GB190218766A - Improvements in Alternating Current Electricity Meters. - Google Patents

Abstract

18,766. Ferranti, S. Z. de, and Hamilton, W. Aug. 26. Energy meters.- Relates to watthour meters of the induction - motor type for alternating currents. In the form shown in Fig. 1, a series magnet c is placed below a rotary disc a, and a magnet b excited by a shunt coil d is placed with its pole above the disc, and opposite the gap between the poles of the series magnet. In order to increase magnetic leakage, the lower end of the core b is thickened, and it is fitted with side arms. The effect of the magnetic leakage is to produce a difference of phase between the current induced in the disc by the shunt magnet and the currents induced by the series magnet, and thus cause the disc to rotate at a rate proportional to the watts. The difference of phase should be 90‹, and it may be adjusted by displacing the coil d on its core or by the use of non-inductive resistances. In other forms of the instrument, multipolar magnets are used. Fig. 6 is a section of an instrument of this kind. The shunt magnet, which is placed below the disc, is of the cylindrical type, the shunt coil d being placed on the central core n. The polar ends of the cylinder m and core n divide into a number of equidistant pieces o, r, Fig. 7, which follow each other alternately. The polar surface of the series magnet is divided into equal sections by a number of radial grooves, in which the series wire is wound backwards and forwards. Permanent magnets s are used to brake the disc. In order to obtain a weak torque to overcome the friction of the meter, the shunt magnet is mounted so that it can be slightly displaced to right or left, or the same result may be obtained by replacing one or more of the shunt poles by adjustable iron poles magnetically insulated from the action of the shunt coil. In the case of a three-phase circuit, two meter elements are considered to be sufficient, though more may be used.