CN113315103B - Flexible direct-current power distribution network protection method based on single-ended current transient quantity - Google Patents

Flexible direct-current power distribution network protection method based on single-ended current transient quantity Download PDF

Info

Publication number
CN113315103B
CN113315103B CN202110610017.9A CN202110610017A CN113315103B CN 113315103 B CN113315103 B CN 113315103B CN 202110610017 A CN202110610017 A CN 202110610017A CN 113315103 B CN113315103 B CN 113315103B
Authority
CN
China
Prior art keywords
current
line
protection
power distribution
distribution network
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
CN202110610017.9A
Other languages
Chinese (zh)
Other versions
CN113315103A (en
Inventor
贾科
陈聪
陈淼
刘鑫
钮厚敏
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
North China Electric Power University
Original Assignee
North China Electric Power University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by North China Electric Power University filed Critical North China Electric Power University
Priority to CN202110610017.9A priority Critical patent/CN113315103B/en
Publication of CN113315103A publication Critical patent/CN113315103A/en
Application granted granted Critical
Publication of CN113315103B publication Critical patent/CN113315103B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • 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
    • 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
    • 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]

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Photovoltaic Devices (AREA)

Abstract

The invention discloses a flexible direct-current power distribution network protection method based on single-ended current transient state quantity, belonging to the technical field of control and protection of flexible direct-current power distribution systems. The method is used for analyzing fault transient current characteristics when bipolar short-circuit faults occur at different line positions of a direct current system aiming at a flexible direct current power distribution network which contains photovoltaic fields and is accessed through a DC/DC converter, and deducing corresponding expressions; further analyzing the inherent boundary characteristics of the DC/DC converter to the transient high-frequency quantity, and extracting the current high-frequency signal through discrete wavelets; on the basis, different protection setting values are set for the extracted high-frequency current information, so that protection configuration and setting matching of the power distribution network are achieved. According to the invention, the fault line is quickly and effectively cut off through the matching between two sections of setting values and the step time delay, the whole length of the line is protected, the selectivity and the quick action are achieved, and the fault line has certain transition resistance tolerance capability.

