Power distribution network fault line selection method and system based on zero-sequence active power regulation and control

Abstract

The invention discloses a power distribution network fault line selection method and system based on zero-sequence active power regulation and control, and aims to solve the problem of line selection failure caused by disorder of the zero-sequence active power direction of each feeder line when an unbalanced power distribution network has a high-resistance grounding fault. A flexible grounding device with four-quadrant operation capability is used for regulating and controlling the voltage of a neutral point of a system, the difference between non-fault feeder lines and fault feeder lines in a zero-sequence active direction discrimination angle is actively amplified, the influence of asymmetry of three-phase distribution parameters of a line is eliminated in principle, the technical bottleneck of a passive line selection method is broken through, and the line selection efficiency is improved. And accurate line selection of the unbalanced power distribution network high-resistance grounding fault is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of power protection, and in particular relates to a method and system for fault line selection in a distribution network based on zero-sequence active power regulation. Background Art

[0002] The structure of medium voltage distribution network is complex, the operating environment is changeable, and the line is very prone to single-phase grounding faults. In order to limit the grounding fault current, medium voltage distribution network generally adopts small current grounding method, mainly including ungrounded and grounding through arc suppression coil.

[0003] At present, the line selection for ground fault mainly includes two types: transient quantity line selection and steady-state quantity line selection. The line selection method based on transient quantity has a fast response speed and obvious fault characteristics under low-resistance fault conditions, but the transient process is short, the transient algorithm is cumbersome, and the collection and processing of fault transient information are required to be high. It is also easily affected by distribution line disturbances, transition resistance, asymmetry and other conditions. The steady-state line selection method has relatively low requirements for software and hardware and is easy to implement in engineering. Therefore, it is more suitable for the actual environment with many distribution network points. It mainly includes zero-sequence admittance method, fifth harmonic method, active and reactive direction method and other line selection methods. Among them, the steady-state active direction method is not affected by the compensation output of the arc suppression coil in principle, and has been widely used and developed in actual engineering. However, the existing steady-state zero-sequence active direction method still faces great challenges when applied to unbalanced power grids, especially when dealing with high-resistance ground faults. For example, some literature has proposed a zero-sequence active power line selection scheme to eliminate unbalanced current, but it still has certain limitations in the case of high-resistance grounding faults. The active power component is small in the case of high-resistance faults, making it difficult to extract reliably, and the actual application effect is difficult to guarantee; another literature has proposed a line selection method using a neutral point switching parallel resistor, which increases the active power component in the fault feeder to improve the line selection sensitivity, but ignores the influence of the asymmetric three-phase admittance to ground, and is only applicable to resonant grounding systems. It can be seen that the existing steady-state zero-sequence active power direction methods have their own scope of application, but for high-resistance grounding fault scenarios under asymmetric conditions, the accurate selection of the fault feeder still faces challenges and cannot be applied to both "unbalanced power grid" and "high-resistance fault" scenarios.

[0004] In addition, in the traditional zero-sequence active power method, when considering the asymmetry of the three-phase insulation parameters of the distribution network, especially in the case of high-resistance faults, the zero-sequence active direction of the feeder is prone to disorder, which leads to the limitations of the traditional zero-sequence active power method, making it difficult to accurately identify the fault line and achieve fault isolation. Summary of the invention

[0005] The purpose of the present invention is to solve the technical obstacle that the traditional zero-sequence active power cannot be used in the scenarios of "unbalanced power grid" and "high-resistance fault" at the same time, and to overcome the technical problem that the zero-sequence active power direction of the feeder in the traditional method is prone to disorder, thereby leading to the misjudgment of the non-fault feeder. To this end, the technical solution of the present invention provides a distribution network fault line selection method and system based on zero-sequence active power regulation. In order to eliminate the influence of the asymmetric parameters of the three phases to the ground of the system, a new zero-sequence active power direction discrimination angle is constructed. At this time, the zero-sequence active power direction discrimination angle on the non-fault feeder is always equal to the zero-sequence admittance angle, which is located in the first quadrant. The zero-sequence active power of the non-fault feeder flows from the bus to the line, and the direction is positive. At the same time, the constructed zero-sequence active power direction discrimination angle μ of the fault feeder f With transition resistance R f , multiple k and θ, so the present invention explores the zero-sequence active power direction discrimination angle μ of the fault feeder f With transition resistance R f , multiple k and θ, select the multiple k and the angle θ, and adjust the system neutral point voltage so that the zero-sequence active power direction of the faulty feeder is negative and the corresponding transition resistance interval increases until at least the preset size requirement is met (it can be adaptively adjusted according to the accuracy requirements and the effect to meet the corresponding application needs); thereby amplifying the difference between the faulty feeder and the non-faulty feeder, avoiding the situation where the zero-sequence active power direction of the feeder is prone to disorder, and meeting the scenario requirements of "unbalanced power grid" and "high-resistance fault".

