when were 15 kV, 25 kV and 35 kV started in the U.S. for primary distribution voltages

[magoo2]

As a distribution voltage, where service transformers were connected to it to serve customers, when did
- 15 kV
- 25 kV
- 35 kV
come about.

 

[HornTootinEE]

When 7200, 14400, and 19900 Delta Systems were no longer "cool" Sorry, I know that doesn't help you at all.

I am curious to see what the responses are as well.

 

[Alaska60]

The City of Seattle Municipal Utility (SCL) used 26.4kV subtransmission to serve 4kV unit subs in the '30's. After WWII transformer mfgs. figured out how to build a 15kv L-G pole top transformer so SCL started to use 26.4 distribution in the early '60's. A few other utilities also use the same voltage, Jacksonville, and (I think) Duke. It's not common.