problem with hydraulic spring operating mechanism generator circuit breaker


Thread Starter


We use in our power plant generator circuit breaker type ABB HMB 4.5 2CO and i have problem with the pump.

The pump is not working for a long time (days).

Can you explain somebody if i take a trip the breaker will open? Do i have sufficient hydraulic oil pressure to have a breaker opening in case of a trip? How can i understand that i have enough oil pressure to open the breaker?

All i can see is the energy storage device, position (compressed-expanded) through a small window. In what position should it be?
Dear Sir,

That seems to be an usual issue with an operated mechanism where fluids are used to store energy:
--> Fluids under pressure = gaskets = possible leakages = risk !

Depending on the age of your installed equipment, you should move on cutting-edge technology for such equipement, I think about full spring operated mechanism.
Thank you very much for reply. I would also like to ask you if you have any suggestions for the existed equipment.



I do not have experience of the ABB breakers. However, from experience with others, the design is usually failsafe - i.e. if there is a failure, the breaker can be opened - but it cannot be closed.

With ones I have experience on, the charging mechanism [which in your case is hydraulic] loads a spring system; then the breaker is closed with one of the springs. The closing of the breaker loads another spring which is then tensioned to allow the breaker to be opened later.

I would GUESS that you can open the breaker - but it would be wise to check the actual operating manual for the breaker etc.


(i) Is your plant connected to the grid?
(ii) Do you have more than one generator?
(iii) How did you know that the pump was not working?
(iv) Do you have drawings, manuals for the breaker?
You need to check your breaker manual to confirm this. The breaker interlock diagram usually states whether the breaker could be operated with low pressure condition.

Based on my experience, (ABB pneumatic GCB and Alsthom hydraulic GCB) both could not be operated in low pressure condition. The spring tension is only meant to assist only.

Please check and get some assistance from OEM to address the matter ASAP if the breaker has interlock to avoid operation in low pressure condition.

This is crucial as if the unit trips, the GCB would not open and lead into generator motoring.

Good Luck!
ABB Manual/Generator Circuit-Breaker Systems HECS, HEC 7/8

"The operating mechanism is based on the so-called differential piston principle (between the larger piston head side area and the smaller piston rod side area). For the closing operation the piston head side is isolated from the low pressure and simultaneously connected to the high pressure oil volume. As long as the pressure is maintained, the piston remains in the "CLOSED" position. A pressure controlled mechanical interlock prevents movement of the piston to the OPEN' position in case of a pressure drop."