Generator stator core feedthrough screw insulation fault monitoring circuit and method

Abstract

The application discloses a generator stator core through-core screw rod insulation fault monitoring circuit and method, and relates to the technical field of generator online monitoring.The application comprises a main unit, a measuring unit and a protection unit.The application has the beneficial effects that the application directly connects wires at both ends of the through-core screw rod, and the connection can be carried out when the generator is overhauled, so that the connection is convenient and reliable, and the possibility of poor insulation of the through-core screw rod caused by the connection is extremely small; the method can monitor the insulation condition of the through-core screw rod in real time, and can timely and effectively find one-point grounding, multi-point grounding and ground current change conditions, thereby providing a reference basis for safe operation and emergency shutdown and overhaul of the generator; the application has the effect of early and accurate prediction on large-area burning accidents of the synchronous generator stator core caused by insulation faults of the through-core screw rod, and ensures long-term safe and stable operation of the generator.

Description

Technical Field

[0001] This invention relates to the field of generator online monitoring technology, and in particular to a generator stator core through-bolt insulation fault monitoring circuit and method. Background Technology

[0002] The stator core tensioning screw is a crucial structure for securing the silicon steel sheets of the generator stator core. In large and medium-sized hydro-generators, due to the height and large area of ​​the stator core, a metal screw is often used to tighten the core by passing through the yoke of the stator core; this is called a stator core through-bolt. During unit operation, the stator core generates an alternating magnetic field with high magnetic flux density, which will induce a significant voltage on the through-bolt.

[0003] Currently, there are two main methods for detecting the insulation condition of the stator core bolts in generators: the first method uses a megohmmeter to measure the insulation resistance, but this method requires the generator to be shut down and cannot achieve real-time online measurement. The second method is described in "Monitoring Method for Short Circuit Faults in the Stator Core and Bolts of Synchronous Generators" invented by Wu Yucai of North China Electric Power University (Baoding), see [link to article]. Figure 1 and Figure 2 The principle is based on the induced electromotive force E=BLV of the through-screw. The through-screw is divided into several equal parts, each with the same induced voltage. When the through-screw is well-insulated, the current in the series resistor loop is 0, and the voltage across the resistor is also 0. When a ground fault occurs at position 1, it forms a closed loop with the resistor, generating a ground current. A voltage drop occurs across the resistor, indicating a ground fault in the through-screw. By measuring the voltage across a 100Ω resistor, the induced voltage between the device wiring and the grounding point can be calculated, thus determining the location of the grounding point.

[0004] Although this measurement method can measure the insulation status of the stator through-core screw online in real time, it still has many shortcomings. Disadvantage 1: The measuring wire needs to be connected to the middle of the stator through-core screw. The ventilation groove of this 600MW hydro-generator is 6mm high, and the distance between the through-core screw and the back of the iron core is 205mm. Theoretically, the wire can be connected from the middle of the back of the generator stator iron core by removing the air cooler. The lead wire connection is difficult. If the lead wire insulation is not properly treated, it is easy to cause the through-core screw to contact the iron core directly, resulting in the through-core screw grounding. At the same time, the stator iron core between the air coolers is in a fully enclosed state and the wire cannot be connected from the middle, so online monitoring is not possible. Disadvantage 2: It can only measure the distance between the grounding point and the device lead wire, corresponding to two points, which cannot accurately determine the grounding point. Disadvantage 3: The error in determining the grounding point position is large. (I) The induced voltage of the through-core screw is proportional to the generator stator output voltage. When the generator is running at a non-rated voltage, there is a deviation in the measurement of the grounding point position. It should be multiplied by the ratio of the rated voltage to the operating voltage as a correction. (II) When the grounding resistance is large, such as when the ground resistance reaches 10000Ω, the measured grounding point location is only 1 / 2 of the actual grounding location. The low insulation resistance caused by the accumulation of dirt is a slow process. This method is only suitable for measuring the insulation monitoring of through-core screws with low grounding resistance values, and cannot effectively detect the development trend of insulation deterioration. Disadvantage 4: The grounding current generated when the through-core screw is grounded at a single point is almost 0 (which may cause a local short circuit of the silicon steel sheets in the iron core. Since the induced potential difference between the silicon steel sheets is on the order of mV, if there is a non-metallic stable short circuit and a large number of short-circuited sheets, the short-circuit resistance will be close to 0 and will not immediately cause damage to the iron core). It cannot be used as a necessary condition for emergency shutdown. This device can only measure a single grounding point. When the two grounding points are located on both sides of the device lead position, the induced current forms a circulating current through the two grounding points. The current in the series circuit of the resistor is almost zero, causing the device to judge that there is no insulation fault in the through-core screw.

