ABB 380kV Circuit Breaker (Hydromechanical Spring Drive HMB-1)

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Each HMB-1 employs a two-stage control module to actuate its motion -- the pilot stage and the main stage. This eliminates need for high force control coils due to the reduction of the inertia load of the actuating method. Moreover, initiating main spool motion within the control module by hydraulic fluid eliminates valve seating concerns, an otherwise potential issue with direct fastacting coil operation.
This configuration results in highly consistent breaker operating times, a prime requirement for reliable synchronous switching operation. The two-stage configuration has been a standard feature on ABB’s higher energy AHMA and HMB-4/8 class springhydraulic mechanisms, providing excellent performance history.

Closing
In the pilot stage, following close solenoid energization, high pressure fluid (red areas) passes through its pilot valve and enters the control module where it imparts the main spool.
In a second activity stage, fluid pressure drives the main spool in a direction which permits high pressure flow to the piston in the operating cylinder.
With high pressure fluid now imparting both sides of the piston, the greater force is on the piston head due its larger surface area. That force moves the drive rod, closing the breaker contacts.

Tripping
The pilot stage of a trip operation begins upon activation of its solenoid, which permits the high pressure fluid previously held on one side of the valve to continue through the unit and enter the control module.
Within the module, the resulting force differential on the main spool reverses its position. (Low pressure areas shown in blue.) The new position permits the high pressure fluid formerly imparting the drive piston, to flow through the control module and return to the mechanism’s low pressure reservoir.
The now unbalanced pressures on either side of the piston redirects the drive rod, thereby opening the interrupter contacts.