Patent GB-434110-A (GB)
Title: Improvements in and relating to instruments for measuring surge currents
IPC: A23C9/18
Filed: 1933-11-27
Abstract: 434,110. Current meters; magnetic measurements. BRITISH THOMSONHOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Foust, C. M. ; 47, Van Cortlandt Street, and Kuehni, H. P. ; 1298, Baker Avenue, both in Schenectady, U.S.A.) Nov. 27, 1933, No. 33189. Convention date, Nov. 26, 1932. [Class 37] An apparatus for recording surge currents in a conductor comprises a magnetizable element so constituted and arranged with respect to the conductor as to have its magnetization changed by the magnetic field due to the surge current from one predetermined valve or orientation to another and means for indicating or measuring the change in the magnetization of the element caused by the surge. In one form of instrument, the magnetizable element 13 may comprise a number of thin strips 12 of cobalt steel, or other material with a high degree of retentivity, in a non-magnetic casing 14, Fig. 3, or it may consist of small particles of magnetic material enclosed in a casing, Fig. 4 (not shown). In the instrument shown in Fig. 5, the element 13 is supported at the back of a bracket 18 carrying the instrument, the bracket being mounted close to the conductor 44 in which the surges are to be measured, in such a position that the axis of the element 13 is at right angles to the axis of the conductor. A bar-shaped magnetic member 25, preferably a permanent magnet, is mounted on a spindle 24 and is normally maintained in a position with its axis parallel to that of the conductor 44 by springs 27. When a surge passes through the conductor 44 the element 13 is magnetized, the bar 25 is deflected, and the deflection, which is proportional to the magnitude of the surge, is measured by a pointer 26 and scale 20. The spindle 24 also carries a flag 40 which is moved to a position in which it is visible through one or other of a pair of windows 38, 39, so that in cases where the instrument is placed in an elevated position, as in overhead transmission systems, it is possible to determine from the ground whether or not the instrument has been operated. In a modification, Fig. 7, (not shown), errors due to a change in the relative positions of the magnetic element 13 and the conductor are avoided by providing the instrument with a semicircular conducting strap partly surrounding the magnetic element, the strap being connected in series with the conductor in which the surges are to be measured. In another construction, Fig. 8, the instrument comprises a stationary magnet 54, so placed that it is not influenced by the current flow in the conductor 44, and a rotatably mounted disc 56 magnetized along a diameter. If a surge passes along the conductor 44, the axis of magnetization of the disc is varied, and the disc moves to a new position indicating the strength of the surge. The cover 19 of the instrument has a pointer 57 co-operating with a scale on the disc, the scale being visible through a window 58. One sector 55 of the disc is painted black and is normally opposite a second window 60, the remainder of the disc being painted white, so that any movement of the disc is rendered visible from a distance by the appearance of the white portion opposite the window 60. Another construction, Fig. 12, comprises two concentric strips of magnetic material 73, 74, the strip 73 being fixed and the strip 74 being rotatable from a normal position against the action of a spring 78. The conductor 82, in which the surges are to be measured, is connected in series with a rod 79. On the passage of a surge the strips are magnetized, and the strip 74 is rotated carrying with it a pointer 75 and a flag 76, which becomes visible through a window. The strips are demagnetized by passing alternating current through a coil 85 which surrounds them. The Specification as open to inspection under Sect. 91 comprises also methods of measuring surge currents in which magnetizable elements are placed in the vicinity of the conductor in which surges are to be measured and are subsequently tested to determine the degree of magnetization produced. One form of instrument for this purpose is similar to that shown in Fig. 5, but is provided with a recess at a fixed distance from the magnetic bar 25 in which the element 13 is placed after it has been magnetized. In another arrangement, Fig. 14 (Cancelled), the magnetization retained by the element 13 is measured by means of a ballistic galvanometer comprising a stationary coil 89 and a movable coil 92 rotatably mounted between the poles of a permanent magnet 91. The magnetized element 13 is placed within the coil 89 and released by drawing away a slide 104, the voltage thereby induced in the coil being measured by means of a mirror 102 and scale 103. The time elements and wave form of a surge may be determined by placing a number of magnetic elements having different degrees of retentivity in the magnetic field produced by the surge and separately testing the magnetization retained by the elements after the passage of the surge. This subjectmatter does not appear in the Specification as accepted.