Description

Flexible direct-current power distribution network protection method based on single-ended current transient quantity
Technical Field
The invention belongs to the technical field of control and protection of power distribution systems, and particularly relates to a flexible direct-current power distribution network protection method based on single-ended current transient quantity.
Background
Currently, with the proposition of the "carbon neutralization and carbon peak reaching" target, more and more new energy power generation, power electronic equipment and direct current loads are connected to the power grid. The flexible direct-current power distribution network gradually becomes an important link for connecting a distributed power supply and a direct-current load to a large power grid by virtue of the advantages that the flexible direct-current power distribution network does not need synchronous frequency and phase, has low line loss, excellent electric energy quality, high power density and the like. However, when a bipolar short-circuit fault occurs in the flexible direct-current power distribution network, the capacitor in the inverter can discharge to the fault point rapidly, so that the fault current rises rapidly and has a high peak value, and meanwhile, the transient impact current resistance of the power electronic device is very limited. The method has important research significance for protecting power electronic devices from being damaged, accurately identifying and cutting out fault lines in a short time and realizing reliable protection of the flexible direct-current power distribution network.
The protection principle of the existing flexible direct current system is mainly divided into protection based on time domain and protection based on frequency domain according to the type of fault information adopted for protection. The protection method based on the time domain mainly directly utilizes voltage and current information to design low-voltage overcurrent criterion, although the rapid start can be realized, the fault line cannot be accurately judged; the improved method realizes the selective action of protection by measuring the voltage change of the line reactor before and after the fault, but the harmonic wave existing in the system still has certain interference to the voltage change. Protection methods based on frequency domain are divided into two categories according to whether current-limiting reactors are configured in the system: one is based on the boundary formed by a line reactor, transient current, voltage frequency domain information and impedance angle difference are analyzed to realize protection, but the stable operation of the power grid is influenced by adding excessive reactance into the power grid; the other type is to introduce a machine learning method, and the protection method has strong anti-interference capability and good robustness, but needs a large number of samples. Therefore, it is necessary to research a new protection method with selectivity and fast mobility suitable for the flexible dc power distribution network.
Disclosure of Invention
The invention provides a flexible direct current distribution network protection method based on single-ended current transient quantity, which is characterized by comprising the following steps of:
the method comprises the following steps that 1, fault transient state current characteristics of a direct current system when bipolar short circuit faults occur at different line positions are analyzed and corresponding expressions are deduced for a flexible direct current power distribution network which contains photovoltaic fields and is connected into the direct current power distribution network through a DC/DC converter;
step 2, analyzing the inherent boundary characteristics of the DC/DC converter to the transient high-frequency quantity based on the fault transient current characteristics when the bipolar short-circuit fault occurs in the step 1, and extracting a current high-frequency signal through discrete wavelet;
and 3, setting different protection setting values for the extracted high-frequency current information based on the high-frequency boundary characteristics of the current converter in the step 2, so as to realize protection configuration and setting coordination of the power distribution network.
In the step 1, when a bipolar short-circuit fault occurs in the flexible direct-current power distribution network, because the voltage at the fault position drops instantaneously, a step voltage source can be introduced approximately equivalently, and the transient current is a corresponding response generated by the step voltage source in the system, equivalent operation can be correspondingly performed on relevant parameters in the flexible direct-current power distribution network in a complex frequency domain, and further, the fault transient current detected by protection measuring points at different fault positions is finally obtained through pull-type inverse transformation; when a fault occurs on a line where a measuring point is located, the current expression is as follows:
