Composition of ring main unit

The ring main unit generally consists of four parts: switch room, fuse room, operating mechanism room and cable room (chassis).

The switch room is composed of various functional circuits (including earthing switches and load switches) sealed in the metal shell and the bus bars between the circuits. The shell is welded by 3mm cold-rolled steel plate (or non-embroidered steel plate). Each functional circuit includes a load switch and grounding switch. The load switch is composed of a vertically moving moving contact system and a static contact located at the lower end. When the switch is closed, the moving contact moves downward and the load switch is turned on. The grounding switch is composed of a moving contact blade and a static contact blade. During the movement of the spring, the grounding switch is quickly turned on. There are 4 rectangular assembly process holes in the upper and rear of the switch room. The front of the ring main unit is equipped with an observation window, which can see the "open" and "close" positions of the grounding switch. An explosion-proof device is installed at the rear of the ring main unit.

The load switch adopts a compressed air blowing structure, which has strong arc extinguishing ability and does not affect the insulation between phases and ground. Both the dynamic and static contacts have arc contacts, which greatly improves the breaking times.

The fuse and the load switch room constitute the transformer protection circuit. The high-voltage current-limiting fuse is installed in an epoxy-cast insulating shell. After the fuse is blown, the striker is ejected, and the load switch is opened.

The operating mechanism room is located in front of the ring main unit. In each functional circuit, the load switch is equipped with a human (or electric) energy storage spring operating mechanism, the grounding switch is equipped with a human energy storage spring operating mechanism, and the panel is equipped with a load switch closing operation and manual opening respectively. The opening and closing operation holes of the rotary knob and the grounding switch, the opening and closing position indicator lights of the load switch and the electric opening and closing buttons are provided with analog lines, switch status display cards and lock positions. The operation of the load switch and earthing switch has an interlock to prevent misoperation.