[0006] To this end, the present invention provides the following technical solutions:

[0007] On the one hand, the present invention provides a method for fault line selection in a distribution network based on zero-sequence active power regulation, comprising the following steps:

[0008] Step 1: Select the multiple k and angle θ, and adjust the system neutral point voltage The zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval increases until the transition resistance interval at least meets the preset size requirement, U N is the neutral point voltage, For the system Phase supply potential, j is an imaginary unit, θ is the angle between the fault phase power supply potential and the zero-sequence voltage;

[0009] Among them, the characteristics of the constructed zero-sequence active power direction discrimination angle are: the zero-sequence active power direction discrimination angle on the non-fault feeder is located in the first quadrant, the zero-sequence active power of the non-fault feeder flows from the bus to the line, and the direction is positive; the zero-sequence active power direction discrimination angle μ of the fault feeder f With transition resistance R f , multiple k and angle θ;

[0010] Step 2: Calculate the zero-sequence active power direction discrimination angle μ of each feeder x And identify the faulty feeder, if |μ x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the faulty feeder.

[0011] Preferably, the zero-sequence active power direction discrimination angle μ of the non-fault feeder and the fault feeder is x The formula is as follows:

[0012]

[0013] In the formula, I bdx is the natural unbalanced current on feeder x; 3I 0x is the zero-sequence current on feeder x; when x is i, it represents the non-fault feeder i, and when x is f, it represents the fault feeder f.

[0014] Preferably, the zero-sequence active power direction discrimination angle μ of the non-fault feeder and the fault feeder is x The expansion of is as follows:

[0015]

[0016] In the formula, μ i is the zero-sequence active power direction discrimination angle of the non-fault feeder i, which is always equal to the zero-sequence admittance angle, g 0i is the leakage conductance of the non-fault feeder i to ground, ω is the power frequency angular frequency, C 0i is the capacitance to ground of the non-fault feeder i;

[0017]

[0018] In the formula, μ f is the zero-sequence active power direction determination angle of the fault feeder f, g 0f is the leakage conductance of the fault feeder f to ground, g f is the fault conductance of the faulted feeder f, C 0f is the capacitance of the fault feeder f to ground.

[0019] Preferably, the zero-sequence active power direction discrimination angle μ of the fault feeder in step 1 is f With resistor R f , multiple k and θ, the corresponding rules are as follows:

[0020] When θ∈[-90°, 90°], the direction of the zero-sequence active power of the faulty feeder is positive, flowing from the busbar to the feeder;

[0021] When θ∈[-180°, -90°)∪(90°, 180°], under the same multiple k, the larger |θ| is, the larger the transition resistance interval corresponding to the negative direction of the zero-sequence active power of the fault feeder is;

[0022] When θ∈[-180°, -90°)∪(90°, 180°], under the same |θ| value, as the multiple k decreases, the zero-sequence active power direction of the fault feeder is negative, and the corresponding transition resistance interval becomes larger;

[0023] Then, the multiple k and the angle θ are selected, and the neutral point voltage of the system is regulated so that the zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval increases.

[0024] Preferably, the value range of the multiple k is [0.1, 0.15], and the value range of the angle θ is [180°-30°, 180°+30°].

[0025] Preferably, the process of determining the value of the multiple k is:

[0026] First determine the value of the angle θ, and then calculate the zero-sequence active power direction discrimination angle μ of the fault feeder f f = k value function when ±90°;

[0027] Determine the multiple k and the transition resistance R based on the k value function f Function of

[0028] Furthermore, based on the set transition resistance R f Determine the multiple k.

[0029] Preferably, in step 1, a flexible grounding device with four-quadrant operation capability is used to control the neutral point voltage of the system, and the flexible grounding device adopts a voltage-type three-phase half-bridge controlled rectifier structure on the rectifier side;

[0030] Among them, when the regulated neutral point voltage is located in the 1st and 4th quadrants, the flexible grounding device emits active power and releases electric energy; when the regulated neutral point voltage is located in the 2nd and 3rd quadrants, the flexible grounding device absorbs the active power backflowed from the distribution network system and absorbs electric energy.

[0031] The technical solution of the present invention fully considers the control of the system neutral point voltage according to the idea of ​​step 1. When the difference between the non-fault feeder and the fault feeder is enlarged, the discrimination angle of the non-fault feeder is always in the first quadrant, while the discrimination angle of the fault feeder will be in the second and third quadrants, and the zero-sequence active power direction of the fault feeder is negative. If a traditional flexible grounding device with three-phase uncontrolled rectification on the rectifier side is used, it can only work in two quadrants, and the electric energy cannot be fed back, resulting in the active power transmitted by the rectification and system side being all supplied by the DC side capacitor C. dc During the period of active power backflow in the system, the instantaneous active power Pdc Greater than 0, and there is no energy-consuming component on the DC side of the flexible grounding device to C dc The active power is absorbed and consumed, so C dc Continuous charging will cause the energy stored in the capacitor to increase, which will have an adverse effect on the operation and regulation performance of the flexible grounding device. If the flexible grounding device is in this state for a long time, it is easy to cause the DC side voltage U dc Exceeding capacitance C dc The withstand voltage limit causes the capacitor C dc Breakdown, which in turn forces the device to actively lock out and exit operation, making it impossible to promptly and effectively handle the grounding fault, posing a major safety hazard and the risk of the grounding fault spreading and expanding.

