Patent GB-387815-A (GB)
Title: Arrangement for the suppression of the harmonics in the magnetising current of saturated choking coils or transformers
IPC: H01F27/38
Filed: 1932-01-05
Abstract: 387,815. Supply systems ; automatic regulation ; transformers ; inductances. SIEMENS-SCHUCKERTWERKE AKT.- GES., Siemensstadt, Berlin. Jan. 5, 1932, No. 319. Convention date, Aug. 3, 1931. [Classes 38 (ii) and 38 (iv).] In order to suppress higher harmonics, particularly the fifth, in the magnetizing current of three-phase transformers or choking- coils, which work on or above the bend of the magnetization curve, and possess one or more unwound limbs or comprise three single-phase transformers or choking-coils, means are provided by which the magnitude of the higher harmonics divisible by three in the limb fluxes, preferably the third harmonic, are so influenced that the other harmonics, particularly the fifth, are suppressed. In one arrangement, Fig. 1, a three-phase star-connected choking-coil 1, on a core with an additional limb 5, is provided with a delta-connected winding, the circuit of which is closed through an inductance 6 so dimensioned that the fifth harmonic in the magnetizing current is reduced to a minimum. If it is desired to suppress the seventh, eleventh, or other higher harmonics, the delta winding may be loaded with capacities and ohmic resistances as well as with inductances, so selected that for each of the harmonics divisible by three, the compensating currents most suitable for balancing the neighbouring waves circulate. In a modification, three separate single-phase star-connected choking-coils are provided, the delta winding being distributed over the three cores. The inductance 6 may be dispensed with by employing a shortcircuited delta winding with very large leakage, obtained, for example, by inserting bundles of iron between the main and delta windings. The delta winding itself may be dispensed with by providing the main choking-coil 1 with additional limbs formed with air gaps, Fig. 3, or so dimensioned that the third harmonic flux obtains the value required to suppress the fifth harmonic in the magnetizing circuit. In another arrangement, Fig. 4, the magnitude of the inductance 6 in circuit with the delta winding is varied automatically in accordance with the exciting primary voltage, i.e. with the degree of over-saturation, by means of a wattmeter relay 10 provided with two coils, one of which is movable and carries a contact arm adapted to close the circuit of a motor 12 and cause the latter to rotate in one or the other direction to adjust the magnitude of the inductance 6. One of the coils of the relay is energized from the magnetizing current of the main choking-coil 1, while the other is supplied with a constant fifth harmonic, synchronous with the supply voltage, obtained by means of a small over-saturated auxiliary choke and filter circuit 11. In another arrangement for automatic regulation, Fig. 5, a differential relay 21 is used, the coils of which are influenced by the magnetizing current, and by the current supplied from a battery 23 through a resistance 22, respectively. Operation of the relay causes a motor 24 to run in one or the other direction and to adjust simultaneously the value of the inductance 6 and the resistance 22. In a further modification, a relay responsive to the magnetizing current or terminal voltage moves a contact arm over contact segments connected to tappings on the inductance 6, so that a definite value of the inductance is associated with each value of the magnetizing current. In another arrangement, Fig. 7, the main choking-coil comprises three single-phase chokes 7, 8, 9, and the inductance 6 is replaced by three choking-coils 16 distributed among the individual phases of the delta winding, so that the delta winding may be loaded for other purposes within certain limits. The main choking-coils may be employed for compensating long transmission lines, where choking- coils are installed section by section along the line. An arrangement of this kind is shown in Fig. 8, where saturated choking-coils 32, with delta windings short-circuited through inductances, are connected to transformers 31 at definite intervals in the line 30. The transformers have two secondary windings, one of which is connected to the choking-coils, while the other serves for connection of consumers. Resonance circuits, comprising capacities 33 and choking-coils 34, tuned to the seventh harmonic, may be provided for suppressing the latter in the magnetizing currents. Additional condensers 35 may also be connected in parallel with the choking-coil 32 in order to supply leading wattless current with decreasing supply voltages.