CN113131453B - Single-ended traveling wave protection method for flexible direct current transmission line - Google Patents
Single-ended traveling wave protection method for flexible direct current transmission line Download PDFInfo
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- CN113131453B CN113131453B CN202110569961.4A CN202110569961A CN113131453B CN 113131453 B CN113131453 B CN 113131453B CN 202110569961 A CN202110569961 A CN 202110569961A CN 113131453 B CN113131453 B CN 113131453B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/265—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 making use of travelling wave theory
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/261—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 involving signal transmission between at least two stations
- H02H7/263—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 involving signal transmission between at least two stations involving transmissions of measured values
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
- H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Abstract
The invention discloses a single-end-amount traveling wave protection method for a flexible direct-current transmission line, which is based on the oscillogram characteristics of three types of forward traveling wave faults, namely an internal fault, an external fault and lightning stroke interference, and firstly utilizes a starting criterion to determine a fault moment and a timing starting point; and if and only if the valley point is detected by the traveling wave before the one-mode fault in the valley point setting time and the zero crossing point is not detected by the traveling wave before the one-mode fault in the zero crossing point setting time, protecting and identifying the traveling wave as the in-zone fault. The protection method has the advantages of reliable principle, simple criterion, high action speed and strong transition resistance tolerance, lightning stroke resistance and noise interference resistance.
Description
Technical Field
The invention belongs to the technical field of control and protection of a flexible direct current transmission system, and particularly relates to a single-end protection method for a flexible direct current transmission line.
Background
Flexible direct-current transmission of a Voltage Source Converter (VSC) based on a fully-controlled switching device has the advantages of flexible control and high electric energy quality, has better new energy consumption capacity compared with traditional high-voltage direct-current transmission, and can effectively relieve the impact of intermittence and randomness of new energy generation such as wind and light on a power grid. However, the current capacity of the full-control device is limited, and meanwhile, higher requirements are provided for the protection technology, the existing research shows that the protection needs to complete fault identification within 3ms, and only single-end protection is expected to meet the action speed requirement.
The single-end quantity protection principle of the flexible direct-current transmission line depends on the analysis of the fault traveling wave process, and the extraction of fault information carried by the fault traveling wave by using a proper mathematical method is an effective way for constructing a protection criterion. Mainstream fault information extraction methods can be divided into a frequency domain method and a time domain method.
In the prior art, a frequency domain method is based on the blocking effect of line boundary elements such as a current-limiting reactor and the like on the high-frequency component of a fault traveling wave head, high-frequency information carried by the fault traveling wave is quantified by using mathematical methods such as wavelet transformation, S transformation and the like, the protection has better transition resistance capability, but the high-frequency information carried by a lightning current wave head is similar to the short-circuit fault traveling wave in a region, and the protection is difficult to deal with lightning stroke interference.
In the prior art, a time domain method utilizes numerical characteristics or waveform characteristics to extract fault information, wherein the time domain protection based on the numerical characteristics mainly utilizes a differential or integral algorithm to extract the fault characteristics. The time-domain protection based on the waveform characteristics is established on the complete fault loop analysis, and compared with a time-domain protection method based on numerical characteristics, the principle is more complete and reliable, because the method is theoretically irrelevant to transition resistance, the protection criterion has better transition resistance tolerance, but the lightning stroke interference is similar to the steepness of a fault traveling wave head of a short-circuit fault in a region, so that the scheme can be subjected to false operation.
Therefore, in order to overcome the defects of the prior art, it is necessary to research a flexible direct current transmission line single-end protection which can resist lightning stroke interference.
Object of the Invention
The invention aims to overcome the defects of the prior art and provide a single-end quantity protection method of a flexible direct current transmission line which can resist lightning stroke interference, in particular to a single-end quantity protection method for the flexible direct current transmission line. According to the method, off-zone faults are eliminated by using valley time, lightning stroke interference is eliminated by using zero-crossing time, and short-circuit faults in the zone are effectively identified finally. The method has reliable principle and simple criterion, and improves the lightning interference resistance of single-end quantity traveling wave protection.
