Test and verification method for suitability of parameters of generator neutral point grounding system

Abstract

The invention discloses a method for testing and verifying the applicability of parameters of a generator neutral point grounding system, comprising the following steps: S1, connecting a measuring instrument and a grounding device to the generator neutral point grounding system; S2, measuring and verifying the neutral point asymmetric voltage of the neutral point grounding system; S3, measuring and verifying the neutral point displacement voltage of the neutral point grounding system; S4, measuring and verifying the single-phase grounding maximum capacitance current of the neutral point grounding system; S5, measuring and verifying the single-phase grounding maximum fault current of the neutral point grounding system; wherein, the order of steps S2 to S5 can be adjusted arbitrarily; the verification method proposed by the invention can effectively verify the performance indicators of different neutral point grounding methods of the generator and determine whether the neutral point grounding method of the generator and the parameters of the grounding device meet the engineering requirements by conducting a generator neutral point grounding system parameter test by simulating faults before and after the neutral point of the generator is connected to the grounding device.

Description

Technical Field

[0001] The invention discloses a generator neutral point grounding system parameter adaptability test verification method, belongs to the technical field of power system generators, and is suitable for unit-connected generator neutral point grounding system parameter testing. Background Art

[0002] Generator neutral point grounding methods usually include ungrounded, grounded via arc suppression coils, and grounded via high resistance. With the commissioning of large hydroelectric generators, the single-phase capacitive current of the generator to ground is getting larger and larger, and the above three traditional grounding methods can no longer meet engineering requirements. Among them, the ungrounded method has problems such as high arc grounding overvoltage, the arc suppression coil grounding method has high displacement voltage, and the high resistance grounding method has problems such as excessive single-phase grounding current.

[0003] When the arc grounding overvoltage of the generator neutral point is too high, there is a risk of insulation breakdown. When the displacement voltage is too high, there is a risk of false tripping of the stator winding single-phase grounding protection and affecting the power quality. When the single-phase grounding current of the generator stator winding is too large, there is a risk of burning the stator core. In recent years, high-impedance grounding has emerged. The high-impedance grounding method is achieved by connecting a grounding device with a resistor and a reactance in parallel on the secondary side of the grounding transformer, which can take into account both the displacement voltage and the single-phase grounding current.

[0004] The parameters of the generator neutral point grounding system directly affect the safe operation of the generator. In order to verify whether the generator neutral point grounding method and grounding device parameters meet the engineering requirements, it is necessary to conduct an adaptability test of the generator neutral point grounding system parameters. At present, there is no method and technology to test and verify the parameters of the generator neutral point grounding system. Summary of the invention

[0005] The purpose of the present invention is: the present invention proposes an adaptability test verification method for the grounding system parameters of the above-mentioned grounding method of the generator neutral point, including the generator neutral point asymmetric voltage, displacement voltage, single-phase grounding maximum capacitance current, and single-phase grounding maximum fault current test methods. The present invention conducts a generator neutral point grounding system parameter test by simulating faults before and after the generator neutral point is connected to the grounding device, which can effectively verify the performance indicators of different grounding methods of the generator neutral point and determine whether the generator neutral point grounding method and the grounding device parameters meet the engineering requirements.

[0006] The technical solution of the present invention:

[0007] The generator neutral point grounding system parameter applicability test verification method includes the following steps:

[0008] S1, connect the measuring instrument and grounding device to the generator neutral point grounding system;

[0009] S2, measurement and verification of neutral point asymmetric voltage in neutral point grounding system;

[0010] S3, measurement and verification of neutral point displacement voltage in neutral point grounding system;

[0011] S4, measurement and verification of the maximum capacitance current of single-phase grounding in neutral point grounding system;

[0012] S5, measurement and verification of the maximum single-phase ground fault current in the neutral point grounding system;

[0013] The order of steps S2 to S5 can be adjusted arbitrarily.

[0014] Furthermore, the generator neutral point grounding system includes a generator, a generator neutral point grounding device, a main transformer, and an excitation transformer between the generator and the main transformer, a plant transformer, a cable and a busbar.

[0015] Further, in step S1, the grounding device JZ is connected to the neutral point of the generator via the circuit breaker QS, and the other end of the grounding device JZ is grounded via the current transformer TA; the voltage transformer TV is connected to the neutral point of the generator via the relay KC, and the other end of the voltage transformer TV is grounded via the current transformer TA; the current transformer TA1 is connected to any one of the three-phase windings at the generator output via the relay KG, and the other end of the current transformer TA1 is grounded, and the three-phase winding of the generator is connected to the main transformer through the circuit breaker QF.

