Patent GB-458716-A (GB)
Title: Improvements in or relating to electric transmission and rectifying equipment
IPC: H02M7/06
Filed: 1936-02-19
Abstract: 458,716. Rectifying alternating currents; transformers; automatic regulation. ERICSSON TELEPHONES, Ltd., 67, Kingsway, London, and DISTIN, L. S., Ericsson Telephone Works, Beeston, Nottingham. Feb. 19, 1936, No. 5035. [Classes 38 (ii) and 38 (iv)] Direct current supply is obtained from an A.C. source through a step-down transformer M, Fig. 1, and a rectifying bridge RB, a saturable choke 3, which forms the primary winding of a step-up transformer AT and has a saturating winding 5 connected in series with the D.C. output circuit, being connected in the A.C. circuit supplying the bridge RB. A condenser C which resonates with the choke 3 to reduce the A.C. voltage supplied to RB at a given D.C. output current is connected across the secondary winding of the transformer AT, which winding, if AT is an auto-transformer comprises windings 3 and 4 in series. With this arrangement, increase of load above the given D.C. output current causes reduction of the impedance of the circuit C, 3, 4 so that increased A.C. voltage is applied to RB. Additional apparatus comprising a barretter bridge BB, Fig. 3, supplied across the A.C. mains from an auxiliary step-down transformer BT and feeding a rectifier bridge rb which supplies saturating D.C. current through winding 10 to step-down transformer MT feeding rectifier bridge RB, may be provided to compensate for voltage variations in the A.C. supply. The bridge BB is balanced when the A.C. supply voltage is maintained at its maximum value and permits an out of balance current to be supplied to bridge rb when the supply voltage falls so that saturating D.C. current is supplied to windings 10 of MT causing the output voltage of MT to rise. Instead of the auto-transformer AT, Fig. 1, two transformers AT, AT2 having their primaries 3a, 3b connected in series and having their saturating windings 5a, 5b cross-connected may be used. The windings 3a, 3b, 5a, 5b may be tapped, the condenser C being connected in series with the secondaries through a variable resistance VR. An arrangement for compensating for fluctuations in the supply voltage and comprising two or more barretter bridges is described in which the bridge supplying saturating current to the main step-down transformer is balanced under maximum voltage while the other bridge or bridges control the voltage supplied to this bridge and are balanced at minimum supply voltage so as to magnify the effect of supply voltage variation on this bridge. Fig. 4 shows one construction of the transformer MT, Fig. 3, in which a four-limbed core has the primary and secondary windings 8, 9 arranged on limbs L3, L4 respectively, the limbs L1, L2 acting as a magnetic shunt and having the saturating winding 10 arranged thereon so that the leakage flux is reduced as the saturating current increases. The barretter bridges may be replaced by an arrangement comprising a single barretter and a resistance connected respectively in series with the two differentially wound primary windings of a transformer, the secondary of which delivers a current when the voltage supplied to the primaries varies to cause variation in the current passing through the barretter. This secondary output is then rectified and used to compensate for the effect of variation of the voltage of the supply. The barretters or the resistances in the barretter bridge arrangements may be replaced by copper oxide rectifiers.