Patent GB-1522844-A (GB)
Title: No-break supply circuitry for an a c load
IPC: H02J9/06
Filed: 1975-09-26
Abstract: 1522844 Emergency supply systems SIEMENS AG 26 Sept 1975 [27 Sept 1974 (2) 10 Oct 1974 21 July 1975 8 Sept 1975 11 Sept 1975] 39623/75 Heading H2H An emergency supply system comprises a plurality of loads normally supplied from an A.C. source and in an emergency, from a D.C. source by way of an inverter, the inverter comprising semiconductor devices and the changeover from the A.C. to the D.C. supply being automatic and of the "no-break" type, by virtue of energy stored in a filter 2. A plurality of loads la, 1b, lc are connected to bus-bars 10 by way of overload cut-outs 11, 12, 13 respectively, the bus-bars 10 being supplied normally from an A.C. source 4, in the absence of the A.C. source, from a battery 7 by way of an inverter 5. Connection of the A.C. source 4 to a filter device 2 is made by way of a transformer 24, a pair of back-to-back thyristors 25a and an electro-mechanically operated switch 3a, the filter 2 being connected to the bus-bars 10 by electro-mechanically operated switch 9a and a pair of back-to-back thyristors 9b. Whilst the bus-bars 10 are supplied from the A.C. supply 4 pulses generated by a pulse generator 5c, under the control of a regulator 5d, are blocked by a unit 5b such that the inverter 5a is inoperative. Upon failure of the A.C. supply 4 switch 3a opens, thyristors 25a become non- conductive, an electro-mechanically operated switch 6a closes and the unit 5b releases the pulses from the generator 5c whereupon the inverter 5a becomes operative so that the busbars 10 are supplied from the battery 7 without a break in the supply to the filter 2 and hence the bus-bars 10. Should one or more of the loads 1 develop a fault when the bus-bars 10 are being supplied from the A.C. source 4 switch 9a opens, thyristors 9h become non-conductive but at the same time a switch 14a closes and thyristors 14b become conductive so that the bus-bars 10 are supplied directly fom the A.C. source 4 without the aid of the filter 2, the switches &c. reverting to their previous states when the load faults disappear. Various voltage and current sensing devices are provided, such as 36, 29, 17, 30, 16, 28, 38, 27, 15, the signals from which are fed to control units 20 or 21 as required so as to provide command signals for the various thyristors and electro-mechanically operated switches. The breaking of the current in a circuit is effected by opening the electro-mechanical switches, the associated thyristors becoming non-conductive at the first subsequent zero voltage crossing whereafter the electro-mechanical switch then recloses the restoration of a circuit being made by the thyristors. Various logic elements are used in the control circuit and a device is used for computing the firing angle for the thyristors 25a to prevent a voltage discrepancy when the A.C. supply 4 is restored. The inverter 5a is modified so as to enable the battery 7 to be recharged when the A.C. supply 4 exists and the battery 7 may be in two sections, chargeable in parallel but placed in series when supplying the busbars 10. Alternatively the battery may have only one section but the transformer 8 provided with additional windings which are used when charging the battery.