Switchover of motors on one VFD without interruption

Which may be best suitable method ?


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May 2017
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Karnataka
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Could anyone guide me as to how we can switchover motor 1 (main) to motor 2 (standby/Aux) without Interruption in Load (Pump maintaining liquid level in column head) running at variable speed control from one single VFD (ACS550-01) ??

Both motors are of same rating and require switchover happening manually as per user requirement (not periodical)​
 
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I may get corrected, and if proven wrong, I apologize.

As far as I know you cannot do what you are asking.
when a vfd starts, it performs certain tasks to limit motor current and start the motor smoothly.

Suddenly switching the motor will do the following (my opinion)
1. vfd will see no load and will think the motor tripped.
2. you will introduce a full dead load motor to a vfd that is up and running - causing a motor current fault.
3. you can damage / destroy the vfd.

regards,
james
 
I may get corrected, and if proven wrong, I apologize.

As far as I know you cannot do what you are asking.
when a vfd starts, it performs certain tasks to limit motor current and start the motor smoothly.

Suddenly switching the motor will do the following (my opinion)
1. vfd will see no load and will think the motor tripped.
2. you will introduce a full dead load motor to a vfd that is up and running - causing a motor current fault.
3. you can damage / destroy the vfd.

regards,
james
There's an option to reduce the load, if that can help. But there must not be zero torque in the pump at any point.
 
We have tried to electrically couple the second motor to VFD output at No load, and VFD seamlessly accepted the switchover (at around 15% of Rated frequency) , but the doubt is at Full / High Load
 
Many VFD suppliers have something available called synchronous transfer. You can start one motor on the VFD, and when it is at full speed the motor is transferred from the VFD to across the line. The VFD is then available to start and accelerate another motor. I think this is what you want to accomplish.

Note:
- This is expensive, and usually only cost effective on large hp motors
- When you start the second motor you go from 100% to 150% pump flow (approximately). This can be a process upset
 
Ok, english is quite far from my native language, but I make difference in switch of motors to a single VFD and switch of pumps. Switch of load, as you mentioned means load is common to both motors, i.e. two motors run one pump. then you make "Start on-the-fly". Lot of VFDs support it. I've seen such gearboxes, but not on a pump, so maybe, due to my poor english I didn't understand, that you want to speed-up the secondary pump, then shut-off the first pump. So you need to make it with the proper instruments (pressure, flow or whatever you controll, so it happens bumpless)


Edit, I didn't see "ONE VFD, 2 motors switch" - then I dont see a way to do it without messing the process
 
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Many VFD suppliers have something available called synchronous transfer. You can start one motor on the VFD, and when it is at full speed the motor is transferred from the VFD to across the line. The VFD is then available to start and accelerate another motor. I think this is what you want to accomplish.

Note:
- This is expensive, and usually only cost effective on large hp motors
- When you start the second motor you go from 100% to 150% pump flow (approximately). This can be a process upset

But what if it is necessary to cut-off one motor and transfer load to another ? That's what is necessary, like for maintanence or so. But both motors need VFD control and there should not be interruption in output.
 
But what if it is necessary to cut-off one motor and transfer load to another ? That's what is necessary, like for maintanence or so. But both motors need VFD control and there should not be interruption in output.

There is a few articles out there on achieving this sort of thing, they may give you a starting point to see whats possible, not specific to pumps but soem reading non the less.

http://hpac.com/building-controls/redundant-drives

http://www.csemag.com/single-articl...you-use/6086198bc601d4800cc10f1369f9fb38.html

http://www.csemag.com/single-articl...rations/55dc7089737d856f58b6bff2515beafa.html

https://library.e.abb.com/public/a9644d7cc8bb5eaa85257b350066cabd/ACH550-EOPF01U-EN.pdf
 
So, do you have two motors on a single pump?

I bet that the gearbox for this is a couple of times the couple of VFDs that we are talking about. If I had this gear I would ask a couple of VFDs and even one spare, just in case and then I would do it really bumpless with no issue.
 

Thanks for the valuable information. Most of these require multiple VFDs or Interruption. Yeah I guess it is difficult to get uninterrupted switchover between motors from a single VFD output. If you come across any such source please let me know.
 
If it's two pumps the easiest thing is to use two VFDs and make a intelligent switchover using a PLC to keep the pressure/flow constant. Could be done without PLC as well with a lot of configuration of the ACS550s.

If it's the same pump you need to use a switch that can switch the power to the motor under load without being destroyed.

You must run the VFD in scalar mode on the ACS550. This is how you set it up when you're running multiple motors from the same VFD.


PS. I saw the post above. Option one it is => two VFDs.

If the pumps are very small and can be started immediately without ramping, option 2 would work as well. Problem is that it will not be 100% bumpless.

Option 2B is to add one clutch on each motor. Then you can switch on the second motor and it will run along with no load. And then you use the clutches to remove the running pump and clutch in the backup. Can be done with valves as well instead of clutches so the pump is running but not contributing.

It depends on how big the pumps are. The problem is that the second motor will be connected at whatever voltage/frequency the VFD is running. Option one will work no matter how big things are and are the smoothest way to get it done.
 
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Ok, but what is the reason?

1. You have 2 pumps, but only one "starter", if it goes wrong, everything is wong
2. price - what is the differnce? is it so big? The VFD will protect the pump for sure, also with VFD you will have some energy savings.

You can make it even with flow-control valve, so you make sure for the process during simultaneous run of 2 pumps, but why would you?
 

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