Method for expanding parameter simulation test of generator neutral grounding system with unit connection

Abstract

The application discloses a method for simulating the parameters of a generator neutral point grounding system of an extended unit connection, which comprises an actual generator system and a simulated generator system in parallel operation, wherein the simulated generator system comprises a low zero sequence impedance transformer, a three-phase capacitor bank and a simulated generator neutral point grounding device; the parameter simulation test comprises the following steps: S1, relay protection configuration; S2, neutral point asymmetric voltage test of the generator neutral point grounding system of the extended unit connection; S3, neutral point displacement voltage test of the generator neutral point grounding system of the extended unit connection; S4, maximum capacitive current test of single-phase grounding of the generator neutral point grounding system of the extended unit connection; and S5, maximum fault current test of single-phase grounding of the generator neutral point grounding system of the extended unit connection. The application can effectively verify the grounding system performance of different grounding modes of the generator of the extended unit connection and determine whether the generator neutral point grounding mode meets the technical requirements.

Description

Technical Field

[0001] This application belongs to the field of power system technology, and in particular relates to a parameter simulation test method for a generator neutral point grounding system with expanded unit wiring. Background Technology

[0002] The expanded unit connection consists of two generators connected to one transformer. When a single-phase ground fault occurs at the generator outlet, the single-phase ground fault current is the vector sum of the single-phase grounding capacitive current during the operation of the two generators and the neutral point current of the two generators. The single-phase grounding capacitive current is the sum of the ground capacitance currents of all equipment from the generator outlets to the low-voltage side of the transformer, including the generator stator windings, the main transformer low-voltage windings, the excitation transformer, the station service transformer, cables, busbars, etc. The generator neutral point grounding system parameter test involves the generator, the neutral point grounding device, the main transformer, and all connecting equipment between the generator and the main transformer, such as the excitation transformer, the station service transformer, cables, busbars, etc. The grounding device parameter design values ​​for the expanded unit connection are different from those for the unit connection, and it is not possible to conduct the test using islanded dual-generator parallel operation.

[0003] Therefore, it is necessary to develop a parameter simulation test method for generator neutral grounding system with expanded unit wiring. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a method for simulating the parameters of a generator neutral point grounding system with expanded unit wiring. This method effectively evaluates the performance parameters of the generator neutral point grounding device with expanded unit wiring and verifies whether the grounding method meets the technical requirements. The technical solution is as follows:

[0005] This application provides a parameter simulation test method for a generator neutral point grounding system with expanded unit wiring. The method includes an actual generator system and a simulated generator system, wherein the actual generator system and the simulated generator system are operated in parallel for parameter simulation testing. The simulated generator system includes a low zero-sequence impedance transformer, a three-phase capacitor bank, and a simulated generator neutral point grounding device. The parameter simulation test includes the following steps:

[0006] S1, relay protection configuration;

[0007] S2, Neutral point asymmetric voltage test of generator neutral point grounding system with expanded unit wiring;

[0008] S3, Neutral point displacement voltage test of generator neutral point grounding system with expanded unit wiring;

[0009] S4, Test of maximum capacitive current for single-phase grounding in generator neutral grounding system with expanded unit wiring;

[0010] S5, Test of maximum single-phase ground fault current in generator neutral grounding system with expanded unit wiring;

[0011] The order of steps S2 to S5 can be adjusted arbitrarily.

[0012] For example, in a method for simulating the parameters of a generator neutral grounding system with an expanded unit connection provided in one embodiment, in step S1, the relay protection configuration includes protection settings for the maximum capacitive current test and the maximum fault current test of a single-phase grounding of the expanded unit generator: modifying the protection settings of the fundamental zero-sequence overvoltage protection or the third harmonic voltage single-phase grounding protection, with the zero-sequence voltage setting higher than the single-phase grounding zero-sequence voltage value under the highest test voltage; appropriately reducing the resistance setting of the injection-type stator grounding protection, appropriately increasing the current setting, or removing it from operation; and setting the protection settings according to the current flowing through the generator when the secondary side of the low zero-sequence impedance transformer is short-circuited in three phases.

