Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
  • H02H9/001—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection limiting speed of change of electric quantities, e.g. soft switching on or off
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
  • H02H9/005—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection avoiding undesired transient conditions
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
  • H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current

Definitions

• the present invention relates to an apparatus for assisting or controlling the electric power transmission in a direct current power transmission system comprising at least one direct current transmission or distribution line for carrying direct current, DC, the apparatus comprising a transformer having a primary winding and at least one secondary winding, the primary winding being connect- able in series with the DC transmission or distribution line to carry the current of the transmission or distribution line, and the secondary winding is connected to an electrical load.
• the present invention relates to a direct current power transmission system comprising at least one DC transmission or distribution line for carrying direct current and at least one apparatus of the above-mentioned sort.
• HVDC power transmission system uses direct current for the transmission of electrical power, in contrast to the more common AC systems. For long-distance distribution, HVDC systems may be less expensive and may suffer lower electrical losses.
• a HVDC power transmission system comprises at least one long-distance HVDC link or cable for carrying direct current a long distance, e.g. under sea, and converter stations for converting alternating current to direct current for input to the HVDC power transmission system and converter stations for converting direct current back to alternating current.
• US 7,408,755 B1 discloses a circuit for inrush/transient current limitation and overload/short circuit protection for a DC voltage power supply.
• US 7,974,059 B2 describes a power supply apparatus comprising a DC power source that outputs DC voltage, a power supply circuit to which the DC voltage output from the DC power source is applied, and a current limiting unit connected in series between the DC power source and the power supply circuit.
• US 6,624,993 B1 discloses a fault current limiting system for DC and pulsed circuit systems.
• EP 1 526 624 A2 describes an assembly which rapidly identifies a short circuit in an alternating current or direct current power supply system and shuts down the system at once.
• the short circuit current flows through a high tempera- ture super-conductor current limiter (HTS) in series with a switchgear station.
• HTS high tempera- ture super-conductor current limiter
• US 5,596,472 discloses an apparatus for controlling an over-current tripping device of a high-speed DC circuit breaker, at least partially based on an output signal generated by a current transformer.
• JP 54137646 describes a protective circuit for DC current transformer.
• WO 201 1/057675 A1 discloses a breaking device for breaking a direct current flowing through a HVDC power transmission or distribution line.
• the breaking device comprises a parallel connection of a main breaker and a non-linear resistor, the main breaker comprising at least one power semiconductor switch of a first current direction, and a series connection of a high speed switch and an auxiliary breaker, the high speed switch comprising at least one mechanical switch, and the auxiliary breaker has a smaller on-resistance than the main breaker and comprises at least one power semiconductor switch of the first current direction, where the series connection is connected in parallel to the parallel connection.
• the object of the present invention is to improve the electric power transmission in a DC power transmission system, especially in a HVDC power transmission system. It is also an object of the present invention to provide an improved control of the electric power transmission in a DC power transmission system. Another object of the present invention is to provide an improved DC power transmission system, especially a HVDC power transmission system.
• an apparatus for assisting or controlling the electric power transmission in a direct current power transmission system comprising at least one direct current transmission or distribution line for carrying direct current, DC
• the apparatus comprising a transformer having a primary winding and at least one secondary winding, the primary winding being connectable in series with the DC transmission or distribution line to carry the current of the DC transmission or distribution line, and the secondary winding is connected to an electrical load, wherein the transformer is arranged to supply a secondary current to the electrical load, the secondary current being at least partially based on a surge current of the DC transmission or distribution line, and wherein the apparatus is arranged to limit the surge current by introducing at least one opposing voltage in series with the DC transmission or distribution line, the at least one opposing voltage being at least partially based on the current of the electrical load.
• transient surge currents occurring in the system are efficiently limited and the system is effi- ciently protected against surge currents, also called fault currents or over-currents.
• an improved control of the electric power transmission in a DC power transmission system is provided, and the electric power transmission in a DC power transmission system, especially in a HVDC power transmission system, is improved.
