Patent GB-883279-A (GB)
Title: Improvements relating to a.c. electric supply arrangements
Inventor: DRAKE BERNARD
IPC: H04B3/44
Filed: 1958-08-06
Abstract: 883,279. Valve supply circuits. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. July 10, 1959 [Aug. 6, 1958], No. 25259/58. Class 40(6). An A.C. supply arrangement has at least two self-sustaining oscillators each with an output connection and a synchronizing connection. The oscillators are connectable to an output combining circuit through respective interrupting switches included in the output connections and each is automatically controlled to be closed for normal operation, but opened to disconnect its generator in response to reduction in the output voltage of that generator by more than a certain amount. The arrangement also includes a means to open the switch of one of the generators in response to any failure of the synchronization. Further relay contacts are included to short out part of the output impedance when one of the oscillators is disconnected. A number of voltage supply bus bars 1MB, 2MB, 3MB may each be supplied by a pair of oscillators, e.g. 1GA, 1GB for 1MB, each pair having a different frequency, the equipment for each frequency being coupled into a common alarm circuit (shown above the chain line in Fig. 1). Unbalance condition. If the output from one of the oscillators is reduced, an unbalance signal is developed between the points j1, j2 and fed via a voltage double rectifier circuit 1UD over line l1 to a valve V3. Application of this signal to valve V3 causes the valve to cut off and release relay U, UU and hence complete the circuit to alarm AL1. A number of pairs of oscillators each pair having its own individual frequency may be connected to valve V3 over further lines 12, 13. Key switches 3KT, 2KT, 1KT may be operated to determine which of the pairs of oscillators has originated the alarm signal. These keys remove any unbalance signal to cancel the alarm. Variation in bus-bar volts on line MB. The output on the line 1MB is measured by means of a voltmeter 1VM having a pair of limit contacts 1VM1 inset to predetermine low and high limits. If relay LTR is operated closure of contact 1VM1 to either the low or high contact will short out relay VA causing it to release completing the circuit to alarm lamp AL2. Oscillator fault. The output from the oscillator 1GA is fed over a line XA on to the grid of a valve V4 where it overcomes standing bias on the valve to hold a relay lA locked in. A similar arrangement obtains to the oscillator 1GB and the relay 1B. In the event of the output from one of the oscillators, e.g. oscillator 1GA falling, the relay 1A releases and energizes relay 1AA. Contact 1AA2 opens to disconnect oscillator 1GA from the output bus-bar and contact 1AA3 closes to short out resistor R6 to maintain the output impedance substantially constant, and the alarm lamp AL1 lights due to the unbalance voltage developed. The circuit will restore to normal if the fault ceases. Synchronization failure. Failure of synchronization will produce both a low output on the bus-bar and also an unbalance condition resulting in both alarms AL1 and AL2 lighting. In addition the circuit to relay 1SF is made via contact UU2 contact 1BB4 and contact 1AA4 via the voltmeter contact 1VM1. This relay is thus energized and contact 1SF2 changes over to light the alarm lamp AL3 and to disconnect the resistor in the cathode circuit of valve V5 thus releasing relay 1B and thus disconnecting the oscillator 1GB from the combining circuit 1C. When the voltage on bus-bar MB restores, relay 1SF is held in over its self-hold contact until released by key KR1. Manual operation. One or other of the oscillators may be manually disconnected by operation of a key KA/KB to either its KA position or its KB position. When the key is operated into its KA position, contact 1KA3 disconnects the oscillator 1GA from the combining unit 1C and also disconnects this oscillator from the control circuit for valve V4 thus releasing relay 1A and operating relay 1AA. Contact 1KA1 opens as does relay contact 1AA1 disconnecting the synchronization line between oscillators. A similar procedure follows if the key is operated into the KB position, in which case the oscillator 1GB is disconnected. If the key is moved from one position to the other a delayed contact 1AA3 (or 1BB3) ensures that one or other of the oscillators is always connected to the bus-bar. Contacts 1AA4 or 1BB4 open when the manual switch is operated to prevent a synchronization failure alarm being given. Test equipment (not shown). Test equipment may be provided comprising an instrument for measuring the anode current of valve V3, for example a voltmeter across R18. A phase comparator either audible or visual may be provided to measure the beat frequency or phase difference between the two oscillator frequencies, and the frequency of an oscillator may be checked by an oscilloscope using Lissajou's Figures formed with one or other of the other oscillators for example that providing bus-bar volts 2MB. A voltmeter may be selectively switched to measure any of the bus-bar voltages or the outputs on lines 11, and an ammeter may be also switched to measure anode current. Modifications. In a modification in Fig. 2 (not shown) the synchronization circuit is permanently connected to each oscillator from the bus-bar MB, and the contacts 1AA2, 1BB2 are replaced by contacts on the 1A, 1B relays. Fig. 3 shows a modification of the circuit for three or more oscillators. The three oscillators Ga, Gb, Gc, are connected by a combining unit CC to three unbalance detectors UDac, UDab, UDbc all similar to the unit 1UD of Fig. 1. The outputs of the oscillators are also connected via voltage doubler rectifiers DRa &c. to valves which control relays Aa, Ab, Ac. Assuming a synchronization failure due to oscillator Ga, the unbalance detectors UDab, UDac will go out of balance causing relays Uac, Uab to operate and to operate relays UUac, UUab. Contacts on these relays complete the circuit to the synchronization failure alarm SFa which operates changing over contact SFa2 to light the alarm lamp ALa and to release the relay Aa which disconnects the oscillator Ga from the combining unit by way of the contact Aa1.