NEMA Enclosures Questions and Variable Frequency Drives 3

[orrodriguez]

I am the Owner rep. that recently inaugurated an ocean front resort in the Caribbean. The resort has a mechanical building that has two chillers, heat exchange system and three boilers to supply chilled and hot water to 21 buildings. On that same building we have ten Variable Frequency Drives with NEMA 1 Enclosures. The mechanical systems have been working for a year and so far we have five VFDs failures. The manufacturer claims that NEMA 1 is an unacceptable choice of enclosure because the building is non conditioned and is less than a mile from the sea. The contractors claim that NEMA 1 is an acceptable enclosure as long as is used in doors. Do you have an experience with VFD’s failures and Nema 1 enclosures? Are Nema 1 enclosures industry standard in mechanical spaces? Suggestions and comments are welcome

 

[rbulsara]

So who connected NEMA 1 enclosures to failures? On what basis? Sounds like a stretch to me.

What does failure mean? What happens? Shuts down? Blows up? Shorts out? Component failures?

If components failing/shorting humidity and condensation may be a factor. But you need to describe the failures better.

Rafiq Bulsara

http://www.srengineersct.com

 

[orrodriguez]

Response: Two of the damaged VFD’s were send to factory for an analysis. The report received from factory concluded: “Unit was being used in an unprotected environment causing corrosion on the power BD. The corrosion led to arcing between traces causing the input bridge rectifier to open. Unit needs new power BD and cooling fans.”

We place a call to factory and they indicated that NEMA 12 drives should have been used in the mechanical areas because NEMA 1 enclosures don’t offer adequate protection.

Response: two types of failure one that the drive completely shuts down and there is no way to power it back and the second is drive is showing the following fault message: HF28 Power stage thermistor 2 fault. In the manual the diagnosis is: Hardware fault – return drive to supplier.

 

[rbulsara]

Thanks, this little better. Pictures of "corrosion" would help. It would be great to know if the corrosion is due to salt or water only or both. I am not trying to solve the problem remotely, but a few comments. Others may have better ideas.

NEMA 12 does not necessarily provide protection against corrosion but its gasketed covers may help ingress of water or oil if that is the issue. I am not sure if it could prevent ingress of humidity and airborne salt though.

Your best bet may be to use NEMA 12 enclosure and air-conditions the space just to dehumidify it. Or use space heaters in the drive enclosures when drives are not active. Ask the mfr it they have such an option. Some combination of the above should solve the issue, if it is indeed due to corrosion as described.



Rafiq Bulsara

http://www.srengineersct.com

 

[rbulsara]

Also it may be informative if you could talk to your counterparts of other resorts in the area and see if they have similar issues with similar equipment.

Rafiq Bulsara

http://www.srengineersct.com

 

[jraef]

Must be an Emerson Commander drive.

"Indoors" in a tropical area is something less than absolute in my experience. Yes, VFDs in close proximity to salt spray air will corrode and deteriorate very rapidly. I have had that happen may times in sewage pump stations that are near beaches. Even if indoors in air conditioned spaces, there just is no way to keep out 100% of the salt spray when your VFD is sucking in hundreds or even thousands of CFM through the vents with blowers.

I was just at one yesterday at a water intake fish screen facility in central California, 100+ miles from the ocean. The VFD was in a sealed stainless steel enclosure with an air conditioner, the installation is about 8 years old. The VFD was fine, but they have gone through 3 air conditioners in 8 years. There just is no way out of corrosion problems with gear exposed to weather.

NEMA 12 would definitely help, but you also need anti-condensation heaters with thermostats to keep the enclosure temperature above the dew point. Keep in mind that the dew point in 90% humidity can be very high! There are also some anti-corrosion emitters that out gas a vapor which helps to prevent corrosion. Hoffman sells them here in the US, I don't know if they actually make them or not however. but neither of these strategies will help if the enclosure is not sealed, and if it is sealed, it will need air conditioning. You can, by the way, get stainless steel air conditioners.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[jraef]

Do a web search on "VPI, vapor corrosion inhibitors". Keep in mind these have a life span and must be periodically replaced.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[orrodriguez]

