GB1235434A - On load tap changing arrangement for a three phase tap transformer - Google Patents

Abstract

1,235,434. Transformer tap-changers. E. SCHEUBECK. 13 June, 1969 [19 June, 1968], No. 30050/69. Headings H1N and H1T. In a three-phase tap-changing system on-load tap changing is effected phase by phase in succession using controlled rectifiers 7, 8, 9, 10 connected in reverse parallel (or two triacs) and three pole switches 6, 11, 12. In changing, e.g. from tap W2 to W1 movement of the spindle carrying the moving contacts of switches 6, 11, 12 and 30 first brings contact 126 of 12 on to fixed contact 123 thus connecting thyristors 9, 10 to tapping W2. Then contact 116 of 11 comes on to fixed contact 113 connecting tap W1 to thyristor pair 7 and 8 and so applying a voltage from transformer 371 to one of the inputs of AND gate 36. At the same time the other input to AND 36 is energized from switch 30 and bi-stable flip-flop 34 so that pulse generator 42 fires thyristor pair 9, 10. Thyristor pair 9, 10 then carries the load current from tap 2 of phase W when contact 69 of switch 6 leaves fixed contact 66. On further rotation of the common switch spindle, moving contact 33 of switch 30 moves on to contact set 31 whereupon flip-flop 34 switches to its other position, and the ignition pulses on thyristor pair 9, 10 disappear. On cessation of current through thyristors 9, 10, transformer 381 provides an input to AND gate 35 (which is already receiving an input from flip-flop 34) and ignition pulses are provided by generator 39 to thyristor pair 7, 8 which then connects Y to tapping W1. Further movement then brings contact 69 of 6 on to fixed contact 65 thereby connecting tapping W1 direct to line Y. Contact 126 of 12 then leaves fixed contact 123 de-energizing thyristors 9, 10 and causing stoppage of the switching pulses to thyristors 7, 8. Further movement brings movable contact 33 on to contact group 32 and switches 12 and 11 i connect the thyristor pairs 9, 10 and 7, 8 in succession to respective tappings V2 and V1, the operation then proceeding as before. Tap changing from taps 1 to taps 2 takes place in the sequence U, V, W instead of W, V, U. The arrangement of the three pole switches 6, 11, 12 with a common operating spindle 57 linked to operating shaft 56 of switch 30 is shown in Fig. 2. The moving contact members of the switches 6, 11 and 12 are in the form of spring- pressed roller contacts such as 68, 115 and 125 which act as bridging contacts between the fixed contact members such as 64, 112, 122 and conducting rings 13, 14, 15. The movable spring contacts 320 of switch 30 connect the contacts 31 or 32 to a conducting ring 310. The thyristors 7, 8, 9, 10 are contained in a housing 55 attached to housing 52 which contains spring means for producing snap action switching of 6. The drive gearing is contained in the tap - changer head 51. Connection is made between the switches and the thyristors by spring-pressed contacts at 80.