Electrical transmission or interconnection systems – With harmonic filter or neutralizer
Patent
1995-05-26
1998-07-14
Shoop, Jr., William M.
Electrical transmission or interconnection systems
With harmonic filter or neutralizer
307 76, 363 39, 363 40, 363 44, 333179, H02J 102
Patent
active
057809399
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for determining orders of non-characteristic harmonic currents of a second power supply grid, which is coupled to a first power supply grid by means of a high-voltage DC transmission system, and for compensating for these non-characteristic harmonic currents, which are produced as a result of distortion of the supply voltage, which distortion exists in the first power supply grid because of a low-frequency harmonic and passes through the system.
High-voltage DC transmission short couplings are used in order to exchange electrical power between interconnected grids, as a result of which the supply reliability in the individual interconnected grids is improved. In addition, a high-voltage DC transmission (HVDCT) short coupling, also known as a DC grid coupling, permits important and cost-effective power transactions, using normal exchange methods, and has at least a delaying influence on the construction of necessary additional power-station power.
The outline circuit diagram of the Etzenricht DC grid coupling is disclosed in the magazine "etz", Volume 110 (1989), Issue 14, pages 712 to 714. This Etzenricht DC grid coupling connects the West European interconnected grid to the East European interconnected grid. The two grid unions admittedly use the same rated frequency of 50 Hz, but the frequency and voltage in the two grids are at the same time regulated on the basis of different concepts, so that a defined transmission power can be achieved only by decoupling in frequency terms. crosses frontiers! by R. Walz and J. Gorke, printed in the magazine "Elektrie", Berlin 45 (1991) 3, pages 94 to 96 contains more details of the method of operation and construction, instrumentation and control techniques, control, regulation and protection and alarm systems. The three-phase filter circuits which are arranged on the busbars of the grids absorb (characteristic) harmonics produced by the converters and produce the capacitive reactive volt-amperes which are required to compensate for the inductive converter reactive volt-amperes. The filter circuits are connected and disconnected by the controller as a function of the reactive volt-ampere balance in the grid and of the operating point of the HVDCT.
With the increasing reference to energy quality, attention is increasingly being paid in electrical power supply grids to reducing harmonics, since the occurrence of harmonics can reduce the electrical energy quality.
As a result of asymmetries in equipment impedances, the grid voltage and the asymmetry of the delay angles of the rectifiers and invertors in the HVDCT system, non-characteristic harmonics occur in addition to the characteristic converter harmonics.
The article "Harmonische in Drehstromnetzen bei Betrieb einer HGU-Kupplung" E. Bauer and G. Winkler, "Elektrie", Berlin 45 (1991) 3, pages 97 to 100, discloses that the amplitudes of the individual non-characteristic current harmonics are considerably smaller than those of the characteristic current harmonics. When designing HVDCT systems, particular attention must be paid to the magnitude of the non-characteristic harmonics which are below the lowest tuning frequency of the filters, since the filters act capacitively for these harmonics and form a tuned circuit with the grid impedance. If this tuned circuit has a parallel resonance point in the region of the non-characteristic harmonics, it is excited by the resonance point and unexpectedly high voltage harmonics can occur in the grid. According to this article, a filter should also be provided for these very low harmonics in the event of excitation, which filter is expediently tuned to the lowest, non-characteristic (i.e., the third) harmonic.
In addition to the non-characteristic harmonics which are produced by asymmetries, the power supply grid has low-frequency, non-characteristic harmonics, such as the 3rd, 5th, 7th, and 9th etc., which are caused by industrial loads, for example converter drives, and small loads, for exam
REFERENCES:
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Elektrie, vol. 46, No. 3, Mar. 1992, Berlin, DE, pp. 114-121; Gretsch et al.: Einsatz eines Oberschwingungs-Me.beta.gerates an einer HGU-Kurzkupplung.
IEEE/CSEE Joint Conference on High-Voltage Transmission Systems in China, 17 Oct. 1987, Beijing, China, pp. 148-153, Christl et al.: Double Tuned Harmonic AC-Filters For HVDC-Converter Stations.
Elektrie, vol. 45, No. 3, (1991), Berlin, DE, pp. 97-100; Bauer et al.: Harmonische in Drehstromnetzen bei Betrieb einer HGU-Kurzkupplung.
etz. vol. 110 (1989), No. 14, pp. 712-714; R. Gampenrieder et al.: HGU-Bruckenschlag Zwischen Bayern und der Tschechoslowakei.
Elektrie, vol. 45, No. 3, (1991), Berlin, DE, pp. 94-96; R. Walz et al.: HGU: Technik, die Grenzen uberwindet.
Christl Norbert
Lutzelberger Peter
Sadek Kadry
Ganjian Peter
Shoop Jr. William M.
Siemens Aktiengesellschaft
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