[0016] Furthermore, in step S2, when measuring the neutral point asymmetric voltage, the circuit breaker QS is disconnected, the neutral point of the generator is not grounded, and at the same time, the relay KG is disconnected, the relay KC is closed, the circuit breaker QF is closed, the generator stator is connected to the test voltage, the generator is operated with the main transformer, and the generator speed is increased to the rated speed n N , and stabilize at n N ±0.05%n N Finally, read the three-phase voltage of the generator stator winding and the neutral point voltage measured by the voltage transformer TV. At this time, the neutral point voltage measured by the voltage transformer TV is the neutral point asymmetric voltage, and compare the neutral point asymmetric voltage with the standard requirement value.

[0017] Furthermore, when the test voltage of the generator stator is the highest, that is, 100% of the rated stator voltage, there may be safety hazards due to the excessively high test voltage. By reducing the test voltage to 30% of the rated voltage of the generator, and then converting the neutral point voltage measured by the voltage transformer TV at this time to 100% of the rated voltage, the converted generator neutral point voltage is the neutral point asymmetric voltage.

[0018] Further, in step S3, the neutral point displacement voltage of the neutral point grounding system is measured and verified, the circuit breaker QS is closed, and the neutral point of the generator is connected to the grounding device JZ. At the same time, the relay KG is disconnected, the relay KC is closed, the circuit breaker QF is closed, the generator is operated with the main transformer, and the generator speed is increased to the rated speed n N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 30% ~ 100% of the rated voltage, and the three-phase voltage and neutral point voltage of the generator stator winding are read. The neutral point voltage of the generator at 100% of the rated voltage is the neutral point displacement voltage, and the neutral point asymmetric voltage is compared with the standard requirement value.

[0019] Further, in step S4, when measuring and verifying the single-phase grounding maximum capacitance current of the neutral point grounding system, the circuit breaker QS is disconnected, and the neutral point of the generator is not grounded. At the same time, the relay KG is closed, the relay KC is closed, the circuit breaker QF is closed, the generator is operated with the main transformer, the stator winding is single-phase grounded, and the generator speed is increased to the rated speed n N , stable at n N ±0.05%n N Afterwards, the test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed the threshold current. The three-phase voltage of the generator stator winding is read, the single-phase grounding capacitance current is read and the waveform is recorded. The single-phase grounding capacitance current is linearly converted to 100% of the rated voltage. This single-phase grounding capacitance current is the maximum single-phase grounding capacitance current of the generator.

[0020] Furthermore, the single-phase grounding capacitor current is read by an oscilloscope and the waveform is recorded.

[0021] Furthermore, the test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed 4A.

[0022] Further, in step S5, when measuring and verifying the single-phase grounding maximum fault current of the neutral point grounding system, the circuit breaker QS is closed, and the neutral point of the generator is connected to the grounding device JZ. At the same time, the relay KG is closed, the relay KC is closed, the circuit breaker QF is closed, the generator is operated with the main transformer, the generator outlet is single-phase grounded, and the generator speed is increased to the rated speed n N , stable at n N ±0.05%n N Afterwards, the test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed the threshold current. The three-phase voltage of the generator stator winding is read, the single-phase grounding fault current and the generator neutral point current are read and the waveform is recorded. The single-phase grounding fault current is linearly converted to 100% of the rated voltage. This single-phase grounding fault current is the maximum single-phase grounding fault current of the generator.

[0023] Furthermore, the single-phase ground fault current and the generator neutral point current are read by an oscilloscope and the waveforms are recorded.

[0024] Furthermore, the test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed 4A.

[0025] Beneficial effects of the present invention: The present invention proposes an adaptability test verification method for the grounding system parameters of the above-mentioned grounding methods for the neutral point of the generator, including a test method for the asymmetric voltage, displacement voltage, single-phase grounding maximum capacitance current, and single-phase grounding maximum fault current of the neutral point of the generator. The present invention conducts a generator neutral point grounding system parameter test by simulating faults before and after the neutral point of the generator is connected to the grounding device, which can effectively verify the performance indicators of different grounding methods for the neutral point of the generator and determine whether the neutral point grounding method of the generator and the parameters of the grounding device meet the engineering requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the equivalent circuit schematic diagram of the generator neutral point grounding system;

[0027] Figure 2 This is a system wiring schematic diagram of the testing method of the present invention. DETAILED DESCRIPTION