[0013] For example, in one embodiment of the generator neutral grounding system parameter simulation test method with expanded unit wiring provided, in step S2, during the neutral point asymmetric voltage test of the generator neutral grounding system with expanded unit wiring, the generator in the simulated generator system operates with the main transformer connected, and the generator speeds up to the rated speed n. N Stable at n N ±0.05%n N Then, the three-phase voltage and neutral point voltage of the actual generator and the simulated stator winding are read. At this time, the neutral point voltage measured by the voltage transformer TV is the neutral point asymmetry voltage, and the neutral point asymmetry voltage is compared with the standard requirement value.

[0014] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, when the actual generator stator test voltage is the highest, that is, 100% of the rated stator voltage, since the test voltage is too high, there may be safety hazards. By reducing the test voltage to 30% of the generator rated voltage, and then reducing the neutral point voltage measured by the voltage transformer TV at this time to 100% of the rated voltage, the reduced generator neutral point voltage is the neutral point unbalanced voltage.

[0015] For example, in one embodiment of the generator neutral grounding system parameter simulation test method with expanded unit wiring provided, in step S3, during the neutral point displacement voltage test of the generator neutral grounding system with expanded unit wiring, the generator in the simulated generator system operates with the main transformer, and the generator speeds up to the rated speed n. N Stable at n N ±0.05%n NAfterwards, the test voltage was gradually increased to 30% to 100% of the rated voltage. The three-phase voltage of the stator winding and the neutral point voltage of the actual generator and the simulated generator were read. The neutral point voltage of the generator at 100% of the rated voltage is the neutral point displacement voltage. The neutral point asymmetry voltage was then compared with the standard requirement value.

[0016] For example, in a method for simulating the parameters of a generator neutral point grounding system with an expanded unit connection provided in one embodiment, in step S4, during the test of the maximum capacitive current of a single-phase ground fault in the generator neutral point grounding system with an expanded unit connection, the generator neutral point is not grounded, the generator in the simulated generator system is running with the main transformer connected, the stator winding is grounded in a single phase, and the generator speeds 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 while controlling the single-phase ground fault current to not exceed the threshold current. The three-phase voltages of the actual generator and the simulated stator winding are read, the single-phase grounding capacitor current is read and the waveform is recorded. The single-phase grounding capacitor current is linearly reduced to 100% of the rated voltage. This single-phase grounding capacitor current is the maximum single-phase grounding capacitor current of the generator.

[0017] For example, in a method for simulating the parameters of a generator neutral grounding system with the expanded unit wiring provided in one embodiment, a waveform recorder is used to read the single-phase grounding capacitor current and record the waveform.

[0018] For example, in a generator neutral grounding system parameter simulation test method provided in one embodiment, the test voltage is gradually increased to 20% to 50% of the rated voltage while controlling the single-phase ground fault current to not exceed 4A.

[0019] For example, in one embodiment of the generator neutral point grounding system parameter simulation test method with expanded unit wiring provided, in step S5, during the single-phase grounding maximum fault current test of the generator neutral point grounding system with expanded unit wiring, the generator neutral point is connected to the grounding device, the generator in the simulated generator system 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 while controlling the single-phase ground fault current to not exceed the threshold current. The three-phase voltage of the stator winding of the actual generator and the simulated generator is read, and the single-phase ground fault current and the neutral point current of the actual generator and the simulated generator are read and the waveforms are recorded. The single-phase ground fault current is linearly reduced to 100% of the rated voltage. This single-phase ground fault current is the maximum single-phase ground fault current of the generator.

[0020] For example, in a generator neutral point grounding system parameter simulation test method provided in one embodiment, the single-phase ground fault current and the neutral point current of the actual generator and the simulated generator are read and the waveforms are recorded by a waveform recorder.

