Simulation test method for parameters of generator neutral point grounding system

Abstract

The present application discloses a parameter simulation test method for 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, configuring the neutral point asymmetric voltage of the neutral point grounding system; S3, measuring the neutral point asymmetric voltage of the neutral point grounding system; S4, measuring the neutral point displacement voltage of the neutral point grounding system; S5, measuring the maximum single-phase grounding capacitance current of the neutral point grounding system; S6, measuring the maximum single-phase grounding fault current of the neutral point grounding system; S7, measuring the transfer overvoltage of the neutral point grounding system; S8, measuring the operating overvoltage of the neutral point grounding system; S9, measuring the transient overvoltage of the neutral point grounding system; the present application can effectively verify the performance of different grounding methods of the generator, determine whether the neutral point grounding method of the generator meets the requirements, and provide ideas and basis for type testing of the neutral point grounding device of the generator.

Description

Technical Field

[0001] The present application belongs to the technical field of power system generators, and in particular relates to a parameter simulation test method for a generator neutral point grounding system. Background Art

[0002] The generator neutral point is typically grounded using either ungrounded, grounded via arc suppression coils, or high-resistance grounding. With the commissioning of large hydroelectric generators, the single-phase capacitive current in the generator is increasing, making these three grounding methods no longer sufficient. Ungrounded grounding poses problems such as high arc grounding overvoltage, arc suppression coil grounding poses high displacement voltage, and high-resistance grounding poses high single-phase grounding current. Excessive arc grounding overvoltage in the generator poses a risk of insulation breakdown. Excessive displacement voltage can cause false tripping of the stator winding single-phase grounding protection and compromise power quality. Excessive single-phase grounding current in the generator stator winding can burn the stator core. Recently, high-impedance grounding has emerged. This method utilizes a grounding device with a resistor and reactance connected in parallel to the secondary side of the grounding transformer, effectively accounting for both displacement voltage and single-phase grounding current. Testing the generator neutral point grounding system parameters faces the risk of overvoltage and cannot be performed on a real machine. Therefore, a method is needed to simulate grounding system parameters for different generator neutral point grounding methods in a dynamic test laboratory. Summary of the Invention

[0003] To address the above issues, the present invention provides a generator neutral point grounding system parameter simulation test method, which can effectively verify whether the generator neutral point grounding method and grounding device parameters meet engineering requirements, and provides ideas and basis for type testing of generator grounding devices. The technical solution is as follows:

[0004] The present application provides a generator neutral point grounding system parameter simulation test method, comprising the following steps:

[0005] S1, connect the measuring instrument and grounding device to the generator neutral point grounding system;

[0006] S2, neutral point asymmetric voltage configuration of neutral point grounding system;

[0007] S3, neutral point asymmetric voltage measurement of neutral point grounding system;

[0008] S4, neutral point displacement voltage measurement of neutral point grounding system;

[0009] S5, single-phase grounding maximum capacitance current measurement of neutral point grounding system;

[0010] S6, single-phase grounding maximum fault current measurement of neutral point grounding system;

[0011] S7, transfer overvoltage measurement for neutral-grounded systems;

[0012] S8, measurement of switching overvoltage in neutral-grounded systems;

[0013] S9, transient overvoltage measurement of neutral-grounded system;

[0014] The order of steps S3 to S9 can be adjusted arbitrarily.

[0015] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, the generator neutral point grounding system includes a generator, a generator neutral point grounding device, a main transformer, and an excitation transformer, a plant transformer, a cable, and a busbar between the generator and the main transformer.

[0016] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S2, the three-phase-to-ground shunt capacitors of the generator are manually adjusted to make the three-phase-to-ground voltage of the generator asymmetric. The neutral point asymmetric voltage is:

[0017]

[0018] Among them, U bd is the neutral point asymmetric voltage, V;

[0019] C A 、C B 、C C are the single-phase-to-ground capacitances of generators A, B, and C respectively;

[0020] Y A 、Y B 、Y C are the three-phase admittances of generators A, B, and C respectively;

[0021] α and α 2 is an operator, α is to rotate the original phase quantity 120° counterclockwise, α 2 It is to rotate the original phase quantity 240° counterclockwise;

[0022] ω is the angular velocity.

[0023] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, when measuring the neutral point asymmetric voltage, the generator neutral point is not grounded, the generator stator is externally connected to the test voltage, the generator is running 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.

