GB346926A - Improvements in or relating to apparatus for measuring alternating electric magnitudes - Google Patents

Abstract

346,926. Current and pressure meters ; synchronism indicators ; power meters ; frequency measurements ; protective cut - out arrangements. SOC. ANON. OFF. ELETTROMECC. SCARPA ET MAGNANO, Via Fiume, Savona, Italy. March 4, 1930, No. 7079. Convention date, March 6, 1929. [Class 37.] A current transformer having an iron core M1 surrounding a bushing through which passes the conductor P1 is adapted also to measure voltage by providing a primary winding T1 connected between earth and a condenser coating C1 placed on the bushing and having capacity with respect to the conductor Pl. The winding T1 thus carries a capacity current proportional to the voltage. As shown, a second similar transformer is placed on the bushing of a second conductor P2 of the same phase and connected by a switch I to the conductor P1. The secondary windings S1, S2 are connected through switches 11 .. 14, k, and choking coils R1, R2 to an ammeter A and voltmeter V. With the switch k on the contact 10, switches I, 11 open, and switches 12, 13, 14 closed, the voltmeter V indicates the voltage between the conductor P2 and earth. Similarly by opening the switch 12 and closing the switch 11, the voltage of the conductor P1 is measured. By opening the switches 13, 14 and placing the switch k on the contact 9 the vectorial sum of these two voltages is measured, enabling the instrument to be used for synchronizing. With the switch I closed, switches 11 .. 14 closed, and the switch k on the contact 10, the currents induced in the secondary windings S1, S2 by the capacity currents in the windings T1, T2 are added in the circuit of the voltmeter V but annul one another in the circuit of the ammeter A. The currents induced by the current in the conductors P1, P2 are added in the circuit of the ammeter A but annul one another in the circuit of the voltmeter V. Current and voltage are thus separately measured. The apparatus may be modified for measuring power or frequency or for the operation of relays for remote control.