[0005] In summary, the most effective method for measuring insulation faults in generator stator core through-bolts is currently offline measurement of the insulation resistance to ground. Online measurement methods are difficult to fully cover the through-bolts and pose safety hazards. Furthermore, they cannot effectively detect two-point grounding of the through-bolts, which are highly destructive to the generator stator core. Therefore, there is an urgent need to develop an online, highly accurate, easy-to-implement, safe, and reliable device and method for detecting insulation faults in stator core through-bolts. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the prior art, the present invention is proposed.

[0008] Therefore, the technical problem to be solved by the present invention is the inability to achieve online monitoring of insulation faults in the through-bolt of the generator stator core.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a generator stator core through-bolt insulation fault monitoring circuit, comprising a main unit including a through-bolt, wherein the through-bolt, when energized, induces an equivalent circuit consisting of a first resistor, a first power supply, a second resistor, a second power supply, a third resistor, and a third power supply connected in alternating series; a measuring unit including a first voltmeter and a second voltmeter, wherein one end of the first voltmeter is connected to one end of the through-bolt and the other end is grounded, and both ends of the second voltmeter are respectively connected to both ends of the through-bolt; and a protection unit including two identical fuses connected in series with the second voltmeter.

[0010] As a preferred embodiment of the generator stator core through-bolt insulation fault monitoring circuit of the present invention, wherein: both ends of the through-bolt are respectively connected to a second voltmeter by a shielded cable.

[0011] As a preferred embodiment of the generator stator core through-bolt insulation fault monitoring circuit of the present invention, the first voltmeter and the second voltmeter are both selected as high internal resistance voltmeters, with an internal resistance of not less than 10MΩ.

[0012] In a preferred embodiment of the generator stator core through-bolt insulation fault monitoring circuit of the present invention, the protection threshold of the fuse is 0.5A.

[0013] To solve the above-mentioned technical problems, the present invention also provides the following technical solution: a method for monitoring insulation faults in a generator stator core through-bolt, implemented through the aforementioned generator stator core through-bolt insulation fault monitoring circuit, comprising the following steps: calculating the induced voltage E of the through-bolt; measuring the voltage U1 of one end of the through-bolt to ground using a first voltmeter; measuring the voltage U2 between the two ends of the through-bolt using a second voltmeter; when both U1 and U2 are constant, determining that the through-bolt insulation is good; comparing U1 with a single-point grounding fault threshold Y1, and when U1 exceeds Y1, determining that the through-bolt has a single-point grounding fault; comparing U2 with a two-point grounding fault threshold Y2, and when U2 is lower than Y2, determining that the through-bolt has two or more grounding faults; when a single-point grounding fault occurs, determining the grounding point location based on the ratio of U1 to U2; when a two-point grounding fault occurs, analyzing the development of the short-circuit current inside the through-bolt based on the rate at which the U2 value decreases.

[0014] As a preferred embodiment of the generator stator core through-bolt insulation fault monitoring method of the present invention, wherein: the formula for calculating the induced voltage E of the through-bolt is:

[0015]

[0016] Wherein, U0 is the rated phase voltage of the generator, N is the number of stator bars connected in series in a single-phase winding, L1 is the width of the stator core yoke, and L2 is the distance between the through-bolt and the bottom positioning rib of the yoke.

[0017] As a preferred embodiment of the generator stator core through-bolt insulation fault monitoring method of the present invention, wherein: the single-point grounding fault threshold Y1 is taken as 0.45 to 0.55 times the through-bolt induced voltage E value.

[0018] As a preferred embodiment of the generator stator core through-bolt insulation fault monitoring method of the present invention, wherein: the two-point grounding fault threshold Y2 is taken as 0.95 times the through-bolt induced voltage E value.