[0028] The following is a further detailed description of the specific implementation of the present invention, such as the shape, structure, mutual position and connection relationship between the various components involved, the function and working principle of each part, the manufacturing process and the operation method, etc., through the description of the embodiments with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solution of the present invention:

[0029] The invention discloses a method for testing and verifying the adaptability of parameters of a generator neutral point grounding system, and relates to the technical field of generators in power systems. The parameters of the generator neutral point grounding system directly affect the safe operation of the generator. In order to verify whether the neutral point grounding mode and grounding device parameters of the generator meet the engineering requirements, it is necessary to conduct a test on the adaptability of the parameters of the generator neutral point grounding system, including the asymmetric voltage of the generator neutral point, the displacement voltage, the maximum capacitance current of the single-phase grounding, and the maximum fault current of the single-phase grounding; the invention proposes a test method for the above four parameters of the generator neutral point grounding system, and has been demonstrated on a number of large and medium-sized hydro-turbine generators and individual steam turbine generators. The test method is applicable to four grounding modes: the neutral point of the generator is not grounded, grounded through an arc suppression coil, grounded through a high resistance, and grounded through a high impedance.

[0030] The generator neutral point grounding system parameter applicability test verification method provided by the present invention specifically comprises the following steps:

[0031] S1, connect the measuring instrument and grounding device to the generator neutral point grounding system;

[0032] S2, measurement and verification of neutral point asymmetric voltage in neutral point grounding system;

[0033] S3, measurement and verification of neutral point displacement voltage in neutral point grounding system;

[0034] S4, measurement and verification of the maximum capacitance current of single-phase grounding in neutral point grounding system;

[0035] S5, measurement and verification of the maximum single-phase ground fault current in the neutral point grounding system;

[0036] The order of steps S2 to S5 can be adjusted arbitrarily.

[0037] The generator neutral point grounding system includes the generator, the generator neutral point grounding device, the main transformer, and the excitation transformer, plant transformer, cable and busbar between the generator and the main transformer. The stator winding to ground capacitance is a distributed capacitance. For the convenience of analysis, the stator winding to ground distributed capacitance is regarded as a concentrated capacitance and connected in parallel between the stator winding outlet of the generator and the ground. The generator neutral point grounding device can be equivalent to a parallel equivalent circuit of resistance and inductance. The general schematic diagram of the generator neutral point grounding system is as follows: Figure 1 When calculating the neutral point voltage of a generator, it is usually assumed that the three-phase resistance of the generator to the ground is equal, and the phase-to-phase capacitance of the conductors is ignored.

[0038] The theoretical parameters of the neutral point grounding system can be calculated as follows:

[0039] 1) Neutral point asymmetric voltage

[0040] Neutral point asymmetric voltage U bd for

[0041]

[0042] Where:

[0043] U bd ——Neutral point asymmetric voltage, V.

[0044] 2) Displacement voltage

[0045] General displacement voltage expression for

[0046]

[0047] Where:

[0048] α and α 2——Operator, α is to rotate the original phase quantity 120° counterclockwise, α 2 It is to rotate the original phase quantity 240° counterclockwise;

[0049] ω——angular velocity, 314rad / s;

[0050] Y0——generator neutral point admittance;

[0051] Y A , Y B , Y C ——The three-phase admittance of generator A, B and C.

[0052] 3) Displacement voltage coefficient m

[0053] The displacement voltage coefficient m is

[0054]

[0055] Where:

[0056] V——Detuning degree, the ratio of the maximum capacitive current of the generator single-phase grounding fault to the maximum capacitive current of the generator single-phase grounding, that is, V=(I C -I L ) / I C ;

[0057] d——damping rate, the ratio of the maximum resistive current of the generator single-phase grounding fault to the maximum capacitive current of the generator single-phase grounding, that is, d=I r / I c ;

[0058] I c ——Maximum capacitive current of single-phase grounding, A;

[0059] I L ——Equivalent inductive current on the primary side of the grounding transformer, A;

[0060] I r ——Equivalent resistive current on the primary side of the grounding transformer, A.

[0061] The allowable value of the displacement voltage coefficient can be determined as 1.5.

[0062] 4) Maximum capacitive current of single-phase grounding

[0063] Single-phase grounding maximum capacitive current I C∑ for

[0064]

[0065] Where:

[0066] U n ——Rated line voltage of generator stator winding, V;

[0067] C ∑ ——Total capacitance of generator stator circuit per phase to ground, F.

