Patent GB-852185-A (GB)
Title: Improvements in or relating to devices for measuring and regulating high voltages
IPC: G01R15/14
Filed: 1957-01-07
Abstract: 852,185. Measuring voltages; capacitors. PHILIPS ELECTRICAL INDUSTRIES Ltd. Jan. 7, 1957 [Jan. 10, 1956], No. 576/57. Class 37 [Also in Group XXXV] Apparatus for measuring and regulating a high direct voltage comprises a first high tension electrode 1 connected thereto, Fig. 1, partially screened by a second envelope electrode 2 from a third electrode 4; electrode 2 or 4 is caused to vibrate and these electrodes 2 and 4 are given an adjustable voltage V2 one with respect to the other, the shape and position of the electrodes 1, 2, 4 being such that the resultant A.C. induced in electrode 4 may be reduced to zero by adjustment of voltage V2. The envelope 2 has a partition 3 behind which the electrode 4 is situated, the capacity between electrodes 1 and 4 and between 3 and 4 varying periodically due to the vibrating electrode. The electrode 4 is earthed via a high resistor 5 and the adjustable voltage V2, opposite to that on electrode 1, is applied to envelope 2 from potentiometer 6 and measured by meter 10. If VI is the voltage on electrode 1 then for a given ratio of VI and V2 the A.C. in resistor 5 is zero, this being detected on meter 8 after amplification at 7. Apertures 31 in partition 3 are so proportioned that this ratio, which is dependent on the shape and position of the electrodes, is independent of small variations in the mean spacing between electrodes 4 and 3. Variations in capacity between 3 and 4 are greater than between 1 and 4 so that V2 is much smaller than VI and can be measured with high precision, this being a measure of VI. The electrodes are preferably housed in a vacuum or a high pressure gas-filled housing. In Fig. 2, not shown, the voltage on electrode 4 is adjustable to give zero deflection in meter 8 and the envelope 2 is earthed. In an embodiment (Fig. 3) for regulating a high voltage on electrode 1, a winding 15 fed from A.C. source 16 vibrates electrode 4 or partition 3, and the output voltage of amplifier 7 and an auxiliary voltage from source 16 are fed to a phase-sensitive detector 14 producing a D.C. voltage of polarity depending on the phase sense of the A.C. voltage across resistor 5, the D.C. voltage being applied to a regulating device 17 which regulates the alternating voltage supplied from terminals 30 to device 18, which may comprise a transformer and a rectifier, in such a manner that when the voltage at electrode 1 is unduly high a control operates to reduce this voltage and conversely. The voltage at electrode, 1 is adjusted to a desired value by. potentiometer 6. In a modified regulating device, (Fig. 4), the envelope 2 is secured to a metallic cylinder 19, 26 sealed in a vacuum tight manner to a glass cap 20. An apertured electrode 25 conductively connected by springs 24 to electrode 2 and cylinder 19, 26, has a fixed electrode 23 below it which is connected to earth via resistor 5 and a voltage source 28, the envelope 2 being earthed via cylinder 19. Electrode 25 is set into vibration so that the A.C. induced in electrode 23 is, when the voltages at 'electrode 1 is suitably adjusted compensated by A.C. resulting from differences, in the direct voltage between electrodes 23 and 25. A vibration exciter 21 supplied from oscillatory amplifier 16, sets the envelope 19, 20 vibrating by means of pin 22. The retroactive coupling required for exciting the oscillation is derived from a feedback electrode 27 opposite a conductive part of the vibrating electrode excited from D.C. source 29 and connected via a capacitor to the input of amplifier 16 which receives, due to the oscillatory movement of electrode 27, an excitation alternating voltage at the frequency thereof.