Fluid actuating device for an electric circuit breaker

A fluid actuating device for an electric switching apparatus such as a high-voltage power circuit breaker or the like comprising an actuator for actuating the electric switching apparatus, said actuator including a cylinder and an actuator differential piston movable in said cylinder between first and second positions corresponding to the open and closed positions of the switching apparatus, said actuator differential piston having two end-faces for receiving fluid pressure force;

• high-pressure fluid supply means for supplying fluid under high-pressure to said end-faces;
• a main-valve arrangement including a main-valve differential piston movable between two end positions for alternately interrupting and connecting the fluid from said fluid supply means to one of said end-faces of said actuator differential piston whereby said actuator differential piston is caused to move between said first and second positions, said main-valve differential piston having two end-faces fluidly connected to said fluid supply means;
• and, a control valve arrangement including a control differential piston movable between two end positions for interrupting and connecting the fluid supply from said fluid supply means to one of said end-faces of said main-valve differential piston, said control differential piston having two end-faces also fluidly connected to said fluid supply means, and control means for actuating said control differential piston in response to inputs for opening and closing the switching apparatus by alternately interrupting and connecting the fluid from said fluid supply means to one of said end-faces of said control differential piston;
• said other one of said end-faces of each of said differential pistons being connected directly to said high-pressure fluid supply means to cause the same to be subjected continuously to the pressure of said fluid, said other one of said end-faces of each of said differential pistons being smaller than said one end-face thereof;
• said actuator differential piston, said main-valve differential piston and said control differential piston being actuable exclusively by the pressure of the fluid of said fluid supply means whereby said two end positions of each of said differential pistons are maintained independent of the instantaneous value of the pressure of the fluid.