Ultrahigh voltage shunt reactor turn-to-turn fault detection method based on equivalent resistance change
By constructing Kirchhoff voltage-current equations and equivalent impedance calculation, the inter-turn faults of ultra-high voltage shunt reactors are identified, solving the problems of difficult detection and false operation, and achieving accurate fault identification and reliable protection.
Patent Information
- Application Number
- CN202510851858.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-24
- Publication Date
- 2025-09-19
AI Technical Summary
When detecting inter-turn faults in ultra-high voltage shunt reactors, the existing technology has weak characteristics of externally measurable electrical quantities, making detection difficult, and there is a risk of false operation under operating conditions such as no-load closing and resonance.
By dividing the faulty phase winding into a non-short-circuited section on the grid side, a short-circuited turn section, and a non-short-circuited section on the neutral point side, a group of Kirchhoff voltage and current equations is constructed, the phasor relationship between the current at the head end of the faulty phase and the current within the turn is derived, the equivalent impedance is calculated, the short-circuit turns ratio and the transition resistance threshold are set, the voltage and current data are collected in real time, the fundamental wave phasor is extracted, and the equivalent resistance change characteristics are determined to identify inter-turn faults.
The accurate identification of inter-turn faults in ultra-high voltage shunt reactors is achieved, false operation is avoided, and the sensitivity and reliability of detection are improved.
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Figure CN120668997A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of relay protection technology of power systems and automation thereof in electrical technology, and in particular relates to a method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance changes. Background Art
[0002] Ultra-high voltage shunt reactors are critical equipment for regulating reactive power in power systems, suppressing system overvoltages, and ensuring long-distance power transmission. They are widely used in ultra-high and ultra-high voltage transmission systems. As large, oil-immersed devices, shunt reactors pose a risk of complete damage if internal faults are not promptly isolated, resulting in significant economic losses. Turn-to-turn faults, a typical internal fault in shunt reactors, only produce a large localized fault current. However, the externally measurable electrical characteristics of the shunt reactor are very weak, making turn-to-turn fault detection difficult. Therefore, in-depth analysis and identification of fault characteristics with significant variations are crucial for detecting turn-to-turn faults in shunt reactors.
[0003] The problem of interturn fault detection has received widespread attention within the industry, resulting in numerous research findings and conclusions. Existing research primarily utilizes zero-sequence current, zero-sequence voltage, and other sequence components, along with their combined impedance, to identify interturn faults. However, this presents the risk of false tripping under abnormal operating conditions such as no-load switching and resonance, which can cause core saturation. Therefore, a method for detecting interturn faults in ultra-high voltage shunt reactors based on equivalent resistance changes is urgently needed. Summary of the Invention
[0004] To solve the above technical problems, the present invention proposes a method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance changes, thereby achieving accurate identification of inter-turn faults of ultra-high voltage shunt reactors.
[0005] To achieve the above objectives, the present invention provides a method for detecting inter-turn faults in ultra-high voltage shunt reactors based on equivalent resistance changes, comprising:
[0006] The fault phase winding is divided into a non-short-circuited section on the grid side, a short-circuited turn section and a non-short-circuited section on the neutral point side, and the number of turns, resistance, self-inductance and mutual inductance parameters of each section are defined respectively;
[0007] Based on the electrical parameters of each winding section, Kirchhoff's voltage and current equations are constructed. Combined with the short-circuit current relationship, the phasor relationship between the current at the first end of the fault phase and the current within the turn is derived.
[0008] By using the equivalent impedance calculation formula, the voltage at the shunt reactor terminal is expressed as a function of the first-terminal current, and an analytical expression for the equivalent impedance including the short-circuit turns ratio and transition resistance is obtained.
