GB924130A - On load tap-changing equipment for an electrical transformer - Google Patents

Abstract

924,130. Transformers. BRUSH ELECTRICAL ENGINEERING CO. Ltd. Jan. 6, 1961 [July 12, 1960], No. 24216/60. Class 38 (2). In a single or multi-phase on-load tapchanging system vacuum switches of a type employing solid contacts are used as tap selecting switches or as load-breaking switches or to perform both functions combined. Fig. 1 shows a divided transformer winding A1, A9 with tapping points including vacuum switches 3-8 on the upper part connected respectively to the lower part of the winding via saturable reactors T1, T2. A further vacuum switch 2 is connected across T1 and T2. With any one tapping in operation reactors T1 and T2 are saturated and vacuum switch 2 is closer so that the load current flows equally through T1 and T2. To change tapping 3 to 4, T1 is brought to maximum impedance and the vacuum switch connected to tapping 4 is closed after which T1 is brought to minimum impedance and T2 to maximum impedance and the vacuum switch connected to tapping 3 is opened. Fig. 3 shows another embodiment incorporating a conventional tapping selector switch with two movable contacts C1 and C2 each connected through a vacuum switch S1 or S2. Resistances or inductances may be used instead of the saturable reactors. The sequencing of the steps can be effected by movement of an external selector and a self-cycling switch may make the various changes in the saturating current of the reactors. The external selector may be operated automatically in response to variation of a characteristic of the load circuit. The vacuum switches may either be of the kind having their contacts secured to the relatively movable walls of an enclosing evacuated envelope or of the kind having a rigid envelope enclosing an electromagnetic coil by which at least one biased contact can be moved relatively to the other. The complete tap-changing equipment may be housed in the main transformer tank.