CN116417976A - Direct current distribution network ground fault protection method based on positive and negative current correlation - Google Patents

Direct current distribution network ground fault protection method based on positive and negative current correlation Download PDF

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CN116417976A
CN116417976A CN202310407795.7A CN202310407795A CN116417976A CN 116417976 A CN116417976 A CN 116417976A CN 202310407795 A CN202310407795 A CN 202310407795A CN 116417976 A CN116417976 A CN 116417976A
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fault
protection
current
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薛士敏
王正阳
李玥轩
张旭
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Tianjin University
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Tianjin University
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H1/00—Details of emergency protective circuit arrangements
    • H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
    • 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
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S10/00—Systems supporting electrical power generation, transmission or distribution
    • Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
    • Y04S10/52—Outage or fault management, e.g. fault detection or location

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Abstract

The invention provides a direct current distribution network grounding fault protection method based on anode and cathode current correlation, which is based on a symmetrical unipolar wiring VSC, and uses neutral point grounding current as a protection starting criterion to rapidly detect faults; based on the characteristic that the symmetry of a system fault loop is destroyed, the Pearson correlation coefficient is used as an analysis and calculation tool, the change trend characteristics of the positive and negative fault currents of the circuit are utilized to carry out fault location and fault pole selection, the related bipolar current principle only utilizes a communication channel to transmit logic signals, the requirements on the synchronism and the channel capacity of a communication system are low, and the cost of communication equipment is saved while the protection reliability, the transition resistance tolerance and the noise capability are ensured. The method has low requirements on communication equipment, needs less communication resources and does not require strict synchronization of data at two ends.

Description

Direct current distribution network ground fault protection method based on positive and negative current correlation
Technical Field
The invention relates to the field of power distribution of power grids, relates to an automation technology, and in particular relates to a direct current distribution network grounding fault protection method based on positive and negative current correlation.
Background
Compared with an alternating current power grid, the direct current power grid has the advantages of being high in efficiency of accessing a distributed power supply, beneficial to power grid connection, large in power supply capacity, good in anti-interference performance and the like, and has high research value and application prospect. In recent years, the direct current power grid protection technology is widely applied to medium-low voltage power distribution network engineering, well adapts to a new scene of wide access of a distributed power supply, and deeply changes the development pattern of a future power grid. However, the existing low-voltage direct-current power distribution network protection technology still has a plurality of technical difficulties in fault detection, fault positioning, fault recovery and the like, so that the reasonable utilization and the solution of the deep contradiction between the four aspects of protection become key propositions for guaranteeing the safe and stable operation of a power grid.
According to the method, the generation of the ground fault is detected by utilizing the sum of all-line currents of all protection installation positions in a direct current sub-network aiming at the direct current ground fault in the alternating current-direct current hybrid power distribution network, then the sum of all-line currents of all protection elements on the downstream adjacent lines is obtained based on 5G communication, and the section where the fault is located is judged according to the amplitude relation. In addition, a capacitance type pole selection factor is introduced, fault reliable pole selection is carried out according to the direct current bipolar current of the voltage source converter and the alternating current ground connection current, and a 5G network is utilized to transmit a pole selection result, so that protection selective tripping and fault accurate isolation are realized. The invention realizes the effective identification and positioning of the direct current ground fault by utilizing the current amplitude information and the 5G rapid communication in the alternating current-direct current hybrid power distribution network, can adapt to different direct current sub-network power supply topologies, and is beneficial to improving the operation economy and the power supply reliability of the alternating current-direct current power distribution network.
However, the power grid environment and the scheme of the patent are different, and the adopted fault monitoring and positioning modes are different from the technical scheme of the scheme.
At present, a new method based on double-end current correlation protection is proposed by Peng Tao and the like (high-voltage direct-current transmission line protection based on current correlation analysis, journal name of electric power system and its automated chemistry report, 2018 (030) 004) by adopting double-end current correlation analysis to record fault current of the high-voltage direct-current transmission line. According to the method, correlation comparison is carried out according to the characteristics that the current change directions of the two ends are opposite when the faults in the area occur, and the current change directions of the two ends of the faults outside the area are the same, so that the faults in the area and the faults outside the area can be rapidly and accurately identified. The method does not need strict time synchronization of protection devices at two ends of the line, has low sampling frequency requirement, can be realized under the hardware condition of the current high-voltage direct-current control and protection system, has high reliability and strong practicability, and can meet the requirement of the high-voltage direct-current line on the protection performance. The PSCAD and MATLAB simulation results verify the feasibility and effectiveness of the method.
The protection principle of the low-voltage direct-current power distribution network is distinguished according to a communication mode and can be divided into a single-end quantity protection principle and a double-end communication-based protection principle. The single-end quantity protection principle only utilizes the electric quantity information of a single side to construct protection, and fault positioning can be completed without communication, but the single-end quantity protection principle is slightly deficient in selectivity, and part of the method is seriously dependent on line boundary reactance. The protection principle based on double-end communication directly utilizes the electric quantity information on two sides of the element, is based on a pilot protection method to construct and protect, is simple in principle realization, has absolute selectivity, has strong transitional resistance tolerance, and has high requirement on the synchronism of communication.
At present, the protection principle based on double-end communication has high requirements on communication channels and equipment, and strict requirements on the synchronism of electric quantity at two sides of a line, so that the communication cost is increased, and the economical principle of a low-voltage direct current system is not met. Therefore, a novel protection method needs to be proposed on the premise of ensuring the protection reliability.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, the invention provides a direct current distribution network grounding fault protection method based on anode and cathode current correlation.
The specific technical scheme is as follows:
a DC distribution network grounding fault protection method based on anode and cathode current correlation comprises the following steps:
(1) The fault detection method comprises the following steps:
capacitor neutral point grounding ground current I g Can be suddenly broken after failureThe fault can be reflected rapidly and accurately, the fault is used as a protection starting criterion, and after the fault is detected, the IGBT in the system is locked, so that the self-protection of the VSC is realized; the IGBT between the VSC three-phase bridge arm and the DC side outlet capacitor is rapidly turned off, and the connection of the two sides of the AC and the DC is cut off;
(2) The fault positioning method comprises the following steps:
(1) sampling the current of the positive electrode and the negative electrode of each protection installation part in the system, and calculating Pearson correlation coefficients of each side of each line;
(2) judging the S side according to the protection criterion, if the S side judges that the positive direction is faulty, transmitting an permission signal to the L side, waiting for response of the opposite side, and if the section of line is a system end line, judging that the fault in the line area is faulty directly according to the judgment result of the S side;
(3) after the L side receives the protection signal, if the L side also meets the positive direction fault criterion, the L side can judge that the fault exists in the line area and simultaneously send an action signal to the S side; if the local side does not meet the positive direction fault criterion, judging that the local line is out of the area fault, and locking the local side for protection;
(4) and after receiving the L-side confirmation signal, the S-side starts fault pole selection.
(3) The fault pole selection method comprises the following steps:
according to the change characteristics of the fault current on the S side of the line, after the fault is determined to occur in the positive direction, the current of the positive electrode and the current of the negative electrode on the S side are used as the basis of selecting the electrode, when the positive electrode is grounded, the current of the positive electrode is rapidly increased, the current of the negative electrode is slightly reduced, the amplitude of the current of the positive electrode is far higher than that of the negative electrode, and when the grounding fault of the negative electrode occurs, the situation of complete opposite occurs; the two sides of the line S, L respectively trip the corresponding circuit breakers according to the fault pole selection criteria, and the fault line is cut off.
Further, the fault detection described in step (1) causes the capacitive neutral point to ground the ground current I g The starting criterion when the change occurs is shown as follows:
|ΔI g |＞ΔI g.set
wherein, |ΔI g I is the absolute value of the abrupt current change of the grounded ground branch of the neutral point of the capacitor, and delta I g.set To start upThe threshold value should be given enough margin for protection in view of engineering practical conditions.