[0009] Set the minimum identification threshold of the short-circuit turns ratio and the maximum tolerance threshold of the transition resistance, traverse all the equivalent resistance calculation values within the two thresholds, and select the minimum value multiplied by the reliability coefficient as the fault judgment setting value;
[0010] The three-phase voltage and current data are collected in real time, and the fundamental phasor is extracted to calculate the equivalent resistance measurement value. If the measurement value of any phase exceeds the set value, it is determined to be an inter-turn fault.
[0011] Optionally, considering the relationship between the number of turns, the resistance, self-inductance and mutual inductance of each part can be expressed as:
[0012]
[0013] Optionally, constructing Kirchhoff's voltage and current equations includes:
[0014]
[0015] Further sorting out the phasor equations for the current phasor at the first end of the fault phase and the current phasor within the turn is obtained:
[0016]
[0017] When the terminal voltage of the shunt reactor, the resistance and inductance parameters of the shunt reactor and the specific number of short-circuit turns are known, the first-end current and the intra-turn current of the shunt reactor inter-turn short-circuit fault phase are obtained.
[0018] Optionally, the equivalent impedance is uniquely determined by resistance-inductance parameters, the number of short-circuit turns, and the magnitude of the short-circuit transition resistance.
[0019] Optionally, the equivalent impedance is calculated as:
[0020]
[0021] Optionally, the set value is calculated as:
[0022] R set = kmin(R eq_cal ).
[0023] Optional, three-phase data acquisition and processing includes:
[0024] The full-wave Fourier algorithm is used to extract the fundamental phasors of voltage and current. The real part of the three-phase measurement impedance is calculated as the equivalent resistance measurement value. The three-phase measurement values are compared and the maximum value is taken as the basis for fault judgment.
[0025] Alternatively, the criterion for detecting inter-turn faults in shunt reactors based on the equivalent resistance variation characteristics is expressed as follows:
[0026]
[0027] Technical effect of the invention: The present invention discloses a method for detecting inter-turn faults of ultra-high voltage shunt reactors based on changes in equivalent resistance. The equivalent resistance setting value is flexibly set according to the short-circuit turns ratio and the ability to withstand transition resistance required for fault detection, and accurate fault identification is performed. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:
[0029] Figure 1 Schematic diagram of the circuit model structure of a shunt reactor turn-to-turn short-circuit fault according to an embodiment of the present invention;
[0030] Figure 2 The present invention is a flowchart of a method for detecting inter-turn faults in ultra-high voltage shunt reactors based on equivalent resistance changes according to an embodiment of the present invention. DETAILED DESCRIPTION
[0031] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.
[0032] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.
[0033] This embodiment provides a method for detecting inter-turn faults in an ultra-high voltage shunt reactor based on equivalent resistance changes, including:
[0034] The fault phase winding is divided into a non-short-circuited section on the grid side, a short-circuited turn section and a non-short-circuited section on the neutral point side, and the number of turns, resistance, self-inductance and mutual inductance parameters of each section are defined respectively;
[0035] Based on the electrical parameters of each winding section, Kirchhoff's voltage and current equations are constructed. Combined with the short-circuit current relationship, the phasor relationship between the current at the first end of the fault phase and the current within the turn is derived.
[0036] By using the equivalent impedance calculation formula, the voltage at the shunt reactor terminal is expressed as a function of the first-terminal current, and an analytical expression for the equivalent impedance including the short-circuit turns ratio and transition resistance is obtained.
[0037] Set the minimum identification threshold of the short-circuit turns ratio and the maximum tolerance threshold of the transition resistance, traverse all the equivalent resistance calculation values within the two thresholds, and select the minimum value multiplied by the reliability coefficient as the fault judgment setting value;
[0038] The three-phase voltage and current data are collected in real time, and the fundamental phasor is extracted to calculate the equivalent resistance measurement value. If the measurement value of any phase exceeds the set value, it is determined to be an inter-turn fault.
