CN113872169A - Magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter and current limiting method - Google Patents
Magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter and current limiting method Download PDFInfo
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 163
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- QJVKUMXDEUEQLH-UHFFFAOYSA-N [B].[Fe].[Nd] Chemical compound [B].[Fe].[Nd] QJVKUMXDEUEQLH-UHFFFAOYSA-N 0.000 claims description 4
- 229910001172 neodymium magnet Inorganic materials 0.000 claims description 4
- 239000003302 ferromagnetic material Substances 0.000 claims description 3
- 229910052761 rare earth metal Inorganic materials 0.000 claims description 3
- 150000002910 rare earth metals Chemical class 0.000 claims description 3
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/24—Magnetic cores
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/28—Coils; Windings; Conductive connections
- H01F27/30—Fastening or clamping coils, windings, or parts thereof together; Fastening or mounting coils or windings on core, casing, or other support
- H01F27/303—Clamping coils, windings or parts thereof together
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/28—Coils; Windings; Conductive connections
- H01F27/30—Fastening or clamping coils, windings, or parts thereof together; Fastening or mounting coils or windings on core, casing, or other support
- H01F27/306—Fastening or mounting coils or windings on core, casing or other support
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F29/00—Variable transformers or inductances not covered by group H01F21/00
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- 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
- H02H9/021—Current limitation using saturable reactors
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Abstract
The invention relates to a saturated iron core type direct current fault current limiter technology, in particular to a magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter and a current limiting method, wherein the current limiter comprises an iron core, a direct current main branch winding, a coupling branch peripheral circuit and a permanent magnet; the iron core is of a square solid structure and comprises a left iron core column, a right iron core column, an upper transverse yoke and a lower transverse yoke, wherein the upper transverse yoke and the lower transverse yoke are respectively positioned at the upper end and the lower end of the left iron core column and the right iron core column; the direct current main branch winding is wound on the left iron core column and the right iron core column, and the coupling branch winding is wound on the outer side of the direct current main branch winding and connected with a coupling branch peripheral circuit. The current limiter can realize the quick absorption of short-circuit fault energy, effectively limit the direct-current power grid fault current, reduce the time of the fault current acting on a current limiter winding in the current reduction stage, reduce the energy absorption and overvoltage of a direct-current circuit breaker, and simultaneously can quickly absorb and consume the short-circuit fault energy of a direct-current system.
Description
Technical Field
The invention belongs to the technical field of saturated iron core type direct current fault current limiters, and particularly relates to a magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter and a current limiting method.
Background
The rapid rise of the fault current of the high-voltage direct-current system threatens the safe operation of the high-voltage direct-current system, so that a fault current limiter for limiting the rise speed of the fault current is indispensable for the safe operation of the system. The existing traditional magnetic saturation core type direct current fault current limiter is shown in figure 1, a permanent magnet is embedded in an iron core to generate variable inductance, the direction of a magnetic field of the permanent magnet is opposite to that of a magnetic field generated by direct current in a coil, and the magnetic field of the permanent magnet enables the iron core to be in a magnetic saturation state. When the transformer works normally, the magnetomotive force generated by the rated current of the system is not enough to make the iron core separate from the saturation region, so that the coil is in a low inductance state in the power grid. When short-circuit fault occurs, the magnetic flux generated by large current is enough to offset the magnetic flux of the permanent magnet, the iron core is separated from the saturation state, and the current limiter quickly generates high inductance, so that the rising speed of the short-circuit current is limited. However, when the conventional magnetic saturation core type current limiter is turned on or off, the dc circuit breaker can bear high overvoltage and increase energy absorption of the dc circuit breaker, and meanwhile, the system fault current reduction time is prolonged. The existing fast response direct current limiter topology is shown in fig. 2, and a method of coupling a traditional magnetic saturation core type direct current fault current limiter with a resistance energy absorption branch is adopted, so that the fast response direct current limiter topology has the advantages of being capable of absorbing fault energy, but has the defects that the energy absorption speed is low, the fault current acts on a winding for a long time, the winding and an iron core are heated, and the service life is influenced. The existing topology of the rapid energy storage type magnetically saturated iron core direct current fault current limiter is shown in fig. 3, and the method of coupling an energy storage branch circuit with the traditional magnetically saturated iron core direct current fault current limiter has the advantages of being capable of storing fault energy, but has the defects of high overall cost due to the adoption of a large number of high-capacity thyristors and high-voltage high-capacity energy storage capacitors. Meanwhile, the secondary windings of the two current limiters in fig. 2 and 3 are wound separately on the left and right poles, are in a loose coupling state, and have large magnetic flux leakage, low energy transfer efficiency and certain loss.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a novel magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter.