[0021] For example, in a generator neutral grounding system parameter simulation test method provided in one embodiment, the test voltage is gradually increased to 20% to 50% of the rated voltage while controlling the single-phase ground fault current to not exceed 4A.

[0022] For example, in a method for simulating the parameters of a generator neutral grounding system with an expanded unit connection provided in one embodiment, the rated voltage of the low zero-sequence impedance transformer is higher than the highest test voltage, the rated current is higher than 1 / 3 of the current flowing through the neutral grounding device under the highest test voltage, and the zero-sequence impedance of the transformer is not greater than 3% to 5% of the actual generator neutral grounding device impedance.

[0023] For example, in one embodiment of the generator neutral grounding system parameter simulation test method with the extended unit connection provided, the three-phase capacitor bank consists of three single-phase capacitors connected in a star configuration. The rated voltage is higher than the highest test voltage, the rated current is higher than the current flowing through the capacitor under the highest test voltage, and the capacitance to ground of each phase is consistent with the capacitance to ground of each phase of the generator being simulated.

[0024] For example, in one embodiment of the generator neutral grounding system parameter simulation test method for the extended unit wiring provided, the parameters of the simulated generator neutral grounding device are consistent with those of the grounding device in the simulated generator system.

[0025] The beneficial effects of the generator neutral point grounding system parameter simulation test method of this application are as follows: This application realizes the generator neutral point grounding system parameter test by constructing a simulated generator, designs the relevant equipment technical parameters of the simulated generator, builds a test platform, and carries out grounding system parameter tests of different grounding devices. It proposes a generator neutral point grounding system parameter simulation test method using a single-machine parallel capacitor and an external transformer to simulate dual-machine operation, including generator neutral point asymmetric voltage, neutral point displacement voltage, single-phase grounding capacitance current, and single-phase grounding maximum fault current tests. This application can effectively evaluate the parameter performance of the generator neutral point grounding device of the expanded unit connection and verify whether the grounding method meets the technical requirements. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 Electrical schematic diagram of dual-machine simulation test;

[0028] Figure 2 This is the equivalent circuit diagram of the expanded unit grounding system. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] Unless otherwise defined, the technical or scientific terms used in this disclosure shall have the ordinary meaning understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described objects changes.

[0031] This application provides a method for simulating the parameters of a generator neutral point grounding system with an expanded unit connection. The method includes an actual generator system and a simulated generator system, which are connected in parallel for parameter simulation testing. The simulated generator system includes a low-sequence impedance transformer, a three-phase capacitor bank, and a simulated generator neutral point grounding device. This method uses a unit consisting of two generators and one transformer connected together. To explore the parameters and performance of the grounding device under different grounding methods for the generator neutral point in the expanded unit connection, parameter tests are conducted. Parameters include generator neutral point asymmetry voltage, displacement voltage, single-phase grounding capacitance current, and maximum single-phase grounding fault current. Addressing the limitation that dual-generator parallel operation in an isolated grid cannot directly test these parameters, a method is proposed to test the generator neutral point grounding system parameters by operating an actual generator and a simulated generator in parallel. The simulated generator includes a neutral point grounding device, parallel capacitors, a distribution transformer, and measuring devices. The actual generator's neutral point is connected to the grounding device. The simulated generator is connected in parallel with the actual generator and then tested with a step-up transformer. This application can effectively evaluate the parameter performance of the generator neutral point grounding device with expanded unit wiring and verify whether the grounding method meets the technical requirements.

[0032] The test wiring includes the actual generator system, the simulated generator system, and the main transformer, expanding the unit wiring. A schematic diagram of the simulated test wiring is shown below. Figure 1 As shown, Figure 1 Chinese: C A C B C C C is the equivalent single-phase total capacitance of all primary electrical equipment between the generator and the main transformer; A1 C B1 C C1 This application aims to simulate the total single-phase-to-ground capacitance of a generator system. It constructs a simulated generator to conduct parameter tests on the neutral point grounding system of an expanded unit-connected generator, designs the technical parameters of related equipment for the simulated generator, builds a test platform, and carries out parameter tests on grounding systems with different grounding devices.