[0032] To this end, based on the technical idea of ​​the technical solution of the present invention and taking full account of the backflow problem, it is preferred to use a flexible grounding device with a voltage-type three-phase half-bridge controlled rectifier structure on the rectifier side. By adopting appropriate pulse width modulation (PWM) rectifier control technology, it can not only play a regulatory role, but also achieve power backflow and absorb electric energy for stable operation.

[0033] In another aspect, the present invention provides a line selection device based on the above method, comprising:

[0034] Neutral point voltage control module, used to select multiple k and angle θ, and control the system neutral point voltage The zero-sequence active power direction of the fault feeder is made negative and the corresponding transition resistance interval increases until the transition resistance interval at least meets the preset size requirement;

[0035] The discrimination angle calculation module is used to calculate the zero-sequence active power direction discrimination angle μ of each feeder. x ;

[0036] A line selection module is used to use the zero-sequence active power direction to determine the angle μ x Identify the faulty feeder, if |μ x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the faulty feeder.

[0037] In a third aspect, the present invention provides a distribution network system, which is provided with the above-mentioned line selection device, wherein the neutral point voltage control module in the line selection device is a control circuit, and the control circuit is connected to the distribution network for controlling the neutral point voltage of the system.

[0038] In a fourth aspect, the present invention provides a computer-readable storage medium storing a computer program, wherein the computer program is called by a processor to execute:

[0039] Select the multiple k and the angle θ to generate a command to control the neutral point voltage of the system The zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval increases until the transition resistance interval at least meets the preset size requirement, U N is the neutral point voltage, For the system Phase supply potential, j is an imaginary unit, θ is the angle between the fault phase power supply potential and the zero-sequence voltage;

[0040] Calculate the zero-sequence active power direction discrimination angle μ of each feeder x And identify the faulty feeder, if |μ x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the fault feeder;

[0041] Send control instructions based on the identified faulty feeder to eliminate the impact of the fault;

[0042] Among them, the zero-sequence active power direction discrimination angle on the non-fault feeder is located in the first quadrant. The zero-sequence active power of the non-fault feeder flows from the bus to the line in a positive direction. The zero-sequence active power direction discrimination angle μ f With transition resistance R f , multiple k and θ.

[0043] Beneficial Effects

[0044] Compared with the existing method, the advantages of the present invention are:

[0045] 1. The technical solution of the present invention provides a brand-new technical means for fault line selection based on zero-sequence active power. In order to eliminate the influence of the asymmetric parameters of the three-phase system to the ground, a new zero-sequence active power direction discrimination angle is constructed. The new zero-sequence active power direction discrimination angle is significantly different between the non-fault feeder and the fault feeder, that is, the zero-sequence active power direction discrimination angle on the non-fault feeder is always equal to the zero-sequence admittance angle, which is located in the first quadrant. The zero-sequence active power of the non-fault feeder flows from the bus to the line in a positive direction; while the zero-sequence active power direction discrimination angle μ of the fault feeder is f With transition resistance R f , multiple k and θ. Therefore, the technical solution of the present invention proposes for the first time to select appropriate multiples k and θ so that the zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval is larger, thereby amplifying the difference between the fault feeder and the non-fault feeder and improving the line selection accuracy and reliability.

[0046] 2. The new zero-sequence active power direction discrimination angle proposed in the present invention is proposed to eliminate the influence of the asymmetry of the three-phase parameters of the system, and the technical solution can theoretically realize the fault line selection of the 20kΩ fault scenario. Therefore, it can meet the scenario requirements of "unbalanced power grid" and "high resistance fault" at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the process of the best embodiment of the present invention;

[0048] Figure 2 is the μ of the faulted feeder at different θ values f With R f , schematic diagram of the change of k; where (a), (b), (c), and (d) correspond to θ=-150°, θ=-135°, θ=120°, and θ=180° respectively;

[0049] Figure 3 This is a schematic diagram of the curve of k changing with transition resistance (μ k = ±90°);

[0050] Figure 4 This is a typical 10kV flexible grounding distribution network single-phase grounding fault simulation topology diagram;

[0051] Figure 5 It is a schematic diagram of the zero-sequence active power direction discrimination angle of the fault feeder under different transition resistances;

[0052] Figure 6 It is a structural diagram of a four-quadrant operating flexible grounding device. DETAILED DESCRIPTION

