wye delta closed transition motor control circuit

[jerm]

Anyone have a diagram showing control wiring for one of these with reverse? I understand the concepts, and have a straightforward schematic (non-reversing), and read in a SqD book that they supposedly can make such a thing to be reversing, and I can even see where you'd put the reversing contactor, but I don't see how it's possible to build it right since NEMA requires electrical and mechanical interlocks between the contactors that can not be in at the same time. Where do I get a three-way/three-contactor mechanical interlock?

I think I'd need another ondelay timer for the reverse too, is that right?

And finally, don't I need some way to allow a required interval between forward and reverse (or stop - reverse)? What are the effects of reversing after start but before transition?

It's just an exercise. If I left out any important details, you can feel free to assume.

I've never hooked one of these up, so feel free to bash me on everything I got wrong so far. I'm ready to learn!

This is a timed test. Begin!

 

[billsnuff]

try this link.......
http://www.automationnotebook.com/2005_Issue_5/fyi_issue5_2005.html

 

[Jraef]

The only way I know of to do it for a closed transition Y-Delta starter is to put a set of reversing contactors completely upstream of the entire Y-Delta assembly. Then you must interlock the entire Y-Delta control circuit with the reversing contactor to ensure that giving a Fwd-Rev command will reset the Y-Delta sequence and that the Fwd-Rev command is disabled until the Y-Delta is finished with it's complete transition, otherwise things will have a tendency to let their magic smoke out. So all in all, it will require 6 contactors and a butt load of timers and relays, or better yet a programmable relay or small PLC.

By the time you are done with all that, a VFD is probably cheaper even if you never vary the speed. For sure, a Solid State Soft Starter is already cheaper than a closed transition Y-Delta, so adding a reversing contactor is a wash. I would go that way at the very least. So all you would need to do then is have a Fwd-Rev control station and use Aux. contactors of both contactors in parallel to be the Run command to the soft starter. Pick a soft starter with a built-in bypass and you are golden. Simpler, cleaner, less room for error and easier for some future electrician to troubleshoot.

 

[jerm]

try this link.......
http://www.automationnotebook.com/2005_Issue_5/fyi_issue5_2005.html

haha. that's actually the link that started the whole discussion a few days ago between a buddy and I. I don't think they got the ontimer right btw, at least not the way we I looked at it. The timer only triggers when power is applied to to the control voltage transformer- not when the FWD button is pressed.

That same diagram (exactly) is also copied on about 4 other places on the web. Some people have re-drawn it, but the lines are so identical you can tell they just copycatted the original at automationnotebook.

SqD has a better diagram, with an ontimer wired in such a way that it at least looks correct. In case you find their PDF (I don't have the link handy) it starts on page 10 and continues to page 11. We have that diagram copied to a whiteboard.

 

[jerm]

put a set of reversing contactors completely upstream of the entire Y-Delta assembly. Then you must interlock the entire Y-Delta control circuit with the reversing contactor

That's what I figured, but there is a NEMA rule that says you have to mechanically interlock the thing- and that's what I'm not sure how to accomplish. We came up with 5 contactors, two for forward/reverse (in front of everything) and then the three for the start, transition, and run.

a butt load of timers and relays

lol! I'll lake a picture of the white board (maybe tomorrow if I make it back by the office) it's a mess!

I agree that a PLC or VFD would probably cost less, would certinly be simpler, but like I said, it's just a mental exercise. We aren't going to build this thing.

Thanks for the replies, guys!

Happy New Year!