Figure BDA0003095561550000021
in the formula of Uf(s) is the equivalent step source in the complex frequency domain, Zmmc(s) is the MMC converter equivalent impedance in complex frequency domain, ZL(s) is the reactor impedance in the complex frequency domain, Zline1(s) is the upper adjacent line impedance in the complex frequency domain, Zdc(s) is the equivalent impedance of the DC/DC converter in the complex frequency domain, Zline2(s) is the impedance of the line at this stage in the complex frequency domain, d1The distance from the fault position to the protection measuring point of the line accounts for the percentage of the total length of the line, and the symbol L is calculated-1And (DEG) represents the pull type inverse transformation.
When a fault occurs in an adjacent line at the lower stage of a measuring point, the current expression is as follows:
Figure BDA0003095561550000022
in the formula, Zline3(s) is the lower line impedance in the complex frequency domain, d2It represents the distance from the fault location to the next protection station as a percentage of the total length of the line.
In the step 2, the line inductor, the reactor and the MMC current converter are inductive at high frequency, and the impedance modulus value is increased along with the increase of the frequency; the DC/DC converter presents a capacitive characteristic due to the function of the support capacitor at the outlet, and presents a very small high-frequency impedance module value compared with the former three under a high-frequency section; in the flexible direct-current power distribution network, the photovoltaic is boosted and connected in parallel through the DC/DC converter, so that the system is equivalently connected with a plurality of capacitive impedances in parallel; when a system fails, full frequency domain information exists in transient current generated by a fault point step signal; when high-frequency-band information of transient current is transmitted in a system and flows through a DC/DC converter which is connected in parallel with a line and has a very small impedance modulus value, a large amount of high frequency can flow into the DC/DC converter due to the shunting principle of the circuit; compared with the current-stage line with faults, the high-frequency components flowing through the adjacent lines at the lower stage are greatly reduced, and equivalently, a parallel boundary is formed on the flexible direct-current power distribution network.
Through discrete wavelet transform, a high-frequency signal of the transient current can be extracted, and further quantified into an intensity value, so that the boundary effect of the DC/DC converter on the high-frequency quantity is reflected:
Figure BDA0003095561550000031
wherein N is the length of the wavelet transform coefficient,
Figure BDA0003095561550000032
is the transform coefficient of the nth discrete wavelet under the j scale.
In the step 3, setting values of the section I and the section II and action time delay of the section II are calculated aiming at faults occurring at different positions of the line by detecting the numerical value significant difference of current transient state information with the frequency band of 1.25-2.5kHz existing inside and outside the region, so that single-end transient state quantity circuit protection with the mutual matching of the two-section setting values is set to realize the protection of the whole length of the line.
The transient action after the protection I section fault is carried out, no action time delay exists, and the transient action can be carried out rapidly only when the fault occurs on the circuit of the current stage, so that the setting is carried out according to the condition that the bipolar short circuit fault occurs at the tail end of the circuit of the current stage, and the theoretical transient current is as follows:
Figure BDA0003095561550000033
to pair
Figure BDA0003095561550000034
After discrete wavelet transformation is carried out to extract corresponding high-frequency information, an I-section setting value is obtained:
Figure BDA0003095561550000035
in the formula (I), the compound is shown in the specification,
Figure BDA0003095561550000041
is a wavelet transformation coefficient theoretically extracted when the tail end of the line at the current level fails,
Figure BDA0003095561550000042
in order to protect the reliability coefficient of the I end, in order to effectively avoid the resonance energy of an adjacent outlet and simultaneously consider the influences of mutual inductor errors, parameter measurement errors and the like, the value is 1.2-1.3.
The setting value of the protection II section needs to be matched with the protection I section of the adjacent line, the protection I section can only protect 60% -70% of the total length of the line, the protection II section needs to be used as a near backup of the protection I section of the line of the current stage to protect the total length and cannot exceed the protection I section range of the adjacent line of the next stage to prevent the trip of the next stage, therefore, the setting of the protection II section is carried out according to the protection range to 50% of the total length of the adjacent line of the next stage, and the theoretical transient current measured by a measuring point at the moment is as follows:
Figure BDA0003095561550000043
for is to
Figure BDA0003095561550000044
After discrete wavelet transform is carried out to extract corresponding high-frequency information, II sections of setting values are obtained:
Figure BDA0003095561550000045
in the formula (I), the compound is shown in the specification,
Figure BDA0003095561550000046
is a wavelet transform coefficient theoretically extracted when 50% of adjacent lines of a lower level have faults,
Figure BDA0003095561550000047
to protect the reliability factor of end II, it is taken as 1.1.
When a lower line breaks down, the protection of the I end of the lower line needs to be ensured to remove the fault preferentially, and the action time limit of the protection II end is higher than that of the I end of the lower line by one time stage:
tset＝tw+top+tm
in the formula, twFor extracting a data window of the signal, topFor circuit breaker actuation time, tmTime margins for other influencing factors.
The invention has the following beneficial effects:
(1) an electric reactor does not need to be additionally configured in the system to form a protection boundary, and the boundary characteristic existing in the system is adopted, so that the stable operation of the direct-current power distribution network is facilitated;
(2) the single-ended protection of the flexible direct-current power distribution network is realized only by means of mutual matching between setting values and step time delay, communication is not needed, and the requirements on selectivity and quick action are met;
(3) the action performance is better, and simultaneously, the resistance to transition resistance is certain.
Drawings
Fig. 1 is a flow chart of protection of a flexible dc distribution network.
Fig. 2 is a topological structure diagram of a multi-photovoltaic access radial flexible direct current distribution network.
Fig. 3 is an equivalent circuit diagram when a double-pole short-circuit fault occurs at different line positions of the power distribution network.
Fig. 4 is a simulation diagram comparing a high frequency quantity with a protection setting value when a bipolar short-circuit fault occurs at different positions.
Fig. 5 is a simulation of the effect of transition resistance on protection.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings. It should be emphasized that the following description is merely exemplary in nature and is in no way intended to limit the scope of the invention or its applications.
Fig. 1 is a flowchart of a method for protecting a flexible dc power distribution network based on a single-ended current transient, which includes the following steps:
step 1, analyzing fault transient current characteristics when bipolar short-circuit faults occur at different line positions of a direct current system aiming at a flexible direct current power distribution network which contains photovoltaic fields and is accessed through a DC/DC converter, and deducing corresponding expressions;
step 2, analyzing the inherent boundary characteristics of the DC/DC converter to the transient high-frequency quantity based on the fault transient current characteristic research of the step 1, and extracting a current high-frequency signal through discrete wavelets;
and 3, setting different protection setting values for the extracted high-frequency current information based on the high-frequency boundary characteristics of the current converter in the step 2, so as to realize protection configuration and setting coordination of the power distribution network.
In the step 1, when a bipolar short-circuit fault occurs in the flexible direct-current power distribution network, due to the instantaneous voltage drop at the fault position, the introduction of a step voltage source can be approximately equivalent, and the transient current is a corresponding response generated by the step voltage source in the system. Under a complex frequency domain, corresponding equivalent operation can be carried out on related parameters in the flexible direct distribution power grid, and finally fault transient currents detected by protection measuring points at different fault positions are obtained through pull type inverse transformation; when a fault occurs on a line where a measuring point is located, the current expression is as follows:
Figure BDA0003095561550000051
in the formula of Uf(s) is the equivalent step source in the complex frequency domain, Zmmc(s) is the equivalent impedance of the MMC current converter in the complex frequency domain, ZL(s) is the reactor impedance in the complex frequency domain, Zline1(s) is the upper adjacent line impedance in the complex frequency domain, Zdc(s) is the equivalent impedance of the DC/DC converter in the complex frequency domain, Zline2(s) is the impedance of the line at this stage in the complex frequency domain, d1The distance from the fault position to the protection measuring point of the line accounts for the percentage of the full length of the line, and the operatorNumber L-1And (DEG) represents the pull type inverse transformation.
When a fault occurs in an adjacent line at the lower stage of a measuring point, the current expression is as follows:
Figure BDA0003095561550000061
in the formula, Zline3(s) is the lower line impedance in the complex frequency domain, d2It represents the distance from the fault location to the next protection station as a percentage of the total length of the line.
In the step 2, the line inductor, the reactor and the MMC current converter are inductive at high frequency, and the impedance modulus value is increased along with the increase of the frequency; the DC/DC converter presents a capacitive characteristic due to the function of the support capacitor at the outlet, and presents a very small high-frequency impedance modulus value in a high-frequency section compared with the former three. In the flexible direct-current power distribution network, the photovoltaic is boosted and connected in parallel through the DC/DC converter, so that the system is equivalently connected with a plurality of capacitive impedances in parallel. When a system has a fault, the transient current generated by the step signal of the fault point has full frequency domain information. When high-frequency-band information of transient current is transmitted in a system and flows through a DC/DC converter with a very small impedance modulus value connected in parallel with a line, a large amount of high frequency can flow into the DC/DC converter due to the shunt principle of the circuit. Compared with the current-stage line with faults, the high-frequency components flowing through the adjacent lines at the lower stage are greatly reduced, and equivalently, a parallel boundary is formed on the flexible direct-current power distribution network.
Through discrete wavelet transform, a high-frequency signal of the transient current can be extracted, and further quantified into an intensity value, so that the boundary effect of the DC/DC converter on the high-frequency quantity is reflected:
Figure BDA0003095561550000062
wherein N is the length of the wavelet transform coefficient,
Figure BDA0003095561550000063
is the transform coefficient of the nth discrete wavelet under the j scale.
In the step 3, the invention calculates the setting values of the section I and the section II and the action delay of the section II aiming at the faults at different positions of the line by detecting the numerical value significant difference of the current transient state information with the frequency band of 1.25-2.5kHz inside and outside the region, thereby setting the single-end transient state quantity circuit protection with the mutual matching of the two-section setting values to realize the protection of the whole length of the line.
The transient action after the protection I section fault is carried out, no action time delay exists, and the transient action can be carried out rapidly only when the fault occurs on the circuit of the current stage, so that the setting is carried out according to the condition that the bipolar short circuit fault occurs at the tail end of the circuit of the current stage, and the theoretical transient current is as follows:
Figure BDA0003095561550000071
to pair
Figure BDA0003095561550000072
After discrete wavelet transformation is carried out to extract corresponding high-frequency information, an I-section setting value is obtained:
Figure BDA0003095561550000073
in the formula (I), the compound is shown in the specification,
Figure BDA0003095561550000074
is a wavelet transformation coefficient theoretically extracted when the tail end of the line at the current level fails,
Figure BDA0003095561550000075
for protecting I end reliable coefficient, for effectively avoiding adjacent exit resonant energy, consider influences such as mutual-inductor error and parameter measurement error simultaneously, take 1.2 ~ 1.3.
The setting value of the protection II section needs to be matched with the protection I section of the adjacent line, the protection I section can only protect 60% -70% of the total length of the line, the protection II section needs to be used as a near backup of the protection I section of the line of the current stage to protect the total length and cannot exceed the protection I section range of the adjacent line of the next stage to prevent the skip trip, therefore, the setting of the protection II section is carried out according to the protection range to 50% of the total length of the adjacent line of the next stage, and the theoretical transient current measured by a measuring point at the moment is as follows:
Figure BDA0003095561550000076
to pair
Figure BDA0003095561550000077
After discrete wavelet transform is carried out to extract corresponding high-frequency information, II sections of setting values are obtained:
Figure BDA0003095561550000078
in the formula (I), the compound is shown in the specification,
Figure BDA0003095561550000079
is a wavelet transformation coefficient theoretically extracted when 50% of adjacent lines of a lower level have faults,
Figure BDA00030955615500000710
to protect the reliability factor at end II, take 1.1.
When a lower line breaks down, the protection of the I end of the lower line needs to be ensured to remove the fault preferentially, and the action time limit of the protection II end is higher than that of the I end of the lower line by one time stage:
tset＝tw+top+tm
in the formula, twFor extracting a data window of the signal, topTime of circuit breaker actuation, tmTime margins for other influencing factors.
Fig. 2 is a topological structure diagram of a multi-photovoltaic accessed radial flexible direct current distribution network. The voltage grade +/-10 kV direct-current power distribution network realizes alternating current and direct current conversion through the modular multilevel converter, and photovoltaic direct-current boosting access to the power distribution network is realized through the plurality of DC/DC converters. And direct-current quick switches are installed at the outlets of the current converters of the power distribution network and are used for switching when the system operates normally. And current measuring points and direct current circuit breakers are arranged at two ends of each distribution line, and the direct current circuit breakers remove faults when the lines break down. In the figure, F1, F2, and F3 indicate line faults.
Fig. 3 is an equivalent circuit diagram when a double-pole short-circuit fault occurs at different line positions of the power distribution network. When faults occur at different locations of the distribution network, the resulting equivalent circuit diagrams are not the same, and fig. 3 shows the equivalent circuits in the case of a fault F1 and F2, respectively, where u isfIs the source of the step introduced at the fault.
Fig. 4 is a simulation diagram comparing a high frequency quantity with a protection setting value when a bipolar short-circuit fault occurs at different positions. In fig. 4, taking the fault at F1 as an example, the high frequency quantities measured by bipolar short-circuit fault measuring points at different positions of the line are different, and the high frequency quantities all meet the setting value of the protection section i in the first 50% of the full length of the line, so that the protection acts rapidly. If the fault position is 70% of the total length of the line and far away, the high-frequency component of the transient current can not meet the setting value of the I section of the current protection, the I section of the protection does not act, but can still meet the setting value of the II section of the protection, and the II section of the protection acts reliably after time delay. The mutual cooperation between the I section and the II section of the current protection enables the whole length of the circuit to be effectively protected.
Fig. 5 is a simulation of the effect of transition resistance on protection. A transition resistance of 20 ohms was set at fault point F1 to verify its effect on protection, and it can be seen from the figure that the proposed protection has the ability to withstand a certain transition resistance.
Simulation results show that in a flexible direct-current power grid with multiple photovoltaic devices connected in through a DC/DC converter, when a bipolar short-circuit fault occurs in the system, two-section type single-ended quantity protection matched with each other through a transient current high-frequency quantity setting value can be constructed through the high-frequency boundary characteristics of the power distribution network. The protection method has good applicability in the flexible direct-current power distribution network, can quickly and effectively remove fault lines, has selectivity and quick action, and has certain transition resistance tolerance capability.

