Supplying a 3-wire (delta) system from a delta-wye source

[tinfoil]

I am in the process of replacing and upgrading the supply transformer for a small utility of 3000 customers.

The source is 44kV delta, and the existing transformer steps down the voltage via a delta-delta connection to supply a three-wire medium voltage (26.4kV) subtransmission system.

My dilemma is that 26.4kV delta is a VERY rare voltage in my general area, which is domininated by 16/27.6kV Wye systems. I would like to evaluate the conversion of my system to 27.6kV wye, by specing the appropriate transformer and reconstructing my 44-27.6kV substation as appropriate.

Much of the 26.4 delta system already has underbuilt 2400/4160V four-wire distribution present (complete with a neutral), and there is sufficient clearance on the rest to accommodate the addition of a neutral.

Obviously, all of my 26400:4160 stations are presently connected delta-wye, as are several industrial customers. There are several small hydroelectric facilities connected to the delta subtransmission system as well. Each such transformer has off-load tapchangers which could make the adjustment from 26.4 line-to-line to 27.6kV line-to-line.


Does anyone forsee any issues with continuing to connect each customer and substation transformer as a three-wire primary (now 27.6kV) and supplying as before?

Any problems with connecting the low-side neutral of any of these existing delta-wye transformers with a 4-wire secondary to the new 27.6kV neutral?

 

[weh3]

Do I have this straight: your area is dominated by 27.6Y/16 systems, but your substations and customers are delta-wye?

If your customers are delta-wye, why do you need to propagate a neutral?

I'm a little confused.

William

 

[tinfoil]

I can find 44-27.6KV delta-wye transformers more easily than 44-26.4 delta-delta transformers, and they seem to be cheaper as well.

Furthermore, I would like to be able to supply small and moderate sized customers (one and three phase) directly from a '4-wire' 'subtransmission' system via distribution-class 16kV transformers rather than placing further burden on my 4160V feeders and stations, since the 'subtransmission' has to carry that load anyways. I already have a good inventory of single-phase 16kV xmfrs from another region of my utility.

I am looking for advice regarding leaving the existing stations alone, but supplying them from a 27.6 wye source rather than a 26.4 delta.