and should the u/f ratio then be 400V/87Hz = 4,6?
If this is the case, will I then get 1.73 more power, and keep nominal torque up to 87Hz?
Christian

 

[Skogsgurra]

Yes. Why didn't you say so from the beginning?

Makes this thread more or less meaningless. I told you about frequency inverters in my post. But no reaction from your side. I do not like that.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Biering]

As I said I'm sorry. I am new here, so I didn’t know that the response time was so quick.

 

[sreid]

Can your motor actually be re-connected for delta? This is a little unusual in a 1.1 kW motor.

 

[aolalde]

As almost everybody stated above you can not increase the voltage 1.73 times which is equivalent to reconnect the motor in delta and apply 400 Volts. It probably last a few minutes.

However the variable frequency driver could increase the accelerating torque from 60% to 100% and only with full load current and probably you can "boost" it 10 or 15% more, but only during the starting process, all that with no change in the motor connection, that means connect the motor as the nameplate states for the operating voltage and frequency.The driver must be set properly.

After the motor has started and now it is under continuous load, you must keep the Volts/Hertz design ratio up to the nominal or nameplate frequency and with constant HP above the nameplate data frequency ( constant HP) but limited by the centrifugal forces on the rotor and bearings.

If the motor is not constructed for VFD Duty, you could have short term problems with bearing currents and premature insulation failures.

I assume the motor is designed for 400 Volts, 50 Hertz then ramp the motor not to exceed 115% of full load current and then keep the ratio V/HZ close to 8. For the small size of your motor 150% overspeed will probably be reached without problem but be aware of cast metal motor cooling fans.

 

[ozmosis]

Unless I'm misunderstanding this then I feel there is a certain misunderstanding been created in this thread.
Biering has already apologised for not providing all the facts originally so we won't dwell on that.
The classic use of a motor and VFD at 87Hz to achieve 'more torque from a lower rated power motor' is really only possible when used in combination with a gearbox. By connecting the motor in Y setting the base voltage and frequency of the VFD as 400V/87Hz, then this will provide a constant magnetic flux (contstant torque) to 87Hz. Speeding the motor up to this and maintaining the torque rating provides a higher gear ratio to achieve the same rated final output speed but with a higher torque output.
This is a typical 'trick' used by a lot of motor gearbox companies to be competitive. A lot of Italian companies seem to offer this.
Expecting more torque from either the motor or VFD will only lead to problems.