[0024] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, when the test voltage of the generator stator is the highest, that is, 100% of the rated stator voltage, there may be a safety hazard due to the excessively high test voltage. By reducing the test voltage to 30% of the generator rated voltage, 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.

[0025] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S4, when measuring the neutral point displacement voltage of the neutral point grounding system, the neutral point of the generator is connected to the grounding device, the generator is running 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.

[0026] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S5, when measuring the single-phase grounding maximum capacitance current of the neutral point grounding system, the generator neutral point is not grounded, 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 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.

[0027] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, the single-phase grounding capacitance current is read and the waveform is recorded by an oscilloscope.

[0028] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, 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.

[0029] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, when measuring the single-phase grounding maximum fault current of the neutral point grounding system, the generator neutral point is connected to the grounding device, 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 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.

[0030] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, the single-phase grounding fault current and the generator neutral point current are read and the waveforms are recorded by an oscilloscope.

[0031] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, 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.

[0032] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S7, when measuring the transfer overvoltage of the neutral point grounding system, the neutral point of the generator is connected to the grounding device, the generator is running 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 20% to 50% of the rated voltage, the high-voltage side of the transformer is suddenly short-circuited, the three-phase voltage of the generator stator winding is read and the waveform is recorded, and then the neutral point voltage measured by the voltage transformer TV at this time is converted to 100% of the rated voltage. The converted generator neutral point voltage is the transferred overvoltage.

[0033] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S8, when measuring the operating overvoltage of the neutral point grounding system, the generator neutral point is connected to the grounding device, the generator is running with the main transformer, the neutral point of the main transformer is not grounded, the high voltage side is connected with a parallel capacitor to simulate a long line, 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 50% of the rated voltage, the capacitor is switched on and off, and the overvoltage of the generator stator winding converted to the rated stator voltage is the switching overvoltage.

[0034] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S9, when measuring the transient overvoltage of the neutral point grounding system, the neutral point of the generator is connected to the grounding device, the generator is running with the main transformer, and the generator is accelerated to the rated speed n N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 50% of the rated voltage, and the generator stator winding outlet is suddenly single-phase grounded by switching on and off the grounding switch. The transient overvoltage of the healthy phase converted to the rated voltage is the generator single-phase grounding transient overvoltage.

[0035] The beneficial effects brought about by the generator neutral point grounding system parameter simulation test method of the present application are: the present application configures the generator neutral point grounding device (including arc suppression coil, high resistance grounding device, high impedance grounding device), parallel capacitors and proportionally reduced generators and transformers, changes the three-phase different capacitance values ​​of the parallel capacitors to cause asymmetric voltage, changes the secondary resistance and reactance of the grounding transformer, changes the reactance value of the arc suppression coil to adjust the test conditions, and can effectively verify whether the generator neutral point grounding method and grounding device parameters meet the engineering requirements, and provides ideas and basis for the type test of the generator grounding device. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] Figure 1 It is a general schematic diagram of the generator neutral point grounding system;

[0038] Figure 2 This is the electrical schematic diagram of the generator neutral point grounding system parameter simulation test;

[0039] Figure 3a This is an approximate simplified circuit diagram for calculating the transferred overvoltage when the neutral point on the high-voltage side of the main transformer is directly grounded.

[0040] Figure 3b This is an approximate simplified circuit diagram for calculating the transferred overvoltage when the neutral point on the high-voltage side of the main transformer is not grounded.

[0041] Figure 4 This is the relationship curve between the solitary light grounding overvoltage and the 1 / K value. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0043] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by persons of ordinary skill in the field to which this disclosure belongs. The words "first", "second" and similar terms used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0044] The present application provides a generator neutral point grounding system parameter simulation test method, comprising the following steps:

[0045] S1, connect the measuring instrument and grounding device to the generator neutral point grounding system;

[0046] S2, neutral point asymmetric voltage configuration of neutral point grounding system;

[0047] S3, neutral point asymmetric voltage measurement of neutral point grounding system;

[0048] S4, neutral point displacement voltage measurement of neutral point grounding system;

[0049] S5, single-phase grounding maximum capacitance current measurement of neutral point grounding system;

[0050] S6, single-phase grounding maximum fault current measurement of neutral point grounding system;

[0051] S7, transfer overvoltage measurement for neutral-grounded systems;

[0052] S8, measurement of switching overvoltage in neutral-grounded systems;

[0053] S9, transient overvoltage measurement of neutral-grounded system;

[0054] The order of steps S3 to S9 can be adjusted arbitrarily.

