Patent GB-292454-A (GB)
Title: Means for measuring electric tensions in electric transmission systems
IPC: G01R19/22
Filed: 1927-08-30
Abstract: 292,454. Siemens & Halske Akt.-Ges. June 18, 1927, [Convention date]. Current and pressure meters; calibrating instruments; pressure at distant places, measuring; thermal current and pressure meters. - In apparatus for measuring alternating current voltages, particularly the energy level in electric transmission systems, rectification of the alternating currents is effected by means of a valve rectifier connected in parallel or in series with a loading resistance having a value between that of the rectifier for negative and positive currents. In the example shown an alternating tension is supplied, for example from a buzzer G, to the distributor IV, from which there can be taken off a tension which is conducted either for measurement to other stations through the terminals S, or for calibration purposes to the grid of the ampliner valve R. This is connected through a variable resistance V and a capacity to a rectifier U, in which the grid and anode are connected. In parallel with this is connected a direct-current instrument A having shunt resistances R1, r1, the combined resistance of the ammeter A and resistance R1, r1 lying between the resistance values of the valve U for positive and negative currents. By adjusting the galvanometer A, the value of the input voltage can be read. For energy level measurements the scale of the instrument may be calibrated logarithmicallv in attenuation values so that the level may be read in neper units. Under working conditions the contacts 1 are closed, the instrument A reading the energy level at a distant station connected to terminals M, tension being also transmitted from the source G to a distant station connected to terminals S. For calibrating the instrument A at one particular reading, contacts 2 are closed, causing a current to flow from the heating battery H through the instrument A, resistances r2 and II, and the right-hand side of a therman cross K. The resistance II is adjusted to give the desired reading on the instrument A. Contacts 2 are then opened and contacts 3 closed, by which operation the resistance r3 is substituted for the instrument A in the circuit of the right-hand side of the thermal cross K, the lefthand side of which generates a current passing through a resistance III to the instrument A. The resistance III is adjusted to give the same reading on the instrument A as before. Contacts 3 are then opened and contacts 4 closed, causing alternative current from the source G to pass through the right-hand side of the thermal cross K. This current is adjusted by means of the resistance IV until the previous reading is obtained on the instrument A. Contacts 4 are then opened and contacts 5 closed, replacing the thermal cross by the resistance r6 and supplying the adjusted alternating voltage through a transformer T to the grid of the amplifier R. The anode resistance V is then adjusted in order to obtain the previous reading on the instrument A. The operation of the various contacts during the process of calibation is preferably effected by means of a roller switch.