[0053] Aiming at the problem of line selection failure caused by disordered zero-sequence active power direction of each feeder when a high-resistance grounding fault occurs in an unbalanced distribution network, the technical solution of the present invention proposes a distribution network fault line selection method and system based on zero-sequence active power regulation, wherein, in order to eliminate the influence of asymmetric parameters of the three-phase to ground of the system, a new zero-sequence active power direction discrimination angle is constructed, so that the zero-sequence active power direction discrimination angle on the non-fault feeder is always equal to the zero-sequence admittance angle, and the zero-sequence active power of the non-fault feeder flows from the bus to the line in a positive direction; while the zero-sequence active power direction discrimination angle μ of the fault feeder is f With transition resistance R f , multiple k and θ, and then appropriate multiples k and θ are selected to make the zero-sequence active power direction of the faulty feeder negative and the corresponding transition resistance interval increase, thereby actively amplifying the difference in zero-sequence active power direction judgment angle between the non-fault and faulty feeders, and eliminating the influence of the asymmetry of the three-phase distribution parameters of the line in principle, breaking through the technical bottleneck of the passive line selection method, and realizing accurate line selection of high-resistance grounding faults in unbalanced distribution networks.

[0054] The present invention will be further described below with reference to the embodiments.

[0055] For non-fault feeders: when the asymmetry of feeder-to-ground parameters is large and under high-resistance grounding fault conditions, it is easy to cause the phase angle difference in the direction of non-fault feeders to be negative. For fault feeders: due to the influence of multiple factors such as transition resistance, asymmetry, grounding method, etc., the values ​​and intervals of these influencing factors are uncertain, resulting in the phase angle difference changing in any quadrant. Therefore, it is impossible to accurately select the fault line using the phase angle difference. The core of the technical solution of the present invention is to construct a new zero-sequence active power direction discrimination angle. Among them, in order to solve the problem that the traditional zero-sequence active power direction method is prone to failure under the condition of high-resistance grounding fault in unbalanced distribution network, eliminate the influence of the asymmetry of the three-phase-to-ground parameters of the system, and define the feeder x zero-sequence active power direction discrimination angle. Among them, the present invention fully considers that due to the influence of line asymmetry, natural unbalanced current will be generated on the feeder, so the natural unbalanced current can reflect the line asymmetry. For this reason, the present invention constructs the following zero-sequence active power direction discrimination angle. It effectively solves the problem that the traditional zero-sequence active power direction method is prone to failure under the condition of high-resistance grounding fault in unbalanced distribution network, eliminates the influence of the asymmetry of the three-phase-to-ground parameters of the system, and defines the feeder x zero-sequence active power direction discrimination angle. Among them, the present invention fully considers that due to the influence of line asymmetry, natural unbalanced current will be generated on the feeder, so the natural unbalanced current can reflect the line asymmetry. For this reason, the present invention constructs the following zero-sequence active power direction discrimination angle.

[0056] The expression is:

[0057]

[0058] Where: U N is the neutral point voltage, I bdx is the natural unbalanced current on feeder x, and there are many methods to accurately measure it. 0x is the zero-sequence current on feeder x.

[0059] Among them, when |μ x |<90°, the feeder zero-sequence active power flows from the bus to the line in a positive direction; when |μ x When |>90°, the feeder zero-sequence active power flows from the line to the busbar in a negative direction.

[0060] Table 1 Feeder zero-sequence active power direction and δ x Relationship

[0061]

[0062] According to formula (1), the zero-sequence active power direction discrimination angle μ of the non-fault feeder i can be obtained: i The expression is:

[0063]

[0064] In the formula, μ i is the zero-sequence active power direction discrimination angle of the non-fault feeder i, which is always equal to the zero-sequence admittance angle, g 0i is the leakage conductance of the non-fault feeder i to ground, ω is the power frequency angular frequency, C0i is the ground capacitance of the non-fault feeder i. From equation (2), we can see that the zero-sequence active power direction discrimination angle on the non-fault feeder is always equal to the zero-sequence admittance angle arg[g 0i +jωC 0i ], from the expression of its real and imaginary parts, it can be seen that it is always located in the first quadrant, and the feeder zero-sequence active power flows from the bus to the feeder in a positive direction.

[0065] Similarly, the zero-sequence active power direction discrimination angle μ on the fault feeder f is obtained f The expression is:

[0066]

[0067] In the formula, μ f is the zero-sequence active power direction determination angle of the fault feeder f, 3I 0f is the zero sequence current on the fault feeder f, g 0f is the leakage conductance of the fault feeder f to ground, g f is the fault conductance of the faulted feeder f, C 0f is the ground capacitance of the fault feeder f. From equation (3), we can see that the zero-sequence active power direction discrimination angle μ of the fault feeder is f Same as transition resistance R f , multiple k and θ.

[0068] The present invention aims to explore the zero-sequence active power direction discrimination angle μ of the fault feeder. f Same as transition resistance R f =1 / g f , multiples k and θ, the specific rules are analyzed as follows:

[0069] When θ∈[-90°, 90°], μ f The real part of the expression is always positive, that is, the discriminant angle μ f It is always located in the first and fourth quadrants, and the feeder zero-sequence active power flows from the bus to the feeder.

