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Operating mechanism HMB

Operating mechanism for high voltage circuit-breakers from 52 to 1,100 kV

High degree of acceptance worldwide

  • More than 20 different manufacturers with more than 100 switchgear applications trust in HMB operating mechanisms for their high-voltage circuit-breakers. Up to now, more than 110’000 units of HMB and its predecessor have been delivered.

HMB, if “time-to-market” is critical

  • Each of the operating mechanisms of the entire HMB family comes as a single unit, combining in a modular design all the functional components. Combination of standard modules with specific modules results in the required variant of the operating mechanism. Prior to the delivery the product is submitted to the most stringent quality and functional testing. Owing to the well devised adaptation program, it takes only a few steps to provide the user with an optimized system of circuit-breaker and operating mechanism.


  • Live tank breakers (LTB)
  • Gas-insulated switchgear (GIS)
  • Dead tank breakers (DTB)
  • Hybrid systems
  • Operating mechanisms of type HMB are also used for breakers outside the high-voltage application: Generator circuit-breakers (GCB)

Why Hitachi Energy?

  • 30 years of experience in design and manufacturing of operating mechanism
  • More than 110,000 mechanisms produced
  • More than 100 different product applications
  • Low life cycle costs due to minimum maintenance requirements and modular design
  • Highest power density in the market for compact switchgear designs
  • Easy and fast adaptation on new circuit-breaker applications
  • Long term stability







Stored operating sequence






Stored energy, last O [kJ]

0.8 / 1.7

2.3 / 2.7

3.7 / 5.3

8.1 / 11.8

19.6 / 21.7

Stored energy, last C [kJ]

0.4 / 0.8

1.0 / 1.2

2.0 / 3.0

3.0 / 4.8

5.1 / 7.4

Stroke [mm]

75 / 115


205 / 220 / 230

180 / 205

205 / 230

O = Opening of the circuit-breaker; C = Closing of the circuit-breaker
Specifications are subject to change without notice

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