• the surge current limitation provided by the inventive apparatus the stress on the at least one DC line and any converter stations is reduced.
• an improved DC power transmission system is provided.
• the inventive apparatus provides a "passive" surge current limitation and electric power transmission control, i.e. no active measures performed by an operator are necessary to provide the surge current limitation and the control, as the surge current limitation automatically reacts. The performance of the apparatus is energized by the surge current per se, and no additional power source is required for the apparatus.
• the control of the electric power transmission or the surge current limita- tion is attained by the apparatus' introduction, or injection, of an opposing voltage in series with the DC transmission or distribution line.
• the injected opposing voltage produces a fictive resistance.
• the fictive resistance provides an active power extraction or output from the DC transmission or distribution line (since a resistance consumes power/energy).
• the apparatus' active power extraction or output from the DC transmission or distribution line results in a decrease or limitation of a surge current arising in the DC line.
• the active power extracted from the DC transmission or distribution line may be absorbed by the electrical load.
• the opposing voltage opposes the transient current increase of a surge current.
• the opposing voltage may be introduced as a positive voltage in series with the DC transmission or distribution line for reducing or limiting a surge current arising in the line.
• a surge current may be defined as a short-duration, high-amperage electric current wave that may sweep through an electrical network, as a power trans- mission network, when some portion of it is influenced by a fault or failure.
• the electrical load may comprise an electric circuit, at least one electrical device or an electric circuit comprising at least one electrical device.
• the DC transmission or distribution line may be any electrical conductor or electrically conductive element or means arranged between a first position and a second position for carrying direct current.
• the apparatus comprises a plurality of transformers, the pri- mary winding of each transformer is connectable in series with the DC transmission or distribution line to carry the current of the DC transmission or distribution line, and the secondary winding of each transformer is connected to an electrical load.
• the surge current limitation and the electric power transmission control are further improved.
• the flexibility of the surge current limitation and of the electric power transmission control is improved as the number of transformers may easily be increased or reduced for specific applications.
• the primary windings of the plurality of transformers are connected in series with one another.
• the transformer is arranged to DC isolate the electric load from the DC transmission or distribution line.
• the electric load is DC isolated in that no DC path exists or is provided between the DC transmission or distribution line and the electric load.
• the electric load does not influence the electric power transmission of the DC transmission or distribution line when the line carries a correct direct current.
• the surge current limitation and the electric power transmission control are further improved.
• the electrical load comprises an electrical device of a group of electrical devices comprising a nonlinear resistor, an inductor and a linear resistor.
• the surge current limitation and the electric power transmission control are further improved.
• the electrical load may comprise more than one electrical device, i.e. a plurality of electrical devices.
• the transformers may be connected to different types of electrical devices in relation to one another, or they may be connected to the same type of electrical device.
• the electrical load comprises an electrical device of a group of electrical devices comprising a nonlinear resistor and an inductor.
• the electrical load comprises an electrical device comprising a nonlinear resistor.
• the nonlinear resistor comprises a voltage-dependent nonlinear resistor.
• a voltage-dependent nonlinear resistor is a device which has a voltage-dependent nonlinear resistance. I general, a voltage-dependent nonlinear resistor conducts a very low current, but when the voltage across the voltage-de- pendent nonlinear resistor exceeds a certain level it will conduct a substantially increased current.
• the threshold or clamping voltage, of each voltage-dependent nonlinear resistor may be adapted to specific applications. By means of this embodiment, the surge current limitation and the electric power transmission control are further improved.
• the voltage-dependent nonlinear resistor comprises a surge arrester.
• the surge arrester or lightning arrester, per se can be structured in various suitable ways known to the skilled person, and may e.g. be in the form of a zinc oxide surge arrester, which is also denominated MOV (Metal Oxide Varistor).
• MOV Metal Oxide Varistor
• other types of surge arresters are possible.
• the surge arrester normally conducts a very low current, but when the voltage across the surge arrester exceeds a certain level it will conduct a substantially increased current. By means of this embodiment, the surge current limitation and the electric power transmission control are further improved.
