CN118213946A - Fast switching type fault current limiter - Google Patents
Fast switching type fault current limiter Download PDFInfo
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Abstract
The invention provides a fast switching type fault current limiter, and belongs to the field of power supply equipment protection. The fault current limiter is arranged at a neutral point of the transformer for voltage measurement and comprises a current limiting module and a control measuring module; the current limiting module comprises a fast switch and a current limiting reactor which are connected in parallel; the control measurement module comprises a current transformer and a remote controller; the first end of the parallel connection of the fast switch and the current limiting reactor is connected with a neutral point, and the second end of the parallel connection is grounded; the remote controller is respectively connected with the current transformer and the fast switch; the current transformer is arranged on a connecting line between the first end and the neutral point which are connected in parallel; the remote controller is used for controlling the rapid switch to open and close at the zero crossing point of the current when judging the occurrence of the current according to the waveform curvature of the current sent by the current transformer and the change rate of the current, so that the current limiting reactor is put into. The invention can limit the asymmetric short-circuit current of the medium-voltage three phases at the same time, and can realize larger current limiting depth while reducing the current limiting cost.
Description
Technical Field
The invention relates to the technical field of power supply equipment protection, in particular to a fast switching type fault current limiter.
Background
In recent years, with the rapid development of economy, the industrial production scale is expanding, and the demand for electric power is growing at an extremely rapid rate. The power generation sets are more and more installed in the power grid, the interconnection degree of the power system network is higher and higher, when the power grid has short-circuit faults, the short-circuit current level is continuously improved, and under partial conditions, the short-circuit instantaneous current exceeds 100kA.
The short-circuit current resistance of the transformer which runs for a certain period is designed in advance, and once a short-circuit fault occurs, the transformer winding can be heated quickly due to the excessively high short-circuit current to cause fire disaster, and huge stress can be generated in the transformer to cause deformation and even damage of the transformer winding. In order to ensure the safety, stability and reliability of the power grid, the operation load of the power equipment is reduced, and the limitation of the short-circuit current of the transformer is an urgent problem to be solved in the construction of the power grid.
In the power grid, the low-voltage side of the three-winding transformer is often the most loaded, most failed, and the greatest short-circuit current. However, when the unbalanced short-circuit fault occurs on the medium-voltage side along with the expansion of the power grid, because the short-circuit impedance of the winding on the medium-voltage side is smaller, and the zero-sequence current caused by unbalanced load and nonlinear load is added, the larger short-circuit current also occurs on the neutral point grounding wire on the medium-voltage side, and the magnitude of the short-circuit current can sometimes even exceed the three-phase short-circuit current on the low-voltage side. Therefore, a new technical scheme is needed to limit the short-circuit fault current of the voltage side in the transformer.
The traditional short-circuit current suppression means, such as grounding of a neutral point arc suppression coil, replacement of a high-capacity circuit breaker or series connection of a current limiting reactor, are often applied to the incoming line and the outgoing line of a transformer, and corresponding equipment is required to be installed in three phases. The high voltage class of the medium voltage side has high requirements on the insulation level of equipment, so that the current limiting cost is too high, the method cannot be applied to a neutral point of the medium voltage measurement of a transformer, and the method is difficult to popularize in a large range in a power grid.
Disclosure of Invention
The embodiment of the invention provides a fast switching type fault current limiter, which aims to solve the problems that the current limiting cost is too high and the current limiting method cannot be suitable for a neutral point of voltage measurement in a transformer.
In a first aspect, an embodiment of the present invention provides a fast switching fault current limiter, which is installed at a neutral point of a voltage measurement in a transformer, and includes a current limiting module and a control measurement module; the current limiting module comprises a fast switch and a current limiting reactor which are connected in parallel; the control measurement module comprises a current transformer and a remote controller;
The first end of the parallel connection of the fast switch and the current limiting reactor is connected with the neutral point, and the second end of the parallel connection of the fast switch and the current limiting reactor is grounded; the remote controller is respectively connected with the current transformer and the fast switch; the current transformer is arranged on a connecting line between a first end of the parallel connection of the fast switch and the current limiting reactor and the neutral point;
The remote controller is used for receiving the current sent by the current transformer, judging whether a short circuit fault occurs according to the waveform curvature of the current and the change rate of the current, and controlling the rapid switch to open at the zero crossing point of the current when the short circuit fault occurs, so that the current limiting reactor is put into operation.
In one possible implementation, the fast switching fault current limiter further comprises an overvoltage protection module; the overvoltage protection module comprises a lightning arrester and a gap which are connected in parallel;
The first end of the parallel connection of the lightning arrester and the gap is connected with the neutral point, and the second end of the parallel connection of the lightning arrester and the gap is grounded.
In one possible implementation, the control measurement module further comprises a control box;
the remote controller is connected with the quick switch through the control box.
In one possible implementation, the current limiting module further comprises a knife switch;
The second end of the parallel connection of the fast switch and the current limiting reactor is grounded through a disconnecting link.
