Created Date: February 19,2012

Created by: Do-more PE

Putting any manual disconnect on the motor side of the drive is a really bad idea. IGBT's don't take too well to having the load disconnected. Even if you are absolutely positive that no one will ever turn that handle with power applied, at some point someone will and at that point they will get to buy a new VFD.

With that being said, use the contactor on the motor side of the VFD and interlock it with the PLC so that the drive has to be stopped to disable the contactor and also interlock so that it can never engage with the VFD already running. My personal thought is to use a mechanically interlocked reversing contactor so that the VFD bypass and drive contactor cannot ever be engaged at the same time as an additional safety measure.

The supply side disconnect for the VFD is a matter of adhering to the NEC and local code. It may or may not be required.

Created Date: February 24,2012

Created by: Do-more PE

How would you go about doing a manually interlocked disconnect?

I wouldn't for the reasons already mentioned. One smoked drive was enough to teach me a lesson. :)

Would a aux contact on the disconnect be fast enough to single the drive to stop before the disconnect broke the contract?

I doubt it.

Created Date: February 24,2012

Created by: Cap

I'm running 4) 100 HP Screw Blowers to feed air to my Wastewater Treatment Plant. 2) Have Across the Line Starting, Two have Freq Drives.

ALL Four blowers have Motor Disconects at the Motor. We are working toward having Disconects at each Motor for Safty. When I toss a Lock on that Disconect I know what machine I'm Locking out.. If I blow a Drive.. Oh Well..

I like this system.. and there are no Interconects to prevent the Motor from Being pulle at the switch while running.. Just Training for the Team..

The two Freq Drives were killed when the A/C for the Control Pannel died one Summer, and fried the two Drives. No overtemp warning or Pannel Shutdown was installed to prevent this.. ( They were not AD Drives )..

The motors HAD to run ( Wastewater in the Summer.. you bet! ).. the Pannels were laid out using "Welding Cable " for feeders.. There was enough room to take the Cabels off the Supply and Output of the Drive and use Split Nut Conectors to hook them together.. Now the Knife Switch was my Disconect.. they ran while replacements were on the way..

Not the best way to do it.. but it works..

Cap

Created Date: February 19,2012

Created by: dieseltwitch

Im working a project where I need to install a 75HP drive but I also need a bypass on that drive. I 've been looking into way of doing VFD bypasses. I 've seen the Automatic Method and the Manual Method. Auto being a 3 contactors on vfd and the manual mode being nothing but manual disconnects. I'm wondering if a hybrid of the two would be a good idea. 3 contactors cost almost as much as the drive!!!

I'm thinking of using a a simple non-fueable disconnect on the output side of the vfd as well as one contractor to connect the line to the load. However, I'm not sure if I need a disconnect on the supply side of the vfd? The vfd will be controlled from the vfd using the ethernet connection. I was going to wire an program an interlock in to the disconnect so that if the output disconnect is triggered that the drive will be disabled from running in side the PAC, at the same time any command to run the motors (fans & pumps only) will trigger the bypass contactor instead of the drive. I don't see much point in totally isolating the drive on the supply side unless I wanted to be able to replace the drive on the active system... I don't. if a repair is need I will wait until i can shut it all down and replace the drive.

Let me know if I'm wrong or if you have any other thoughts on doing things.