ES351709A1 - Tap preselector for load switching system - Google Patents

Abstract

A transformer tap changer comprises two rings S 1 , S 2 of fixed contacts which are respectively connected to the odd taps 1, 3, 5, 7 and the even taps 2, 4, 6, 8 of transformer 10 and surround a control shaft 21 carrying movable contacts 19, 20 which are alternately connected to a load 9 by an on-load change-over switching device I, II, the spacing and arrangement of the two sets of fixed contacts S 1 , S 2 and movable contacts 19, 20 being such that in each stable position of the tap changer one of the movable contacts, e.g. 19 engages the centre of one of the co-operating contacts, e.g. 13 and the other movable contact, e.g. 20 is between and spaced from two contacts, e.g. 12, 14 of its co-operating fixed contacts. Starting from the position shown switch I, which comprises thyristors in antiparallel, is closed but the load is supplied through a parallel circuit completed through movable contact 24 and one of the contacts 22. As the shaft 21 rotates clockwise contact 20 engages fixed contact 14 while contacts 13 and 19 are still engaged, but movable contact 24 and its co-operating fixed contact 22, and a further movable contact 25 and its co-operating fixed contact 23, are opened thereby ensuring that switch I carries al] the current to the load 9. In this continued movement from one tap to another the switch I is then opened before switch II is closed. In this position the load is connected to tap 4 and the current passes to the load through contacts 23, 25 of switch C/cII. The switches I + II are thyristors which may be rendered conducting or non-conducting by gate cathode circuits opened and closed by sealed magnetic contact devices actuated by permanent magnets carried by shaft 21. As shown, however, the thyristor switches I, II are controlled by photo-electric devices 26, 28, and 27, 29 respectively. Each device comprises a light source, e.g. 28 and a photo diode 28, a slotted disc 30 keyed to shaft controlling the illumination of the diode. A servomechanism (Fig. 4, not shown) positions the shaft 21 in accordance with an adjustable reference member, Application No. 535/68, Serial No. 1,204,612 is referred to.