In one possible implementation, the fast switch includes a fixed contact, a moving contact, a copper plate, a buffer pad, a closing coil, a separating coil, a fixed plate, a vacuum arc extinguishing chamber, a fixed conductive rod, a moving conductive rod, a transmission rod and an energy storage capacitor;
The static conductive rod is respectively connected with the static contact and the neutral point; the movable conductive rod is respectively connected with the movable contact and the transmission rod; the transmission rod is connected with the copper disc; the copper plate is provided with a fixed plate, and the closing coil and the opening coil are arranged on different fixed plates; the moving contact and the fixed contact are arranged in the vacuum arc-extinguishing chamber;
The buffer cushion is arranged below the copper disc, and is used for limiting excessive action of the copper disc when the quick switch is opened and closed and providing buffer for the copper disc when the copper disc acts downwards;
The energy storage capacitor is used for supplying power to the opening coil when the quick switch is controlled to open, so that the copper plate corresponding to the opening coil generates electromagnetic force to drive the transmission rod and the movable conducting rod to move downwards, and the movable contact and the fixed contact are separated; when the quick switch is controlled to be switched on, power is supplied to the switching-on coil, so that the copper plate corresponding to the switching-on coil generates electromagnetic force to drive the transmission rod and the movable conducting rod to move upwards, and the movable contact is contacted with the fixed contact.
In one possible implementation, the fast switching fault current limiter further comprises a device housing;
The device shell comprises a first cylindrical shell of the current limiting reactor positioned above, a second cylindrical shell of the fast switch positioned below and a third cylindrical shell positioned in the middle position;
the third cylindrical shell is used for connecting the first cylindrical shell and the second cylindrical shell;
a grounding box shell is arranged on the side surface of the lower end of the second cylindrical shell; and a control box shell is arranged on the side surface of the upper end of the second cylindrical shell.
In one possible implementation, the remote controller is specifically configured to determine that a short circuit fault has occurred when the waveform curvature of the current is greater than or equal to a curvature threshold, and/or the rate of change of the current is greater than or equal to a rate of change threshold.
In one possible implementation, the remote controller is further configured to predict zero crossings of the current when a short circuit fault occurs.
In one possible implementation, predicting zero crossings of the current includes:
Determining an expression of the real part of the first n-th harmonic component and an expression of the imaginary part of the first n-th harmonic component based on the first set of current sample values; the first current sampling value set comprises current sampling values of half period;
Determining an expression of the real part of the second n-th harmonic component and an expression of the imaginary part of the second n-th harmonic component based on the second set of current sample values; the second current sampling value set is obtained by removing a first current sampling value in the first current sampling value set and adding a new current sampling value at last;
Determining an expression of the real part of the third n-th harmonic component and an expression of the imaginary part of the third n-th harmonic component based on the third set of current sample values; the third current sampling value set is obtained by removing the first two current sampling values in the first current sampling value set and adding the two new current sampling values at last;
Determining an expression of a fault current when a short-circuit fault occurs based on the expression of the real part of the first n-th harmonic component, the expression of the imaginary part of the first n-th harmonic component, the expression of the real part of the second n-th harmonic component, the expression of the real part of the third n-th harmonic component, and the expression of the imaginary part of the third n-th harmonic component;
based on the expression of the fault current, zero crossings of the current are predicted.
In one possible implementation manner, the remote controller is further configured to, after controlling the fast switch to open, re-determine whether the transformer still has a short-circuit fault after a first preset period of time, determine that the transformer has a permanent short-circuit fault if the transformer still has a short-circuit fault, control the circuit breaker of the transformer to open, and control the fast switch to close after a second preset period of time, determine that the transformer has a transient short-circuit fault if the short-circuit fault of the transformer has been released, and control the fast switch to close.
The embodiment of the invention provides a fast switch type fault current limiter, which can detect the current on a neutral point grounding wire which is measured by a transformer through a fast switch, a current limiting reactor, a current transformer and a remote controller, judge whether a short circuit fault occurs or not, and control the fast switch to open and close at the zero crossing point of the current when the short circuit fault occurs, so that the current limiting reactor is put into and the short circuit current is limited; the fast switch type fault current limiter can be arranged at a neutral point of a medium voltage measurement of a transformer, can simultaneously limit asymmetric short-circuit current of the medium voltage measurement three phases, and can realize larger current limiting depth while reducing current limiting cost compared with the fault current limiter arranged on a line and at the inlet and outlet ends of the transformer.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a fast switching fault current limiter according to an embodiment of the present invention;
Fig. 2 is a schematic structural view of a fast switching fault current limiter according to still another embodiment of the present invention;
FIG. 3 is a schematic diagram of a fast switch according to an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a device housing according to an embodiment of the present application.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth such as the particular system architecture, techniques, etc., in order to provide a thorough understanding of the embodiments of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the following description will be made by way of specific embodiments with reference to the accompanying drawings.
