Large wave winding generator stator grounding fault positioning method

Abstract

The invention provides a large wave winding generator stator grounding fault positioning method, and provides a stator grounding fault accurate positioning method based on bifunction coupling analysis innovatively for a specific cross-pole connection structure of a wave winding generator. The limitation of a traditional single function positioning model is broken through, and synchronous and accurate identification of the fault position and the transition resistance is realized by establishing a correlation model of fundamental wave potential distribution and zero sequence voltage response.

Description

Technical Field

[0001] The present invention relates to the technical field of design and manufacture of large-scale generators and relay protection of main equipment of power systems, and in particular to a method for locating stator grounding faults of large-scale wave winding generators. Background Art

[0002] During the operation of large synchronous generators, single-phase ground faults in the stator winding are a frequently occurring electrical insulation failure mode. While the direct damage is relatively limited compared to more severe faults such as inter-turn short circuits, statistics from the International Electrotechnical Commission (IEC) indicate that approximately 83% of interphase faults are caused by untreated ground faults. Current relay protection regulations require that when the ground capacitance current exceeds a safety threshold, the protective device must be activated promptly to quickly clear the fault. This places stringent technical demands on the rapid and accurate location of the fault point.

[0003] Existing fault location technologies primarily rely on the analysis of the fundamental zero-sequence voltage component, and their accuracy is closely related to the motor winding structure. This is particularly true for low-speed, multi-pole generators employing wave winding designs, where the winding distribution exhibits unique circumferential symmetry. Traditional linear location models can produce significant errors. In engineering practice, wave winding structures optimize the winding layout, maximizing electromotive force while minimizing the configuration of inter-pole connecting conductors. This unique topology renders existing location algorithms based on stacked winding models inapplicable.

[0004] For example, CN 112180290 A discloses a method for locating a generator stator ground fault. This invention determines the fault phase by calculating the generator zero-sequence voltage vector; calculates the lead angle and characteristic vector angle of the zero-sequence voltage vector ahead of the fault phase; and determines whether the fault occurs externally or internally to the generator by comparing the lead angle and characteristic vector angle. Furthermore, the ratio of the number of windings from the generator end to the generator neutral point is calculated based on the amplitude and phase angle of the zero-sequence voltage. This invention uses a formula to calculate the ratio of the number of windings from the generator end to the number of windings from the generator neutral point. This method is relatively simple and does not consider the distribution characteristics of the generator windings, resulting in potential deviations in the positioning results. If the distribution characteristics of the generator windings are taken into account, the fundamental potential becomes more complex, and the formula used in this invention becomes inapplicable.

[0005] For example, CN 108490304 A discloses a method for locating a single-phase ground fault in a generator stator winding. This method first simulates a single-phase ground fault at the generator end and calculates characteristic parameters. Then, based on the stator winding connection diagram, it calculates the fundamental voltage phasor of each bar and the fundamental voltage phasor at each bar end. Next, when a single-phase ground fault in the stator winding actually occurs, it measures and calculates the three-phase fundamental voltage and zero-sequence voltage at the generator end to identify the faulty phase. Assuming a ground fault at each bar end, it calculates the fundamental zero-sequence voltage under these fault conditions and compares it with the actual fault fundamental zero-sequence voltage to determine the fault location. This method uses the fundamental voltage phasor at each bar end as a reference value and, through comparative calculation, identifies the bar closest to the fault location and identifies it as the fault point. This algorithm's accuracy is limited to identifying the faulty bar, but cannot be further refined to the fault point. Furthermore, when the fundamental voltage vectors at multiple bar ends closely match the voltage vector characteristics at the fault location, it is prone to misjudgment. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for locating stator grounding faults in large wave winding generators. The present invention aims to quickly locate the fault point, avoid fault expansion, reduce unplanned downtime, ensure safe and stable operation of the generator and reduce downtime losses.

[0007] In order to achieve the above technical features, the purpose of the present invention is achieved as follows: A method for locating a stator ground fault of a large wave winding generator comprises the following steps: Step 1: Based on the dynamic segmented modeling method of the wave winding cross-pole characteristics, a piecewise linear function with slope continuity is constructed; Step 2: Establish an equivalent circuit including ground capacitance and ground transformer leakage reactance, and derive the analytical expression of the fundamental zero-sequence voltage characteristic quantity; Step 3: Based on the phasor trajectory-frequency domain impedance joint decoupling algorithm, the influence of transition resistance is eliminated and the pure fault location characteristic function is extracted; Step 4: Based on the dual-function coupling analysis, the stator grounding fault is accurately located.