[0070] When θ∈[-180°, -90°)∪(90°, 180°], the direction of zero-sequence active power of the fault feeder is affected by R f and k, that is, under the same k value, the larger the |θ|, the larger the transition resistance interval corresponding to the negative zero-sequence active power direction of the fault feeder. Under the same |θ| value, as the k value decreases, the larger the transition resistance interval corresponding to the negative zero-sequence active power direction of the fault feeder.

[0071] The following example is used to illustrate that the leakage conductance of the fault feeder to ground is g 0f =3×10 -4 S, capacitance to ground C 0f =2.5×10 -5F, according to formula (3), the fault feeder μ under different θ values ​​can be obtained f With R f The changes of k are as follows Figure 2 In the figure, the dotted line indicates That is μ f =±90°.

[0072] Depend on Figure 2 It can be seen that for different θ values ​​(|θ|>90°), the discrimination angle μ f Absolute value and R f , k are negatively correlated, this is because as R f or the decrease of k, μ f The degree of reduction of the real part in the expression will increase, so the phase angle μ f The absolute value also increases, approaching 180°, making μ f From the first and fourth quadrants to the second and third quadrants. Figure 2 Analysis shows that the larger |θ| is, the smaller μ is under the same transition resistance. f = ±90° The larger the k value corresponding to the curve, the greater the increase in |θ| will also promote μ f The real part in the expression decreases, so the k value taken under the same zero-sequence active power direction discrimination angle is larger; at the same time, the larger |θ| is, the larger the transition resistance interval corresponding to the negative zero-sequence active power direction of the fault feeder is under the same k value.

[0073] In summary, under the same k value, the larger |θ| is, the larger the transition resistance interval corresponding to the negative zero-sequence active power direction of the fault feeder is; therefore, by reasonably selecting θ and k, the transition resistance interval corresponding to the negative zero-sequence active power direction of the fault feeder can be increased, meeting the requirements of amplifying the difference between the fault feeder and the non-fault feeder in the zero-sequence active direction and high resistance. It should be understood that the system neutral point voltage satisfies: U N is the neutral point voltage, For the system Phase supply potential, j is an imaginary unit, therefore, a reasonable selection of θ and k is regarded as regulating the neutral point voltage of the system. Therefore, the present invention derives the following conclusion: by reasonably selecting the neutral point voltage amplitude and phase (i.e., θ and k), the difference between the fault feeder and the non-fault feeder in the zero-sequence active direction can be amplified, ensuring that the zero-sequence active direction of the fault feeder is always negative within a larger transition resistance range, and maintaining a more obvious fault feature for easy acquisition.

[0074] In order to ensure that the proposed fault line selection method has a strong ability to withstand transition resistance and maintain obvious fault characteristics to improve line selection sensitivity, according to Figure 2 The conclusion is that we choose θref =180°, that is At this time, the neutral point voltage phase is opposite to the fault phase power supply potential phase. Therefore, the zero-sequence active power direction discrimination angle μ of the fault feeder in this state is further obtained: f = ±90°, the expression of k is:

[0075]

[0076] It should be understood that the derivation of the k-value function is a conventional technical means in the art, and therefore, its derivation process will not be described in detail.

[0077] According to the Technical Guidelines for Planning and Design of Distribution Networks (Q / GDW 10370-2016), the power supply radius of a 10kV distribution line is usually no more than 15km. At this time, it can be estimated that the capacitance current of a single cable line is no more than 20A. Given that the damping rate of a distribution line is generally 2% to 5%, the leakage conductance g of the fault line to ground can be obtained. 0f ≤1.73×10 -4 S. Considering the worst case, when g 0f =1.73×10 -4 S, we get μ f = ±90° k varies with transition resistance R f The change curve of Figure 3 shown.

[0078] according to Figure 3 It can be seen that as the k value decreases, the larger the transition resistance interval corresponding to the negative direction of the zero-sequence active power of the faulty feeder (strong ability to withstand transition resistance, even in a high-resistance state, the correct line selection can be achieved). Among them, when k=0.15, it can theoretically ensure that the zero-sequence active power direction of the feeder is always negative when a ground fault occurs below a transition resistance of 32.76kΩ, and the ability to withstand transition resistance is strong. However, due to the influence of factors such as the detection accuracy of the transformer and line interference, it is not possible to achieve a high resistance resistance of 32.76kΩ in practice, but it can basically maintain a relatively high level of high resistance resistance. And under this k value, the system zero-sequence voltage can reach about 0.9kV, which is sufficient to maintain a more obvious fault feature, so as to reliably obtain the zero-sequence active power direction of each feeder in the system and realize accurate identification of the ground fault feeder. Therefore, the best embodiment of the present invention proposes to select k ref =0.15, and then the neutral point voltage control value is

[0079] It should be understood that the above are the values ​​of the best embodiment of the present invention, that is, k is 0.15, θ is 180°, corresponding to Figure 1is a flow chart of the best embodiment; in other feasible embodiments, the value range of the multiple k is [0.1, 0.15], and the value range of θ is [180°-30°, 180°+30°]. And the preferred value selection process of the multiple k is:

[0080] First determine the value of θ, and then calculate the zero-sequence active power direction discrimination angle μ of the fault feeder f f = k value function when ±90°;

[0081] Determine the k value and transition resistance R based on the k value function f Function of

[0082] Furthermore, based on the set transition resistance R f Determine the value of k.

