GB385427A - An improved electric transformer for use in superposing single-phase control currents or impulses on to alternating current networks - Google Patents

Abstract

385,427. Systems depending on static transformers. LANDIS ET GYR SOC. ANON., 1, Hofstrasse, Zug, Swizterland. Dec. 23, 1931, No. 35516. Convention date, Dec. 24, 1930. [Classes 38 (ii) and 38 (iv).] Relates to apparatus for superposing a single-phase current on a main network for remote control purposes and consists in forming the superposition transformer and neutral point impedance coil system as a constructive unit. A threephase star connected choke 2, 3, 4, Fig. 1, connected to a three-phase network 11, to obtain a neutral point 10, has a core 1 with a fourth limb 9 on which is mounted a coil 8 supplied with singlephase current for the purpose of superimposing a control current on the network. A condenser 17 may be inserted in the control circuit to tune the system to the control frequency. The winding 8 may be distributed over the limbs 5, 6, 7 if desired. In a modification, Fig. 2, for interconnecting two three-phase networks coupled by a delta-star transformer 17 so that the single phase control current flowing in one is transmitted to the other, three windings 26, 27, 28 are mounted on the same limbs as the windings of the star-connected choke connected to the system 11 and these are connected in series between the star point of the transformer secondary 22 connected to the system 21 and a neutral wire 30. If desired, the neutral 30 may be earthed. When the systems 11, 21 are connected through a deltadelta transformer, the windings 26, 27, 28 are star-connected to the conductors of the network 21, preferably through condensers to prevent load currents flowings, the star point being earthed. In a modification of this lastmentioned arrangement, an auto-transformer connection is used instead of two separate star connected windings.