XFMR Questions

Status
Not open for further replies.

aelectricalman

Senior Member
Location
KY
Say you have a 12.47kV electrical system (theoretically). Then, you have two 12.47 Delta /480 Delta Ungrounded transformers feeding two separate systems at the facility. Then say that you have this anomaly that causes both transformers to become (in essence) "Corner Grounded" on the secondary side (480V). Oddly enough, it appears that both of these corner grounds appear to be on opposite phases in the respective transformers (A and C respectively). This stems from a previously asked question but is not related, so moderators please do not couple this question with prior post.

Keeping the above in your mind......there appears to be no explanation why the facility is causing this corner ground. All of our testing indicates that the systems are wired in such a way that a corner ground is unlikely (much less on two separate transformer). With this all being said, the utility company originally had (2) pole mounted XFMR's (12.47D/480D Ungrounded).. Due to unavailability to get the pole mount replacements they went back with pad mount 12.47kV/480 Wye transformers, and did not use the No bushing (effectively using the XFMR as an ungrounded delta.

So my question is.....with the understanding that the transformed voltage is created through induction...is there anything from the Utility side that can cause the secondary side (480V) to become corner grounded. My strong feeling is NO but I don't want to leave anything on the table.

I've read of system becoming corner grounded through the use of drives having to pull a reference ground from the delta, but wondered.... is this safe. Is this a by product or is it intentional? Could it have anything to do with why power logic boards and drives are burning up left and right. I suspect most of our problems are due to grounding issues from single phasing, and thus need protection but I want to cross this bridge first.

Any thoughts?
 
Last edited:

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Say you have a 12.47kV electrical system (theoretically). Then, you have two 12.47 Delta /480 Delta Ungrounded transformers feeding two separate systems at the facility. Then say that you have this anomaly that causes both transformers to become (in essence) "Corner Grounded" on the secondary side (480V). Oddly enough, it appears that both of these corner grounds appear to be on opposite phases in the respective transformers (A and C respectively). This stems from a previously asked question but is not related, so moderators please do not couple this question with prior post.
A
Keeping the above in your mind......there appears to be no explanation why the facility is causing this corner ground. All of our testing indicates that the systems are wired in such a way that a corner ground is unlikely (much less on two separate transformer). With this all being said, the utility company originally had (2) pole mounted XFMR's (12.47D/480D Ungrounded).. Due to unavailability to get the pole mount replacements they went back with pad mount 12.47kV/480 Wye transformers, and did not use the No bushing (effectively using the XFMR as an ungrounded delta.

Sources my question is.....with the understanding that the transformed voltage is created through induction...is there anything from the Utility side that can cause the secondary side (480V) to become corner grounded. My strong feeling is NO but I don't want to leave anything on the table.

I've read of system becoming corner grounded through the use of drives having to pull a reference ground from the delta, but wondered.... is this safe. Is this a by product or is it intentional? Could it have anything to do with why power logic boards and drives are burning up left and right. I suspect most of our problems are due to grounding issues from single phasing, and thus need protection but I want to cross this bridge first.

Any thoughts?

Have you established how "solid" this corner ground is? You need to be able to distinguish between a wired connection and a leakage resistance or capacitive coupling. Until you do that you are groping blindly.
2. Do you have a working ground detector on both systems? Until you do the installation is non-compliant.
3. Other than electrostatic coupling in anon-shielded transformer, I do not know if anything on the primary side that could affect the ground reference of the secondary.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Whatever happens on the utility primary side, will not affect your secondary grounded or ungrounded status.

What testing have you done?
 
Status
Not open for further replies.
Top