[0039] The shunt reactor with inter-turn short-circuit fault is divided into three sections: short-circuit turn winding and non-short-circuit turn winding. The structural diagram is as follows: Figure 1 As shown. d represents the grid-connected side of the shunt reactor, and n represents the neutral point side of the shunt reactor. Segment de represents the non-short-circuited winding coil on the grid-connected side of the shunt reactor, with N1 turns, L1 self-inductance, and R1 resistance; segment ef represents the short-circuited winding coil, with N2 turns, L2 self-inductance, and R2 resistance; segment fn represents the non-short-circuited winding coil on the neutral point side of the shunt reactor, with N3 turns, L3 self-inductance, and R3 resistance. The mutual inductance between inductors L1 and L2 is M 12 , the mutual inductance between inductors L2 and L3 is M 23 , the mutual inductance between inductors L1 and L3 is M 13 At this time, i1 is the first and last current of the short-circuit fault phase of the shunt reactor, i2 is the current flowing through the short-circuit winding coil, i k is the short-circuit current. Considering the relationship between the number of turns, the resistance, self-inductance and mutual inductance of each part are expressed as:
[0040]
[0041] According to the three-segment series circuit structure of the shunt reactor and the self-mutual inductance relationship between the short-circuit turn winding coil and the non-short-circuit turn winding coil, Kirchhoff's voltage and current equation is written as follows:
[0042]
[0043] Further sorting out equation (2) yields the phasor equations for the fault phase head-end current phasor and the turn-in-turn current phasor:
[0044]
[0045] When the terminal voltage of the shunt reactor, the resistance and inductance parameters of the shunt reactor, and the specific number of short-circuit turns are known, the first-end current and the intra-turn current of the shunt reactor inter-turn short-circuit fault phase can be obtained by solving equation (3).
[0046] Considering the steady-state electrical quantity of inter-turn short-circuit fault, the voltage u across the shunt reactor is dn , the first-end current i1 and the turn current i2 are expressed in phasor form, and the phasor equations of the first-end current phasor and the turn current phasor are established:
[0047]
[0048] According to formula (4), the relationship between the head-end current phasor and the turn-in-turn current phasor is as follows:
[0049]
[0050] Substituting equation (5) into equation (4) yields the phasor equation of the voltage phasor at the shunt reactor terminal with respect to the current phasor at the head end:
[0051]
[0052] The short-circuit equivalent impedance can be expressed as:
[0053]
[0054] At this time, the short-circuit phase equivalent impedance of the shunt reactor with an inter-turn short-circuit fault can be uniquely determined by the resistance-inductance parameters, the number of short-circuit turns, and the size of the short-circuit transition resistance, and can be obtained through calculation.
[0055] In order to improve the universality of the analysis of the short-circuit phase equivalent impedance change characteristics, the short-circuit turns are normalized, and the concept of short-circuit turns ratio is introduced to replace the short-circuit turns. The short-circuit turns ratio is denoted as α:
[0056]
[0057] Therefore, the resistance, self-inductance and mutual inductance of each part in formula (7) can be expressed as a function of the short-circuit turns ratio α. Substituting into formula (7) yields the short-circuit phase equivalent impedance Z eq Function expression of short-circuit turns ratio α:
[0058] Z eq (α)=R eq (α)+jX eq (α)(9);
[0059]
[0060]
[0061] Short circuit transition resistance R k The value of directly determines whether a turn-to-turn short-circuit fault occurs and the type of fault, which is discussed in the following three cases:
[0062] 1) When R k When the value of tends to positive infinity, Figure 1 The short-circuit current i k =0, at this time the shunt reactor is in normal operating condition and no inter-turn short-circuit fault occurs.
[0063] 2) When R k When it is equal to a certain value, the shunt reactor is in a fault condition, and the specific fault type is a turn-to-turn short-circuit fault through the transition resistor.
