Converting Existing 7200/4160Y to 12470/7200Y
Converting Existing 7200/4160Y to 12470/7200Y
(OP)
Have a customer presently being served by utility with a 12.47 primary through step downs distributing/metering at 7200/4160 throughout the facility via aerial distribution. The transformers are overloaded and the current thought is to have utility remove transformers and distribute the 12.47/7.2 throughout, which would then be a direct feed from the utility distribution voltage.
I'm told most existing transformers are 4800/8320Y rated, single phase pole mounted cans, connected phase-gnd primary, with 120/240 1-ph secondary. There are a few 2400x4800 transformers also.
They (facilities electrical group) have the thought that they can retain most of the 4800/8320Y transformers and adjust the tap settings for the new 7200 (L-G) service voltage. Has anyone ever done (or heard of) this? Aren't those xfmr's rated for a maximum L-G nominal voltage of 4800?
There are obviously other issues (such as insulator ratings, cutout and surge ratings, fault current ), but the transformer issue concerned me.
Thanks!
I'm told most existing transformers are 4800/8320Y rated, single phase pole mounted cans, connected phase-gnd primary, with 120/240 1-ph secondary. There are a few 2400x4800 transformers also.
They (facilities electrical group) have the thought that they can retain most of the 4800/8320Y transformers and adjust the tap settings for the new 7200 (L-G) service voltage. Has anyone ever done (or heard of) this? Aren't those xfmr's rated for a maximum L-G nominal voltage of 4800?
There are obviously other issues (such as insulator ratings, cutout and surge ratings, fault current ), but the transformer issue concerned me.
Thanks!






RE: Converting Existing 7200/4160Y to 12470/7200Y
The only transformer that could be directly reused would be any single phase transformers presently connected 7200V line-to-line that could be reconnected 7200V line-to-neutral.
A "4800/8320Y" transformer, my rant not withstanding, suggests a three phase transformer that was connected at a lower tap to the 7200V three phase. It would now need to be connected to the 12470V three phase and I doubt there would be a tap at 150% of rated voltage. Diagram the existing connection, the voltage across the individual windings and the rating of the winding. What will you then connect to that winding? As I said, the only thing you will be able to keep will be any single phase transformers presently connected phase-to-phase and they will require new lightning arrestors and possibly new insulators/bushings.