VFD switching for one vfd to either motor

mordred

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Mar 2004
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I have an application where I have two VFD's with two drives. The application is a incline chain rail system called a hog elevator. We are trying to find some form of master switch module that will allow us to run either motor or elevator from either VFD so that we may service the VFD. The drive is a AB 1336f with an L4 module rated for 10 hp at 600 volts. we use 3 phase, 120 volt and 24 volt on the overall circuitry. the controls are mainly 24 volt however the drive control voltages are primarily 120 volts. On the vfd, we have a preset speed selector switch, a speed pot. start stop commands. jam detect the fault relay to indicate a drive fault. and an auto manual switch. as well as a limit switch for rail full conditions. before and after each VFD we have line reactors on the 3 phase 600 volt power. What I am hoping to find is some form of selector master switching modules with input indicator leds. Any suggestions or links would be greatly appreciated.
 
I don't know of anything other than manual switching. A-B has 6-pole Bulletin 194E load switches, and I have seen a NEMA-rated Cutler-Hammer device similar to this, used in the same type of application you are talking about. Basically a 3-position, non-fusible disconnect with the center position being OFF.
 
What you basically need is some interlocked contactors on the output. You should check with your VFD supplier to see if they have a "canned" package or suggested schematics. You also need to find out if you need to interlock the switching with the VFD run contact. Some drives don't like to loose the load when it is under power.

In my experience this kind of thing is way too expensive to be worth it.
 
As always, Tom has given some good information.

What may, or may not work, is what I will present. You take the the VFD's and back feed them into a modified interlocked reversing contactor, the common point is connected to the common point of another interlocked reversing contactor, with one side going to one motor, and the other side going to the second moter.

You could use small micro plc to control the 4 contactor coils, plus indicator status lights, and also to contact controlling each VFD so you are not dropping and picking up the drive under full load. A stop button or PLC logic would stop the drive before switching the load.

Easier for me to think this, or draw this, then to explain it.

Maybe I can get a drawing below.....

DRIVE------------DRIVE
--A-----------------B--
--v-----------------v--
--v-----------------v--
--v-----------------v--
ST-1A-----x------ST-1B
-----------v-----------
-----------v-----------
-----------v-----------
ST-2A-----x------ST-2B
--v-----------------v--
--v-----------------v--
--v-----------------v--
MTR-1-----------MTR-2

Starter 1 selects eith Drive A or Drive B

Power is fed to Starter 2, which in turn feeds Motor 1 or Motor 2.

If need be, a "real" reversing starter could be installed directly in front of the motor to FOR-REV it.

epending on the duty cycle, and size of the motors, this could run from a couple hundred dollars to several thousand. I used a similar circuit several times before, but utiling one drive and "house power" for the second input. Not really complicated if you understand what you want to do. PLC control is simple and straight forward with basic ladder logic, even with a timer or two controlling the drives.

Hope this helps more then confuses.

Someday maybe I will figure how to put an autocad sketch on a post.

regards.....casey
 
Last edited:
Hog elevator ? use pig oil in the gearboxes , stop them squeaking .

You can do it , but is it worth the trouble ? better to buy a spare drive , program it up , keep the capacitors conditioned and fit it when one goes pear shaped . OK , you will lose a bit of time , but this is the case if you have a failure of the changeover contactors or a chain breaks or whatever else . For this drive , all of the major bits are available as spares , keep a good selection .
Just by way of interest , how many companies spend loads of dough on buying spare drives and other hardware , then never power them up and condition capacitors , or change batteries etc ?
 
Important info !!

The 1336 drive is normally quite tolerant of open circuit loads and you should get away with the changeover scheme described.

However in order to do this properly it would be desirable to interlock the drives with their "Enable" input so that the drive can only run if it is connected to a load.

Little known factoid: The Enable input on AB drives is hardwired to a CPU interrupt. Opening the Enable input absolutely stops the drive. Use this input for interlocking in the scheme described above.
 
Thanks for the useful information I've already considered a scheme to prevent hot switching of the drives. The reason this came up is that on the application they lost 3.5 hours of production when one of the drives fried and the spare elevator was mechanically under repairs. The downtime cost over 100,000 dollars so this has become a high priority issue. I'm currently looking further into the above suggestions will let you know If I have any more questions.
 
No we mount the head on a spike conveyer system that way they can cut off the ears for dog food. The elevator is for the hogs themselves after they've been split in half after that they get cutup into there various cuts such as loins, butts etc
 
Now you are having a laugh - aren't you !?
I wouldn't have thought there was that much money in piggy wiggys . I assumed the hogs you were talking about were tobacco hogs .
Is there a need for variable speed , if not , go back to good old softstarts , which will be on bypass 99% of the time - do you have speed changes in production , or just need mechanical shock protection ?
 
Mordred,

The thought of having mutible live circuits in one controller is kinda scary. If there's a switchgear failure you could end up with some nasty suprises..

My suggestion is to keep another drive on hand, already setup, and just switch out the drive in case of a failure, or just installing a second drive in each controller. The switch over could be done rather simply with a couple of signal relays to switch the control circuits, and a pair of reversing hoist contactors (one to switch the drive power supply, and the other to switch the motor feed).
 
Believe me this project is not my idea however the politics of this project is get it done regardless of my opinion. The concerns posted here I have already mentioned to the management. In order to address the concerns for the safety on the drives I'm looking at a circuit that will allow only one drive to run at any given time. Also if either drive is running then the switch over will not work. Also it should be noted that only the electricians will be able to switch the system. Hopefully they will be intelligent enough to power down the drives first.
 
Now you are having a laugh - aren't you !?
I wouldn't have thought there was that much money in piggy wiggys . I assumed the hogs you were talking about were tobacco hogs .
Is there a need for variable speed , if not , go back to good old softstarts , which will be on bypass 99% of the time - do you have speed changes in production , or just need mechanical shock protection ?

You would be amazed then in how much automation and money goes into a hog slaughter house. I have machines here that if they go down its over 500$ per minute in downtime loss. Our process here runs at 1300 hogs/hour which really stresses the equipment. Combine that with a high washdown for food processes and you get some major headaches. Or excellent job security
 
Switching VFD and loads

Mordred

OK I understand you want to run motor A or B off VFD 1 or 2.

I know you put in the VFD drive part number but I do not know what kind of current you are handling.

WHAT IF

you use SO cord and plug and cap connectors to switch say
motor A from VFD 1 to VFD 2. Then you can get into VFD 1 and do maintenance.

DRAW BACKS
1. UNSAFE ??
MUST ALWAYS shutdown VFD and motors before doing switchover.
2 SO cord on floor to trip on or drive forklift over.

3. Washdown -- more stuff to get water and hog parts into.


Dan Bentler
 
I vote for installing a third drive in a seperate enclosure that could be switched to run either of the two existing lines. This would provide redundency for BOTH lines, and allowing BOTH lines to run at the same time in the event of a drive failure.
 

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