[0068] 5) Maximum single-phase ground fault current

[0069] Maximum single-phase ground fault current I k for

[0070]

[0071] Where:

[0072] I k ——Maximum single-phase ground fault current, A;

[0073] I r ——Maximum resistive current of single-phase grounding, A;

[0074] Ic'——maximum capacitive current of single-phase grounding, A.

[0075] In one embodiment of the present invention, in step S1, specifically, the grounding device JZ is connected to the neutral point of the generator via the circuit breaker QS, and the other end of the grounding device JZ is grounded via the current transformer TA; the voltage transformer TV is connected to the neutral point of the generator via the relay KC, and the other end of the voltage transformer TV is grounded via the current transformer TA, and the voltage transformer TV is used to measure the neutral point voltage of the generator; the current transformer TA1 is connected to any one of the three-phase windings at the generator output via the relay KG, and the other end of the current transformer TA1 is grounded, and the secondary side of the current transformer TA is connected in series with an ammeter A for measuring the neutral point grounding current of the generator, and in addition, the three-phase winding of the generator is connected to the main transformer through the circuit breaker QF.

[0076] In one embodiment of the present invention, in step S2, the generator neutral point asymmetric voltage refers to the neutral point to ground voltage at rated voltage when the generator neutral point is not grounded. When measuring the neutral point asymmetric voltage, the circuit breaker QS is disconnected, the generator neutral point is not grounded, and at the same time, the relay KG is disconnected, the relay KC is closed, the circuit breaker QF is closed, the generator stator is connected to the test voltage, the generator is operated with the main transformer, and the generator speed is increased to the rated speed n. N , and stabilize at n N ±0.05%n NThen, read the three-phase voltage of the generator stator winding and the neutral point voltage measured by the voltage transformer TV. At this time, the neutral point voltage measured by the voltage transformer TV is the neutral point asymmetric voltage, and compare the neutral point asymmetric voltage with the standard requirement value; among them, when the test voltage of the generator stator is the highest, that is, 100% of the rated stator voltage, there may be safety hazards due to the excessively high test voltage. By reducing the test voltage to 30% of the rated voltage of the generator, the neutral point voltage measured by the voltage transformer TV at this time is converted to 100% of the rated voltage, and the converted generator neutral point voltage is the neutral point asymmetric voltage.

[0077] In one embodiment of the present invention, in step S3, the neutral point displacement voltage of the generator refers to the neutral point to ground voltage at the rated voltage after the neutral point of the generator is connected to the grounding device. The neutral point displacement voltage of the neutral point grounding system is measured and verified. The circuit breaker QS is closed, and the neutral point of the generator is connected to the grounding device JZ. At the same time, the relay KG is disconnected, the relay KC is closed, the circuit breaker QF is closed, the generator is operated with the main transformer, and the generator speed is increased to the rated speed n. N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 30% to 100% of the rated voltage, and the three-phase voltage and neutral point voltage of the generator stator winding are read. The neutral point voltage of the generator at 100% of the rated voltage is the neutral point displacement voltage, and the neutral point asymmetric voltage is compared with the standard required value. After the neutral point asymmetric voltage test, the generator neutral point displacement voltage coefficient needs to be calculated. The displacement voltage coefficient refers to the ratio of the neutral point displacement voltage of the generator at the rated voltage to the neutral point asymmetric neutral point voltage. The calculated generator neutral point displacement voltage coefficient is compared with the required value.

[0078] In one embodiment of the present invention, in step S4, the single-phase grounding maximum capacitance current refers to the current flowing through the grounding point when the neutral point of the generator is not grounded and single-phase metallic grounding occurs at rated voltage. When measuring and verifying the single-phase grounding maximum capacitance current of the neutral point grounding system, the circuit breaker QS is disconnected, the neutral point of the generator is not grounded, and at the same time, the relay KG is closed, the relay KC is closed, the circuit breaker QF is closed, the generator is running with the main transformer, the stator winding is single-phase grounded, and the generator speed is increased to the rated speed n N , stable at n N ±0.05%n NAfter that, the test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed the threshold current, the three-phase voltage of the generator stator winding is read, the single-phase grounding capacitance current is read and the waveform is recorded, and the single-phase grounding capacitance current is linearly converted to 100% of the rated voltage. This single-phase grounding capacitance current is the maximum capacitance current of the generator single-phase grounding. Among them, the single-phase grounding capacitance current is read and recorded by the recorder, and the test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed 4A.

[0079] In one embodiment of the present invention, in step S5, the maximum single-phase grounding fault current refers to the current flowing through the grounding point at the rated voltage when the generator neutral point is connected to the grounding device and the generator outlet is single-phase metallic grounded. When measuring and verifying the maximum single-phase grounding fault current of the neutral point grounding system, the circuit breaker QS is closed, the neutral point of the generator is connected to the grounding device JZ, and at the same time, the relay KG is closed, the relay KC is closed, the circuit breaker QF is closed, the generator is running with the main transformer, the generator outlet is single-phase grounded, and the generator speed is increased to the rated speed n N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 20% ~ 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed the threshold current, the three-phase voltage of the generator stator winding is read, the single-phase grounding fault current and the generator neutral point current are read and the waveform is recorded, and the single-phase grounding fault current is linearly converted to 100% of the rated voltage. This single-phase grounding fault current is the maximum single-phase grounding fault current of the generator. Among them, the single-phase grounding fault current and the generator neutral point current are read and the waveform is recorded by a recorder, and the test voltage is gradually increased to 20% ~ 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed 4A.

[0080] (4) Field test examples

[0081] 1) Generator neutral point grounding system parameters

[0082] The rated capacity of the generator is 175MW, the rated voltage is 13.8kV, the single-phase capacitance of the stator winding to ground is 2.281μF, the neutral point of the generator adopts a high-impedance grounding device, the grounding transformer model is FDG-100 / 13.8 / 0.4, the rated capacity is 100kVA, the rated voltage is 13.8kV / 0.4kV, the transformation ratio is 34.5, the resistance value of the secondary resistor of the grounding transformer is 0.67Ω (21℃), and the inductance value of the reactor is 2.19mH. The rated voltage of the main transformer is 242kV / 13.8kV, and the capacitance between the high and low voltage windings is 0.0062μF.

[0083] 2) Test conclusion

[0084] A. At 100% rated stator voltage, after the test process of steps S2 to S5, the generator neutral point asymmetric voltage is 483.71V, the neutral point displacement voltage is 646.70V, which does not exceed the standard requirement of 10% rated phase voltage 796.8V, and the displacement voltage coefficient is 1.336, which does not exceed the required value of 1.5. After the high impedance grounding device is connected, the generator neutral point voltage increases, but the increase is not much. The neutral point asymmetric voltage and displacement voltage test reflects the change of the generator neutral point voltage before and after the grounding device is connected.

[0085] B. The single-phase grounding capacitance current of the generator is 17.12A when converted to the rated voltage, which exceeds the short-term allowable value of the single-phase grounding maximum fault current of 15A. After the neutral point of the generator is connected to the high-impedance grounding device, the single-phase grounding maximum fault current of the generator is 12.37A, which is less than the short-term allowable value of the single-phase grounding fault current of 15A, indicating that the high-impedance grounding device can effectively reduce the single-phase grounding fault current. The single-phase grounding maximum capacitance current and single-phase grounding maximum fault current test reflect the change of the single-phase grounding maximum fault current before and after the grounding device is connected.

[0086] C. The generator neutral point asymmetric voltage, displacement voltage, single-phase grounding maximum capacitance current and single-phase grounding maximum fault current reflect the advantages and disadvantages of the generator neutral point grounding method and grounding device parameter selection. Carrying out the applicability test of the above parameters can guide the selection of the generator neutral point grounding method or optimize the grounding device parameters, which has important engineering practice significance.

[0087] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be equivalent replacement methods and shall be included in the protection scope of the present invention.

Claims

1. A method for testing and verifying the suitability of parameters of a generator neutral point grounding system, characterized in that: The following steps are involved: S1, connect the measuring instrument and grounding device to the generator neutral point grounding system; S2, measurement and verification of neutral point asymmetric voltage in neutral point grounding system; S3, measurement and verification of neutral point displacement voltage in neutral point grounding system; S4, measurement and verification of the maximum capacitance current of single-phase grounding in neutral point grounding system; S5, measurement and verification of the maximum single-phase ground fault current in the neutral point grounding system; Among them, the order between steps S2 to S5 can be adjusted arbitrarily; The generator neutral point grounding system includes the generator, the generator neutral point grounding device, the main transformer, the excitation transformer between the generator and the main transformer, the plant transformer, the cable and the busbar; In step S1, the grounding device JZ is connected to the neutral point of the generator through the circuit breaker QS, and the other end of the grounding device JZ is grounded through the current transformer TA; the voltage transformer TV is connected to the neutral point of the generator through the relay KC, and the other end of the voltage transformer TV is grounded through the current transformer TA; the current transformer TA1 is connected to any one of the three-phase windings at the generator output through the relay KG, and the other end of the current transformer TA1 is grounded, and the three-phase windings of the generator are connected to the main transformer through the circuit breaker QF; In step S2, when measuring the neutral point asymmetric voltage, disconnect the circuit breaker QS, the neutral point of the generator is not grounded, and at the same time, disconnect the relay KG, close the relay KC, close the circuit breaker QF, connect the generator stator to the external test voltage, and run the generator with the main transformer to increase the generator speed to the rated speed n N , and stabilize at n N ±0.05%n N Finally, read the three-phase voltage of the generator stator winding and the neutral point voltage measured by the voltage transformer TV. At this time, the neutral point voltage measured by the voltage transformer TV is the neutral point asymmetric voltage, and compare the neutral point asymmetric voltage with the standard requirement value.

2. The generator neutral point grounding system parameter applicability test verification method according to claim 1 is characterized in that: When the test voltage of the generator stator is the highest, that is, 100% of the rated stator voltage, there may be safety hazards due to the excessively high test voltage. By reducing the test voltage to 30% of the rated voltage of the generator, and then converting the neutral point voltage measured by the voltage transformer TV at this time to 100% of the rated voltage, the converted generator neutral point voltage is the neutral point asymmetric voltage.

3. The generator neutral point grounding system parameter applicability test verification method according to claim 2 is characterized in that: In step S3, the neutral point displacement voltage of the neutral point grounding system is measured and verified, the circuit breaker QS is closed, and the neutral point of the generator is connected to the grounding device JZ. At the same time, the relay KG is disconnected, the relay KC is closed, the circuit breaker QF is closed, the generator is operated with the main transformer, and the generator speed is increased to the rated speed n N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 30% ~ 100% of the rated voltage, and the three-phase voltage and neutral point voltage of the generator stator winding are read. The neutral point voltage of the generator at 100% of the rated voltage is the neutral point displacement voltage, and the neutral point displacement voltage is compared with the standard requirement value.

4. The generator neutral point grounding system parameter applicability test verification method according to claim 3 is characterized in that: In step S4, when measuring and verifying the single-phase grounding maximum capacitance current of the neutral point grounding system, the circuit breaker QS is disconnected, and the neutral point of the generator is not grounded. At the same time, the relay KG is closed, the relay KC is closed, the circuit breaker QF is closed, the generator runs with the main transformer, the stator winding is single-phase grounded, and the generator speed is increased to the rated speed n N , stable at n N ±0.05%n N Afterwards, the test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed the threshold current. The three-phase voltage of the generator stator winding is read, the single-phase grounding capacitance current is read and the waveform is recorded. The single-phase grounding capacitance current is linearly converted to 100% of the rated voltage. This single-phase grounding capacitance current is the maximum single-phase grounding capacitance current of the generator.

5. The generator neutral point grounding system parameter applicability test verification method according to claim 4 is characterized in that: The single-phase grounding capacitance current is read by an oscilloscope and the waveform is recorded.

6. The generator neutral point grounding system parameter applicability test verification method according to claim 5 is characterized in that: The test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed 4A.

7. The generator neutral point grounding system parameter applicability test verification method according to claim 6 is characterized in that: In step S5, when measuring and verifying the single-phase grounding maximum fault current of the neutral point grounding system, the circuit breaker QS is closed, and the neutral point of the generator is connected to the grounding device JZ. At the same time, the relay KG is closed, the relay KC is closed, the circuit breaker QF is closed, the generator is operated with the main transformer, the generator outlet is single-phase grounded, and the generator speed is increased to the rated speed n N , stable at n N ±0.05%n N Afterwards, the test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed the threshold current. The three-phase voltage of the generator stator winding is read, the single-phase grounding fault current and the generator neutral point current are read and the waveform is recorded. The single-phase grounding fault current is linearly converted to 100% of the rated voltage. This single-phase grounding fault current is the maximum single-phase grounding fault current of the generator.

8. The generator neutral point grounding system parameter applicability test verification method according to claim 7 is characterized in that: The single-phase ground fault current and generator neutral point current are read and recorded by an oscilloscope.

9. The generator neutral point grounding system parameter applicability test verification method according to claim 8, characterized in that: The test voltage is gradually increased to 20% to 50% of the rated voltage and the single-phase grounding fault current is controlled not to exceed 4A.

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