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Substation and Pad Mounted Transformers Compared
Both step distribution voltage down to utilisation voltage. The difference is how they connect and who owns them.
| Substation transformer | Pad mounted transformer | |
|---|---|---|
| Enclosure | Open frame, or close coupled to switchgear | Self contained locked cabinet |
| Connection | Bolted throat to primary and secondary gear | Cable, elbows on the primary |
| Location | Indoors or in a fenced yard | Outdoors at grade, public accessible |
| Ownership | Usually the customer | Often the utility, sometimes the customer |
| Typical rating | 750 kVA up to several MVA | 45 to 2500 kVA |
| Who specifies | The electrical engineer | The serving utility standard |
| Primary connection | Bolted bus or cable throat | Load break elbows on dead front bushings |
| Secondary connection | Close coupled to switchgear | Cable to a panel or switchboard |
| Weather | Often indoor or under cover | Fully outdoor rated as supplied |
| Maintenance access | Requires an outage and qualified staff | Front access, locked, utility serviceable |
Which you actually need
If the utility owns the transformer and the service is underground, it is a pad-mount and the utility standard governs everything about it. If you own it and it feeds your own switchgear, a unit substation is often the better answer above about 1000 kVA.
Above roughly 1000 kVA the question usually resolves itself. A unit substation close coupled to your own switchgear removes a set of cable terminations and is easier to protect selectively, so it tends to win on larger customer owned services.
Below that, and wherever the utility owns the transformer, a pad-mount is nearly always what gets installed, because the utility standard says so and the utility standard is not negotiable.
Working from a specification that uses one of these terms loosely? Send it over and we will tell you which equipment it is actually calling for, before you order the wrong thing. Get a quote or call 786 220 2801.