• the apparatus is arranged to limit surge current of the DC transmission or distribution line by introducing, in series with the DC transmission or distribution line, at least one opposing voltage that is at least par- tially based on the electrical device current.
• the surge current limitation and the electric power transmission control are further improved.
• each transformer comprises an air core or a metal core.
• the metal core may be a solid metal core or a laminated metal core.
• the metal core may be an iron core. Other cores may also be possible.
• the primary winding and the secondary winding of the transformer are coaxial.
• the surge current limitation and the electric power transmission control are further improved.
• the apparatus is arranged to assist or control the electric power transmission in a high voltage direct current, HVDC, power transmission system comprising at least one HVDC transmission or distribution line for carrying high voltage direct current.
• the apparatus may also be arranged to assist or control the electric power transmission in an ultra-high voltage direct current, UHVDC, power transmission system, or an extra high voltage direct current power transmission system, each system comprising at least one HVDC transmission or distribution line.
• the apparatus may also be arranged to assist or control the electric power transmission in other DC power transmission systems, e.g. a medium voltage DC power transmission system.
• the inventors have found that the innovative apparatus is especially advantageous for HVDC and UHVDC power transmission system, respectively, and the surge current limitation and the electric power transmission control in these systems are further improved.
• the various components of the apparatus of the present invention may be electrically connected, or connectable, to one another or to other units, e.g. via electrical conductors, e.g. busbars or DC lines, and/or may be indirectly connected, or connect- able, to one another or to other units, e.g. electrically or inductively, e.g. via additional intermediate electric equipment or units located and connected/connectable between the components.
• High Voltage may be about 1 -1 .5 kV and above. However, for HVDC applications and systems, High Voltage may be about 150 kV and above, e.g. 320 kV, 640 kV, 800 kV or 1000 kV, and above.
• the apparatus and/or the system according to the present invention are advantageously adapted for the above-mentioned HVDC voltage levels and above.
• Ultra High Voltage may be about 1 100 kV and above.
• a direct current power transmission system comprising at least one direct current transmission or distribution line for carrying direct current, DC, wherein the system comprises at least one apparatus as claimed in any of the claims 1 -1 1 for assisting or controlling the electric power transmission in the system, and/or at least one apparatus according to any of the above-mentioned embodiments of the appara- tus.
• Positive technical effects of the direct current power transmission system according to the present invention, and its embodiments, correspond to the above- mentioned technical effects mentioned in connection with the apparatus according to the present invention, and its embodiments.
• the at least one direction current transmission or distribution line may be one or a plurality of direct current trans- mission or distribution lines.
• the at least one apparatus may be one or a plurality of apparatuses, e.g. two or more apparatuses. A plurality of apparatuses may be connected to the same DC transmission or distribution line, or to different DC transmission or distribution lines.
• the system comprises a breaking device for breaking the current of the at least one direct current transmission or distribution line, the breaking device being connected in series with the at least one apparatus.
• the breaking device may comprise a mechanical switch and/or at least one power semiconductor switch.
• the breaking de- vice may comprise a parallel connection of a main breaker and a non-linear resistor, the main breaker comprising at least one power semiconductor switch of a first current direction, and a series connection of a high speed switch and an auxiliary breaker, the high speed switch comprising at least one mechanical switch, and the auxiliary breaker has a smaller on-resistance than the main breaker and com- prises at least one power semiconductor switch of the first current direction, where the series connection is connected in parallel to the parallel connection.
• the system comprises a plurality of converters connected to the at least one DC transmission or distribution line, each of the converters being arranged to convert alternating current to direct current for input to the at least one DC transmission or distribution line, and/or direct current to alternating current.
• a plurality of converters may be two or more converters.
• Each converter may be in the form of a converter station, e.g. a VSC (Voltage Sourced Converter), structured in ways known to the person skilled in the art.
• VSC Voltage Sourced Converter
• the system comprises a plurality of DC transmission or distribution lines.
• a plurality of DC trans- mission or distribution lines may be two or more DC transmission or distribution lines.
• the system com- prises at least three converters, each of the converters being arranged to convert alternating current to direct current for input to the at least one DC transmission or distribution line, and/or direct current to alternating current.
• the system comprises at least four converters, or at least five converters.
• the at least one DC transmission or distribution line comprises at least one long-distance HVDC link.
• the HVDC transmission lines may comprise at least two longdistance HVDC links or cables.
• Fig. 1 is a schematic block diagram illustrating a first embodiment of the apparatus according to the present invention
• Fig. 2 is a schematic diagram illustrating the characteristics of an
• Fig. 3 is a schematic block diagram illustrating a second embodiment of the apparatus according to the present invention.
• Fig. 4 is a schematic block diagram illustrating a third embodiment of the apparatus according to the present invention
• Fig. 5 is a schematic block diagram illustrating a fourth embodiment of the apparatus according to the present invention
• Fig. 6 is a schematic block diagram illustrating a fifth embodiment of the apparatus according to the present invention.
• Fig. 7 is a schematic block diagram illustrating aspects of a sixth
• Fig. 8 is a schematic block diagram illustrating a first embodiment of the direct current power transmission system according to the present invention, comprising an apparatus according to the present invention
• Fig. 9 is a schematic block diagram illustrating a second embodiment of the direct current power transmission system according to the present invention, comprising a plurality of apparatuses according to the present invention.
• Fig. 10 is a schematic block diagram illustrating a third embodiment of the direct current power transmission system according to the present invention, comprising an apparatus according to the present invention.
• Fig. 1 1 is a schematic block diagram illustrating a fourth embodiment of the direct current power transmission system according to the present invention, comprising an apparatus according to the present invention.
• each of the Figs. 1 and 3-4 schematically illustrates embodiments of the apparatus 102, 202, 302 according to the present invention, each apparatus 102, 202, 302 being arranged to assist or control the electric power transmission in a direct current power transmission system comprising at least one direct current transmission or distribution line 104 for carrying direct current, DC, / ' ? .
• the DC transmission or distribution line 104 may e.g. comprise a DC cable, busbar, or any other electrical conductor or electrically conductive element or means for carrying direct current.
• Each apparatus 102, 202, 302 comprises a transformer 106, 206, 306 having a primary winding 108, 208, 308 and a secondary winding 1 10, 210, 310, the primary winding 108, 208, 308 being connectable in series with the DC transmission or distribution line 104 to carry the current of the DC transmission or distribution line 104, and the secondary winding 1 10, 210, 310 is connected to an electrical load 1 12, 212, 312.
• the transformer may comprise a plurality of secondary windings each having an electrical load.
• the electrical load 1 12 of the first embodiment of the apparatus 102, shown in Fig. 1 comprises an electrical device 1 14 comprising a nonlinear resistor 216.
• the nonlinear resistor 1 16 may comprise a voltage-dependent nonlinear resistor, e.g. a surge arrester. However, other sorts of voltage-dependent nonlinear resistors are possible.
• the electrical load 212 of the second embodiment of the apparatus 202 comprises an electrical device 214 comprising a linear resistor 216.
• the electrical load 312 of the third embodiment of the apparatus 302, shown in Fig. 4, comprises an electrical device 314 comprising an inductor 316, e.g. a coil.
• a correct direct current i.e. a direct current essentially without any variations in current
• a correct direct current is carried by the DC transmission or distribution line 104 and by the primary winding 108, 208, 308 of the transformer 106, 206, 306.
• Each transformer 106, 206, 306 is arranged to DC isolate the electric load 1 12, 212, 312, from the DC transmission or distribution line 104.
• the electric load 1 12, 212, 312 is DC isolated in that no DC path exists or is provided between the DC transmission or distribution line 104 and the electric load 1 12, 212, 312.
• a correct direct current i.e.
• a non-varying current is carried by the DC transmission or distribution line 104 and by the primary winding 108, 208, 308, no varying magnetic field is created through the secondary winding 1 10, 210, 310, and, consequently, no voltage is induced across the secondary winding 1 10, 210, 310 and no current is supplied to the electrical load 1 12, 212, 312.
• the electrical load 1 12, 212, 312 has no influence on the current / ' ? of the DC transmission or distribution line during steady state, i.e. each transformer 106, 206, 306 DC isolates the electric load 1 12, 212, 312.
• a transient surge current is generated in the DC line 104 and in the primary winding 108, 208, 308 of the transformer 106, 206, 306, e.g. as a result of a transient voltage drop,.
• a surge current may be defined as a short-duration, high-amperage electric current wave that sweeps through the transmission system.
• Each transformer 106, 206, 306 is arranged to supply a secondary current i 2 to the electrical load 1 12, 212, 312, the secondary current i 2 being at least partially based on a surge current of the DC line 104.
• the apparatus 102, 202, 302 is arranged to limit the surge current by introducing at least one opposing voltage vi in series with the DC line 104, the at least one opposing voltage vi being at least partially based on the current i 2 of the electrical load 1 12, 212, 312. More specifically, the apparatus 102, 202, 302 may be arranged to limit surge current of the DC line 104 by introducing, in series with the DC line 104, at least one opposing voltage vi that is at least partially based and dependent on the electrical device current i 2 .
• the control of the electric power transmission or the surge current limitation is attained by the apparatus' 102, 202, 302 introduction, or injection, of an opposing voltage in series with the DC line 104.
• the injected opposing voltage produces a fictive resistance.
• the fictive resistance provides an active power extrac- tion or output from the DC line 104 (since a resistance consumes power/energy).
• the apparatus' 102, 202, 302 active power extraction or output from the DC line 104 results in a decrease, or limitation, of the surge current, which arises in the DC line 104.
• the active power extracted from the DC line 104 may be absorbed by the electrical load 1 12, 212, 312.
• the opposing voltage vi opposes the transient current increase of a surge current.
• the opposing voltage vi may be introduced as a positive voltage in series with the DC line 104 for reducing or limiting a surge current.
• the apparatus 102, 202, 302 provides a "passive" surge current limitation and electric power transmission control, i.e. no active measures performed by an operator are necessary to provide the surge current limitation and the control.
• FIG. 2 is a schematic diagram illustrating the non-linear characteristics of a nonlinear resistor 1 16 of the first embodiment of Fig. 1 , which are well known to the person skilled in the art.
• the transformer relations of the transformer 106 may be given by the following expressions:
• Vl il R 1 + L - M x 2 - [1 ]
• dt dt where vi is the voltage across the primary winding 108, v 2 is voltage across the secondary winding 1 10, is the primary current through the primary winding 102, i 2 is the secondary current through the secondary winding 1 10 and the electrical load 1 12, Ri is the resistance of the primary winding 108, R 2 is the resistance of the secondary winding 1 10, -? is the inductance of the primary winding 108, L 2 is the inductance of the secondary winding 1 10, and M 12 and M 21 are the mutual inductances.
• the mutual inductances M 12 , M 21 may be given by the following expression:
• the secondary voltage v 2 may be equal to the voltage across the nonlinear resistor 1 16 according to the expression:
• Expression [8] clearly illustrates the influence of the nonlinear resistor 1 16 on the voltage vi across the primary winding 108 and thus on the current of the DC line 104 when a varying surge current is generated in the DC line 104.
• the apparatus 502 comprises a plurality of transformers 506, 507, where the primary winding 508, 509 of each transformer 506, 507 is connectable to and connectable in series with the DC line 104 to carry the current of the DC line 104.
• the primary windings 508, 509 of the plurality of transformers 506, 507 may be connected in series with one another.
• the secondary winding 510, 51 1 of each transformer 506, 507 is connected to an electrical load 512, 513. More specifically, the fourth embodiment of the apparatus 502 comprises two transformers 506, 507.
• each electrical load 512, 513 comprises an electrical device 514, 515 comprising a nonlinear resistor 516, 517.
• the fourth embodiment of the apparatus 502 essentially corresponds to the embodiments of Figs. 1 and 3-4.
• Fig. 6 a fifth embodiment of the apparatus 602 is illustrated, which essentially corresponds to the em- bodiment of Fig. 5, but where one of the electrical devices has been replaces and instead comprises an inductor 616.
• the apparatus 702 comprises a plurality of transformers 706, 707, 718, where the primary winding 708, 709, 720 of each transformer 706, 707, 718 is connectable to and connectable in series with the DC line 104 to carry the current of the line 104.
• the primary windings 708, 709, 720 of the plurality of transformers 706, 707, 718 may be connected in series with one another.
• the secondary winding 710, 71 1 , 722 of each transformer 706, 707, 718 is connected to an electrical load 712, 713, 724. More specifically, the sixth embodiment of the apparatus 702 comprises three transformers 706, 707, 718.
• the apparatus with more transformers, or fewer transformers.
• two electrical loads 712, 724 comprise an electrical device 714, 726 comprising an inductor 716, 728, and one electrical load 713 comprises an electrical device 715 comprising a linear resistor 717.
• the sixth embodiment of the apparatus 702 essentially corresponds to the embodiments of Figs. 1 and 3-4.
• the electrical devices of the embodiments of Figs. 5-7, may be replaced by any of the other electrical devices shown in the embodiments of Figs 1 and 3-4.
• Each transformer 106, 206, 306, 506, 507, 606, 607, 706, 707, 718 may comprise a core 130, 230, 330, 530, 630, 730, which may be an air core or a metal core, e.g. an iron core.
• the metal core may be a solid metal core or a laminated metal core.
• the primary winding 108, 208, 308, 508, 509, 608, 609, 708, 709, 720 and the secondary winding 1 10, 210, 310, 510, 51 1 , 610, 61 1 , 710, 71 1 , 722 of the transformer may be coaxial.
• Each of the primary and secondary windings may comprise a coil, and the primary and secondary windings may surround the same core.
• the transformers 506, 507, 606, 607, 706, 707, 718 may be structures in the same manner or they may differ from one another, e.g. with regard to the coupling coefficient, the ratio of the number of turns of the primary and secondary windings, respectively etc.
• the DC line 104 may be a HVDC transmission or distribution line of HVDC power transmission system, and each apparatus 102, 202, 302, 502, 602, 702 may be arranged to assist or control the electric power transmission in the HVDC power transmission system.
• Figs. 1 -7 also illustrates embodiments of the direct current power transmission system according to the present invention, comprising the DC line 104 for carrying direct current, DC, and respective apparatus 102, 202, 302, 502, 602, 702 for assisting or controlling the electric power transmission in the system.
• a further embodiment of the DC power transmission system 802 according to the present invention is schematically illustrated.
• the system 802 comprises at least one DC transmission or distribution line 804 and may comprise a plurality of apparatuses 102 according to the first embodi- ment as disclosed above (see Fig. 1 ). In Fig. 8, only three apparatuses 102 are shown, but is should be understood that the system 802 may comprise more apparatuses 102 than the three shown.
• the DC power transmission system 802 may comprise at least one converter 806, e.g. a converter station, such as a VSC, electrically connected to the DC line 804.
• the converter 806 may be arranged to convert alternating current to direct current for input to the DC transmission line 804 and convert direct current to alternating current for input to at least one neighbouring AC system.
• the system may also comprise a second converter (not shown), e.g.
• the DC power transmission system 802 may be a HVDC power transmission system, and the at least one DC transmission or distribution line 804 may be a HVDC transmission line.
• the DC voltage may be rapidly reduced, e.g. to about zero, resulting in that the current delivered by the converter 806 may be increased, e.g. as illus- trated by the following expression:
• the system 810 may be a HVDC power transmission system and may comprise a plurality of HVDC transmission lines 812, 814, 816, 818, 820 for carrying direct current.
• the HVDC transmission lines 812, 814, 816, 818, 820 may e.g. comprise HVDC cables, busbars, or other DC conductors.
• the HVDC transmission lines 812, 814, 816, 818, 820 may comprise at least one long-distance HVDC link 812, 818.
• a first and a second HVDC transmission line 812, 818 of said plurality of HVDC transmission lines 812, 814, 816, 818, 820 are in the form of longdistance HVDC links.
• HVDC transmission lines and links are well known to the skilled person and thus not discussed in further detail.
• the HVDC power transmission system 810 comprises a plurality of converters 822, 824, 826, 828, e.g. con- verier stations, electrically connected to the HVDC transmission lines 812, 814, 816, 818, 820.
• four converters 822, 824, 826, 828 are provided, but there may be more or fewer converters.
• Each of the converters 822, 824, 826, 828 may be arranged to convert alternating current to direct current for input to the HVDC transmission lines 812, 814, 816, 818, 820 and convert direct current to alternating current for input to neighbouring AC systems.
• One of the long-distance HVDC links 818 is provided with the first embodiment of the apparatus 102, disclosed above, and the other long-distance HVDC link 812 is provided with the fourth embodiment of the apparatus 502 disclosed above.
• the apparatuses 102, 502 may be connected to the system 810 at other locations or connection points.
• the HVDC power transmission system 810 may be adapted for single phase power or multi-phase power, e.g.
• system 810 may instead be provided with one or a plurality of the other embodiments of the apparatus according to the present invention disclosed above, or combinations thereof.
• the system may comprise a breaking device 834 for breaking the current of a DC transmission or distribution line 832.
• the breaking device 834 is connected in series with the apparatus 102.
• the breaking device 834 may comprise a mechanical switch and/or at least one power semiconductor switch. It is to be understood that the system 830 may be provided with more than one apparatus according to the present invention.
• the first embodiment of the apparatus 102 of the system of Fig. 10 may be replaced by any of the embodiments of the apparatus disclosed above.
• FIG. 1 1 still another embodiment of the DC power transmission system 900 according to present invention is schematically illus- trated, comprising a DC transmission or distribution line 914 to which an apparatus 102 according to the first embodiment of the apparatus 102 disclosed above is connected.
• the system 900 may comprise a breaking device 913 connected in series with the apparatus 102 and in series with the DC line 914.
• the breaking device 913 comprises a parallel connection of a main breaker 908 and a non-linear resistor 91 1 , the main breaker 908 comprising at least one power semiconductor switch 901 of a first current direction 904, and a series connection of a high speed switch 910 and an auxiliary breaker 909.
• the high speed switch 910 comprises at least one mechanical switch.
• the auxiliary breaker 909 has a smaller on-resistance than the main breaker 908 and comprises at least one power semiconductor switch 901 of the first current direction 904. Said series connection is connected in parallel to said parallel connection.
• the main breaker 908 may comprise a plurality of power semiconductor switches 901 of the first current direction 904. In Fig.
• each power semiconductor switch 901 is included in a base ele- ment 906.
• the apparatus 102 is also connected in series with a reactor 912, e.g. a coil.
• the reactor 912 may be excluded from the system 900.
• the inventors have found that the combination of the apparatus of the present invention and the breaking device 913 of Fig. 1 1 improves the surge current limitation and the electric power transmission control.
• the semiconductor chip area may be reduced, and the breaking speed of the high speed switch 910 is less crucial, i.e. the high speed switch 910 does not need to be that fast, whereby productions costs are reduced.
• the various components of the apparatus and the system of the present invention which are connected or connectable to one another or to other units, may be electrically connected, or connectable, to one another or to other units, e.g. via electrical conductors, e.g. busbars or DC lines, and/or may be indirectly connected, or connectable, e.g. electrically, to one another or to other units, e.g. via additional intermediate electric equipment or units located and con- nected/connectable between the components.

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Citations (10)

• 2012
  • 2012-05-23 WO PCT/EP2012/059629 patent/WO2013174429A1/fr not_active Ceased

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