A single-end based adaptive protection method for distribution network with distributed power supply

Abstract

The application relates to the field of power system relay protection, in particular to a self-adaptive protection method for a distribution network containing distributed power sources based on single-end data, which comprises the following steps: collecting bus voltage and feeder outlet current of the distribution network; calculating output parameters of the distributed power sources on the feeder under each fault type, and calculating setting impedance of the self-adaptive protection under each fault; judging whether to start the self-adaptive protection according to whether the instantaneous value of the line current power frequency variation is greater than a set threshold value, and starting the protection if the instantaneous value is greater than the set threshold value; judging the fault type and the fault phase of the distribution network, and calculating the measured impedance, the additional impedance angle and the fault impedance under each fault; judging whether the absolute values of the real part and the imaginary part of the fault impedance under the fault are less than or equal to the real part and the imaginary part of the setting value corresponding to the fault; and tripping the circuit breaker if the absolute values are less than or equal to the setting value. The application is not influenced by factors such as short-circuit transient resistance, fault position and system operation mode, and has the advantages of fast speed, good reliability, strong adaptability and independence from communication.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection, specifically to an adaptive protection method for distribution networks with distributed generation based on single-ended quantities. Background Technology

[0002] As traditional power generation methods increasingly consume and pollute environmental resources, new energy power generation, as a less polluting and highly renewable method, is gaining increasing attention. Distributed generation, in particular, is widely integrated into distribution networks due to its simple structure and convenient installation. However, due to the influence of inverter control strategies, distributed generation often exhibits characteristics such as weak feedback and controlled current phase, leading to the risk of failure in relay protection systems in the distribution network, such as adaptive current protection and differential current protection.

[0003] Currently, researchers are studying relay protection for distribution networks containing distributed generation (DG) sources, primarily including adaptive current protection based on DG equivalent models and iterative algorithms, and differential current protection for distribution networks based on multiple criteria. However, these protection methods suffer from drawbacks such as high protection delay and reliance on device communication. Compared to existing protection methods, distance protection calculates and measures impedance and compares it with the protection setting impedance to achieve fault location and protection output functions, offering advantages such as fast response speed and independence from system operating modes. However, distance protection in distribution networks with DG integration suffers from poor resistance to transition resistance and branch coefficient failure. To address these issues, some scholars have improved the calculation formula for distance protection branch coefficients based on composite sequence networks. While this method enhances the reliability of distance protection, it requires acquiring the fault current output by the DG, resulting in high costs and limited practicality. Other scholars have proposed a distance protection fault location method based on the sine theorem, which can accurately calculate the fault location on the feeder, but it is not applicable to distribution networks with multiple DG sources, lacking practical engineering applicability.

[0004] In summary, due to the weak feed and phase-controlled characteristics of distributed generation (DG), existing distribution network protection systems often fail, easily resulting in maloperation or failure to operate. Current DG-based distribution network protection systems suffer from high costs, overly idealized application scenarios, and limited applicability; therefore, no effective protection method for DG-based distribution networks is yet available. Consequently, developing a highly sensitive, reliable, and economical protection method for DG-based distribution networks has become a pressing issue for those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention proposes an adaptive protection method for distribution networks with distributed generation based on single-ended quantities, which specifically includes the following steps:

[0006] S1. Collect the voltage of the distribution network bus and the current output of each feeder;

[0007] S2. Calculate the output parameters of the distributed power supply on the feeder under each fault type, and calculate the setting impedance of the adaptive protection under each fault.

[0008] S3. Determine whether to enable adaptive protection based on whether the instantaneous value of the line current power frequency change is greater than the set threshold. If it is greater, enable protection; otherwise, return to step S1.

[0009] S4. If the protection is activated, determine the fault type and fault phase of the distribution network, and calculate the measured impedance, additional impedance angle and fault impedance for each fault.

[0010] S5. Determine whether the absolute values ​​of the real and imaginary parts of the fault impedance under the fault are both less than or equal to the real and imaginary parts of the setting value corresponding to the fault calculated in step S2.

[0011] S6. If yes, the circuit breaker trips and disconnects the faulty feeder; otherwise, return to step S1.

[0012] Furthermore, the process of calculating the output parameters of the distributed power source on the feeder under each fault type includes:

[0013] S21. The positive sequence voltage of the i-th distributed power source grid connection point under normal operating conditions. and positive sequence current Let k = 1 as the initial value for the iteration;

[0014] S22. In the k-th iteration, for the i-th distributed power source, if the equivalent output current of the power source is... Establish composite sequence networks for the distribution network when single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit occur at the end of the power supply feeder. Solve for the positive sequence voltage of the (k+1)th generation distributed generation grid connection point when single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit occur using composite sequence networks.

[0015] S23. Using the positive sequence voltage of the grid connection point of the (k+1)th generation distributed power source, calculate the positive sequence output current of the (k+1)th generation distributed power source.

