Pad Mount Transformer
A pad-mounted transformer is a ground-level electrical distribution transformer installed on a concrete pad inside a locked, grounded metal cabinet. It steps down utility primary voltage to a lower secondary voltage for customer use, typically on underground distribution systems. CSA C227.4:21 defines it as a three-phase, 60 Hz, liquid-filled unit with a cable entrance compartment and separable insulated high-voltage connectors, up to 3000 kVA and 34.5 kV.
On a shop floor or industrial site, pad-mounted transformers are built as self-contained steel enclosures with transformer tank, primary cable compartment, secondary compartment, grounding provisions, and tamper-resistant access. They are installed outdoors on a pad, allowing placement in accessible areas without a fenced enclosure. Maintenance personnel interact via dead-front separable connectors and hot sticks, avoiding exposed live conductors. Safety focuses on clearance, guarding, locking, and access control due to energized medium-voltage equipment and flammable insulating fluid.
What makes a pad-mounted transformer different from a pole-mounted transformer?
It is ground-installed on a pad, fully enclosed in a grounded steel cabinet, and commonly used with underground distribution rather than overhead lines.
What does 'dead front' imply in practice?
The user should not encounter exposed energized parts during normal operation; access to primary connections is through separable insulated connectors and compartmented construction.
Why are these units considered high-consequence electrical equipment even though they are 'locked boxes'?
Because they still contain medium-voltage primary circuits, transformer oil or other dielectric fluid, and fault energy; the enclosure reduces access but does not remove electrical hazard.