In order to solve the technical problems, the invention adopts the following technical scheme: a magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter comprises an iron core, a first direct current main branch winding, a second direct current main branch winding, a third coupling branch winding, a fourth coupling branch winding, a coupling branch peripheral circuit, a first permanent magnet and a second permanent magnet; the iron core is of a square solid structure and comprises a left iron core column, a right iron core column, an upper transverse yoke and a lower transverse yoke, wherein the upper transverse yoke and the lower transverse yoke are respectively positioned at the upper end and the lower end of the left iron core column and the right iron core column; the first direct-current main branch winding and the second direct-current main branch winding are respectively wound on the left iron core column and the right iron core column and are connected in series with a direct-current power grid; and the third coupling branch winding and the fourth coupling branch winding are wound on the outer sides of the first direct current main branch winding and the second direct current main branch winding respectively in a tight coupling mode and are connected with a peripheral circuit of the coupling branch.
In the above magnetic coupling rapid energy-absorbing saturated core dc fault current limiter, the coupling branch peripheral circuit includes: diode D1And a charging energy storage capacitor C1Energy absorption resistor R1Mechanical switch B1(ii) a Wherein, the diode D1And a charging energy storage capacitor C1The third coupling branch winding and the fourth coupling branch winding are connected in series; mechanical switch B1And an energy absorption resistor R1Connected in series and in parallel with the charging energy storage capacitor C1Two ends.
In the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter, the sections of the left iron core column and the right iron core column are circular, oval or rectangular.
In the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter, the sections of the left iron core column and the right iron core column are rectangular, and the sections and the lengths are the same; the lengths and the sectional areas of the upper transverse yoke and the lower transverse yoke are equal; the sectional areas of the first permanent magnet and the second permanent magnet are equal to the sectional area of the transverse yoke where the first permanent magnet and the second permanent magnet are located, the thicknesses of the first permanent magnet and the second permanent magnet are the same, and the sizes of the first permanent magnet and the second permanent magnet are the same; the sectional areas of the left iron core column and the right iron core column are smaller than the sectional areas of the first permanent magnet and the second permanent magnet.
In the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter, the first permanent magnet and the second permanent magnet are both made of rare earth permanent magnet material neodymium iron boron.
In the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter, magnetic fluxes generated by the first permanent magnet and the second permanent magnet are clockwise in an iron core.
In the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter, the left iron core column and the right iron core column are in a critical saturation state under the normal state of a power grid, and the left iron core column and the right iron core column are in the desaturation speed at the turning point of a B-H curve of a ferromagnetic material during fault.
In the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter, the number of turns of the first direct current main branch winding and the second direct current main branch winding is larger than the number of turns of the third coupling branch winding and the fourth coupling branch winding.
A current limiting method of a magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter comprises the following steps:
under the normal working condition, the working current of the power grid is small, and the bias magnetomotive force generated by the permanent magnet occupies absolute advantage compared with two direct-current main branch winding coils, so that the left iron core column and the right iron core column are influenced by the permanent magnet to be saturated in normal working; the magnetic conductivity of the iron core during saturation is approximately equal to the air magnetic conductivity, and when the system normally operates, the normal impedance of the current limiter is very small, so that the total inductance of the two direct current main branch winding coils is consistent with that of the high-voltage direct current smoothing reactor, and the normal operation of the system is not influenced; meanwhile, the iron core is in a magnetic saturation state, and the coupling branch cannot be conducted due to the fluctuation of system current;
when a fault occurs, the current of a direct current system is increased, and the directions of magnetic fluxes generated by the two direct current main branch winding coils and the two permanent magnets are opposite, so that the left and right iron core columns are quickly desaturated; the magnetic permeability of the iron core after saturation is removed rapidly rises, so that the inductance values of the two direct current main branches are larger, and the short-circuit fault current is limited; the direction of the voltage generated across the current limiter and the diode D during the fault current drop phase1The direction of the breakover voltage is the same, the coupling branch is connected with the direct current main branch in parallel through magnetic coupling, and fault current flows into the coupling branch to the capacitor C through the magnetic coupling1Charging is carried out, and the mechanical switch B is conducted after the charging is finished1Through an energy-absorbing resistor R1Absorbing stored fault energy;
after the fault is eliminated, the fault current is reduced, at the moment, the working state of the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter is recovered to the state under the normal working condition of the line, the integral impedance value is reduced, and the normal operation of the system is not influenced.