Fig. 1 is a schematic structural diagram of a fast switching fault current limiter provided in an embodiment of the present invention, referring to fig. 1, the fast switching fault current limiter is installed at a neutral point of a transformer for voltage measurement, and includes a current limiting module 11 and a control measurement module 12; the current limiting module 11 comprises a fast switch 102 and a current limiting reactor 101 connected in parallel; the control measurement module 12 includes a current transformer 106 and a remote controller 107;
A first end of the parallel connection of the fast switch 102 and the current limiting reactor 101 is connected with a neutral point, and a second end of the parallel connection of the fast switch 102 and the current limiting reactor 101 is grounded; the remote controller 107 is connected with the current transformer 106 and the fast switch 102 respectively; the current transformer 106 is arranged on a connecting line between the first end of the parallel connection of the fast switch 102 and the current limiting reactor 101 and the neutral point;
The remote controller 107 is configured to receive the current sent by the current transformer 106, determine whether a short-circuit fault occurs according to the waveform curvature of the current and the rate of change of the current, and control the fast switch 102 to switch off at the zero crossing point of the current when the short-circuit fault occurs, so that the current limiting reactor 101 is put into operation.
In this embodiment, the current transformer 106 may detect the current on the neutral point ground line of the transformer and transmit the detected current to the remote controller 107 through the transmission line. The remote controller 107 may calculate the waveform curvature of the current and the rate of change of the current according to the received current, and determine a short-circuit fault by using the waveform curvature of the current and the rate of change of the current as feature values, and when determining that the short-circuit fault occurs, control the fast switch 102 to open at the zero crossing point of the current, that is, control the fast switch 102 to open, so that the current limiting reactor 101 is put into operation, and limit the short-circuit current.
During normal operation of the transformer, the fast switch 102 is in a closed state, i.e. a closed state, short-circuiting the current limiting reactor 101.
Wherein the short circuit fault may be an asymmetric short circuit fault.
The fast switch 102 can adopt a novel electromagnetic repulsion transmission mechanism and has the capability of completing opening operation within 2 milliseconds and closing operation within 5 milliseconds so as to control the access state of the current limiting reactor 101.
The current limiting reactor 101 can be a dry hollow current limiting reactor 101, the rated current is 2500A, the rated reactance rate is 10%, the short-time current limit value is 25kA, the whole current limiting reactor is cylindrical, the radius of the bottom surface is 80cm, and the height is 90cm. The shell and the internal supporting structure of the current limiting reactor 101 are made of high-strength low-alloy structural steel, the magnetic core is made of silicon steel sheets, the coil is wound on the magnetic core, and other parts inside the reactor are filled with epoxy resin to serve as insulation. After the current limiting reactor 101 is put into operation, the asymmetric short-circuit current flowing through the neutral point of the transformer can be remarkably reduced, and the transformer is protected from being damaged by the short-circuit current.
The fast switch fault current limiter provided in this embodiment can detect the current on the neutral point grounding line of the transformer through the fast switch 102, the current limiting reactor 101, the current transformer 106 and the remote controller 107, and determine whether a short circuit fault occurs, and when the short circuit fault occurs, control the fast switch 102 to switch off at the zero crossing point of the current, so that the current limiting reactor 101 is put into, and the short circuit current is limited; the fast switch type fault current limiter can be arranged at a neutral point of a medium voltage measurement of a transformer, can simultaneously limit asymmetric short-circuit current of the medium voltage measurement three phases, and can realize larger current limiting depth while reducing current limiting cost compared with the fault current limiter arranged on a line and at the inlet and outlet ends of the transformer.
The rapid switching type fault current limiter can solve the problem that the fault current limiter applicable to the neutral point of the transformer is not available at present, realizes the automatic current limiting treatment of the short circuit fault of the neutral point of the transformer under the condition that the transformer is not replaced, and ensures that the electric energy quality is the same as that of normal power supply. When a short circuit fault occurs, the damage to the transformer can be reduced to the greatest extent, the safe and stable operation of the power system is facilitated, meanwhile, the operation cost of the power grid can be reduced, and powerful technical support is provided for the safe and reliable operation of the transformer equipment.
When no short-circuit fault occurs, the fast switch 102 is closed, no current exists in the current limiting reactor 101, and no power loss is generated, so that the fault current limiter provided by the embodiment can reduce energy resource waste, and the system is more economical and efficient in long-time operation. The fault current limiter is simple in principle and reliable in structure, can improve the usability of the system, and can ensure the reliability and stability under different environments. The fault current limiter has low cost, can be applied to a large scale in a power grid, has high action speed, can realize rapid operation when in short circuit fault, and can improve the flexibility and practicability of the system.
In some embodiments, referring to fig. 2, the fast switching fault current limiter further comprises an overvoltage protection module 13; the overvoltage protection module 13 comprises a lightning arrester 104 and a gap 105 connected in parallel;
the first end of the parallel connection of the arrester 104 and the gap 105 is connected to the neutral point, and the second end of the parallel connection of the arrester 104 and the gap 105 is grounded.
The lightning arrester 104 can be a zinc oxide lightning arrester, and plays roles of lightning and transient overvoltage protection.
The gap 105 may comprise two copper balls, the radius of which is 2cm, and the interval between the copper balls may be set according to actual requirements. The gap 105 may take over the role of operating overvoltage protection while protecting the arrester 104 in case of excessive power frequency overvoltage or excessive residual voltage on the arrester 104.
The overvoltage protection of the transformer can be realized through the lightning arrester 104 and the gap 105; by integrating the conventional fast switching fault current limiter with the lightning arrester 104 and the gap 105 in the transformer neutral grounding device, the installation and use are facilitated.
In setting the reactance value of the current limiting reactor 101, the transformer neutral insulation level needs to be considered. The overvoltage of the neutral point of the transformer is the product of three times of zero sequence current and the reactance value of the current limiting reactor 101, and the overvoltage of the neutral point of the transformer and the reactance value of the current limiting reactor 101 are positively correlated. When the reactance value of the current limiting reactor 101 is too large, the neutral point voltage at the time of failure may rise too high, placing extremely high demands on the insulation level of the transformer, and further resulting in significant increases in technology and cost.
If the maximum voltage that the neutral point can withstand is U z, when the asymmetric short circuit fault occurs, after the current limiting reactor 101 is put into operation, the maximum overvoltage that the neutral point can appear is U c:
In the above formula (1), K is the ratio of the zero sequence impedance x 0 to the positive sequence impedance x 1, i.e., k=x 0/x1; gamma is the oscillation attenuation coefficient of the transformer, the value of the tangled winding is 0.5, and the value of the continuous winding is 0.8; u ph is the maximum operating phase voltage of the transformer.
Insulation safety coefficient of neutral pointWhen the neutral point insulation is maintained in the safe range. That is, the reactance value of the current limiting reactor 101 needs to satisfy/>
In setting the reactance value of the current limiting reactor 101, it is also necessary to consider a cooperative arrangement with the overcurrent protection of the arrester 104 and the gap 105. Neutral overvoltage due to the current limiting reactor 101 negatively affects the normal operation of the arrester 104 and the gap 105 over-current protection when an asymmetrical short circuit fault is prevented.
If the operating voltage of the arrester 104 is U B and the breakdown voltage of the gap 105 is U J, when the influence coefficient xs2=u B/Uc of the arrester 104 is less than 1.5 and the influence coefficient xs3=u J/Uc of the gap 105 is less than 1.5, it is considered that the neutral point overvoltage does not cause the arrester 104 and the gap 105 to enter the conductive state. That is, the reactance value of the current limiting reactor 101 also needs to satisfy xs2=u B/Uc < 1.5 and xs3=u J/Uc < 1.5.
In some embodiments, referring to FIG. 2, the control measurement module 12 further includes a control box 108;
The remote controller 107 is connected to the fast switch 102 through a control box 108.
The remote controller 107 may send a signal to the control box 108 to open the fast switch 102 at the zero crossing point of the current when a short circuit fault occurs, and the control box 108 controls the fast switch 102 to open. The remote controller 107 may also send a signal to the control box 108 to close the fast switch 102 when it is required to close the fast switch 102, where the control box 108 controls the fast switch 102 to close.
The control box 108 may also be manually controlled to open and close the fast switch 102. The control box 108 is provided with a quick switch opening and closing indicator light, a manual opening and closing button and a reset button. When the control box 108 receives the signal of the remote controller 107 or the manual opening and closing button is pressed, the opening and closing of the fast switch 102 can be directly controlled.
In some embodiments, referring to fig. 2, the flow restriction module 11 further includes a knife switch 103;
the second end of the parallel connection of the fast switch 102 and the current limiting reactor 101 is grounded through a knife switch 103.
The disconnecting link 103 is a grounding disconnecting link 103. One end of the knife switch 103 is connected with the ground, and the other end of the knife switch 103 is respectively connected with the fast switch 102 and the current limiting reactor 101 for accurately controlling the grounding state of the neutral point.
In some embodiments, referring to fig. 3, the fast switch 102 includes a stationary contact 201, a moving contact 202, a copper disc 203, a buffer 204, a closing coil 205, a opening coil 206, a fixed plate 207, a vacuum interrupter 208, a stationary conductive rod 209, a moving conductive rod 210, a transmission rod 212, and an energy storage capacitor 211;
The static conductive rod 209 is respectively connected with the static contact 201 and the neutral point; the movable conductive rod 210 is respectively connected with the movable contact 202 and the transmission rod 212; the transmission rod 212 is connected with the copper disc 203; a fixed plate 207 is arranged on the copper plate 203, and a closing coil 205 and a separating coil 206 are arranged on different fixed plates 207; the movable contact 202 and the fixed contact 201 are arranged in the vacuum arc-extinguishing chamber 208;
The buffer pad 204 is arranged below the copper plate 203, and is used for limiting excessive action of the copper plate 203 when the quick switch 102 is switched off and providing buffer for downward action of the copper plate 203;
The energy storage capacitor 211 is used for supplying power to the opening coil 206 when the quick switch 102 is controlled to open, so that the copper disk 203 corresponding to the opening coil 206 generates electromagnetic force to drive the transmission rod 212 and the movable conducting rod 210 to move downwards, and the movable contact 202 is separated from the fixed contact 201; and when the fast switch 102 is controlled to be switched on, power is supplied to the switching-on coil 205, so that the copper disc 203 corresponding to the switching-on coil 205 generates electromagnetic force to drive the transmission rod 212 and the movable conducting rod 210 to move upwards, and the movable contact 202 is contacted with the fixed contact 201.