[0055] Among them, the equipment involved in the generator neutral point grounding system parameters include the generator, the generator neutral point grounding device, the main transformer and all the connected equipment between the generator and the main transformer, such as the excitation transformer, the plant transformer, the cable, the busbar, etc. 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 is connected in parallel between the generator stator winding output terminal and the ground. The generator neutral point grounding device can be equivalent to a parallel equivalent circuit of resistance and inductance. The general principle 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 ground is equal, and the phase-to-phase capacitance of the conductors is ignored.

[0056] This application proposes a simulation test method for the grounding system parameters of four grounding methods of the generator, namely, the generator neutral point is not grounded, grounded through an arc suppression coil, grounded through a high resistance, and grounded through a high impedance. The grounding system parameters include the generator neutral point asymmetric voltage, displacement voltage, single-phase grounding capacitance current, single-phase grounding maximum fault current, transfer overvoltage, operation overvoltage, transient overvoltage, etc. The test system configured in this application includes a simulated generator, a generator neutral point grounding device, a parallel capacitor and a step-up transformer, and related test equipment. This is achieved by changing the capacitance value of the parallel capacitor to cause an asymmetric voltage to be generated at the neutral point of the generator, changing the reactance value of the arc suppression coil or the secondary resistance and reactor of the grounding transformer, and adjusting the test conditions. This application can effectively verify the performance of different grounding methods of the generator, determine whether the neutral point grounding method of the generator meets the requirements, and provide ideas and basis for the type test of the neutral point grounding device of the generator.

[0057] Among them, the generator parameter settings in the test system of this application are proportionally reduced according to the parameters of the simulated generator, the step-up transformer parameter settings are proportionally reduced according to the parameters of the simulated transformer, the shunt capacitor parameter settings are set according to the single-phase grounding capacitance of the simulated generator, and the generator neutral point grounding device parameter settings are set according to the simulated generator neutral point grounding device (including arc suppression coil grounding or high resistance grounding or high impedance grounding) in proportion. A portable recorder is used to collect the generator neutral point voltage, current, single-phase grounding current, and three-phase stator voltage with a sampling frequency of 10kHz. This application provides an effective test method for the type test of the grounding device by constructing a proportionally reduced simulation test physical model, designing relevant equipment technical parameters, and building a test platform to carry out grounding system parameter tests with different generator neutral point grounding methods.

[0058] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S2, during the simulation test, the three-phase-to-ground shunt capacitors of the generator are manually adjusted to make the three-phase-to-ground voltage of the generator asymmetric. The neutral point asymmetric voltage is:

[0059]

[0060] In formula (1):

[0061] U bd is the neutral point asymmetric voltage, V;

[0062] C A 、C B 、C C The single-phase-to-ground capacitance of generators A, B, and C is 2.281 μF in this example;

[0063] Y A 、Y B 、Y C are the three-phase admittances of generators A, B, and C respectively;

[0064] α and α 2 is an operator, α is to rotate the original phase quantity 120° counterclockwise, α 2 It is to rotate the original phase quantity 240° counterclockwise;

[0065] ω is the angular velocity, which is 314 rad / s.

[0066] If the three-phase capacitance to ground is asymmetrical, the three-phase capacitance difference is equal, C A =C B +ΔC,C C =C B -ΔC, the difference is ΔC, then:

[0067]

[0068] It can be seen from equations (2) and (3) that the asymmetric capacitance to ground value to be configured can be determined by setting the asymmetric voltage. Conversely, the asymmetric voltage can also be changed by configuring the three-phase asymmetric capacitance to ground.

[0069] The theoretical parameters of the neutral point grounding system can be calculated as follows:

[0070] 1) Neutral point asymmetric voltage

[0071] Depend on Figure 1 The neutral point asymmetric voltage U can be obtained bd for:

[0072]

[0073] 2) Neutral point displacement voltage

[0074] Depend on Figure 1 The general expression for the neutral point displacement voltage is:

[0075]

[0076] In formula (5):

[0077] Y0 is the generator neutral point admittance.