[0033] The parameter simulation test in this application includes the following steps:

[0034] S1, relay protection configuration;

[0035] S2, Neutral point asymmetric voltage test of generator neutral point grounding system with expanded unit wiring;

[0036] S3, Neutral point displacement voltage test of generator neutral point grounding system with expanded unit wiring;

[0037] S4, Test of maximum capacitive current for single-phase grounding in generator neutral grounding system with expanded unit wiring;

[0038] S5, Test of maximum single-phase ground fault current in generator neutral grounding system with expanded unit wiring;

[0039] The order of steps S2 to S5 can be adjusted arbitrarily.

[0040] The theoretical parameters of a neutral-point grounding system can be calculated in the following ways:

[0041] 1) Total capacitance parameters of single-phase-to-ground of dual machines

[0042] The single-phase ground capacitance C of the dual-machine system is calculated according to formula (1):

[0043] C = C1 + C2 (1)

[0044] In the formula;

[0045] C1—The actual single-phase-to-ground total capacitance of the generator, including the equivalent single-phase-to-ground total capacitance of all primary electrical equipment between the generator and the main transformer;

[0046] C2 – Simulates the total single-phase-to-ground capacitance of the generator, including the equivalent total single-phase-to-ground capacitance of all primary electrical equipment between the generator and the main transformer.

[0047] 2) Total inductance parameters of the two machines

[0048] The total inductance of the two machines is calculated according to formula (2):

[0049]

[0050] In the formula;

[0051] L1—Parallel inductance on the secondary side of the actual generator neutral point grounded transformer;

[0052] L2 — Parallel inductance on the secondary side of the transformer simulating the neutral point grounding of a generator.

[0053] 3) Total capacitance current Ic of dual-machine single-phase-to-ground

[0054] The total capacitance current Ic of the dual-machine single-phase ground is

[0055]

[0056] In the formula;

[0057] U n — Rated voltage of generator, V.

[0058] 4) Total resistive current I at the neutral point of the dual-machine system R

[0059] Total resistive current I at the neutral point of the dual-machine system R for:

[0060]

[0061] In the formula;

[0062] R1—The parallel resistance on the secondary side of the actual generator grounding transformer;

[0063] R2 — Parallel resistance on the secondary side of the generator grounding transformer.

[0064] 5) Total inductive current I at the neutral point of the dual-machine system L

[0065] Total inductive current I at the neutral point of the dual-machine system L for:

[0066]

[0067] 6) Dual-machine single-phase grounding current I d

[0068] Dual-machine single-phase grounding current I d for:

[0069]

[0070] In the formula:

[0071] I d —Single-phase grounding current (A) during dual-machine operation;

[0072] I R —The sum of the resistive currents at the neutral points of the two generators, in A;

[0073] I L —The sum of the inductive currents at the neutral points of the two generators, in A.

[0074] 7) Detuning degree v

[0075] The detuning degree v is:

[0076]

[0077] 8) Damping ratio d

[0078] The damping ratio d is:

[0079]

[0080] 9) Displacement voltage coefficient m

[0081] The displacement voltage coefficient m is:

[0082]

[0083] As can be seen from the above mathematical model, the single-phase grounding current of a dual-machine system is the sum of the grounding currents of the two single-machine systems. Therefore, the grounding device parameters cannot be designed based on the single-phase grounding current of a single machine.

