Temporary barriers for at-risk reclosers

[rkflash]

Hi All,

The company I work for has been experiencing chronic violent failures of type VWVE oil-filled vacuum reclosers. We have approximately 60 of the same model recloser in-service for over 20 years and in the last 14 months we have had 5 fail catastrophically. To date 4-of-5 failures have been gasket failure between the tank and head cover resulting in an extremely hazardous upward-and-outward spray of flaming oil. The 5th actually blew the bottom of the tank out.

We are in the process of replacing them all with solid-dielectric type reclosers but in the interim we have no confidence in the units remaining in-service.

We are hoping to come up with a temporary portable barrier solution that we can send along with our crews whenever they need to work in the vicinity of one of the at-risk units, which they would assemble on-site to surround the unit and block the gush of burning oil should a failure occur while they are on-site. We are currently looking into some galvanized steel barriers or kevlar curtains but I'm wondering if anyone has had a similar experience with equipment that is at-risk of catastrophic failure and what did you do to protect employee safety should they need to get close to it?

 

[DRWeig]

Hi rkflash,

I don't have an answer for your barrier idea (which is a good thought), and am interested to hear suggestions.

I did want to point out that I'd personally dress up all over in nomex like a firefighter to work near something with that high of a failure rate in that disastrous of a failure mode... Personal protective equipment is a personal responsibility to me.

Good on ya,

Goober Dave

 

[rkflash]

An update for any interested. We have reached out to a fiberglass fabric welding barrier manufacturer for assistance. This manufacturer believes they can fabricate a "barbeque cover" style wrap for the at-risk units of sufficient strength to contain the initial burst of burning oil (it's less important that the barrier survives the ensuring fire).

The manufacturer has kindly provided datasheets indicating the burst tolerance of the fabric and we are in the process of calculating the force that the cover will need to withstand.

We are still open to suggestions at this point as well as critique of the proposed "barbeque cover" method. Thank you.

 

[electricpete]

Sounds like a great idea. One possibly-easy thing that might be done in addition is to cordon off a wider buffer zone around the suspect device (as wide as practical) with yellow/black (caution) barrier tape with a sign explaining the hazard. That way you have your primary barrier in place (barbecue cover), but you also don’t take chances with people going close to it that don’t have to.

=====================================
(2B)+(2B)' ?

 

[magoo2]

Why not just bypass them all! You're probably at risk if continue to you let them operate.

 

[davidbeach]

What magoo2 said. Just close the bypass switch; hard for them to fail during interruption when shorted out.

 

[waross]

I agree with magoo2 and davidbeach.
There must be some way to bypass them. I would even consider something as outlandish as a good recloser hung from a crane and connected with hotstick hardware to be better than trying to contain blowing oil. Someone may still be at risk installing the shield. Bypass and de-energize the units before going near them.
Another option that may be even more cost effective:
When work is scheduled in the hazard area of an at-risk recloser, make changing out that recloser part of the work order, to be completed before other work is started..

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

 

[Marmite]

Rkflash, forget your fibre glass screen idea and think about what would happen if one of your colleagues or a member of the public got covered in burning oil, or injured by the shrapnel. Your Company wouldn't have a leg to stand on.
A defence of we "believed that the cover could withstand the burst of burning oil" would not go well for you in court.

Regards
Marmite

 

[dpc]

Just out of curiosity, have you worked with Cooper on these failures and if so, what is their explanation? There are a lot of these old units still in service, so if this were a widespread issue, I'm a little surprised that I haven't heard about it. Is there anything unusual about the application or service conditions?




David Castor

http://www.cvoes.com

 

[rkflash]

Thank you for your comments everyone. To the folks asking why we don't just bypass them all, I'm afraid I'm answering somewhat out of my area of expertise but suffice to say our P&C people told us this was not feasible due to the quantity of distribution feeders we would be leaving stripped of one of their key pieces of protection.

As I mentioned we are in the process of changing them out as fast as we can, the issue we have is that the majority of our suitable spares are the same type of recloser, which only buys us time, not confidence. So if we're being told we can't bypass them and we need several months lead time to receive the solid di-electrics that we will be swapping in, the best option we see for the short term is a method to contain any failures in the interim.