[0078] 3) Maximum capacitive current of single-phase grounding

[0079] Single-phase grounding maximum capacitive current I C∑ for

[0080]

[0081] In formula (6):

[0082] U N is the generator rated line voltage, V;

[0083] C ∑ is the total capacitance of the generator stator circuit per phase to ground, F. The capacitance of the generator stator winding per phase to ground can be calculated based on the capacitive current.

[0084] 4) Maximum single-phase ground fault current

[0085] Maximum single-phase ground fault current I k for:

[0086]

[0087] In formula (7):

[0088] I k is the maximum single-phase ground fault current, A;

[0089] I r is the maximum resistive current of single-phase grounding, A;

[0090] Ic' is the maximum capacitive current of single-phase grounding, A.

[0091] 5) Transmitting overvoltage

[0092] The simplified circuit for calculating the transfer overvoltage is shown in Figure 3, where Figure 3a This is the circuit diagram when the neutral point on the high voltage side of the main transformer is directly grounded; Figure 3b This is the circuit diagram when the neutral point on the high-voltage side of the main transformer is not grounded.

[0093] When the neutral point on the high voltage side of the main transformer is directly grounded;

[0094] The equivalent impedance of the parallel part is:

[0095]

[0096] The delivered overvoltage is:

[0097]

[0098] When the neutral point on the high voltage side of the main transformer is not grounded

[0099] The equivalent impedance of the parallel part is:

[0100]

[0101] The delivered overvoltage is:

[0102]

[0103] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, when measuring the neutral point asymmetric voltage, the generator neutral point is not grounded, the generator stator is externally connected to the test voltage, the generator is running 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 Then, 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.

[0104] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, when the test voltage of the generator stator is the highest, that is, 100% of the rated stator voltage, there may be a safety hazard due to the excessively high test voltage. By reducing the test voltage to 30% of the generator rated voltage, 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.

[0105] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S4, when measuring the neutral point displacement voltage of the neutral point grounding system, the neutral point of the generator is connected to the grounding device, the generator is running 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.

[0106] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S5, when measuring the single-phase grounding maximum capacitance current of the neutral point grounding system, the generator neutral point is not grounded, 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 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, 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 the waveform is recorded by a recorder. 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.

[0107] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, when measuring the single-phase grounding maximum fault current of the neutral point grounding system, the generator neutral point is connected to the grounding device, 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 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 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. Among them, the single-phase grounding fault current and the generator neutral current are read and the waveform is recorded by a recorder. 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.

[0108] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S7, when measuring the transfer overvoltage of the neutral point grounding system, the neutral point of the generator is connected to the grounding device, the generator is running 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 20% to 50% of the rated voltage, the high-voltage side of the transformer is suddenly short-circuited, the three-phase voltage of the generator stator winding is read and the waveform is recorded, and then the neutral point voltage measured by the voltage transformer TV at this time is converted to 100% of the rated voltage. The converted generator neutral point voltage is the transferred overvoltage.

[0109] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S8, when measuring the operating overvoltage of the neutral point grounding system, the generator neutral point is connected to the grounding device, the generator is running with the main transformer, the neutral point of the main transformer is not grounded, the high voltage side is connected with a parallel capacitor to simulate a long line, 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 50% of the rated voltage, the capacitor is switched on and off, and the overvoltage of the generator stator winding converted to the rated stator voltage is the switching overvoltage.

[0110] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, in step S9, when measuring the transient overvoltage of the neutral point grounding system, the neutral point of the generator is connected to the grounding device, the generator is running with the main transformer, and the generator is accelerated to the rated speed n N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 50% of the rated voltage, and the generator stator winding outlet is suddenly single-phase grounded by switching on and off the grounding switch. The transient overvoltage of the healthy phase converted to the rated voltage is the generator single-phase grounding transient overvoltage.

[0111] The parallel inductive reactance of the neutral point grounding loop is connected in parallel with the capacitive reactance of the generator capacitor loop. The capacitive reactance after parallel connection can be regarded as the capacitive reactance of the generator to the ground, and the neutral point parallel resistance can be regarded as the neutral point resistance. This is equivalent to a high-resistance grounding method. The relationship curve between the arc grounding overvoltage multiple and 1 / K (K is the impedance ratio) under the high-resistance grounding method can be used as a reference, as a relationship curve between the arc grounding overvoltage and the impedance ratio of the high-impedance grounding device, such as Figure 4 To meet the arc grounding overvoltage does not exceed 2.6U Φ , where U Φ is the phase voltage, K should be less than 1.25.