Claims (4)

1. A flexible direct-current power distribution network protection method based on single-ended current transient state quantity is characterized by comprising the following steps:
the method comprises the following steps that 1, fault transient state current characteristics of a direct current system when bipolar short circuit faults occur at different line positions are analyzed and corresponding expressions are deduced for a flexible direct current power distribution network which contains photovoltaic fields and is connected into the direct current power distribution network through a DC/DC converter;
step 2, analyzing the inherent boundary characteristics of the DC/DC converter to the transient high-frequency quantity based on the fault transient current characteristics when the bipolar short-circuit fault occurs in the step 1, and extracting a current high-frequency signal through discrete wavelet;
step 3, setting different protection setting values for the extracted high-frequency current information based on the high-frequency boundary characteristics of the current converter in the step 2, and realizing protection configuration and setting matching of the power distribution network; by detecting the numerical value significant difference of current transient state information with frequency band of 1.25-2.5kHz inside and outside the region, setting values of a section I and a section II and action time delay of the section II are calculated aiming at faults at different positions of a line, so that single-end transient state quantity circuit protection with the mutual matching of the two-section setting values is set to realize the protection of the whole length of the line;
in the step 1, when a bipolar short-circuit fault occurs in the flexible direct-current power distribution network, because the voltage at the fault position drops instantaneously, a step voltage source is introduced approximately equivalently, and the transient current is a corresponding response generated by the step voltage source in the system, equivalent operation is performed on relevant parameters in the flexible direct-current power distribution network correspondingly in a complex frequency domain, and further through pull-type inverse transformation, fault transient currents detected by protection measuring points at different fault positions are finally obtained; when a fault occurs on a line where a measuring point is located, the current expression is as follows:
Figure FDA0003600726020000011
in the formula of Uf(s) is the equivalent step source in the complex frequency domain, Zmmc(s) is the MMC converter equivalent impedance in complex frequency domain, ZL(s) is the reactor impedance in the complex frequency domain, Zline1(s) is the upper adjacent line impedance in complex frequency domain, Zdc(s) is the equivalent impedance of the DC/DC converter in the complex frequency domain, Zline2(s) is the impedance of the line at this stage in the complex frequency domain, d1The distance from the fault position to the protection measuring point of the line accounts for the percentage of the total length of the line, and the symbol L is calculated-1() represents a pull-type inverse transform;
when a fault occurs in an adjacent line at the lower stage of a measuring point, the current expression is as follows:
Figure FDA0003600726020000021
in the formula, Zline3(s) is the lower line impedance in the complex frequency domain, d2It represents the distance from the fault location to the next protection station as a percentage of the total length of the line.
2. The method for protecting the flexible direct-current power distribution network based on the single-ended current transient quantity is characterized in that the line reactor and the MMC converter are inductive at high frequency, and the impedance modulus value is increased along with the increase of the frequency; the DC/DC converter presents a capacitive characteristic due to the function of the support capacitor at the outlet, and presents a very small high-frequency impedance modulus value compared with the former three in a high-frequency section; in the flexible direct-current power distribution network, the photovoltaic is boosted and connected in parallel through the DC/DC converter, so that the system is equivalently connected with a plurality of capacitive impedances in parallel; when a system fails, full frequency domain information exists in transient current generated by a fault point step signal; when high-frequency-band information of transient current is transmitted in a system and flows through a DC/DC converter which is connected in parallel with a line and has a very small impedance modulus value, a large amount of high frequency can flow into the DC/DC converter due to the shunting principle of the circuit; compared with the current-stage line with faults, the high-frequency components flowing through the adjacent lines at the lower stage are greatly reduced, and equivalently, a parallel boundary is formed on the flexible direct-current power distribution network.
3. The method for protecting the flexible direct-current power distribution network based on the single-ended current transient quantity is characterized in that the method acts instantaneously after I-section fault protection without action time delay, and acts rapidly only when the fault occurs on the line of the current stage, so that the method is set according to the condition that the bipolar short-circuit fault occurs when the tail end of the line of the current stage is avoided, and the theoretical transient current is as follows:
Figure FDA0003600726020000022
to pair
Figure FDA0003600726020000023
After discrete wavelet transformation is carried out to extract corresponding high-frequency information, an I-section setting value is obtained:
Figure FDA0003600726020000024
in the formula (I), the compound is shown in the specification,
Figure FDA0003600726020000025
is a wavelet transformation coefficient theoretically extracted when the tail end of the line at the current level fails,
Figure FDA0003600726020000026
in order to protect the reliability coefficient of the I end, in order to effectively avoid the resonance energy of adjacent outlets, the influence of mutual inductor errors, parameter measurement errors and the like is considered, and the value is 1.2-1.3.
4. The method for protecting the flexible direct-current power distribution network based on the single-ended current transient quantity, according to claim 1, is characterized in that setting values of a protection II section need to be matched with a protection I section of an adjacent line, the protection I section can only protect 60% -70% of the total length of the line, the protection II section needs to be used as a near backup of the protection I section of the line of the current level to protect the total length and cannot exceed the protection I section range of the adjacent line of a lower level to prevent override tripping, therefore, the protection II section is set according to the protection range to 50% of the total length of the adjacent line of the lower level, and the theoretical transient current measured by a measuring point at the moment is as follows:
Figure FDA0003600726020000031
for is to
Figure FDA0003600726020000032
After discrete wavelet transform is carried out to extract corresponding high-frequency information, II sections of setting values are obtained:
Figure FDA0003600726020000033
in the formula (I), the compound is shown in the specification,
Figure FDA0003600726020000034
is a wavelet transformation coefficient theoretically extracted when 50% of adjacent lines of a lower level have faults,
Figure FDA0003600726020000035
in order to protect the reliability coefficient of the end II, the value is taken as 1.1;
when a lower line breaks down, the protection of the I end of the lower line needs to be ensured to remove the fault preferentially, and the action time limit of the protection II end is higher than that of the I end of the lower line by one time stage:
tset＝tw+top+tm
in the formula, twFor extracting data windows of the signal, topFor circuit breaker actuation time, tmTime margins for other influencing factors.
CN202110610017.9A 2021-06-01 2021-06-01 Flexible direct-current power distribution network protection method based on single-ended current transient quantity Active CN113315103B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202110610017.9A CN113315103B (en) 2021-06-01 2021-06-01 Flexible direct-current power distribution network protection method based on single-ended current transient quantity