[0016] S24. Determine whether the iteration has converged based on the positive sequence voltage amplitudes of the distributed power source grid connection point in the k-th and k+1-th iterations. If converged, output the grid connection point voltage of the distributed power source in the k+1-th iteration. and the output current of distributed power sources

[0017] S25. If the convergence is not achieved, let k = k + 1 and return to step S22.

[0018] Furthermore, the calculation of the adaptive protection setting impedance under various fault conditions includes:

[0019]

[0020] Among them, Z zd Z is the set impedance; L is the line impedance of the feeder; n is the number of distributed power sources on the feeder. Let be the current output by the i-th distributed power source; Let m be the current output by the m-th distributed power source; The feeder output current measured by the protection device; Z setDGi This represents the impedance at position i. When i = 0, it represents the line impedance between the protection installation point and the first distributed power source grid connection point. When i = 1, 2, ..., n-1, it represents the line impedance between the i-th distributed power source and the (i+1)-th distributed power source grid connection point. When i = n, ...

[0021] Furthermore, the process of determining the type and phase of a distribution network fault includes:

[0022] like and Then it is determined that a ground fault has occurred;

[0023] When the fault type is a ground fault, if the following conditions are met... Then it is determined that a ground fault has occurred at point O, and this is taken as the first fault type;

[0024] When the fault type is a ground fault, if the following conditions are met... Then it is determined that a ground fault has occurred between phase o and phase p, and this is regarded as the second fault type;

[0025] like and Then it is determined that a non-grounding fault has occurred;

[0026] When the fault type is a non-grounded fault, and the three phases o, p, and q satisfy the following conditions: There is a short circuit between phase o and phase p, which is considered the third type of fault.

[0027] If the fault type is a non-grounding fault and does not meet the conditions for a two-phase short circuit fault, then a three-phase short circuit fault is determined to have occurred, and this is regarded as the fourth fault type.

[0028] in, These are the phase current amplitudes at the feeder outlets for phase 0, phase 1, and phase 2, respectively. ε1 represents the negative sequence current amplitude at the feeder outlet, and ε2 represents the negative sequence threshold value. ε0 is the zero-sequence current amplitude at the feeder outlet, and ε0 is the zero-sequence threshold value. This represents the fault component of the zero-phase current at the feeder outlet. This refers to the fault component of the p-phase current at the feeder outlet. q represents the fault component of the phase current at the feeder outlet, and k′ is the reliability coefficient.

[0029] Furthermore, when the first type of fault occurs, i.e., if a ground fault occurs at q, the measured impedance is expressed as:

[0030]

[0031] When the first type of fault occurs, the additional impedance angle is expressed as:

[0032]

[0033] in, This represents the voltage phasor of phase q of the busbar as measured by the protection system. Let q be the phasor of the phase current at the feeder outlet. is the zero-sequence current phasor at the feeder outlet, and k0 is the zero-sequence compensation coefficient.

[0034] Furthermore, when the second type of fault occurs, i.e., a ground fault occurs between phase p and phase q, the measured impedance is expressed as:

[0035]

[0036] When the second type of fault occurs, the additional impedance angle is expressed as:

[0037]

[0038] in, This represents the voltage phasor of phase p of the busbar as measured by the protection system. The p-phase current phasor at the feeder outlet; This represents the voltage phasor of phase q of the busbar as measured by the protection system. Let q be the phasor of the phase current at the feeder outlet; This is the zero-sequence current phasor at the feeder outlet. This is the negative sequence current phasor at the feeder outlet.

[0039] Furthermore, if a third type of fault occurs, namely a short circuit between phase p and phase q, the measured impedance is expressed as:

[0040]

[0041] If a third type of fault occurs, the additional impedance angle is expressed as:

[0042]

[0043] Furthermore, if a fourth type of fault occurs, namely a three-phase short circuit, the measured impedance is expressed as:

[0044]

[0045] If the fourth type of fault occurs, the additional impedance angle is expressed as:

[0046]

[0047] Furthermore, the fault impedance is calculated based on the measured impedance and the additional impedance angle for each fault type, including:

[0048]

[0049]

[0050]

[0051] Among them, Z f For fault impedance, Z m To measure impedance, The phase angle for setting the impedance. For the additional impedance angle, The phase angle for measuring impedance.

[0052] Furthermore, in step S5, when determining that the circuit breaker has tripped, the following conditions must be met:

[0053] |ReZ f |≤|ReZ zd |and|ImZ f |≤|ImZ zd |

[0054] Where Re represents the real part of the complex number and Im represents the imaginary part of the complex number.