[0112] To summarize, in order to take into account both the generator single-phase grounding current and arc grounding overvoltage, the value range of K should be 1 to 1.25, and the recommended typical value of K is 1.25.

[0113] Simulation test example

[0114] 1) Simulation test equipment parameter model

[0115] A. Generator and main transformer parameters

[0116] The prototype generator has a rated capacity of 175MW, a rated voltage of 13.8kV, a stator winding single-phase to ground capacitance of 2.281μF, a main transformer rated voltage of 242kV / 13.8kV, and a high- and low-voltage winding capacitance of 0.0062μF.

[0117] B. High Impedance Grounding System Parameters

[0118] Considering the need to minimize the generator neutral point displacement voltage, the generator neutral point ground fault current, IF, is limited to the permissible value for a single-phase ground fault (15A), taking 14.5A. This is calculated based on an impedance ratio (resistance / capacitance) of 1.25 (recommended value). The three-phase capacitance of the generator stator winding to ground is 2.281 × 3 = 6.843 μF. Since the capacitance value cannot be continuously adjusted, a relatively close value of 7.32 μF is used.

[0119] After calculation, the capacity of the grounding transformer is 140kVA, the rated voltage ratio is 13.8kV / 0.345kV=40, the rated current ratio is 10.2 / 405.8=0.025, the short-circuit impedance ratio is 3%, and the overload factor is 1.134.

[0120] C. Impedance parameters of high impedance grounding device

[0121] Considering that the transformer's active power loss typically does not exceed 2% of its rated capacity, and the short-circuit impedance of the grounding transformer in a high-impedance grounding system typically does not exceed 3%, the calculation shows that the secondary resistor has a rated heating capacity of 74.2kW, a rated voltage of 0.345 / kV, a rated heating current of 373A, a rated resistance of 0.513Ω, a resistor temperature rise of ≤450K per minute, and an adjustment range of 15% to +10%. The rated capacity of the secondary resistor is 57kvar, the rated voltage is 0.345 / kV, the rated current is 286A, and the rated inductance is 2.22mH. The reactor temperature rise is ≤105K, with an adjustment range of 15% to +10%.

[0122] 2) Test system and simulation unit parameters

[0123] A.Test system

[0124] The complete test system consists of a simulated 175MW generator #12 at a hydropower station, a high-impedance neutral grounding device, and related measurement systems. A prototype generator was simulated using capacitors connected in parallel with the stator windings of the low-voltage generator. The prototype generator set was manufactured by a motor manufacturer. The dynamic test model and the high-impedance neutral grounding device were designed with reference to the rated parameters of the prototype generator's neutral grounding device and a specific simulation ratio. A 2.281μF capacitor was connected in parallel with each of the three phases of the simulated generator's stator windings. Because the capacitance is not continuously adjustable, the actual parallel capacitance is 2.20μF for phase A, 2.44μF for phase B, and 2.68μF for phase C. The capacitance between the high- and low-voltage windings of the simulated transformer is 2.9nF per phase, comparable to the 3.1nF primary and secondary capacitance of the actual transformer in the field, so no additional parallel capacitance was added. Data acquisition was performed using a ZH-102 portable oscilloscope recorder with a sampling frequency of 10kHz.

[0125] B. Simulated generator set parameters

[0126] The simulation of generator #12 at a hydropower station is a 10-pole salient-pole generator with a rated speed of 300 rpm. Each phase of the stator winding has five branches, with branches 1, 2, 3, and 4, 5 of each phase winding leading to the neutral point, respectively. Each branch winding has several lead-out connectors. The excitation current is provided by the excitation device. The simulated generator has a rated capacity of 31 kVA, a rated voltage of 220 V, a rated current of 81.35 A, a rated power factor of 0.9, and a stator winding with five branches.

[0127] C. Simulate main transformer parameters

[0128] The simulated main transformer has a rated capacity of 31kVA, a rated voltage of 800V / 220V, a rated current of 22.37A / 81.35A, a connection group of Yn, d11, an impedance voltage of 12.1%, a connection method of a three-phase transformer group, and an interphase capacitance of the low-voltage winding of 2.9nF / phase.

