Patent GB-510982-A (GB)
Title: Improvements in the protection of electrical plant and apparatus from lightning flashes and/or from electrical disturbances caused by lightning flashes
IPC: H03G11/00
Filed: 1938-05-03
Abstract: 510,982. Protective arrangements. SCHONLAND, B. F. J. May 3, 1938, No. 13193. [Class 38 (iv)] [Also in Groups XXXVII and XL] A method of protecting electrical apparatus from destructive or obnoxious disturbances caused by lightning includes the step of utilizing the characteristic frequency of the innocuous phenomena of the preliminary discharge which precede the main discharge to initiate switching operations by which means the apparatus is rendered immune, for a time interval of sufficient length substantially to cover the duration of the main discharge, from the waves or surges which are caused by the main discharge and which produce the destructive phenomena. The innocuous phenomena of the preliminary discharge comprise a train of luminous impulses emitted from the path subsequently traversed by the main discharge and having a frequency of 10-30 kc/sec. This train lasts for 1/50 sec. and is accompanied by a train of Hertzian waves and waves travelling along power and phone lines and of the same frequency and duration as the luminous impulses. The similar but severer phenomena accompanying the main discharge are diverted by the anticipatory switching operation in less than 1/50 sec. and preferably less than 1/200 sec. after the arrival of the first preliminary impulses. Fig. 1 shows the output stage 2 of a wireless receiver which is disabled by the means 3 comprising a circuit 11, 12 tuned to receive the waves of frequency 10-30 kc/sec. which are passed to the grid of valve 10 so as intermittently to increase the anode current. This causes a grid-controlled, gas-filled valve 14 to ignite, the anode current therein setting up a p.d. across choke 23 which gives a negative impulse to the anode of a similar but normallyignited valve 15 to extinguish it. After an interval depending on circuit constants, valve 15 re-ignites and sends a negative impulse to anode of valve 14 to extinguish it. During this interval an increased current in resistance 25 biasses an anode-bend detector towards cut-off or (as shown) causes an increased negative bias to grids of valves 7, 8 whereby their anode currents are reduced during the main discharge. The discharge of a condenser or operation of an electromagnet relay may replace valve 15 for extinguishing valve 14 or the duration may be terminated by the arrival of the waves of the main discharge itself. In Fig. 4, oscillations received by the coupled tuned circuits 45. 46 and 11, 12 are rectified at 35 and ignite a valve 47 the anode circuit of which has a relay 48 which, after a delay due to shorted winding 50 opens (and recloses) the anode circuit at contacts 49. As in Fig. 1, the increased p.d. across resistance 25 causes a cold-cathode, gas-filled tube 51 to strike, thus discharging the aerial to earth and diverting the disturbance from the receiverinput circuit 33, 34. The systems of Figs. 1 and 4 may be adapted to protect other plant from lightning, Fig. 5 (not shown), illustrating an arrangement in which a resistance such as 25 is connected across .a cold-cathode, gas-discharge tube containing a number of pairs of electrodes whereby discharges in phone lines are byepassed from the terminal apparatus when the tube strikes.