VFI Transformer


The three-phase VFI Transformer is designed for commercial or industrial applications where conventional transformer or loop protection packages are inadequate, or where space limitations prove to be restrictive. The compact design simplifies installation and requires less real estate than conventional transformer/switchgear packages.

The VFI transformer combines a conventional Cooper Power Systems distribution transformer with the proven Vacuum Fault Interrupter (VFI). This combination provides both voltage transformation and either transformer or loop overcurrent protection in one space saving, money saving package.

The three-phase VFI transformer with transformer protection protects the transformer and provides proper coordination with upstream protective devices. When a transformer fault or overload condition occurs, the VFI breaker trips and isolates the transformer, leaving the feeder uninterrupted. The three-phase VFI transformer with loop protection protects the loop or downstream section of a feeder. When a fault occurs downstream, the VFI breaker trips and isolates the fault, leaving the transformer load uninterrupted.


kVA 45-7500
Primary Voltage 2400-34,500 V (150 kV BIL) Delta or Wye Connected
Secondary Voltage 208Y/120 V to 24,940 V


  • The three-phase VFI breaker has independent single-phase initiation, but is three-phase mechanically gang-tripped.
  • A trip signal on any phase will open all three phases, eliminating single-phasing of three-phase loads.
  • The VFI breaker may be used as a threephase loadbreak switch.
  • Resettable functionality makes restoring three-phase service faster and easier.
  • High efficiency rectangular wound core design offers low excitation current, low losses, and quiet performance.
  • The coils are made compact, rigid, mechanically strong, and electrically balanced with impedances in accordance with ANSI C57.12.26.
  • Available with mineral oil or Envirotemp™ FR3™ fluid
  • Tanks are formed of precision cut cold-rolled steel.
  • Patented high security features exceed ANSI requirements.
  • An advanced multi-stage finish process exceeds ANSI standards.

Envirotemp™ and FR3™ are licensed trademarks of Cargill, Incorporated.