Distribution line fault location method and system for capacitive node delay compensation

Abstract

The invention discloses a capacitive node delay compensation distribution line fault distance measurement method and system. The system comprises a fault signal acquisition module, a fault signal processing module and a fault distance measurement analysis module. And the fault ranging analysis module obtains a distribution line fault ranging result based on a formula. The capacitive node delay compensation distribution line fault distance measurement method and system are easy to implement and high in distance measurement precision.

Description

Technical Field

[0002] This invention relates to a method and system for fault location in power distribution lines with capacitive node delay compensation. Background Technology

[0003] As an important component of the new power system, the distribution network has changed from the traditional tree-shaped radial network to a complex network with "multiple branches, overhead-cable hybrid, and ring network connection". Compared with the transmission line, the distribution line has multiple distribution transformers connected in parallel. Under the action of high-frequency signals, the distribution transformer is equivalent to a capacitor, which changes the fault traveling wave transmission mechanism. These phenomena expose the shortcomings of traditional fault diagnosis methods in the distribution network scenario: (1) Lack of quantitative consideration of the time delay accumulation of capacitive distribution transformer groups: Existing theories have failed to fully characterize the effect of the transmission time delay accumulation effect when the traveling wave passes through multiple parallel distribution transformer nodes. (2) Insufficient accuracy in fault identification and ranging: First, the existing FTU traveling wave positioning module, distribution network distributed fault monitoring device and fault indicator can only monitor the main line and large branch line of the distribution network, but cannot monitor the small branch line or end of the distribution network, and cannot effectively perform full coverage fault ranging of the distribution network line; Second, the fault identification capability is insufficient. For single-phase grounding high resistance grounding faults, the fault indicator has insufficient identification capability, or its applicability is limited by the line load current. The CT power supply of the distribution network distributed fault monitoring device requires a load current greater than 5A. The FTU traveling wave positioning module needs to be integrated with the FTU of the pole-mounted circuit breaker, which limits its application range.

[0004] Therefore, it is necessary to design a new fault location method and system. Summary of the Invention

[0005] The purpose of this invention is to propose a method and system for fault location in power distribution lines with capacitive node delay compensation, so as to improve the accuracy and speed of fault location.

[0006] A method for fault location in distribution lines with capacitive node delay compensation is proposed, which monitors and locates faults on a specific feeder in a distribution line. In this feeder, distribution transformer m1 is connected in parallel. A monitoring terminal is installed on the secondary side of distribution transformer n1 as a monitoring point for fault traveling wave monitoring; m1>n1 The network fault ranging formula based on dual-end positioning is: ； In the formula: L MiNj Monitoring point M i to monitoring point N j The shortest distance along the faulty line; L MF Monitoring point M To the fault point F The distance is the line distance from the specified monitoring point M (such as the first monitoring point M1 closest to the substation outgoing line) to the fault point.

[0007] L MiM Monitoring point M i to monitoring point M The shortest distance of the route; T Mi , T Nj The initial traveling waves of the fault reach the line monitoring points respectively. M i , N j Time; T Mi , T Nj It is installed in M i Monitoring terminals at monitoring points and N j The first wave time point of the traveling wave in the fault traveling wave waveform recorded by the monitoring terminals at each monitoring point (e.g., M i monitoring points and N j The time point corresponding to 10% of the first wave amplitude in the fault traveling wave waveform recorded by the monitoring terminal at the monitoring point.

[0008] Z: Wave impedance of power distribution line; Wave impedance is the inherent traveling wave impedance value of power distribution line. It is about 300 ohms for overhead power distribution lines and about 160 ohms for cable distribution lines.

[0009] C k From fault point F to monitoring point M i The equivalent inlet capacitance of n distribution transformers is used to first calculate a preliminary distance using a double-ended positioning formula, without considering transformer delay, to determine the approximate location of the fault point. Then, the distance from the approximate fault point to the monitoring point M is used... i n distribution transformers connected in parallel, with different capacities, have an input capacitance C. k It needs to be measured first; it's a fixed value.