The movable contact 202 and the fixed contact 201 are used for connecting or disconnecting loops, and are made of beryllium copper alloy, and the radius of the contact surface of the movable contact 202 and the fixed contact 201 is 15cm and the thickness is 6cm. The movable conductive rod 210 and the static conductive rod 209 are respectively used for connecting the movable contact 202, the static contact 201 and a circuit, and are also made of beryllium copper alloy, and have the length of 45cm and the radius of 3cm. The static conductive rod 209 is respectively connected with the static contact 201 and the neutral point; the movable conductive rod 210 is connected to the movable contact 202, the transmission rod 212 and the ground (or the knife switch 103), respectively.
The copper disk 203 can generate upward or downward repulsive force with the exciting coil in an induction way, so that the moving contact 202 is pushed to move, and electrolytic copper with a tin-plated surface is adopted as the material, the radius is 90cm, and the thickness is 30cm. Referring to fig. 3, the number of copper plates 203 may be two, two copper plates 203 are disposed up and down, a fixing plate 207 and a corresponding switching-on coil 205 are disposed on the copper plate 203 located above, and a fixing plate 207 and a corresponding switching-off coil 206 may be disposed on the copper plate 203 located below. The two copper plates 203 and the copper plate 203 and the movable conductive rod 210 can be connected through a transmission rod 212.
The buffer pad 204 is arranged below the lower copper disk 203, is used for limiting excessive action of the copper disk 203 during opening and providing buffer for the copper disk 203 to move downwards, and is made of Nitrile Butadiene Rubber (NBR), is in the shape of an oblate cylinder, has a radius of 100cm and has a thickness of 30cm.
The opening coil 206 is used for being electrified when the fast switch 102 is controlled to open, and the closing coil 205 is used for being electrified when the fast switch 102 is controlled to close, so that an upward or downward repulsive force is generated between the closing coil and the copper plate 203.
The fixing plate 207 is used for fixing the opening coil 206 or the closing coil 205, and simultaneously limiting excessive action of the copper plate 203, and is made of high-strength steel material and has a thickness of 9cm. Referring to fig. 3, two fixing plates 207 may be disposed on the upper copper plate 203, a closing coil 205 may be disposed on the fixing plates 207, and two fixing plates 207 may be disposed on the lower copper plate 203, and a separating coil 206 may be disposed on the fixing plates 207.
The vacuum interrupter 208 uses the insulating property of the vacuum tube to rapidly extinguish the arc, cut off the short circuit and suppress the current.
The number of the storage capacitors 211 may be two, wherein one storage capacitor 211 charges the opening coil 206 and the other storage capacitor 211 charges the closing coil 205, thereby generating electromagnetic force. The energy storage capacitor 211 may be connected to the control box 108 or the remote controller 107, and charges the opening coil 206 or the closing coil 205 according to a control signal of the remote controller 107.
The fast switch 102 is operated by: the charged energy storage capacitor 211 discharges to energize the opening coil 206 or the closing coil 205, so as to generate pulse current, electromagnetic force is generated in the copper disc 203 due to eddy current induction, and the copper disc 203 drives the transmission rod 212 to move, so that the movable contact 202 is contacted with or separated from the fixed contact 201, and the purpose of opening and closing the current is achieved.
When the copper plate 203 of the quick switch 102 moves downwards, the quick switch 102 is opened, and when the copper plate 203 moves upwards, the quick switch 102 is closed, so that the opening speed is increased by means of gravity.
In some embodiments, the fast switching fault current limiter further comprises a device housing;
Referring to fig. 4, the device housing includes a first cylindrical housing 401 of the current limiting reactor 101 located above, a second cylindrical housing 404 of the fast switch 102 located below, and a third cylindrical housing 402 located in an intermediate position;
The third cylindrical housing 402 is used to connect the first cylindrical housing 401 and the second cylindrical housing 404;
A grounding box shell 405 is arranged on the side surface of the lower end of the second cylindrical shell 404; a control box housing 403 is provided on the side of the upper end of the second cylindrical housing 404.
The material of the first cylindrical shell 401 adopts high-strength low-alloy structural steel, the height is 100cm, the radius is 100cm, the current-limiting reactor 101 is arranged in the first cylindrical shell, the second cylindrical shell 404 forms the shell of the fast switch 102, the material adopts high-strength low-alloy structural steel, the height is 200cm, the radius is 150cm, the fast switch 102 is arranged in the second cylindrical shell, the third cylindrical shell 402 serves as a connecting part of the first cylindrical shell 401 and the second cylindrical shell 404 and plays a role of structural support, the material adopts high-strength low-alloy structural steel, the height is 50cm, and the radius is 60cm. The control box housing 403 is internally provided with a control box 108 for controlling the fast switch 102, and is made of high-strength low-alloy structural steel, and the length, width and height of the control box are 30cm,20cm and 40cm respectively. The control box housing 403 may be provided with a quick switch on/off indicator, a manual switch on/off button, a reset button, and the like. The grounding box shell 405 is internally provided with devices such as a disconnecting link 103, a lightning arrester 104, a gap 105 and the like, and is made of high-strength low-alloy structural steel, and the length, the width and the height are respectively 80cm,60cm and 90cm.
The upper end of the second cylindrical shell 404 is provided with a connecting terminal which can be connected with a neutral point of the transformer through a connecting wire; the lower side of the grounding box housing 405 is provided with a connecting terminal, which should be connected to the ground reliably. An in-out wire terminal is arranged between the grounding box shell 405 and the second cylindrical shell 404 and is used for leading out the wiring of the fast switch 102 and the current limiting reactor 101.
In some embodiments, the remote controller 107 is specifically configured to determine that a short circuit fault has occurred when the waveform curvature of the current is greater than or equal to a curvature threshold, and/or the rate of change of the current is greater than or equal to a rate of change threshold.
In the embodiment of the invention, the waveform curvature of the neutral point current is selected to be matched with the change rate of the current as the characteristic quantity to judge the short circuit fault, no matter what method is to identify the short circuit fault first, the remote controller 107 sends a signal to the control box 108 to switch off the fast switch 102.
The short-circuit fault is detected by setting a change rate threshold YZ1 when the change rate of the current is real-timeAnd determining that the short circuit fault occurs.
The waveform curvature of the current detects the short-circuit fault by setting a curvature threshold YZ2, and when the waveform curvature QL of the current in real time is more than YZ2, the short-circuit fault is determined to occur.
If it isAnd QL is less than or equal to YZ2, and determining that the short circuit fault does not occur.
The method for calculating the waveform curvature of the current is as follows:
where I represents the I-th sampling point, l and I are sampling step length and current value, and since the two units are different, the calculation processing should be performed before the calculation is performed. In general curvature definition, curvature is a positive value, and here, curvature considers positive and negative in order to sufficiently consider a change in a bending direction of a waveform when calculating an average value of curvature.
The values of the change rate threshold value YZ1 and the curvature threshold value YZ2 should consider the asymmetric short-circuit current characteristic differences at the neutral point of the transformer, the outlet end of the transformer and the line. During normal operation, the current flowing through the neutral point is far lower than the current on the outgoing line end and the line of the transformer; in the case of an asymmetrical short-circuit fault, the current flowing through the neutral point is usually significantly higher than the single-phase current at the transformer outlet and on the line. Therefore, the current change rate and the current waveform curvature of the neutral point of the transformer are more remarkable in the asymmetric short-circuit fault. When setting the threshold, a higher value may be selected to prevent false triggering.
In some embodiments, the remote controller 107 is also configured to predict zero crossings of the current in the event of a short circuit fault.
When a short-circuit fault occurs, the remote controller 107 predicts the zero crossing point of the current first, so that the fast switch 102 can be controlled to be switched off at the zero crossing point of the current, and the current-limiting reactor 101 is put into operation.
In some embodiments, predicting zero crossings of the current includes:
Determining an expression of the real part of the first n-th harmonic component and an expression of the imaginary part of the first n-th harmonic component based on the first set of current sample values; the first current sampling value set comprises current sampling values of half period;
Determining an expression of the real part of the second n-th harmonic component and an expression of the imaginary part of the second n-th harmonic component based on the second set of current sample values; the second current sampling value set is obtained by removing a first current sampling value in the first current sampling value set and adding a new current sampling value at last;
Determining an expression of the real part of the third n-th harmonic component and an expression of the imaginary part of the third n-th harmonic component based on the third set of current sample values; the third current sampling value set is obtained by removing the first two current sampling values in the first current sampling value set and adding the two new current sampling values at last;
Determining an expression of a fault current when a short-circuit fault occurs based on the expression of the real part of the first n-th harmonic component, the expression of the imaginary part of the first n-th harmonic component, the expression of the real part of the second n-th harmonic component, the expression of the real part of the third n-th harmonic component, and the expression of the imaginary part of the third n-th harmonic component;
based on the expression of the fault current, zero crossings of the current are predicted.
The short-circuit fault current of the power system mainly comprises an attenuation direct current component, a fundamental wave and harmonic waves. Therefore, in the event of a short-circuit fault, the fault current I (t) may be expressed as:
Wherein I 0 is the initial value of the attenuation direct current component; τ is the decay time constant of the DC component; i m (n) is the amplitude of the n-th harmonic; phase for the n-th harmonic; n omega is the angular frequency of the n-th harmonic.
The discrete expression of the real part of the n-order harmonic component is calculated by a half-wave Fourier algorithm expressed by discrete sampling values:
the discrete expression of the imaginary part of the n-th harmonic component is:
in the formula, k represents the number of sampling points from the occurrence of a short circuit, and N represents the number of sampling points per cycle.
When the signal does not contain an attenuated direct current component, the theoretical error of the amplitude and the phase of the fundamental wave and each subharmonic is zero, and after discretization, the error is related to the sampling frequency. The half-wave Fourier algorithm has strong processing capacity on the signal without the direct current component, and when the sampled data points are very many (50 MHz), the amplitude and phase errors to be solved are very small and can be ignored. As the sampling frequency decreases, the difference between the amplitude and phase and the actual value increases as the error generated by trapezoidal summation instead of integration increases.
When the signal contains an attenuated dc component, since the analysis of the fourier algorithm is based on the periodic signal, when the short-circuit current contains a dc component, the error theoretically calculated by the half-wave fourier algorithm becomes large, and the short-circuit current containing the error has the following calculation formula:
In the method, in the process of the invention, Delta a and delta b are errors of a n and b n, respectively, and T represents the period of the periodic component in the current, i.e. the period of the current.
