Tap changer having a vacuum interrupter assembly with an improved damper

An on-load tap changer, comprising:

• a vacuum interrupter assembly for immersion in a dielectric fluid, the vacuum interrupter assembly comprising:
• (a.) a vacuum interrupter with contacts;
• (b.) an actuation assembly having a shaft connected to the contacts of the vacuum interrupter and operable upon movement to open and close the contacts;
• and
• (c.) a damper operable to dampen the movement of the shaft, the damper comprising:
• a housing having a wall with an opening and defining an interior chamber into which the shaft extends, the interior chamber being in communication with the opening;
• a piston disposed in the interior chamber and secured to the shaft so as to be movable therewith, the piston having one or more first openings and one or more second openings, the one or more first openings being larger than the one or more second openings;
• a blocking structure disposed in the interior chamber such that the piston is disposed between the opening and the blocking structure, the blocking structure having a body through which the shaft movably extends, the blocking structure being movable between being proximate and distal to the piston, wherein when the blocking structure is proximate to the piston, the blocking structure closes the one or more first openings, but not the one or more second openings, and wherein when the blocking structure is distal to the piston, the blocking structure does not close either the one or more first openings or the one or more second openings ;
• a spring biasing the blocking structure toward the piston;
• wherein during the movement of the shaft to close the contacts, the blocking structure is disposed proximate to the piston;
• and
• wherein when the shaft moves to open the contacts, the blocking structure moves against the bias of the spring to be distal from the piston, thereby opening the one or more first openings.