Patent GB-788224-A (GB)
Title: Spark gap device
IPC: H01T1/00
Filed: 1954-08-16
Abstract: 788,224. Protective arrangements. ALL. MANNA SVENSKA ELEKTRISKA AKTIEBOLAGET. Aug. 16, 1954 [Sept. 2, 1953], No. 23749/54. Class 38 (4). [Also in Group XL (a)] A high voltage spark gap device for protecting electrical apparatus connected in parallel therewith, comprising two electrode parts forming an ignition gap and two electrode parts forming a quenching gap, is characterized by means for producing a difference in potential between one of the electrode parts in said ignition gap and one of the electrode parts in said quenching gap after ignition, said difference in potential causing one arc root to jump from said ignition gap electrode part to said quenching gap electrode part, by means for moving the other arc root from the other ignition gap electrode part to the other quenching gap electrode part, and by means for directing a blast of quenching air towards the quenching gap. The device shown comprises a cylinder 2 of insulating material connected by a pipe 3 and a valve 4 to a container 5 supported on two insulators 6 and connected by a hollow insulating pillar 7 to a supply of compressed air. An ignition gap 21 is formed between two electrodes 19 and 20, and a quenching gap 18 is formed between a cylindrical electrode 16 and a hollow electrode 17. Electrodes 16 and 19 are connected together and through a coil 27 to a terminal 11. Electrode 17 is connected directly to a terminal 12 and through a resistance 26 to electrode 20. Terminal 12 is connected through an operating coil in the valve 4 to a terminal 15. The equipment to be protected is connected between the terminals 11 and 15 either directly or via a series impedance. When an over-voltage breaks down the ignition gap 21 the current flowing through the coil 27 produces a magnetic field which causes one arc root to move helically from the electrode 19 to the electrode 16, and the current flowing through the resistance 26 produces a voltage drop so that the electrode 17 assumes a lower potential than the electrode 20 and captures the other arc root. The magnetic field of the coil 27 causes the arc to rotate on the surfaces of the electrodes 16 and 17.. The current flowing through the operating coil of the valve 4 causes the latter to open. Air passing through the electrode 17 and the surrounding passage 25 quenches the arc. If necessary an additional air stream may be directed against the electrode 16, by means not shown, for quenching very high currents. Air passing through the passage 28 de-ionizes the ignition gap. A throttle device 29 may have a scale graduated in KV ignition value for a certain gap current or in KA gap current for a certain fixed ignition value, or the throttle device may be omitted. The quenching may be facilitated by connecting the gap 18 in series with a non-linear impedance. The electrode 17 may be a pointed rod and a permanent magnet may be used instead of or in addition to the coil 27. Movement of the outer arc root may be caused, or assisted, by a gas stream directed against the ignition gap 21. Two or more spark-gap assemblies may be combined in a single unit with a common support and/or with common valve operating means, and the throttle devices of the assemblies controlled by a common operating member.