Order theThen
Comparing equations (6), (7) and (8) shows that when the current contains a direct current component, the real part and the imaginary part obtained by the half-wave fourier algorithm contain errors of δ a and δ b, respectively.
Aiming at the inherent defects of the half-wave Fourier algorithm, in order to eliminate the influence of delta a and delta b by utilizing sampling information, the zero point of short-circuit current is accurately measured, two more data are acquired for the sampled signal, namely two sampling values (the sampling value serial numbers are from 2 to N/2+1 and from 3 to N/2+2) at the (T/2+2) and (T+DeltaT) moments are added, deltaT is the minimum sampling period, and the auspicious data are subjected to moving iterative processing.
Taking T epsilon (delta T, T/2+delta T), namely removing a first current sampling value, adding a current sampling value (namely a second current sampling value set) at last, and performing half-wave Fourier transform to obtain the composite material:
where d=e -ΔT/τ,ka＝cosnωΔT,kb = sinn ωΔt.
Taking T epsilon (2deltaT, T/2+2deltaT), namely removing the first two current sampling values, adding two current sampling values (namely a third current sampling value set) at last, and performing half-wave Fourier transformation to obtain the three-phase current sampling value:
Where k 'a＝cos(2nωΔT),kb' =sin (2nωΔt).
The combination of formulas (9), (10), (11) can be obtained:
Finally, according to the sampling data and the calculation, each parameter in the short-circuit current shown in the formula (5) can be calculated, so that an expression of the fault current when the short-circuit fault occurs is obtained, and the zero point moment of the short-circuit current is predicted according to the expression.
The first current sampling value set may include current sampling values acquired by T epsilon (0, T/2), and the sampling period may be Δt; the second set of current sample values may include current sample values collected by T e (Δt, T/2+Δt); the third set of current sample values may include current sample values acquired at e (2Δt, T/2+2Δt).
The expression of the real part a n of the first n-th harmonic component and the expression of the imaginary part b n of the first n-th harmonic component are expression (9); the expression of the real part a n 'of the second n-th harmonic component and the expression of the imaginary part b n' of the second n-th harmonic component are expression (10); the expression of the real part a n "of the third n-th harmonic component and the expression of the imaginary part b n" of the third n-th harmonic component are expression (11). When a short-circuit fault occurs, the expression of the fault current is expression (5) in which the respective parameters have been calculated.
In some embodiments, the remote controller 107 is further configured to, after controlling the fast switch 102 to open, re-determine whether the transformer still has a short-circuit fault after a first preset period of time, determine that the transformer has a permanent short-circuit fault if the transformer still has a short-circuit fault, control the circuit breaker of the transformer to open, and after a second preset period of time, control the fast switch 102 to close, determine that the transformer has a transient short-circuit fault if the short-circuit fault of the transformer has been released, and control the fast switch 102 to close.
The first preset duration and the second preset duration may be set according to actual requirements, for example, the first preset duration may be 3 seconds, the second preset duration may be 1 second, and so on.
Illustratively, the control flow of the remote controller 107 is:
Initially, the fast switch 102 is closed, the current limiting reactor 101 is short-circuited, the remote controller 107 calculates a rate of change of the current and a waveform curvature of the current according to the collected current, and judges whether a short-circuit fault occurs according to the calculated rate of change of the current and the waveform curvature of the current. When the change rate of the current and the waveform curvature of the current are both smaller than the corresponding threshold values, judging that the short circuit fault does not occur, and keeping the fast switch 102 closed; when the change rate of the current or the waveform curvature of the current is greater than or equal to a corresponding threshold value, the short circuit fault is judged to occur, the remote controller 107 predicts the zero crossing point of the current, and when the current crosses the zero point, a switching-off signal is sent to the control box 108, the control box 108 controls the fast switch 102 to switch off, and the current limiting reactor 101 is put into a loop. After 3s of current limiting, the remote controller 107 again determines whether the rate of change of the current and the waveform curvature of the current exceed corresponding thresholds. When the change rate of the current and the waveform curvature of the current are both smaller than the corresponding threshold values, judging that an instantaneous short-circuit fault occurs, controlling the fast switch 102 to be switched on, and enabling the current-limiting reactor 101 to be shorted again; when the change rate of the current or the waveform curvature of the current is larger than or equal to a corresponding threshold value, the permanent short circuit fault is judged to occur, the breaker of the transformer acts, and after the time delay is 1s, the quick switch 102 is closed and reset.
Corresponding to the fast switching type fault current limiter, the embodiment of the application also provides a control method of the fast switching type fault current limiter, which is used for controlling any one of the fast switching type fault current limiters and is applied to the remote controller.
The specific implementation process of the control method can be used for parameterizing the specific control method of the remote controller in the embodiment of the fast switching fault current limiter, and is not repeated.
In the foregoing embodiments, the descriptions of the embodiments are emphasized, and in part, not described or illustrated in any particular embodiment, reference is made to the related descriptions of other embodiments.
The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention.
Claims (10)
1. The fast switching type fault current limiter is characterized by being arranged at a neutral point of a transformer for voltage measurement and comprising a current limiting module and a control measuring module; the current limiting module comprises a fast switch and a current limiting reactor which are connected in parallel; the control measurement module comprises a current transformer and a remote controller;
A first end of the parallel connection of the fast switch and the current limiting reactor is connected with the neutral point, and a second end of the parallel connection of the fast switch and the current limiting reactor is grounded; the remote controller is respectively connected with the current transformer and the fast switch; the current transformer is arranged on a connecting line between the neutral point and a first end of the parallel connection of the fast switch and the current limiting reactor;
the remote controller is used for receiving the current sent by the current transformer, judging whether a short circuit fault occurs according to the waveform curvature of the current and the change rate of the current, and controlling the rapid switch to open at the zero crossing point of the current when the short circuit fault occurs, so that the current limiting reactor is put into operation.
2. The fast switching fault current limiter of claim 1 further comprising an overvoltage protection module; the overvoltage protection module comprises a lightning arrester and a gap which are connected in parallel;
the first end of the arrester and the gap are connected in parallel is connected with the neutral point, and the second end of the arrester and the gap are connected in parallel is grounded.
3. The fast switching fault current limiter of claim 1 wherein the control measurement module further comprises a control box;
the remote controller is connected with the quick switch through the control box.
4. The fast switching fault current limiter of claim 1 wherein the current limiting module further comprises a knife switch;
and the second end of the parallel connection of the fast switch and the current limiting reactor is grounded through the disconnecting link.
5. The fast switching fault current limiter of claim 1, wherein the fast switch comprises a fixed contact, a moving contact, a copper disc, a buffer pad, a closing coil, a breaking coil, a fixed plate, a vacuum interrupter, a fixed conductive rod, a moving conductive rod, a transmission rod and an energy storage capacitor;
The static conductive rod is respectively connected with the static contact and the neutral point; the movable conductive rod is respectively connected with the movable contact and the transmission rod; the transmission rod is connected with the copper disc; the copper plate is provided with the fixing plate, and the closing coil and the opening coil are arranged on different fixing plates; the movable contact and the fixed contact are arranged in the vacuum arc-extinguishing chamber;
the buffer cushion is arranged below the copper disc, and is used for limiting excessive action of the copper disc when the quick switch is opened and used for providing buffer for downward action of the copper disc;
The energy storage capacitor is used for supplying power to the opening coil when the quick switch is controlled to open, so that the copper plate corresponding to the opening coil generates electromagnetic force to drive the transmission rod and the movable conducting rod to move downwards, and the movable contact and the fixed contact are separated; and when the rapid switch is controlled to be switched on, power is supplied to the switching-on coil, so that the copper plate corresponding to the switching-on coil generates electromagnetic force to drive the transmission rod and the movable conducting rod to move upwards, and the movable contact is contacted with the fixed contact.
6. The fast switching fault current limiter of claim 1 further comprising a device housing;
The device shell comprises a first cylindrical shell of the current limiting reactor positioned above, a second cylindrical shell of the fast switch positioned below and a third cylindrical shell positioned in the middle position;
the third cylindrical shell is used for connecting the first cylindrical shell and the second cylindrical shell;
A grounding box shell is arranged on the side surface of the lower end of the second cylindrical shell; and a control box shell is arranged on the side surface of the upper end of the second cylindrical shell.
7. The fast switching fault current limiter of claim 1 wherein the remote controller is configured to determine that a short circuit fault has occurred when the waveform curvature of the current is greater than or equal to a curvature threshold and/or the rate of change of the current is greater than or equal to a rate of change threshold.
8. The fast switching fault current limiter of claim 1 wherein the remote controller is further configured to predict zero crossings of the current when a short circuit fault occurs.
9. The fast switching fault current limiter of claim 8 wherein the predicting the zero crossing of the current comprises:
Determining an expression of the real part of the first n-th harmonic component and an expression of the imaginary part of the first n-th harmonic component based on the first set of current sample values; the first current sampling value set comprises current sampling values of half period;
Determining an expression of the real part of the second n-th harmonic component and an expression of the imaginary part of the second n-th harmonic component based on the second set of current sample values; the second current sampling value set is obtained by removing a first current sampling value in the first current sampling value set and adding a new current sampling value at last;
Determining an expression of the real part of the third n-th harmonic component and an expression of the imaginary part of the third n-th harmonic component based on the third set of current sample values; the third current sampling value set is obtained by removing the first two current sampling values in the first current sampling value set and adding two new current sampling values at last;
Determining an expression of a fault current when a short circuit fault occurs based on the expression of the real part of the first n-th harmonic component, the expression of the imaginary part of the first n-th harmonic component, the expression of the real part of the second n-th harmonic component, the expression of the real part of the third n-th harmonic component, and the expression of the imaginary part of the third n-th harmonic component;
Based on the expression of the fault current, a zero crossing of the current is predicted.
10. The fast switching-type fault current limiter according to any one of claims 1 to 9, wherein the remote controller is further configured to, after controlling the fast switching-off, re-determine whether the transformer still has a short-circuit fault after a first preset period of time, determine that the transformer has a permanent short-circuit fault if the transformer still has a short-circuit fault, control the circuit breaker of the transformer to open, and control the fast switching-on after a second preset period of time, determine that the transformer has a transient short-circuit fault if the short-circuit fault of the transformer has been released, and control the fast switching-on.
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