GB190501563A - Improvements in Electrical Measuring Instruments. - Google Patents

Abstract

1563. Field, M. B. Jan. 26. Energy meters; testing.-A watt-meter is proprovided with two or more separate scales and arranged in connexion with switches and resistances or transformers to read either the true power or the product of the electric pressure and the idle current in a circuit. If the pressure be constant, the instrument may also be graduated to read the idle current directly. The instrument is arranged to indicate on either side of the zero according to whether power is being generated or absorbed, or whether the current is lagging or leading in the circuit, the scales being suitably marked to that effect. The change-over switch may be arranged as part of the instrument itself or may be placed at a distance, and is provided with a spring to keep it in the position for indicating the power, when released. For a single-phase circuit, with a watt-meter of the dynamometer type, a large non-inductive resistance and a highly inductive resistance may be substituted for one another in the pressure circuit. For a two-phase circuit, the connexions are arranged as in Fig. 2. The current coil D' of the watt-meter is connected in one of the mains directly or through a transformer E, and the pressure coil D<2> is connected by means of a single-pole two-way switch S to the secondary of either a pressure transformer F between the mains of that phase, or of a similar transformer F<1> between the other mains. The phase of the latter being at right-angles to that of the former, the readings give the true watts and the "idle watts" respectively. For a three-phase circuit with a balanced system, a single watt-meter D<2> may be connected as shown in Fig. 3. The secondaries of the pressure transformers F, F<1> are connected in series in the circuit of the pressure coil D<2>, and by means of the double-pole switch S the connexions may be reversed ; by provision of a connexion between the centres of the secondaries of the pressure transformers, a single-pole switch may be used. In another arrangement, the primary of one pressure transformer is connected between the main in which the current coil is connected and the mid-point of another primary connected between the two other mains ; the secondaries may be substituted for one another in the pressure coil circuit. When two watt-meters are employed in a three-phase circuit, a single-pole two-way switch is arranged to connect the pressure coil of one instrument to the secondary of either pressure transformer.