Electricity: power supply or regulation systems – Including a transformer or an inductor – Polyphase or plural transformers
Patent
1998-11-12
2000-11-28
Berhane, Adolf Deneke
Electricity: power supply or regulation systems
Including a transformer or an inductor
Polyphase or plural transformers
336 55, 336 59, 336 60, H01F 2914, H01F 2708
Patent
active
061540196
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a controllable inductor comprising at least a tubular core, a main winding surrounding the core and a control winding passing substantially axially through the core.
BACKGROUND OF THE INVENTION
Such controllable inductors may through the main winding thereof be connected to any electrical circuit, such as a power line, to provide the circuit with an inductance, for example for extinguishing higher harmonic currents generated in the circuit. The magnetic permeability of the core and thus the inductance of the inductor may then be controlled by changing the electric control current brought to flow axially through the core in the control winding. By connecting such a controllable inductor in series to a capacitor a so called harmonic filter may be obtained, which is already known through Applicants' for example, WO 94/11891 of the applicant, and in which the impedance may be controlled to be low for certain frequencies by controlling the inductance of the inductor for eliminating higher harmonic currents having a frequency being a multiple, for example 11, of the fundamental frequency of the network.
Another conceivable field of use for a controllable inductor of this type, in the case that such may deliver an inductance being sufficiently high, is the switching in thereof into alternating current power lines, having a high capacitance stored therein, for example cable networks. By an intercoupling of such an inductor an inductance of a desired size may then be connected thereto and the reactance of the power line may thus be reduced for a more efficient energy transfer through the line.
These controllable inductors have of course only a useful influence upon an alternating voltage, but it is not completely necessary that the main winding is connected to an alternating voltage. For example, it could also be connected to a direct voltage with an alternating voltage superimposed. A disadvantage of such controllable inductors already known is the fact that the alternating voltage in the main winding induces an alternating voltage in the control winding having a frequency being twice the fundamental frequency in the main winding. This voltage gives rise to harmonic currents in the network and causes losses in the core.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a controllable inductor as defined in the introduction, in which the above problems have been solved to a large extent.
This object is according to the invention obtained by adapting such an inductor for connection to a three-phase alternating current network and it has for each phase, a main winding for connection to the phase, a core and a control winding. The control windings of the three phases are electrically connected in series with respect to each other.
Due to the provision of one controllable inductor with means including a main winding, a core and a control winding, for connection of a controllable inductance to all the three phases of an alternating current network and the control winding of the three phases being connected in series to each other, an inductor may be formed, in which the voltages induced through the alternating voltage in the respective phase of the respective control winding will cancel each other out, since the sum thereof in the control winding connected in series will be zero due to the displacement of the alternating voltages of the phases by 120 electrical grades with respect to each other. As a result, the problems deriving from voltages induced in the control winding are not created, and the control current in the control winding will not be influenced by the alternating current network and for example in the case of a direct current remain a direct current.
According to a preferred embodiment of the invention at least one of the cores has a second control winding passing substantially axially therethrough, the second control winding being separated from the first control winding connected in series. The second control winding
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Von Werner Kramer, Drehstromtransformator mit regelbarem Magnetisierungsstrom, ETZ Elektrotechnische Zeitschrift, 1959, vol. 80, No. 14, pp. 441-445.
Liljestrand Lars
Valdemarsson Stefan
ABB AB
Berhane Adolf Deneke
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