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VSD with Star Delta Starting

02/19/2021 4:25 PM

Hi, I have just got in for repair a 15kW Ribbon Blender

We have to modify the electrical system from 220v 3 Phase To 400v 3 Phase.

When I was dismantling the existing control system, I noticed that it had a Star Delta Contactors wired between the VSD Output and the motor. I can't see why this would be necessary when using a VSD.

Any Ideas why it would be wired this way?

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#1

Re: VSD with Star Delta Starting

02/19/2021 7:04 PM
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#2
In reply to #1

Re: VSD with Star Delta Starting

02/19/2021 8:15 PM

Hi Solar Eagle, I am thinking that what may have happened is that it was originally fitted with Star / Delta Starter and then at some later stage the Vsd was fitted for Speed Control. We are fitting a Delta MS300 Vsd and these Vsd's have a feature where you can program in Star / Delta using Par 05-23 and 05-24 but I am not going to use this feature, I believe that the motor should run without the Star Delta Feature.

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#3
In reply to #2

Re: VSD with Star Delta Starting

02/19/2021 9:29 PM

I would agree, but I would check with the machine operator to see if there is some reason for this, perhaps there's some purpose that I am unaware of...in any case with the equipment you are installing having the option available, they can always adapt it if necessary...I always like to get any history that I can on the equipment and failure characteristics if possible...but that is not always possible, so you just go with what you know...sticking to best practices...

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#4
In reply to #3

Re: VSD with Star Delta Starting

02/19/2021 11:23 PM

Hi Solar Eagle, the machine was imported from the US, so we don't have any Operator Experience!

But just to give an example of electrical designers inexperience. I had a problem with a mobile vsd control, it was only 1.5kW but it weighed over 40Kg! I took the unit back to the workshop for repair for further investigation.

It was a 230v single-phase unit, but the designers had fitted 3 line transformers to boost the Vsd output voltage to 400v. The design had to have been done by a very inexperienced designer it was a very expensive and heavy unit. Someone did not understand that motors of that size can operate on 230-400 depending on the wiring configuration!

I removed the transformers and then back on site I changed the motor connection to delta for a 230v operation. It worked fine.

I think some people haven't gained the experience that we have and still look at the old ways we used to do things and this is why they have implemented the star/delta design

Thanks for your Feedback Solar Eagle you are Flying High!

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#5

Re: VSD with Star Delta Starting

02/20/2021 2:35 AM

Are you sure it is a S-D starter, or is it a Dahlander (2 speed 1 winding consequent pole) motor? The starter looks the same. They might do this is they want full speed adjustment capability within the two separate base motor speeds.

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#6
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Re: VSD with Star Delta Starting

02/20/2021 10:32 AM

...."Dahlander motors have advantages compared to other speed control systems like variable frequency drives, as there is less power loss. This is because most of the power is used to drive the motor and no electrical pulse switching is done. The system is much simpler and easier to use compared to other speed control methods available. However, the Dahlander motor has the disadvantage of fast mechanical wear and tear due to changing speeds in such a drastic ratio; this type of connection also produces high harmonic distortion during the shifting of poles as the angular distance between the power generated increases as the poles are decreased in the motor.[9] "...

Dahlander motor wiring for low speed (delta connection) and high speed (double star connection)

https://en.wikipedia.org/wiki/Dahlander_pole_changing_motor

http://www.gohz.com/how-to-install-motor-dahlander-on-vfd

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#7
In reply to #5

Re: VSD with Star Delta Starting

02/20/2021 12:12 PM

Thanks! I definitely learned something new today! I was not aware of the Dahlander motor.

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#8
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Re: VSD with Star Delta Starting

02/20/2021 3:54 PM

..."A "Dahlander" motor is the IEC term for what we call a 2 speed 1 winding motor.

There are 3 types of 2S1W motor designs, so what you do in hooking up a VFD is going to depend on which type you have and what you need from the machine.

2S1W Variable Torque motors will list two different HP values on the nameplate, and the slow speed will be 1/4 of the high speed. In this case, you want to use the High speed connection to get the maximum torque using the VFD.

2S1W Constant Torque motors provide the same torque at either speed, so the HP values on the nameplate will match the ratio of the speeds, i.e. if the Low speed is 1/2 of the Hi speed, the Low HP is 1/2 of the Hi HP. In that case it really doesn't matter which speed you connect the VFD to, but if you connect to low speed, you will not be able to go faster than that(without losing torque).

2S1W Constant HP motors will only show one HP value even though it has 2 speeds. In that case, the motor torque at the low speed is HIGHER than it is at the high speed, so which speed you use with the VFD will affect the motor shaft torque."...

https://www.electriciantalk.com/threads/dahlander-motor-control.279712/

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#9
In reply to #5

Re: VSD with Star Delta Starting

02/21/2021 12:56 PM

Hi, it is definitely a single-speed motor, thanks for all the advice given.

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