Hydraulic tap changer

Claim 1

In a step-switching device for changing the taps on a transformer winding connected to a load line, the combination comprising a tap selector mechanism including at least two contact members movable sequentially along different taps of the transformer winding, a precontact switch including two stationary contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectively connectable with said stationary contacts, a first double-acting hydraulic motor the piston of which is connected to said movable contact member of said precontact switch, a resistance element connected between said movable contact member of said precontact switch and said load line, a changeover switch including two stationary contacts connected respectively with said movable contact members of said tap selector mechanism and a movable contact member selectably connectable with said stationary contacts, a second double-acting hydraulic motor the piston of which is connected to said movable contact member of said changeover switch, a vacuum switch connected between said movable contact member of said changeover switch and said load line, a third hydraulic motor the piston of which is connected to and controls the opening and closing of the contacts of said vacuum switch, a drive mechanism actuated in synchronism with said movable contact members of said tap selector mechanism, first and second single-acting hydraulic pumps the pistons of which are connected to said drive mechanism such that said hydraulic pumps execute pumping strokes in alternation as said drive mechanism executes consecutive movements correlated to consecutive movements of said contact members of said tap selector mechanism, a first set of outlet ports from said hydraulic pumps connected via hydraulic lines directly to opposite ends of the cylinder of said first double-acting hydraulic motor, a second set of outlet ports from said hydraulic pumps connected via hydraulic lines indirectly to opposite ends of the cylinder of said second double-acting hydraulic motor through a control valve, a third single-acting hydraulic pump connected to said drive mechanism such that said pump executes one pumping stroke for each movement of said drive mechanism, a hydraulic line extending from an outlet port from said third hydraulic pump to the cylinder of said third hydraulic motor at one side of the piston for twice actuating the piston and the vacuum switch contacts to open and closed position for each movement of said drive mechanism, and a hydraulic line extending from the cylinder of said third hydraulic motor at the other side of the piston therein to the cylinder of said control valve for actuating the piston therein to control flow of hydraulic fluid in the lines extending to the cylinder of said second doubleacting hydraulic motor.