GB190521181A - Improvements relating to Electrical Measuring Instruments - Google Patents

Abstract

21,181. Varley, T. W. Oct. 18. Current and energy meters.-Stationary coils and movable coils are so arranged in connexion with permanent magnets that the distortion of the field - produced by the current in the former causes the rotation of the latter coils. The instruments may be arranged as watt-meters, watt-hour meters, ammeters, or volt-meters for either direct or alternating currents. In the watt-hour meter shown in sectional plan in Fig. 4, a permanent magnet 1 is provided with soft-iron pole-pieces 2 and a central core (not shown). On an aluminium cup 6 surrounding the central core are mounted windings arranged in this case to form a four-pole armature. The brushes 12, 13 are so arranged that in the undistorted field the armature is in balance. The stationary coils 14, 15, 16, 17, connected as a shunt to a resistance 19 in the main circuit, are so arranged that the current in them tends to shift the magnetic flux towards the pole-tips 20, 23. The armature is connected with an adjustable resistance 33 across the mains. In a modification, a two-pole armature is used, the stationary coils being arranged to shift the flux in a rotary direction. The pole-pieces may be slotted for the reception of the stationary coils. In the form shown in Fig. 5, a three-pole magnet is used, the central pole 36 being of opposite polarity to the outer poles 35. The latter are joined by a laminated soft-iron ring 37, surrounding a similar ring 38 mounted on the central pole. Stationary coils 49, 50 are mounted in slots 39 in the outer ring 37, one of them, 50, being connected with the main circuit and the other being connected in series with the two-pole armature to compensate for friction. This latter object may also be effected by a magnetic shunt consisting of a soft-iron bridge-piece 52, indicated in dotted lines. The retardation by eddy currents induced in the aluminium cup is unaffected by the distortion of the flux.