[0010] C p From fault point F to monitoring point N jThe equivalent inlet capacitance of m distribution transformers is used to first calculate a preliminary distance using a double-ended positioning formula, without considering transformer delay, to determine the approximate location of the fault point. Then, the distance from the approximate fault point to the monitoring point N is used... j m distribution transformers connected in parallel, with different capacities and their input capacitance C. p It needs to be measured first; it's a fixed value.

[0011] v Traveling wave velocity refers to the wave velocity of a traveling wave. For stationary lines, it is basically a constant value, approximately 2.8 x 10⁻⁶ for overhead distribution lines. 8 The power distribution cable line has a speed of m / s and a length of approximately 1.6 * 10 m / s. 8 m / s.

[0012] Calculate the two-way traveling wave ranging results between all two monitoring points and remove the deviation. L MF The result of the calculation error λ (which is usually taken as 300m) is taken as the arithmetic mean of the result and used as the final distance measurement result of the network traveling wave ranging.

[0013] The calculation error λ is taken as 300m.

[0014] A fault location system for distribution lines with capacitive node delay compensation includes a fault signal acquisition module, a fault signal processing module, and a fault location analysis module. Fault signal acquisition module: The monitoring terminal is directly connected to the voltage signal on the low-voltage side of the distribution transformer and the secondary signal of the current transformer on the low-voltage side. The sensor is used to collect the traveling wave signal of the grounding wire fault of the distribution transformer and send it to the fault signal processing module. The monitoring terminal is an existing mature device, consisting of a fault signal acquisition module and a fault signal processing module, which is responsible for the acquisition and processing of voltage and current traveling waves on the secondary side of the distribution transformer; the fault location analysis module is a fault location system.

[0015] Fault signal processing module: Processes the fault voltage traveling wave, current traveling wave and zero-mode traveling wave on the distribution transformer grounding line from the fault signal acquisition module, including traveling wave signal amplification, AD conversion and traveling wave signal calibration time. It collects fault traveling wave data including voltage traveling wave, current traveling wave and zero-mode traveling wave in real time. When the set recording threshold is met, it forms a traveling wave recording file, stores it and sends it to the fault location analysis module. Fault location analysis module: The final location result of network traveling wave location is calculated using the aforementioned method (i.e., the distribution line fault location method with capacitive node delay compensation), thereby realizing fault location.

[0016] Fault location principle explanation: (1) Two-end distance measurement formula:

[0017] (2) Formula for double-ended distance measurement with transformer delay compensation:

[0018] (3) Network ranging formula:

[0019] (4) Normalized network ranging formula from fixed point M to fault point F:

[0020] (5) Network ranging formula with normalized time delay compensation from fixed point M to fault point F: Beneficial effects

[0021] The present invention relates to a method and system for fault location in distribution lines with capacitive node delay compensation. This method and system are applied in complex distribution networks with distributed energy access. Based on a new model, it can quickly and accurately locate fault points, thus achieving fast and accurate fault location. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the topology of a 10kV power distribution system. Figure 2 An equivalent model of distributed parameters for a three-phase distribution transformer; Figure 3 A simplified model of the distributed capacitance of a three-phase distribution transformer; Figure 4 This is a schematic diagram of a transient fault simulation of a 10kV power distribution system. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] system: The power distribution line fault location system includes a fault signal acquisition module, a fault signal processing module, and a fault location analysis module. (1) Fault signal acquisition module The monitoring terminal directly connects to the voltage signal on the low-voltage side of the distribution transformer and the secondary signal from the current transformer on the low-voltage side. It uses sensors to collect the traveling wave signal of a grounding fault in the distribution transformer and sends it to the fault signal processing module. Using the transformer's turns ratio, it feeds back the primary fault information of the distribution transformer.