[0083] Based on the above theoretical analysis, an embodiment of the present invention provides a method for fault line selection in a distribution network based on zero-sequence active power regulation, comprising the following steps:

[0084] Step 1: Select the multiple k and angle θ to control the system neutral point voltage The zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval is larger, which meets the preset size requirement. This embodiment preferably uses the four-quadrant operation flexible grounding device to control the zero-sequence voltage of the system to be

[0085] In view of the fact that the existing flexible grounding device can only operate in two quadrants, in order to prevent the device from being locked out of operation due to the system backflow of active power to the device side during the neutral point voltage regulation process, affecting the execution of the line selection program, it is preferred to use the four-quadrant operation of the flexible grounding device to regulate the system zero-sequence voltage, such as Figure 6 As shown in the figure, I sa ,I sb ,I sc is the three-phase current on the rectifier input side, U sa , U sb , U scis the three-phase power supply potential on the rectifier input side, L is the filter inductance on the rectifier input side, and R is the equivalent resistance of the filter inductance L. It is preferred that the four-quadrant operation flexible grounding device adopts a voltage-type three-phase half-bridge controlled rectifier structure on the rectifier side, replacing the original three-phase uncontrolled rectifier structure. Although it will increase the cost of the device and the complexity of control, it adopts a suitable pulse width modulation (PWM) rectifier control technology. According to various distribution network grounding fault conditions and operating conditions, the four-quadrant operation flexible grounding device is put into operation to regulate the system neutral point voltage, and the relationship between the neutral point voltage and the neutral point injection current is obtained as follows: when the regulated neutral point voltage is in the 1st and 4th quadrants, the flexible grounding device emits active power and releases electric energy; when the regulated neutral point voltage is in the 2nd and 3rd quadrants, the flexible grounding device absorbs the active power backflow of the distribution network system and absorbs electric energy.

[0086] Therefore, the technical solution of the present invention preferably uses a four-quadrant operating flexible grounding device, which can absorb electric energy and ensure the smooth operation of the distribution network system even if power backflow occurs when the neutral point voltage is regulated.

[0087] Step 2: Calculate the zero-sequence active power direction discrimination angle μ of each feeder x And identify the faulty feeder, if |μ x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the faulty feeder.

[0088] The embodiment measures the zero-sequence active power direction discrimination angle of each feeder in the system (the zero-sequence active power direction discrimination angle μ of each feeder is calculated according to formula (1) x ) to obtain the zero-sequence active power direction of each feeder; then the faulty feeder is identified according to the difference between the zero-sequence active power directions of the non-faulty and faulty feeders, and the feeder with a negative zero-sequence active power direction is determined to be the faulty feeder, otherwise, it is determined to be the non-faulty feeder.

[0089] simulation:

[0090] In order to verify the effectiveness of the proposed method for high-resistance fault line selection in distribution network based on active regulation of zero-sequence active power, a simulation model was constructed using PSCAD / EMTDC software. Figure 4 The typical 10kV flexible grounding distribution network single-phase grounding fault model is shown in Table 2. Table 2 shows the system feeder simulation parameters. When the arc suppression coil is grounded, the overcompensation degree is 10%, and the system feeder simulation parameters are shown in Table 2. bd1 =0.400∠-156.38°, I bd2 =0.339∠90.44°, I bd3 =1.001∠-121.60°, E cThe phase is equal to 30°.

[0091] Table 2 System feeder simulation parameters

[0092]

[0093] After determining that a permanent ground fault has occurred, according to the proposed line selection method, the system is set to put the four-quadrant flexible grounding device into operation at 0.25s, and adjust the neutral point voltage U N =-0.15E c , further measure the zero-sequence current on each feeder, and use formula (1) to calculate the zero-sequence active direction discrimination angle on each feeder, and obtain the measurement data of each feeder of the system and the fault feeder judgment results under different transition resistance faults under the proposed method as shown in Table 3.

[0094] Table 3 Measurement data of each feeder in the system and the results of fault feeder determination under the proposed line selection method

[0095]

[0096]

[0097] It can be seen from Table 2 that for different grounding fault conditions, the proposed line selection method can completely eliminate the influence of the asymmetry of the three-phase-to-ground parameters, forcing the zero-sequence active power direction discrimination angle on the non-fault feeder to be always equal to the zero-sequence admittance angle of the feeder, and the zero-sequence active power direction is positive; while the zero-sequence active power direction discrimination angle of the fault feeder is negatively correlated with the transition resistance. As the transition resistance increases, its direction discrimination angle will decrease towards the zero-sequence admittance angle of the fault feeder, such as Figure 4 shown.

[0098] Combined with the data in Table 3, it can be seen that this method can still maintain the zero-sequence active power discrimination angle of the fault feeder at a larger value, greater than 90°, when a 5000Ω high-resistance grounding fault occurs, forcing the zero-sequence active power direction of the fault feeder to be negative. Therefore, the proposed method can reliably realize the accurate discrimination and selection of the fault feeder in the unbalanced distribution network based on the difference in the zero-sequence active direction discrimination angle between the non-fault feeder and the fault feeder.

[0099] In addition, the present invention provides a line selection device based on the above method, including: a neutral point voltage control module, a discrimination angle calculation module and a line selection module.

[0100] Among them, the neutral point voltage control module is used to select the multiple k and the angle θ to control the system neutral point voltage The zero-sequence active power direction of the faulty feeder is negative and the corresponding transition resistance interval is larger, which meets the preset size requirements; the discrimination angle calculation module is used to calculate the zero-sequence active power direction discrimination angle μ of each feeder x ; The line selection module is used to use the zero-sequence active power direction to determine the angle μ xIdentify the faulty feeder, if |μ x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the faulty feeder.

[0101] It should be understood that the specific implementation process of each module refers to the above method content, and the present invention will not be repeated here, and the division of the above functional modules is only for example. In some embodiments, some functional modules can be combined, some functional modules can be split, and each functional module can be implemented in software or hardware or a combination of software and hardware. Among them, the software and hardware equipment includes but is not limited to general-purpose computer equipment, programmable gate arrays, digital signal processors, microprocessors and their corresponding programming or burning software. In some embodiments, the neutral point voltage control module is a four-quadrant operation flexible grounding device.

[0102] In some embodiments, a distribution network system provided by the present invention is provided with the above-mentioned line selection device, and the neutral point voltage control module in the line selection device is a control circuit, which is connected to the distribution network and is used to control the neutral point voltage of the system.

[0103] In some embodiments, the present invention provides a computer-readable storage medium storing a computer program, wherein the computer program is called by a processor to execute:

[0104] Select the multiple k and the angle θ to generate a command to control the neutral point voltage of the system The zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval is larger, meeting the preset size requirement;

[0105] Calculate the zero-sequence active power direction discrimination angle μx of each feeder and identify the faulty feeder. x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the fault feeder;

[0106] Send control instructions based on the identified faulty feeder to eliminate the impact of the fault;

[0107] Among them, the zero-sequence active power direction discrimination angle on the non-fault feeder is located in the first quadrant. The zero-sequence active power of the non-fault feeder flows from the bus to the line in a positive direction. The zero-sequence active power direction discrimination angle μ f With transition resistance R f , multiple k and θ.

[0108] For the specific implementation process of each step, please refer to the description of the above method.

[0109] The readable storage medium is a computer-readable storage medium, which may be an internal storage unit of the software and hardware device described in any of the aforementioned embodiments, such as a hard disk or memory of a controller. The readable storage medium may also be an external storage device of the controller, such as a plug-in hard disk, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. equipped on the controller. Furthermore, the readable storage medium may also include both an internal storage unit of the controller and an external storage device. The readable storage medium is used to store the computer program and other programs and data required by the controller. The readable storage medium may also be used to temporarily store data that has been output or is to be output.

[0110] Based on this understanding, the technical solution of the present invention, in essence or in other words, the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned readable storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., various media that can store program codes.

[0111] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-readable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The present application is a device for realizing the function specified in one flow or multiple flows of the flow chart and / or one or multiple blocks of the block diagram with reference to the instructions executed by the processor according to the method, device (system) and computer program product of the embodiment of the present application. These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device, which realizes the function specified in one flow or multiple flows of the flow chart and / or one or multiple blocks of the block diagram. These computer program instructions may also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0112] It should be emphasized that the examples described in the present invention are illustrative rather than restrictive, and therefore the present invention is not limited to the examples described in the specific embodiments. Any other embodiments derived by those skilled in the art based on the technical solution of the present invention that do not depart from the purpose and scope of the present invention, whether modified or replaced, also fall within the scope of protection of the present invention.

Claims

1. A method for fault line selection in a distribution network based on zero-sequence active power regulation, characterized in that: The following steps are involved: Step 1: Select the multiple k and angle θ, and adjust the system neutral point voltage The zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval increases until the transition resistance interval at least meets the preset size requirement, U N is the neutral point voltage, For the system Phase supply potential, j is an imaginary unit, and the angle θ is the angle between the fault phase power supply potential and the zero-sequence voltage; Among them, the characteristics of the constructed zero-sequence active power direction discrimination angle are: the zero-sequence active power direction discrimination angle on the non-fault feeder is located in the first quadrant, the zero-sequence active power of the non-fault feeder flows from the bus to the line, and the direction is positive; the zero-sequence active power direction discrimination angle μ of the fault feeder f With transition resistance R f , multiple k and angle θ; Step 2: Calculate the zero-sequence active power direction discrimination angle μ of each feeder x And identify the faulty feeder, if |μ x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the faulty feeder.