[0064] 3) When R k When is equal to 0, the shunt reactor is in a fault condition, and the specific fault type is a metallic turn-to-turn short-circuit fault. At this time, equations (10) and (11) can be further simplified:
[0065]
[0066] Given the minimum identification threshold of the short-circuit turns ratio and the maximum tolerance threshold of the short-circuit transition resistance of the shunt reactor, the short-circuit turns ratio and the short-circuit transition resistance are changed with a fixed gradient, and all the equivalent resistance calculation values R within the identification accuracy range matrix composed of the above two thresholds are traversed using formula (10). eq_cal , minimum value min(R eq_cal ) is the identification threshold of the inter-turn short-circuit fault. At the same time, in order to further ensure the reliability of the judgment criterion, the identification threshold is multiplied by the reliability coefficient k, and the final setting value of the equivalent resistance of the inter-turn short-circuit phase is obtained:
[0067] R set = kmin(R eq_cal )(14).
[0068] When a turn-to-turn short circuit fault occurs in one of the three phases A, B, and C of the shunt reactor, the equivalent resistance measurement value of the faulty phase rises rapidly, while the equivalent resistance measurement value of the non-faulty phase remains basically unchanged. eq_mea , maximum value max(R eq_mea ) is the equivalent resistance measurement value of the fault phase. The criterion for the shunt reactor turn-to-turn fault detection method based on the equivalent resistance variation characteristics can be expressed as:
[0069]
[0070] The detection process of inter-turn short circuit fault is as follows: Figure 2 As shown, the core steps are as follows:
[0071] 1) According to the detection requirements, the minimum identification threshold of the short-circuit turns ratio and the maximum tolerance threshold of the short-circuit transition resistance of the shunt reactor are given, and all equivalent resistance values within this range are calculated to obtain the setting value of the inter-turn short-circuit phase equivalent resistance as shown in formula (14); this step can be completed offline.
[0072] 2) Collect the three-phase voltage and current data of the shunt reactor, use the full-wave Fourier algorithm to extract the voltage and current fundamental phasors, obtain the three-phase measurement impedance, and further obtain the three-phase equivalent resistance measurement value.
[0073] 3) The inter-turn short-circuit fault is identified using the criterion proposed in formula (15). When the maximum value of the three-phase equivalent resistance measurement value exceeds the set value, it is determined that an inter-turn short-circuit fault has occurred. Otherwise, it is determined that no inter-turn short-circuit fault has occurred.
[0074] In the MATLAB / Simulink simulation environment, a shunt reactor turn-to-turn short-circuit simulation model was built, and the simulation parameters are shown in Table 1.
[0075] Table 1
[0076] Parameter name Numerical Three-phase rated capacity 150Mvar Rated voltage 550kV Rated current 157.46A Single-phase main reactance 2+j2016Ω Neutral point small reactance 0.5+j504Ω
[0077] First, the correctness of the theoretical calculation results was verified. The simulation model set a turn-to-turn short-circuit fault on phase A of the shunt reactor, with the fault duration being 20 seconds. The grid-connection point voltage, neutral point voltage, and head-end current of phase A of the shunt reactor were measured, and the equivalent resistance of phase A was obtained by combining the logic operation module. By varying the short-circuit turns ratio α, metallic turn-to-turn short-circuit faults and transition resistance turn-to-turn short-circuit faults of varying fault severity were simulated. The simulated equivalent resistance of phase A was compared with the theoretical value calculated using Equation (10). The results are shown in Table 2.
[0078] Table 2
[0079]
[0080] It can be seen from Table 2 that under different inter-turn short-circuit fault levels, the maximum error percentage between the theoretical calculation value and the simulation value is 0.209%, which verifies the correctness of the theoretical calculation results.
[0081] The sensitivity and reliability of this identification method and the zero-sequence electrical quantity identification method for inter-turn short-circuit faults of different fault types and fault severity are then analyzed. The fault conditions listed in Table 3 are simulated and the inter-turn protection actions of the two methods are compared.