[0129] 3) Experimental conclusion

[0130] A. The asymmetric voltage at the generator neutral point changes with the change of asymmetric capacitance.

[0131] B. The parameters of the generator neutral point grounding device have a great influence on the displacement voltage, and the displacement voltage can be made to reach the optimal value through optimization design.

[0132] C. The displacement voltage of the generator is closely related to the neutral point grounding method. The arc suppression coil grounding method has the highest displacement voltage, the high impedance grounding method has the second highest displacement voltage, and the high resistance grounding method has the lowest displacement voltage.

[0133] D. The single-phase grounding fault current of the generator is related to the grounding method of the generator. The single-phase grounding fault current of the arc suppression coil grounding method is the smallest, the single-phase grounding fault current of the high-impedance grounding method is the second, and the single-phase grounding fault current of the high-resistance grounding method is the largest.

[0134] E. The harmonic current of single ground fault is related to the grounding method of the generator. The harmonic component of the single-phase grounding current of the stator winding is larger under the arc suppression coil grounding method, and the harmonic component of the single-phase grounding fault current of the stator winding is smaller under the high-impedance grounding and high-resistance grounding methods.

[0135] F. The overvoltage transferred at the generator outlet is related to the grounding method of the generator. The overvoltage transferred under high-impedance grounding is lower. The overvoltage transferred when the neutral point on the high-voltage side of the transformer is not grounded is higher than the overvoltage transferred when the neutral point on the high-voltage side of the transformer is grounded.

[0136] G. The operating overvoltage at the generator outlet is related to the grounding method of the generator. When the generator carries a 100km simulated line and the line is suddenly disconnected, the operating overvoltage at the generator outlet when the generator neutral point is grounded through a high impedance is lower than the operating overvoltage when the generator neutral point is not grounded, both within 2.6 times, meeting the requirements.

[0137] H. Under high-impedance grounding mode, the transient overvoltage of the generator when single-phase is grounded is within 2.6 times, which meets the requirements.

[0138] I. When the generator grounding system impedance ratio is optimized to a design value of 1.25, the displacement voltage, switching overvoltage, transient overvoltage, and grounding current all meet the requirements, breaking through the traditional design concept of an impedance ratio of 1.

[0139] J. All performance parameters of high-impedance grounding device meet the requirements and are the best choice for neutral point grounding device of large and medium-sized hydro-generators. At present, high-impedance grounding device has been applied to many large and medium-sized hydro-generators and has been widely recognized by the industry.

[0140] Although the embodiments of the present application have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

1. A generator neutral point grounding system parameter simulation test method, characterized in that: The following steps are involved: S1. Connect the measuring instrument and grounding device to the generator neutral point grounding system. The generator neutral point grounding system includes a simulated generator, a generator neutral point grounding device, a shunt capacitor, a step-up transformer, and related test equipment. S2, neutral point asymmetric voltage configuration of neutral point grounding system; S3, neutral point asymmetric voltage measurement of neutral point grounding system; S4, neutral point displacement voltage measurement of neutral point grounding system; S5, single-phase grounding maximum capacitance current measurement of neutral point grounding system; S6, single-phase grounding maximum fault current measurement of neutral point grounding system; S7, transfer overvoltage measurement for neutral-grounded systems; S8, measurement of switching overvoltage in neutral-grounded systems; S9, transient overvoltage measurement of neutral-grounded system; The order of steps S3 to S9 can be adjusted arbitrarily.

2. The generator neutral point grounding system parameter simulation test method according to claim 1, characterized in that: In step S2, the three-phase parallel capacitance of the simulated generator is manually adjusted to make the three-phase voltage of the simulated generator asymmetric. The neutral point asymmetric voltage is: Among them, U bd is the neutral point asymmetric voltage; C A 、C B 、C C are the single-phase-to-ground capacitances of generators A, B, and C respectively; Y A 、Y B 、Y C are the single-phase-to-ground admittances of generators A, B, and C respectively; α and α 2 is an operator, α is to rotate the original phase quantity 120° counterclockwise, α 2 It is to rotate the original phase quantity 240° counterclockwise; ω is the angular velocity.

3. The generator neutral point grounding system parameter simulation test method according to claim 1, characterized in that: In step S3, when measuring the neutral point asymmetric voltage, simulate the generator neutral point is not grounded, simulate the generator stator external test voltage, simulate the generator running with the main transformer, and increase the simulated generator speed to the rated speed n N , and stabilize at n N ±0.05%n N Then, read the three-phase voltage of the simulated 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.

4. The generator neutral point grounding system parameter simulation test method according to claim 3 is characterized in that: When the test voltage of the simulated 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 simulated generator rated voltage, and then converting the neutral point voltage measured by the voltage transformer TV at this time to 100% of the rated voltage, the converted simulated generator neutral point voltage is the neutral point asymmetric voltage.

5. The generator neutral point grounding system parameter simulation test method according to claim 1, characterized in that: In step S4, when measuring the neutral point displacement voltage of the neutral point grounding system, the generator neutral point is simulated to be connected to the grounding device, the generator is simulated to run with the main transformer, and the generator is simulated to increase the speed 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 simulated generator stator winding are read. The neutral point voltage of the simulated generator at 100% of the rated voltage is the neutral point displacement voltage.

6. The generator neutral point grounding system parameter simulation test method according to claim 1, characterized in that: In step S5, when measuring the single-phase grounding maximum capacitance current of the neutral point grounding system, it is simulated that the neutral point of the generator is not grounded, the generator is simulated to run with the main transformer, the stator winding is single-phase grounded, and the generator is simulated to speed up 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 simulated 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 simulated generator single-phase grounding.

7. The generator neutral point grounding system parameter applicability test verification method according to claim 6, characterized in that: The single-phase grounding capacitance current is read by an oscilloscope and the waveform is recorded.

8. The generator neutral point grounding system parameter applicability test verification method according to claim 6, 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.

9. The generator neutral point grounding system parameter simulation test method according to claim 1, characterized in that: In step S6, when measuring the maximum single-phase ground fault current of the neutral point grounding system, the generator neutral point is simulated to be connected to the grounding device, the generator is simulated to operate with the main transformer, the generator outlet is simulated to be single-phase grounded, and the generator is simulated to be accelerated 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 simulated generator stator winding is read, the single-phase grounding fault current and the simulated 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 simulated generator.

10. The generator neutral point grounding system parameter simulation test method according to claim 9, characterized in that: The single-phase ground fault current and the generator neutral point current are read and recorded using an oscilloscope.

11. The generator neutral point grounding system parameter simulation test method according to claim 9, 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.

12. The generator neutral point grounding system parameter simulation test method according to claim 1, characterized in that: In step S7, when measuring the transfer overvoltage of the neutral point grounding system, the generator neutral point is simulated to be connected to the grounding device, the generator is simulated to run with the main transformer, and the generator is simulated to increase the speed to the rated speed n. N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 20% to 50% of the rated voltage, the high-voltage side of the transformer is suddenly short-circuited, the three-phase voltage of the stator winding of the simulated generator is read and the waveform is recorded, and then the neutral point voltage measured by the voltage transformer TV at this time is converted to 100% of the rated voltage. The converted neutral point voltage of the simulated generator is the transferred overvoltage.

13. The generator neutral point grounding system parameter simulation test method according to claim 1, characterized in that: In step S8, when measuring the operating overvoltage of the neutral point grounding system, the generator neutral point is simulated to be connected to the grounding device, the generator is simulated to operate with the main transformer, the neutral point of the main transformer is not grounded, the high voltage side is connected with a parallel capacitor to simulate a long line, and the generator is simulated to increase the speed to the rated speed n N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 50% of the rated voltage, the capacitor is switched on and off, and the simulated generator stator winding overvoltage converted to the rated stator voltage is the switching overvoltage.

14. The generator neutral point grounding system parameter simulation test method according to claim 1, characterized in that: In step S9, when measuring the transient overvoltage of the neutral point grounding system, the generator neutral point is simulated to be connected to the grounding device, the generator is simulated to run with the main transformer, and the generator is simulated to increase the speed to the rated speed n. N , stable at n N ±0.05%n N After that, the test voltage is gradually increased to 50% of the rated voltage, and the stator winding outlet of the simulated generator is suddenly grounded in single phase by switching on and off the grounding switch. The transient overvoltage of the healthy phase converted to the rated voltage is the transient overvoltage of the simulated generator single-phase grounding.

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