×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Motor emergency stop botton position?

Motor emergency stop botton position?

Motor emergency stop botton position?

(OP)
Hi,

I need your comments on which alternative is better for stoping a 100 kw motor driving a ventilation fan in an underground mine when you push the e-stop botton next to the fan.

The motor is drive by a 100 kw VSD. The manufacture of the VSD is offering a digital input in the equipment to conect the e-stop botton, so in case someone push it the output signal to the IGBT´s stop and the motor stop. The VSD keep energize under this configuration.

The configuration I have seen in other mine sites is that the e-stop botton de-energize the contactor that supply the power to the VSD, so in case someone push the botton the whole system is shut down, VSD and motor. I think this configuration is better since is not subject to issues with the digital input and electronic cards in the VSD.

Please comment.
Thanks.

RE: Motor emergency stop botton position?

I'm no mine expert, but the combination of the words "emergency" and "stop" imply to me that you want to open the circuit as far upstream as reasonably possible. Suppose the VSD fails and catches fire? An E-stop connected to the VSD might then be useless.   

RE: Motor emergency stop botton position?

I'm pretty sure you'll find the answer to that through references within your electrical code, determinent on your industry. There will also be names and thier contact numbers of the various industry representatives, in dealing with code/safety issues.

RE: Motor emergency stop botton position?

The local e-stop button should really be as fail-safe as possible. So if someone presses the button, accidently cuts the e-stop cable, or there is a loose connection in the pushbutton terminals, etc, the motor should stop.

I've always felt that it was bad form to rely on a digital input to do your emergency stopping, so if it were me, I'd insist on a hard-wired e-stop connection to the contactor.

RE: Motor emergency stop botton position?

Maybe the poster has a VFD that has an estop contactor build into the drive.  Most drives in the last few years has this feature now built into the drive.   

RE: Motor emergency stop botton position?

As others have said, the electric code for your industry in your jurisdiction will probably determine what you must do (which is not necessarily what you should do...) Many people have the e-stop button perform multiple functions simultaneously.

A word of warning if you simply drop out the contactors on the power into the VSD: The bus capacitors in the drive store a lot of energy, usually more than the kinetic energy of a motor rotor. If the drive does not automatically disable itself on loss of input power, the motor can be driven for quite a while after power is removed.

Increasingly, I'm seeing regulations that require that an e-stop drop out control power to the "gate driver" circuits inside the drive that allow the power transistors to be turned on. Some of these permit the use of silicon in the path, but none permit the use of software to do this.

Curt Wilson
Delta Tau Data Systems

RE: Motor emergency stop botton position?

well it was common practice that if you had an estop that I would pull the enable by the plc or if the local code required an additional estop contact on the enable you could do this too besides the estop contactor.  Same goes for a local disconnect on the motor, pull enable with the aux disconnect.

But droping power on input side was never my first way to do it.  It seems like the manufacturer's of drives draws it in their docs to pull power on the input feed to the drive,  I think this sets the drive up for premature failure.  

I think the best way is estop contactor on the output of the drive and disable the enable on the drive during estop.  Of course during ramp up or down make sure that the contactor stays pulled in during this stopping and starting for a normal stop/start.  Just seen it both ways, not sure which way is code sanctioned and dont think they do point out this in references.

RE: Motor emergency stop botton position?

Regardless of what you think, manufacturers don't put the contactor on the output because opening the contactor under load has a habit of wiping out the expensive output stage. Manufacturers don't recommend it because it would get them a lot of returns and a reputation for lousy reliability - hardly the way to gain repeat business. If you had a late-making and early breaking auxiliary contact controlling the gate inhibit then it is arguably acceptable technically but it will likely invalidate any warranty because the OEMs specifically say 'do not do this'.

The gate drive inhibit circuits have been through a lot of testing, in some circumstances sufficient to meet Cat 4 of the EN954 machinery safety standard - not an easy requirement to pass, so they're worthy of consideration. Personally I still like to see a physical airgap in the power circuit, so an input contactor is still my initial solution but I am increasingly attracted by the gate inhibits when used with a safety relay such as a Pilz PNOZ or similar.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources