VFD Compatibility

[jimC.]

I read the thread started by Saleh with great interest, and am wondering if I'm not experiencing a compatibility issue with a VFD and motor. We are attempting to use a VFD as a "soft start" controller for crane bridge motors. The VFD is an AB Flex 4, the motor(s) are SEW-eurodrive S/O 880 series. They're for either Delta or Wye wiring.
The motors tend to "stutter" in low, then there is a definite pause when it "shifts" to high speed. Never seen a motor do this when connected to a VFD; but the only time I've dealt with SEW's are when they had their own VFD attached.
Any ideas and/or suggestions?

 

[kwired]

I read the thread started by Saleh with great interest, and am wondering if I'm not experiencing a compatibility issue with a VFD and motor. We are attempting to use a VFD as a "soft start" controller for crane bridge motors. The VFD is an AB Flex 4, the motor(s) are SEW-eurodrive S/O 880 series. They're for either Delta or Wye wiring.
The motors tend to "stutter" in low, then there is a definite pause when it "shifts" to high speed. Never seen a motor do this when connected to a VFD; but the only time I've dealt with SEW's are when they had their own VFD attached.
Any ideas and/or suggestions?

More so than incompatibility I think you just have some parameters that need adjusting, but I am not an expert at telling you which ones are most likely to need changed.

 

[Jraef]

I read the thread started by Saleh with great interest, and am wondering if I'm not experiencing a compatibility issue with a VFD and motor. We are attempting to use a VFD as a "soft start" controller for crane bridge motors. The VFD is an AB Flex 4, the motor(s) are SEW-eurodrive S/O 880 series. They're for either Delta or Wye wiring.
The motors tend to "stutter" in low, then there is a definite pause when it "shifts" to high speed. Never seen a motor do this when connected to a VFD; but the only time I've dealt with SEW's are when they had their own VFD attached.
Any ideas and/or suggestions?

How low is low for the VFD? The PowerFlex 4 is not a Sensorless Vector drive, so it is not going to have good speed regulation below about 15Hz on heavy loads like bridge crane travel motors. Generally, bridge crane drive motors are gear motors with a fairly decent gear ratio like 20:1, so the VFD should be running in a higher speed range where it would be fine. But sometimes people REMOVE the gearbox thinking that the VFD will take care of that now. The problem is, a gearbox not only reduces speed, it INCREASES shaft torque by the same ratio. When you use a VFD instead of a gerearbox, the motor has the SAME torque at lower speed, not the high torque that the gearbox gave you. Very common mistake.

 

[weressl]

I read the thread started by Saleh with great interest, and am wondering if I'm not experiencing a compatibility issue with a VFD and motor. We are attempting to use a VFD as a "soft start" controller for crane bridge motors. The VFD is an AB Flex 4, the motor(s) are SEW-eurodrive S/O 880 series. They're for either Delta or Wye wiring.
The motors tend to "stutter" in low, then there is a definite pause when it "shifts" to high speed. Never seen a motor do this when connected to a VFD; but the only time I've dealt with SEW's are when they had their own VFD attached.
Any ideas and/or suggestions?

Reading tealeaves here.

Are you trying to run multiple motors off of one drive? That could be your first problem.

The other could be the special characteristics of the motor. (I can find nothing on the SEW site for 880 motors, but they do make specialized motors that literally only work with their special drives and not others.)

Need more data.....

 

[jimC.]

We haven't removed any gearboxes. We're either not smart enough or too dumb to think that's a good idea. When I entered the S/O into the SEW website; it didn't recognize the #. Will try again today, and post results here.

 

[vicdog]

Was this originally a two speed? Did you wire it for high speed operation only?

 

[GoldDigger]

Was this originally a two speed? Did you wire it for high speed operation only?

OP:

The motors tend to "stutter" in low, then there is a definite pause when it "shifts" to high speed.

That description leads me to ask some more detailed questions:
Is this just a reference to two motor speed ranges, or is an actual physical gear shifting taking place?
Does anything change about either the motor configuration or the mode of VFD operation between the two regimes? (Change between wye and delta for example?)
Does the gear shifting interlock with the feed to the motor to "clutch" during shifting?

 

[jimC.]

OP:
That description leads me to ask some more detailed questions:
Is this just a reference to two motor speed ranges, or is an actual physical gear shifting taking place?
Does anything change about either the motor configuration or the mode of VFD operation between the two regimes? (Change between wye and delta for example?)
Does the gear shifting interlock with the feed to the motor to "clutch" during shifting?

No actual physical shifting; just a definite pause and a "step" when moving from low to high speed. The motor has two speed windings though we are only using the high set.
It's a little frustrating that I can't even find the motor on the web site. I'm thinking this isn't the vfd we need to be using.
Thanks for the collective input.

 

[kwired]

No actual physical shifting; just a definite pause and a "step" when moving from low to high speed. The motor has two speed windings though we are only using the high set.
It's a little frustrating that I can't even find the motor on the web site. I'm thinking this isn't the vfd we need to be using.
Thanks for the collective input.