[0026] (2) Fault signal processing module The fault signal processing module processes the fault voltage traveling wave, current traveling wave, and zero-mode traveling wave on the transformer grounding line from the fault signal acquisition module. It performs traveling wave signal operational amplifier (OPA), AD conversion, and traveling wave signal calibration time processing. It acquires fault traveling wave data such as voltage traveling wave, current traveling wave, and zero-mode traveling wave in real time. When the set recording threshold is met, it generates a traveling wave recording file, stores it, and uploads it to the fault location and analysis module. (3) Fault location analysis module The fault location module consists of a parameter setting module, a transformer delay compensation module, a fault location module, and a fault statistical analysis module.

[0027] The parameter setting module sets the line length, tower-tower distance, line type, wave velocity, branch point information of branch lines, monitoring terminal installation location, distribution transformer installation location, distribution transformer capacity, distribution transformer voltage ratio, and current transformer ratio on the low-voltage side of the distribution transformer based on the line information provided by the user.

[0028] In a distribution network, for the first fault wave at two monitoring points (excluding reflected waves, which have only one transmission path), there may be multiple transmission paths in the transmission line.

[0029] Distribution transformer delay compensation module: Based on the pre-calculated capacity and number of distribution transformers between the two monitoring points set in the parameter setting module, the surge impedance Z of the distribution line, and the equivalent capacitance C of the high-voltage side inlet of the distribution transformer, the pre-calculated delay time between the two monitoring points i and j is calculated. Where k is the equivalent capacitance at the high-voltage inlet of a certain distribution transformer, and n is the pre-calculated number of distribution transformers between the two monitoring points. Compensation is performed for the time difference of the first wave of the traveling wave at any two monitoring points M and N, using the following formula: T M T N The traveling wave front times measured at monitoring points M and N are respectively, where m is the number of distribution transformers between fault point F and monitoring point M, and C is the number of transformers between fault point F and monitoring point M. P This is the equivalent capacitance of the high-voltage side inlet of the distribution transformer between the fault point F and the monitoring point M.

[0030] Fault location module: Based on the time difference of the first wave of the traveling wave at different monitoring points of the distribution transformer delay compensation module, a compensation formula is used to obtain the compensated time difference between two calculation points. The network ranging formula based on dual-end ranging is as follows: ,in L MF For monitoring points M To the fault point F distance, L MiNj For monitoring points M i to monitoring point Nj The shortest distance along the faulty line. L MiM For monitoring points M i to monitoring point M The shortest distance of the route.

[0031] In the event of a fault, all distance measurement results from the network ranging system are processed within a certain distance window (e.g., 300m) to account for calculation errors. Starting from the small pole along the faulty line, the window is slid, and the result with the most positioning results within a certain distance window is considered a valid ranging result. Other ranging results are considered invalid and are discarded. The arithmetic mean of the valid results is then used as the ranging result of the network traveling wave ranging system.

[0032] Remove the deviation using the method described above. L MF The arithmetic mean of all two-ended traveling wave ranging results that exceed the calculation error is taken as the ranging result of the network traveling wave ranging.

[0033] method: (1) Construct the equivalent voltage traveling wave propagation equation of the capacitive node

[0034] Where: V(t) is the incident voltage traveling wave, I(t) is the current traveling wave, For the capacitive node delay term, C k For the k-th equivalent capacitance, V k (t) represents the refracted voltage wave at the k-th capacitive node. (2) Under the action of high-frequency traveling waves, the distribution transformer is equivalent to an equivalent capacitor. Under the influence of high-frequency transient traveling wave signals, distribution transformers can be represented by distributed parameters as follows: Figure 3 As shown, the inlet capacitance of phase A in a three-phase distribution transformer is C. A The input capacitance of phase B is C. B The input capacitance of phase C is C C C1 is the distributed capacitance of the primary winding of the transformer to the transformer casing, and C2 is the distributed capacitance of the secondary winding of the transformer to the transformer casing. 12 The distributed capacitance between the primary and secondary windings of the distribution transformer is C. For the primary side of a three-phase distribution transformer, the equivalent distributed capacitance C of phase A is... A C 12 After being connected in series with C2, it is connected in parallel with C1; the analysis of phases B and C is the same as that of phase A. Therefore, the equivalent capacitance of the primary side inlet of the three-phase distribution transformer is: ； (3) Calculate the travel wave and refracted wave delay of the node voltage of the parallel distribution transformer in the distribution line. The surge impedance of the power distribution line is Z, the equivalent capacitance of the primary input of the parallel distribution transformer is C, V1 is the incident voltage wave, i1 is the incident current wave, V3 is the refracted voltage wave, and i3 is the refracted current wave. According to Peterson's rule:

