On the basis of number of phases transformers can be categorized either as single phase or three. A single-phase transformer comprises of a single-phase primary and a single-phase secondary placed with either core or shell-type construction. On the other hand three phase transformer has three-phase primary and three-phase secondary that is placed with either core or shell-type construction.
The three-phase transformer can be constructed by connecting three single-phase transformers into a three-phase transformer bank.
| Feature/Type | Three-phase transformer | Three-phase transformer bank |
|---|---|---|
| Basic Construction | It comprises a common magnetic circuit for all three phases | Made by connecting three single-phase transformers |
| Number of magnetic circuits | It comprises of a common magnetic circuit for all three phases | It has separate magnetic circuits |
| Volume | Small | Large |
| Cost | Cheaper | Costly |
| Efficiency | High | Less |
| Installation | Easy | Difficult |
| Operations and Maintenance | Easy | Difficult |
| Units | Single unit | Multiple units |
| Faults and clearance | Difficult to clean, as it is a single unit | Easier to clean, as any single unit in which fault has occurred can be replaced |
| Type of connections (Star or Delta) | Can be connected in bothconfigurations | Can be connected in both configurations |