Drive Emergency Stop

[PaulBr]

I have seen recently that few drives manufacturers (Indramat, Control Technique, Rockwell Automation) are providing feature of Safe OFF or Safe Disable, which are certified as a means of removing power without phisically braking power circuits.
I got new copy of NFPA79 2007. It is saying that emergency stop needs to be either category 0 or category 1, which is required that final removal of power needs to be by electro mechanical means. At the end of this paragraph there is a statement that allows to consider safety disable drive circuits as means to final power removal.
My EN 60204-1 is old (1997) and saying that final power removal needs to be done by electromechanical means.
Does anyone knows what current EN 60204-1 is saying on this subject.
Thank you in advance.
PaulBr

 

[controlsdude]

Typically during an estop that has a VFD and motor. We usually use a contactor to open up the line side of the VFD to the motor.

If you have equipment that needs to ramp down during an estop, you would open the contactor after the ramp down period.

I really do not trust the integraded contactors in VFDs and really trust opening the contactor between the VFD and the motor.


Past history on using VFDs, I think the above method is very safe for all people concerned. Some people put the contactor before the VFD and I believe this will cause premature failure of the VFD.

I am not sure about what regs you are asking about but I have been in the MHE industry for 15 years and this is the best practice.

 

[dpc]

I'm not sure opening a contactor between the drive and the motor while it's running is a good idea in terms of equipment protection. I would think this could lead to damage in the VFD. Stay tuned for some expert opinion...

 

[450x]

As long as you stop the VFD from driving the motor before the contactor drops out the drive should be fine. Most drives should have an enable input which could be de-energized before the contactor disconnects the motor.

 

[ozmosis]

PaulBr
This is quite a subject and whilst I can only speak on behalf of my paymaster (Siemens), this is certainly a direction drive technology is taking now and in the future to integrate safety technology within the drive platform itself.
Firstly, as we are talking "Safety", any summary or brief description here is simply that, a brief description and brief summary. It is obviously a topic that needs careful consideration and investigation by the user and so this needs to be borne in mind.
A useful document to read that explains all issues of Safety Integrated Systems via Siemens is this:

http://support.automation.siemens.com/WW/view/en/17711888

(it is a large download [about 12MB] but quite informative)

Regarding "fail-safe drives" then there is a section in above manual on this. A brief overview relating to the standards will show that safety integrated functions will be certified according to Category 3 (EN954-1) and SIL 2 (IEC 61508) levels. Referenced in this particular document are functions known as Safe Standstill and Safe Brake Control.
The “safe standstill” (your "safe off") function directly interrupts the power supply for the pulse transfer in the power module.
This mean that the drive is safely in a no-torque condition. A feedback signal is not required. A higher-level, upstream main contactor is no longer required to implement the “safe standstill” function.
The business in Safety Integrated within drives is becomming big business and industries such as the Automotive industry are demanding certain functionality now such as things like "Safely Reduced Speed" that means the drive is monitoring the speed against an upper limit value, all within the regulations laid out by specific EN/IENC safety standards.

Other drive companies to check out are Lenze (

http://www.lenze.de/images/Produktinformationen/Automation/Dr_b_safety_en.pdf),

Danfoss FC301 [download their Design Guide]

http://www.danfoss.com/BusinessArea...Drive+FC+300&country=GB&language=en&dyn_Lang=

and also the companies you have mentioned.

 

[PaulBr]

Thank you sed2developer. I'll look at the literature you mentioned. I guess, in short my question would be Is current version of EN 60204-1 recognizing "safe standstill" functions as means of final power removal.
The last sentence of the old (1997) copy EN 60204-1 paragraph 9.2.5.4.2 EMERGENCY STOP is saying: "Where a category 1 stop is used for emergency stop function, final removal of power to the machine actuators shall be ensured and carried out by means of electromechanical components." I am interpreting this as need for contactor either on the line side of the drive or between drive and motor.
In the new NFPA 79, paragraph 9.2.5.4.1.4 the last sentence is "Exception: Drives or solid state output devices designed for safety-related functions shall be allowed to be the final switching element when designed according to relevant safety standard" I am interpreting this that "safety standstill" function can serve as final power removal means here in USA.
What is new copy of EN 60204-1 is saying on this subject?

PaulBr.

 

[HCBFlash]

Without yet doing as much study on this subject as I plan to,,,,, what about these factors?

-line AND load side contactors (or is M/G effect too substantial?)

-use of shunt-trip circuit breakers as manually operable lockable disconnecting means (local DM as well as line side MTR circuit overcurrent)

- if feeling really strong about mechanical, but wanting some sort of delay, using an old style fluid-mechanical TDR to actuate the line-side shunt trip