CN112865048B - Protection method and device for alternating current-direct current series-parallel power transmission system and terminal equipment - Google Patents
Protection method and device for alternating current-direct current series-parallel power transmission system and terminal equipment Download PDFInfo
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- 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
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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Abstract
The invention is suitable for the technical field of high-voltage power transmission, and provides a method and a device for protecting an alternating-current and direct-current series-parallel power transmission system and terminal equipment, wherein the method for protecting the alternating-current and direct-current series-parallel power transmission system comprises the following steps: acquiring electric parameters of an alternating current line of an alternating current and direct current series-parallel power transmission system; determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters; determining the fault type of the alternating current-direct current hybrid power transmission system based on zero sequence current phasors at two ends of the alternating current circuit, and controlling a protection device of the alternating current-direct current hybrid power transmission system according to the fault type of the alternating current-direct current hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault. The invention can avoid the refusal of distance protection and improve the safety of the AC/DC series-parallel power transmission system.
Description
Technical Field
The invention belongs to the technical field of high-voltage power transmission, and particularly relates to a method and a device for protecting an alternating current-direct current hybrid power transmission system and terminal equipment.
Background
Most of high-voltage direct-current transmission systems above +/-500 kV put into operation at present are based on a Line Commutated Converter (LCC), a Converter element of the high-voltage direct-current transmission system adopts a thyristor, and alternating-current faults on an inverter side easily cause phase change failure of the direct-current system. When the phase change fails, the electric quantity of the alternating current side and the direct current side is affected, and the correct work of the alternating current relay protection system can be affected.
In an alternating current-direct current hybrid power transmission system, a short-circuit fault that a power grid commutation converter passes through a transition resistor on an alternating current side may cause commutation failure of the power grid commutation converter, the transition resistor may cause measurement impedance of distance protection on the alternating current side to generate additional impedance, and the additional impedance may cause rejection of the distance protection to affect safety of the alternating current-direct current hybrid power transmission system. At present, a solution based on single-side electric quantity is mostly adopted, however, the calculation of the solution is complex, the influences of transition resistance, commutation failure and fault positions and types are difficult to overcome simultaneously, and the rejection of conventional distance protection under complex scenes such as commutation failure caused by alternating-current side faults cannot be well avoided.
Disclosure of Invention
In view of this, embodiments of the present invention provide a method and an apparatus for protecting an ac/dc series-parallel power transmission system, and a terminal device, so as to solve the problem in the prior art that the rejection of conventional distance protection in complex scenes, such as a commutation failure caused by an ac side fault, cannot be well avoided.
A first aspect of an embodiment of the present invention provides a method for protecting an ac/dc series-parallel power transmission system, including:
acquiring electric parameters of an alternating current line of an alternating current and direct current series-parallel power transmission system;
determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters;
determining the fault type of the AC-DC hybrid power transmission system based on zero sequence current phasors at two ends of the AC line, and controlling a protection device of the AC-DC hybrid power transmission system according to the fault type of the AC-DC hybrid power transmission system;
the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault.
A second aspect of an embodiment of the present invention provides an ac/dc series-parallel power transmission system protection device, including:
the acquisition module is used for acquiring the electric parameters of an alternating current circuit of the alternating current-direct current hybrid power transmission system;
the calculation module is used for determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters;
the control module is used for determining the fault type of the alternating current-direct current hybrid power transmission system based on the zero sequence current phasors at the two ends of the alternating current circuit and controlling a protection device of the alternating current-direct current hybrid power transmission system according to the fault type of the alternating current-direct current hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault.
A third aspect of embodiments of the present invention provides a terminal device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, where the processor implements the steps of the method for protecting an ac/dc hybrid power transmission system according to any one of the first aspect when executing the computer program.
A fourth aspect of the embodiments of the present invention provides a computer-readable storage medium, where a computer program is stored, and when the computer program is executed by a processor, the steps of the method for protecting an ac/dc hybrid power transmission system according to any one of the first aspect above are implemented.
Compared with the prior art, the embodiment of the invention has the following beneficial effects:
according to the method, the electric parameters of an alternating current circuit of the alternating current-direct current series-parallel power transmission system are obtained; determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters; determining the fault type of the alternating current-direct current hybrid power transmission system based on zero sequence current phasors at two ends of the alternating current circuit, and controlling a protection device of the alternating current-direct current hybrid power transmission system according to the fault type of the alternating current-direct current hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault. The fault type of the alternating current-direct current series-parallel power transmission system is judged through the zero sequence current phasor, the interference of other factors can be avoided, the reliability is high, and the protection device can accurately and efficiently judge the fault and carry out protection action.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a schematic flow chart illustrating an implementation of a protection method for an ac/dc series-parallel power transmission system according to an embodiment of the present invention;
fig. 2 is an ac/dc series-parallel power transmission system provided in an embodiment of the present invention;
fig. 3 is a fault network in which only the ac system is considered when the ac line MN is in a unidirectional ground short circuit in the system shown in fig. 2 according to the embodiment of the present invention;
fig. 4 is a fault network in which only the dc system is considered when the unidirectional ground short circuit occurs in the ac line MN in the system shown in fig. 2 according to the embodiment of the present invention;
fig. 5 is a zero sequence network of a fault in a region where a unidirectional ground short circuit occurs in an ac line MN in the system shown in fig. 2 according to an embodiment of the present invention;
fig. 6 is a zero sequence network for an external fault when an unidirectional ground short circuit occurs in the ac line MN in the system shown in fig. 2 according to an embodiment of the present invention;
fig. 7 is an additional reactance curve provided by the present invention when a single-phase ground fault with different transition resistances occurs within the MN area of the ac line 8km from the M terminal;
fig. 8 is an additional reactance curve provided by the present invention when a single-phase ground fault with different transition resistances occurs within the MN area of the ac line 15km from the M terminal;
fig. 9 is a graph of the amplitude vector ratio H when a single-phase ground fault occurs in a region where the distance between the ac line MN and the M terminal is 8 km;
fig. 10 is a graph of the amplitude vector ratio H when a single-phase ground fault occurs in a region where different transition resistances occur 15km away from the M end in the ac line MN according to the present invention;
FIG. 11 is an outside-area line L provided by the present invention 1 A curve of amplitude vector ratio H when a single phase generated at the midpoint passes through a 25 omega transition resistor ground fault;
FIG. 12 is a graph of amplitude vector ratio H for a single-phase-to-ground fault in a region where a single-phase through 25 Ω transition resistance occurs 8km away from the M terminal in an AC line MN in consideration of data synchronization effects as provided by the present invention;
FIG. 13 is a graph of amplitude vector ratio H for a single-phase-to-ground fault occurring in a region of a 25 Ω transition resistance of a single-phase line 15km away from the M terminal in consideration of data synchronization effects provided by the present invention;
FIG. 14 is a diagram of an out-of-area line L considering data synchronization effects provided by the present invention 1 A curve of amplitude vector ratio H when a single phase generated at the midpoint passes through a 25 omega transition resistor ground fault;
fig. 15 is a schematic diagram of an ac/dc hybrid power transmission system protection device according to an embodiment of the present invention;
fig. 16 is a terminal device according to an embodiment of the present invention.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the 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.
In order to explain the technical means of the present invention, the following description will be given by way of specific examples.
Referring to fig. 1, which shows an ac/dc series-parallel power transmission system provided by an embodiment of the present invention,
referring to fig. 1, a schematic implementation flow diagram of a protection method for an ac-dc hybrid power transmission system according to an embodiment of the present invention is shown.
As shown in fig. 1, in some embodiments of the present invention, a method for protecting an ac/dc hybrid power transmission system may include:
s101, obtaining electric parameters of an alternating current line of the alternating current and direct current series-parallel power transmission system.
Optionally, the electrical parameters of the ac line may be collected in real time through a voltage transformer and a current transformer, and the electrical parameters of the ac line may include line impedance, three-phase voltage, three-phase current, and the like of the ac line MN.
And S102, determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters.
Optionally, the zero-sequence current phasor at the M end of the ac line and the zero-sequence current phasor at the N end of the ac line may be determined according to the electrical parameter of the ac line.
S103, determining the fault type of the alternating current and direct current hybrid power transmission system based on the zero sequence current phasors at the two ends of the alternating current circuit, and controlling a protection device of the alternating current and direct current hybrid power transmission system according to the fault type of the alternating current and direct current hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault.
According to the method, the electric parameters of an alternating current circuit of the alternating current-direct current series-parallel power transmission system are obtained; determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters; determining the fault type of the alternating current-direct current hybrid power transmission system based on zero sequence current phasors at two ends of the alternating current circuit, and controlling a protection device of the alternating current-direct current hybrid power transmission system according to the fault type of the alternating current-direct current hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault. The fault type of the alternating current-direct current hybrid power transmission system is judged through the zero sequence current phasor, the interference of other factors can be avoided, the reliability is high, and the protection device can accurately and efficiently judge faults and carry out protection action.
By way of example, the invention is schematically illustrated below:
referring to fig. 2, an ac/dc series-parallel power transmission system provided by an embodiment of the present invention is shown; referring to fig. 3, it shows a fault network of the ac system only when the ac line MN is unidirectionally grounded and shorted in the system shown in fig. 2 according to an embodiment of the present invention; referring to fig. 4, it shows a fault network in which only the dc system is considered when the unidirectional ground short circuit occurs in the ac line MN in the system shown in fig. 2 according to the embodiment of the present invention, and f denotes a fault point.
Take phase A ground fault as an example, wherein Z LM 、Z LN Respectively representing the line impedance of the M side and the line impedance of the N side of the fault point, Z SN Representing the equivalent impedance, Z, of the N-side system C Is equivalent impedance, R, of AC filter and reactive power compensation device f Denotes the transition resistance, U f Voltage, U, representing a point of failure busMA Representing the A-phase voltage, I, at the M end of the AC bus MN Mac 、I Nac 、I fac Respectively, the current flowing through the M, N terminal and the fault point, I, when only the AC system action is considered dc Equivalent power frequency current source, I, of DC system under failure of commutation Mdc 、I Ndc 、I fdc Respectively, the voltage flows through the M, N terminal and the fault point when only the action of a DC system is consideredThe current of (2).
Measured impedance Z of N-terminal distance protection of AC line MN M Comprises the following steps:
wherein, U M Measurement voltage, I, representing M-side distance protection M Denotes the current flowing through the M-terminal distance protection, C denotes the zero sequence current compensation factor, C = (z) 0 -z 1 )/3z 1 ，z 1 、z 0 Respectively representing the positive and zero sequence impedances, L, of the line per unit length f Denotes the distance of the M-terminal from the protection to the fault point, I M0 Representing the zero sequence current flowing through the M-terminal distance protection.
When the LCC alternating current side has a short circuit fault through the grounding of the transition resistor, the existence of the transition resistor causes the measured impedance to generate additional impedance, and the characteristic quantity of the additional impedance in the alternating current-direct current hybrid system has the following characteristics:
considering only the ac system function, it can be seen in conjunction with fig. 3:
wherein, C M1 、C M2 、C M0 Distribution coefficients of positive, negative and zero sequence currents of a fault point at an M end are respectively represented, and the magnitude relation is as follows:
wherein Z is LMm 、Z LNm 、Z SNm (m =0,1,2) respectively represents the positive, negative and zero sequence impedances of the line and the N-side system at two sides of the fault point, Z C Representing the equivalent impedance, Z, of the AC filter and the reactive power compensator T0 Representing the zero sequence impedance of the converter.
The composite sequence network with single-phase grounding short circuit can obtain:
wherein E represents Dai Weining electromotive force, Z, looking into the positive sequence net fault port 1Σ 、Z 2Σ 、Z 0Σ Respectively representing the sequence impedance seen into the positive, negative and zero sequence networks by the fault point.
Considering only the ac system function, we can see in connection with fig. 4:
combining the combined action of ac and dc systems, the additional impedance can be expressed as:
on one hand, after the single-phase transition resistance at the AC side is grounded to cause the failure of DC phase commutation, the DC system injects the equivalent power frequency current I of the AC system Mdc Ahead of mains voltage U busMA And the leading angles are all within 90 degrees, and as can be seen from the above, 3I f0 Lags behind U busMA 。
On the other hand, combining the above formulas, X 1 I Mdc Ahead of I Mdc But the latter has a larger amplitude than the former, X 2 I f0 And I f0 In phase.
In summary, according to X after phase commutation failure 1 I Mdc Advance I Mdc 、I Mdc Leading U busMA The relative position relationship of each variable can be divided into two types:
I Mdc 、X 1 I Mdc at-3I f0 Two sides;
I Mdc 、X 1 I Mdc is located at-3I f0 On the same side.
When I is Mdc 、X 1 I Mdc Is located at-3I f0 On both sides, there is always 3I f0 +X 1 I Mdc Lags behind X 2 I f0 +I Mdc The additional impedance is constant and capacitive; when I is Mdc 、X 1 I Mdc at-3I f0 When the same side is used, the additional impedance is capacitive;
when X is present 2 When the value is larger than a certain value l, 3I f0 +X 1 I Mdc Will lead X 2 I f0 +I Mdc The additional impedance is inductive, wherein the specific value of l is 3I f0 、I Mdc 、X 1 I Mdc Relative magnitude of amplitude effects.
When the additional impedance is inductive, the measured impedance is increased and possibly exceeds the action range of the distance protection I section, so that the fault removal time is prolonged; when the additional impedance is capacitive, the measured impedance is reduced, which is beneficial to the rapid action of the protection, but under extreme conditions, the measured impedance can be negative, and the protection fails. Period of commutation failure I Mdc Has different fluctuation of phase, and has 3I under different fault scenes f0 、I Mdc 、X 1 I Mdc The additional impedance corresponding to the side protection may be inductive or capacitive.
Referring to fig. 5, a zero sequence network of an internal fault when a unidirectional ground short circuit occurs in an ac line MN in the system shown in fig. 2 according to an embodiment of the present invention is shown; referring to fig. 6, a zero sequence network of an out-of-range fault when the ac line MN is in a unidirectional ground short circuit in the system shown in fig. 2 according to an embodiment of the present invention is shown;
wherein Z is LM0 、Z LN0 、Z SN0 Respectively representing zero sequence impedance, U, of lines on both sides of the fault point and the N-side system k0 And indicating the zero sequence power supply of the fault point.
In some embodiments of the invention, the electrical parameter may comprise a zero sequence impedance of the ac line;
the step S102 of determining the zero-sequence current phasor at two ends of the ac line according to the electrical parameter may include:
when the alternating-current voltage of a receiving end of the alternating-current and direct-current hybrid transmission system is not larger than a first preset voltage value, determining zero-sequence current phasors at two ends of an alternating-current circuit according to zero-sequence impedance of the alternating-current circuit;
and when the receiving end alternating voltage of the alternating current-direct current hybrid transmission system is greater than a first preset voltage value and not greater than a second preset voltage value, determining zero-sequence current phasors at two ends of the alternating current circuit according to the current of the distributed capacitors at the two ends of the alternating current circuit and the zero-sequence impedance of the alternating current circuit.
Optionally, when the alternating-current voltage at the receiving end of the alternating-current/direct-current hybrid power transmission system is greater than the second preset voltage value, the zero-sequence current phasor at the two ends of the alternating-current line may also be determined according to the current of the distributed capacitors at the two ends of the alternating-current line and the zero-sequence impedance of the alternating-current line.
Optionally, the first preset voltage value may be 500kV, and the first preset voltage value may also be set according to actual needs; the second preset voltage value may be 1000kV, and the second preset voltage value may also be set according to actual needs.
Illustratively, when the receiving end alternating current voltage level of the alternating current-direct current hybrid power transmission system is 500kV or below, line distributed capacitance current compensation is not needed; and when the alternating voltage level of the receiving end reaches 1000kV, respectively calculating the capacitance currents at the two ends of the line, and respectively carrying out vector summation with the zero sequence currents at the corresponding ends to obtain zero sequence current phasors at the two ends compensated by the distributed capacitance currents.
Optionally, as for the fault in the area, as can be known from fig. 4, the zero-sequence currents at the M-terminal and N-terminal protection installation positions of the ac line are respectively:
wherein Z is SM0 ＝Z T0 //Z C 。
For an external fault, as can be known from fig. 6, zero sequence currents at the M-terminal and N-terminal protection installation positions of the ac line are respectively:
wherein Z is MN0 Representing zero-sequence impedance, Z, of AC line MN Nf0 And the zero sequence impedance of the line from the N end to the fault point f.
In some embodiments of the present invention, the "determining the fault type of the ac-dc series-parallel transmission system based on the zero-sequence current phasors at two ends of the ac line" in S103 may include:
determining an amplitude vector ratio according to zero sequence current phasors at two ends of the alternating current circuit;
and determining the fault type of the AC-DC series-parallel power transmission system according to the amplitude vector ratio.
In some embodiments of the invention, the magnitude vector ratio may be expressed as:
wherein, I M0 Is the M-end zero-sequence current phasor of the AC line, I N0 The M end is a first end of the alternating current circuit, and the N end is a second end of the alternating current circuit.
Optionally, the amplitude vector ratio is a vector sum amplitude of the M-terminal zero-sequence current phasor of the ac line, the N-terminal zero-sequence current phasor of the ac line, and a vector difference amplitude of the M-terminal zero-sequence current phasor of the ac line and the N-terminal zero-sequence current phasor of the ac line, and a formula of the amplitude vector ratio may be expressed as:
in some embodiments of the present invention, determining the fault type of the ac/dc series-parallel power transmission system according to the magnitude vector ratio may include:
if the amplitude vector ratio is larger than the preset ratio, the fault type of the alternating current-direct current series-parallel power transmission system is an intra-area fault;
and if the amplitude vector ratio is smaller than the preset ratio, determining that the fault type of the AC-DC hybrid power transmission system is an out-of-range fault.
In some embodiments of the present invention, the preset ratio may be 1.
Optionally, the fault identification criterion may be configured as:
optionally, in the high-voltage alternating-current system, the line impedance and the power supply impedance of the system mainly comprise reactance components, and according to a vector magnitude ratio formula, for the in-zone fault, H is greater than 1; for out-of-range faults, H =0 < 1; and the fault judgment is carried out according to the vector amplitude ratio formula without being influenced by the direct current commutation failure, the transition resistance and the fault position, although the fault position can influence the size of H, the relative size relation between H and the threshold value 1 can not be influenced, and therefore, the reliability is high.
Optionally, the following argument is made to verify that the vector magnitude ratio fault criterion provided by the embodiment of the present invention is not affected by data synchronization, in order to consider that the influence of data synchronization is required to determine the fault type of the ac-dc series-parallel power transmission system by zero-sequence current information at two ends of the ac line:
m-end zero-sequence current I under the assumption of fault in MN (alternating Current) area of alternating current line M0 Delay delta t in transmission channel due to delay and N-terminal zero sequence current I N0 The resulting asynchronous angle is θ. Then I M0 And I N0 Can be expressed as:
then for intra-zone faults, the magnitude vector ratio considering data synchronization is:
for out-of-range faults, the magnitude vector ratio considering data synchronization is:
it can be known from the above that when the asynchronous angle θ is less than 90 °, H is still greater than 1 under the internal fault, and H is still less than 1 under the external fault, so that the vector amplitude ratio provided by the embodiment of the present invention is not affected by data synchronization than the fault criterion, i.e., strict synchronization of data at two ends of the ac line is not required.
In some embodiments of the invention, the protection device comprises a circuit breaker;
according to the protection device of the fault type control alternating current-direct current series-parallel connection transmission system of alternating current-direct current series-parallel connection transmission system, include:
obtaining the measured reactance of each phase grounding impedance of the alternating current circuit;
if the measured reactance of each phase of grounding impedance is greater than the preset reactance value and the measured reactance of each phase of grounding impedance is positioned in the action area of the adopted impedance element, controlling the circuit breaker at the tripping outlet to be switched off;
if the measured reactance of each phase grounding impedance is smaller than a preset reactance value and the fault type is an intra-area fault, determining a single-phase fault or an interphase fault based on the phase selection element; and if the fault is a single-phase fault, controlling the breaker of the fault phase to be switched off, and if the fault is an interphase fault, controlling the breakers of the three phases to be switched off.
Optionally, if the end point of the measured reactance is located in the action region of the adopted impedance element, which indicates that the corresponding fault is located in the protection range of the impedance element, the determination may be completed by conventional impedance protection or distance protection, and if the measured impedance is located in the action region of the adopted impedance element, it is determined that the conventional distance protection criterion is satisfied.
Optionally, at present, there are multiple phase selection elements, which respectively determine whether the occurred fault is a single-phase fault or an inter-phase fault according to multiple criteria. And after the fault occurs, judging the fault as the type of the fault correspondingly according to which criteria are met.
Optionally, the preset reactance value may be 0, or may be set according to actual needs.
Illustratively, the protection logic provided by the embodiment of the present invention is as follows:
the protection devices at two ends of the alternating current circuit respectively and correspondingly acquire three-phase voltage of the alternating current circuit and three-phase current of the alternating current circuit in real time through a voltage transformer and a current transformer.
Zero sequence current phasors at two ends of an alternating current circuit are respectively calculated, and when the receiving end alternating current voltage level of the alternating current-direct current hybrid power transmission system is 500kV or below, line distributed capacitance current compensation is not needed; and when the alternating voltage level of the receiving end reaches 1000kV, respectively calculating the capacitance currents at two ends of the line, and respectively carrying out vector summation with the zero sequence currents at the corresponding ends to obtain zero sequence current phasors at two ends subjected to distributed capacitance current compensation.
Respectively calculating the amplitude of the vector sum of zero-sequence currents compensated by distributed capacitance currents at two ends of an alternating current circuit and the amplitude of the difference between the vectors of the zero-sequence currents at the two ends, and obtaining an amplitude vector ratio H according to the amplitude of the vector sum and the amplitude of the vector difference;
the local side protection device calculates a reactance vector in the grounding impedance;
respectively calculating reactance phasor in each phase of grounding impedance;
and respectively calculating the measured reactance of each phase, judging whether the measured reactance is positioned in the action characteristic region of the adopted impedance element, and if so, judging that the traditional distance protection criterion is established.
If the measured reactance is greater than 0 and meets the traditional distance protection criterion, controlling the circuit breaker at the tripping outlet to be switched off;
if the measured reactance is less than 0 and the H value is greater than 1, judging as an internal fault, and jointly judging by combining option elements: if the fault is a single-phase fault, tripping off the circuit breaker of the fault phase at the side; and if the fault is a two-phase grounding fault, tripping off the three-phase circuit breaker on the side.
Illustratively, the present invention provides a case as follows:
carrying out simulation verification on the problems of the traditional distance protection:
building an alternating current-direct current series-parallel connection power transmission system model of +/-800 kV direct current/500 kV alternating current as shown in figure 2 in power system software PSCAD/EMTDC; the related parameters of the direct current system are taken from a direct current transmission project of +/-800 kV, the alternating current circuit adopts a Bergon model, and the parameters are set as follows:
R 1 ＝0.0208Ω/km，x 1 ＝0.2822Ω/km，R 0 ＝0.1148Ω/km，x 0 ＝0.7190Ω/km，x c1 ＝273.5488(MΩ·m)，x c0 =414.164 (M Ω · M), ac line MN length 30km 1 Length of 20km, L 2 The length is 80km, the sampling frequency is set to 4kHz, and faults in the simulation are all set to start in 3s and last for 0.05s.
A phase-A grounding faults are arranged at the positions 8km and 15km away from an M end of an alternating current line MN, and transition resistances are 5 omega, 25 omega, 40 omega and 90 omega in sequence. All the faults cause the commutation failure of the direct current system, the full-period Fourier algorithm is adopted to extract the power frequency quantity, and the given waveforms all start 20ms after the faults occur.
Referring to fig. 7, it shows an additional reactance curve provided by the present invention when a single-phase ground fault with different transition resistances occurs within the area of the ac line MN at a distance of 8km from the M terminal; referring to fig. 8, there is shown an additional reactance curve provided by the present invention when a single-phase ground fault of different transition resistances occurs within the area of the ac line MN at a distance of 15km from the M-terminal.
As can be seen from fig. 7, when the fault location is 8km away from the M end, the additional reactance is less than 0 for all 4 fault conditions, and the additional impedance is capacitive. Under the fault working condition corresponding to the transition resistance of 25 omega, 40 omega and 90 omega, the absolute value of the additional reactance is smaller than the line reactance value 2.2576 omega corresponding to the fault position at the moment in a period of 3.02 s-3.05 s, so that the measured reactance value is negative, which is equivalent to a fault in the opposite direction, and the M-end distance protection rejects.
As can be seen from fig. 8, when the fault location is 15km away from the M terminal, the additional impedances are capacitive within a period of 3.02s to 3.05s under the fault condition corresponding to the transition resistances of 25 Ω and 90 Ω, and the absolute values of the additional impedances are all smaller than the line reactance value 4.233 Ω corresponding to the fault location, so that the measured reactance value is negative, which is equivalent to a fault in the opposite direction, and the distance protection is rejected; when the transition resistance is 40 Ω, the additional reactance changes from negative to positive at 3.038s, and the additional impedance changes from capacitive to inductive, but before that, the absolute value of the additional reactance is smaller than the line reactance value 4.233 Ω, and the distance protection still has the possibility of being rejected.
In summary, when a single-phase earth fault occurs on the ac side and the dc commutation fails, the distance protection configured on the ac line of the inverter side may be rejected due to the influence of the transition resistance, the dc equivalent current, and the like.
The implementation mode and the effectiveness provided by the invention are verified:
building an alternating current-direct current series-parallel connection power transmission system model of +/-800 kV direct current/500 kV alternating current as shown in figure 2 in power system software PSCAD/EMTDC; the related parameters of the direct current system are taken from a direct current transmission project of +/-800 kV, the alternating current circuit adopts a Bergon model, and the parameters are set as follows:
R 1 ＝0.0208Ω/km，x 1 ＝0.2822Ω/km，R 0 ＝0.1148Ω/km，x 0 ＝0.7190Ω/km，x c1 ＝273.5488(MΩ·m)，x c0 =414.164 (M Ω · M), ac line MN length 30km 1 Length of 20km, L 2 The length is 80km, the sampling frequency is set to 4kHz, and the faults in the simulation are all set to 3s start and last for 0.05s.
Referring to fig. 9, it shows a curve of the amplitude vector ratio H when a single-phase ground fault occurs in a region where different transition resistances occur 8km away from the M terminal in the ac line MN according to the present invention; referring to fig. 10, it shows a graph of the amplitude vector ratio H when a single-phase ground fault occurs in a region where different transition resistances occur in the ac line MN 15km away from the M terminal.
As can be seen from fig. 9, when a single-phase ground fault with different transition resistances occurs in the area of the ac line MN at a distance of 8km from the M terminal, the amplitude vector ratio H between the two terminals of the ac line MN is about 3.5 in a period of 3.02s to 3.05s, and is always greater than 1.
As can be seen from fig. 10, when a single-phase ground fault with different transition resistances occurs in the area of the ac line MN at a distance of 15km from the M terminal, the amplitude vector ratio H between the two ends of the ac line MN is about 5 in a period of 3.02s to 3.05s, and is always greater than 1. Therefore, the faults in the area can be reliably judged through the fault identification criterion formula (13), and the problem that the traditional distance protection is rejected when a single-phase transition resistance earth fault occurs on the alternating current side in the alternating current-direct current hybrid power transmission system is solved.
Referring to fig. 11, there is shown an out-of-range line L provided by the present invention 1 And the amplitude vector ratio H curve of the single-phase earth fault through the transition resistance of 25 omega at the middle point.
As can be seen from fig. 8, the amplitude vector ratio H is approximately 0 and reliably smaller than 1 at this time, and it can be seen that the out-of-range fault can be reliably determined by the fault identification criterion equation (13).
Simulating the data synchronization influence:
protection criteria at two ends of the alternating current line MN have certain requirements on data synchronism, so that the degree of influence of data synchronism on the fault identification criterion formula (13) is verified, and zero-sequence currents at two ends are sequentially set to have a difference of 30 degrees, 45 degrees, 60 degrees and 80 degrees under different fault conditions inside and outside the area, namely, the time delays are correspondingly delayed for 1.67ms, 2.5ms, 3.33ms and 4.44ms.
Referring to fig. 12, it shows a curve of the amplitude vector ratio H considering the influence of data synchronization when a single-phase earth fault occurs in a region of a single-phase passing through a 25 Ω transition resistor 8km away from the M terminal of the ac line MN provided by the present invention; referring to fig. 13, it shows a graph of the amplitude vector ratio H considering the influence of data synchronization when a single-phase earth fault occurs in a region of a single-phase passing through a 25 Ω transition resistor 15km away from the M terminal of an ac line MN provided by the present invention; referring to FIG. 14, it shows the out-of-range line L provided by the present invention to take into account the data synchronization effect 1 And the amplitude vector ratio H curve of the single-phase earth fault through the transition resistance of 25 omega at the middle point.
From equation (12), the minimum value of H occurs at the head end of the line in the area of the fault, and fig. 12 shows that even when the zero sequence currents at the two ends are different by 80 ° due to the transmission delay, the H value corresponding to the fault in the area at the head end of the line is higher than the preset ratio 1. Similarly, as shown in fig. 13, when the fault location is changed to a location 15km away from the M end, under the condition that the zero-sequence currents at the two ends have a difference of 30 °, 45 °, 60 °, and 80 ° due to transmission delay, the calculated amplitude vector ratio H is always greater than the preset ratio 1 in a time period of 3.02s to 3.05s, that is, the fault identification criterion shown in equation (13) can still accurately determine that the fault is an in-region fault.
As for the external fault, as can be seen from fig. 14, under the condition that the zero-sequence currents at the two ends have a difference of 30 °, 45 °, 60 °, and 80 ° due to transmission delay, the maximum amplitude vector ratio H obtained by calculation is about 0.8, and the fault identification criterion shown in the formula (13) can still be accurately determined as the external fault.
Therefore, the fault identification criterion shown in the formula (13) can resist synchronous time setting errors within 90 degrees, and the requirement on data synchronization is low.
The comprehensive simulation result shows that the provided fault identification criterion is not influenced by transition resistance and fault positions, and the data transmission at two ends is not required to be strictly synchronous, so that the fault identification criterion can be better applied to distance protection optimization.
The scheme of the invention has the beneficial effects that:
in an alternating current-direct current hybrid power transmission system, when an LCC alternating current side has a short-circuit fault through a transition resistor and an LCC converter fails to change phase, the transition resistor causes the measurement impedance of the distance protection of the alternating current side to generate an additional impedance, and the additional impedance causes the measurement impedance of the distance protection to be possibly resistive or capacitive. When the additional impedance is inductive, the measured impedance is increased and possibly exceeds the action range of the distance protection I section, so that the fault removal time is prolonged; when the additional impedance is capacitive, the measured impedance may be made negative in extreme cases, and the protection will be rejected.
Based on the method, the alternating current-direct current series-parallel power transmission system protection method is provided by utilizing the isolation effect of the converter transformer on the zero sequence current.
1) The problem of refusing the conventional distance protection under complex scenes such as phase change failure caused by AC side faults is solved, so that the distance protection in an AC-DC hybrid power transmission system is not influenced by the phase change failure, and the protection reliability is improved.
2) The method is not influenced by transition resistance, fault point positions and direct current commutation failure, and can reliably judge the faults inside and outside the area;
3) The method does not require strict synchronization for the data transmission at two ends, reduces the requirements of data synchronization and data communication, and has wide application occasions.
It should be understood that, the sequence numbers of the steps in the foregoing embodiments do not imply an execution sequence, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.
Corresponding to the protection method of the alternating current-direct current hybrid power transmission system, the embodiment of the invention also provides a protection device of the alternating current-direct current hybrid power transmission system, and the protection device has the same beneficial effects as the protection method of the alternating current-direct current hybrid power transmission system. Referring to fig. 15, a schematic diagram of an ac/dc hybrid power transmission system protection device according to an embodiment of the present invention is shown, and as shown in fig. 15, in an embodiment of the present invention, an ac/dc hybrid power transmission system protection device 20 may include:
an obtaining module 201, configured to obtain an electrical parameter of an ac line of an ac-dc series-parallel power transmission system;
the calculating module 202 is used for determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters;
the control module 203 is configured to determine a fault type of the ac/dc hybrid power transmission system based on zero-sequence current phasors at two ends of the ac line, and control a protection device of the ac/dc hybrid power transmission system according to the fault type of the ac/dc hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault.
In some embodiments of the invention, the calculation module comprises a first phasor calculation unit and a second phasor calculation unit; the electrical parameter comprises a zero sequence impedance of the ac line;
the first phasor calculation unit is used for determining zero-sequence current phasors at two ends of an alternating current circuit according to zero-sequence impedance of the alternating current circuit when alternating current voltage at a receiving end of the alternating current-direct current hybrid transmission system is not larger than a first preset voltage value;
and the second phase quantity calculating unit is used for determining the zero-sequence current phasor at the two ends of the alternating current circuit according to the current of the distributed capacitors at the two ends of the alternating current circuit and the zero-sequence impedance of the alternating current circuit when the alternating current voltage at the receiving end of the alternating current-direct current hybrid power transmission system is greater than the first preset voltage value and not greater than the second preset voltage value.
In some embodiments of the invention, the control module comprises a magnitude vector ratio determination unit and a fault type determination unit;
the amplitude vector ratio determining unit is used for determining an amplitude vector ratio according to zero sequence current phasors at two ends of the alternating current circuit;
and the fault type determining unit is used for determining the fault type of the alternating current-direct current hybrid power transmission system according to the amplitude vector ratio.
In some embodiments of the invention, the magnitude vector ratio is expressed as:
wherein, I M0 Is the M-end zero-sequence current phasor of the AC line, I N0 The zero-sequence current phasor of the N end of the alternating current circuit is obtained, the M end is a first end of the alternating current circuit, and the N end is a second end of the alternating current circuit.
In some embodiments of the present invention, the fault type determination unit may include an intra-area fault determination subunit and an extra-area fault determination subunit;
the in-zone fault judging subunit is used for judging the fault type of the alternating current-direct current hybrid power transmission system to be an in-zone fault if the amplitude vector ratio is greater than a preset ratio;
and the external fault judging subunit is used for judging the fault type of the alternating current-direct current hybrid power transmission system to be an external fault if the amplitude vector ratio is smaller than a preset ratio.
In some embodiments of the invention, the predetermined ratio is 1.
In some embodiments of the present invention, the protection device comprises a circuit breaker, and the control module may further comprise a reactance obtaining unit, a first control unit, and a second control unit;
a reactance obtaining unit for obtaining a measured reactance of each phase ground impedance of the alternating current line;
the first control unit is used for controlling the circuit breaker at the tripping outlet to be switched off if the measured reactance of each phase of grounding impedance is greater than a preset reactance value and is positioned in the action area of the adopted impedance element;
the second control unit is used for determining single-phase fault or interphase fault based on the phase selection element if the measured reactance of each phase of grounding impedance is smaller than a preset reactance value and the fault type is an intra-area fault; and if the fault is a single-phase fault, controlling the breaker of the fault phase to be switched off, and if the fault is an interphase fault, controlling the breakers of the three phases to be switched off.
It can be clearly understood by those skilled in the art that, for convenience and simplicity of description, the foregoing division of each functional unit and module is merely used for illustration, and in practical applications, the foregoing function distribution may be performed by different functional units and modules as needed, that is, the internal structure of the terminal device is divided into different functional units or modules to perform all or part of the above-described functions. Each functional unit and module in the embodiments may be integrated in one processing unit, or each unit may exist alone physically, or two or more units are integrated in one unit, and the integrated unit may be implemented in a form of hardware, or in a form of software functional unit. In addition, specific names of the functional units and modules are only for convenience of distinguishing from each other, and are not used for limiting the protection scope of the present application. The specific working processes of the units and modules in the above-mentioned apparatus may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
Fig. 16 is a schematic block diagram of a terminal device according to an embodiment of the present invention. As shown in fig. 16, the terminal device 30 of this embodiment includes: one or more processors 301, a memory 302, and a computer program 303 stored in the memory 302 and operable on the processors 301. The processor 301, when executing the computer program 303, implements the steps in the above-described embodiment of the ac/dc hybrid power transmission system protection method, such as S101 to S103 shown in fig. 1. Alternatively, the processor 301 executes the computer program 303 to implement the functions of the modules/units in the above-described embodiment of the protection apparatus for the ac/dc hybrid power transmission system, for example, the functions of the modules 201 to 203 shown in fig. 15.
Illustratively, the computer program 303 may be divided into one or more modules/units, which are stored in the memory 302 and executed by the processor 301 to accomplish the present application. One or more modules/units may be a series of computer program instruction segments capable of performing specific functions, which are used to describe the execution of the computer program 303 in the terminal device 30. For example, the computer program 303 may be divided into an acquisition module 201, a calculation module 202 and a control module 203.
An obtaining module 201, configured to obtain an electrical parameter of an ac line of an ac-dc series-parallel power transmission system;
the calculating module 202 is used for determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters;
the control module 203 is configured to determine a fault type of the ac/dc hybrid power transmission system based on zero-sequence current phasors at two ends of the ac line, and control a protection device of the ac/dc hybrid power transmission system according to the fault type of the ac/dc hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault.
Other modules or units can be referred to the description of the embodiment shown in fig. 15, and are not described again here.
The Processor 301 may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic device, discrete hardware component, etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.
The storage 302 may be an internal storage unit of the terminal device, such as a hard disk or a memory of the terminal device. The memory 302 may also be an external storage device of the terminal device, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), and the like provided on the terminal device. Further, the memory 302 may also include both internal storage units of the terminal device and external storage devices. The memory 302 is used for storing the computer program 303 and other programs and data required by the terminal device. The memory 302 may also be used to temporarily store data that has been output or is to be output.
In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to the related descriptions of other embodiments for parts that are not described or illustrated in a certain embodiment.
Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the technical solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
In the embodiments provided in the present application, it should be understood that the disclosed terminal device and method may be implemented in other ways. For example, the above-described terminal device embodiments are merely illustrative, and for example, a module or a unit may be divided into only one logical function, and may be implemented in other ways, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be through some interfaces, indirect coupling or communication connection of devices or units, and may be in an electrical, mechanical or other form.
Units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit may be implemented in the form of hardware, or may also be implemented in the form of a software functional unit.
The integrated modules/units, if implemented in the form of software functional units and sold or used as separate products, may be stored in a computer readable storage medium. Based on such understanding, all or part of the flow in the method according to the embodiments described above may be implemented by a computer program, which is stored in a computer readable storage medium and used by a processor to implement the steps of the embodiments of the methods described above. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer readable medium may include: any entity or device capable of carrying computer program code, recording medium, U.S. disk, removable hard disk, magnetic disk, optical disk, computer Memory, read-Only Memory (ROM), random Access Memory (RAM), electrical carrier wave signals, telecommunications signals, software distribution media, and the like. It should be noted that the computer readable medium may include any suitable increase or decrease as required by legislation and patent practice in the jurisdiction, for example, in some jurisdictions, computer readable media may not include electrical carrier signals and telecommunications signals in accordance with legislation and patent practice.
The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.
Claims (7)
1. A method for protecting an AC/DC series-parallel power transmission system is characterized by comprising the following steps:
acquiring electric parameters of an alternating current line of an alternating current-direct current hybrid power transmission system;
determining zero sequence current phasors at two ends of the alternating current circuit according to the electrical parameters;
determining the fault type of the alternating current and direct current hybrid power transmission system based on the zero sequence current phasors at the two ends of the alternating current circuit, and controlling a protection device of the alternating current and direct current hybrid power transmission system according to the fault type of the alternating current and direct current hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault;
the determining the fault type of the alternating current-direct current hybrid power transmission system based on the zero sequence current phasors at the two ends of the alternating current circuit comprises the following steps:
determining an amplitude vector ratio according to zero sequence current phasors at two ends of the alternating current circuit;
determining the fault type of the alternating current-direct current series-parallel power transmission system according to the amplitude vector ratio;
the magnitude vector ratio is expressed as:
wherein, I M0 Is the M-terminal zero-sequence current phasor, I, of the AC line N0 The zero-sequence current phasor of the N end of the alternating current circuit is obtained, the M end is a first end of the alternating current circuit, and the N end is a second end of the alternating current circuit;
the determining the fault type of the alternating current-direct current hybrid power transmission system according to the amplitude vector ratio comprises the following steps:
if the amplitude vector ratio is larger than a preset ratio, the fault type of the alternating current-direct current series-parallel power transmission system is an intra-area fault;
and if the amplitude vector ratio is smaller than the preset ratio, determining that the fault type of the alternating current-direct current hybrid power transmission system is an out-of-area fault.
2. The method of protecting an ac-dc series-parallel transmission system according to claim 1, wherein the electrical parameter comprises a zero-sequence impedance of the ac line;
the determining zero sequence current phasors at two ends of the alternating current circuit according to the electrical parameters comprises:
when the alternating-current voltage at the receiving end of the alternating-current and direct-current hybrid transmission system is not larger than a first preset voltage value, determining zero-sequence current phasors at two ends of the alternating-current circuit according to the zero-sequence impedance of the alternating-current circuit;
and when the receiving end alternating voltage of the alternating current-direct current hybrid transmission system is greater than the first preset voltage value and not greater than a second preset voltage value, determining zero-sequence current phasors at two ends of the alternating current circuit according to the current of the distributed capacitors at the two ends of the alternating current circuit and the zero-sequence impedance of the alternating current circuit.
3. The method for protecting an ac-dc hybrid power transmission system according to claim 1, wherein the predetermined ratio is 1.
4. A method of protecting a dc-dc hybrid transmission system according to any of claims 1 to 3, wherein the protection device comprises a circuit breaker;
the protection device for controlling the alternating current-direct current hybrid power transmission system according to the fault type of the alternating current-direct current hybrid power transmission system comprises:
obtaining the measured reactance of each phase grounding impedance of the alternating current circuit;
if the measured reactance of each phase of grounding impedance is larger than the preset reactance value and is positioned in the action area of the adopted impedance element, controlling the circuit breaker at the tripping outlet to be switched off;
if the measured reactance of each phase grounding impedance is smaller than a preset reactance value and the fault type is an intra-area fault, determining the single-phase fault or the interphase fault based on the phase selection element; and if the fault is a single-phase fault, controlling the breaker of the fault phase to be switched off, and if the fault is an interphase fault, controlling the breakers of the three phases to be switched off.
5. An alternating current-direct current series-parallel connection power transmission system protection device is characterized by comprising:
the acquisition module is used for acquiring the electric parameters of an alternating current circuit of the alternating current-direct current series-parallel power transmission system;
the calculation module is used for determining zero sequence current phasors at two ends of the alternating current circuit according to the electric parameters;
the control module is used for determining the fault type of the alternating current and direct current hybrid power transmission system based on the zero sequence current phasors at the two ends of the alternating current circuit and controlling a protection device of the alternating current and direct current hybrid power transmission system according to the fault type of the alternating current and direct current hybrid power transmission system; the fault types of the alternating current-direct current hybrid power transmission system comprise an intra-area fault and an extra-area fault;
the control module comprises an amplitude vector ratio determining unit and a fault type determining unit;
the amplitude vector ratio determining unit is used for determining an amplitude vector ratio according to zero sequence current phasors at two ends of the alternating current circuit;
the fault type determining unit is used for determining the fault type of the alternating current-direct current hybrid power transmission system according to the amplitude vector ratio;
the magnitude vector ratio is expressed as:
wherein, I M0 Is the M-terminal zero-sequence current phasor, I, of the AC line N0 The zero sequence current phasor of the N end of the alternating current circuit is obtained, the M end is a first end of the alternating current circuit, and the N end is a second end of the alternating current circuit;
the fault type determination unit comprises an intra-area fault judgment subunit and an extra-area fault judgment subunit;
the intra-area fault judging subunit is configured to determine that the fault type of the alternating current/direct current hybrid power transmission system is an intra-area fault if the amplitude vector ratio is greater than a preset ratio;
and the external fault judging subunit is configured to determine that the fault type of the alternating current/direct current hybrid power transmission system is an external fault if the amplitude vector ratio is smaller than the preset ratio.
6. A terminal device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that the processor implements the steps of the method for protection of a hybrid ac/dc power transmission system according to any one of claims 1 to 4 when executing the computer program.
7. A computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, carries out the steps of the method for protection of an ac/dc hybrid power transmission system according to any one of claims 1 to 4.
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