I still think you need some tweaking on some acceleration related paramaters

 

[weressl]

I still think you need some tweaking on some acceleration related paramaters

Not so sure. It could be that two different set speeds controlled by two different discrete inputs and the pause comes from the crane controls, eg. there is a time delay between the two contacts from the crane controller for whatever reason.

 

[jim dungar]

Not so sure. It could be that two different set speeds controlled by two different discrete inputs and the pause comes from the crane controls, eg. there is a time delay between the two contacts from the crane controller for whatever reason.

If the original controller was a wye-delta, I can believe that the crane 'master switch' imposed a slight time delay to insure an open-transition switch occurred.

 

[Cow]

I'm thinking this isn't the vfd we need to be using.

How can you question the VFD when you're not even confident the programming is right? I agree with Kwired, I think some parameters related to acceleration might need to be tweaked. For the record, I've had good luck with PF 4's.

 

[ptonsparky]

How do you accomplish the speed changes? What causes the shift from low to high? What is the time lapse? Is mechanical braking involved in any way?

 

[kwired]

If the original controller was a wye-delta, I can believe that the crane 'master switch' imposed a slight time delay to insure an open-transition switch occurred.

If the controls had a delay in them then I could see this also. Otherwise once the VFD was introduced the wye-delta controller and any associated controls should have been eliminated, maybe there is still some controls in the circuit causing a delay.

 

[weressl]

If the original controller was a wye-delta, I can believe that the crane 'master switch' imposed a slight time delay to insure an open-transition switch occurred.

The OP talks about hi/low speed motor and wye/delta motor connection. I think he may be mistaken as a Y/D starter does not produce speed change. In the EU they love to put Y/D starters on all sort of motors that we would never think of, like 30kW. Perhaps on the crane it is to avoid the high torque jump as the motor energized at full voltage. A Y/D start certainly provides a low torque start and certainly would give more credence to the time delay between the contactor closure.

 

[jimC.]

How do you accomplish the speed changes? What causes the shift from low to high? What is the time lapse? Is mechanical braking involved in any way?

Speed change is handled via the inputs: we have a two speed switch, initial press gives direction of travel (low speed), fully depressing gives high speed (input 6). Initial experiment settings are 30 for low and 60 for high. Input signals are provided via relays. The relays are controlled by the original control wiring (120V) which then allows the 24V signal to hit its input.
The original wiring had time delays between operations. The original wiring is still there; but now is by-passed. The brake contactor is still in play though. Power button energizes brake contactor, which is also what allows our control circuit to begin. Its the only contactor still in play.

The motors can be used either delta or wye. And for full disclosure sake, I believe we are delta; just didn't address that specifically.

We could have a conflict within the inputs and/or parameters: direction of travel (inputs 2 & 3) are also our low speed, and then high speed (input 6) is high speed. Both direction & high speed are energized when on high speed.

Initially we had 1 vfd controlling both motors, and without a load it worked almost perfectly. Once we introduced loading, it has all gone down hill horribly quickly.

Thank you to all who are/have/will participate/share.

 

[jimC.]

How can you question the VFD when you're not even confident the programming is right? I agree with Kwired, I think some parameters related to acceleration might need to be tweaked. For the record, I've had good luck with PF 4's.

Had good luck with them too over the years. Over 30 years in this trade, this is the first time I've ever touched a crane. I'm on a steep learning curve. Trying hard to meet the expectations/goals given to me.

 

[jim dungar]

Speed change is handled via the inputs: we have a two speed switch, initial press gives direction of travel (low speed), fully depressing gives high speed (input 6).

Most crane controllers do not really 'shift' between speeds, rather they keep adding the new speed to the previous one. It is possible that at high speed both of your VFD speed inputs are active. VFDs can be programmed to react to multiple speed inputs in different ways.

 

[jimC.]

Most crane controllers do not really 'shift' between speeds, rather they keep adding the new speed to the previous one. It is possible that at high speed both of your VFD speed inputs are active. VFDs can be programmed to react to multiple speed inputs in different ways.

I knew/remembered that. I have a better/thicker manual somewhere....that's on todays to-do list.

 

[Jraef]

The perception that it is Wye Delta but that it worked with two speeds and is an IEC motor likely means it is what they call a "Dahlander" motor, what we call a "2S1W" for 2speed 1winding. To the untrained eye, it appears similar to a Wye Delta starting scheme, but it is different in that it changes the number of motor poles, not just the connection pattern. If that was the case, the original control system would have had to introduce a delay when changing speeds because there was a phase shift between the Delta and Y-Y connections that made the two speeds happen. If all you did was remove the contactors, replace them with the drive and used the speed relays that turned on the different contactors to provide preset speed inputs to the VFD, you may have inadvertently left behind the pole changing delay in the relay logic and introduced it into the VFD's run command signal.