Abstract: A power converter adapted for use in a high-voltage circuit and equipped with a plurality of arms each comprising a plurality of thyristor elements connected in series, wherein an overvoltage limiter having an overvoltage limiting element and means for short-circuiting the ends of the overvoltage limiting element in response to flow of a load current therein are connected between the anode and the cathode of each thyristor element. The short-circuiting means has a gap between the two electrodes connected respectively to the anode and the cathode of each thyristor element, and also a metal layer of a low melting point which is molten by heat generated due to the flow of a load current in the overvoltage limiting element to fill the gap.

Abstract: A lightning arrester comprises nonlinear resistance discs 2 stacked within a ceramic casing 1, with annular metal cover rings 3, 4 being fixed to the opposite outer ends of the casing. Conductive plates 5, 19 having reduced thickness rupturable central portions are sealed to the inner ends of the casing, with the lower plate 19 being insulated from the lower ring 4 by an insulating ring 20. An ammeter 16 is connected between the conductive plate 19 and ground by a lead wire 21 passing through the ring skirt but insulated therefrom, whereby only leakage current passing through the nonlinear resistance discs is sensed.

Abstract: A lightning arrester device for power transmission line comprises a lightning arrester comprising a sintered product made of a main component such as zinc oxide; a serial connection of a reactor and a fusible wire connected to the lightning arrester in series and a gap connected in parallel with the serial connection. The lightning arrester is disconnected from a power transmission line when the lightning arrester is broken.

Abstract: A main arrester body is formed of a stack of superposed nonlinear resistors composed of sintered zinc oxide and longitudinally disposed within an enclosed housing filled with SF.sub.6. A plate-shaped conductor extends from the higher voltage end of the stack to run radially outward and downward, and a lead is connected to the conductor to be transversely extended and sealed through the housing until it is connected to a horizontally disposed bus.

Abstract: In a grounded metallic housing of circular cross section three electrodes are disposed at equal angular intervals in a circle concentric with the housing to extending parallel to the axis of the latter. Three stacks of non-linear resistors are connected at one end to a corresponding one of the electrodes and at the other end to the peripheral edge of the bottom of the housing to be tilted radially outward.

Abstract: A protective device for protecting from abnormal voltage such as a lightning arrester comprises an earthing cylindrical metallic casing; an electrode or conductive substrate which is disposed to the direction of the axis of the metallic casing; an insulating pipe which is in spread-out shape and is disposed between the metallic casing and the electrode or the conductive substrate; and a plurality of non-linear resistors which are disposed in said insulating pipe wherein said non-linear resistors are respectively connected so as to be substantially similar to the potential distribution in said metallic casing.