[0082] According to the requirements of inter-turn short circuit identification, the following two cases are analyzed. Assuming that the minimum identification threshold of the short-circuit turns ratio of metallic inter-turn short circuit is 0.2% and the maximum tolerance threshold of short-circuit transition resistance is 0Ω, the setting value R of the inter-turn short circuit identification criterion (15) in this paper is calculated. set is 30.4Ω; the minimum identification threshold of the short-circuit turns ratio with transition resistance is 0.2%, and the maximum tolerance threshold of the short-circuit transition resistance is 3Ω. The setting value R of the turn-to-turn short-circuit identification criterion (15) in this paper is calculated. set is 5.9Ω.
[0083] Table 3
[0084]
[0085]
[0086] The simulation results in Table 3 show that in all the above fault conditions, the short-circuit phase equivalent resistance of the judgment criterion proposed by this method exceeds the set value, and the interturn protection operates reliably. However, the zero-sequence electrical quantity identification method fails to operate when the transition resistance between turns with a small number of turns is short-circuited. The reason for this is that both the zero-sequence power direction action equation and the zero-sequence impedance action equation are satisfied, but the zero-sequence current is extremely small and does not reach the zero-sequence current startup threshold of the interturn protection, resulting in the interturn protection failing to operate.
[0087] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.
Claims
1. A method for detecting inter-turn faults in ultra-high voltage shunt reactors based on equivalent resistance change, characterized in that: include: The fault phase winding is divided into a non-short-circuited section on the grid side, a short-circuited turn section and a non-short-circuited section on the neutral point side, and the number of turns, resistance, self-inductance and mutual inductance parameters of each section are defined respectively; Based on the electrical parameters of each winding section, Kirchhoff's voltage and current equations are constructed. Combined with the short-circuit current relationship, the phasor relationship between the current at the first end of the fault phase and the current within the turn is derived. By using the equivalent impedance calculation formula, the voltage at the shunt reactor terminal is expressed as a function of the first-terminal current, and an analytical expression for the equivalent impedance including the short-circuit turns ratio and transition resistance is obtained. Set the minimum identification threshold of the short-circuit turns ratio and the maximum tolerance threshold of the transition resistance, traverse all the equivalent resistance calculation values within the two thresholds, and select the minimum value multiplied by the reliability coefficient as the fault judgment setting value; The three-phase voltage and current data are collected in real time, and the fundamental phasor is extracted to calculate the equivalent resistance measurement value. If the measurement value of any phase exceeds the set value, it is determined to be an inter-turn fault.
2. The method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance change according to claim 1, wherein: Considering the relationship between the number of turns, the resistance, self-inductance and mutual inductance of each part are expressed as:
3. The method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance change according to claim 1, wherein: Constructing Kirchhoff's voltage and current equations includes: Further sorting out the phasor equations for the current phasor at the first end of the fault phase and the current phasor within the turn is obtained: When the terminal voltage of the shunt reactor, the resistance and inductance parameters of the shunt reactor and the specific number of short-circuit turns are known, the first-end current and the intra-turn current of the shunt reactor inter-turn short-circuit fault phase are obtained.
4. The method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance change according to claim 1, wherein: The equivalent impedance is uniquely determined by the resistance-inductance parameters, the number of short-circuit turns and the size of the short-circuit transition resistance.
5. The method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance change according to claim 1, wherein: The equivalent impedance is calculated as:
6. The method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance change according to claim 1, wherein: The set value is calculated as: R set =kmin(R eq_cal )。 7. The method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance change according to claim 1, wherein: Three-phase data acquisition and processing includes: The full-wave Fourier algorithm is used to extract the fundamental phasors of voltage and current. The real part of the three-phase measurement impedance is calculated as the equivalent resistance measurement value. The three-phase measurement values are compared and the maximum value is taken as the basis for fault judgment.
8. The method for detecting inter-turn faults of ultra-high voltage shunt reactors based on equivalent resistance change according to claim 1, wherein: The criterion for the detection of inter-turn faults in shunt reactors based on the equivalent resistance variation characteristics is expressed as follows: