GB593909A - Means for exciting synchronous alternating current machines through rectifiers - Google Patents

Abstract

593,909. Alternators. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET, and FORSSELL, H. Dec. 21; 1944, No. 25615. [Class 35] In a synchronous A.C. machine self-excited through rectifiers fed from a voltage transformer and a current transformer, the latter is normally inoperative, but becomes automatically effective on the occasion of a short-circuit across the machine. In Fig. 1, the field winding 2 of the alternator 1 is supplied through rectifier 6 by current transformers 5 having their secondary windings in series with those of a voltage transformer 3. Normally, the current transformers are ineffective because a tertiary winding 10 on each is short-circuited through anodes 11 in rectifier 6-possibly through a regulating resistance and a D.C. source ; the path through these anodes is blocked by grid control means (not shown) if the alternator voltage is considerably reduced. The transformers are shown connected Y/Y, but may be connected Y/Z. In Fig. 4, the transformers supply the field winding 2 through rectifier 4, the current transformer secondary windings being shortcircuited only while the rectifier 6 is in operation. Other arrangements use separate rectifiers connected in parallel to the field winding. In one modification, the current transformer secondary windings are short-circuited by voltage-responsive resistances while their terminal voltage exceeds a certain value; in another, the current transformers are normally kept out of action by D.C.-supplied saturating coils on their cores. The alternator may, for starting, be initially excited by a battery.