A method and system for fault line selection in distribution network based on zero-sequence active power regulation

Abstract

The present invention discloses a distribution network fault line selection method and system based on zero-sequence active power regulation. In order to solve the problem of line selection failure caused by the disorder of the 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 constructs a line zero-sequence active power direction discrimination angle equation, utilizes a flexible grounding device with four-quadrant operation capability to regulate the system neutral point voltage, and actively amplifies the difference in zero-sequence active power direction discrimination angle between non-fault and fault feeders. In principle, the influence of the asymmetry of the three-phase distribution parameters of the line is eliminated, breaking through the technical bottleneck of the passive line selection method, and realizing accurate line selection for high-resistance grounding faults in unbalanced distribution networks.

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] Medium-voltage distribution networks are complex and operate in a volatile environment, making single-phase ground faults highly likely to occur. To limit ground fault currents, medium-voltage distribution networks generally employ low-current grounding methods, primarily ungrounded and grounded via arc suppression coils.

[0003] Currently, ground fault line selection primarily involves transient and steady-state methods. Transient-based methods offer fast response times and more distinct fault characteristics for low-resistance faults. However, these methods require shorter transients, more complex transient algorithms, and require high-level acquisition and processing of transient fault information. Furthermore, they are susceptible to significant impacts from distribution line disturbances, transition resistance, and asymmetry. Steady-state methods, on the other hand, require less hardware and software, are easier to implement, and are therefore more suitable for the diverse and diverse distribution network environments. These methods primarily include the zero-sequence admittance method, the fifth harmonic method, and the active and reactive power direction method. The steady-state active power direction method, in principle, is unaffected by the arc suppression coil compensation output and has been widely used and developed in practical applications. However, existing steady-state zero-sequence active power direction methods still face significant challenges when applied to unbalanced power grids, particularly when addressing high-resistance ground faults. For example, some literature has proposed a zero-sequence active power selection scheme to eliminate unbalanced currents, but it still has certain limitations in high-resistance ground faults. The active power component in high-resistance faults is small, making it difficult to reliably extract and ensuring practical application effectiveness. Other literature has proposed a line selection method using a neutral point switching parallel resistor to increase the active power component in the fault feeder to improve line selection sensitivity, but it ignores the impact of three-phase-to-ground admittance asymmetry and is only applicable to resonant grounded systems. As can be seen, existing steady-state zero-sequence active power direction methods have their own scope of application. However, for high-resistance ground fault scenarios under asymmetric conditions, accurate fault feeder selection remains challenging and cannot be applied to both "unbalanced 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 power 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 easily disordered, 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 asymmetry of the three-phase-to-ground parameters 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 easily disordered, 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 is 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 fault 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.

[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] Where, 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] Where 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 ground leakage conductance of the non-fault feeder i, ω is the power frequency angular frequency, C 0i is the capacitance to ground of the non-fault feeder i;

[0017]

[0018] Where μ f is the zero-sequence active power direction discrimination 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 fault 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 direction of the zero-sequence active power 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 to adjust the system neutral point voltage so that the zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance range is increased.

[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;

[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 expanded, 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. The zero-sequence active power direction of the fault feeder is negative. If a traditional flexible grounding device with three-phase uncontrolled rectification is used on the rectifier side, it can only operate in two quadrants and 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. dc The absorbed active power is 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 forces the device to actively lock and exit operation, making it impossible to handle the grounding fault in a timely and effective manner, posing a major safety hazard and the risk of the grounding fault spreading and expanding.

[0032] To this end, based on the technical ideas 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, absorb electrical energy and operate stably.

[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 the 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 is increased 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] Line selection module, 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 fault 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 system neutral point voltage.

[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 the 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 fault 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 fault impact;

[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, and the direction is positive. The zero-sequence active power direction discrimination angle μ of the fault feeder is 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 new technical means for fault line selection based on zero-sequence active power. In order to eliminate the influence of the asymmetry of the three-phase-to-ground parameters of the system, 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 and is located in the first quadrant. The zero-sequence active power of the non-fault feeder flows from the busbar 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-to-ground parameters of the system, and this technical solution can theoretically realize the fault line selection in the 20kΩ fault scenario. Therefore, it can simultaneously meet the scenario requirements of "unbalanced power grid" and "high-resistance fault". 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 μ of the fault feeder at different θ values f With R f , schematic diagram of the change of k; among them, (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 This 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 the disorder of the 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. In order to eliminate the influence of the asymmetry of the three-phase-to-ground parameters 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. The zero-sequence active power of the non-fault feeder flows from the busbar 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 fault 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 fault feeders, 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: under the condition of large asymmetry of feeder-to-ground parameters and high-resistance grounding fault, it is easy to cause the phase angle difference of the non-fault feeder direction 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 easy to fail 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 easy to fail 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 When |<90°, the feeder zero-sequence active power flows from the busbar 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] Where 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 ground leakage conductance of the non-fault feeder i, ω is the power frequency angular frequency, C0i is the ground capacitance of the non-fault feeder i. From formula (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] Where μ f is the zero-sequence active power direction discrimination 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 formula (3), we can know 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 The influence of |θ| and k is that, under the same k value, the larger the |θ|, the larger the transition resistance interval corresponding to the negative direction of the zero-sequence active power of the faulted feeder. Under the same |θ| value, as the k value decreases, the larger the transition resistance interval corresponding to the negative direction of the zero-sequence active power of the faulted feeder.

[0071] The following example illustrates that the leakage conductance to ground on the fault feeder is g 0f =3×10 -4 S, capacitance to ground C 0f =2.5×10 -5According to formula (3), the μ of the fault feeder 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 f = The larger the k value corresponding to the ±90° curve, the greater the value of |θ|. This is because 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 range corresponding to the negative zero-sequence active power direction of the fault feeder is. Therefore, by reasonably selecting θ and k, the transition resistance range corresponding to the negative zero-sequence active power direction of the fault feeder can be increased, meeting the requirements of amplifying the difference in zero-sequence active power direction between the fault feeder and the non-fault feeder 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, properly selecting θ and k can be considered as regulating the system neutral point voltage. Therefore, the present invention derives the following conclusion: By properly selecting the neutral point voltage amplitude and phase (i.e., θ and k), the difference in zero-sequence active power between the faulty feeder and the non-faulty feeder can be amplified, ensuring that the zero-sequence active power of the faulty feeder is always negative within a large transition resistance range, while maintaining a relatively clear fault signature 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 more obvious fault characteristics to improve the 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 this field, 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. In this case, it can be estimated that the capacitive 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. Consider the worst case, when g 0f =1.73×10 -4 When S, we get μ f = ±90°k 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 range corresponding to the negative direction of the zero-sequence active power of the fault feeder (the ability to withstand transition resistance is strong, and the correct line selection can be achieved even in a high-resistance state). 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 mutual inductor 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 high resistance resistance level. 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 values ​​are 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 process of determining the value 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;

[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] Since 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 backflow of active power from the system to the device side during the neutral point voltage control process, affecting the execution of the line selection program, it is preferred to use the four-quadrant operation of the flexible grounding device to control 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 inductor L. The preferred four-quadrant flexible grounding device uses a voltage-type three-phase half-bridge controlled rectifier structure on the rectifier side, replacing the original three-phase uncontrolled rectifier structure. Although this increases the device cost and control complexity, it can be improved by adopting appropriate pulse width modulation (PWM) rectifier control technology. For various distribution network grounding fault conditions and operating conditions, the four-quadrant flexible grounding device is put into operation to regulate the system neutral point voltage. The relationship between the neutral point voltage and the neutral point injection current is as follows: when the regulated neutral point voltage is within the 1st and 4th quadrants, the flexible grounding device generates active power and releases electrical energy; when the regulated neutral point voltage is within the 2nd and 3rd quadrants, the flexible grounding device absorbs the active power backflow from the distribution network system and absorbs electrical 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 during the regulation of the neutral point voltage.

[0087] Step 2: Calculate the zero-sequence active power direction discrimination angle μ of each feeder x And identify the fault 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.

[0088] In this embodiment, the zero-sequence active power direction discrimination angle of each feeder of the measurement system is calculated according to formula (1): x ) to obtain the zero-sequence active power direction of each feeder; then the faulty feeder is identified based on the difference between the zero-sequence active power directions on the non-fault 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 selecting high-resistance fault lines in distribution networks 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. The system feeder simulation parameters are shown in Table 2. When the arc suppression coil is grounded, the overcompensation degree is 10%. The simulation parameters of each feeder in the system 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 enter the four-quadrant operation flexible grounding device at 0.25s, and the neutral point voltage U is regulated. 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. The measurement data of each feeder in the system and the fault feeder judgment results under different transition resistance faults under the proposed method are shown in Table 3.

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

[0095]

[0096]

[0097] As shown in Table 2, for different ground 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 direction of the zero-sequence active power 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 closer to the zero-sequence admittance angle of the fault feeder, such as Figure 4 shown.

[0098] Combined with the data in Table 3, we can see that this method can maintain the zero-sequence active power discrimination angle of the faulted feeder at a large value, greater than 90°, even in the case of a 5000Ω high-resistance ground fault, forcing the zero-sequence active power direction of the faulted feeder to be negative. Therefore, the proposed method can reliably and accurately identify and select the faulty feeder in an unbalanced distribution network based on the difference in the zero-sequence active power direction discrimination angle between the non-faulty feeder and the faulty 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 fault 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 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 fault feeder.

[0101] It should be understood that the specific implementation process of each module is described in the above method and will not be further elaborated herein. The above functional module division is merely illustrative; in some embodiments, some functional modules may be combined or separated. Each functional module may be implemented in software, hardware, or a combination of software and hardware. Such hardware and software devices include, but are not limited to, general-purpose computers, 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 flexible grounding device.

[0102] In some embodiments, the present invention provides a distribution network system, which 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 system neutral point voltage.

[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 the 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 requirements;

[0105] Calculate the zero-sequence active power direction discrimination angle μx of each feeder and identify the fault 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;

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

[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, and the direction is positive. The zero-sequence active power direction discrimination angle μ of the fault feeder is 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 can 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 can also be an external storage device of the controller, such as a plug-in hard disk equipped on the controller, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), etc. Furthermore, the readable storage medium can 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 can 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, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned readable storage medium includes various media that can store program code, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[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 code. The present application is a flow chart according to the method, device (system), and computer program product of the embodiment of the present application and / or the instructions executed by the processor to generate a device for realizing the function specified in one flow chart or multiple flows and / or one box or multiple boxes of the block diagram. 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 generate a product comprising an instruction device, which realizes the function specified in one flow chart or multiple flows and / or one box or multiple boxes 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. 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 by: 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 is 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 fault 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.

2. The method according to claim 1, wherein: Zero-sequence active power direction discrimination angle μ of non-fault feeder and fault feeder x The formula is as follows: Where, 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; when x is f, it represents the fault feeder f.

3. The method according to claim 2, wherein: Zero-sequence active power direction discrimination angle μ of non-fault feeder and fault feeder x The expansion of is as follows: Where 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 ground leakage conductance of the non-fault feeder i, ω is the power frequency angular frequency, C 0i is the capacitance to ground of the non-fault feeder i; Where μ f is the zero-sequence active power direction discrimination 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, wherein: 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 fault 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 to adjust the system neutral point voltage so that the zero-sequence active power direction of the fault feeder is negative and the corresponding transition resistance range is increased.

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 the 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; Furthermore, based on the set transition resistance R f Determine the multiple k.

7. The method according to claim 1, wherein: In step 1, a flexible grounding device with four-quadrant operation capability is used to control the neutral point voltage of the system. 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 the 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 is increased 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 ; Line selection module, 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 fault feeder.

9. A 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 system neutral point voltage.

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 the 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 fault 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 fault impact; 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, and the direction is positive. The zero-sequence active power direction discrimination angle μ of the fault feeder is f With transition resistance R f , multiple k and θ.

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