[0084] For example, in a method for simulating the parameters of a generator neutral grounding system with an expanded unit connection provided in one embodiment, in step S1, the relay protection configuration includes protection settings for the maximum capacitive current test and the maximum fault current test of a single-phase grounding of the expanded unit generator: modifying the protection settings of the fundamental zero-sequence overvoltage protection or the third harmonic voltage single-phase grounding protection, with the zero-sequence voltage setting higher than the single-phase grounding zero-sequence voltage value under the highest test voltage; appropriately reducing the resistance setting of the injection-type stator grounding protection, appropriately increasing the current setting, or removing it from operation; and setting the protection settings according to the current flowing through the generator when the secondary side of the low zero-sequence impedance transformer is short-circuited in three phases.

[0085] For example, in one embodiment of the generator neutral grounding system parameter simulation test method with expanded unit wiring provided, in step S2, during the neutral point asymmetric voltage test of the generator neutral grounding system with expanded unit wiring, the generator in the simulated generator system operates with the main transformer connected, and the generator speeds up to the rated speed n. N Stable at n N ±0.05%n N Then, the three-phase voltage and neutral point voltage of the actual generator and the simulated stator winding are read. At this time, the neutral point voltage measured by the voltage transformer TV is the neutral point asymmetry voltage, and the neutral point asymmetry voltage is compared with the standard requirement value.

[0086] For example, in the generator neutral point grounding system parameter simulation test method provided in one embodiment, when the actual generator stator test voltage is the highest, that is, 100% of the rated stator voltage, since the test voltage is too high, there may be safety hazards. By reducing the test voltage to 30% of the generator rated voltage, and then reducing the neutral point voltage measured by the voltage transformer TV at this time to 100% of the rated voltage, the reduced generator neutral point voltage is the neutral point unbalanced voltage.

[0087] For example, in one embodiment of the generator neutral grounding system parameter simulation test method with expanded unit wiring provided, in step S3, during the neutral point displacement voltage test of the generator neutral grounding system with expanded unit wiring, the generator in the simulated generator system operates with the main transformer, and the generator speeds up to the rated speed n. N Stable at n N ±0.05%n NAfterwards, the test voltage was gradually increased to 30% to 100% of the rated voltage. The three-phase voltage of the stator winding and the neutral point voltage of the actual generator and the simulated generator were read. The neutral point voltage of the generator at 100% of the rated voltage is the neutral point displacement voltage. The neutral point asymmetry voltage was then compared with the standard requirement value.

[0088] For example, in a method for simulating the parameters of a generator neutral point grounding system with an expanded unit connection provided in one embodiment, in step S4, during the test of the maximum capacitive current of a single-phase ground fault in the generator neutral point grounding system with an expanded unit connection, the generator neutral point is not grounded, the generator in the simulated generator system is running with the main transformer connected, the stator winding is grounded in a single phase, and the generator speeds up to the rated speed n. N Stable at n N ±0.05%n N Afterwards, the test voltage was gradually increased to 20%–50% of the rated voltage while controlling the single-phase ground fault current to not exceed the threshold current. The three-phase voltages of the actual generator and the simulated stator winding were read, and the single-phase ground fault current was read and its waveform was recorded. The single-phase ground fault current was linearly reduced to 100% of the rated voltage. This single-phase ground fault current is the maximum single-phase ground fault current of the generator. The single-phase ground fault current was read and its waveform was recorded by a waveform recorder. The test voltage was gradually increased to 20%–50% of the rated voltage while controlling the single-phase ground fault current to not exceed 4A.

[0089] For example, in one embodiment of the generator neutral point grounding system parameter simulation test method with expanded unit wiring provided, in step S5, during the single-phase grounding maximum fault current test of the generator neutral point grounding system with expanded unit wiring, the generator neutral point is connected to the grounding device, the generator in the simulated generator system 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 was gradually increased to 20%–50% of the rated voltage while controlling the single-phase ground fault current to not exceed the threshold current. The three-phase voltage of the stator winding of the actual generator and the simulated generator was read, and the single-phase ground fault current and the neutral point current of the actual generator and the simulated generator were read and the waveforms were recorded. The single-phase ground fault current was linearly reduced to 100% of the rated voltage. This single-phase ground fault current is the maximum single-phase ground fault current of the generator. Among them, the single-phase ground fault current and the neutral point current of the actual generator and the simulated generator were read and the waveforms were recorded by a waveform recorder. The test voltage was gradually increased to 20%–50% of the rated voltage while controlling the single-phase ground fault current to not exceed 4A.