2. The method according to claim 1, characterized in that: Zero-sequence active power direction discrimination angle μ of non-fault feeder and fault feeder x The formula is as follows: In the formula, I bdx is the natural unbalanced current on feeder x; 3I 0x is the zero-sequence current on feeder x; when x is i, it represents the non-fault feeder i, and when x is f, it represents the fault feeder f.

3. The method according to claim 2, characterized in that: Zero-sequence active power direction discrimination angle μ of non-fault feeder and fault feeder x The expansion of is as follows: In the formula, μ i is the zero-sequence active power direction discrimination angle of the non-fault feeder i, which is always equal to the zero-sequence admittance angle, g 0i is the leakage conductance of the non-fault feeder i to ground, ω is the power frequency angular frequency, C 0i is the capacitance to ground of the non-fault feeder i; In the formula, μ f is the zero-sequence active power direction determination angle of the fault feeder f, g 0f is the leakage conductance of the fault feeder f to ground, g f is the fault conductance of the faulted feeder f, C 0f is the capacitance of the fault feeder f to ground.

4. The method according to claim 1, characterized in that: The zero-sequence active power direction discrimination angle μ of the fault feeder in step 1 f With resistor R f , multiple k and θ, the corresponding rules are as follows: When θ∈[-90°,90°], the direction of the zero-sequence active power of the faulty feeder is positive, flowing from the busbar to the feeder; When θ∈[-180°,-90°)∪(90°,180°], under the same multiple k, the larger |θ| is, the larger the transition resistance interval corresponding to the negative direction of the zero-sequence active power of the fault feeder is; When θ∈[-180°,-90°)∪(90°,180°], under the same θ value, as the multiple k decreases, the direction of the zero-sequence active power of the fault feeder is negative, and the corresponding transition resistance interval becomes larger; Then, the multiple k and the angle θ are selected, and the neutral point voltage of the system is regulated so that the zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval increases.

5. The method according to claim 4, characterized in that: The value range of the multiple k is [0.1, 0.15], and the value range of the angle θ is [180°-30°, 180°+30°].

6. The method according to claim 4, characterized in that: The process of determining the value of multiple k is: First determine the value of the angle θ, and then calculate the zero-sequence active power direction discrimination angle μ of the fault feeder f f = k value function when ±90°; Determine the multiple k and the transition resistance R based on the k value function f Function of Furthermore, based on the set transition resistance R f Determine the multiple k.

7. The method according to claim 1, characterized in that: In step 1, a flexible grounding device with four-quadrant operation capability is used to control the neutral point voltage of the system, wherein the flexible grounding device adopts a voltage-type three-phase half-bridge controlled rectifier structure on the rectifier side; Among them, when the regulated neutral point voltage is located in the 1st and 4th quadrants, the flexible grounding device emits active power and releases electric energy; when the regulated neutral point voltage is located in the 2nd and 3rd quadrants, the flexible grounding device absorbs the active power backflowed from the distribution network system and absorbs electric energy.

8. A line selection device based on the method according to any one of claims 1 to 7, characterized in that: include: Neutral point voltage control module, used to select multiple k and angle θ, and control the system neutral point voltage The zero-sequence active power direction of the fault feeder is made negative and the corresponding transition resistance interval increases until the transition resistance interval at least meets the preset size requirement; The discrimination angle calculation module is used to calculate the zero-sequence active power direction discrimination angle μ of each feeder. x ; A line selection module is used to use the zero-sequence active power direction to determine the angle μ x Identify the faulty feeder, if |μ x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the faulty feeder.

9. A power distribution network system, characterized in that: A line selection device according to claim 8 is provided, wherein the neutral point voltage control module in the line selection device is a control circuit, and the control circuit is connected to the distribution network to control the neutral point voltage of the system.

10. A computer-readable storage medium, characterized in that: A computer program is stored, which is called by a processor to execute: Select the multiple k and the angle θ to generate a command to control the neutral point voltage of the system The zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance interval increases until the transition resistance interval at least meets the preset size requirement, U N is the neutral point voltage, For the system Phase supply potential, j is an imaginary unit, θ is the angle between the fault phase power supply potential and the zero-sequence voltage; Calculate the zero-sequence active power direction discrimination angle μ of each feeder x And identify the faulty feeder, if |μ x |≤90°, the corresponding feeder x is a sound feeder; otherwise, |μ x |>90°, the corresponding feeder x is the fault feeder; Send control instructions based on the identified faulty feeder to eliminate the impact of the fault; Among them, the zero-sequence active power direction discrimination angle on the non-fault feeder is located in the first quadrant. The zero-sequence active power of the non-fault feeder flows from the bus to the line in a positive direction. The zero-sequence active power direction discrimination angle μ f With transition resistance R f , multiple k and θ.

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