GB1334571A - Circuit for stabilising electricity supply reactive power - Google Patents

Abstract

1334571 Automatic control of reactive power BROOKHIRST IGRANIC Ltd 22 Dec 1971 [13 Jan 1971] 1729/71 Heading G3R The reactive power in an electricity supply system is maintained constant by the difference between measured and reference reactive power signals, the difference being used to switch capacitor banks into and out of the supply system. A D. C. signal representing the actual reactive power of a polyphase A. C. supply system, as sensed by a phase sensitive full wave rectifier 10, is compared with a reference signal, which may be adjustable in a comparator 18, which is an amplifier with adjustable gain and rate of change limit, providing an error signal to switching means 22 that successively switches shunt connected capacitor banks in or out of the supply circuit until the error is eliminated. The switching means 22 comprises transistor switching stages 24a-24e, each connected to the comparator output and to a point on an impendance chain 30a- 30e, across supply V V', such that, for example, on increasing error due to lagging power factor, stage 24a first switches on, exciting reed relay 34a to connect an associated capacitor bank (not shown), via a contactor (also not shown) into the supply circuit. If the correction is insufficient and the error continues to increase, further switching stages will be successively triggered on and further capacitor banks switched into the system until the error is reduced to zero. Similarly the stages 24a-24e are successively switched off if the error changes in the opposite sense due to a change in load. If the circuit power supply fails, upon re-establishment of it, the capacitor banks are not reconnected for a period, then re-inserted into the supply circuit as required.