Patent GB-191009580-A (GB)
Title: Improvements in and relating to Alternating Current Power Measurement and Instruments for the same.
Inventor: ARNO RICCARDO
IPC: G01R11/48
Filed: 1910-04-20
Granted: 1911-07-20
Abstract: 9580. Arno, R. April 20. Power meters; induction motor meters; combinations of instruments; power factors, measuring; rate, changing.-A power or energy meter which takes account of the proportions of cost due to the useful current and watt-less current, measures the sum of the true power and a fraction of the difference between the apparent and true power, the value of the fraction being about one-third. The quantity thus obtained is called the " compound " power or load. By changing the fraction to unity, the apparent power or load in a circuit may be measured. The voltage coil of the ordinary moving-coil or induction instrument is arranged so that the flux is out of phase with the potential difference by an angle which may be 5¢ degrees for a moving-coil instrument, or 95¢ degrees for an induction instrument, used for measuring " compound " power on an ordinary lighting circuit, and 13 degrees and 103 degrees for measuring apparent power, the corresponding angles for instruments used in power circuits being 15 degrees, 105 degrees, and 42 degrees, 132 degrees. An instrument of this type may be used with an ordinary wattmeter for measuring the power factor, two scales with pointers crossing each other being used as shown in Fig. 16, or the two instruments may be combined to form a single instrument. The instruments may also be adapted for use as integrating or recording instruments and as maximum demand indicators. In a balanced 3-phase circuit, a single instrument may be used, the voltage coil having a phase displacement between the flux and the potential difference, and being connected so as to use any of the E.M.F's and phase differences in the circuit. For instance, in the arrangement shown in Fig. 2, the voltage coil S0 has a phase displacement of 45 degrees and is connected across the line E.M.F. c, a which leads the phase potential difference between o and a by 30 degrees. For measuring on an unbalanced 3-phase circuit, two instruments may be used having phase displacements of 24 degrees and 5¢ degrees, or 30 degrees and 0 degrees in the case of moving-coil instruments, or 114 degrees and 95¢ degrees or 120 degrees and 90 degrees in the case of induction instruments, one of these being an ordinary wattmeter. Other phase displacements may be used. The phase displacements may be obtained by means of an inductance coil in series with the voltage coil, and by utilizing the phase differences existing between the phases and line E.M.F.'s. Thus in the arrangement shown in Fig. 6, the voltage coil Sv<I> of one instrument has a phase displacement of 30 degrees and is connected as in the ordinary two wattmeter method, the voltage coil Sv<II> of the other instrument having a phase displacement of 30 degrees and being connected across the phase o, b which leads the line E.M.F. between band c by 30 degrees. Instead of using the neutral point as shown in Fig. 6, the single coil Sv<II> may be replaced by two coils connected across c, b and a, b. Apparent power or load can also be measured by means of two instruments having phase displacements. Specifications 25,746/99 and 10,134/00 are referred to.