Rest assured that we are not taking any chances with people's safety around these units, we have restricted access to all facilities where these reclosers are being used unless they are first de-energized and isolated. We will also be thoroughly testing the cover's actual capabilities before we start deploying and trusting people's safety to them.

We have been in contact with the recloser manufacturer after every failure and they have not been overly helpful. They have certainly helped us determine the immediate cause of the failure (dielectric breakdown of a fiberglass board that is part of the closing solenoid assembly between 2 phases due to water in the insulating oil that in turn impregnates the fiberglass and provides an arcing path). Our own studies have shown that 4 of 5 failures happened in cold weather when the oil-water saturation point is lower, and all 5 failures happened 2-3 days after very wet weather. So the immediate cause is obvious to us, what is less clear is how the water is getting in and why all the failures started occuring within the last 14 months. The manufacturer's only corrective action to date has been to update their maintenance practice which as far as we can tell has not resolved the issue.

It's certainly puzzling to us as well as to why we have not heard of this issue being more wide-spread than our part of the world. We have people thoroughly reviewing our maintenance practices and design specifications for something that we may be doing to cause the failures but we have not yet found anything conclusive or otherwise.

Again thank you all for your comments and I hope for your continued feedback as we work towards a solution we can feel confident will keep our workers safe.

 

[dpc]

rkflash,

Thanks for the additional information. What is the voltage of the closing solenoid? In the VWVE the main arc interruption occurs in vacuum bottles, I believe, with oil used for insulation only. So the main arc interrupters are not part of the failure?



David Castor

http://www.cvoes.com

 

[magoo2]

You can't bypass 60 reclosers! Give me a break. How big is your system?

Sounds like you have ticking time bombs on your system. Bypasses with solid blade disconnects are standard installation procedures. Just do it.

 

[racobb]

Are these all in substations or out on the lines? If they are in substations then yes I can see that bypassing would be a problem. If on the line, then as others have said, just bypass them. You could install fuse cutouts in the interim where loading permits for sectionalizing. Many units on distribution lines are installed with fuse cutouts for bypass as normal practice.

Alan

 

[rkflash]

Nominal voltage on the solenoid is 23-24.9 kV, and that's correct, the main arc interrupters are not involved in the fault. In 4 of the 5 units that have failed the vacuum bottles have been completely intact.

In response to magoo2/racobb, the reclosers are all in substations, so your comment racobb echoes what our P&C group said.

 

[davidbeach]

Breakers belong in substations, reclosers belong out on lines well away from substations and fitted with bypass switches. Penny wise and pound foolish and all that. Replace 'em all with breakers and be rid of the problem once and for all.

 

[magoo2]

Amen, David! I agree.

 

[racobb]

Could not have said it better! More of the Amen corner.

Alan

 

[dpc]

Breakers belong in substations, reclosers belong out on lines

I understand this sentiment and generally agree, but the line between reclosers and circuit breakers gets a little less distinct all the time as recloser ratings increase. For large urban distribution substations, I agree that breakers are the best choice. For small rural substations with limited available fault current, it can be hard to make the case for the advantages of circuit breakers over (solid dielectric)reclosers.

And even if they decided to replace all of these reclosers with breakers, there is still a need to deal with the issue at hand in the interim.

Oil circuit breakers used to be commonplace in substations and they occasionally failed in interesting ways as well.

To me the bigger issue is getting the oil-filled switching equipment out of the substations - and everywhere else.


David Castor

http://www.cvoes.com

 

[racobb]

While I am all for getting the oil out, haven't figured out how to do it with the power transformers and voltage regulators yet.

No question that any piece of equipment can fail violently. I expect that most of us have had a part of cleaning up the mess.

It has been my experience that when you dress up a recloser to look like a breaker, ie. OC relays and the like, the reclosers actually get more expensive than the breakers equally equipped. I have tried it both ways, although not recently.

rkflash:

I am sure someone is attempting to determine a best stragety for replacement of the units. I would consider available fault duty at the station, time in service, # of operations annually at a minimum although not 100% sure that is the proper order just yet. Maybe someone else will jump in here.

Have you developed a profile of the failed units with these types of data so far?

Good Luck!

Alan