Disclosure of Invention
The invention provides a single-magnitude traveling wave protection method for a flexible direct current transmission line, which is based on the forward waveform characteristic of the flexible direct current transmission line, wherein the flexible direct current transmission line is a true bipolar two-end flexible direct current transmission system and comprises two transmission lines which are connected in parallel, one transmission line is an overhead line, and the other transmission line is an overhead line;
the protection method comprises the following steps:
the protection is started and the point where the line voltage is lower than the normal voltage for the first time within 0.2ms before and after the protection starting moment is marked as the timing starting point t 0 In the formula (1),
is the voltage gradient value, Δ, at the current sampling instant set To start the threshold;
step 4, starting the timing t in step 1 0 On the basis of t 1,set The forward traveling wave u of the one-mode fault is detected f1 At the same time, cannot be at t 2,set Internal detection of one-mode fault pre-travelling wave u f1 And judging the zone short-circuit fault and executing protection action.
Preferably, in step 1, the
The formula (2) is shown as follows:
wherein u (k-j) is the voltage sampling value before the j sampling period.
Preferably, in step 2, the one-mode fault forward-traveling wave u f1 The formula (3) is shown as follows:
wherein u 1 、i 1 Expressed as shown in formula (4):
in the formula u 1 ，i 1 Fault-mode voltage, fault-mode current; u. of p ，u n ，i p ，i n The measured positive and negative fault voltages and currents at the installation position are protected; z c1 Is a mode wave impedance of the transmission line;
the determination method of the valley point is represented by the formula (5):
in the formula, t 1 To determine the time of the valley point, T s Is the sampling interval.
Preferably, in step 3, the zero-crossing point determination method is as shown in equation (6):
in the formula, t 2 For zero crossing time of decision, T s Is the sampling interval.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced 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 the drawings without creative efforts.
FIG. 1 is a schematic diagram of a true bipolar two-terminal flexible DC power transmission system topology;
FIG. 2 is a waveform diagram of three exemplary pre-fault traveling waves;
FIG. 3 shows the operating results of single-pole ground faults under different remote transition resistances;
FIG. 4 is a result of actions under different fault types;
FIG. 5 illustrates the behavior of the protection under noise;
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a topological schematic diagram of a true bipolar two-terminal flexible direct current transmission system including two parallel-connected transmission lines, one of which is an overhead line and the other is an overhead line, to which the method of the present invention is applied;
fig. 2 is a waveform diagram of three typical fault preceding waves, that is, a waveform diagram of a preceding wave interfered by an intra-area fault, an extra-area fault, and a lightning stroke, it can be known from the diagram that a wave trough point of the fault preceding wave can represent the wave head steepness of the fault first wave, a zero crossing point of the fault preceding wave can represent the wave tail decline of the fault first wave, and under three different fault preceding waves, the action condition of protection is:
1) when an external short circuit fault occurs, the valley point of the traveling wave before the fault cannot be detected before the valley point setting value, and protection is restored.
2) During lightning interference, a valley point of the traveling wave before the fault can be detected before the valley point setting value, and meanwhile, a zero crossing point of the traveling wave before the fault is detected before the zero crossing point setting value, so that protection and resetting are realized.
3) And when the short circuit occurs in the area, the valley point of the traveling wave before the fault can be detected before the valley point setting value, and meanwhile, the zero crossing point of the traveling wave before the fault cannot be detected before the zero crossing point setting value, so that the action is protected.
Fig. 3 and fig. 4 show the protection action conditions under different fault distances, transition resistances and fault types, respectively, and it can be seen that the protection is not affected by the short-circuit fault type and the transition resistance, and the change of the fault distance causes the valley point and the zero crossing point to lag relatively, but still within the protection threshold, the protection acts reliably.
The single-ended protection method for the flexible direct current transmission line according to the present invention is described in detail below with reference to the following embodiments.
Example 1
A +/-500 kV true bipolar flexible direct-current transmission system is built in a PSCAD/EMTDC mode and is shown in figure 1. The length of a direct current line is 500km, an overhead line frequency-dependent model is adopted, a lightning conductor is not eliminated, a multi-wave impedance model is adopted for a tower model, and 3 towers are arranged at lightning stroke positions; the guard sampling frequency is 50 kHz. Fault-mode traveling waves all arrive at the protection installation site at 0 ms.
Simulating fault types of fault setting in the middle area, namely positive electrode grounding, negative electrode grounding and bipolar short circuit; the fault distance is 250km and 450 km; the transition resistance is 0 omega, 300 omega and 500 omega; the out-of-range fault is set as a metallic fault at the outlet of the current-limiting reactor close to the converter station; the lightning stroke interference is 25kA lightning stroke conductor interference.
Fig. 3 and 4 show the action results of the protection under different fault conditions, and it can be seen that the protection still has higher sensitivity when the far end in the zone is high-resistance, and the protection can reliably eliminate the lightning stroke interference. Noise with a signal-to-noise ratio of 30db is added to protection sampling data in the case of an out-of-range fault, and the action condition of the corresponding protection is shown in fig. 5.
It can be seen that the disturbance caused by the noise forms a valley point (interference point) at the 3 rd sampling point, but it does not satisfy the determination method of the valley point, i.e., equation (5), and thus is not determined as the valley point. The protection can not detect the valley point before the valley point setting value, identifies the fault outside the area and is reliable and does not act. The protection algorithm is able to tolerate 30db of noise over multiple tests.
By adopting the single-ended traveling wave protection method based on the forward traveling wave waveform characteristic in the flexible direct current transmission system, the beneficial effects can be obtained as follows:
(1) the protection method has reliable principle and simple criterion, can realize the promotion of the protection capability by only utilizing two time criteria, and has low realization difficulty.
(2) The protection principle utilizes two different waveform information to eliminate the external fault and the lightning interference respectively, and has stronger transition resistance tolerance and anti-interference capability.
It is noted that those skilled in the art will recognize that embodiments of the present invention are not described in detail herein.
The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (4)
1. A single-end amount traveling wave protection method for a flexible direct current transmission line is based on the waveform characteristics of the forward traveling wave of the flexible direct current transmission line, the flexible direct current transmission line is a true bipolar two-end flexible direct current transmission system and comprises two transmission lines which are connected in parallel, one transmission line is an overhead line, and the other transmission line is also an overhead line, and the protection method is characterized by comprising the following steps of:
step 1, respectively detecting the oscillograms of traveling waves before three faults, namely an internal fault, an external fault and lightning stroke interference of the flexible direct current transmission line, sampling, if protection meets the protection starting criterion shown in the formula (1),
the protection is started, and the point where the line voltage is firstly lower than the normal voltage and floats within 0.2ms before and after the protection starting moment is marked as a timing starting point t 0 In the formula (1),
is the voltage gradient value, Δ, at the current sampling instant set Is a starting threshold value;
step 2, starting the timing t in step 1 0 On the basis of t, if not at 1,set Internal detection of forward traveling wave u of one-mode fault f1 The valley point is judged as an intra-area fault, and protection is recovered;
step 3, starting the timing t in step 1 0 On the basis of t 1,set Internal detection of one-mode fault pre-travelling wave u f1 And at t 2,set Internal detection of one-mode fault pre-travelling wave u f1 Judging lightning stroke interference and protecting resetting;
step 4, starting the timing t in step 1 0 On the basis of t 1,set The forward traveling wave u of the one-mode fault is detected f1 At the same time, cannot be at t 2,set Internal detectionOne-mode fault forward traveling wave u f1 And judging the zone short-circuit fault and executing protection action.
2. The single-ended magnitude traveling wave protection method for the flexible direct current transmission line according to claim 1, wherein in step 1, the single-ended magnitude traveling wave protection method is adopted
The formula (2) is shown as follows:
in the formula, u (k-j) is a voltage sampling value before the jth sampling period.
3. The single-ended-quantity traveling wave protection method for the flexible direct current transmission line according to claim 1, wherein in the step 2, the one-mode fault forward traveling wave u f1 The formula (3) is shown as follows:
wherein u 1 、i 1 Expressed as shown in formula (4):
in the formula u 1 ，i 1 Fault-mode voltage, fault-mode current; u. of p ，u n ，i p ，i n The measured positive and negative fault voltages and currents at the installation position are protected; z c1 Is a mode wave impedance of the transmission line;
the determination method of the valley point is represented by the formula (5):
where t1 is the determined valley point time and Ts is the sampling interval.
4. The single-ended magnitude traveling wave protection method for the flexible direct current transmission line according to claim 1, wherein in step 3, the zero-crossing point determination method is as shown in formula (6):
where t2 is the zero crossing time of the decision and Ts is the sampling interval.
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