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Old 06-26-2012, 04:48 PM   #21
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That's a really weird looking setup. I've never seen cutouts in that position before.
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Old 06-26-2012, 05:14 PM   #22
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Yea, that does look pretty weird...
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Old 06-26-2012, 05:47 PM   #23
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That's a really weird looking setup. I've never seen cutouts in that position before.
It's not a primary cutout, it sure looks like it's on the transformer neutral, but I don't know why they did it.

-John
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Old 06-26-2012, 09:37 PM   #24
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It's not a primary cutout, it sure looks like it's on the transformer neutral, but I don't know why they did it.

-John
yes you are right there are three jacks above that shut all power off but why would they have one jack that grounds the neutral
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Old 06-26-2012, 09:43 PM   #25
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Quote:
Originally Posted by Big John View Post
It's not a primary cutout, it sure looks like it's on the transformer neutral, but I don't know why they did it.

-John
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yes you are right there are three jacks above that shut all power off but why would they have one jack that grounds the neutral
Do a Google search on "Ferroresonance" and you will find your answers.
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Old 06-26-2012, 09:45 PM   #26
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Do a Google search on "Ferroresonance" and you will find your answers.
why don't you enlighting us
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Old 06-26-2012, 09:54 PM   #27
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why don't you enlighting us
Because I couldn't remember all the details, but is is something along these lines:

With certain configurations of circuit (delta usually), the capacitance of the lines and the transformers forms a resonant circuit which creates a large flow of undesired current, and by selectively loading the transformers or grounding them out to operate in a different configuration fuses can be closed in without blowing.

I am drawing from memory after a very long workday so I am not sure that is 100% accurate.
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Old 06-26-2012, 09:57 PM   #28
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i wish i would have seen it while the lineman was there i would have asked him
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Old 06-26-2012, 09:58 PM   #29
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Originally Posted by mxslick View Post
Because I couldn't remember all the details, but is is something along these lines:

With certain configurations of circuit (delta usually), the capacitance of the lines and the transformers forms a resonant circuit which creates a large flow of undesired current, and by selectively loading the transformers or grounding them out to operate in a different configuration fuses can be closed in without blowing.

I am drawing from memory after a very long workday so I am not sure that is 100% accurate.
does this not happen with wye configerations
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Old 06-26-2012, 10:00 PM   #30
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I'll be damned: To sum up what I'm reading, it sounds like a condition can exist when closing the cutouts one at a time, where essentially all the reactance in the transformer is cancelled out, so the only thing opposing current flow is the resistance of the winding; you get really high current flow and can cook the tranny (think of locked-rotor in a motor).

For some reason having the transformer grounded while opening or closing changes this.

Ampman, this is a delta-delta?

-John
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Old 06-26-2012, 10:01 PM   #31
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does this not happen with wye configerations

If I recall correctly that is right, wye setups don't see that problem.
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Old 06-26-2012, 10:03 PM   #32
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If I recall correctly that is right, wye setups don't see that problem.
I've got some memories stirring around in my brain: I think this is also one of the reasons that utilities love wye-wye, which might also explain why I've never noticed a fourth cutout before.

-John
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Old 06-26-2012, 10:04 PM   #33
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I'll be damned: To sum up what I'm reading, it sounds like a condition can exist when closing the cutouts one at a time, where essentially all the reactance in the transformer is cancelled out, so the only thing opposing current flow is the resistance of the winding; you get really high current flow and can cook the tranny (think of locked-rotor in a motor).

For some reason having the transformer grounded while opening or closing changes this.

-John
Yep that is a pretty good summary of it, the problem has a lot more detailed (and unpredictable) conditions that cause it.

I have a (very expensive) Electrical Engineering book that goes into the details...
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Old 06-26-2012, 10:08 PM   #34
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Quote:
Originally Posted by Big John View Post
I'll be damned: To sum up what I'm reading, it sounds like a condition can exist when closing the cutouts one at a time, where essentially all the reactance in the transformer is cancelled out, so the only thing opposing current flow is the resistance of the winding; you get really high current flow and can cook the tranny (think of locked-rotor in a motor).

For some reason having the transformer grounded while opening or closing changes this.

Ampman, this is a delta-delta?

-John
delta secondary as far as the primary -- i don't know
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Old 06-26-2012, 10:12 PM   #35
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ferroresonance typically will happen on a short section of primary underground. The wire will build voltage thru the trans bank with this setup if they are not all closed in together. (Urd wire is made like a capacitor with a conductor surrounded by an insulator surrounded by a conductor etc) The cutout is closed to energize the trans bank and then opened up after they are all on line. If left in with this bank setup and one trans goes bad you won't know it because the remaining trans will just pick up the load until it burns out and it is operating the bank at around 2/3 power. When the floating neutral is opened up after energizing and somethings happens to one trans you will know it and won't loose both trans. (unscientific explanition disclosure)
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Old 06-26-2012, 10:13 PM   #36
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I've got some memories stirring around in my brain: I think this is also one of the reasons that utilities love wye-wye, which might also explain why I've never noticed a fourth cutout before.

-John
around here we have a lot of delta sec. (high leg) services but this is the first i've seen this but they did rebuild this from scratch
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Old 06-26-2012, 10:13 PM   #37
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delta secondary as far as the primary -- i don't know

It there are 4 primary wires, it is Wye...if only 3 it is delta. If only 2 it is open delta.

EDIT: See the pic..three wires, so Delta primary it is:

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Old 06-26-2012, 10:15 PM   #38
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ferroresonance typically will happen on a short section of primary underground. The wire will build voltage thru the trans bank with this setup if they are not all closed in together. (Urd wire is made like a capacitor with a conductor surrounded by an insulator surrounded by a conductor etc) The cutout is closed to energize the trans bank and then opened up after they are all on line. If left in with this bank setup and one trans goes bad you won't know it because the remaining trans will just pick up the load until it burns out and it is operating the bank at around 2/3 power. When the floating neutral is opened up after energizing and somethings happens to one trans you will know it and won't loose both trans. (unscientific explanition disclosure)
this is an overhead service
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Old 06-26-2012, 10:16 PM   #39
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It there are 4 primary wires, it is Wye...if only 3 it is delta. If only 2 it is open delta.

EDIT: See the pic..three wires, so Delta primary it is:

good eye but at this point they had not brought up the ground yet
so this must be a wye delta
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Last edited by ampman; 06-26-2012 at 10:19 PM.
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Old 06-26-2012, 10:22 PM   #40
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good eye but at this point they had not brought up the ground yet
so this must be a wye delta
Don't be so sure..if you are talking about a ground wire running up the pole form the pole butt ground or ground rod it is still a delta primary..the ground is for safety only. (Like our EGC and ground rod/electrode systems.)

If it is wye there will be four overhead wires and one of them is the system neutral.

EDIT: Here's a pole outside my palatial estate, the top three lines are 16kv delta, the four below it are 4kv wye primary. The system neutral is on the left, the line with the white insulator. But, be aware that a white insulator is NOT a definite indicator of neutral in POCO land!!



Note the pole in the background with a brand-new load break GOAB switch..mounted upside-down!!
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