Line grounding fault detection method based on longitudinal zero-sequence impedance under zero-sequence network

Abstract

The invention relates to the technical field of relay protection of a power system, and discloses a line grounding fault detection method based on longitudinal zero-sequence impedance under a zero-sequence network, and a proposed longitudinal zero-sequence impedance calculation process based on the zero-sequence network is characterized in that during normal operation, when external and reverse direction faults occur, the line grounding fault detection method can be used for detecting the line grounding fault. The zero-sequence impedance calculation starting criterion can prevent further detection from being carried out, maloperation during external faults and reverse faults can be effectively avoided, longitudinal zero-sequence impedance calculation can be reliably started when internal short circuit occurs, and meanwhile, the detection accuracy is improved. Compared with a line high-resistance grounding fault detection method based on distribution parameter zero-sequence impedance amplitude characteristics, the protection action criterion provided by the invention is simpler and more reliable, zero-sequence impedance calculation on the local side and the opposite side is carried out based on zero-sequence voltage and zero-sequence current on the two sides of the line, the risk of action refusal does not exist, and the reliability of the line high-resistance grounding fault detection method based on the distribution parameter zero-sequence impedance amplitude characteristics is improved. The problem that a traditional line high-resistance grounding fault detection method refuses to operate when a center point has a fault is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system relay protection technology, in particular to a line ground fault detection method based on longitudinal zero sequence impedance under zero sequence network. BACKGROUND

[0002] Impedance protection is the key step to judge whether the line ground fault occurs and whether the impedance protection acts to trip by comparing the positive sequence impedance Z1 from the protection installation to the short-circuit point with the setting value in the impedance protection.

[0003] The existing impedance calculation methods include:

[0004] Using the current on the side Voltage Zero sequence current And zero sequence compensation coefficient K to directly calculate, the calculation formula is: When the line ground fault occurs, it is usually through the transition resistance grounding, this method calculates the transition resistance R into the short-circuit impedance in the impedance calculation process, and the calculated whole positive sequence impedance is from the protection installation to the point where the voltage is zero, that is, the grounding point. However, due to the different objects caused by short circuit and the different transition resistances, the transition resistance of the same object will change during the short circuit process due to arc burning. At the same time, the modern high voltage level power grid is in loop operation, and the electromotive force on both sides of the line will provide fault current to the fault point. In the case of power supply on both sides of the line, the additional impedance generated by the transition resistance on the power transmission side is capacitive, and the impedance calculation is small. On the power receiving side, the additional impedance generated by the transition resistance is inductive, and the impedance calculation is large. Influenced by this, the traditional impedance calculation method is not accurate, thereby affecting the action correctness of the protection. The fault location based on impedance calculation is also affected, and the measured distance is often greatly deviated from the reality.

[0005] There is also a line high resistance ground fault detection method based on distributed parameter zero sequence impedance amplitude characteristic in Chinese patent No. CN105866619B, which measures the zero sequence voltage and zero sequence current at both ends of the line, calculates the distributed parameter zero sequence impedance from the single-phase ground fault point to the protection installation of m substation by using the long line equation, calculates the distributed parameter zero sequence impedance from the single-phase ground fault point to the protection installation of n substation by using the long line equation, and then uses the distributed parameter zero sequence impedance amplitude to form a line single-phase high resistance ground fault detection criterion by the monotonic decreasing characteristic from the single-phase ground fault point to both ends of the line. However, this method is only suitable for single-phase high resistance grounding, and the calculation formula is complex, involving hyperbolic cosine function and hyperbolic sine function. The calculation amount is large in the practical process, the error is also large, and there is a risk of refusal to act. According to the protection action criterion, if the fault occurs at the midpoint of the line, it is possible that both criteria are not met, resulting in protection refusal.

