The subject was grounding

Many thanks to Toby Grotz for sharing these two files on the critical 
subject of grounding and bonding of electrical circuitry.    My main 
interest in this stems from personally witnessing a very large 
transformer explode from the ferroresonance phenomenon.  The faulty 
grounding of power distribution systems up in dairy farming area of the 
mid West where cattle were electrocuted added to my interest.  When the 
huge HVDC transmission distribution systems came on line, there seamed 
to be a complex set of problems introduced especially in the single line 
type of system which relies on an earth/ocean return path. I believe you 
can see the unique set of problems here. See

Ole and Fredric Fletcher, pay attention to the polarity and methodology 
of transmission of the HVDC.  Remember the articles regarding the earth 
ground return problems up in dairy country, Wisconsin where cattle were 
being electrocuted by poor grounding systems in rural electric grid.  I 
can recite a real life problem with imposing a potential into the earth 
on the dealing with ground return.  One of our Nursing facilities had 
three separate buildings that shared a two pipe chilled / hot water 
system with buried steel 4 inch lines (supply/ return).   The electrical 
system was 480VAC backbone with delta/Wye step down transformers which 
gave a base 208VAC with center tap ground for 120VAC. The facility 
operated just fine for 50 years.  Along came an Electrical Contractor 
that installed a new distribution transformer (100 KVA) during an 
upgrade to one of the out buildings. After operation for several years 
the buried 4 inch steel AC/heating lines developed leaks and sections of 
the removed lines showed electrolytic (galvanic) erosion.  I discovered 
that the Contractor had installed a delta/delta step-down (100 KVA) 
transformer and grounded one (L-2) of the Secondary terminals to get a 
neutral buss common for 120VAC.  A huge NO,NO cause you had a potential 
of 230V to earth ground.  The difference in ground potential between 
buildings created the galvanic erosion because there was a ground return 
current back to the 480/208VAC backbone in the mains building.  This was 
a huge lesson on the problems encountered with relying on earth ground 
return path.

https://www.electronicshub.org/high-voltage-dc-transmission-system/

https://circuitglobe.com/different-types-hvdc-links.html

See attached files.

Hi Norman,

"I discovered that the Contractor had installed a delta/delta step-down (100 KVA) 
 transformer and grounded one (L-2) of the Secondary terminals to get a 
 neutral buss common for 120VAC.  A huge NO,NO cause you had a potential 
 of 230V to earth ground."
Was the ground wire also used as neutral for carrying current? The ground wire must be used only for safety in case of some other insulation failure putting a person between a phase and ground. The ground wire should carry no current when no fault condition exists. Connecting one of the phases to ground should give no problem if it is only used as neutral. But physical earth must exist separate from the neutral line even though they are at the same neutral ground potential. As I understand in the US there are two phases 180 degrees out of phase. This won't work with the above way of connection with two phases out of a three phased transformer. Here each phase is 120 degrees apart from each other. Thus the voltage between two phases is square root 2 times the voltage of a single phase to neutral. Neutral of course doesn't exist in the delta connection. Three similar loads connected in star connection can make a neutral reference point for measuring the phases to neutral (of the three phases).

Regards
Ole
 

---In [email protected], <nwootan@...> wrote :

 Many thanks to Toby Grotz for sharing these two files on the critical 
 subject of grounding and bonding of electrical circuitry.    My main 
 interest in this stems from personally witnessing a very large 
 transformer explode from the ferroresonance phenomenon.  The faulty 
 grounding of power distribution systems up in dairy farming area of the 
 mid West where cattle were electrocuted added to my interest.  When the 
 huge HVDC transmission distribution systems came on line, there seamed 
 to be a complex set of problems introduced especially in the single line 
 type of system which relies on an earth/ocean return path. I believe you 
 can see the unique set of problems here. See
 
 Ole and Fredric Fletcher, pay attention to the polarity and methodology 
 of transmission of the HVDC.  Remember the articles regarding the earth 
 ground return problems up in dairy country, Wisconsin where cattle were 
 being electrocuted by poor grounding systems in rural electric grid.  I 
 can recite a real life problem with imposing a potential into the earth 
 on the dealing with ground return.  One of our Nursing facilities had 
 three separate buildings that shared a two pipe chilled / hot water 
 system with buried steel 4 inch lines (supply/ return).   The electrical 
 system was 480VAC backbone with delta/Wye step down transformers which 
 gave a base 208VAC with center tap ground for 120VAC. The facility 
 operated just fine for 50 years.  Along came an Electrical Contractor 
 that installed a new distribution transformer (100 KVA) during an 
 upgrade to one of the out buildings. After operation for several years 
 the buried 4 inch steel AC/heating lines developed leaks and sections of 
 the removed lines showed electrolytic (galvanic) erosion.  I discovered 
 that the Contractor had installed a delta/delta step-down (100 KVA) 
 transformer and grounded one (L-2) of the Secondary terminals to get a 
 neutral buss common for 120VAC.  A huge NO,NO cause you had a potential 
 of 230V to earth ground.  The difference in ground potential between 
 buildings created the galvanic erosion because there was a ground return 
 current back to the 480/208VAC backbone in the mains building.  This was 
 a huge lesson on the problems encountered with relying on earth ground 
 return path.
 
 https://www.electronicshub.org/high-voltage-dc-transmission-system/ https://www.electronicshub.org/high-voltage-dc-transmission-system/
 
 https://circuitglobe.com/different-types-hvdc-links.html https://circuitglobe.com/different-types-hvdc-links.html
 
 See attached files.