[0035] If the voltage incident wave is a high-slope slope function: ， The voltage-refracted wave V3 function can be obtained as follows: ,in It is an attenuation function. When the incident voltage wave passes through the node of the distribution transformer connected in parallel with the power distribution line, the refracted voltage wave will generate... Delayed transmission.

[0036] (4) Distribution transformer node delay compensation The formula for calculating the delay time of the capacitive node of the distribution transformer between monitoring points i and j is as follows: Where Z is the surge impedance of the distribution line, and C is the equivalent capacitance at the high-voltage inlet of the distribution transformer with different capacities. k Where n is the number of distribution transformers between monitoring points. The formula for compensating the time difference of the first wave of the traveling wave at monitoring points M and N is as follows: T M T N The traveling wave front times measured at monitoring points M and N are respectively, where m is the number of distribution transformers between fault point F and monitoring point M, and C is the number of transformers between fault point F and monitoring point M. P C represents the equivalent capacitance of the high-voltage side inlet of the distribution transformer between fault point F and monitoring point M; n represents the number of distribution transformers between fault point F and monitoring point N; C represents the equivalent capacitance of the high-voltage side inlet of the distribution transformer between fault point F and monitoring point N. k This refers to the equivalent capacitance at the high-voltage side inlet of the distribution transformer between the fault point F and the monitoring point N.

[0037] (5) Network fault location method A network ranging formula based on two-end ranging for distribution transformer delay compensation is as follows:

[0038] In the formula: L MiNj Monitoring point M i to monitoring point N j The shortest distance along the faulty line; L MF Monitoring point M To the fault point F The distance; L MiM :: Monitoring point Mi to monitoring point M The shortest distance of the route; T Mi , T Nj The initial traveling waves of the fault reach the line monitoring points respectively. M i , N j time ; Z: Wave impedance of power distribution line; C k From fault point F to monitoring point M i The equivalent inlet capacitance of n distribution transformers; C p From fault point F to monitoring point N j The equivalent inlet capacitance of m distribution transformers; v Traveling wave velocity; Analyze all two-ended traveling wave ranging results and remove those with deviations. L MF The result of the calculation error is taken as the arithmetic mean of the result and used as the ranging result of the network traveling wave ranging. Example 1: Substation M has n feeders on its 10kV busbar. Fault monitoring is performed on feeder 1. QF is a pole-mounted circuit breaker. Monitoring terminals are installed on the secondary side of the distribution transformers for traveling wave monitoring. Feeder 1 is divided into support point zones, such as M1 to M6. Multiple distribution transformers are connected in parallel to the distribution line. Monitoring is performed on the secondary side of 6 distribution transformers, as shown by the monitoring terminals indicated by the boxes. Comprehensive fault monitoring of the distribution line is then performed. Figure 1 As shown. The distributed parameters of the distribution transformer are as follows. Figure 2 As shown, the distributed capacitance of the distribution transformer is as follows: Figure 3 As shown.

