GB765177A - Improvements in or relating to electrical switches of the kind utilising a conducting liquid - Google Patents

Abstract

765,177. Mercury and other conducting- liquid switches. NATIONAL RESEARCH DEVELOPMENT CORPORATION. July 14, 1953 [July 9, 1952], No. 17259/52. Class 38(5) [Also in Group XXXVI] Conductor parts 1, Fig. 1, are separated by a narrow gap 2 which is bridged by mercury or other conducting liquid 3 on which the current flowing through the conductor exerts a pinch effect. When the current is sufficiently large to cause the pinch effect to overcome the surface tension of the liquid, the latter is squeezed into a central cavity 4 and the circuit broken. Magnetic material may be used in the gap to augment the pinch effect. Fig. 3 shows an automatic. circuitbreaker in which the gap 2 is shaped to contain the liquid 3 by gravity. A fusible metal such as tin-lead alloy may be used in the gap, such metal liquifying before an overload occurs. In Fig. 4 a duct 8 communicating with the gap 2 is brought out through the side of the conductor and is connected to a valve V1 and a vertical tube 7 carrying a contact 9. When the current attains a predetermined overload value, the pinch effect in the gap 2 drives the liquid up the tube 7 until it completes a circuit through contact 9 to a motor M for operating valve V1. On opening of the latter, the liquid drains from the gap and the duct. It may be assisted by gas blown into a chamber 10 surrounding the gap. Alternatively the tube 7 may terminate in a reservoir into which the liquid is driven. In Fig. 5 one of the conductor parts is extended into the duct in the other part as a tongue 15 of resistance metal and means are provided for raising and lowering the level of liquid 3 to vary the amount of series resistance between the parts. Overload protection is provided by a tube 18 and contact 9 as in Fig. 4. The tongue 15 may be brought out through an insulating bush 19, Fig. 6, in the side of the conductor and connected to the duct through a switch 20 capable of operating at the reduced current when all the resistance is in circuit. This switch is opened after the liquid has broken contact with the tongue, to avoid sparking. Specification 765,178 is referred to.