Transformer Soak

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EmagSamurai

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Is there a ANSI/NEMA/etc. guideline for minimum transformer soak time for large high-voltage transformers? Or is this based on the manufacturer's requirements for commissioning? I've always heard 24 hours minimum, but I'm struggling to find where that number came from.
 
Quick update. It looks like IEEE C57.93 provides some guidance, but it is not a requirement unless the manufacturer specifies it. I would still be interested to know if there are other specifications that might come into play here.

Thanks in advance.
 
That and manufacturers specs.
Generally I soak for 24 hours at least.
the mobile is in, or if it’s a new station the load isn’t that critical it be switched over in a day or two...

it gives the XF time to warm up, and all components time to show any failures.
just for me, I will IR before load, and several times that week under load.
ALWAYS, the soak is with all protections.... 50,51,87, etc...
 
GoldDigger said:
Get possible moisture out of the windings rather than suddenly turning it to steam?
Click to expand...
The oven, vacuum and the N2 blanket from the factory should have taken care of that.
Transformer is a sealed unit. Shouldn’t be any in there.
 
Do all transformers need that?
I heard/read the term "soak" and immediately my mind went to "saturated". I see now that was not what was meant.
 
So based on what you’re saying, it’s a little to the benefit of the transformer, and a little to make sure nothing is obviously wrong with it before adding a load?

Interested to hear the answer to Little Bill’s question also. Wondering at what point this becomes typical.
 
Usually only 10MVA and above.
This period is used to listen and watch the transformer as it comes up to temperature.
Interesting enough, I went to a commissioning a few years back, and the system engineer there energized the XF and transferred load in two hours..
Too quick for me...
It’s a time to note noises, pings, etc. watch the gauges, note the temperatures, etc. with transformers starting at about 1 million, you want to monitor your investment carefully.
 
This is one of those things I've always heard, and I believe is good practice. I was a little surprised when I actually went looking for where it's written down that I couldn't find anything solid, and IEEE C57.93 only recommends a no-load operation period of 8-12 hours depending on the voltage (It also defers to the manufacturer if there is conflicting guidance). The most surprising part is C57.93 clearly states this period is not required.

That said, for a large transformer, it really makes sense to have a no-load operation period to monitor for any issues, and during our commissioning it usually happens while running through the remaining checks whether we intended to or not.

EDIT - BTW, C57.93 uses the term "soak" for a different period before the transformer is energized. This time (ranging from 12 to 72 hours) is intended to allow oil to fully soak into the insulating material and to absorb residual gas. I'll have to be careful with my terminology in the future.
 
IEEE / ANSI are consensus standards so when the final language is such that it recommends and doesn't require, then goes on to defer to manufacturer's guidance, you can imagine that when creating this standard that it was muddy and nobody agreed, so they left it so it could be read that way.
 
I have never read a REQUIREMENT that it be done.
Neither by manufacturer or IEEE.
Only some recommendations..

Manufacturers can recommend it, and used to on every one.
The last two we bought a no load energized period was ever mentioned.

I like to do it, I just feel better knowing it sat there humming happy for a while before I make it work for a living...

Old school habits are hard to break.
 
@ron and @Hv&Lv, agreed on both accounts.

There is really little downside to having a no-load operation period, and potentially a lot of benefit. That said, it is good to understand when these practices are "requirements" vs when they are "recommendations." Until this, I thought the no-load period was a requirement, now I know differently. It doesn't change that I will push to do it, but I also understand there are times when it may not make sense.
 
This is an old terminology based on power transformers that were free breathers with no gas blanket. These older units often had a silica-gel jar attached to them on a breathing tube. Transformers of this type often were found sitting in storage and no one remember to maintain the silica-gel to ensure minimum moisture intrusion into the transformer oil and thus into the paper insulation. Paper insulation will absorb 50 to 80% of the water in the oil when the transformer is cold. So, when these types of transformers were placed into service, it was often a standard practice "soak" the transformer to indeed heat it up and drive any moisture from the paper insulated windings. This requirement is not required for gas blanketed transformers or units using conservator oil expansion tanks with rubber separation bladders'. Last any of our large power transformers that were exposed to moisture were then processed out by a hot oil flush and high vacuum treatment until the dew points were reduced to an extremely low value. then vacuum filled with degasified clean oil. Hot soaks are generally no longer done or required unless you have a free breather.
 
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