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Indian Point SD

Indian Point SD

RE: Indian Point SD

Here's the link to the NRC preliminary notificaiton: http://www.nrc.gov/reading-rm/doc-collections/event-status/prelim-notice/2010/.  It leads to an NRC ADAMS document (where I've not had success on posting links): PNO-I-10-006.

However, it seems a pretty straight forward non-nuclear transformer explosion.  Unfortunately, those happen with some regularity at power stations (nuclear or non-nuclear) or substations.  They're a pretty spectacular fire whether at a nuclear plant or at the substation in your neighborhood.  But there is no link between them and the nuclear side of things.

Patricia Lougheed

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RE: Indian Point SD

(OP)
Thanks, but I was looking for details of the cause (If known), transformer type (Dry, liquid), size, etc.

Sounds to me like liquid filled. Wondering about protective relays involved, this type of failure should be rare with proper maintenence and protection.  

RE: Indian Point SD

According to the link it is the "main transformer" otherwise known as "generator stepup transformer".  They don't make dry transformers that big so it's gotta be oil-filled.

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

RE: Indian Point SD

True.

All that size are oil-filled.  Fans circulate air across the sets of coolers behind each transformer.  

Used to use PCB's inside as coolant.  Now oil.    

RE: Indian Point SD

Generally, the most frequent cause of transformer fires is a lightening strike.  Protective relaying probably worked fine as it separated the plant from the grid.  

Since they're not a nuclear component, the level of maintenance is pretty much the same whether they're at a nuclear plant, a coal-fired plant, or a local sub-station.  Unfortunately, with deregulation, the level of maintenance of infrastructure has decreased, because no one wants to pay for it.

 

Patricia Lougheed

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RE: Indian Point SD

(OP)
A DGA is really all you need to do.  

RE: Indian Point SD

Probably a lighning strike or internal fault. If a lightning strike, nothing you can do. You regularly see 3-10 rapid strikes hit a transmission line prior to the protective relay/station class breaker operating. I've seen the MCOV's go with as little as 2 strikes on a 161kV line. For an internal fault, Zogzog is right. If they followed proper testing schedules, they would have seen an imminent failure by DGA.

Kimberly-Clark in Loudon, Tn had such a failure (lightning) about 3 years ago. Burned for three days.  

RE: Indian Point SD

Quote (zogzog):

A DGA is really all you need to do.
Interesting comment.

I find no reason to assume that a nuke plant doesn't sample and trend DGA on their Generator Stepup Unit transformer. Quite the contrary, based on my firsthand experience I would think dga testing is done at least quarterly and trended. There are NEIL and ANI insurance requirements that drive this, among other things.  

You imply that simple DGA testing would have prevented this event. In general, we have to consider:
1 - There are situations when a problem is detected but immediate action cannot be taken based on plant conditions.
2 -  More importantly, not all failures stretch out over a time-frame that allows detection/action through dga.  In addition to lightning mentioned above, there can be through-fault leading to mechanical-induced turn-to-turn fault which can escalate rapidly. There are other scenarios as well...

For this particular event, according to the link, the failure was initiated by a bushing.   If the failure originates inside a bushing without heating the main-tank oil, it gives no dga evidence.  (The bushing oil is separate from the main tank oil)  If it is associated with externally visible connection of hv bushing, it might show on infrared (we don't know if that's the case).  If it's associated with the bushing internal insulation degradation/contamination, then likely wouldn't show up on anything other than power factor testing of the bushings, but the time-frame for that testing is limited to outages.

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

RE: Indian Point SD

Electricpete,

I fully agree. Question for you since you seem more familiar with nuc plants than myself. I know on a decent amount of civilian plants, on HV transformers, they have installed automated DGA units that sample periodically over a set period.

I'm curious to see when the last Doble test on the bushings (C1, C2 tests) were done.  

RE: Indian Point SD

(OP)
OK, I worded that poorly. I was refering to vpl's comment regarding the level of maintenence decreasing because no one wants to pay for it. Of course a full battery of tesing should be done, but if you only do one thing and have a very small budget for PM's, I would do a DGA.  

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