Patent GB-804940-A (GB)
Title: A device for recording transient electric voltages
IPC: G01R19/00
Filed: 1955-05-03
Abstract: 804,940. Measuring peak transient voltages and currents. LICENTIA PATENT-VERWALTUNGS-G.m.b.H. May 3, 1955 [May 3, 1954], No. 12810/55. Class 37. A device for measuring the peak values of transient voltages comprises high-vacuum valves 5, 6, measuring condensers 7, 8 which may be connected alternately through switches 9, 10 firstly through the valves 5, 6 to the source of charge voltage and then to discharge through the switches, an amplifier 13, and a registering apparatus 14. A high-voltage conductor 1 is connected to two measuring systems each consisting of a vacuum valve 5 or 6 and a measuring condenser 7 or 8 through a high-voltage condenser 2 and a low-voltage condenser 3. The switches 9 and 10 are rotated by an electric motor 20 and in the Figure the condenser 7 is measuring while the condenser 8 is connected via a screened cable 12 to a high-resistance amplifier 13 and a chopper bar recording device 14. Thereafter the motor 20 makes the switch 19 to connect the condenser 8 to earth and erase the measurement so that the recorder 14 returns to its zero position. The switching devices continue to rotate, connecting the condensers 7 and 8 to measurement and recording positions alternately, and the switches 9 and 10 are set to permit a small angular overlap during which time both 7 and 8 are ready for operation during a short period so that there is no gap in respect of ascertaining a magnitude to be measured. Damping resistances 15, 16 and 17 are provided for suppressing disturbing equalizing phenomena. The capacity of the cable 12 with the condenser 11 and the amplifier 13 is several times greater than the capacity of the condensers 7 and 8, and the input voltage of the amplifier is several volts whilst the condensers 7 and 8 operate at a range of peak voltages from 100 to several thousand volts. As a result of this leak resistance is reduced in importance due to the high relative capacity of the amplifier etc.; and the cable 12 may therefore be very long. If it is required to record separately excess voltages of both polarities then two additional measuring systems consisting of valves, condensers and change-over devices are required, but if the switching times are suitably chosen only one amplifier and one recorder 14 is required, and the recorder may be designed as a two-colour recorder, one colour for each polarity, or even as a four-colour recorder. Voltages having a certain minimum magnitude can be recorded by providing a relay spark gap in series with a small condenser and connected in parallel with the condenser 3, which spark gap energizes a further relay causing the switching motor 20 to perform one revolution. For measuring high voltages the recording device may be connected to the plates of capacitances such as are often built into condenser bushes of high-voltage apparatus, or current transformers may be provided with such bushes. The peak values of electric currents may be measured by means of a wide-band amplifier producing a voltage suitable for the measuring apparatus, and a current transformer may be used having a secondary winding with a large number of turns so that this winding may be loaded by a highresistance resistor and voltages derived therefrom. It is advantageous to transform the current in two current transformers connected in cascade. Non-electric magnitudes such as velocities &c. may be measured provided they may be represented by voltages. A mathematical equation is derived for determining the capacity of the measuring condenser and resistances of the vacuum valves which will enable excess voltages of microsecond duration to be measured. In this connection it may be desirable to heat the diode below normal and provide it with a thorium-coated filament, and it is also desirable to accommodate the measuring device in a dry airtight casing. If it is required to use high-vacuum valves then two measuring systems are necessary for measuring magnitudes of both polarities, but if polarity is not to be determined then the apparatus may be such that the condensers are charged through four valves in a bridge rectifier connection.