Arc extinguishing apparatus for ring main unit

An arc extinguishing apparatus for a ring main unit, the apparatus comprising:

• a housing in which an insulating gas is charged;
• a plurality of fixed contactor assemblies for an electric power circuit fixed to be protruded toward a center in the housing and formed by inserting a permanent magnet for arc extinguishing by a magnetic force between a pair of main circuit fixed contacts;
• a plurality of earthing fixed contactors fixed to be protruded toward the center in the housing and installed to be spaced apart from the fixed contactor assemblies at a predetermined angle;
• a rotational shaft, which is common to three phases, installed to be rotatable at the center of the housing;
• and
• a rotatable movable contactor assembly formed to extend from the rotational shaft, having a plurality of puffer guide plate sections having opening portions with a narrow opening width to accelerate the velocity of flow of insulating gas to extinguish arc by blowing it, and rotatable to a circuit closing position in which the rotatable movable contactor assembly is in contact with the main circuit fixed contacts of the fixed contactor assembly, an earthing position in which the rotatable movable contactor assembly is in contact with the earthing fixed contactor, and a circuit opening position in which the rotatable movable contactor assembly is separated from the main circuit fixed contact and separated from the earthing fixed contactor, according to a rotation or the rotational shaft,
• wherein each of the fixed contactor assemblies comprises an insulating cover having a width larger than that of the main circuit fixed contact and made of an electrical insulating material, and the puffer guide plate section allowing the fixed contactor assembly for a power circuit to enter when the movable contactor assembly operates to a circuit closing position has an opening portion having a width which is large at an end portion thereof to allow the insulating cover to pass therethrough and becomes narrower toward the rotational shaft to allow the main circuit fixed contact to pass therethrough,
• wherein the insulating cover comprises a cutaway portion formed to be trimmed slantingly to have a width reduced toward the permanent magnet, so as to freely pass through the opening portion of the puffer guide plate section when the movable contactor assembly operates to the circuit closing position or the circuit opening position.