[0039] A transient simulation diagram of power distribution line faults in substation M was built using PSCAD, as shown below. Figure 4 As shown, the branch points or line endpoints of distribution feeder 1 are denoted by Mi. The distance between M1 and M2 is 8.5 km, with 8 transformers; the distance between M2 and M3 is 10 km, with 12 transformers; the distance between M2 and M4 is 5 km, with 6 transformers; the distance between M4 and M5 is 6.5 km, with 7 transformers; the fault point F is 2 km away from M4 (the distance between M4 and F is 2 km, with 3 transformers; the distance between F and M6 is 4 km, with 4 transformers). MT1 to MT6 are intelligent terminals. Assume the wave velocity of the distribution line is 2.98 × 10⁻⁶. 8The transformer has a speed of m / s, a surge impedance of 300Ω, a transition resistance of 300Ω, and a rated capacity of 315kVA. Actual measurements of the 315kVA three-phase transformer show that the primary side capacitance to ground is 1600pF, the phase-to-phase capacitance is 2300pF, and the secondary side capacitance to ground is 3300pF. (Based on the formula...) The equivalent capacitance on the primary side can be calculated to be 2955pF, from the formula. The calculation shows that the traveling wave refraction delay of a single distribution transformer is 443.25ns. The fault location error analysis table, including the fault traveling wave head recording time of monitoring terminals MT1 to MT6, the correction time after distribution transformer time delay correction, the fault location distance, and the fault location error, is shown in Table 1.

[0040] Table 1. Analysis of Fault Distance Measurement Errors in Monitoring Terminals (Unit: Time in μs, Distance in m) Referring to Table 1, the maximum error in fault location is 1059m when the transformer delay is not compensated. After compensating for the transformer delay, the maximum error in fault location is within 100m.

Claims

1. A method for fault location in distribution lines with capacitive node delay compensation, characterized in that: Monitoring and fault location of a specific feeder in a power distribution line: The feeder line has a parallel m1 distribution transformer. A monitoring terminal is installed on the secondary side of the n1 distribution transformer as a monitoring point to monitor and measure the fault traveling wave. The network fault location formula based on two-end ranging is:

2. In the formula: L MiNj Monitoring point M i to monitoring point N j The shortest distance along the faulty line; L MF Monitoring point M To the fault point F The distance; L MiM Monitoring point M i to monitoring point M The shortest distance of the route; T Mi , T Nj The initial traveling waves of the fault reach the line monitoring points respectively. M i , N j time ; Z: Wave impedance of power distribution line; C k From fault point F to monitoring point M i The equivalent inlet capacitance of n distribution transformers; C p From fault point F to monitoring point N j The equivalent inlet capacitance of m distribution transformers; v Traveling wave velocity; Calculate the two-way traveling wave ranging results between all two monitoring points and remove the deviation. L MF The results of calculations exceeding the preset error λ are averaged and taken as the final ranging result of the network traveling wave ranging.

3. The method for fault location in distribution lines with capacitive node delay compensation according to claim 1, characterized in that: The traveling wave velocity of an overhead power distribution line is 2.8*10. 8 The traveling wave velocity of the power distribution cable line is 1.6*10 m / s. 8 m / s.

4. The method for fault location in distribution lines with capacitive node delay compensation according to claim 1 or 2, characterized in that: The calculation error λ is taken as 300m.

5. A distribution line fault location system with capacitive node delay compensation, characterized in that, It includes a fault signal acquisition module, a fault signal processing module, and a fault location analysis module; Fault signal acquisition module: The monitoring terminal is directly connected to the voltage signal on the low-voltage side of the distribution transformer and the secondary signal of the current transformer on the low-voltage side. The sensor is used to collect the traveling wave signal of the grounding wire fault of the distribution transformer and send it to the fault signal processing module. Fault signal processing module: It amplifies, converts, and calibrates the traveling wave signals of the fault voltage traveling wave, current traveling wave, and zero-mode traveling wave on the distribution transformer grounding line from the fault signal acquisition module. It collects fault traveling wave data including voltage traveling wave, current traveling wave, and zero-mode traveling wave in real time. When the set recording threshold is met, it forms a traveling wave recording file, stores it, and sends it to the fault location analysis module. Fault ranging analysis module: The final ranging result of network traveling wave ranging is calculated by the method described in any one of claims 1-3, thereby realizing fault ranging.

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