Composite polyphase on-load tap-changers for regulating polyphase transformers and polyphase transformers provided with such tap-changers

Claim 1

Composite polyphase on-load tap-changer for a regulating transformer, said tap-changer consisting of at least two switches connected in series, of which one switch is a polyphase diverter switch comprising at least one circular series of angularly equidistanced fixed contacts, of which the number is an integer multiple of the number of phases, at least one group of mechanically rigidly interconnected equal sets of relatively fixed movable contacts, the number of said sets of movable contacts being equal to the number of phases, said sets of movable contacts cooperating with said fixed contacts and being mounted for rotation about the axis of said circular series of fixed contacts and said sets being equiangularly spaced by angles which are equal to an even multiple of the angle between the fixed contacts and each consisting of one main contact and at least one auxiliary contact, and transition resistances cooperating with said auxiliary contacts, said main and auxiliary contact being relatively mounted and said auxiliary contacts cooperating with the transition resistances, in such a manner, that during each changeover operation a bridge of resistance is formed between the fixed contacts between which the changeover operation takes place, and the other switch is a currentlessly switching polyphase tap selector comprising for each phase two series of pairs forming fixed contacts and two alternately movable bridging contacts, of which each one cooperates with an individual one of said series of fixed contacts for the interconnection of the fixed contacts of each individual pair of the relative series, one contact of each one of said pairs of fixed contacts being connected with a fixed contact of the diverter switch and the other contact thereof being intended for connection to a tapping of a regulating winding of the transformer, said diverter switch being connected between said tap selector and a star point, characterized in that for each phase all fixed contacts belonging to the same series of the tap selector and connected to the diverter switch are connected both with each other and with one single individual fixed contact of each circular series of fixed contacts of the diverter switch.