METHOD AND APPARATUS FOR SWITCHING TAPPINGS OF TRANSFORMER WINDING Russian patent published in 1999 - IPC

FIELD: electrical engineering, possibly controlling voltage of power and conversion live transformers. SUBSTANCE: method and apparatus are designed for transformer with switching device including two thyristorized switches connected with transformer winding tappings and control system. The last includes voltage pickup, four synchronization units having saw-tooth voltage generator and null-balance organ, setters and pulse shapers whose number is equal to number of switches for realizing ON- and OFF-operation, 2AND-NON and 3AND-NON gates, R-S flip-flops, each having two 2AND-NON gates, order shapers (HIGHER and LOWER orders), matching units connected with circuits for controlling switches. Method comprises steps of turning ON and OFF thyristorized switches in predetermined time moments before passing voltage of control winding stage over zero. Turning-ON is realized at advance period equal to θ. In each half-wave of said voltage reference voltages, for example saw-tooth voltages are formed; reference voltage is compared with first set voltage, and when both voltages are the same first clock pulses are generated. OFF-pulses with duration τ=1-2 electric degrees are formed at leading edge of first clock pulses. Formed reference voltage is compared with second set voltage, and when both voltages are the same, second clock pulses are formed. ON-pulses with duration τ are generated at leading edge of second clock pulses. Value of first voltage is selected in such a way that OFF-pulses are formed during time interval between moment of zero crossing by electric current of thyristorized switch and time moment before voltage passing over zero by period θ = γ+ε, where γ- switching interval of thyristorized switches at controlling voltage step- up, ε- time interval of thyristor OFF-turning. Value of second voltage is selected in such a way that ON-pulses are generated before voltage passing over zero by period θ.. EFFECT: enhanced reliability of transformer with thyristorized switching device. 2 cl, 2 dwg