[0006] There is also longitudinal current differential protection, which adds the current vectors on both sides of the line and compares the sum with a differential setting to determine whether to act. Although this method is simple to implement, when the line has a high resistance ground fault, the fault current flowing through the fault point to the ground is small, at which time the differential current may not reach the setting, and the differential protection may refuse to act. If the differential current setting is adjusted too low, it may cause the differential protection to malfunction due to the line capacitance current.

[0007] The application provides a line ground fault detection method based on longitudinal zero sequence impedance under a zero sequence network to solve the above problems. SUMMARY

[0008] The application aims to provide a line ground fault detection method based on longitudinal zero sequence impedance under a zero sequence network to solve the problem that the conventional line high resistance ground fault detection method refuses to act when a center point fault occurs.

[0009] The application is implemented by the following technical scheme:

[0010] The line ground fault detection method based on longitudinal zero sequence impedance under a zero sequence network comprises the following steps:

[0011] Step A1: The protection device continuously monitors the zero sequence current and voltage values at the protection installation on the line side and the zero sequence current and voltage values at the protection installation on the opposite side of the line, and checks them. When the values of two or more variables trigger the corresponding alarm conditions, the next step is entered.

[0012] Step A2: A zero sequence impedance calculation starting criterion is constructed. When the difference between the zero sequence current amplitudes on the line side and the opposite side of the line meets the zero sequence impedance calculation starting criterion, the next step is entered.

[0013] Step A3: A zero sequence network of the line is constructed, and the zero sequence impedances from the protection installations on the line side and the opposite side of the line to the fault point are calculated, respectively.

[0014] Step A4: A zero sequence impedance setting is set. When the zero sequence impedance of any side is less than the zero sequence impedance setting, the protection device determines that a ground fault occurs on the corresponding side of the line, issues a trip command, and otherwise determines that it is normal.

[0015] Further, in step A1, when only one variable value triggers the corresponding alarm condition, step A1 is continuously performed and an abnormal alarm of the corresponding variable is issued.

[0016] Further, in step A1, the alarm condition is that the value of the variable is greater than or equal to the corresponding alarm threshold.

[0017] Further, in step A2, the expression of the constructed zero sequence impedance starting criterion is as follows:

[0018]

[0019] In the formula, represents the zero sequence current value at the line self side protection installation, represents the zero sequence current value at the line opposite side protection installation, represents the zero sequence current amplitude at the line self side protection installation, represents the zero sequence current amplitude at the line opposite side protection installation, and k represents a reliability coefficient.

[0020] Further, in the constructed zero sequence impedance starting criterion, k = 0.8.

[0021] Further, in step A2, the zero sequence impedance from the line self side protection installation to the fault point and the zero sequence impedance from the line opposite side protection installation to the fault point are both obtained by substituting the zero sequence voltage source into the longitudinal zero sequence impedance calculation formula.

[0022] Further, the calculation formula of the zero sequence impedance from the line self side protection installation to the fault point is as follows:

[0023]

[0024] In the formula, Z 0l is the line zero sequence impedance, which is obtained before the line is put into operation, represents the zero sequence current value at the line self side protection installation, represents the zero sequence voltage value at the line self side protection installation, represents the zero sequence current value at the line opposite side protection installation, represents the zero sequence voltage value at the line opposite side protection installation.

[0025] The calculation formula of the opposite side zero sequence impedance from the line opposite side protection installation to the fault point is as follows:

[0026]

[0027] Further, the method further comprises the following steps:

[0028] After it is judged that the ground fault occurs at the line self side or the line opposite side, the distance from the fault point to the protection installation can be obtained based on the zero sequence impedance from the corresponding side protection installation of the line to the fault point.

[0029] Further, based on the ratio of the zero sequence impedance from the corresponding side protection installation of the line to the fault point to the zero sequence impedance of the line, after being multiplied by the full length of the line, the distance from the fault point to the protection installation can be obtained.

[0030] Further, the calculation formula of the distance from the fault point to the line self side protection installation is as follows:

[0031]

[0032] In the formula, l is the total length of the line, Z 0l is the zero sequence impedance of the line, obtained before the line is put into operation, Z 0M is the zero sequence impedance from the installation of the protection on the line side to the fault point.

