Converting Distribution System from Delta to Wye

[tmet]

I have started working for a client that currently has two (2) 67 delta to 14.4 delta power transformers in their respective substations. A zig-zag transformer is connected to the low-side bus to provide the "neutral/ground" for the wye distribution system. The previously mentioned client is looking to add another power transformer to increase their capacity. What is the most efficient/best type of transformer connection to use to maintain the wye distribution system? For ex, is it best to stay with the same "wye" setup or is there a better way?

Thanks in advance for any help!

 

[busbar]

A delta-zigzag transformer will preserve the 0° phase shift of the existing ∆-∆ transformers, while permitting a grounded-wye secondary without an external grounding transformer.

 

[gordonl]

I wonder if there is an issue here with the sizing of the zig-zag. If it is a 4 wire system, as it seems your saying, then the zig-zag has to supply neutral current for the system. So adding more load may overload the zigzags at times of single phase loading. So another zigzag may be required to guarantee full neutral supply. (I'm not farmiliar with 4 wire design, perhaps an assumption that single phase loading won't occur is acceptable.) I don't think using Y-Y is an option because of the neutral currents that would be forced on the utility.

 

[jbartos]

Suggestions to tmet (Electrical) Aug 5, 2003 marked ///\\I have started working for a client that currently has two (2) 67 delta to 14.4 delta power transformers in their respective substations. A zig-zag transformer is connected to the low-side bus to provide the "neutral/ground" for the wye distribution system.
///Would you clarify the wye distribution system in terms of delta connections on those two transformers.\\ The previously mentioned client is looking to add another power transformer to increase their capacity. What is the most efficient/best type of transformer connection to use to maintain the wye distribution system? For ex, is it best to stay with the same "wye" setup or is there a better way?
///Another delta-delta transformer would be most compatible with the existing two delta-delta transformers. The grounding zig-zag transformer may need to be upgraded depending on its present design margin and on the size of the coming new transformer. Also, grounding delta-wye transformer may potentially be used for the high-resistance system grounding or medium resistance system grounding depending on an outcome of the system grounding calculations.\\