[0019] As a preferred embodiment of the generator stator core through-bolt insulation fault monitoring method of the present invention, when a single-point grounding fault occurs, the upper end ground voltage U1 becomes the sum of the power supply electromotive force above the grounding point, while U2 remains unchanged. The location of the grounding point is calculated based on the ratio of U1 to U2.

[0020] In a preferred embodiment of the generator stator core through-bolt insulation fault monitoring method of the present invention, when a two-point grounding fault occurs at both ends of the second resistor and the second power supply, the smaller U2 is, the larger the induced current I is, and the easier it is for the generator stator core to burn out, according to the following formula:

[0021] R7 = R5 + R6

[0022] I = E² / (R² + R⁷)

[0023] U R7 =E2*R7 / (R2+R7)

[0024] U2=E1+E3+U R7

[0025] Where R5 and R6 are the grounding resistances at the two points at this time, R7 is the equivalent resistance of R5 and R6, I is the induced current of the equivalent circuit, E1, E2 and E3 are the electromotive forces of the first power supply, the second power supply and the third power supply, respectively, and U R7 This is the voltage across R7.

[0026] The beneficial effects of this invention are:

[0027] This invention allows for direct wiring at both ends of the through-bolt, which can be performed during generator maintenance. The wiring is convenient and reliable, and the possibility of insulation failure due to wiring is extremely low. This method enables real-time online monitoring of the through-bolt insulation, promptly and effectively detecting single-point grounding, multi-point grounding, and changes in grounding current, providing a reference for safe generator operation and emergency shutdown maintenance. Furthermore, this invention can accurately predict large-scale burn-out accidents in the synchronous generator stator core caused by through-bolt insulation faults, ensuring the long-term safe and stable operation of the generator. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0029] Figure 1 This is an existing generator stator core through-bolt insulation fault monitoring circuit;

[0030] Figure 2 This is another form of a generator stator core through-bolt insulation fault monitoring circuit based on existing technology;

[0031] Figure 3 This is a schematic diagram of the generator stator core through-bolt insulation fault monitoring circuit according to the present invention;

[0032] Figure 4 This is a schematic diagram of the various states of the generator stator core through-bolt insulation fault monitoring circuit described in this invention;

[0033] Figure 5 This is a schematic diagram of the equivalent state of two-point grounding of the generator stator core through-bolt insulation fault monitoring circuit described in this invention;

[0034] Figure 6 This is a flowchart illustrating the generator stator core through-bolt insulation fault monitoring method according to the present invention. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0038] Example 1

[0039] Reference Figure 3 This is the first embodiment of the present invention, which provides a generator stator core through-bolt insulation fault monitoring circuit, including a main unit 100, including a through-bolt C, which, when energized, induces an equivalent circuit consisting of an alternating series connection of a first resistor R1, a first power supply E1, a second resistor R2, a second power supply E2, a third resistor R3, and a third power supply E3; a measuring unit 200, including a first voltmeter V1 and a second voltmeter V2, one end of the first voltmeter V1 being connected to one end of the through-bolt C and the other end being grounded, and both ends of the second voltmeter V2 being connected to both ends of the through-bolt C; and a protection unit 300, including two identical fuses Fu, which are connected in series with the second voltmeter V2.

[0040] Both ends of the through-hole screw C are connected to the second voltmeter V2 by shielded cables.

[0041] Both the first voltmeter V1 and the second voltmeter V2 are high-resistance voltmeters, with an internal resistance of not less than 10MΩ.

[0042] The protection threshold of the fuse Fu is 0.5A.

[0043] Here, the measurement is performed using the leads at both ends of the through-hole screw C, replacing the intermediate measurement method of the existing technology.

[0044] Example 2

[0045] Reference Figures 3-6This is the second embodiment of the present invention, which provides a method for monitoring insulation faults in a generator stator core through-bolt. The method is implemented using the aforementioned generator stator core through-bolt insulation fault monitoring circuit and includes the following steps: calculating the induced voltage E of the through-bolt; measuring the voltage U1 to ground at one end of the through-bolt C using a first voltmeter V1; measuring the voltage U2 between the two ends of the through-bolt C using a second voltmeter V2; determining that the insulation of the through-bolt C is good when both U1 and U2 remain constant; comparing U1 with a single-point grounding fault threshold Y1, determining that a single-point grounding fault exists in the through-bolt C when U1 exceeds Y1; comparing U2 with a two-point grounding fault threshold Y2, determining that two or more grounding faults exist in the through-bolt C when U2 is lower than Y2; calculating the location of the grounding point based on the ratio of U1 to U2 when a single-point grounding fault occurs; and analyzing the development of the internal short-circuit current of the through-bolt C based on the rate at which the value of U2 decreases when a two-point grounding fault occurs.

