Patent GB-367244-A (GB)
Title: Means for measuring high electrical potentials, more particularly in rontgen installations
IPC: G01R15/14
Filed: 1931-05-01
Abstract: 367,244. Pressure meters ; resistances. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. May 1, 1931, No. 12958. Convention date, July 4, 1930. [Class 37.] For measuring high potentials with a potential dividing resistance or a series resistance, this resistance is composed of helically-arranged elements and is arranged in a container filled with insulating liquid such as oil. As shown in Fig. 1, a potential-dividing resistance 3 is connected between the high-potential lines 1, 2, and consists of elements such as hard carbon layers applied to a glass or porcelain rod with terminal metal caps. The caps are soldered together so as to form a helical assembly of elements, which is arranged inside an insulating container 4 filled with oil or other liquid insulating medium for equalizing the temperature of the various parts. Around the container 4 is arranged a " potential cage " consisting of a helical hard carbon strip resistance 5 connected between the lines 1, 2, so that its potential at any point corresponds with that of the adjacent point of the resistance 3, thus minimizing discharge currents and capacity effects. The measuring instrument 8, for example an electrostatic voltmeter, is enclosed in a metallic container 9, which is connected to a suitable potential in order to screen the instrument. The potential applied to the instrument is tapped from the part 3a of the resistance 3. In order to balance the effect of the capacity of the instrument 8 in parallel with the element 3a, a condenser is connected across the remaining part of the resistance 3. This condenser may consist of a strip 10, Fig. 2, of dielectric, on opposite sides of which coatings 10a are arranged in staggered relation, so as to form a number of part condensers in series. The condenser 10 is inserted in the container 4 in helical form as shown in Fig. 1, one end being connected to the line 1 and the other end to the tapping lead 6. The potential distribution along the condenser is similar to that along the resistance 3, which it assists in screening. The ratio of the capacity across the points 1, 6 to that across the section 3a is adjusted by means of a variable condenser 11 in parallel with the instrument 8. For measuring peak values, for example in R÷ntgen installations, a condenser 14 is connected in parallel with the instrument 8 and with a leakage resistance 15. A glow-cathode rectifier 12 is connected in series with the tapping lead 6, its cathode being supplied with heating current from a battery or from the heating transformer of the R÷ntgen tube. For measuring effective value of the potential instead of the peak value, the rectifier 12, condenser 14, and resistance 15 are dispensed with. Instead of the strip condenser 10, the condenser shown in Fig. 3 may be employed. This consists of a tube 16 of porcelain or other dielectric, which is provided with inside and outside coatings 16a displaced with respect to one another. This condenser may be arranged in the axis of the resistance 3, as shown in Fig. 5. In this modification the " potential cage " consists of resistance elements 17 connected by wires 18, which may form a foursided assembly, as shown, or one of triangular section. A second measuring resistance 3, constructed as shown in Fig. 1, may be connected between the measuring apparatus and the line 2, the potential applied to the measuring instrument being tapped from the sections on each side of the instrument. The casing 9 may in this case be earthed.