GB612362A - Improvements in or relating to electric fault alarm circuits - Google Patents

Abstract

612,362. Repeating systems. STANDARD TELEPHONES & CABLES, Ltd., and JACOBSEN, B. B. May 21, 1946, No. 15353. [Class 40 (iv)] [Also in Groups XXXVI and XL (c)] In an arrangement for indicating failure of one of a number of electrical devices such as valves or fuses, a potential derived from each is applied through one of a number of rectifiers to the fault indicator. When a fault occurs, the potential changes and the resulting current through the corresponding rectifier operates the indicator and also causes the potential at the common end of the rectifiers to decrease the remaining rectifiers thus being blocked. Fig. 1, illustrating the basic invention, shows two valves having cathode resistors 3, 4 producing test potentials which are applied via rectifiers 7, 8 to a common test conductor 9. To this conductor is also applied a balancing voltage 14 through resistor 15. When a valve current decreases, the potential at the cathode also decreases and the corresponding rectifier passes a current, which, flowing through resistance 15, causes the test potential at conductor 9 to fall, thus blocking the remaining rectifiers. The rectifier current is used to operate the fault indicator over the alarm line either by operating contact 12 or by changing the resistance of a thermistor (Figs. 4 and 5, not shown). If the rectifiers are reversed, an indication of an abnormal rise in valve current may be obtained. In Fig. 3 each of devices 20-23 are connected to a pair of oppositely arranged rectifiers to give indications in test conductors 9A and 9B of an abnormal rise or fall of potential. These conductors connect to the grids of valves 16A, 16B, the anode circuits of which contain a relay having two oppositely connected windings so that both types of fault cause the relay to operate. Potentiometer 48 permits the adjustment of the balancing voltage for the rectifiers and resistors 50, 51, the operating point of the relay. A switch 38 is provided to connect motor 37 to any of devices 20-23 to locate the fault. If the fault is to be indicated by an A.C. signal, the potential on conductors 9A or 9B may be applied to the grid of an oscillator valve to start or stop oscillation (Fig. 11, not shown), or it may be applied to a thermistor connected in series or parallel with the feedback circuit of the oscillator (Fig. 6, not shown) Alternatively, a line amplifier may be caused to oscillate at a frequency outside the range occupied by the message. Thus, in Fig. 7, line amplifier 69 has a feed-back circuit through filter 72, phase correcting condenser 77, transformer 73, a bridge circuit and finally a frequency controlling crystal 76. The bridge comprises an amplitude stabilizing lamp 75 and a thermistor 52, the latter controlling the starting and stopping of oscillation in accordance with the test potential from the rectifiers. Various alternative forms of bridge are suggested (Figs. 8, 9, 10, not shown). Fig. 12 shows an arrangement for locating the faulty one of the devices connected to points 20-23. The occurrence of a fault causes contact 35 to make and thus operate start relay X. 83, 84 and 85 are banks of a rotary switch which is caused to step when the start relay operates by magnet 5 and slow to operate release relay Y. Contacts X2, X3 of the start relay disconnect the faulty equipment releasing contacts 35 and bringing into circuit a pair of test rectifiers 86A, 86B which are connected in turn to the devices by switch-bank 85. When the faulty device is reached, contact 35 re-operates connecting an earth through contact X4 to the appropriate one of self-holding relays A, B, C-N, causing the corresponding alarm lamp La-Ln to light. The switch completes its travel to the home position, but on the occurrence of a further fault will restart, no further alarm being given at the original fault since this circuit is disconnected at the appropriate one of contacts A2-N2. Specifications 510,379, [Group XL], 541,922, [Group XXXVI], 545,866; 555,563, 557,559, [both in Group XXXVI], and 587,610, [Group XL], are referred to.