[0055] Current research on relay protection for distribution networks with distributed generation (DG) mainly includes adaptive current protection based on DG equivalent models and iterative algorithms, and differential current protection for distribution networks based on multiple criteria. However, these protection methods suffer from drawbacks such as high protection delay and reliance on device communication. Compared with existing protection methods, distance protection calculates and compares measured impedance with protection setting impedance to achieve fault location and protection output functions, offering advantages such as fast response speed and insensitivity to system operation. However, distance protection for distribution networks with DG integration suffers from poor resistance to transition resistance and branch coefficient failure. To address these issues, some scholars have improved the calculation formula for distance protection branch coefficients based on composite sequence networks. While this method enhances the reliability of distance protection, it requires the acquisition of fault current output from the DG, resulting in high cost and limited practicality. Other scholars have proposed a distance protection fault location method based on the sine theorem, which can accurately calculate the fault location on the feeder, but it is not applicable to situations where multiple DGs are connected to the distribution network, lacking practical engineering applicability. Compared with existing technologies, this invention has the following beneficial effects:

[0056] 1. This invention uses the output parameters of the distributed power source during normal operation as the initial values ​​for iteration, and uses an iterative algorithm to calculate the grid connection point voltage and output current of the distributed power source under various fault types. While conforming to the actual operation of the distribution network, it avoids the situation of relying on the communication system to obtain the fault parameters of the distributed power source, and reduces the configuration cost and complexity of protection.

[0057] 2. Based on the traditional distribution network protection setting impedance, this invention incorporates the feeder line impedance affected by the output current of distributed generation into the protection setting impedance, so that the additional impedance only includes the transition impedance and its branch coefficient, avoiding the incalculability of additional impedance due to the uncertainty of the fault location, and improving the accuracy of the adaptive protection setting impedance.

[0058] 3. Based on the negative sequence and zero sequence paths of multi-feeder distribution networks under fault conditions, this invention uses the negative sequence and zero sequence currents at the feeder outlet to be equivalent to the negative sequence and zero sequence currents flowing through the transition resistor. While ensuring calculation accuracy, it solves the problem that the current flowing through the transition resistor cannot be measured, and greatly simplifies the calculation complexity of the additional impedance angle.

[0059] 4. This invention utilizes the impedance triangle formed by the measured impedance, the additional impedance, and the fault impedance to propose a fault impedance calculation method based on the triangle sine theorem. By using only single-ended quantities and set values, the influence of the additional impedance on the measured impedance is eliminated, and a fault impedance reflecting the actual fault condition is obtained. This fault impedance is then compared with the set impedance to achieve action judgment, significantly improving the reliability of adaptive protection.

[0060] 5. The implementation method of this invention is clear. It only requires collecting the bus voltage and feeder outlet current of the distribution network, and calculating the adaptive protection setting impedance under single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit conditions through an iterative algorithm. Based on the sine theorem, the influence of additional impedance on the measured impedance is eliminated to obtain the fault impedance and complete the protection action determination. The overall scheme is easy to implement and has strong economic efficiency and practicality. Attached Figure Description

[0061] Figure 1 This is a flowchart of the adaptive protection method for distribution networks with distributed power sources based on single-ended quantities disclosed in this invention;

[0062] Figure 2 This is a diagram of the power distribution network topology in an embodiment of the present invention;

[0063] Figure 3 This is a comparison of the fault impedance and the set impedance during a single-phase ground fault in an embodiment of the present invention.

[0064] Figure 4 This is a comparison of the fault impedance and the set impedance in a two-phase ground fault embodiment of the present invention.

[0065] Figure 5 This is a comparison of the fault impedance and the set impedance during a two-phase short-circuit fault in an embodiment of the present invention.

[0066] Figure 6 This is a comparison of the fault impedance and the set impedance during a three-phase short-circuit fault in an embodiment of the present invention. Detailed Implementation

[0067] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] This invention proposes an adaptive protection method for distribution networks with distributed generation based on single-ended quantities, specifically including the following steps:

[0069] S1. Collect the voltage of the distribution network bus and the current output of each feeder;

[0070] S2. Calculate the output parameters of the distributed power supply on the feeder under each fault type, and calculate the setting impedance of the adaptive protection under each fault.

[0071] S3. Determine whether to enable adaptive protection based on whether the instantaneous value of the line current power frequency change is greater than the set threshold. If it is greater, enable protection; otherwise, return to step S1.

[0072] S4. If the protection is activated, determine the fault type and fault phase of the distribution network, and calculate the measured impedance, additional impedance angle and fault impedance for each fault.

[0073] S5. Determine whether the absolute values ​​of the real and imaginary parts of the fault impedance under the fault are both less than or equal to the real and imaginary parts of the setting value corresponding to the fault calculated in step S2.

[0074] S6. If yes, the circuit breaker trips and disconnects the faulty feeder; otherwise, return to step S1.

[0075] To address the shortcomings of existing technologies, the practical problems this invention aims to solve are: how to determine the grid connection point voltage and output current of distributed power sources under various fault types without relying on the device's communication function; how to adaptively modify the protection setting impedance of the distribution network to eliminate the interference of the uncertainty of the fault location on the protection setting; how to calculate the additional impedance angle under various fault conditions using bus voltage and feeder current; how to use the collected and calculated parameters to eliminate the additional impedance caused by weak feeder and phase-controlled characteristics and its influence on the measured impedance, so as to obtain the fault impedance reflecting the actual fault location; and how to design appropriate protection action criteria to achieve reliable operation of adaptive protection.

[0076] like Figure 1 As shown in this embodiment, an adaptive protection method for a distribution network with distributed generation based on single-ended quantities includes the following steps:

[0077] S101: Collects the bus voltage and feeder output current of the distribution network;

[0078] S102: Based on the feeder outlet current and bus voltage, calculate the grid connection point voltage and output current of the distributed power source on the feeder under single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit conditions respectively;

[0079] S103: Calculate the setting impedance of adaptive protection under single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit conditions in the distribution network, respectively.

[0080] S104: Determine whether adaptive protection is started. If protection is started, proceed to step S105; otherwise, proceed to step S101.

[0081] S105: Determine the type and phase of a fault in the distribution network;

[0082] S106: Calculate the measurement impedance using bus voltage and feeder current;

[0083] S107: Calculate the additional impedance angle using bus voltage, feeder current, and measured impedance;

[0084] S108: Calculate the fault impedance using the set impedance, measured impedance, and additional impedance angle;

[0085] S109: Determine whether the action criteria are met based on the fault impedance and the set impedance. If they are met, it is determined that a fault has occurred in the protected feeder, and a trip or alarm signal is issued. Otherwise, it is determined that the fault is located outside the protected feeder, and the process returns to S101.

[0086] In this embodiment of the invention, based on the bus voltage and feeder outlet current of the distribution network, an iterative algorithm is used to calculate the adaptive protection setting impedance under single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit conditions, respectively. The influence of additional impedance on the measured impedance is eliminated based on the sine law to obtain the fault impedance, thus completing the protection action determination. This invention can accurately determine whether a short-circuit fault has occurred on the protected feeder and perform corresponding protection actions, ensuring the safe and stable operation of the distribution network.

[0087] In specific implementation, the distribution network topology adopted is as follows: Figure 2 As shown. The upstream grid voltage is 110kV, with an equivalent impedance of 0.05 + 0.0044jΩ. The distribution network bus voltage is 10kV. The transformer uses an arc suppression coil and is grounded with a resistor. The lengths of feeders L1, L2, and L3 are 20km, 40km, and 10km, respectively, with an impedance per unit length of 0.58-6.58jΩ / km. Load LD1 has a capacity of 2MVA and a power factor of 0.672; load LD2 has a capacity of 5MVA and a power factor of 0.826; load LD3 has a capacity of 3MVA and a power factor of 0.741; load LD4 has a capacity of 2MVA and a power factor of 0.729; and load LD5 has a capacity of 2MVA and a power factor of 0.815. The reference values ​​for active and reactive power of all distributed power sources connected to feeder L2 during normal operation are 0.866MW and 0.5Mvar, respectively. On feeder L2, a single-phase ground fault, a two-phase ground fault, a two-phase short circuit fault, and a three-phase short circuit fault are set to occur at 0.1 seconds, and each fault lasts for 0.1 seconds.

[0088] In specific implementation, step S102 involves calculating the grid connection point voltage and output current of the distributed power source under various fault types using an iterative algorithm, specifically including the following steps:

[0089] Step S201: Use the positive sequence voltage and positive sequence current at the grid connection point of the distributed power source under normal operating conditions as the initial values ​​for iteration. and i represents the i-th distributed power source.

[0090] Step S202, convert the distributed power source into an equivalent output current of The current source is used to establish a composite sequence network of the distribution network when single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit occur at the end of the feeder, respectively. The positive sequence voltage of the k+1 generation distributed generation grid connection point is solved by the composite sequence network when single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit occur. Where k is the iteration number, k = 0, 1, 2, ..., k = 0 represents the initial iteration value, that is, in this embodiment, the positive sequence voltage and positive sequence current of the distributed power source grid connection point under normal operating conditions are used as the initial iteration values. and Iterations can be carried out based on this.

[0091] Step S203: Using the positive sequence voltage of the (k+1)th generation distributed power source grid connection point, calculate the positive sequence current output of the (k+1)th generation distributed power source according to the following formula:

[0092]

[0093] in, Let be the complex power command value for the i-th distributed power source. It outputs positive sequence current for the (k+1)th generation of distributed power source.

[0094] Step S204: Determine whether the (k+1)th iteration has converged according to the following formula:

[0095]

[0096] In the formula, Let ε be the positive sequence voltage amplitude at the grid connection point of the distributed power source in the kth and k+1th generations, and ε be the threshold value for iterative convergence.

[0097] Step S205: If the (k+1)th generation converges, then stop the iteration. The grid connection point voltage of the distributed power source can be calculated as follows: The output current of the distributed power source is If the (k+1)th generation does not converge, then set k = k+1 and return to step S202.

[0098] In specific implementation, in step S103, the setting impedance of the adaptive protection under single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit conditions in the distribution network is calculated as follows:

[0099]

[0100] In the formula, n is the number of distributed power sources on the feeder, and Z zd For the set impedance, Z L The line impedance of the feeder. The feeder output current measured by the protection device, Z represents the output current of the i-th and m-th distributed power sources.setDGi Let i be the impedance at position i, expressed as:

[0101]

[0102] when Figure 2 When a single-phase grounding, two-phase grounding, two-phase short circuit, or three-phase short circuit fault occurs on the distribution network feeder L2 shown, the set impedance calculated in step S103 is shown in Table 1.

[0103] Table 1 Setting impedance under various fault types

[0104]

[0105] In specific implementation, in step S104, the protection startup adopts the line current mutation startup criterion, the specific form of which is as follows:

[0106]

[0107] Where, ΔI zd The starting setpoint for the sudden change in line current; ΔI T It is a floating threshold that automatically adjusts itself gradually as the output changes. The instantaneous value of the line current frequency change can be calculated using the following formula:

[0108]

[0109]

[0110]

[0111] in, These are the instantaneous values ​​of the line current between any two phases (including between phase A and phase B, phase C and phase A, and phase B and phase C) at time t, tT, and t-2T, respectively. These are the effective values ​​of the line current between any two phases at times tT, t-2T, and t-3T, respectively; T is the period, which is 20ms in this embodiment, and t is the time when the fault occurs.

[0112] In specific implementation, step S105 determines the fault type based on the magnitude of the negative-sequence and zero-sequence currents at the feeder outlet. The ground fault criterion is as follows:

[0113] and

[0114] In the formula, ε0 is the zero-sequence current amplitude at the feeder outlet; ε0 is the threshold value corresponding to the zero-sequence current. ε1 represents the negative sequence current amplitude at the feeder outlet; ε2 represents the threshold value corresponding to the negative sequence current.

[0115] The criterion for non-grounding faults is:

[0116] and

[0117] In specific implementation, in step S105, the faulty phase is determined based on the magnitude of the phase current at the feeder outlet.

[0118] When a ground fault occurs, it is necessary to determine whether it is a single-phase ground fault or a two-phase ground fault. In this embodiment, if a ground fault occurs in phase 0, the phase selection criterion for a single-phase ground fault in a three-phase power system is as follows:

[0119]

[0120] in, These are the phase current amplitudes at the feeder outlets of phase o, phase p, and phase q, respectively.

[0121] Specifically, when a phase A ground fault occurs:

[0122]

[0123] In the formula, This represents the amplitude of phase A current at the feeder outlet. This represents the amplitude of the B-phase current at the feeder outlet. The magnitude of the C-phase current at the feeder outlet; k sg Let k′ be the phase coefficient for a single-phase ground fault, taken as 3. sg The coefficient for the non-faulty phase of a single-phase grounding fault is set to 0.2.

[0124] When a phase B ground fault occurs:

[0125]

[0126] When a C-phase ground fault occurs:

[0127]

[0128] In a three-phase power system, if a ground fault occurs between any two phases, assuming a ground fault occurs between phase o and phase p, the following condition holds:

[0129]

[0130] Specifically, if a two-phase ground fault occurs between phases A and B in a three-phase power system, the following conditions must be met:

[0131]

[0132] In the formula, k dg The phase coefficient for a two-phase ground fault is 3; k′ dg This is the coefficient for the non-faulty phase of the two-phase grounding system, and its value is 0.2.

[0133] When a fault occurs between phases B and C, the following condition must be met:

[0134]

[0135] When a fault occurs between phase C and phase A, the following conditions must be met:

[0136]

[0137] When an ungrounded fault occurs, it is necessary to determine whether it is a two-phase short-circuit fault or a three-phase short-circuit fault. In this embodiment, if a short-circuit fault occurs between any two phases in a three-phase power system, the following condition must be met:

[0138]

[0139] in, This represents the fault component of the zero-phase current at the feeder outlet. This refers to the fault component of the p-phase current at the feeder outlet. This represents the fault component of the q-phase current at the feeder outlet.

[0140] Specifically, if a two-phase short-circuit fault occurs between phases A and B, the following conditions must be met:

[0141]

[0142] In the formula, These represent the fault components of phase A, B, and C currents at the feeder outlet. k′ is the reliability coefficient, typically taken as 2.

[0143] If a two-phase short-circuit fault occurs between phases B and C, the following conditions must be met:

[0144]

[0145] If a two-phase short-circuit fault occurs between phase C and phase A, the following conditions must be met:

[0146]

[0147] When the current at the feeder outlet meets the non-grounding fault criterion but not the above three two-phase short circuit phase selection criteria, a three-phase short circuit fault is determined to have occurred on the feeder.

[0148] In specific implementation, in step S106, when calculating the measurement impedance of a single-phase ground fault, it is assumed that a ground fault occurs at phase q, and the measurement impedance is expressed as:

[0149]

[0150] in, This represents the voltage phasor of phase q of the busbar as measured by the protection system. q is the phasor of the q-phase current at the feeder outlet, and k0 is the zero-sequence compensation coefficient; q phase is any one of phases A, B, and C in a three-phase power system.

[0151] Specifically, if a fault occurs in phase A of a three-phase power system, the measured impedance is expressed as:

[0152]

[0153] In the formula, Z m To measure impedance, To protect the measured phase A voltage phasor of the busbar, Let A be the phase current phasor at the feeder outlet. Here, k is the zero-sequence current phasor at the feeder outlet, and k0 is the zero-sequence compensation coefficient, calculated using the following formula:

[0154]

[0155] In the formula, Z1 and Z0 are the positive sequence impedance and zero sequence impedance per unit length of the feeder.

[0156] Similarly, the measured impedance when a single-phase ground fault occurs in phase B is:

[0157]

[0158] In the formula, To protect the measured bus phase B voltage phasor, This is the B-phase current phasor at the feeder outlet.

[0159] Similarly, the measured impedance when a single-phase ground fault occurs in phase C is:

[0160]

[0161] In the formula, To protect the measured C-phase voltage phasor of the busbar, This is the C-phase current phasor at the feeder outlet.

[0162] In this embodiment, if a ground fault occurs between phase p and phase q, the measured impedance is expressed as:

[0163]

[0164] in, This represents the voltage phasor of phase p of the busbar as measured by the protection system. q is the p-phase current phasor at the feeder outlet; both q and p are any one of phases A, B, and C in a three-phase power system, and q and p are not the same phase.

[0165] Specifically, the measured impedance when phase A and phase B in a three-phase power system are short-circuited to ground is:

[0166]

[0167] Similarly, the measured impedance when phases B and C are short-circuited to ground is:

[0168]

[0169] Similarly, the measured impedance when phase C and phase A are short-circuited to ground is:

[0170]

[0171] When calculating the measured impedance of a two-phase short-circuit fault, assuming a short circuit occurs between phase p and phase q, the measured impedance is expressed as:

[0172]

[0173] In this context, phase q and phase p are any one of phases A, B, and C in a three-phase power system, and phase q and phase p are not the same phase.

[0174] Specifically, if a two-phase short circuit occurs between phases A and B in a three-phase power system, the measured impedance is:

[0175]

[0176] Similarly, the measured impedance when there is a short circuit between phases B and C is:

[0177]

[0178] Similarly, the measured impedance when there is a short circuit between phase C and phase A is:

[0179]

[0180] If a three-phase short circuit occurs in a three-phase power system, when calculating the measured impedance, it is only necessary to calculate the measured resistance between any two phases. The measured impedance is calculated as follows:

[0181]

[0182] Specifically, this embodiment takes the calculation of phase A and phase C in a three-phase power system as an example, and the measured impedance is expressed as:

[0183]

[0184] In specific implementation, in step S107, if a single-phase ground fault occurs, that is, if a ground fault occurs between phases q, the additional impedance angle is expressed as:

[0185]

[0186] Specifically, the additional impedance angle when phase A of a three-phase power system is grounded is expressed as:

[0187]

[0188] In the formula, For the additional impedance angle, This represents the A-phase current at the feeder outlet. denoted as zero-sequence current at the feeder outlet, and k0 as the zero-sequence compensation coefficient.

[0189] Similarly, the additional impedance angle when phase B is grounded is expressed as:

[0190]

[0191] In the formula, This represents the B-phase current at the feeder outlet.

[0192] Similarly, the additional impedance angle when phase C is grounded is expressed as:

[0193]

[0194] In the formula, This represents the C-phase current at the feeder outlet.

[0195] If a ground fault occurs between phase p and phase q, the measured impedance is expressed as:

[0196]

[0197] Specifically, the additional impedance angle during a short circuit to ground between phases A and B in a three-phase power system is expressed as:

[0198]

[0199] In the formula, This is the negative sequence current at the feeder outlet.

[0200] Similarly, the additional impedance angle when phases B and C are short-circuited to ground is expressed as:

[0201]

[0202] Similarly, the additional impedance angle when phase C and phase A are short-circuited to ground is expressed as:

[0203]

[0204] If a short circuit occurs between phase p and phase q, the additional impedance angle is expressed as:

[0205]

[0206] Specifically, if a short circuit occurs between phase A and phase B in a three-phase power system, the additional impedance angle is expressed as:

[0207]

[0208] Similarly, the additional impedance angle during a short circuit between phases B and C is expressed as:

[0209]

[0210] Similarly, the additional impedance angle during a short circuit between phase C and phase A is expressed as:

[0211]

[0212] If a three-phase short-circuit fault occurs in a three-phase power system, the additional impedance angle is calculated as follows:

[0213]

[0214] In specific implementation, the fault impedance in step S108 is calculated as follows:

[0215]

[0216] In the formula, Z f For fault impedance, Z m To measure impedance, The phase angle for setting the impedance, where j represents the imaginary unit; The calculation method is as follows:

[0217]

[0218] In the formula, For the additional impedance angle, The calculation method is as follows:

[0219]

[0220] In the formula, The phase angle for measuring impedance.

[0221] when Figure 2 When a single-phase grounding, two-phase grounding, two-phase short circuit, or three-phase short circuit fault occurs on the distribution network feeder L2 shown, the fault impedance calculated in step S108 is shown in Table 2.

[0222] Table 2 Fault impedance under various fault types

[0223]

[0224]

[0225] In specific implementation, the protection action criterion in step S109 is as follows:

[0226] |ReZ f |≤|ReZ zd |and|ImZ f |≤|ImZ zd |

[0227] In the formula, Re represents the real part of the complex number, Im represents the imaginary part of the complex number; Z f For fault impedance, Z zd This is the set impedance.

[0228] when Figure 2 When a single-phase ground fault, a two-phase ground fault, a two-phase short circuit, or a three-phase short circuit occurs on the distribution network feeder L2, the comparison results between the fault impedance and the set impedance in step S109 are as follows:

[0229] The comparison results of single-phase ground faults are as follows: Figure 3 As shown; the comparison results of two-phase ground faults are as follows. Figure 4 As shown; the comparison results of two-phase short-circuit faults are as follows. Figure 5 As shown; the comparison results of three-phase short-circuit faults are as follows. Figure 6 As shown.

[0230] Figure 3 , Figure 4 , Figure 5 , Figure 6 This indicates that when a single-phase grounding, two-phase grounding, two-phase short circuit, or three-phase short circuit fault occurs on feeder L2, the adaptive protection method proposed in this invention can correctly determine whether a short circuit fault has occurred on the protected feeder, and then activate the circuit breaker to trip, promptly disconnecting the faulty feeder and ensuring the safe and stable operation of the distribution network.

[0231] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, which may include ROM, RAM, disk, or optical disk, etc.

[0232] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An adaptive protection method for distribution networks with distributed generation based on single-ended quantities, characterized in that, Specifically, the following steps are included: S1. Collect the voltage of the distribution network bus and the current output of each feeder; S2. Calculate the output parameters of the distributed power supply on the feeder under each fault type, and calculate the setting impedance of the adaptive protection under each fault. S3. Determine whether to enable adaptive protection based on whether the instantaneous value of the line current power frequency change is greater than the set threshold. If it is greater, enable protection; otherwise, return to step S1. S4. If the protection is activated, determine the fault type and fault phase in the distribution network. The process of determining the fault type and fault phase in the distribution network includes: like If so, it is determined that a ground fault has occurred; When the fault type is a ground fault, if the following conditions are met... If so, it is determined that a ground fault has occurred at point O, and this is taken as the first fault type; When the fault type is a ground fault, if the following conditions are met... If so, it is determined that a ground fault has occurred between phase o and phase p, and this is regarded as the second fault type; like If so, it is determined that a non-grounding fault has occurred; When the fault type is a non-grounded fault, and the three phases o, p, and q satisfy the following conditions: If a short circuit exists between phase o and phase p, this is considered the third type of fault. If the fault type is a non-grounding fault and does not meet the conditions for a two-phase short circuit fault, then a three-phase short circuit fault is determined to have occurred, and this is regarded as the fourth fault type. in, , , These are the phase current amplitudes at the feeder outlets for phase 0, phase 1, and phase 2, respectively. This represents the negative sequence current amplitude at the feeder outlet. The threshold value is negative. This represents the zero-sequence current amplitude at the feeder outlet. This is the zero-order threshold value; This refers to the fault component of the zero-phase current at the feeder outlet. This refers to the fault component of the p-phase current at the feeder outlet. This represents the fault component of the q-phase current at the feeder outlet. The reliability coefficient; The phase coefficient for a single-phase ground fault; For single-phase grounding non-fault phases; The phase coefficient for a two-phase ground fault; For the non-faulty phases of a two-phase ground fault; And calculate the measured impedance, additional impedance angle, and fault impedance for each fault type, including: in, For fault impedance, To measure impedance, The phase angle for setting the impedance. For the additional impedance angle, The phase angle for measuring impedance; S5. Determine whether the absolute values ​​of the real and imaginary parts of the fault impedance under the fault are both less than or equal to the real and imaginary parts of the setting value corresponding to the fault calculated in step S2. S6. If yes, the circuit breaker trips and disconnects the faulty feeder; otherwise, return to step S1.

2. The adaptive protection method for a distribution network with distributed power sources based on single-ended quantities according to claim 1, characterized in that, The process of calculating the output parameters of the distributed generation on the feeder under various fault types includes: S21. The positive sequence voltage of the i-th distributed power source grid connection point under normal operating conditions. and positive sequence current Let k=1 as the initial value for the iteration; S22. In the k-th iteration, for the i-th distributed power source, if the equivalent output current of the power source is... A composite sequence network is established for the distribution network when single-phase grounding, two-phase short circuit, two-phase grounding, and three-phase short circuit occur at the end of the power supply feeder. The positive sequence voltage of the (k+1)th generation distributed power supply grid connection point is then calculated using the composite sequence network for these scenarios. ; S23. Using the positive sequence voltage of the grid connection point of the (k+1)th generation distributed power source, calculate the positive sequence output current of the (k+1)th generation distributed power source. S24. Determine whether the iteration has converged based on the positive sequence voltage amplitudes of the distributed power source grid connection point in the k-th and k+1-th iterations. If converged, output the grid connection point voltage of the distributed power source in the k+1-th iteration. and the output current of distributed power sources ; S25. If the convergence is not achieved, let k = k + 1 and return to step S22.

3. The adaptive protection method for a distribution network with distributed power sources based on single-ended quantities according to claim 1, characterized in that, The calculation of the adaptive protection setting impedance under various fault conditions includes: in, For setting impedance; is the line impedance of the feeder; n is the number of distributed power sources on the feeder. Let be the current output by the i-th distributed power source; Let m be the current output by the m-th distributed power source; The feeder output current measured by the protection device; This represents the impedance at position i. When i=0, it represents the line impedance between the protection installation point and the first distributed power source grid connection point. When, it represents the line impedance between the i-th distributed power source and the (i+1)-th distributed power source grid connection point. hour, .

4. The adaptive protection method for a distribution network with distributed power sources based on single-ended quantities according to claim 1, characterized in that, When the first type of fault occurs, i.e., if a ground fault occurs at q, the measured impedance is expressed as: When the first type of fault occurs, the additional impedance angle is expressed as: in, This represents the voltage phasor of phase q of the busbar as measured by the protection system. Let q be the phasor of the phase current at the feeder outlet. This is the zero-sequence current phasor at the feeder outlet. It is the zero-order compensation coefficient.

5. The adaptive protection method for a distribution network with distributed power sources based on single-ended quantities according to claim 1, characterized in that, When the second type of fault occurs, i.e., a ground fault occurs between phase p and phase q, the measured impedance is expressed as: When the second type of fault occurs, the additional impedance angle is expressed as: in, This represents the voltage phasor of phase p of the busbar as measured by the protection system. This represents the voltage phasor of phase q of the busbar as measured by the protection system. The p-phase current phasor at the feeder outlet; Let q be the phasor of the phase current at the feeder outlet. This is the zero-sequence current phasor at the feeder outlet. This is the negative sequence current phasor at the feeder outlet.

6. The adaptive protection method for a distribution network with distributed power sources based on single-ended quantities according to claim 1, characterized in that, If a third type of fault occurs, namely a short circuit between phase p and phase q, the measured impedance is expressed as: If a third type of fault occurs, the additional impedance angle is expressed as: in, This represents the voltage phasor of phase p of the busbar as measured by the protection system. This represents the voltage phasor of phase q of the busbar as measured by the protection system. The p-phase current phasor at the feeder outlet; Let q be the phasor of the phase current at the feeder outlet. This is the negative sequence current phasor at the feeder outlet.

7. The adaptive protection method for a distribution network with distributed power sources based on single-ended quantities according to claim 1, characterized in that, If the fourth type of fault occurs, namely a three-phase short circuit, the measured impedance is expressed as: If the fourth type of fault occurs, the additional impedance angle is expressed as: in, This represents the voltage phasor of phase p of the busbar as measured by the protection system. This represents the voltage phasor of phase q of the busbar as measured by the protection system. The p-phase current phasor at the feeder outlet; Let q be the phasor of the phase current at the feeder outlet.

8. The adaptive protection method for a distribution network with distributed power sources based on single-ended quantities according to claim 1, characterized in that, When determining whether the circuit breaker has tripped in step S5, the following conditions must be met: in, Represents the real part of a complex number. Represent the imaginary part of a complex number; For fault impedance, This is the set impedance.

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