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202110610017.9A CN113315103B (en) 2021-06-01 2021-06-01 Flexible direct-current power distribution network protection method based on single-ended current transient quantity

Publications (2)

Publication Number Publication Date
CN113315103A CN113315103A (en) 2021-08-27
CN113315103B true CN113315103B (en) 2022-07-15

Family

ID=77376850

Family Applications (1)

Application Number Title Priority Date Filing Date
CN202110610017.9A Active CN113315103B (en) 2021-06-01 2021-06-01 Flexible direct-current power distribution network protection method based on single-ended current transient quantity

Country Status (1)

Country Link
CN (1) CN113315103B (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113640622B (en) * 2021-08-31 2023-09-22 广东电网有限责任公司 Fault detection method and system for medium-low voltage direct current micro-grid

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104977502A (en) * 2015-06-11 2015-10-14 昆明理工大学 Extra-high-voltage DC power transmission line area internal and external fault identification method
CN109617027A (en) * 2018-12-11 2019-04-12 华北电力大学 A kind of flexible direct current distribution system high frequency Sudden Changing Rate distance protecting method

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102005740B (en) * 2010-10-29 2013-05-15 昆明理工大学 Extra-high voltage direct current line boundary element method adopting polar wave wavelet energy ratio
EP3093675B1 (en) * 2015-05-14 2019-01-16 General Electric Technology GmbH Improvements in or relating to direct current protection schemes
CN109613395A (en) * 2018-12-03 2019-04-12 华中科技大学 It is a kind of that soft straight electric network fault detection method is maked somebody a mere figurehead based on ANN
CN110850230B (en) * 2019-11-07 2022-04-29 天津大学 Method for extracting interpolar short circuit fault characteristic quantity of direct current distribution network based on multi-wavelet theory

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104977502A (en) * 2015-06-11 2015-10-14 昆明理工大学 Extra-high-voltage DC power transmission line area internal and external fault identification method
CN109617027A (en) * 2018-12-11 2019-04-12 华北电力大学 A kind of flexible direct current distribution system high frequency Sudden Changing Rate distance protecting method

Also Published As

Publication number Publication date
CN113315103A (en) 2021-08-27

Similar Documents

Publication Publication Date Title
Song et al. DC line fault identification based on pulse injection from hybrid HVDC breaker
CN106908693B (en) Single-phase grounding route selection method of arc suppression coil grounding system with high accuracy
CN109617027B (en) High-frequency sudden-change distance protection method for flexible direct-current power distribution system
Jamali et al. Protection of transmission lines in multi-terminal HVDC grids using travelling waves morphological gradient
Jia et al. Transient high-frequency impedance comparison-based protection for flexible DC distribution systems
Jia et al. Distance protection scheme for DC distribution systems based on the high-frequency characteristics of faults
CN109617026B (en) Ultrahigh-speed protection method for earth fault of direct-current power grid converter station
CN110661238A (en) Multi-terminal flexible direct-current power distribution network protection method based on current-limiting inductive voltage
EP2446283A1 (en) Method for identifying type of fault on power line
CN114295935B (en) Low-voltage measurement-based low-current system medium-voltage single-phase grounding fault positioning method
EP3747100B1 (en) Surge arrestor dimensioning in a dc power transmission system
CN113315103B (en) Flexible direct-current power distribution network protection method based on single-ended current transient quantity
CN110768206B (en) Single-phase earth fault protection method for small-resistance earth system
CN114512966B (en) Pilot protection method and system for direct-current power distribution network based on S-transform frequency domain impedance
CN112952775B (en) Method for protecting voltage quantity of power distribution network containing distributed photovoltaic power supply
CN107942204B (en) Comprehensive protection method and device for direct current collecting cable
CN108599116B (en) Direct-current line protection method suitable for alternating-current and direct-current hybrid power distribution network
Dai et al. Protection scheme for DC lines in AC/DC hybrid distribution grids with MMCs
Ruffing et al. Resonance phenomena and dc fault handling during intersystem faults in hybrid ac/dc transmission systems with partial dc cabling
CN109449896A (en) A kind of override trip prevention method of switching station
Ke et al. Protection schemes and settings of DC distribution systems
CN109861188B (en) Grounding protection method and system based on centralized new energy grid-connected mode
Nadeem et al. Transient harmonic voltage based protection scheme for multi-terminal HVDC transmission networks
CN114498574A (en) High-frequency impedance differential protection method for high-proportion photovoltaic power distribution network
CN110429572B (en) Rapid protection method for interelectrode fault of direct-current power distribution network

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant