The coils are former wound and mounted in layers stacked with insulation between them. A shell type transformer may have a simple rectangular form (as shown in above fig), or it may have a distributed form.
(B) On the basis of their purpose
- Step up transformer: Voltage increases (with a subsequent decrease in current) at secondary.
- Step down transformer: Voltage decreases (with subsequent increase in current) at secondary.
(C) On the basis of type of supply
- Single phase transformer
- Three phase transformer
(D) On the basis of their use
- Power transformer: Used in transmission network, high rating
- Distribution transformer: Used in distribution network, comparatively lower rating than that of power transformers.
- Instrument transformer: Used in relay and protection purpose in different instruments in industries
- Current transformer (CT)
- Potential transformer (PT)
(E) On the basis of cooling employed
- Oil-filled self cooled type
- Oil-filled water cooled type
- Air blast type (air cooled)