[0090] For example, in a method for simulating the parameters of a generator neutral grounding system with an expanded unit connection provided in one embodiment, the rated voltage of the low zero-sequence impedance transformer is higher than the highest test voltage, the rated current is higher than 1 / 3 of the current flowing through the neutral grounding device under the highest test voltage, the zero-sequence impedance of the transformer is not greater than 3% to 5% of the actual impedance of the generator neutral grounding device, and the transformer connection group should preferably be YN, d, or ZN.

[0091] For example, in one embodiment of the generator neutral grounding system parameter simulation test method with the extended unit connection provided, the three-phase capacitor bank consists of three single-phase capacitors connected in a star configuration. The rated voltage is higher than the highest test voltage, the rated current is higher than the current flowing through the capacitor under the highest test voltage, and the capacitance to ground of each phase is consistent with the capacitance to ground of each phase of the generator being simulated.

[0092] For example, in one embodiment of the generator neutral grounding system parameter simulation test method for the extended unit wiring provided, the parameters of the simulated generator neutral grounding device are consistent with those of the grounding device in the simulated generator system.

[0093] Field test examples

[0094] 1) Parameters of generator neutral grounding system

[0095] A. Basic Overview of the Generating Unit

[0096] Generators #5 and #6 at a hydropower plant are connected in an expanded unit configuration, with a rated capacity of 110MW and a rated voltage of 15.75kV. The stator winding single-phase-to-ground capacitance is 0.946μF. Capacitors are installed at both ends of the outlet circuit breaker to ground; the single-phase-to-ground capacitance of the generator-side capacitor is 0.132μF, and the single-phase-to-ground capacitance of the low-voltage side capacitor of the main transformer is 0.260μF. The neutral point of generators #5 and #6 uses a high-impedance grounding device. The parameters of both devices are identical. The design current flowing through the primary side of the grounding device is 7.36A. The grounding transformer in the grounding device has a rated capacity of 50kVA, a rated voltage of 15.75kV / 0.4kV, a turns ratio of 52.5, a secondary resistor resistance of 0.66Ω, and a reactor inductance of 1.52mH.

[0097] B. Selection of Simulated Generator System Parameters

[0098] like Figure 2As shown, during the expanded unit wiring simulation test, the highest voltage rises to 30% of the rated voltage, which is 4.725kV. The rated voltage of the low zero-sequence impedance transformer in the simulated generator system can be selected as 10.5kV, and the rated current can be selected as greater than (7.36×0.3) / 3=0.736A. The equivalent impedance of the secondary side resistance and reactance of the grounding transformer converted to the primary side is 1066Ω. The generator's zero-sequence impedance is very small and negligible. The transformer's zero-sequence impedance should be less than 1066×0.03=31.98Ω. Therefore, the low zero-sequence impedance transformer can be selected with a standard capacity of 160kVA, a rated voltage of 10.5kV / 0.4kV, a connection group of YN,d, and a zero-sequence impedance of 8Ω.

[0099] The capacitance of each phase of the three-phase capacitor bank is the sum of the single-phase-to-ground capacitance of the generator stator winding and the single-phase parallel capacitance of the circuit breaker generator side, which is 0.946 + 0.132 = 1.078 μF. The actual selected single-phase capacitor capacitance is 1.1 μF. The current flowing through each phase capacitor is 314 × 1.1 × 15.75 / 1.732 × 0.3 = 0.942 A. The standard rated capacity of each phase capacitor is selected as 50 kvar, the rated voltage is 10.5 kV, and the rated current is 4.76 A.

