Padmount Transformers on 3 wire systems

[Kartracer087]

After visiting California and noticing their electrical systems, I got thinking about their single phase services. Out there, the utility company connects all of their single phase pole transformers phase to phase and their three phase transformers in delta (primary), and I got wondering if they can do the same with pad mount transformers. Typically, I know that most single phase padmount transformers are mounted by connecting the primary winding phase to neutral, but has anyone ever seen connections on the primary winding be phase to phase on a single phase padmounted transformer for underground distribution?

I am mainly asking this since it appeared as though a lot of the areas I saw were on three wire distribution instead of the typical 4 wire multigrounded system (a few I saw were 4 wire).

 

[bob]

Out there, the utility company connects all of their single phase pole transformers phase to phase and their three phase transformers in delta (primary), and I got wondering if they can do the same with pad mount transformers. Typically, I know that most single phase padmount transformers are mounted by connecting the primary winding phase to neutral

That type of connection is used by some utilities. They are using a delta system and no need for the neutral. The single transformers are rated phase to phase voltage. A 13.2 system with a neutral is rated 7.6 kv phase to neutral. System with out a neutral would require the single transformer to be rated 13.2 kv. A pad mount transformer would also have to be rate for
the phase to phase voltage. The delta system is easier to maintain a balanced system.

 

[Kartracer087]

If they did connect between phase to phase, I would assume they would need to have two high voltage bushings (H1 and H2) instead of just using the H1 bushing and tank ground correct? I know the transformers typically have two bushings, H1A and H1B. The H1A and H1B are connected together for loop feed and the other side of the primary winding is then connected to the tank ground for using a 4 wire Y system connection for a single phase transformer. I can only assume that on a 3 wire system, the single phase transformer would have to have another high voltage bushing instead of just using the tank ground for the other side of the primary winding.

 

[bob]

If they did connect between phase to phase, I would assume they would need to have two high voltage bushings (H1 and H2) instead of just using the H1 bushing and tank ground correct? I know the transformers typically have two bushings, H1A and H1B. The H1A and H1B are connected together for loop feed and the other side of the primary winding is then connected to the tank ground for using a 4 wire Y system connection for a single phase transformer. I can only assume that on a 3 wire system, the single phase transformer would have to have another high voltage bushing instead of just using the tank ground for the other side of the primary winding.

Something like this.