ALERT: VFD Motors Used in Classified Areas

[Shortstub]

I just learned of a safety issue that may exist with medium voltage VFD driven motors used in Class 1, Division 2 classified areas.

In some configurations, the stored electrical potential energy between the motor shaft and grounded surfaces may exceed the minimum ignition energy for the location in which they are operating.

If your VFD motor installation is in a classified area, I suggest you contact your vendor.

So far, I haven't learned of any incident or event leading to this alert!

 

[RadarRay]

Did you come across this with a specific application? If it is existing I would like to know if the motor is Explosion Proof or Purged? Is it UL (if in the US) certified? Will grounding brushes prevent the problem and if so are they certified by UL as OK? If it is not medium voltage, isn't what you say still true?

Sorry for all the questions, but every once in a while, the explosion proof dragon raises its head on something I am involved with.

 

[pablo02]

ditto on any details you could provide -- I currently install a significant number of 480v VFD motors in Class 1, Div 2 areas, (we always spec XP but some of our vendors and contractors have been pushing the TEFC for use in these areas...) any info would be of interest..

 

[Shortstub]

Neither application nor location is stated. Just that motor(s) approved for Class 1, Div 2. Method to achieve stated Approval was not mentioned.

No mention of LV... just MV!

Strongly suggest web search for Product Safety Alert.

 

[mishlove]

Division 2 Class I:
Where ignitable concentrations of flammable gases, vapours or liquids are not likely to exist under normal operating conditions.

Note: Only hazardous under ABNORMAL conditions.
---------------------------------------------------------
Occurance of all items taking place at exactly the same time, with the correct percetanges of air/vapour, ignition point, amount of stored energy being discharged....and other relevant factors, highly unlikely.
-----------------------------------------------------------
Some LV, all MV and HV motor shafts must be grounded on VFD applications. Common current configuration should be that MV and HV motors include both insulated bearing - NDE, and shaft ground brush on DE. Always ensure that shaft voltage are discharged.
-----------------------------------------------------------
Are the motor(s) certified as Div 2, Class I. and can the manufacturer issue a Certification of Compliance.
-----------------------------------------------------------
Space Heaters in Div 2, Class I motors can be ignition source. (They could be on for long periods).

 

[jbartos]

Suggestion: Visit

http://www.buhlergroup.com/gd/en/masch_kugel.asp

for ATEX and drive of explosion proof design

 

[jbartos]

Suggestion: The VFD may be housed in an explosion proof enclosure. The VFD display is offered explosion-proof. Visit

http://www.mining-technology.com/contractors/controls/saminco/

for the explosion-proof display

 

[Shortstub]

Jbartos,
My alert applied to existing motors, previously approved for Class I, Div 2 classified areas, but had not been specifically approved for use with VFD drives.

Mishlove,
While your statement regarding probability is technically correct, i.e. highly unlikely, the value of 1 hour in 10,000 hours is the usual prescribed limit.

Space heaters are considered as being equal to the main windings, i.e., not normally sparking! But, if shaft arcing is likely to occur, then, that arcing presence will likely exceed the 1 in 10,000 hour duration.

My alert was intended for users of Medium-Voltage VFD installations to check with their vendor.

 

[mishlove]

Shortstub
Thanks for the clarification. Out of interest....Does this value relate to Divisions or Zones ? EU (ATEX) or North American.

I'm not clear on yr Space Heater comment. Our primary concern would be for surface temp and type of heater.

I believe yr alert to be well received, especially with respect to retrofits. I have not found any guidelines governing this area, by any Standards Organizations, and beleive that caution should be the order of the day.

Cheers

 

[Shortstub]

Mishlove,
The alert was for USA Class I, Div 2, classified areas.