STAR-DELTA starter converted to vfd with 6 leads motor(100hp /400vac/3phase/60hz)

Status
Not open for further replies.
E

eufemiano

Member
Location
philippines
Occupation
technicAL
Hello everyone,

I would like to ask about our case where in we would like to convert the control from star -delta starter to vfd and at the same time retaining the star delta starter contactors. What considerations do we have to point out, and do we need to replace the motor wires sizes when running it with VFD?

motor specs: 100hp, 400vac, 3phase, 60hz

Thanks in advance.
 
ptonsparky said:
Curious.
Why would you want to maintain the contactors? Redundancy?
Click to expand...
Hello,
Yes.. Retaining the wye-delta starter will be the back up of the vfd. If the vfd is in maintenance/ for outside repair, the motor can still run since the wye delta is still available.
 
The motor would need to be connected in delta (run) configuration for use with the VFD. You may be able use the existing wiring by paralleling phase conductors.

There are probably other concerns that others more qualified will point out.

You will likely not be able end up with a solution where you can merely flip a switch and revert back to star-delta.
 
eufemiano said:
Hello,
Yes.. Retaining the wye-delta starter will be the back up of the vfd. If the vfd is in maintenance/ for outside repair, the motor can still run since the wye delta is still available.
Click to expand...
How often do you think you would need maintenance maintenance for a 75 kW VFD? You might to clean out the fan filters from time to time but how long would that take? Probably rather longer than rearranging the WYE-Delta starter.
 
I would put a pair of bypass contactors on the VFD and put it all upstream of the wye-delta, then interlock the control wiring so that the VFD won't run until you are in the delta position. You would need control power at the wye-delta fed from upstream of the VFD.

With the bypass contactors in the VFD position, turn on the wye-delta. The motor won't start until the VFD gets the "in-delta" signal and ramps it up. With the bypass contactors in the Bypass position, just start with the wye-delta.
 
Replacing the cable depends on the length of the run. If it is too long of a run, the cables are going to burn up at the motor terminations. I would recommend replacing it with VFD cable, but you would need six-lead cable and I don't know if they make it. If you did it with two three-lead cables the currents go out on one cable and come back on the other and that can't be good.

And there's always a risk of feeding an non-inverter-duty motor from a VFD. How big is the motor?
 
JoeStillman said:
I would recommend replacing it with VFD cable, but you would need six-lead cable and I don't know if they make it. If you did it with two three-lead cables the currents go out on one cable and come back on the other and that can't be good.
Click to expand...

Yes, with two three-lead cables, one side of each motor winding would be fed by one cable and the other side of the winding fed by the other cable. If the winding currents were balanced, then the currents in the conductors of each cable would be equal and at 120 degrees from each other. But if there was imbalance then there could be zero sequence currents in the cables.

Another issue is that mismatches between the lengths of two three wire cables might have adverse effects, because the voltage transitions from the VFD output would be shifted in time on one side of a winding compared to the other side.
 
JoeStillman said:
Replacing the cable depends on the length of the run. If it is too long of a run, the cables are going to burn up at the motor terminations. I would recommend replacing it with VFD cable, but you would need six-lead cable and I don't know if they make it. If you did it with two three-lead cables the currents go out on one cable and come back on the other and that can't be good.

And there's always a risk of feeding an non-inverter-duty motor from a VFD. How big is the motor?
Click to expand...
This ^ ^ ^

Running a motor with a VFD introduces additional stresses because of the high frequency switching transitions that the VFD uses to modulate its output. These high frequency transitions cause voltage impulses which can damage winding insulation, and also cause capacitive coupled currents which can damage bearings.

The star-delta starter makes little difference in this regard. In fact you can use a star-delta arrangement with a VFD to get a boost in low speed inverter limited torque. (Not common; IMHO on the VFD for your situation you will want to simply run in delta.)

The issue is that this is likely an older motor with older insulation.

IMHO you should be looking at sine wave filters on the output of your VFD, and if you desire to keep the star-delta starter as a backup, figure out how to leave it in storage nearby.

-Jon
 
modern VFDs are pretty reliable. I would not be all that worried about having a backup star delta motor starter. if the load is that critical buy a spare VFD.

If there is a chance someone will screw up and forget to rewire it before they change it from VFD to MS when it fails at zero dark 30, they will.
 
petersonra said:
modern VFDs are pretty reliable. I would not be all that worried about having a backup star delta motor starter. if the load is that critical buy a spare VFD.

If there is a chance someone will screw up and forget to rewire it before they change it from VFD to MS when it fails at zero dark 30, they will.
Click to expand...
I agree. I said something similar. As it happens I have quite a bit if variable speed drive systems experience. I don't recall ever having the need to use a DYo.
 
Last edited:
You can also purchase a VFD with a bypass or even a soft start bypass if you need the extra reliability. Modern VFDs are reliable and inexpensive enough that I don't see the bypass being used very often anymore.
 
I would yank out the Y-D starter and use a Soft Starter as the emergency bypass. One minor mistake with the Y-D starter and you lose the VFD.

You will still need 2 mechanically interlocked contacts or a manual transfer switch to fully isolate the VFD output and the bypass starter from each other. By the time you are done with all that, it might be cheaper to just have a spare VFD hooked up and ready to go.
 
Jraef said:
I would yank out the Y-D starter and use a Soft Starter as the emergency bypass. One minor mistake with the Y-D starter and you lose the VFD.

You will still need 2 mechanically interlocked contacts or a manual transfer switch to fully isolate the VFD output and the bypass starter from each other. By the time you are done with all that, it might be cheaper to just have a spare VFD hooked up and ready to go.
Click to expand...
Or three contacts if you want to be able to replace the drive with the motor running.
 
Jraef said:
I would yank out the Y-D starter and use a Soft Starter as the emergency bypass. One minor mistake with the Y-D starter and you lose the VFD.

You will still need 2 mechanically interlocked contacts or a manual transfer switch to fully isolate the VFD output and the bypass starter from each other. By the time you are done with all that, it might be cheaper to just have a spare VFD hooked up and ready to go.
Click to expand...
Totally agree.
 
Jraef said:
I would yank out the Y-D starter and use a Soft Starter as the emergency bypass. One minor mistake with the Y-D starter and you lose the VFD.

You will still need 2 mechanically interlocked contacts or a manual transfer switch to fully isolate the VFD output and the bypass starter from each other. By the time you are done with all that, it might be cheaper to just have a spare VFD hooked up and ready to go.
Click to expand...
Agree. We lost many VFD units due to inadvertent switching over to the the old control mode! VFDs won't be happy if load is disconnected while running!
 
The first VFD I installed in 1995 was on a 1985 motor. The motor was not inverter duty rated and it lasted 2 weeks, the high voltage from the VFD damaged the windings
Drives I had installed in 2000 were still working 20 years later, but the drives were obsolete, there were AB 1336+ models. The newer AB Powerflex drives have been reliable, and easier to integrate
your motor will not last if it’s not inverter duty rated.
I would recommend a new motor and new drive, and a backup system, SS or VFD. And realize there is a limited lifetime of the drive
 
topgone said:
Agree. We lost many VFD units due to inadvertent switching over to the the old control mode! VFDs won't be happy if load is disconnected while running!
Click to expand...
VFD's won't be happy if you inadvertently feed voltage to the output terminals either.

As mentioned not really any great way to allow simple flip of a switch to go back and forth between the VFD and the old starter, without some additional switches/contactors preferably something with a double throw type of operation to assure no cross connection to the drive output can happen. Be kind of pricey for something that may never get utilized as well.
 
Status
Not open for further replies.
Top