The specific method for calculating the Pearson correlation coefficient at each side of each line in the step (2) is as follows: the correlation of the current change trend of the positive electrode and the negative electrode at one side of the line is reflected by using a Pearson correlation coefficient, and the Pearson correlation coefficient is defined as follows:
Figure BDA0004182073860000031
wherein i is P ＝{x 1 ,x 2 ,…,x n Is positive electrode current sampling value, i N ＝{y 1 ,y 2 ,…,y n And is the negative current sample value,
Figure BDA0004182073860000032
Figure BDA0004182073860000033
for the mean of the sampled data, m is the line two-sided (S, L-sided) number.
And, the fault pole selection in the step (3) uses the current ratio of two poles as a fault pole selection criterion, and the defined current ratio K is shown in the following formula:
Figure BDA0004182073860000034
after the S side has positive fault, the current ratio K is far greater than 1 or far less than 1, and the fault pole selection criterion is set as shown in the following formula in consideration of due margin and measurement error in the system:
Figure BDA0004182073860000035
moreover, the Pearson correlation coefficient P m The value range is [ -1,1]，P m When=1, a complete positive correlation is present; p (P) m When= -1, a complete negative correlation is present; p (P) m =0, uncorrelated.
Further, for the S-side protection, the protection operation condition may be set as follows, taking into consideration the margin that the protection should have:
P S ＜0.7；
for the L-side protection, a blocking element needs to be added, and the protection can be opened only after receiving the permission signal sent by the S-side protection, so the operation condition of the L-side protection can be set as follows:
Figure BDA0004182073860000041
and the current ratio K takes the sampling point number N=10 of each comparison, and the fault pole can be determined by adopting a sliding time window to continuously calculate 3 times to meet the criterion.
And as for the criterion, the calculation window length of the Pearson correlation coefficient algorithm is 20 sampling points, and the criterion is continuously satisfied for 3 times under the sliding window length, so that the side protection forward fault and the protection action can be judged.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention is based on the VSC of symmetric monopole wiring, and uses the neutral point grounding support current as the starting criterion of protection to rapidly detect faults; based on the characteristic that the symmetry of a system fault loop is destroyed, the Pearson correlation coefficient is used as an analysis and calculation tool, the change trend characteristics of the positive and negative fault currents of the circuit are utilized to carry out fault location and fault pole selection, the related bipolar current principle only utilizes a communication channel to transmit logic signals, the requirements on the synchronism and the channel capacity of a communication system are low, and the cost of communication equipment is saved while the protection reliability, the transition resistance tolerance and the noise capability are ensured. The method has low requirements on communication equipment, needs less communication resources and does not require strict synchronization of data at two ends.
2. The direct current distribution network grounding fault protection method based on the anode-cathode current correlation has absolute selectivity, can accurately and reliably identify fault sections aiming at grounding faults, and has strong transition resistance and noise immunity.
3. The direct current distribution network grounding fault protection method based on the anode-cathode current correlation provided by the invention is used for constructing protection according to anode-cathode symmetric characteristics of a system after faults, and has strong adaptability to distributed power supply access and system load fluctuation.
4. The direct current distribution network grounding fault protection method based on the correlation of the positive and negative currents samples the positive and negative currents at each protection installation position in the system, and compared with the protection principle based on differential state quantity, the direct current distribution network grounding fault protection method based on the correlation of the positive and negative currents can more effectively utilize sampling information and has higher reliability.
Drawings
Fig. 1 is a topology diagram of a low voltage dc system including distributed power access.
Fig. 2 is an equivalent circuit model of a low voltage dc system with positive ground fault.
Fig. 3 is a logic diagram of the fault detection scheme and the IGBT latch-up determination.
Fig. 4 is an equivalent circuit of the discharging phase of the capacitor on the dc side of the VSC.
Fig. 5 is a logic flow diagram of a protection action.
Detailed Description
The technical scheme of the invention is further described below with reference to specific examples.
The invention provides a direct current distribution network grounding fault protection method based on anode and cathode current correlation, which utilizes the grounding current mutation property of a neutral point of a capacitor at a DC side outlet of a VSC and the correlation characteristic construction protection principle of the anode and cathode current of a line, and the process mainly comprises the following three stages:
1) Fault detection
Grounding the neutral point of the capacitor at the DC side of the VSC to obtain the current I g After the fault occurs, the fault can be quickly and accurately reflected, so that the fault is used as a protection starting criterion. Taking measurement errors into consideration, a starting criterion is set as follows:
|ΔI g |＞ΔI g.set
wherein, |ΔI g Ground circuit of neutral point of capacitorAbsolute value of flow mutation quantity, Δi g.set For the threshold to be started, the engineering practical situation should be considered, and enough margin is reserved for protection.
After detecting that a fault occurs, the IGBT in the system is locked, so that the self-protection of the VSC is realized; the IGBT between the VSC three-phase bridge arm and the DC side outlet capacitor is rapidly turned off, and the connection of the two sides of the AC and the DC is cut off.
2) Fault location
It is assumed that a fault occurs at the positive pole of a certain line and that the side of the line closer to the VSC neutral point is defined as the S-side and the side farther from the VSC neutral point is defined as the L-side. After the direct-current side fault occurs, the positive current of a fault loop (namely between a capacitor outlet of the VSC direct-current side and a fault point) rapidly rises, and slowly decreases after reaching a peak value; the negative electrode current firstly drops rapidly, then rises gradually, and finally drops slowly. Therefore, the positive and negative current change trends of the fault line S side are different, and the positive and negative current change trends of the L side are the same, so that a grounding fault protection principle based on the correlation of the positive and negative currents can be provided according to the fault characteristics.
The invention utilizes Pearson correlation coefficient to reflect the correlation of the current change trend of the positive electrode and the negative electrode at one side of the line. Definition of Pearson correlation coefficients is shown in the following formula:
Figure BDA0004182073860000051
wherein i is P ＝{x 1 ,x 2 ,…,x n Is positive electrode current sampling value, i N ＝{y 1 ,y 2 ,…,y n And is the negative current sample value,
Figure BDA0004182073860000052
Figure BDA0004182073860000053
for the mean of the sampled data, m is the line two-sided (S, L-sided) number.
Pearson correlation coefficient P m The value range is [ -1,1]。P m When=1, a complete positive correlation is present; p (P) m When= -1, a complete negative correlation is present; p (P) m =0, uncorrelated.
For S-side protection, considering the margin that the protection should have, the protection operation condition may be set as:
P S ＜0.7
for the L-side protection, a blocking element needs to be added, and the blocking element is set to enable protection to be opened only after receiving an permission signal sent by the S-side protection. Therefore, the operation condition of the L-side protection can be set as:
Figure BDA0004182073860000061
and for the criteria, the calculation window length of the Pearson correlation coefficient algorithm is 20 sampling points, and the criterion is continuously met for 3 times under the sliding window length, so that the side protection forward fault and the protection action can be judged.
The protection action logic of the fault recognition stage is as follows:
(1) Sampling the current of the positive electrode and the negative electrode of each protection installation part in the system, and calculating Pearson correlation coefficients of each side of each line;
(2) Judging the S side according to the protection criterion, if the S side judges that the positive direction fails, transmitting an permission signal to the L side, and waiting for the response of the opposite side; if the section of line is a system terminal line, the section of line can be directly judged to be a fault in the line area according to the S-side judging result;
(3) After the L side receives the protection signal, if the L side also meets the positive direction fault criterion, the L side can judge that the fault exists in the line area and simultaneously send an action signal to the S side; if the local side does not meet the positive direction fault criterion, judging that the local line is out of the area fault, and locking the local side for protection;
(4) And after receiving the L-side confirmation signal, the S-side starts fault pole selection.
3) Fault pole selection
The change characteristics of the fault current on the S side of the line can be known, and after the fault is determined to occur in the positive direction, the positive and negative currents on the S side can be used as the basis of pole selection. After the positive electrode ground fault occurs, the positive electrode current rises rapidly, the negative electrode current is slightly reduced, and the positive electrode current amplitude is far higher than that of the negative electrode. And when a negative electrode ground fault occurs, the reverse situation will occur.
Thus, the ratio of the two-pole current can be used as a fault pole selection criterion. The current ratio K is defined as follows:
Figure BDA0004182073860000062
after the S side fails in the positive direction, the current ratio K is far greater than 1 or far less than 1. Considering due margin and measurement error in the system, setting fault pole selection criteria as shown in the following formula:
Figure BDA0004182073860000071
and taking the sampling point number N=10 of each comparison, and adopting a sliding time window to continuously calculate for 3 times to meet the criterion so as to determine the fault pole. The two sides of the line S, L respectively trip the corresponding circuit breakers according to the fault pole selection criteria, and the fault line is cut off.
Fig. 1 is a schematic diagram of a topology of a radial low-voltage dc distribution network including distributed power access. To generate a transition resistance R at the positive electrode of the circuit 1 g For example, in order to more intuitively analyze the change rule of the fault current, the topology structure of the system is reasonably simplified, and a series of circuits and loads downstream of the circuit 1 are converted into an equivalent load, and the equivalent circuit model is shown in fig. 2.
Fig. 3 is a fault detection method and IGBT latch-up logic. After the ground fault occurs, the ground point is communicated with the neutral point of the VSC through the ground to form a fault loop, so that the circuit of the ground branch of the neutral point of the VSC after the fault is suddenly changed. With the grounding via a higher transition resistance, the neutral grounding current still produces a significant abrupt change. If the absolute value |DeltaI of the current abrupt change is detected g If the I is larger than the starting threshold, the ground fault can be judged to occur, the IGBT in the system is locked, the starting is protected, and the VSC three-phase bridge arm and the direct current side are protectedThe IGBT (G1) between the outlet capacitors is turned off to cut off the connection of the two sides of the alternating current and the direct current.
Fig. 4 is a fault equivalent circuit diagram of the discharging phase of the VSC dc side outlet capacitance. After the fault occurs, the direct current side of the VSC can be equivalent to a capacitor second-order free discharge circuit. In a DC power distribution network, the equivalent resistance of a DC line is small, and the damping of the equivalent resistance generally meets the following requirements
Figure BDA0004182073860000072
Therefore, the capacitor discharge can be regarded as a second-order underdamped oscillation process, and the positive fault current I p And rapidly rises. As the positive electrode capacitance is continuously discharged, the positive electrode current change rate is continuously reduced. After that, the capacitor discharge is basically completed, the capacitor discharge speed is smaller than the inductor discharge speed, and the positive fault current i p And starts to slowly descend.
While for the negative current, the negative current fluctuates although the negative line is not directly connected in the fault loop. The change in the negative current (the same current as that flowing through the load) is closely related to the dc side load voltage. Before failure occurs, due to inductance L 1 Smaller, load R load Voltage U on load Close to the DC side voltage U dc . In the initial stage of fault occurrence, the load voltage U load Drop to less than the non-fault pole voltage (DC side voltage U dc Half) of the current in the negative electrode, thus n And rapidly drops. Then, as the discharge proceeds, the positive electrode current change rate dI p /d t Continuously decrease according to the inductance L 1 Voltage-current relationship U L1 ＝L 1 (dI p /d t )，U L1 Also continuously decreases, the partial pressure of the non-fault loop increases, and the negative electrode current I n And begin to rise gradually. As the capacitor discharge continues, the load voltage will eventually decrease, the negative fault current I n Will also start to drop slowly.
The side of the prescribed line close to the VSC capacitance neutral point is the S side, and the side far from the VSC capacitance neutral point is the L side. As can be seen from the above analysis, for the protection of the line S side, the positive and negative electrode symmetrical structure is destroyed when a positive fault occurs, and the current change trend of the positive and negative electrodes at the protection installation position is different; when reverse fault or normal fluctuation of load occurs, the anode and cathode symmetrical structure is not destroyed, and the current change trend of the anode and the cathode at the protection installation position is basically the same. The opposite is true for the L-side protection, but the L-side protection cannot distinguish between a positive fault and load fluctuations, and therefore a blocking element needs to be added to the L-side protection. By utilizing the characteristic that S-side protection can distinguish positive direction faults and load fluctuation, L-side action logic can be set as: the S side firstly judges the fault direction, the result is transmitted to the L side by communication, and if the S side confirms that the fault occurs in the positive direction of the self side and the L side meets the positive direction criterion, the fault can be considered to occur in the self line.
Fig. 5 is a protection overall action logic, which can be specifically divided into three parts of fault detection, fault positioning and fault pole selection.
Firstly, fault detection is carried out by utilizing the neutral point grounding ground connection current of the outlet capacitor of the direct current side of the VSC, when the absolute value of the current abrupt change is larger than the starting threshold value, the ground fault can be judged to occur, the starting is protected, the IGBT is locked, and the connection between the alternating current side and the direct current side of the system is cut off.
And then, sampling the current of the positive electrode and the negative electrode at each protection installation position in the system in real time, and calculating Pearson correlation coefficients at each side of each line. The algorithm calculates the window length to be 20 sampling points, and continuously meets 3 criteria under the sliding time window, so that the side protection positive direction fault can be judged. The communication process on both sides of S, L is as follows: (1) Judging the S side according to the protection criterion of the S side, if the S side judges that the positive direction fails, transmitting an permission signal to the L side, and waiting for the response of the opposite side; if the line is a terminal line, the line can be directly judged as the fault in the line area according to the S-side protection judging result. (2) After the L side receives the protection signal, if the L side also judges that the positive direction fails, the L side can determine that the failure occurs in the line area and simultaneously send a response signal to the S side; if the fault is judged to be the reverse fault, the protection of the side is locked. And (3) after the S side receives the L side confirmation signal, starting fault pole selection.
And finally, calculating a current ratio K according to the current sampling data of the S side, taking the sampling point number N=10 compared each time, and continuously satisfying the pole selection criterion for 3 times under the sliding time window to determine the fault pole. The two sides of the line S, L respectively trip the corresponding circuit breakers according to the fault pole selection criteria, and the fault line is cut off.

Claims (8)

1. A DC distribution network grounding fault protection method based on anode and cathode current correlation is characterized in that: the method comprises the following steps:
(1) The fault detection method comprises the following steps:
capacitor neutral point grounding ground current I g The fault can be suddenly changed after the fault, the fault can be rapidly and accurately reflected and used as a protection starting criterion, and after the fault is detected, the IGBT in the system is locked, so that the self-protection of the VSC is realized; the IGBT between the VSC three-phase bridge arm and the DC side outlet capacitor is rapidly turned off, and the connection of the two sides of the AC and the DC is cut off;
(2) The fault positioning method comprises the following steps:
(1) sampling the current of the positive electrode and the negative electrode of each protection installation part in the system, and calculating Pearson correlation coefficients of each side of each line;
(2) judging the S side according to the protection criterion, if the S side judges that the positive direction is faulty, transmitting an permission signal to the L side, waiting for response of the opposite side, and if the section of line is a system end line, judging that the fault in the line area is faulty directly according to the judgment result of the S side;
(3) after the L side receives the protection signal, if the L side also meets the positive direction fault criterion, the L side can judge that the fault exists in the line area and simultaneously send an action signal to the S side; if the local side does not meet the positive direction fault criterion, judging that the local line is out of the area fault, and locking the local side for protection;
(4) and after receiving the L-side confirmation signal, the S-side starts fault pole selection.
(3) The fault pole selection method comprises the following steps:
according to the change characteristics of the fault current on the S side of the line, after the fault is determined to occur in the positive direction, the current of the positive electrode and the current of the negative electrode on the S side are used as the basis of selecting the electrode, when the positive electrode is grounded, the current of the positive electrode is rapidly increased, the current of the negative electrode is slightly reduced, the amplitude of the current of the positive electrode is far higher than that of the negative electrode, and when the grounding fault of the negative electrode occurs, the situation of complete opposite occurs; the two sides of the line S, L respectively trip the corresponding circuit breakers according to the fault pole selection criteria, and the fault line is cut off.
2. The direct current distribution network grounding fault protection method based on anode-cathode current correlation according to claim 1, wherein the method is characterized by comprising the following steps: the fault detection described in the step (1), the neutral point of the capacitor is grounded to the ground current I g The starting criterion when the change occurs is shown as follows:
ΔI g ＞ΔI g.set
wherein DeltaI g Grounding the absolute value of the current abrupt change, ΔI, for the capacitive neutral point g.set For the threshold to be started, the engineering practical situation should be considered, and enough margin is reserved for protection.
3. The direct current distribution network grounding fault protection method based on anode-cathode current correlation according to claim 1, wherein the method is characterized by comprising the following steps:
the specific method for calculating the Pearson correlation coefficient of each side of each line in the step (2) is as follows: the correlation of the current change trend of the positive electrode and the negative electrode at one side of the line is reflected by using a Pearson correlation coefficient, and the Pearson correlation coefficient is defined as follows:
Figure FDA0004182073850000021
wherein i is P ＝{x 1 ,x 2 ,…,x n Is positive electrode current sampling value, i N ＝{y 1 ,y 2 ,…,y n And is the negative current sample value,
Figure FDA0004182073850000022
Figure FDA0004182073850000023
for the mean of the sampled data, m is the line two-sided (S, L-sided) number.
4. The direct current distribution network grounding fault protection method based on anode-cathode current correlation according to claim 1, wherein the method is characterized by comprising the following steps: and (3) fault pole selection, wherein the two-pole current ratio is used as a fault pole selection criterion, and the defined current ratio K is shown in the following formula:
Figure FDA0004182073850000024
after the S side has positive fault, the current ratio K is far greater than 1 or far less than 1, and the fault pole selection criterion is set as shown in the following formula in consideration of due margin and measurement error in the system:
Figure FDA0004182073850000025
5. the direct current distribution network grounding fault protection method based on anode-cathode current correlation according to claim 3, wherein the method is characterized in that: the Pearson correlation coefficient P m The value range is [ -1,1]，P m When=1, a complete positive correlation is present; p (P) m When= -1, a complete negative correlation is present; p (P) m =0, uncorrelated.
6. The direct current distribution network grounding fault protection method based on anode-cathode current correlation according to claim 5, wherein the method is characterized in that: for S-side protection, considering the margin that the protection should have, the protection operation condition may be set as:
P S ＜0.7；
for the L-side protection, a blocking element needs to be added, and the protection can be opened only after receiving the permission signal sent by the S-side protection, so the operation condition of the L-side protection can be set as follows:
Figure FDA0004182073850000026
7. the direct current distribution network grounding fault protection method based on anode-cathode current correlation according to claim 4, wherein the method is characterized in that: the current ratio K is obtained by taking the sampling point number N=10 compared each time, and the fault pole can be determined by adopting a sliding time window to calculate for 3 times continuously so as to meet the criterion.
8. The direct current distribution network grounding fault protection method based on anode-cathode current correlation according to claim 6, wherein the method is characterized in that: and for the criterion, the calculation window length of the Pearson correlation coefficient algorithm is 20 sampling points, and the criterion is continuously met for 3 times under the sliding window length, so that the side protection positive direction fault and the protection action can be judged.
CN202310407795.7A 2023-04-17 2023-04-17 Direct current distribution network ground fault protection method based on positive and negative current correlation Pending CN116417976A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117233532A (en) * 2023-09-21 2023-12-15 中科智寰(北京)科技有限公司 DC power grid ground fault on-line positioning and protecting system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117233532A (en) * 2023-09-21 2023-12-15 中科智寰(北京)科技有限公司 DC power grid ground fault on-line positioning and protecting system
CN117233532B (en) * 2023-09-21 2024-02-09 中科智寰(北京)科技有限公司 DC power grid ground fault on-line positioning and protecting system

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