Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H33/00—High-tension or heavy-current switches with arc-extinguishing or arc-preventing means
  • H01H33/02—Details
  • H01H33/59—Circuit arrangements not adapted to a particular application of the switch and not otherwise provided for, e.g. for ensuring operation of the switch at a predetermined point in the ac cycle
  • H01H33/596—Circuit arrangements not adapted to a particular application of the switch and not otherwise provided for, e.g. for ensuring operation of the switch at a predetermined point in the ac cycle for interrupting dc
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
  • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
  • H02H3/087—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current for dc applications
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
  • H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
  • H01H9/541—Contacts shunted by semiconductor devices
  • H01H9/542—Contacts shunted by static switch means
  • H01H2009/543—Contacts shunted by static switch means third parallel branch comprising an energy absorber, e.g. MOV, PTC, Zener
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
  • H01H9/54—Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere
  • H01H9/548—Electromechanical and static switch connected in series

Definitions

• the present invention generally relates to high voltage power systems. More particularly the present invention relates to a current limiting device for a high voltage power system as well as to a high voltage direct current arrangement and high voltage power system comprising such a current limiting device.
• conductors and comprising disconnectors may be used in a variety of high voltage applications, such as for instance as direct current circuit breakers of high voltage direct current power transmission systems.
• One realization of such a circuit breaker is known from WO 2011/057675 where there is a first branch comprising a main circuit breaker in parallel with a second branch comprising a disconnector and a load commutation switch.
• surge arresters are connected in parallel with the main breaker and possibly also with the load commutation switch.
• the main breaker as well as the load commutation switch may be realized through the use of series-connected electronic switches such as transistors.
• the disconnector may be permanently closed during steady state operation and may need to be opened in case of abnormal operation such as due to a fault. Both the load commutation switch and the main breaker may need to be opened.
• One problem of such circuit breakers is the powering of the
• US 2015/03724474 describes one powering solution where a transformer connected in a filter is used as a current source injecting a current into a branch of the circuit breaker for powering the semiconductors, where the filter is also used for filtering away the injected current.
• Another problem is associated with the handling of faults.
• One type of fault that can occur is a ground fault.
• the power line conductor comprises an overhead line
• such a ground fault may cause the generation of high frequency currents caused by reflections at the fault location. This current may in turn lead to problems in the opening of the disconnector. There is thus a need for handling these high frequency currents that are caused by ground faults in overhead lines.
• the present invention addresses the problem of handling high-frequency currents in high voltage equipment comprising disconnectors when there are ground faults in overhead lines.
• This object is according to a first aspect of the present invention achieved through a current limiting device for high voltage equipment in a high voltage direct current power system, where the high voltage equipment is connected in series with a power line conductor of the high voltage direct current power system and comprises a disconnector operable to obtain a mechanical separation from the power line conductor.
• the current limitation device comprises a first current limiting circuit for connection between the power line conductor and a first connection terminal of the equipment and is operable to reduce alternating currents in the frequency range of 70 - 200 kHz.
• the object is according to a second aspect of the invention achieved through a high voltage direct current arrangement comprising a current limiting device according to the first aspect and a high voltage equipment equipped with a disconnector (UFD) for connection in series with a power line conductor of a high voltage direct current system.
• the object is according to a third aspect of the invention achieved through a high voltage direct current system comprising a high voltage equipment equipped with a disconnector, a power line conductor connected in series with the high voltage equipment and a current limiting circuit according to the first aspect.
• the present invention has a number of advantages. It allows the disconnector of the high voltage equipment to be safely opened without having to consider where a fault occurs. Furthermore, any disconnector control mechanism that is used to open the disconnector does not have to consider when high-frequency currents appear. This also simplifies such control substantially.
• Fig. 1 schematically shows a first type of DC power transmission system in the form of a single power line comprising a DC circuit breaker and interconnecting two converter stations,
• fig. 2 schematically shows a second type of DC power transmission system in the form of DC grid interconnecting several converter stations
• fig. 3 schematically shows a first type of DC circuit breaker connected between mechanical switches and current limiting inductors
• fig. 4 schematically shows the circuit breaker, mechanical switches and current limiting inductors of fig. 3 together with two current limiting circuits of a current limiting device
• fig. 5 schematically shows a first embodiment of a current limiting device together with the DC circuit breaker and first and second current limiting inductors
• fig. 6 schematically shows voltages at a first terminal of the circuit breaker and at the second current limiting inductor of fig. 3 together with a current through the circuit breaker in relation to a fault on the DC link,
• fig. 7 shows the same voltages and current in relation to a fault on the DC link for the Dc circuit breaker, second current limiting inductor and current limiting device of fig. 4,
• fig. 8 shows an alternative placing of the current limiting device according to a variation of the first embodiment
• fig. 9 shows a second embodiment the current limiting device together with the DC circuit breaker and first and second current limiting inductors
• fig. 10 shows a third embodiment of the current limiting device together with the DC circuit breaker
• fig. 11 schematically shows a second type of DC circuit breaker that can be combined with the current limiting device.
• Fig. 1 shows a simplified Direct Current (DC) power system 10, such as a
• High Voltage Direct Current (HVDC) power system comprising a first converter station 11 and a second converter station 12.
• the two converter stations 11 and 12 are interconnected by a first DC link 18, which first DC link 18 comprises a DC circuit breaker 20, which may be a hybrid HVDC circuit breaker.
• the system 10 in fig. 1 is a point-to-point power transmission system for connection between two Alternating Current (AC) power transmission systems.
• the HVDC system 10 includes a first and a second converter station 11 and 12, where the first converter station 11 includes a first transformer TRi.
• the first converter station 11 also comprises a first converter 14 for conversion between AC and DC, which converter 14 therefore comprises an AC side connected to the transformer TRi and a DC side connected to the first DC link 18.
• the first transformer TRi thus connects the first converter 14 to a first AC power transmission system (not shown).
• the first converter 14 is connected to a second converter 16 of a second converter station 12 via the first DC link 18, which first DC link 18 may comprise a power line or cable with at least one power line conductor.
• the first DC link 18 may more particularly comprise an overhead line.
• the second converter 16 also converts between AC and DC and may be an inverter.
• the second converter station 12 may also include a second transformer TR2, which connects the second converter 16 to a second AC power transmission system (not shown).
• the DC system 10 and the AC systems are all examples of high voltage power systems, and in this case also examples of high voltage power transmission systems.
• the converters 14 and 16 may both be forced commutated voltage source converters (VSCs) and may be either two-level converters or multilevel converters comprising cells, i.e. voltage source converters employing cells for forming multiple voltage levels.
• VSCs forced commutated voltage source converters
• the conversion may be made between DC and three-phase AC. Therefore, both converters 14 and 16 may have three phase legs, one for each phase.
• voltage source converters such as neutral-point clamped three-level converters and various n-level converters.
• the converters may furthermore also be realized as current source converters, such as line- commutated current source converters.
• DC circuit breaker 20 in the DC link 18.
• This DC circuit breaker 20 may be placed on a considerable distance from both converter stations.
• the DC circuit breaker 20 is more particularly connected in series with power line conductors of the DC link, which conductors may be the conductors of a pole of the DC system.
• the DC circuit breaker 20 is thus connected in the first DC link 18 between the two converter stations 11 and 12. Although only one is shown, it should be realized that there may be one such DC circuit breaker in the proximity of each converter station.
• Such a DC circuit breaker at a converter station may be connected in series with only one power line conductor.
• the HVDC system 10 in fig. 1 is a monopole system. It should however be realized that the system may also be a bipole system.
• Fig. 2 shows another type of HVDC system.
• the system is here a multi- terminal HVDC system 22, such as an HVDC system comprising a number of converters converting between AC and DC.
• Each converter comprises an AC side and a DC side, where the DC side of a third converter 24 is connected to the DC side of a fourth converter 26 via a second DC link 32, the DC side of a fifth converter 28 is connected to the DC side of a sixth converter 30 via a third DC link 34.
• a DC circuit breaker 20 connected in all the DC links 32, 34, 36 and 38.
• Fig. 3 shows a first variation of a DC circuit breaker 20, which in this case is the previously mentioned HVDC hybrid circuit breaker.
• the DC circuit breaker 20 has a first and a second connection terminal Ti and T2, where the second connection terminal T2 is connected to a first current limiting inductor CLI_i, which in turn is connected to a first mechanical switch MSi.
• the first connection terminal Ti is connected to a second current limiting inductor CLI_2, which in turn is connected to a second
• the mechanical switches MSi and MS2, current limiting inductors CLI_i and CLI_2 and the DC circuit breaker 20 are intended to be connected in series between two converter stations using a DC link, where one or two conductors of a power line of the DC link may also be placed in this series connection. Furthermore such an HVDC link will comprise an overhead line.
• the circuit breaker 20 may thus be connected in series with the conductor of an overhead line of the DC link.
• one side of the hybrid HVDC breaker 20 may be connected to an Over-head-line (OHL) or to a DC cable, while the other side may be connected to an High-Voltage DC (HVDC) converter station or another overhead line or cable.
• OTL Over-head-line
• HVDC High-Voltage DC
• a series-connection of a disconnector UFD which may be an ultrafast disconnector
• a load commutation switch LCS between the second and first connection terminal T2 and Ti.
• a main breaker MB connected in parallel with the series connection of disconnector UFD and load commutation switch LCS, where a first surge arrester SAi is connected in parallel with the main breaker MB and a second surge arrester SA2 is connected in parallel with the load commutation switch LCS.
• the main breaker MB may be made up of a series connection of switches of the turn-off type with anti-parallel diodes, which switches may be transistors such as Junction Field Effect Transistors (JFET), Insulated Gate Bipolar Transistors (IGBT), or Bi-mode Insulated Gate Transistors (BIGT) or thyristors, such as Integrated Gate-Commutated Thyristors (IGCT) or Bi-mode Gate Commutated Thyristors (BGCT).
• JFET Junction Field Effect Transistors
• IGBT Insulated Gate Bipolar Transistors
• BIGT Bi-mode Insulated Gate Transistors
• thyristors such as Integrated Gate-Commutated Thyristors (IGCT) or Bi-mode Gate Commutated Thyristors (BGCT).
• the load commutation switch LCS may have the same realization. The difference between the two elements is generally the rating, where the main breaker MB is able to handle higher currents than the load commutation switch L
• the disconnector UFD is in turn a mechanical switch that obtains a mechanical separation of the disconnector branch from the power line conductors.
• a first current In leading into the second connection terminal T2 of the DC circuit breaker 20 which is divided into a second current h 2 into the main breaker MB and a third current 3 ⁇ 4 into the disconnector UFD.
• a first voltage Vi at the first connection terminal Ti which is a voltage of the junction point between the circuit breaker 20 and the second current limiting inductor CLI_2 with respect to ground
• a second voltage V 2 which is a voltage of the junction point between the second current limiting inductor CLI_2 and the second mechanical switch MS2 with respect to ground.
• Fig. 4 schematically shows the DC breaker 20 connected to the first mechanical switch MSi via the first current limiting inductor CLI_i using the second connection terminal T2 and to the second mechanical switch MS2 via the second current limiting inductor CLI_2 using the first connection terminal Ti.
• the second mechanical switch MS2 is further connected to a converter station, while the second current limiting inductor CLI_2 is connected to a conductor 44 of the power line in the DC link 18.
• a current limiting device 41 comprising a first and a second current limiting circuit 42 and 43, where the first current limiting circuit 42 is connected between the DC circuit breaker 20 and the second current limiting inductor CLI_2, while the second current limiting circuit 43 is connected between the DC circuit breaker 20 and the first current limiting inductor CLI_i.
• the first current limiting circuit 42 is thereby connected between the first connection terminal Ti of the DC circuit breaker 20 and the conductor 44, which in this case is also between the first connection terminal Ti of the DC circuit breaker 20 and the second current limiting inductor CLI_2.
• the second current limiting circuit 43 is connected between the second connection terminal Ti of the DC breaker 20 and the first current limiting inductor CLI_i.
• a current limiting device only comprises one current limiting circuit, either the first or the second.
• Each current limiting circuit may more particularly be operable to reduce alternating currents in the frequency range of 70 - 200 kHz.
• the combination of current limitation device and DC circuit breaker also make up a high voltage direct current arrangement.
• the two voltages Vi and V 2 are shown, where the first voltage Vi in this case is the voltage at the junction between the first connection terminal Ti of the DC circuit breaker 20 and the first current limiting circuit 42.
• Fig, 5 schematically shows a first embodiment of the current limiting device.
• the current limiting device only comprises the first current limiting circuit.
• the current limiting device thus consists of the first current limiting circuit.
• the first current limiting circuit also comprises a first capacitor.
• the first current limiting circuit only comprises the first capacitor Ci. It thus consists of the first capacitor Ci.
• This capacitor can according to the variation shown in fig. 5 be added before the second current limiting inductor CLI_2 and may have a value in the range of 0.5 - 4 ⁇ and may for instance have the value of 1 ⁇ .
• the first capacitor Ci is thus connected at a junction between the first connection terminal Ti and an inductor, here the second current limiting inductor CLI_2, leading to the power line conductor 44.
• the first capacitor Ci is in the disclosed variation of the first embodiment connected between the first connection terminal Ti of the DC circuit breaker 20 and the second current limiting inductor CLI_2. It is more particularly connected between this second connection terminal T2 and ground. Thereby it is connected in shunt with the power line conductor and to the junction between the second current limiting inductor CLI_2 and the circuit breaker 20.
• the DC circuit breaker 20 which is one type of high voltage equipment equipped with a disconnector, is used for safety purposes to obtain a disconnection of elements in the DC transmission system when there is a fault on a DC link such as a pole-to-ground fault.
• the general operation of the DC circuit breaker 20 is normally the following: ⁇ Stage a. Normal operation: the disconnector UFD, load commutation switch LCS and main breaker MB are closed. Thereby a load current 3 ⁇ 4 flows through the disconnector branch comprising the disconnector UFD and load commutation switch LCS.
• Stage b Under fault, the load commutation switch LCS is opened after the fault current crosses a certain threshold. A Fault current IT2 is then diverted into the main breaker MB.
• Stage d the main breaker MB is opened, whereby the fault current ⁇ 2 is diverted into arresters SAi connected across the main breaker MB.
• Arresters SAi limit the fault current and mechanical switches MS2 and possibly also MSi are opened to isolate the fault.
• the disconnector UFD is a key component in the circuit breaker 20 used for obtaining a mechanical separation from a power line conductor.
• the DC link may comprise an overhead line.
• an overhead line such as a pole-to-ground fault
• the fault may give rise to fault current reflections. These may make it hard to open the
• fig. 6 shows the first and second voltages Vi and V 2 in kV and the current 3 ⁇ 4 through the disconnector UFD in kA when there is a ground fault on the overhead line conductor 44 for the DC circuit breaker 20 in fig. 3, i.e. when there is no current limiting device.
• the circuit breaker 20 will then operate stages a and b described above. Now, due to the fault, the DC link voltage at the fault location will experience high dv/dt and this disturbance travels through the overhead line from the location of the fault to reach the circuit breaker 20. It is to be noted that the circuit breaker 20 is connected in series with the conductor 44 of the DC link 18 and hence is at pole potential with respect to ground. Because of this, there may exist some stray capacitances between various points of the DC circuit breaker 20 and ground. Moreover, the associated voltage disturbance or high dv/dt causes high-frequency currents flows through the stray capacitances.
• Fig. 6 shows the disconnector current 3 ⁇ 4, and the voltages before V 2 and after Vi the second fault limiting inductor CTI_2. From the waveform of V 2 it can be observed that reflections ri, r2 and r3 due to the DC link conductor being an overhead line causes high-frequency oscillations.
• disconnector current 3 ⁇ 4 still experiences oscillations, as can also be observed from Fig. 6. These oscillations are in the frequency range of 70 - 200 kHz. Further, the amplitude of current due to reflections is quite high, and is higher than the above-mentioned limit. The amplitude as well as the instance of high-frequency currents due to reflections is a strong function of the fault location and is very difficult to predict. It is difficult to determine when the disconnector UFD is to be opened. Hence, the best possible solution is to mitigate the effect of reflections.
• the current limiting device is provided for addressing this situation.
• the current limiting device 41 is thus provided for mitigating the effect of reflections.
• a current limiting circuit of the current limiting device may furthermore operate in two ways in order to limit the current amplitude, where one is to keep the voltage stiff and the other is to filter out the currents.
• the first embodiment shown in fig. 5 operates to keep the voltage Vi stiff in order to reduce the high-frequency oscillations in the disconnector current IT 3 due to reflections.
• Fig. 7 shows the voltages Vi and V 2 and the disconnector current 3 ⁇ 4 for the circuit breaker with the same fault as in fig. 6, but where the current limiting device according to the first embodiment is used.
• the circuit is thus the circuit of fig. 4, but where the current limiting device 41 only comprises the first current limiting circuit 42, which in turn consists of the first capacitor Ci.
• the first capacitor Ci was connected between the first connection terminal Ti of the DC circuit breaker 20 and the second current limiting inductor CLI_2.
• the second current limiting inductor is divided into two separate inductors CLI_2a and CLI_2b.
• one end of the first capacitor Ci is then connected between these two inductors CLI_2a and CLI_2b, with the other connected to ground. This situation is schematically shown in fig. 8.
• the first capacitor Ci is thus connected at a junction between a first part of an inductor CLI_2a leading to the first connection terminal Ti and a second part of the inductor CLI_2b leading to the power line conductor 44.
• the current limiting device may comprise the previously mentioned second current limiting circuit connected to the second connection terminal T2 of the DC circuit breakers, which would be between the DC circuit breaker 20 and the first current limiting inductor CL_i.
• the second current limiting circuit comprises a shunt-connected second capacitor C2 connected to the second connection terminal T2.
• the second capacitor C2 has the same purpose as the first capacitor Ci, namely to keep the voltage stiff at the second connection terminal T2 and thereby reduce alternating currents in the frequency range of 70 - 200 kHz.
• the second capacitor C2 may therefore have the same value as the first capacitor Ci.
• fig. 10 shows a third embodiment of the current limiting device comprising a first and a second current limiting circuit.
• the first current limiting circuit is in this case a first filter Fi and the second current limiting circuit is a second filter F2, where the first filter Fi is connected between the first connection terminal Ti of the circuit breaker 20 and the second current limiting inductor (not shown) and the second filter F2 is connected between the second connection terminal T2 of the circuit breaker 20 and the first current limiting inductor (not shown).
• each filter comprises two capacitors connected between the line and ground and separated by a resistor in parallel with an inductor.
• each filter is here set to - filter out high frequency currents in the frequency range of 70 - 200 kHz in order to allow the disconnector UFD of the circuit breaker 20 to be opened.
• the specific filter realization shown is only exemplifying and that each filter may have a different realization.
• a filter need not comprise the first and second capacitor, respectively, but may be realized only using inductors as reactive elements possibly together with resistors.
• a filter may be realized only using capacitors as reactive elements, possibly combined with resistors.
• the circuit breaker 45 is a full-bridge based DC circuit breaker and comprises a main branch MB comprising an ultrafast disconnector UFD in series with a full- bridge cell FBM.
• a transfer branch TB of series connected full-bridge cells FBi, FB2 ....FBn-i and FBn.
• an absorber branch AB in parallel with the main and transfer branches MB and TB, which absorber branch AB compromises one or more surge arresters SA3 and SA4.
• the main and transfer branches may each additionally comprise inductors.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Driving Mechanisms And Operating Circuits Of Arc-Extinguishing High-Tension Switches (AREA)
• Direct Current Feeding And Distribution (AREA)

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Applications Claiming Priority (1)

Publications (1)

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ID=55538245

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Cited By (3)

Citations (5)

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• 2016
  • 2016-03-17 WO PCT/EP2016/055754 patent/WO2017157440A1/en active Application Filing
  • 2016-03-17 CN CN201680082120.8A patent/CN109075555B/zh active Active

Patent Citations (5)

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