GB151294A - Improvements in or relating to the transmission of single-phase currents over poly-phase mains - Google Patents

Abstract

151,294. Taylor, A. M. June 21, 1919. Systems depending on the use of static transformers; distributing mains, arrangement of; polyphase systems.-A single-phase current is imposed upon the three outgoing and the three returning phases of a three-phase supply system, the connexions including static transformers or balancers at each end. The single-phase current is taken from the delta-connected secondaries of the receiving-transformers without interfering with the three-phase supply. In the arrangement shown in Fig. 1,. the alternators A<3> are connected to the bus-bars B to which are connected the three-phase leads F<3>, F<4>. The two special feeders F<1>, F<2> are supplied from the busbars through star-star transformers T<1>, T<2>, the neutral points of the secondaries being connected by the cable D. Each of the transformers carries windings C<1>, C<2>, C<3> connected to a singlephase alternator A<1> of any desired frequency, or instead of this connexion a large single-phase transformer may be connected in the cable D and additional windings in short-circuited delta may be placed on each transformer to nullify self-induction. The primaries of the receiving-transformers T<3>, T<4> are star connected and their neutral points are connected. The secondaries are connected in delta and the circuit is interrupted at one or more points to lead to the furnaces or other single-phase consuming-devices H<1>, H<2>, or both transformers may feed one device. In a modification, Fig. 2, the three-phase alternators A<3> feed into bus-bars B and the primaries of the two star-delta transformers T', T<2> with connected neutral points are connected to the feeders F<1>, F<2>. The delta connected secondaries are connected to a single-phase generator A<1> and the bus-bars are broken between the feeders F<1>, F<2> to avoid a short circuit of the single-phase energy. In another modification, one of the three-phase generators is connected to one feeder alone and not to the bus-bars, and its neutral point is connected to the neutral point of one of the other generators. Impulses of single-phase current are introduced into the phase connexions of the generators by means of transformers supplied from a single-phase generator. The generators with connected neutrals should preferably be mechanically coupled. In some cases the ends of the feeders F<1>, F<2> are joined and one feeder is cut at the place of the single-phase demand. A I to I three-phase transformer T<5>, Fig. 4, is introduced and two additional star-delta transformers T<3>, T<4> are connected to supply the singlephase load. Any existing low tension cable may be utilized as a return path by connexion between the star points of the receiving and sending ends. A slight variation about a definite value of the frequency of the single-phase supply will distribute uniformly the heating effects and voltage drops. The single-phase current may be obtained by means of a static frequency changer of the type described in Specification 8853/11, [Class 38 (ii), Electric currents, Converting &c.].