Thanks for such good feedback with little information. I am surprise you guess the manufacturer of the VFD’s. Have you used Emerson VFD’s before? Do you have any bad experiences with them?
I spoke to a nearby hotel management and they indeed have a substantial amount of VFD’s failures, but their failures were in a period of two years and not in one year. The only common denominator has been NEMA 1 enclosures.
Regarding your observations about the enclosure I have spoke to several consultants and most of them agree that NEMA 12 in a high humidity environment next to the ocean would not work. They mentioned that the VFD’s must have a NEMA 4x enclosure with control temperature and humidity. But the factory insists that the NEMA 12 drives will solve the problem which for me does not make sense since my understanding is that NEMA 12 does not protect against a corrosive environment.
Any experiences with NEMA 12 or NEMA 4x enclosures?
I have enclosed the full diagnostic report and some pictures send by factory

 

[orrodriguez]

Board Pictures

 

[DRWeig]

I should let jraef answer the 4X question since he's giving you great feedback thus far, but since I'm sitting here I'll put in my comment...

NEMA 12 and NEMA 4X will do an approximately equal job of keeping air exchange to the outside in check as long as they're gasketed and conduit entries are sealed. The big difference is that the NEMA 4X enclosure is corrosion-resistant itself, while the NEMA 12 is probably just painted steel.

In other words, either will help your situation if you control temperature and humidity inside the enclosure I think. The NEMA 12 version might begin to corrode itself, though.

Make sense?

Good on ya,

Goober Dave

 

[rbulsara]

If you do not condition the space or use space heaters, you will only delay the inevitable.

Rafiq Bulsara

http://www.srengineersct.com

 

[stevenal]

We find that NEMA 4/4X does a great job of keeping the water in. You cannot expect to keep it out since temperature cycling will cause the water to get sucked in past the gaskets. Suggest NEMA 3RX with heater, vent, and drain.

 

[jraef]

NEMA 12 and NEMA 4X will do an approximately equal job of keeping air exchange to the outside in check as long as they're gasketed and conduit entries are sealed. The big difference is that the NEMA 4X enclosure is corrosion-resistant itself, while the NEMA 12 is probably just painted steel.

In other words, either will help your situation if you control temperature and humidity inside the enclosure I think. The NEMA 12 version might begin to corrode itself, though.

I thought that was a great answer. The only thing I'll add is that although NEMA 12 does not have a salt-spray corrosion test component to it, because many manufacturers now have simplified and consolidated their painting / treating systems for NEMA 12 and NEMA 3R production runs, there is no real difference and indirectly, NEMA 12 enclosures end up with a modicum of corrosion resistance. That said, if the application is indoors I think the NEMA 12 enclosures would likely out last anything else in the system. The NEMA 12 would serve to just keep the corrosive atmospheric salt from the most sensitive parts. But it will need external cooling when the VFDs are running and heating for when not running, to prevent condensation from forming.

Yes, I have used the Commander drives. Nothing in particular wrong with them, I just recognized the fault code.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[itsmoked]

What is the approximate size of the enclosures?
What is the voltage and approximate HP rating of these drives?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Compositepro]

In my experience, conformal coatings on the circuit boards are very effective at preventing this type of failure. It seemed much more commonly done in industrial electronics, years ago.

 

[jraef]

Yes, but conformal coating got complicated by SMT, RoHS and a general issue of an increase in current on the traces (conformal coating is also a thermal insulator of sorts). There are newer products that work, but for a while they were hard to come by and expensive to implement, so a lot of people that regularly did it stopped doing so as a matter of course. Some people still offer it as an option though.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[waross]

Condensation can occur at almost any temperature in the tropics. My experience has been with generators where there is a greater thermal lag than with a VFD. One mechanism for condensation is a rising temperature and a sea breeze with a high relative humidity. Although the ambient conditions may be above the dew point, the iron and copper mass may be below the dew point due to the thermal lag and slow warm-up of the generator.
For this reason, anti condensation heaters are typically run at 50% voltage and without thermostats. An occasional issue is locating a heater with a low enough rating. (It doesn't take much heat to stay above the dew point.)
50% voltage drops the wattage to 25%. This may be an advantage when selecting a heater, along with long life.


Bill
--------------------
"Why not the best?"
Jimmy Carter