[0100] 2) Experimental Conclusions

[0101] A. The neutral point asymmetric voltage of generator #5 in the expanded unit is 302.61V, and the displacement voltage is 314.35V, both of which do not exceed 10% of the rated phase voltage of 909V as specified in the standard. The displacement voltage coefficient is 1.039, which does not exceed the reference value of 1.5, and both meet the requirements. After connecting the high-impedance grounding device, the generator neutral point voltage increases. By adjusting the grounding device parameters, the generator neutral point voltage can be limited to a controllable range.

[0102] B. The maximum total capacitive current of a single-phase ground fault in the stator windings of the two generators is 21.19A, which exceeds the short-term allowable value of 15A for single-phase ground fault current. After the generator neutral point is connected to a high-impedance grounding device, the maximum single-phase ground fault current of the generator is 12.37A, which is less than the short-term allowable value of 15A for single-phase ground fault current. This indicates that the high-impedance grounding device can effectively reduce the single-phase ground fault current.

[0103] C. The generator neutral point asymmetric voltage, displacement voltage, single-phase grounding capacitance current, and single-phase grounding fault current collectively reflect the parameter performance of the generator neutral point grounding system. The parameters of the generator neutral point grounding system with expanded unit connection are different from those with unit connection. Since the two generators cannot be directly connected in parallel on an isolated grid, it is of great engineering significance to conduct parameter simulation tests on the generator neutral point grounding system with expanded unit connection by using one generator connected in parallel with an external transformer and capacitor to simulate dual-machine operation.

[0104] Although embodiments of this application have been disclosed for illustrative purposes, those skilled in the art will recognize that various modifications, additions, and substitutions can be made without departing from the scope and spirit of the invention as disclosed in the appended claims.

Claims

1. A method for simulating test parameters of a generator neutral grounding system with expanded unit wiring, characterized in that, The test includes an actual generator system and a simulated generator system, which are operated in parallel for parameter simulation testing. The simulated generator system includes a low-zero-sequence impedance transformer, a three-phase capacitor bank, and a simulated generator neutral grounding device. The parameter simulation test includes the following steps: S1, relay protection configuration; S2, Neutral point asymmetric voltage test of generator neutral point grounding system with expanded unit wiring; S3, Neutral point displacement voltage test of generator neutral point grounding system with expanded unit wiring; S4, Test of maximum capacitive current for single-phase grounding in generator neutral grounding system with expanded unit wiring; S5, Test of maximum single-phase ground fault current in generator neutral grounding system with expanded unit wiring; The order of steps S2 to S5 can be adjusted arbitrarily. In step S1, the relay protection configuration includes the protection settings for the maximum capacitive current test and the maximum fault current test of the single-phase grounding of the generator in the extended unit: modifying the protection settings of the fundamental zero-sequence overvoltage protection or the third harmonic voltage single-phase grounding protection, with the zero-sequence voltage setting higher than the single-phase grounding zero-sequence voltage value under the highest test voltage; appropriately reducing the resistance setting of the injection-type stator grounding protection, appropriately increasing the current setting, or removing it from operation; setting the protection settings according to the current flowing through the generator when the secondary side of the low zero-sequence impedance transformer is short-circuited in three phases. In step S2, during the test of the neutral point asymmetric voltage in the generator neutral point grounding system with expanded unit wiring, the generator in the simulated generator system operates with the main transformer, and the generator speeds up to the rated speed n. N Stable at n N ±0.05%n N Then, read the three-phase voltage and neutral point voltage of the actual generator and the simulated stator winding. At this time, the neutral point voltage measured by the voltage transformer TV is the neutral point unbalanced voltage, and the neutral point unbalanced voltage is compared with the standard requirement value. When the actual generator stator test voltage 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 generator rated voltage, and then recalculating the neutral point voltage measured by the voltage transformer TV at this time to 100% of the rated voltage, the recalculated generator neutral point voltage is the neutral point unbalanced voltage. In step S3, during the neutral point displacement voltage test of the generator neutral point grounding system with expanded unit wiring, the generator in the simulated generator system operates with the main transformer, and the generator speeds up to the rated speed n. N Stable at n N ±0.05%n N Afterwards, the test voltage was gradually increased to 30% to 100% of the rated voltage. The three-phase voltage and neutral point voltage of the stator winding of the actual generator and the simulated generator were read. The neutral point voltage of the generator at 100% of the rated voltage is the neutral point displacement voltage. The neutral point asymmetry voltage was then compared with the standard requirement value. In step S4, during the test of the maximum capacitive current of a single-phase ground fault in the generator neutral point grounding system with expanded unit wiring, the generator neutral point is not grounded. In the simulated generator system, the generator is running with the main transformer connected, the stator winding is grounded in a single phase, and the generator speeds 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 while controlling the single-phase ground fault current to not exceed the threshold current. The three-phase voltages of the actual generator and the simulated stator winding are read, the single-phase grounding capacitor current is read and the waveform is recorded. The single-phase grounding capacitor current is linearly reduced to 100% of the rated voltage. This single-phase grounding capacitor current is the maximum single-phase grounding capacitor current of the generator.

