CN112039036B - Alternating current line instantaneous value variation distance protection method and system - Google Patents
Alternating current line instantaneous value variation distance protection method and system Download PDFInfo
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- CN112039036B CN112039036B CN202010920971.3A CN202010920971A CN112039036B CN 112039036 B CN112039036 B CN 112039036B CN 202010920971 A CN202010920971 A CN 202010920971A CN 112039036 B CN112039036 B CN 112039036B
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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
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0092—Details of emergency protective circuit arrangements concerning the data processing means, e.g. expert systems, neural networks
Abstract
The invention discloses a method and a system for protecting the distance of the instantaneous value variation of an alternating current line, which comprises the steps of calculating the voltage of a setting point according to the collected three-phase voltage and three-phase current by combining a power transmission line model; constructing a virtual fault point voltage according to the fault time and the collected three-phase voltage and three-phase current by combining a power transmission line model; processing the setting point voltage and the virtual fault point voltage through the same digital low-pass filter; calculating the voltage variation of the setting point by using the voltage of the setting point processed by the digital low-pass filter; calculating the voltage variation of the virtual fault point by using the voltage of the virtual fault point processed by the digital low-pass filter; and judging whether the intra-area fault occurs according to the voltage variation of the setting point and the absolute value of the voltage variation of the virtual fault point within the preset time after the fault. The method has the advantages of simple criterion and high action speed, can effectively improve the action speed of alternating current line distance protection, and can improve the safety and stability of an alternating current power grid.
Description
Technical Field
The invention belongs to the field of relay protection of power systems, and particularly relates to a method and a system for protecting the distance of the change of an instantaneous value of an alternating current circuit.
Background
At present, the interconnection of each large regional power grid in China is realized by ultra/extra-high voltage alternating current and direct current transmission lines, and an alternating current and direct current hybrid power grid with the largest scale and the highest voltage grade in the world is formed. Under the large grid pattern of alternating current-direct current series-parallel connection of large-scale new energy access, a high-voltage alternating current transmission line is used as a main artery for power transmission, and the operation safety of the high-voltage alternating current transmission line directly concerns the safety and stability of the whole power system, so that higher requirements are put forward on the removal speed of line faults.
The distance protection is widely applied to an alternating current transmission system, the transmission capacity is further expanded along with the improvement of the alternating current transmission voltage level, and higher requirements are put forward on the action speed of the distance protection. The improvement of the distance protection action speed has important significance for ensuring the safe and stable operation of the system.
At present, the traditional distance protection is generally based on power frequency phasor, the action speed of the traditional distance protection is limited by a time window of a power frequency phasor extraction algorithm, the action speed is slow, and the fault removal time is long, so that the safety and the stability of a system are not facilitated. Meanwhile, the theoretical basis of the distance protection based on the power frequency phasor is a fault analysis method based on the power supply characteristics of the synchronous generator, however, the fault transient characteristics of new energy and a direct current system are obviously different from those of the synchronous generator, and the distance protection based on the power frequency phasor has the problem of performance degradation under the new potential of a power grid.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a distance protection method and a distance protection system for the change of the instantaneous value of an alternating current line, and aims to solve the technical problems of low action speed and long fault clearing time of alternating current line distance protection in the prior art.
In order to achieve the above object, an aspect of the present invention provides a method for protecting a distance of an ac line instantaneous value variation, where the method is based on a system structure including: the first equivalent power supply is connected with the first bus through the first alternating current circuit, the first bus is connected with the second bus through the protected alternating current circuit, and the second bus is connected with the second equivalent power supply through the second alternating current circuit; the first relay protection device is installed at the first bus outlet, and the second relay protection device is installed at the second bus outlet.
The method comprises the following steps:
s1: calculating a setting point voltage according to the collected three-phase voltage and three-phase current by combining a power transmission line model;
s2: constructing a virtual fault point voltage according to the fault time and the collected three-phase voltage and three-phase current by combining a power transmission line model;
s3: processing the setting point voltage and the virtual fault point voltage through the same digital low-pass filter;
s4: calculating the voltage variation of the setting point by using the voltage of the setting point processed by the digital low-pass filter;
s5: calculating the voltage variation of the virtual fault point by using the voltage of the virtual fault point processed by the digital low-pass filter;
s6: and judging whether the in-zone fault occurs according to the absolute value of the voltage variation of the setting point and the voltage variation of the virtual fault point within the preset time after the fault. Tripping if the fault in the area is judged to occur; if it is determined that an out-of-range fault has occurred, the system waits for the next fault, and if an ac line has a fault, the process proceeds to step S1.
Further, in step S1, the method for calculating the set point voltage includes: u. ofSETk(t)＝f1[uk(t)，ik(t)]；
Where k is a, b, c, respectively, a phase, b phase and c phase, t is time, uSETk(t) is the set point voltage, uk(t) three-phase voltage, ik(t) three-phase currents collected, f1[uk(t)，ik(t)]Is uk(t) and ik(t) a function representing the set point voltage calculated from the line model and corresponding line parameters.
Further, in step S2, the virtual fault point voltage reconstruction method includes: before the fault moment, the voltage of a virtual fault point is the voltage of a certain point on a protected line; after the fault moment, the voltage of the virtual fault point is zero; the method for calculating the virtual fault point voltage before the fault time in step S2 includes: u. ofFAULTk(t)＝f2[uk(t)，ik(t)]；
Where k is a, b, c, respectively, a phase, b phase and c phase, t is time, uFAULTk(t) is the set point voltage, uk(t) three-phase voltage, ik(t) three-phase currents collected, f2[uk(t)，ik(t)]Is uk(t) and ik(t) function, representation according to line model and correspondingAnd calculating the virtual fault point voltage according to the line parameters.
Further, in step S3, the cut-off frequency of the digital low-pass filter is selected according to the length of the protected line.
Further, in step S4, the method for calculating the set point voltage variation amount includes: u. of1k(t)＝uSET_LPFk(t)-uSET_LPFk(t0)；
Where, k is a, b, c, respectively representing a phase, b phase and c phase, t is the current time, t is0Is a time, u, before the current time1k(t) is the set point voltage variation, uSET_LPFkAnd (t) is the setting point voltage processed by the digital low-pass filter.
Further, in step S5, the method for calculating the virtual fault point voltage variation includes: u. of2k(t)＝uFAULT_LPFk(t)-uFAULT_LPFk(t0)；
Where k is a, b, c, respectively, a phase, b phase and c phase, t is time, t is0Is a time, u, before the current time2k(t) is the virtual fault point voltage variation, uFAULT_LPFk(t) is the virtual fault point voltage processed by the digital low pass filter;
further, in step S6, the method for determining the inside/outside fault includes:
if the absolute value of the voltage variation of the setting point calculated is always larger than the absolute value of the voltage variation of the virtual fault point within the preset time after the fault, the occurrence of the intra-area fault is considered; and if the absolute value of the voltage variation of the setting point does not meet the condition that the absolute value is continuously larger than the absolute value of the voltage variation of the virtual fault point within a period of time after the fault, determining that an out-of-area fault occurs. Tripping if the fault in the area is judged to occur; if it is determined that an out-of-range fault has occurred, the system waits for the next fault, and if an ac line has a fault, the process proceeds to step S1.
The invention provides a distance protection system for the instantaneous value variation of the alternating current line, which comprises a setting point voltage acquisition module, a transmission line model and a control module, wherein the setting point voltage acquisition module is used for calculating the setting point voltage according to the collected three-phase voltage and three-phase current by combining the transmission line model;
the virtual fault point voltage acquisition module is used for constructing a virtual fault point voltage according to the fault moment, the collected three-phase voltage and the collected three-phase current by combining a power transmission line model;
the filtering module is used for processing the setting point voltage and the virtual fault point voltage through the same digital low-pass filter;
the setting point voltage variation acquiring module is used for calculating the setting point voltage variation by using the setting point voltage processed by the digital low-pass filter;
the virtual fault point voltage variation obtaining module is used for calculating the virtual fault point voltage variation by using the virtual fault point voltage processed by the digital low-pass filter;
the judging module is used for judging whether an intra-area fault occurs according to the absolute value of the voltage variation of the setting point and the voltage variation of the virtual fault point within the preset time after the fault occurs, and tripping if the intra-area fault is judged to occur; and if the occurrence of the out-of-area fault is judged, the protection does not act.
Through the technical scheme, compared with the prior art, the method utilizes the three-phase voltage and the three-phase current collected by the relay protection device, and combines a power transmission line model to calculate the voltage of the setting point; constructing a virtual fault point voltage according to the fault time and the three-phase voltage and the three-phase current collected by the relay protection device in combination with a power transmission line model; calculating the voltage variation of the setting point by using the voltage of the setting point processed by the digital low-pass filter; calculating the voltage variation of the virtual fault point by using the voltage of the virtual fault point processed by the digital low-pass filter; and comparing the voltage variation of the setting point in the preset time after the fault with the absolute value of the voltage variation of the virtual fault point to judge whether the intra-area fault occurs. The distance protection method for the instantaneous value variation of the alternating current circuit is simple in criterion and short in required data window, and can effectively improve the distance protection action speed of the alternating current circuit and improve the safety and stability of a system.
Drawings
Fig. 1 is a schematic structural diagram of an ac power transmission system according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a typical 500kV ac transmission system provided by an embodiment of the present invention;
FIG. 3 shows that a-phase short circuit fault occurs at 40% of the positive direction protected line of the first relay protection device of the 500kV alternating-current transmission system (f in FIG. 2)1Point), a setting point voltage variation and a virtual fault point voltage variation curve calculated by the first relay protection device;
FIG. 4 shows that a-phase short circuit fault occurs at 90% of the positive direction protected line of the first relay protection device of the 500kV alternating-current transmission system (f in FIG. 2)2Point), a setting point voltage variation and a virtual fault point voltage variation curve calculated by the first relay protection device;
the attached drawings are marked as follows:
1 is a first equivalent power supply, 2 is a first alternating current line, 3 is a first bus, 4 is a protected alternating current line, 5 is a second bus, 6 is a second alternating current line, 7 is a second equivalent power supply, 8 is a first relay protection device, and 9 is a second relay protection device.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a distance protection method for the variation of the instantaneous value of an alternating current circuit, aiming at the problems of low action speed and long fault removal time of the traditional alternating current circuit distance protection.
In the embodiment of the invention, the three-phase voltage and the three-phase current collected by the relay protection device are combined with a power transmission line model to calculate the voltage of a setting point; constructing a virtual fault point voltage according to the fault time and the three-phase voltage and current information acquired by the relay protection device by combining a power transmission line model; calculating the voltage variation of the setting point by using the voltage of the setting point processed by the digital low-pass filter; calculating the voltage variation of the virtual fault point by using the voltage of the virtual fault point processed by the digital low-pass filter; and comparing the voltage variation of the setting point in the preset time after the fault with the absolute value of the voltage variation of the virtual fault point to judge whether the intra-area fault occurs. The distance protection method for the instantaneous value variation of the alternating current circuit is simple in criterion and short in required data window, and can effectively improve the distance protection action speed of the alternating current circuit and improve the safety and stability of a system.
As shown in fig. 1, a system structure based on a method for protecting a distance of an ac line instantaneous value variation according to an embodiment of the present invention includes: the system comprises a first equivalent power source 1, a first alternating current circuit 2, a first bus 3, a protected alternating current circuit 4, a second bus 5, a second alternating current circuit 6, a second equivalent power source 7, a first relay protection device 8 and a second relay protection device 9, wherein the first equivalent power source 1 is connected with the first bus 3 through the first alternating current circuit 2, the first bus 3 is connected with the second bus 5 through the protected alternating current circuit 4, and the second bus 5 is connected with the second equivalent power source 7 through the second alternating current circuit 6; the first relay protection device 8 is installed at the outlet of the first bus 3, and the second relay protection device 9 is installed at the outlet of the second bus 5.
The method comprises the following steps:
s1: calculating a setting point voltage according to the three-phase voltage and the three-phase current collected by the relay protection device by combining a power transmission line model;
s2: constructing a virtual fault point voltage according to the fault time and the three-phase voltage and the three-phase current collected by the relay protection device in combination with a power transmission line model;
s3: processing the setting point voltage and the virtual fault point voltage through the same digital low-pass filter;
s4: calculating the voltage variation of the setting point by using the voltage of the setting point processed by the digital low-pass filter;
s5: calculating the voltage variation of the virtual fault point by using the voltage of the virtual fault point processed by the digital low-pass filter;
s6: judging whether an intra-area fault occurs according to the absolute value of the voltage variation of the setting point and the voltage variation of the virtual fault point within preset time after the fault occurs, and tripping if the intra-area fault is judged to occur; if it is determined that an out-of-range fault has occurred, the system waits for the next fault, and if an ac line has a fault, the process proceeds to step S1.
Further, in step S1, the method for calculating the set point voltage includes: u. ofSETk(t)＝f1[uk(t)，ik(t)]；
Where k is a, b, c, respectively, a phase, b phase and c phase, t is time, uSETk(t) is the set point voltage, uk(t) three-phase voltage, i, collected by the protection devicek(t) three-phase current collected by the protection device, f1[uk(t)，ik(t)]Is uk(t) and ik(t) a function representing the set point voltage calculated from the line model and corresponding line parameters.
Further, in step S2, the virtual fault point voltage reconstruction method includes: before the fault moment, the voltage of a virtual fault point is the voltage of a certain point on a protected line; after the fault moment, the voltage of the virtual fault point is zero; the method for calculating the virtual fault point voltage before the fault time in step S2 includes: u. ofFAULTk(t)＝f2[uk(t)，ik(t)]；
Where k is a, b, c, respectively, a phase, b phase and c phase, t is time, uFAULTk(t) is the set point voltage, uk(t) three-phase voltage, i, collected by the protection devicek(t) three-phase current collected by the protection device, f2[uk(t)，ik(t)]Is uk(t) and ik(t) a function representing the virtual fault point voltage calculated from the line model and corresponding line parameters.
Further, in step S3, the cut-off frequency of the digital low-pass filter needs to be selected according to the length of the protected line.
Further, in step S4, the method for calculating the set point voltage variation amount includes: u. of1k(t)＝uSET_LPFk(t)-uSET_LPFk(t0)；
Where, k is a, b, c, respectively representing a phase, b phase and c phase, t is the current time, t is0Is a time, u, before the current time1k(t) is the set point voltage variation, uSET_LPFkAnd (t) is the setting point voltage processed by the digital low-pass filter.
Further, in step S5, the method for calculating the virtual fault point voltage variation includes: u. of2k(t)＝uFAULT_LPFk(t)-uFAULT_LPFk(t0)；
Where k is a, b, c, respectively, a phase, b phase and c phase, t is time, t is0Is a time, u, before the current time2k(t) is the virtual fault point voltage variation, uFAULT_LPFkAnd (t) is the virtual fault point voltage processed by the digital low-pass filter.
Further, in step S6, the method for determining the inside/outside fault includes:
if the absolute value of the voltage variation of the setting point calculated is always larger than the absolute value of the voltage variation of the virtual fault point within a period of time after the fault, the occurrence of the intra-area fault is considered; and if the absolute value of the voltage variation of the setting point does not meet the condition that the absolute value is continuously larger than the absolute value of the voltage variation of the virtual fault point within a period of time after the fault, determining that an out-of-area fault occurs.
To further explain the method for protecting the distance of the ac line instantaneous value variation according to the embodiment of the present invention, the following is detailed with reference to the accompanying drawings and specific examples:
the specific embodiment is described by taking a typical 500kV ac transmission system as an example, and as shown in fig. 2, the typical 500kV ac transmission system includes a first equivalent power source 1, a first ac line 2, a first bus bar 3, a protected ac line 4, a second bus bar 5, a second ac line 6, a second equivalent power source 7, a first relay protection device 8, and a second relay protection device 9, where the first equivalent power source 1 is connected to the first bus bar 3 through the first ac line 2, the first bus bar 3 is connected to the second bus bar 5 through the protected ac line 4, and the second bus bar 5 is connected to the second equivalent power source 7 through the second ac line 6; the first relay protection device 8 is installed at the outlet of the first bus 3, and the second relay protection device 9 is installed at the outlet of the second bus 5.
By adopting the system, the alternating current line transient state quantity distance protection method is implemented according to the following steps:
step 1: calculating a setting point voltage according to the three-phase voltage and the three-phase current collected by the relay protection device by combining a power transmission line model;
step 2: constructing a virtual fault point voltage according to the fault time and the three-phase voltage and the three-phase current collected by the relay protection device in combination with a power transmission line model;
and step 3: processing the setting point voltage and the virtual fault point voltage through the same digital low-pass filter;
and 4, step 4: calculating the voltage variation of the setting point by using the voltage of the setting point processed by the digital low-pass filter;
and 5: calculating the voltage variation of the virtual fault point by using the voltage of the virtual fault point processed by the digital low-pass filter;
step 6: and judging whether the intra-area fault occurs according to the absolute value of the voltage variation of the set point and the voltage variation of the virtual fault point in a short time after the fault.
In the embodiment of the invention, in step 1, based on the RL model of the alternating-current transmission line, the calculation method of the setting point voltage specifically comprises the following steps:
wherein t is time; u. ofseta(t)，usetb(t)，usetc(t) setting point three-phase voltage; u. ofa(t)，ub(t)， uc(t) three-phase voltage collected by the protection device; i.e. ia(t)，ib(t)，ic(t) three-phase current collected by the protection device; r issIs a unit length self-resistance of a protected circuit; r ismIs a unit length mutual resistance of a protected circuit; lsIs a unit length self-inductance of a protected circuit; lmThe mutual inductance is the unit length mutual inductance of the protected circuit; l issetFor protection, the protection range is set to 80% of the total length of the protected line in the present embodiment.
In the embodiment of the present invention, in step 2, the method for reconstructing the voltage of the virtual fault point specifically includes: before the fault moment, the voltage of a virtual fault point is the voltage of a certain point on a protected line; after the fault moment, the voltage of the virtual fault point is zero; based on an RL model of the AC transmission line, the method for calculating the voltage of the virtual fault point before the fault moment specifically comprises the following steps:
wherein t is time; u. ofseta(t)，usetb(t)，usetc(t) setting point three-phase voltage; u. ofa(t)，ub(t)， uc(t) three-phase voltage collected by the protection device; i.e. ia(t)，ib(t)，ic(t) three-phase current collected by the protection device; r issIs a unit length self-resistance of a protected circuit; r ismIs a unit length mutual resistance of a protected circuit; lsIs a unit length self-inductance of a protected circuit; lmThe mutual inductance is the unit length mutual inductance of the protected circuit; l isdFor the line length, it is set to 50% of the total length of the protected line in the present embodiment.
In the embodiment of the present invention, in step 3, the cutoff frequency of the digital low-pass filter is selected according to the length of the protected line, and in the embodiment, the cutoff frequency of the digital low-pass filter is selected to be 200Hz when the length of the protected line is 200 km.
In the embodiment of the present invention, in step 4, a method for calculating a voltage variation of a setting point includes: u. of1k(t)＝uSET_LPFk(t)-uSET_LPFk(t0)；
Wherein k ═ a, b, c, represents phases a, b, and c, respectively; t is the current time; t is t0Is a time before the current time, in the embodiment of the present invention, t0Setting as a fault occurrence time; u. of1k(t) to set point voltageMelting; u. ofSET_LPFk(t) is the setting point voltage processed by the digital low-pass filter;
in the embodiment of the present invention, the method for calculating the voltage variation of the virtual fault point includes: u. of2k(t)＝uFAULT_LPFk(t)-uFAULT_LPFk(t0)；
Wherein k ═ a, b, c, represents phases a, b, and c, respectively; t is the time, t0Is a time before the current time, in the embodiment of the present invention, t0Setting as a fault occurrence time; u. of2k(t) is the virtual fault point voltage variation; u. ofFAULT_LPFkAnd (t) is the virtual fault point voltage processed by the digital low-pass filter.
In the embodiment of the present invention, in step 6, the method for distinguishing the internal and external faults specifically includes:
if u1k(t)|＞|u2k(t) | continuously holds for more than 1ms within 3ms after the fault, and then the fault in the k-phase area is considered to occur; wherein k ═ a, b, c, represents phases a, b, and c, respectively; if u1k(t)|＞|u2k(t) | is continuously established within 3ms after the fault and does not exceed 1ms, then the k-phase out-of-area fault is considered to occur; wherein, k is a, b and c, which respectively represent a phase, b phase and c phase.
In the present embodiment, a-phase short circuit fault occurs at 40% of the positive direction protected line of the first relay protection device 8 (f in fig. 2)1Point), the absolute value of the setting point voltage variation which is greater than the absolute value of the virtual fault point voltage variation calculated by the first relay protection device 8 is continuously established for more than 1ms within 3ms after the fault, so that the fault is determined as an intra-area fault, and a trip instruction can be issued 1ms after the fault, as shown in fig. 3.
In the embodiment, a-phase short circuit fault occurs at 90% of the positive direction protected line of the first relay protection device 8 (f in fig. 2)2Point), the setting point voltage variation amount and the virtual fault point voltage variation amount calculated by the first relay protection device 8 are as shown in fig. 4, and it is determined that the absolute value of the setting point voltage variation amount larger than the virtual fault point voltage variation amount does not continuously become more than 1ms within 3ms after the fault, soIs an out-of-range fault.
Referring to fig. 3 and 4, fig. 3 shows that a single-phase earth fault (f) occurs in 40% of the positive direction protected line of the first relay protection device 8 of the typical 500kV alternating-current transmission system of the invention1) Then, the first relay protection device calculates 8 a curve of the voltage variation of the setting point and the voltage variation of the virtual fault point; FIG. 4 shows that a single-phase earth fault (f) occurs in 90% of the positive direction protected line of the first relay protection device 8 of the typical 500kV alternating-current transmission system of the invention2) And then, a curve of the voltage variation of the setting point and the voltage variation of the virtual fault point calculated by the first relay protection device is obtained. As can be seen from fig. 3 to fig. 4, the method provided by the embodiment of the present invention can quickly determine whether an intra-area fault occurs.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (7)
1. A distance protection method for AC line instantaneous value variation is characterized by comprising the following steps:
s1: calculating a setting point voltage according to the collected three-phase voltage and three-phase current by combining a power transmission line model;
s2: constructing a virtual fault point voltage according to the fault time and the collected three-phase voltage and three-phase current by combining a power transmission line model;
s3: processing the setting point voltage and the virtual fault point voltage through the same digital low-pass filter;
s4: calculating the voltage variation of the setting point by using the voltage of the setting point processed by the digital low-pass filter;
s5: calculating the voltage variation of the virtual fault point by using the voltage of the virtual fault point processed by the digital low-pass filter;
s6: judging whether an intra-area fault occurs according to the absolute values of the voltage variation of the setting point and the voltage variation of the virtual fault point within the preset time after the fault, and if the absolute value of the voltage variation of the setting point calculated within the preset time after the fault is always larger than the absolute value of the voltage variation of the virtual fault point, determining that the intra-area fault occurs; if the absolute value of the voltage variation of the setting point does not meet the condition that the absolute value is continuously larger than the absolute value of the voltage variation of the virtual fault point within the preset time after the fault, the occurrence of an outside fault is considered; tripping if the fault in the area is judged to occur; if it is determined that an out-of-range fault has occurred, the system waits for the next fault, and if an ac line has a fault, the process proceeds to step S1.
