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The type DTW™ de-energized tap-changer of Hitachi Energy is a versatile tap-changing switch, which is mounted inside the main transformer compartment attached to the cleat and lead structure of the transformer. The tap-changer is a modular design, which allows a wide variety of configurations to suit the needs of the transformer designer.

The tap-changer can be applied through a BIL of 1,050 kV and has a base current rating of  845 A per deck. Each phase of the transformer requires at least one deck module of the tap-changer. Using multiple deck modules per phase extends the range of the tap changer to many different winding configurations.

Operation of the tap-changer is via a manual gearbox mounted on the exterior surface of the transformers. The switch is suitable for use as a dual voltage switch or as a delta-wye switch with appropriate modifications.


Product scope

  • Maximum rated through-current: 3400 A (850 A per deck)
  • Highest rated lightning impulse/power frequency withstand to earth: 1,050 kV / 460 kV
  • Lightning impulse/power frequency withstand between adjacent contacts: 180 kV / 75 kV (when contacts B and E are removed, 280 kV / 110 kV)    
  • Maximum number of operating positions: 5


Why Hitachi Energy for DTW™ de-energized tap-changers?

  • The DTW tap changer is extremely versatile due to its modular design
  • BIL and current rating cover a broad range of transformer applications

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