[0008] Preferably, the step 1 specifically includes: Based on the unique cross-pole connection topology of wave winding, a piecewise potential analytical model is established in the rectangular coordinate system. Different linear intervals are divided according to different winding spans and fundamental wave potential vectors, and a piecewise linear function with slope continuity is constructed.

[0009] Preferably, the neutral point-machine end direction in the rectangular coordinate system is the X-axis.

[0010] Preferably, the piecewise linear function is: ; Where: is the slope of the linear function, is the horizontal coordinate of the piecewise function, is a constant term, Number the piecewise functions, is the total number of piecewise functions.

[0011] Preferably, the analytical expression of the fundamental zero-sequence voltage characteristic quantity in step 2 is: ; Where, is the fundamental zero-sequence voltage, is the fundamental wave potential from neutral point to fault point, is the equivalent impedance of the generator system, is the equivalent capacitive reactance of the generator system, is the ground transition resistance, Is an imaginary unit.

[0012] Preferably, the step 3 specifically includes: Eliminate the influence of transition resistance by phasor trajectory analysis and extract the pure fault location characteristic function .

[0013] Preferably, the pure fault location characteristic function in step 3 is It is the straight line function where DA is located, and this function can be decoupled from the transition resistance; ; Where, is the slope of the straight line DA, is the coordinate of point D, point D is the starting point of the fundamental zero-sequence voltage vector, and point A is the fault point.

[0014] Preferably, the step 4 specifically includes: Simultaneous piecewise linear functions and pure fault location characteristic function , solve the intersection of the two functions, which is the fault location.

[0015] Preferably, the fault location solved simultaneously in step 4 is: ; Where, It is the percentage of the distance from the fault point to the neutral point to the distance from the generator end to the neutral point.

[0016] Preferably, the transition resistance solved simultaneously in step 4 is: ; Where, It is the vector from the starting point of the fundamental zero-sequence voltage vector to the fault point.

[0017] The present invention has the following beneficial effects: 1. The present invention can quickly locate the fault point: Improve the speed of locating fault points, reduce downtime, and deal with fault points in time to ensure safe and stable operation of generators and reduce downtime losses.

[0018] 2. The present invention can accurately locate the fault point: Improve positioning accuracy, reduce the time to find the fault point after shutdown, solve the problem that some fault points are hidden and difficult to find, and greatly reduce fault handling time. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings and examples.

[0020] Figure 1 Fundamental zero-sequence equivalent circuit.

[0021] Figure 2 Fundamental zero-sequence voltage vector diagram.

[0022] Figure 3 Generator fundamental potential fitting function.

[0023] Figure 4 Schematic diagram of finding the intersection point of the fitting function.

[0024] Figure 5 Schematic diagram of wave winding. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1: See also Figure 1-5 ,Step 1, based on the unique cross-pole connection topology of the wave winding, a segmented potential analytical model is established in the rectangular coordinate system (neutral point-machine end direction is the X-axis). According to different winding spans and fundamental wave potential vectors, different linear intervals can be divided to construct a segmented linear function with slope continuity; The piecewise linear function is: ; Where: is the slope of the linear function, is the horizontal coordinate of the piecewise function, is a constant term, Number the piecewise functions, is the total number of piecewise functions.

[0027] Step 2: Establish an equivalent circuit including ground capacitance and ground transformer leakage reactance, and derive the analytical expression of the fundamental zero-sequence voltage characteristic quantity: ; Where, is the fundamental zero-sequence voltage, is the fundamental wave potential from neutral point to fault point, is the equivalent impedance of the generator system, is the equivalent capacitive reactance of the generator system, is the ground transition resistance, Is an imaginary unit.

[0028] Step 3: Eliminate the influence of transition resistance through phasor trajectory analysis and extract the pure fault location characteristic function , that is, the straight line function where DA is located, which can be decoupled from the transition resistance; ; Where, is the slope of the straight line DA, is the coordinate of point D, point D is the starting point of the fundamental zero-sequence voltage vector, and point A is the fault point.