2. The method of claim 1, wherein in step S1, the method for calculating the set point voltage is:
uSETk(t)＝f1[uk(t),ik(t)]
where k is a, b, c, respectively, a phase, b phase and c phase, t is time, uSETk(t) is the set point voltage, uk(t) three-phase voltage, ik(t) three-phase currents collected, f1[uk(t),ik(t)]Is uk(t) and ik(t) a function representing the set point voltage calculated from the line model and corresponding line parameters.
3. The method as claimed in claim 1, wherein in step S2, the virtual fault point voltage reconstruction method comprises: before the fault moment, the voltage of a virtual fault point is the voltage of a certain point on a protected line; after the fault moment, the voltage of the virtual fault point is zero; the method for calculating the voltage of the virtual fault point before the fault moment comprises the following steps:
uFAULTk(t)＝f2[uk(t),ik(t)]
where k is a, b, c, respectively, a phase, b phase and c phase, t is time, uFAULTk(t) is the set point voltage, uk(t) three-phase voltage, ik(t) three-phase currents collected, f2[uk(t),ik(t)]Is uk(t) and ik(t) function representing the model of the line and the corresponding lineAnd (4) calculating the virtual fault point voltage by the parameters.
4. The method of claim 1, wherein in step S3, the cut-off frequency of the digital low-pass filter is selected according to the length of the line to be protected.
5. The method of claim 1, wherein in step S4, the method of calculating the variation of the set point voltage is:
u1k(t)＝uSET_LPFk(t)-uSET_LPFk(t0)
where, k is a, b, c, respectively representing a phase, b phase and c phase, t is the current time, t is0Is a time, u, before the current time1k(t) is the set point voltage variation, uSET_LPFkAnd (t) is the setting point voltage processed by the digital low-pass filter.
6. The method of claim 1, wherein in step S5, the virtual fault point voltage variation is calculated by:
u2k(t)＝uFAULT_LPFk(t)-uFAULT_LPFk(t0)
where k is a, b, c, respectively, a phase, b phase and c phase, t is time, t is0Is a time, u, before the current time2k(t) is the virtual fault point voltage variation, uFAULT_LPFkAnd (t) is the virtual fault point voltage processed by the digital low-pass filter.
7. An alternating current line instantaneous value variation distance protection system is characterized by comprising:
the fixed point voltage acquisition module is used for calculating the fixed point voltage according to the collected three-phase voltage and three-phase current by combining a power transmission line model;
the virtual fault point voltage acquisition module is used for constructing a virtual fault point voltage according to the fault moment, the collected three-phase voltage and the collected three-phase current by combining a power transmission line model;
the filtering module is used for processing the setting point voltage and the virtual fault point voltage through the same digital low-pass filter;
the setting point voltage variation acquiring module is used for calculating the setting point voltage variation by using the setting point voltage processed by the digital low-pass filter;
the virtual fault point voltage variation obtaining module is used for calculating the virtual fault point voltage variation by using the virtual fault point voltage processed by the digital low-pass filter;
the judging module is used for judging whether an intra-area fault occurs according to the absolute values of the voltage variation of the setting point and the voltage variation of the virtual fault point within the preset time after the fault, and if the absolute value of the voltage variation of the setting point calculated within the preset time after the fault is always greater than the absolute value of the voltage variation of the virtual fault point, the intra-area fault is considered to occur; if the absolute value of the voltage variation of the setting point does not meet the condition that the absolute value is continuously larger than the absolute value of the voltage variation of the virtual fault point within the preset time after the fault, the occurrence of an outside fault is considered; tripping if the fault in the area is judged to occur; and if the occurrence of the out-of-area fault is judged, the protection does not act.
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