Compared with the prior art, the invention has the beneficial effects that: 1. the topological structure of the invention adopts the saturated iron core and the permanent magnet to generate variable reactance, and the method has good effect on limiting the extremely fast rising speed of the fault current in the rising stage of the fault current. 2. The fault current can be limited within millisecond-level time after the fault occurs, and when the fault current is matched with a direct current circuit breaker, the fault current can be effectively cut off at the early stage of the fault, so that a circuit breaker with smaller capacity can be used, and the stability of a direct current system is ensured. 3. In the fault current limiting stage, a control system is not required to be additionally arranged, and the current limiter can automatically and quickly respond to the fault. 4. Compared with the traditional magnetic saturation iron core type fault current limiter, the direct current breaker can greatly reduce the energy absorption and reduce the overvoltage to a certain degree. 5. Compared with a quick response direct current limiter topology, the direct current limiter topology has the advantages that the energy absorption speed is greatly improved, the time of fault current acting on a winding is reduced, and the service life of the current limiter is prolonged. Meanwhile, the breaking electrical stress (overvoltage and energy absorption) generated when the direct current breaker is cut off is lower. 6. Compared with the rapid energy storage type magnetic saturation iron core direct current fault current limiter, the invention utilizes the mechanical switch matched with the energy absorption resistor to replace a large number of high-capacity thyristors, reduces the use of a high-voltage high-capacity capacitor and greatly reduces the overall cost. On the premise of better economy, the current limiting device ensures the superior current limiting characteristic and has more remarkable effect of reducing the breaking electrical stress of the circuit breaker. 7. The invention improves the primary and secondary winding method of two current limiters in the topology of the quick response direct current limiter shown in figure 2 and the topology of the quick energy storage type magnetic saturation iron core direct current fault current limiter shown in figure 3, changes the loose coupling state into the tight coupling state, reduces the external magnetic leakage and the energy loss, and improves the efficiency of energy transfer.
Drawings
FIG. 1 is a schematic diagram of a conventional magnetic saturation type DC current limiter;
FIG. 2 is a schematic diagram of a fast response DC current limiter topology;
FIG. 3 is a schematic diagram of a topology of a fast energy storage type magnetically saturated core DC fault current limiter;
FIG. 4 is a magnetic coupling fast energy absorbing DC current limiter electromagnetic topology according to an embodiment of the present invention;
FIG. 5 is an equivalent circuit diagram of a magnetic coupling fast energy absorption DC current limiter and a DC circuit breaker connected in series according to an embodiment of the present invention;
fig. 6a is a diagram of a current flowing path of a current limiter in a normal phase of a magnetically-coupled fast energy-absorbing saturated core dc fault current limiter according to an embodiment of the present invention;
fig. 6b is a diagram of a current flowing path of the current limiter at a fault current rising stage of the magnetic coupling rapid energy absorption type saturated core direct current fault current limiter according to the embodiment of the present invention;
fig. 6c is a diagram of a current flowing path of the current limiter in a fault current reduction stage (energy storage stage) of the magnetic coupling rapid energy absorption type saturated core direct current fault current limiter according to the embodiment of the present invention;
fig. 6d is a diagram of a current flowing path of the current limiter in the stage of completing energy storage of the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter according to the embodiment of the present invention;
fig. 6e is a current flow path diagram of the magnetic coupling rapid energy absorption type saturated iron core dc fault current limiter in the rapid energy absorption stage according to the embodiment of the present invention;
FIG. 7 is a comparison diagram of the magnetic coupling fast energy absorption type DC current limiter of the embodiment of the present invention and the energy absorption of the circuit breaker when various current limiters are matched with the DC circuit breaker;
FIG. 8 is a diagram showing the comparison of the overvoltage of the magnetic coupling rapid energy absorption type DC current limiter and the DC circuit breakers matched with various current limiters according to the embodiment of the present invention;
FIG. 9 is a comparison of the fault current withstand time of the windings of the magnetically coupled fast energy absorbing DC current limiter and the fast response DC current limiter according to the embodiment of the present invention;
fig. 10 is a waveform comparison graph of an experimental result and a small-capacity simulation result of a magnetic coupling rapid energy absorption type direct current limiter small-capacity prototype according to an embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention.
The embodiment provides a novel topological structure of a magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter, and a coupling branch is additionally arranged on the outer side of a direct current winding on left and right iron core columns of a traditional magnetic saturation direct current limiter in a magnetic coupling mode to reduce overvoltage and energy absorption of a direct current breaker and achieve rapid absorption of short-circuit fault energy, so that the time of fault current acting on the winding is reduced, the winding is prevented from being overheated, and the service life of the winding is prolonged.
