My POCO transformer failed
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mbrooke
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Ahhhh, ok, that its! My POCO uses T and K links... so I forgot that D links even existed.
So I want to ask... what is the purpose of D links? Why couldn't they just put a T or K link in like everyone else?
MD Automation
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So it was a "10DI" link. The first lineman let me take a picture...
And I have no idea how to tell if the new can is Completely Self Protected? Is there a physical feature that would tell you? The best picture I can get of the label looks like this...
If a transformer has an internal primary fuse, I assume that's not field serviceable? Just curious. Almost every transformer I see on a pole around here in MD has a cutout fuse. At least I think so.
Thanks all for the information.
And I have no idea how to tell if the new can is Completely Self Protected? Is there a physical feature that would tell you? The best picture I can get of the label looks like this...
If a transformer has an internal primary fuse, I assume that's not field serviceable? Just curious. Almost every transformer I see on a pole around here in MD has a cutout fuse. At least I think so.
Thanks all for the information.
mbrooke
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Take a pic of the nameplate. It will tell all.
The internal fuse is not serviceable. There are two if I remember right, a primary and a back-up current limiting fuse for hard faults. The back-up fuses limits the short circuit energy in the can if I'm correct reducing the odds of the lid blowing off or oil going everywhere.
CSP units usually have a lever near the LV bushings.
The internal fuse is not serviceable. There are two if I remember right, a primary and a back-up current limiting fuse for hard faults. The back-up fuses limits the short circuit energy in the can if I'm correct reducing the odds of the lid blowing off or oil going everywhere.
CSP units usually have a lever near the LV bushings.
mbrooke
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Alright, found a spec sheet for standard vs self protected and everywhere in between (yes hybrids exist!)
The internal fuse operates 8-14 times the full load current. You can choose a current limiting link in series with it.
The internal fuse operates 8-14 times the full load current. You can choose a current limiting link in series with it.
MD Automation
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I see no lever on the side with the LV bushings, just a bonding strap...
After you mentioned the nameplate, I realized I was taking a picture of an ordering label. I assume the nameplate is that black label on the bottom bracket for the pole mount - it's partly visible in my post #23. That's a tomorrow problem for sure, getting that picture. Sure would have been easier to snap that picture while it was on the ground
Thanks kindly again for the info.
kwired
Electron manager
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I don't think that one has a lever, if it does it is probably a little further around the right side in that image. Lever will have a loop so it can be operated with a hook-stick.I see no lever on the side with the LV bushings, just a bonding strap...
After you mentioned the nameplate, I realized I was taking a picture of an ordering label. I assume the nameplate is that black label on the bottom bracket for the pole mount - it's partly visible in my post #23. That's a tomorrow problem for sure, getting that picture. Sure would have been easier to snap that picture while it was on the ground
Thanks kindly again for the info.
mbrooke
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I see no lever on the side with the LV bushings, just a bonding strap...
After you mentioned the nameplate, I realized I was taking a picture of an ordering label. I assume the nameplate is that black label on the bottom bracket for the pole mount - it's partly visible in my post #23. That's a tomorrow problem for sure, getting that picture. Sure would have been easier to snap that picture while it was on the ground
Thanks kindly again for the info.
Yes, the black label will tell all! In so far not a CSP as I can tell. I have a soft spot for that red overload light.
MD Automation
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I promise I will let this post die after this
But MBrooke mentioned about the label, and I went to the trouble of getting a ladder to snap a picture so...
Don't see any mention of "CSP", just an Oil Natural Air Natural designation (ONAN). I assume this is just a boring old 25 kVA 7620 -> 120/240 pot.
Did not see a lever anywhere, and certainly no Rudolph The Red Nosed Overload Light.
Quick question... I understand the 2 schematics at the bottom, the right side is more standard for 120/240V but you could put both halves of the secondary in parallel to get 2x the current for 120V only (as shown on the left). But how do you rewire it? Do you have to take the top off? Are the connections inside buried under oil? And would this 120V re-wire be fairly unusual to do in the field?
Again, thanks all for the answers. Interesting stuff to me at any rate.
mbrooke
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Its a typical unit, none CSP, 7620 volts primary, You take the lid off to reconfigure the secondary leads leading up to the LV bushings on the other side. 120 only is for 120/208Y banks.
mbrooke
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BTW, now do you see why they consider the incoming service "unfused"? 10 amp fuse with time current curve that starts at about 20 amps. You would have to load the bank well over 150kva to blow something quickly.
mbrooke
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See this, 10 amp fuse starts at 20:
"DR" speed:
"DR" speed:
No. We do it daily.
Quick question... I understand the 2 schematics at the bottom, the right side is more standard for 120/240V but you could put both halves of the secondary in parallel to get 2x the current for 120V only (as shown on the left). But how do you rewire it? Do you have to take the top off? Are the connections inside buried under oil? And would this 120V re-wire be fairly unusual to do in the field.
ask any lineman about “alley cat, bad dog”
mbrooke
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But you still take the cover off, right?
LarryFine
Master Electrician Electric Contractor Richmond VA
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Yes, the internal secondary conductors must be reconfigured by hand.
There is usually air space above the submerged transformer core.
MD Automation
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- Maryland
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Yes, I do. Yikes - if I am reading those curves correctly, you'd need to draw ~45A to open that 10 amp fuse in 1 sec. That's almost 14x the rating of the transformer. Clearly the fuse is for serious problems and they are happy to let the pot ride out small overloads like you pointed out earlier. And when mine let go on Friday, that kind of energy "input" likely let some serious heat build up. Can't fault the oil for wanting to find its way out of Dodge.
And yes, I now understand how the 120 only is for building a 3 phase bank, I assume it would have to built as Wye-Wye, since this transformer has one side of the primary grounded to the can? Whereas a Delta primary would need pots with 2 floating bushings?
I like the Mnemonic! Easy to remember. I had assumed that you would not take the cover off out in the field, thinking moisture and humidity might make the manufacturer fret and lose sleep. Clearly I worry too much
Thanks all again for the replies. I learned a lot on Friday and from this thread. I especially enjoyed finding out how the fuse works and drops out mechanically. Nothing like holding it in your hand to see how it operates.
mbrooke
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A bolted fault on the secondary would produce 193 amps on the primary if I'm doing the math right- but the secondary service adds significant impedance to that.
See page 6:
Yup, wye-wye. Delta would need two bushings.
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