[0033] The calculation formula of the distance from the fault point to the installation of the protection on the opposite side of the line is as follows:

[0034]

[0035] In the formula, Z 0N is the zero sequence impedance from the installation of the protection on the opposite side of the line to the fault point.

[0036] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0037] 1. The zero sequence impedance calculation process proposed in the present application is based on the decomposition of the zero sequence network when the line is faulty. No matter whether the line is single-phase ground short-circuit, two-phase ground short-circuit, single-phase open-circuit or two-phase open-circuit, the zero sequence network is the same according to the decomposition of the positive sequence, negative sequence and zero sequence network. Therefore, the longitudinal zero sequence impedance calculation process based on the zero sequence network proposed in the present application is more concise in calculation, more rapid in action in practical application and more widely applicable.

[0038] 2. The longitudinal zero sequence impedance calculation process based on the zero sequence network proposed in the present application does not satisfy the zero sequence impedance calculation starting criterion for the difference between the zero sequence currents on the line side and the opposite side of the line when the line is normally operated, when a zone-out fault occurs and when a reverse direction fault occurs. Therefore, the zero sequence impedance calculation starting criterion can prevent the further detection when a zone-out fault or a reverse direction fault occurs, which can effectively avoid the misoperation when a zone-out fault or a reverse direction fault occurs. When a short-circuit in the zone occurs, the longitudinal zero sequence impedance calculation can be reliably started. Meanwhile, compared with the "distributed parameter zero sequence impedance amplitude characteristic line high resistance ground fault detection method", the protection action criterion proposed in the present application is simpler and more reliable. The zero sequence voltage and the zero sequence current on both sides of the line are used to calculate the zero sequence impedance on the line side and the opposite side, which does not have the risk of refusal to operate and solves the problem of refusal to operate of the traditional line high resistance ground fault detection method when a center point fault occurs. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation to the scope. Other related drawings can also be obtained by those skilled in the art without paying any creative labor, and the drawings are as follows:

[0040] Figure 1 The flow chart of the line ground fault detection method based on the longitudinal zero sequence impedance under the zero sequence network for the embodiments of the present application;

[0041] Figure 2 The schematic diagram of the zero sequence network of the line for the embodiments of the present application. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present application more clear and understandable, the following will further describe the present application in combination with the embodiments and drawings. The exemplary embodiments of the present application and their descriptions are only used to explain the present application, and should not be considered as a limitation to the present application.

[0043] The line ground fault detection method based on the longitudinal zero sequence impedance under the zero sequence network, the embodiments as shown in Figure 1 include the following steps:

[0044] Step A1: the protection device continuously monitors the zero sequence current value at the protection installation of the line and the zero sequence voltage value and the zero sequence current value and the zero sequence voltage value at the protection installation of the opposite side of the line, and checks whether the value of the variable triggers the corresponding alarm condition: greater than or equal to the corresponding alarm threshold value, and then enters the next step.

[0045] Specifically, in the process of continuously monitoring the zero sequence current value at the protection installation of the line and the zero sequence voltage value and the zero sequence current value and the zero sequence voltage value at the protection installation of the opposite side of the line, it is necessary to check in real time whether the value of the variable triggers the corresponding alarm condition: greater than or equal to the corresponding alarm threshold value, and in the present embodiment, the alarm threshold value includes the zero sequence current alarm threshold value corresponding to the zero sequence current value, and the zero sequence voltage alarm threshold value corresponding to the zero sequence voltage value.

[0046] If the values of the four variables are all less than the corresponding alarm threshold, step A1 is continued. If only one of the four variables triggers the corresponding alarm condition, step A1 is continued and an abnormal alarm of the corresponding variable is issued. Only when the values of two or more variables trigger the corresponding alarm condition, i.e., are greater than or equal to the corresponding alarm threshold, the next step is entered.

[0047] Step A2: A zero sequence impedance calculation starting criterion is constructed. When the difference between the zero sequence currents at the line local side and the line opposite side satisfies the zero sequence impedance calculation starting criterion, the next step is entered.

[0048] Specifically, in normal operation or when an out-of-zone fault or a reverse direction fault occurs, the zero sequence current is a transient current, and the amplitudes are equal and the directions are opposite, so the sum of the zero sequence current amplitude at the line local side protection installation and the zero sequence current amplitude at the line opposite side protection installation: is substantially 0, and the difference between them: is 2 times When an in-zone short circuit occurs, and the amplitudes are equal and the directions are the same, so the amplitude of is the sum of the amplitudes of is and the amplitude of is the difference between the amplitudes of is. Therefore, the zero sequence impedance starting criterion is constructed as follows to check the currents at the line local side and the line opposite side:

[0049]

[0050] In the formula, k is a reliability coefficient, k=0.8.

[0051] In normal operation or when an out-of-zone fault or a reverse direction fault occurs, is 2 times the zero sequence impedance calculation starting criterion is not satisfied, and the step A3 starting condition is not satisfied. When an in-zone short circuit occurs, and the amplitudes are equal and the directions are the same, so the amplitude of is the sum of the amplitudes of is the amplitude of is The difference between the amplitudes of the zero sequence currents is subtracted, a zero sequence impedance calculation starting criterion is met, the next step is entered, and step A3 starts. Therefore, when a circuit within the area is broken, the longitudinal zero sequence impedance calculation can be reliably started, and when normal operation or an out-of-area fault or a reverse direction fault occurs, the longitudinal zero sequence impedance calculation can be reliably blocked.

[0052] For a line triggering an alarm condition, the difference between the amplitudes of the zero sequence currents on the line local side and the line opposite side is obtained. If the difference between the amplitudes of the zero sequence currents meets a zero sequence impedance calculation starting criterion, it is indicated that a circuit within the area is broken, and the next step is entered.

[0053] If the difference between the amplitudes of the zero sequence currents does not meet the zero sequence impedance calculation starting criterion, it is indicated that an out-of-area fault or a reverse direction fault is misoperated.

[0054] Step A3: A zero sequence network of the line is constructed, and zero sequence impedances from the line local side and the line opposite side protection installation to the fault point are respectively calculated, i.e., a local side zero sequence impedance and an opposite side zero sequence impedance.

[0055] Specifically, the local side zero sequence impedance calculation formula of the line local side protection installation to the fault point is as follows:

[0056]

[0057] In the formula, Z 0l is a line zero sequence impedance, which is obtained before the line is put into operation.

[0058] The opposite side zero sequence impedance calculation formula of the line opposite side protection installation to the fault point is as follows:

[0059]

[0060] Through the local side zero sequence impedance calculation formula and the opposite side zero sequence impedance calculation formula, it can be known that the local side zero sequence impedance calculation formula and the opposite side zero sequence impedance calculation formula of the line local side protection installation and the line opposite side protection installation to the fault point do not have a transition resistance R, the influence of the transition resistance on the distance protection is successfully eliminated, and the impedance protection is more accurate.

[0061] Step A4: A zero sequence impedance setting value Z 0set When any one side zero sequence impedance, i.e., the local side zero sequence impedance Z 0M or the opposite side zero sequence impedance Z 0N is less than the zero sequence impedance setting value Z 0set , the protection device judges that a ground fault occurs on the corresponding side of the line, issues a trip command, and otherwise judges as normal.

[0062] Further, in the embodiment, the following steps are further included:

[0063] After judging that the line local side ground fault occurs, the ratio of the zero sequence impedance from the local side protection installation to the fault point to the zero sequence impedance of the line is multiplied by the full length of the line to obtain the distance from the fault point to the protection installation.

[0064] After judging that the line opposite side ground fault occurs, the ratio of the opposite side zero sequence impedance from the opposite side protection installation to the fault point to the zero sequence impedance of the line is multiplied by the full length of the line to obtain the distance from the fault point to the protection installation.

[0065] Specifically, after the line local side ground fault occurs, the distance l from the fault point to the line local side protection installation is calculated as follows: KM The calculation formula of the distance l from the fault point to the line opposite side protection installation after the line opposite side ground fault occurs is as follows:

[0066]

[0067] In the formula, l is the full length of the line.

[0068] The calculation formula of the distance l from the fault point to the line opposite side protection installation after the line opposite side ground fault occurs is as follows: KN The calculation formula of the distance l from the fault point to the line opposite side protection installation after the line opposite side ground fault occurs is as follows:

[0069]

[0070] In the present application, the zero sequence network of the line is constructed as shown in Figure 2 As shown in Figure 2 Whether it is single-phase grounding, two-phase short-circuit grounding or line breakage fault, the zero sequence component decomposition is applied, and the zero sequence network is the same, and according to the constructed zero sequence network, the following can be obtained:

[0071]

[0072] The above two formulas can be integrated as follows:

[0073]

[0074] Finally, the calculation formula of the local side zero sequence impedance from the local side protection installation to the fault point is obtained as follows:

[0075]

[0076] Of course, the construction process of the opposite side zero sequence impedance calculation formula from the opposite side protection installation to the fault point is the same as that of the local side zero sequence impedance calculation formula.

[0077] The application judges whether the line local side or opposite side ground fault occurs by calculating the local side and opposite side zero sequence impedance of the fault point from the protection device at the line two ends, and by comparing the local side and opposite side zero sequence impedance with the zero sequence impedance setting value.

[0078] The local side and opposite side zero sequence impedance calculation process proposed by the application is based on the zero sequence network decomposition when the line fault occurs, and the zero sequence network is the same for single-phase ground short circuit, two-phase ground short circuit, single-phase open circuit or two-phase open circuit fault, according to the positive sequence, negative sequence and zero sequence network decomposition. Therefore, the longitudinal zero sequence impedance calculation process based on the zero sequence network proposed by the application is more concise, and in practical application, it is more rapid and has wider applicability.

[0079] The longitudinal zero sequence impedance calculation process based on the zero sequence network proposed by the application does not satisfy the zero sequence impedance calculation starting criterion when the line local side and opposite side zero sequence current amplitudes do not satisfy the zero sequence impedance calculation starting criterion during normal operation, when the out-of-zone fault or reverse direction fault occurs, so the zero sequence impedance calculation starting criterion can prevent the further detection, which can effectively avoid the misoperation of the out-of-zone fault or reverse direction fault, and when the internal short circuit occurs, the longitudinal zero sequence impedance calculation can be reliably started. At the same time, compared with the "high resistance ground fault detection method based on the distributed parameter zero sequence impedance amplitude characteristic line", the protection action criterion proposed by the application is more simple and reliable, and the local side and opposite side zero sequence impedance calculation is based on the zero sequence voltage and zero sequence current on both sides of the line, and there is no risk of refusal to operate.

[0080] At the same time, the longitudinal zero sequence impedance calculation strategy based on the zero sequence network proposed by the application has no transition resistance in the calculation formula, and compared with the traditional distance impedance protection, it has no influence of transition resistance. And in step A1, based on the constructed alarm condition and corresponding alarm threshold, the data checking function is added, because at least two variables of the zero sequence voltage and zero sequence current on both sides of the line will change when the line fault occurs, and the data checking function prevents the calculation error caused by the abnormality of a single variable.

[0081] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the application, and it should be understood that the above description is only a specific embodiment of the application, and is not used to limit the protection scope of the application, and any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A method for line ground fault detection based on zero sequence network based pilot zero sequence impedance, characterized in that, The method comprises the following steps: Step A1: The protection device continuously monitors the zero sequence current value and the zero sequence voltage value at the line local protection installation and the zero sequence current value and the zero sequence voltage value at the line opposite protection installation, and checks. When the values of two or more variables trigger the corresponding alarm condition, the next step is entered. Step A2: A zero sequence impedance calculation starting criterion is constructed. When the difference between the zero sequence current amplitudes at the line local side and the line opposite side meets the zero sequence impedance calculation starting criterion, the next step is entered. Step A3: A zero sequence network of the line is constructed, and the zero sequence impedance from the line local protection installation and the line opposite protection installation to the fault point is calculated respectively. Step A4: A zero sequence impedance setting value is set. When the zero sequence impedance of any side is less than the zero sequence impedance setting value, the protection device judges that the ground fault occurs at the corresponding side of the line, and issues a trip command, otherwise, it is judged to be normal.

2. The method for line ground fault detection based on zero sequence network down pilot zero sequence impedance according to claim 1, characterized in that, In step A1, when only the value of one variable triggers the corresponding alarm condition, step A1 is continuously performed and an abnormal alarm of the corresponding variable is issued.

3. The method of claim 1 or 2, wherein the line ground fault detection method based on the zero sequence network down pilot zero sequence impedance is characterized by, In step A1, the alarm condition is that the value of the variable is greater than or equal to the corresponding alarm threshold value.

4. The method for line ground fault detection based on zero sequence network down pilot zero sequence impedance according to claim 1, characterized in that, In step A2, the expression of the constructed zero sequence impedance starting criterion is as follows: In the formula, represents the zero sequence current value at the installation of the line local protection, represents the zero sequence current value at the installation of the line opposite protection, represents the zero sequence current amplitude at the installation of the line local protection, represents the zero sequence current amplitude at the installation of the line opposite protection, and k represents a reliability coefficient.

5. The method of claim 4, wherein the line ground fault detection method is based on a zero sequence network down pilot zero sequence impedance. In the constructed zero sequence impedance starting criterion, k=0.

8.

6. The method for line ground fault detection based on zero sequence network down pilot zero sequence impedance according to claim 1, characterized in that, In step A2, the zero sequence impedance from the line local protection installation and the line opposite protection installation to the fault point is obtained by substituting the zero sequence voltage source into the longitudinal zero sequence impedance calculation formula.

7. The method of claim 6, wherein the line ground fault detection method is based on a zero sequence network down pilot zero sequence impedance. The calculation formula of the zero sequence impedance from the line local protection installation to the fault point is as follows: wherein Z 0l is the line zero sequence impedance, obtained before the line is put into operation, denotes the zero sequence current value at the installation of the local protection of the line, denotes the zero sequence voltage value at the installation of the local protection of the line, denotes the zero sequence current value at the installation of the remote protection of the line, denotes the zero sequence voltage value at the installation of the remote protection of the line. The opposite side zero sequence impedance calculation formula from the line opposite protection installation to the fault point is as follows:

8. The method for line ground fault detection based on zero sequence network down pilot zero sequence impedance according to claim 1, characterized in that, The method further comprises the following steps: After it is judged that the ground fault occurs at the line local side or the line opposite side, the distance from the fault point to the protection installation can be calculated based on the zero sequence impedance from the protection installation at the corresponding side of the line to the fault point.

9. The method of claim 8, wherein the line ground fault detection method is based on a zero sequence network down pilot zero sequence impedance. The distance from the fault point to the protection installation can be calculated based on the ratio of the zero sequence impedance from the protection installation at the line local side or the line opposite side to the fault point to the zero sequence impedance of the line, multiplied by the full length of the line.

10. The method of claim 8, wherein the line ground fault detection method is based on a zero sequence network down pilot zero sequence impedance. The calculation formula of the distance from the fault point to the line local protection installation is as follows: wherein, l is the total length of the line, Z 0l is the zero sequence impedance of the line, obtained before the line is put into operation, Z 0M is the zero sequence impedance of the line from the installation of the local protection to the fault point; The calculation formula of the distance from the fault point to the line opposite protection installation is as follows: wherein Z 0N is the zero sequence impedance from the line pair side of protection installation to the fault point.

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