2. The method for simulating the parameters of a generator neutral point grounding system with expanded unit wiring as described in claim 1, characterized in that, The single-phase grounding capacitor current is read and the waveform is recorded using a waveform recorder.

3. The parameter simulation test method for a generator neutral point grounding system with expanded unit wiring according to claim 1, characterized in that, The test voltage is gradually increased to 20% to 50% of the rated voltage, and the single-phase ground fault current is controlled to not exceed 4A.

4. The method for simulating the parameters of a generator neutral grounding system with expanded unit wiring as described in claim 1, characterized in that, In step S5, during the test of the maximum single-phase ground fault current of the generator neutral point grounding system with expanded unit wiring, the generator neutral point is connected to the grounding device, the generator in the simulated generator system is running with the main transformer, the generator outlet is grounded in a single phase, 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 while controlling the single-phase ground fault current to not exceed the threshold current. The three-phase voltage of the stator winding of the actual generator and the simulated generator is read, and the single-phase ground fault current and the neutral point current of the actual generator and the simulated generator are read and the waveforms are recorded. The single-phase ground fault current is linearly reduced to 100% of the rated voltage. This single-phase ground fault current is the maximum single-phase ground fault current of the generator.

5. The method for simulating the parameters of a generator neutral point grounding system with expanded unit wiring according to claim 4, characterized in that, The waveforms of single-phase ground fault current and neutral point current of actual and simulated generators are recorded using a waveform recorder.

6. The method for simulating the parameters of a generator neutral grounding system with expanded unit wiring as described in claim 5, characterized in that, The test voltage is gradually increased to 20% to 50% of the rated voltage, and the single-phase ground fault current is controlled to not exceed 4A.

7. The method for simulating the parameters of a generator neutral point grounding system with expanded unit wiring according to claim 1, characterized in that, The rated voltage of the low zero-sequence impedance transformer is higher than the maximum test voltage, the rated current is higher than 1 / 3 of the current flowing through the neutral grounding device under the maximum test voltage, and the zero-sequence impedance of the transformer is not greater than 3% to 5% of the actual generator neutral grounding device impedance.

8. The method for simulating the parameters of a generator neutral grounding system with expanded unit wiring according to claim 1, characterized in that, The three-phase capacitor bank consists of three single-phase capacitors connected in a star configuration. The rated voltage is higher than the maximum test voltage, and the rated current is higher than the current flowing through the capacitors under the maximum test voltage. The capacitance per phase to ground is consistent with the capacitance per phase to ground of the generator set being simulated.

9. The method for simulating the parameters of a generator neutral grounding system with expanded unit wiring according to claim 1, characterized in that, The neutral grounding device of the simulated generator has the same parameters as the grounding device in the simulated generator system.

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