[0029] Step 4: Simultaneous piecewise linear functions and pure fault location characteristic function , solve the intersection of the two functions, which is the fault location: ; Where, It is the percentage of the distance from the fault point to the neutral point to the distance from the generator end to the neutral point.

[0030] The transition resistance is: ; Where, It is the vector from the starting point of the fundamental zero-sequence voltage vector to the fault point.

[0031] Example 2: A generator uses integer slots ( ) wave winding (stator winding pitch is 、 ), 48 poles, 576 stator slots, 8 branches per phase, 24 coils per branch. Its winding connection adopts wave winding, in which the fundamental wave potential distribution of one branch is as follows Figure 3 shown.

[0032] The analysis is carried out in a rectangular coordinate system. As a benchmark, the phase difference between the potentials of two adjacent turns of the coil is ,but , , the effective value of the coil group potential is: ; The coordinates of the coil group potential intersection point are: ; The slope of the line of coil potential is: ; The piecewise function is obtained as: ; Taking the ground fault at 75% as an example, the transition resistance is set to 100Ω. The simulation results are as follows: Figure 4 , solve the intersection of straight line DA and the fundamental wave potential fitting function, and get the fault position as 74.98% and the transition resistance as 99Ω.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for locating stator grounding faults in large wave winding generators, characterized in that: The following steps are involved: Step 1: Based on the dynamic segmented modeling method of the wave winding cross-pole characteristics, a piecewise linear function with slope continuity is constructed; Step 2: Establish an equivalent circuit including ground capacitance and ground transformer leakage reactance, and derive the analytical expression of the fundamental zero-sequence voltage characteristic quantity; Step 3: Based on the phasor trajectory-frequency domain impedance joint decoupling algorithm, the influence of transition resistance is eliminated and the pure fault location characteristic function is extracted; Step 4: Based on the dual-function coupling analysis, the stator grounding fault is accurately located.

2. A method for locating a stator ground fault of a large wave winding generator according to claim 1, characterized in that: The step 1 specifically includes: Based on the unique cross-pole connection topology of wave winding, a piecewise potential analytical model is established in the rectangular coordinate system. Different linear intervals are divided according to different winding spans and fundamental wave potential vectors, and a piecewise linear function with slope continuity is constructed.

3. A method for locating a stator ground fault of a large wave winding generator according to claim 2, characterized in that: In the rectangular coordinate system, the neutral point-machine end direction is the X-axis.

4. A method for locating a stator ground fault of a large wave winding generator according to claim 3, characterized in that: The piecewise linear function is: ； Where: is the slope of the linear function, is the horizontal coordinate of the piecewise function, is a constant term, Number the piecewise functions, is the total number of piecewise functions.

5. A method for locating a stator ground fault of a large wave winding generator according to claim 4, characterized in that: The analytical expression of the fundamental zero-sequence voltage characteristic quantity in step 2 is: ； Where, is the fundamental zero-sequence voltage, is the fundamental wave potential from neutral point to fault point, is the equivalent impedance of the generator system, is the equivalent capacitive reactance of the generator system, is the ground transition resistance, Is an imaginary unit.

6. A method for locating a stator ground fault of a large wave winding generator according to claim 5, characterized in that: The step 3 specifically includes: Eliminate the influence of transition resistance by phasor trajectory analysis and extract the pure fault location characteristic function .

7. A method for locating a stator ground fault of a large wave winding generator according to claim 6, characterized in that: The pure fault location characteristic function in step 3 It is the straight line function where DA is located, and this function can be decoupled from the transition resistance; ； Where, is the slope of the straight line DA, is the coordinate of point D, point D is the starting point of the fundamental zero-sequence voltage vector, and point A is the fault point.

8. A method for locating a stator ground fault of a large wave winding generator according to claim 7, characterized in that: The step 4 specifically includes: Simultaneous piecewise linear functions and pure fault location characteristic function , solve the intersection of the two functions, which is the fault location.

9. A method for locating a stator ground fault of a large wave winding generator according to claim 7, characterized in that: The fault location solved in step 4 is: ； Where, It is the percentage of the distance from the fault point to the neutral point to the distance from the generator end to the neutral point.

10. A method for locating a stator ground fault of a large wave winding generator according to claim 7, characterized in that: The transition resistance solved in step 4 is: ； Where, It is the vector from the starting point of the fundamental zero-sequence voltage vector to the fault point.

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