The embodiment is realized by the following technical scheme that the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter comprises an iron core, a direct current winding, a permanent magnet and a coupling branch circuit, as shown in fig. 4. The iron core is of a square solid structure and comprises a left iron core column, a right iron core column, an upper transverse yoke and a lower transverse yoke, wherein the upper transverse yoke and the lower transverse yoke are respectively positioned at the upper end and the lower end of the left iron core column and the right iron core column. The direct current winding comprises a first direct current main branch winding and a second direct current main branch winding which are wound on the left iron core column and the right iron core column respectively and connected into the direct current power grid in series, and the direct current winding is used for conducting direct current system current. The permanent magnet includes first permanent magnet and second permanent magnet, and first permanent magnet inlays in the middle of the last horizontal yoke, and the second permanent magnet inlays in the middle of the horizontal yoke down. The coupling branch comprises a third coupling branch winding, a fourth coupling branch winding and a coupling branch peripheral circuit, wherein the third coupling branch winding and the fourth coupling branch winding are respectively wound on the outer sides of the first direct current main branch winding and the second direct current main branch winding to be in a tight coupling state and are connected with the coupling branch peripheral circuit. When the current limiter is connected to a power transmission line to operate, direct current magnetic flux forms a loop through the iron core, magnetic flux generated by permanent magnet excitation also forms a loop in the iron core, and the two magnetic fluxes jointly act on the whole iron core column.
And, the coupling branch peripheral circuit includes: diode D1And a charging energy storage capacitor C1Energy absorption resistor R1Mechanical switch B1(ii) a Wherein, the diode D1And a charging energy storage capacitor C1The third coupling branch winding and the fourth coupling branch winding are connected in series; mechanical switch B1And an energy absorption resistor R1Connected in series and in parallel with the charging energy storage capacitor C1Two ends.
In addition, the winding mode of the direct current main branch winding coil is a counterclockwise spiral from bottom to top, direct current system current flows in from the top end of the coil, and flows out from the bottom end of the coil; the dc main branch winding coil generates a counterclockwise magnetic flux in the core. The winding mode of the winding of the coupling branch circuit is a counterclockwise spiral from bottom to top, and when the coupling branch circuit is conducted, magnetic flux in a counterclockwise direction is generated in the iron core.
And the number of turns of the direct current main branch winding coil is greater than that of the coupling branch winding coil, so that each electric element in the coupling branch is ensured to be positioned on a relatively low-voltage side.
The working principle of the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter is as follows: under the normal working condition, the left iron leg is enabled to work in a saturation state by utilizing the magnetic saturation characteristic of the ferromagnetic element and the magnetic flux of the permanent magnet, and the inductance of the direct-current winding coil maintains a fixed value at the moment, so that the normal operation of a direct-current system is not influenced, and the conventional smoothing reactor can be replaced; when the fault state is in a fault state, the fault current is increased, the fault current generates magnetomotive force opposite to the direction of the permanent magnet, so that the magnetic flux of the iron core is reduced and desaturated, the impedance of the current limiter is automatically increased at the moment, and the rising gradient of the fault current is effectively restrained. When the fault current is reduced, the short-circuit current quickly supplies to the energy storage capacitor C in a magnetic coupling mode1Charging, and conducting the mechanical switch B after charging1Through an energy-absorbing resistor R1Absorbing stored fault energy. The energy absorption of the direct current circuit breaker is greatly reduced in the process, the overvoltage is reduced to a certain degree, the short-circuit fault energy can be quickly absorbed, the time of the fault current acting on the direct current winding is shortened, and the phenomenon that the direct current winding is overheated and the service life is shortened is avoided.
The current limiting method of the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter comprises the following steps:
under the normal working condition, the working current of the power grid is small, and the bias magnetomotive force generated by the two permanent magnets is absolute advantage compared with that of the two direct-current main branch winding coils, so that the left iron core column and the right iron core column are saturated under the influence of the two upper permanent magnets during normal working; because the magnetic permeability of the iron core is approximately equal to the magnetic permeability of air when the iron core is saturated, when the system normally operates, the normal impedance of the current limiter is small, the total inductance of the two direct current main branch winding coils is consistent with that of the high-voltage direct current smoothing reactor, and the normal operation of the system is not influenced. Meanwhile, the iron core is in a magnetic saturation state, so that the coupling branch cannot be conducted due to the fluctuation of system current.
When a fault occurs, the DC systemThe system current is rapidly increased, and the left and right iron core columns are rapidly out of saturation due to the fact that the directions of magnetic fluxes generated by the two direct current main branch windings and the two permanent magnets are opposite; the magnetic permeability of the iron core after the iron core is out of saturation rapidly rises, so that the inductance value of the direct current main branch winding is large, and short-circuit fault current is limited. The direction of the voltage generated across the current limiter and the diode D during the fault current drop phase1The direction of the conducted voltage is the same, the coupling branch winding is connected with the two direct current main branch windings in parallel through magnetic coupling, and fault current flows into a coupling branch peripheral circuit pair capacitor C through the magnetic coupling1Charging is carried out, and the mechanical switch B is conducted after the charging is finished1Through an energy-absorbing resistor R1Absorbing stored fault energy. The energy absorption of the direct current circuit breaker is greatly reduced in the process, the overvoltage is reduced to a certain degree, the short-circuit fault energy can be quickly absorbed, the time of the fault current acting on the winding is shortened, and the winding is prevented from being overheated, so that the service life is prolonged.
After the fault is eliminated, the fault current is rapidly reduced, at the moment, the working state of the whole system is recovered to the state when the line normally runs, and the integral impedance value of the fault current limiter is rapidly reduced, so that the normal running of the system cannot be influenced.
In specific implementation, as shown in fig. 4, the current limiter for the magnetic coupling rapid energy absorption type saturated iron core direct current fault includes an iron core, a direct current main branch winding and a permanent magnet; the iron core is of a square solid structure and comprises a left iron core column and a right iron core column which are respectively positioned at the left side and the right side, and an upper transverse yoke and a lower transverse yoke which are respectively positioned at the upper end and the lower end. The middle of the upper transverse yoke is embedded with a first permanent magnet, and the middle of the lower transverse yoke is embedded with a second permanent magnet. The direct current main branch winding is wound on the left iron core column and the right iron core column and is connected in series with a direct current power grid, and the coupling branch winding is wound on the outer side of the direct current main branch winding and is in a tight coupling state. When the current limiter is connected to a power transmission line to operate, direct current magnetic flux forms a loop through the iron core, magnetic flux generated by permanent magnet excitation also forms a loop in the iron core, and the two magnetic fluxes jointly act on the whole iron core column.
The peripheral circuit of the coupling branch comprises a diode D1And a charging energy storage capacitor C1Energy absorption resistor R1Mechanical switch B1Wherein, the diode D1And a charging energy storage capacitor C1A mechanical switch B connected in series and directly connected with the coupling branch winding1And an energy absorption resistor R1Are connected in series and are connected in parallel with a charging energy storage capacitor C1Two ends.
Moreover, the cross sections of the left iron core column and the right iron core column can be circular, oval or rectangular, the embodiment adopts a rectangular shape, as shown in fig. 4, the left iron core column and the right iron core column are rectangular, the cross sections are equal, and the lengths are equal; the length and the sectional area of the upper transverse yoke and the lower transverse yoke are equal. The sectional areas of the first permanent magnet and the second permanent magnet are equal to the sectional area of the transverse yoke where the first permanent magnet and the second permanent magnet are located, the two permanent magnets are the same in thickness, and the size and the dimension of the two permanent magnets are completely consistent, so that the symmetry of a magnetic circuit structure is ensured. The sectional area of the left and right core legs is smaller than that of the first and second permanent magnets, so that the first and second permanent magnets can magnetically saturate the core when the system works normally, and the current limiter keeps a small inductance operation state. The magnetic fluxes generated by the first permanent magnet and the second permanent magnet are clockwise in the iron core.
Moreover, first, second permanent magnet all adopt tombarthite permanent magnet material neodymium iron boron, and neodymium iron boron is the tombarthite permanent magnet material of a superior performance, and its advantage has: (1) the magnetic performance is high; the coercive force is 5-10 times of that of a ferrite permanent magnet material and 5-15 times of that of an alnico permanent magnet material; (2) the resources are rich, and the price is low; the main material is iron 2/3, the rare earth material is neodymium 1/3, and the resource is relatively rich; (3) good mechanical property, and can be used for cutting and drilling.
Also, as shown in FIG. 4, the storage capacitor C in the peripheral circuit of the branch is coupled1Higher energy storage capacity is required; diode D1A high forward current capacity and a capability of withstanding a reverse voltage are required. The number of turns of the coil of the direct current main branch winding (primary side) is larger than that of the coil of the coupling branch winding (secondary side), and each power electronic device is positioned on the secondary side of the current limiter and is positioned on a relatively low-voltage side, so that the ground insulation cost is reduced. Mechanical switch B in peripheral circuit of coupling branch1And an energy absorption resistor R1In series connectionThe two are connected in parallel with a charging energy storage capacitor C1Two ends, wherein the mechanical switch B1Capacitor C required to withstand energy storage1Voltage across, energy absorbing resistor R1The value requirement can ensure the peak value of the energy absorption current and the mechanical switch B1Can rapidly absorb energy while being in a bearable range.
In this embodiment, the left and right core legs are in a critical saturation state in a normal state of the power grid, that is, at an inflection point of a B-H curve of a ferromagnetic material, so as to ensure a desaturation speed of the left and right core legs in a fault, and thus the current limiter can be quickly changed into a large-inductance current limiting.
The working process of the embodiment is as follows: an equivalent circuit diagram of the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter and the direct current breaker in series is shown in fig. 5, wherein the directions of magnetic fields induced by direct current in the first and second direct current main branch winding coils are opposite to the directions of the magnetic fields of the first and second permanent magnets; the magnetic flux paths generated by the first and second permanent magnets and the first and second direct current main branch winding coils are shown in fig. 4, the magnetic fluxes generated by the first and second permanent magnets and the first and second direct current main branch winding coils pass through the left and right iron core posts, and under the normal working condition, because the power grid working current IdcThe generated magnetic flux is much smaller than that generated by the permanent magnet, so that the left and right iron core columns are influenced by the permanent magnet to be saturated in normal work; because the magnetic conductivity of the iron core is approximately equal to the air magnetic conductivity when the iron core is saturated, when the system normally operates, the normal impedance of the current limiter is very small, and the total inductance of the two direct current main branch winding coils can be consistent with the smoothing reactor used by the high-voltage direct current system through reasonable design, so that the normal operation of the system is not influenced. At this time, since the core is in a magnetic saturation state, the current limiter coupling branch cannot be in a parallel connection with the main branch through magnetic coupling, and the current circulation path in the current limiter is as shown in fig. 6 a.
When a fault occurs, in the fault current rising stage, the direct current magnetic fluxes generated by the fault current in the first and second direct current main branch winding coils counteract the bias magnetic fluxes generated by the first and second permanent magnets, so that the left and right iron core columns are rapidly desaturated, and the iron core after desaturation is removedAnd the magnetic conductivity is rapidly increased, so that the inductance values of the first and second direct current main branch windings are rapidly increased, and the short-circuit fault current is effectively limited. At this time, due to the diode D1The coupled branch still cannot conduct, and the current path in the current limiter is as shown in fig. 6 b.
During the phase of the action of the direct current breaker and the reduction of the fault current, the left and right iron core columns are still in a desaturation state, the coupling branch is conducted due to the reverse voltage generated on the current limiter, the circulation path of the current in the current limiter is shown as figure 6C, and the direct current fault current is supplied to the energy storage capacitor C in a magnetic coupling mode1And (6) charging. After the charging is completed quickly, the current on the first and second direct current main branch windings of the current limiter drops to 0, the left and right iron legs recover to a saturated state, the overall impedance value of the current limiter is reduced to the size of the smoothing reactor quickly, the normal operation of the system cannot be affected, and the current path of the current in the current limiter is shown in fig. 6 d.
After the fault is eliminated, the fault current is rapidly reduced, at the moment, the working state of the whole system is recovered to the state when the line normally runs, and the integral impedance value of the fault current limiter is rapidly reduced, so that the normal running of the system cannot be influenced.
Because the fault current flows into the current limiter coupling branch, the energy absorption of the direct current breaker is greatly reduced in the process, the overvoltage is reduced to a certain degree, the short-circuit fault energy can be quickly absorbed, the time of the fault current acting on the first direct current main branch winding and the second direct current main branch winding is reduced, and the phenomenon that the first direct current main branch winding and the second direct current main branch winding are overheated to reduce the service life is avoided. Capacitor C1After the charging is finished, the mechanical switch B is switched on1Through an energy-absorbing resistor R1Quickly absorb C1The current flow path through the current limiter is shown in fig. 6 e.
Compared with the rapid energy storage type magnetic saturation iron core direct current fault current limiter, the magnetic coupling rapid energy absorption type saturation iron core direct current fault current limiter saves the use of a large-capacity capacitor and a large-capacity thyristor, optimizes the circuit structure of a coupling branch, wherein the high-voltage large-capacity capacitor and the thyristor occupy extremely high cost, and therefore the overall cost is reduced by 38%. The cost is greatly reduced. Meanwhile, the winding mode of the magnetic coupling winding is improved, the original loose coupling winding method is changed into tight coupling winding, the magnetic leakage is reduced, the electromagnetic energy conversion efficiency is improved, the effect of reducing the breaking electrical stress of the circuit breaker is more remarkable, and the specific analysis is as follows:
when the magnetic coupling rapid energy absorption type saturated iron core direct current limiter, the traditional magnetic saturated iron core direct current limiter, the rapid response direct current limiter and the 100mH smoothing reactor are respectively matched with the hybrid direct current breaker, the breaking stress conditions generated by the breaker are compared. In the aspect of current limiting effect, the current limiting performance of the magnetic coupling rapid energy absorption type saturated iron core direct current limiter is equivalent to that of the traditional magnetic saturated iron core direct current limiter and is 25.4% stronger than that of a 100mH smoothing reactor and a rapid response direct current limiter. In terms of energy absorption of the direct current breaker, as shown in fig. 7, the magnetic coupling rapid energy absorption type saturated iron core direct current limiter reduces the energy absorption of the direct current breaker by 99.8% compared with the conventional magnetic saturation type direct current limiter, and reduces the energy absorption of the direct current breaker by 94.1% compared with the rapid response direct current limiter. Compared with a 100mH smoothing reactor, the energy absorption of the direct current breaker is reduced by 99.7%. In terms of the overvoltage peak value of the dc circuit breaker, as shown in fig. 8, the magnetic coupling fast energy absorption type magnetically saturated iron core dc current limiter reduces the overvoltage peak value of the dc circuit breaker by 25.4% compared with the conventional magnetically saturated dc current limiter, reduces the overvoltage peak value of the dc circuit breaker by 11.6% compared with the fast response dc current limiter, and reduces the overvoltage peak value of the dc circuit breaker by 41.7% compared with the 100mH smoothing reactor. Compared with a rapid energy storage type magnetic saturation iron core direct current fault current limiter, the overvoltage peak value of the direct current breaker is reduced by 15.5%. Therefore, the magnetic coupling rapid energy absorption type direct current limiter can ensure superior current limiting characteristics on the premise of better economical efficiency compared with the rapid energy storage type magnetic saturation iron core direct current fault current limiter, simultaneously greatly reduces the energy absorption of the circuit breaker, and can reduce the overvoltage peak value to a certain extent. The effect of reducing the breaking electrical stress of the circuit breaker is more remarkable.
Fig. 9 illustrates a comparison of the time during which the fault current is applied to the winding of the current limiter. Compared with a fast response direct current limiter, the magnetic coupling fast energy absorption type direct current limiter shortens the time of the fault current acting on the current limiter winding by 200ms, improves the effect of the current limiter by 44ms compared with the fast energy storage type magnetic saturation iron core direct current fault current limiter, and is better in performance. Therefore, the embodiment avoids the overheating damage of the current limiter winding caused by bearing fault current for a long time, and simultaneously avoids the service life influence of the iron core and the permanent magnet caused by overheating.
In order to further prove the implementation effect of the embodiment, a 220V small-capacity experimental prototype of the magnetic coupling rapid energy absorption type direct current limiter is designed, a current limiting experiment is carried out, small-capacity simulation is carried out at the same time, and the comparison of the experiment and the simulation result is shown in fig. 10. The current limiting effect of the magnetic coupling rapid energy absorption type direct current limiter of the embodiment is stronger than 88% of that of a 20mH constant value reactor. Compared with a direct current limiter with quick response in energy absorption, the time of fault current acting on a winding of the current limiter is shortened by 42.9%, simulation and experiment results are basically consistent, and the correctness of the experiment results is proved.
In summary, the following steps:
1) the magnetic coupling rapid energy absorption type saturated iron core direct current limiter can replace a smoothing reactor to maintain small inductance operation in a system normal state, rapid desaturation is changed into large inductance current limiting when a fault occurs, meanwhile, the problem that the rapid response direct current limiter applies fault current to a current limiter winding for too long time and seriously heats is solved, and the service life is prolonged;
2) compared with the traditional magnetic saturation type direct current limiter, the magnetic coupling rapid energy absorption type saturated iron core direct current limiter can obviously reduce the energy absorption of a direct current breaker and can reduce the overvoltage peak value of the breaker to a certain extent. Compared with a direct current limiter with quick response, the effect of reducing the overvoltage peak value of the circuit breaker and absorbing energy is more obvious;
3) compared with the rapid energy storage type magnetic saturation iron core direct current fault current limiter, the magnetic coupling rapid energy absorption type saturation iron core direct current fault current limiter greatly reduces the cost. On the premise of better economy, the current limiting device ensures the superior current limiting characteristic and has more remarkable effect of reducing the breaking electrical stress of the circuit breaker.
4) Compared with the rapid energy storage type magnetic saturation iron core direct current fault current limiter, the magnetic coupling rapid energy absorption type saturation iron core direct current limiter improves the winding mode of a coupling winding, changes loose coupling into tight coupling, and enables the transfer conversion efficiency of electromagnetic energy to be higher.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.
Claims (9)
1. A magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter is characterized in that: the permanent magnet synchronous motor comprises an iron core, a first direct current main branch winding, a second direct current main branch winding, a third coupling branch winding, a fourth coupling branch winding, a coupling branch peripheral circuit, a first permanent magnet and a second permanent magnet; the iron core is of a square solid structure and comprises a left iron core column, a right iron core column, an upper transverse yoke and a lower transverse yoke, wherein the upper transverse yoke and the lower transverse yoke are respectively positioned at the upper end and the lower end of the left iron core column and the right iron core column; the first direct-current main branch winding and the second direct-current main branch winding are respectively wound on the left iron core column and the right iron core column and are connected in series with a direct-current power grid; and the third coupling branch winding and the fourth coupling branch winding are wound on the outer sides of the first direct current main branch winding and the second direct current main branch winding respectively in a tight coupling mode and are connected with a peripheral circuit of the coupling branch.
