Underground Transformers

[ePOWEReng]

Does anyone have experience or knowledge about residential underground direct buried distribution transformers and/or residential distribution transformers in an underground vault? What are reasons that you use or do not use them?

Thanks.

 

[BJC]

Google up submersible transfomrers. These are the transformer that are usually in older residental areas. The were put in vaults for esthetic reasons. The ones I am familiar with were 7200-120/240 single phase, ususally in the 25-75 kva range. They used load break elbows on the high side and were frequenlty submerged without problem.
GE for one made a direct burried transformer. I suppose it was to save the cost of a vault. I don't think they were popular with utilities or line crews. I know some of them lasted a long time.
I know of one when it went bad had to be dug up for replacement. In the years it was there trees had been planted nearby and the thing was completely entangled in roots. One of the trees had to be taken out. The other problem was locating it.

 

[busbar]

Short article at

http://tdworld.com/mag/power_give_transformer_proper/

 

[mc5w]

ABB also makes a direct burial transformer. I have seen enough instances (1) of the Tree Root Circuit Breaker Method with direct burial electrical service laterals that I would not want to use them.

The problem with vaults ( in a residential area ) is that over time they will fill up with leaves, mud, and other debris. In a downtown area that has limited trees this is not so bad if there is a way to clean the vault once every few years. How often depends upon conditions.