[0046] The formula for calculating the induced voltage E of the through-hole screw is:

[0047]

[0048] Wherein, U0 is the rated phase voltage of the generator, N is the number of stator bars connected in series in a single-phase winding, L1 is the width of the stator core yoke, and L2 is the distance between the through-bolt and the bottom positioning rib of the yoke.

[0049] The threshold value Y1 for a single-point grounding fault is 0.45 to 0.55 times the induced voltage E value of the through-hole screw.

[0050] The two-point grounding fault threshold Y2 is taken as 0.95 times the induced voltage E value of the through-hole screw.

[0051] When a ground fault occurs, the voltage U1 at the upper end becomes the sum of the electromotive force of the power supply above the grounding point. At this time, U2 remains unchanged. The location of the grounding point is calculated based on the ratio of U1 to U2.

[0052] When a two-point grounding fault occurs at both ends of the second resistor R2 and the second power supply E2, the distance between the two grounding points can be determined based on the change in U2 using the following formula:

[0053] R7 = R5 + R6

[0054] I = E² / (R² + R⁷)

[0055] U R7 =E2*R7 / (R2+R7)

[0056] U2=E1+E3+U R7

[0057] Where R5 and R6 are the grounding resistances at the two points at this time, R7 is the equivalent resistance of R5 and R6, I is the induced current of the equivalent circuit, E1, E2 and E3 are the electromotive forces of the first power supply E1, the second power supply E2 and the third power supply E3 respectively, and U R7 This is the voltage across R7.

[0058] The two ends of the generator stator core through-bolt are respectively led out with shielded cables to the input terminals of the measuring device, and connected to 0.5A fuses Fu for protection. The voltage between the upper end of the through-bolt and ground, and the voltage between the upper and lower ends are measured respectively. Figure 4 As shown.

[0059] The induced voltage generated by the through-bolts in the stator core of a generator in a magnetic field can be viewed as a circuit diagram of multiple power sources connected in series with resistors, such as... Figure 5 The diagram shows three sets of power supply resistors connected in series to represent three operating states of the through-core screw: good insulation, single-point grounding, and two-point grounding. Since the grounding resistance often gradually decreases with increasing dust and oil contamination during operation, it is not a zero-resistance grounding. Resistors R4, R5, and R6 are used to represent the grounding resistance. The voltage U1 between the upper end and ground, and the voltage U2 between the upper end and lower end are measured (the following analysis assumes the generator output voltage is the rated voltage; when the output voltage varies significantly, the voltage and current data should be corrected by multiplying them by the ratio of the operating voltage to the rated voltage).

[0060] When the stator core through-bolt is well insulated, both U1 and U2 remain constant. When grounded at a single point through resistor R4, the potential at that grounding point is 0. Since no current loop is generated, U2 remains unchanged, and U1 = E1. Because the induced voltage and resistance value generated by each section of the through-bolt are proportional to the length of the through-bolt, the location of the grounding point can be calculated by the ratio of U1 and U2.

[0061] When the two points of the through-hole screw are grounded through resistors R5 and R6, the circuit and current diagram can be simplified as follows: Figure 6 As shown, R7 = R5 + R6, current I = E2 / (R2 + R7), voltage U across R7. R7 =E2*R7 / (R2+R7), U2=E1+E3+U R7 From the above formula, it can be deduced that the magnitude of the induced current is directly proportional to the magnitude of E2. That is, the greater the distance between the two short-circuit points and the smaller the grounding resistance, the greater the induced current and the smaller the voltage U3 across the terminals.

[0062] Since the induced voltage E of the through-screw is proportional to the generator stator outlet phase voltage, for units with large fluctuations in generator stator outlet voltage (such as frequent deviations from the rated voltage exceeding ±5%), the ratio of the real-time generator outlet voltage to the rated voltage should be introduced to correct the voltage threshold of the online monitoring system, thereby improving measurement accuracy. The operating voltage of a hydro-generator is generally specified as 90%-110% of the rated voltage. When high measurement accuracy is not required, the threshold can be appropriately increased to avoid fluctuations in normal operating voltage.

[0063] Example 3

[0064] In the third embodiment of this invention, to verify the effectiveness of the generator stator core through-bolt insulation fault monitoring method, the following type of hydro-generator was used for testing:

[0065] Table 1 Parameters of the Test Hydrogen Generator

[0066]

[0067]

[0068] Each slot consists of two stator bars, one above the other. The number of stator bars is twice the number of stator slots, i.e., 900 bars. The stator connection method is 6 branches. The number of single-phase, single-branch series bars is 900 / (3*6), i.e., 50 bars. The induced voltage of each bar is... The induced voltage of the through-screw is E2 = E1 * L2 / L1 = 137.6V, where L1 is the width of the stator core yoke and L2 is the distance between the through-screw and the bottom positioning rib of the yoke.

[0069] When the generator is running at its rated voltage, the induced voltage U2 between the two ends of the properly insulated through-core screw is measured to be 136.4V-138.2V, which is within the normal range.

[0070] A through-core screw with an unloaded induced voltage of 137.2V was grounded at its lower end through a resistance box (0-99999Ω, rated current 0.5A) to simulate a single-point grounding phenomenon. The resistance box was initially adjusted to 99999Ω and gradually adjusted towards 0Ω. The voltage U2 between the two ends was measured and kept constant at 137.2V. At the same time, a clamp meter was used to measure the grounding current, which was 0A. The voltage U1 at the upper end to ground gradually increased from 134.4V to 137.2V, exceeding the threshold range (61.7V-75.5V), indicating a grounding phenomenon. The distance L between the grounding point and the upper end of the iron core was calculated as L = h * U1 / U 2，In the formula, h represents the stator core height of 3300mm. The calculated distances between the grounding point and the upper end of the core when the grounding resistance is 99999Ω and 0Ω are 3232.7mm and 3300mm, respectively. In summary, the smaller the grounding resistance, the more accurate the measurement. Even when the end grounding resistance reaches 99999Ω, the measurement error is only 67.3mm, with an accuracy of 98%.

[0071] A sliding rheostat with a resistance of 0-50Ω and a rated current of 5A is connected between the upper and lower ends of a through-hole screw to simulate a two-point grounding phenomenon. The initial value of the sliding rheostat is adjusted to the maximum of 50Ω, and the resistance of the sliding rheostat is gradually reduced to a current of 5A. The voltages at the two ends are measured at currents of 3A, 4A, and 5A, respectively: 129.4V, 126.8V, and 124.4V. These are 94%, 92%, and 91% of the voltage of 137.2V when the insulation is in good condition, respectively. This is lower than 0.95 times the voltage threshold at both ends, indicating a two-point or more grounding fault. The smaller the grounding short-circuit resistance and the larger the grounding current, the lower the voltage between the two ends, and the greater the damage to the generator stator core. Therefore, the voltage at both ends can be set as the first-level alarm value, the second-level alarm value, and the emergency shutdown alarm value based on the grounding current that the generator stator core can withstand. To prevent false alarms caused by broken wires at the ends, after a Level 1 alarm, a resistor of about 100Ω can be connected in series to the leads at both ends. The current flowing through the resistor can be measured. If the current value is very low or even 0 (the threshold can be set to 0.1A), it is determined that there is a broken wire. The alarm signal can be blocked, and the wire can be repaired after the unit is shut down.

[0072] The simulation results above show that by extending the leads from both ends of the generator stator core bolt and measuring the voltage to ground at the upper end and the voltage between the upper and lower ends, the insulation condition of the bolt can be monitored in real time. This effectively detects single-point grounding and calculates the approximate location of the grounding point, as well as two-point or more grounding short-circuit faults and their development speed (monitoring the rate of voltage drop at both ends). It features simple wiring, safety and reliability, low cost, and comprehensive functionality, filling the gaps in existing technologies.

[0073] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A generator stator core through-bolt insulation fault monitoring circuit, characterized in that: include, The main unit (100) includes a through-hole screw (C), which, when energized, induces an equivalent circuit consisting of an alternating series connection of a first resistor (R1), a first power supply (E1), a second resistor (R2), a second power supply (E2), a third resistor (R3), and a third power supply (E3); The measuring unit (200) includes a first voltmeter (V1) and a second voltmeter (V2). One end of the first voltmeter (V1) is connected to one end of the through-hole screw (C), and the other end is grounded. The two ends of the second voltmeter (V2) are respectively connected to the two ends of the through-hole screw (C). The protection unit (300) includes two identical fuses (Fu) connected in series with a second voltmeter (V2).

2. The generator stator core through-bolt insulation fault monitoring circuit as described in claim 1, characterized in that: The two ends of the through-hole screw (C) are respectively connected to the second voltmeter (V2) by shielded cables.

3. The generator stator core through-bolt insulation fault monitoring circuit as described in claim 2, characterized in that: Both the first voltmeter (V1) and the second voltmeter (V2) are high-resistance voltmeters with an internal resistance of not less than 10MΩ.

4. The generator stator core through-bolt insulation fault monitoring circuit as described in any one of claims 1 to 3, characterized in that: The protection threshold of the fuse (Fu) is 0.5A.

5. A method for monitoring insulation faults in the through-bolt of a generator stator core, characterized in that: This is achieved through the generator stator core through-bolt insulation fault monitoring circuit as described in any one of claims 1 to 4, including the following steps: Calculate the induced voltage E of the through-hole screw; Measure the voltage U1 at one end of the through-hole screw (C) to ground using the first voltmeter (V1); The voltage U2 between the two ends of the through-hole screw (C) is measured using the second voltmeter (V2); When both U1 and U2 remain constant, the through-core screw (C) is determined to have good insulation. Compare U1 with the single-point grounding fault threshold Y1. When U1 exceeds Y1, it is determined that the through-core screw (C) has a single-point grounding fault. When U2 is compared with the two-point grounding fault threshold Y2, if U2 is lower than Y2, it is determined that the through-core screw (C) has two or more grounding faults. When a ground fault occurs, the location of the ground fault is calculated based on the ratio of U1 to U2. When a two-point grounding fault occurs, the development of the short-circuit current inside the through-core screw (C) is analyzed based on the rate at which the U2 value decreases.

6. The generator stator core through-bolt insulation fault monitoring method as described in claim 5, characterized in that: The formula for calculating the induced voltage E of the through-hole screw is: Wherein, U0 is the rated phase voltage of the generator, N is the number of stator bars connected in series in a single-phase winding, L1 is the width of the stator core yoke, and L2 is the distance between the through-bolt and the bottom positioning rib of the yoke.

7. The generator stator core through-bolt insulation fault monitoring method as described in claim 6, characterized in that: The ground fault threshold Y1 is taken as 0.45 to 0.55 times the induced voltage E of the through-hole screw.

8. The generator stator core through-bolt insulation fault monitoring method as described in claim 7, characterized in that: The two-point grounding fault threshold Y2 is taken as 0.95 times the induced voltage E value of the through-hole screw.

9. The generator stator core through-bolt insulation fault monitoring method as described in claim 5, characterized in that: When a ground fault occurs, R4 represents the grounding resistance at this time. The voltage U1 at one end to ground becomes the sum of the electromotive force of the power supply above the grounding point. At this time, U2 remains unchanged. The location of the grounding point is calculated based on the ratio of U1 to U2.

10. The generator stator core through-bolt insulation fault monitoring method as described in claim 5, characterized in that: When a two-point ground fault occurs at both ends of the second resistor (R2) and the second power supply (E2), the smaller U2 is, the larger the induced current I will be, and the easier it will be for the generator stator core to burn out, according to the following formula: R7 = R5 + R6 I = E² / (R² + R⁷) U R7 =E2*R7 / (R2+R7) U2E1+E3+U R7 Where R5 and R6 are the grounding resistances at the two points at this time, R7 is the equivalent resistance of R5 and R6, I is the induced current of the equivalent circuit, E1, E2 and E3 are the electromotive forces of the first power supply (E1), the second power supply (E2) and the third power supply (E3) respectively, and U R7 This is the voltage across R7.

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