2. The magnetically-coupled fast energy absorbing saturated core dc fault current limiter of claim 1, wherein: the coupling branch peripheral circuit includes: diode D1And a charging energy storage capacitor C1Energy absorption resistor R1Mechanical switch B1(ii) a Wherein, the diode D1And a charging energy storage capacitor C1The third coupling branch winding and the fourth coupling branch winding are connected in series; mechanical switch B1And an energy absorption resistor R1Connected in series and in parallel with the charging energy storage capacitor C1Two ends.
3. The magnetically-coupled fast energy absorbing saturated core dc fault current limiter of claim 1, wherein: the cross sections of the left iron core column and the right iron core column are circular, oval or rectangular.
4. A magnetically-coupled fast energy-absorbing saturated core dc fault current limiter according to claim 3, wherein: the sections of the left iron core column and the right iron core column are rectangular, and the sections and the lengths are the same; the lengths and the sectional areas of the upper transverse yoke and the lower transverse yoke are equal; the sectional areas of the first permanent magnet and the second permanent magnet are equal to the sectional area of the transverse yoke where the first permanent magnet and the second permanent magnet are located, the thicknesses of the first permanent magnet and the second permanent magnet are the same, and the sizes of the first permanent magnet and the second permanent magnet are the same; the sectional areas of the left iron core column and the right iron core column are smaller than the sectional areas of the first permanent magnet and the second permanent magnet.
5. The magnetically-coupled fast energy absorbing saturated core dc fault current limiter of claim 1, wherein: the first permanent magnet and the second permanent magnet are both made of rare earth permanent magnet material neodymium iron boron.
6. The magnetically-coupled fast energy absorbing saturated core dc fault current limiter of claim 1, wherein: the magnetic fluxes generated by the first permanent magnet and the second permanent magnet are clockwise in the iron core.
7. The magnetically-coupled fast energy absorbing saturated core dc fault current limiter of claim 1, wherein: the left iron core column and the right iron core column are in a critical saturation state in a normal state of a power grid, and the left iron core column and the right iron core column are in the saturation velocity reduction state at the turning points of a B-H curve of ferromagnetic materials when a fault occurs.
8. The magnetically-coupled fast energy absorbing saturated core dc fault current limiter of claim 1, wherein: the number of turns of the first direct current main branch winding and the second direct current main branch winding is larger than that of the third coupling branch winding and the fourth coupling branch winding.
9. The current limiting method of the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter according to any one of claims 1 to 8, characterized in that: the method comprises the following steps:
under the normal working condition, the working current of the power grid is small, and the bias magnetomotive force generated by the permanent magnet occupies absolute advantage compared with two direct-current main branch winding coils, so that the left iron core column and the right iron core column are influenced by the permanent magnet to be saturated in normal working; the magnetic conductivity of the iron core during saturation is approximately equal to the air magnetic conductivity, and when the system normally operates, the normal impedance of the current limiter is very small, so that the total inductance of the two direct current main branch winding coils is consistent with that of the high-voltage direct current smoothing reactor, and the normal operation of the system is not influenced; meanwhile, the iron core is in a magnetic saturation state, and the coupling branch cannot be conducted due to the fluctuation of system current;
when a fault occurs, the current of a direct current system is increased, and the directions of magnetic fluxes generated by the two direct current main branch winding coils and the two permanent magnets are opposite, so that the left and right iron core columns are quickly desaturated; the magnetic permeability of the iron core after saturation is removed rapidly rises, so that the inductance values of the two direct current main branches are larger, and the short-circuit fault current is limited; the direction of the voltage generated across the current limiter and the diode D during the fault current drop phase1The direction of the breakover voltage is the same, the coupling branch is connected with the direct current main branch in parallel through magnetic coupling, and fault current flows into the coupling branch to the capacitor C through the magnetic coupling1Charging is carried out, and the mechanical switch B is conducted after the charging is finished1Through an energy-absorbing resistor R1Absorbing stored fault energy;
after the fault is eliminated, the fault current is reduced, at the moment, the working state of the magnetic coupling rapid energy absorption type saturated iron core direct current fault current limiter is recovered to the state under the normal working condition of the line, the integral impedance value is reduced, and the normal operation of the system is not influenced.
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| CN114974830B (en) * | 2022-06-10 | 2024-05-14 | 武汉大学 | High-voltage magnetic saturation current limiter of magnetic integrated decoupling winding and winding inductance calculation method |
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