A power supply system and method for generating a delayed zero-crossing test current

Abstract

The present invention discloses a power supply system and method for generating a delayed zero-crossing test current, which relates to the technical field of high-voltage electrical appliance tests. Among them, the system includes a short-circuit power supply, a short-circuit transformer, an adjustable impedance, a phase-selection closing circuit breaker, a test sample, and a tripping circuit breaker. The short-circuit power supply is a current source for direct tests of medium-voltage circuit breakers and synthetic tests of high-voltage circuit breakers. The short-circuit transformer realizes the required test voltage through positive and reverse wiring. The phase-selection closing circuit breaker closes at a set moment to generate a delayed zero-crossing test current waveform. The adjustable impedance is used to adjust the impedance magnitude in the power supply system. The present invention can realize the performance assessment of the breaking performance of switching electrical appliances and protective electrical appliances under the condition of delayed zero-crossing short-circuit current; its performance test results are accurate and the operation is convenient.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage electrical apparatus tests, and particularly to a power supply system and method for generating a delayed zero-crossing test current. Background Art

[0002] Generator circuit breakers are installed at the outlet end of power plant generator sets and are used to interrupt generator-source short-circuit faults and system-source short-circuit faults, playing an important role in protecting the safe operation of generator sets.

[0003] Theoretical analysis and operating experience show that when a generator fault occurs, when the generator operates at a leading power factor in an underexcited state before the fault, the maximum asymmetry will occur, and the symmetrical component of the generator-source short-circuit current is also lower than the required symmetrical short-circuit current. Analysis of the operating results of a large number of generators shows that the maximum asymmetry is 130%, and at this time, the AC component of the short-circuit current is only 74% of the required value. Therefore, when the generator circuit breaker interrupts the generator-source fault short-circuit current, the per-unit value of the DC component at the moment of contact separation may be greater than 1, which will cause the short-circuit current to delay zero-crossing and the arcing time of the generator circuit breaker to extend.

[0004] In addition, when a single-phase grounding fault occurs in a transmission line and the fault cannot be quickly cleared, when the circuit breakers on both sides of the line reclosing a short-circuit fault, a delayed zero-crossing short-circuit current will occur, which will lead to the failure of the circuit breaker to interrupt. According to operating experience, when a short-circuit fault occurs in a converter station, there will also be a delayed zero-crossing short-circuit current, and the assessment of switching electrical appliances and protective electrical appliances is relatively strict.

[0005] According to the requirements of national standards and electrical design specifications, the ability of high-voltage circuit breakers to interrupt and close short-circuit faults needs to be verified before being put into engineering operation. Therefore, it is necessary to design and develop a power supply system capable of generating a delayed zero-crossing test current and its control method, establish the same or equivalent test conditions, provide reliable test data and correct design directions for the design and research and development of products, and at the same time realize the test assessment of switching electrical appliances and protective electrical appliances and verify their ability to interrupt a delayed zero-crossing short-circuit current. Summary of the Invention

[0006] The purpose of the present invention is to provide a power supply system for generating a delayed zero-crossing test current to achieve the interruption performance assessment of switching electrical appliances and protective electrical appliances under the condition of a delayed zero-crossing short-circuit current.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A power supply system for generating a delayed zero-crossing test current, comprising a short-circuit power supply, a short-circuit transformer, an adjustable impedance, a phase-selection closing circuit breaker, a test sample, and a tripping circuit breaker. The short-circuit power supply is a current source for direct testing of medium-voltage circuit breakers and synthetic testing of high-voltage circuit breakers. The short-circuit transformer realizes the required test voltage through positive and reverse wiring. The phase-selection closing circuit breaker closes at a set moment to generate a delayed zero-crossing test current waveform. The adjustable impedance is used to adjust the impedance magnitude in the power supply system.

[0009] Based on the above technical solution, the present invention also provides the following optional technical solutions:

[0010] In an optional solution: the short-circuit power supply is a short-circuit generator or a dedicated substation power line in a three-phase circuit system, wherein the voltage level of the dedicated substation power line is not less than 220 KV.

[0011] In an optional solution: it further includes a frequency modulation device, which is connected in parallel with the circuit where the test sample is located and is used to adjust the frequency of the current waveform.

[0012] In an optional solution: the switching operation time of the phase-selection closing circuit breaker is 15 - 20 ms, and the closing control accuracy is ±3.

[0013] In an optional solution: the test sample is a switching device or a protective device that needs to perform a delayed zero-crossing short-circuit current interruption.

[0014] In an optional solution: the test sample is a single-phase test sample or a three-phase test sample. When it is a single-phase test sample, the test sample is connected to the phase where the delayed zero-crossing occurs; when it is a three-phase test sample, the test phase of the test sample is connected to the phase where the delayed zero-crossing occurs.

[0015] A control method for generating a delayed zero-crossing test current, which is implemented based on the above-mentioned power supply system for generating a delayed zero-crossing test current, and includes the following steps:

[0016] Select a certain phase (A) as the test phase for generating the delayed zero-crossing test current, then close at the zero-crossing of the line voltage (U AB ) between this phase (A) and the adjacent lagging phase (B);

[0017] Close the adjacent leading phase (C) at an interval of about one-quarter cycle, then a delayed zero-crossing test current is generated on phase A;

[0018] Assume that the per-unit value of the line voltage of the selected phase (A) and the adjacent lagging phase (B) is If the closing moment is t = 0, then the per-unit value expression of the short-circuit test current of the selected phase (A) is:

[0019]

[0020] The DC component I at t = ΔT dc is as follows:

[0021]

[0022] In the above formula, ω is the power supply frequency, a is the closing phase angle, is the power factor angle, ΔT is the closing interval time, and τ is the loop time constant.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The present invention can realize the breaking performance assessment of switchgear and protective electrical appliances under the condition of delayed zero-crossing short-circuit current; its performance test results are accurate and the operation is convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the overall system principle structure in an embodiment of the present invention.

[0026] Figure 2 is a waveform diagram of the delayed zero-crossing short-circuit current of the present invention.

[0027] Annotation of reference numerals in the drawings: short-circuit generator 1, special line of substation power supply 2, opening circuit breaker 4, phase-selection closing circuit breaker 5, regulating impedance 6, short-circuit transformer 7, frequency modulation device 8, test sample 9. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments; in the drawings or descriptions, similar or identical parts are denoted by the same reference numerals, and in actual applications, the shapes, thicknesses or heights of the components can be enlarged or reduced. The embodiments listed in the present invention are only used to illustrate the present invention and are not used to limit the scope of the present invention. Any obvious modification or change made to the present invention does not depart from the spirit and scope of the present invention.

[0029] In one embodiment, as Figure 1 shown, a power supply system for generating a delayed zero-crossing test current is provided, including a short-circuit power supply, a short-circuit transformer 7, a regulating impedance 6, a phase-selection closing circuit breaker 5, a test sample 9, and an opening circuit breaker 4. The short-circuit power supply is a current source for direct testing of medium-voltage circuit breakers and synthetic testing of high-voltage circuit breakers. The short-circuit transformer 7 realizes the required test voltage through positive and reverse wiring. The phase-selection closing circuit breaker closes at a set time to generate a delayed zero-crossing test current waveform; the regulating impedance 6 is used to adjust the impedance magnitude in the power supply system;

[0030] Among them, the test sample 9 is a switching or protective electrical apparatus that needs to perform delayed zero-crossing short-circuit current interruption; the test sample 9 is a single-phase or three-phase test sample. When it is a single-phase test sample, the test sample 9 is connected to the phase where the delayed zero-crossing occurs; when it is a three-phase test sample, the test sample 9's phase to be tested is connected to the phase where the delayed zero-crossing occurs.

[0031] In one embodiment, as Figure 1 shown, the short-circuit power supply is the short-circuit generator 1 or the dedicated substation power line 2 in a three-phase circuit system. Among them, the voltage level of the dedicated substation power line 2 is not less than 220 KV; Figure 1 where, M is the driving motor of the short-circuit generator 1, and If is the excitation current of the short-circuit generator 1.

[0032] In one embodiment, as Figure 1 shown, the switching operation time of the phase-selection closing circuit breaker 5 is 15 - 20 ms, and the closing control accuracy is ±3°.

[0033] In one embodiment, as Figure 1 shown, it further includes a frequency modulation device 8, and the frequency modulation device 8 is connected in parallel with the circuit where the test sample is located and is used to adjust the frequency of the current waveform;

[0034] A control method for generating a delayed zero-crossing test current, which is implemented based on a power supply system for generating a delayed zero-crossing test current described in the above embodiment, and includes the following steps:

[0035] Select a certain phase (A) as the test phase for generating the delayed zero-crossing test current, then close the switch at the zero-crossing of the line voltage (U AB ) between this phase (A) and the adjacent lagging phase (B);

[0036] Close the switch of the adjacent leading phase (C) at an interval of about one-quarter cycle, then a delayed zero-crossing test current is generated on phase A;

[0037] As Figure 2 shown, assume that the asymmetry of the DC component of the short-circuit current at the moment when the breaker contacts separate is required to be 110% in the test, and the shortest arcing time of the breaker is 10 ms. Select phase A as the test phase for generating the delayed zero-crossing test current (it is agreed to interrupt at the end of the second major half-wave of phase A), then close the switch at the zero-crossing of the line voltage (U AB ) between phase A and the adjacent lagging phase B. After an interval of 5 ms, close the switch of the adjacent leading phase C; the per-unit value of the line voltage at the moment when phase A and phase B are closed is If the closing time is t = 0, then the per-unit value expression of the short-circuit test current selected for phase A is:

[0038]

[0039] The DC component I at t = ΔTdc is:

[0040]

[0041] In the above formula, ω is the power supply frequency, a is the closing phase angle, is the power factor angle, ΔT is the closing interval time, and τ is the loop time constant;

[0042] After the simultaneous solution of the two formulas, the time constant of the test system needs to be not less than 135 ms. The calculation results are as shown in the Figure 2 attachment. There is a delayed zero-crossing phenomenon on phase A. The zero-crossing moment at the end of the second major half-wave of phase A is 41 ms, so the contact separation moment is 31 ms, and the DC component at the contact separation moment is 110%, meeting the parameter requirements.

[0043] The above is only the specific implementation manner of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present disclosure can easily think of changes or substitutions, which should all be covered by the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be subject to the protection scope of the claims.

Claims

1. A power supply system for generating a delayed zero-crossing test current, comprising a short-circuit power supply, a short-circuit transformer, an adjustable impedance, a phase-selection closing circuit breaker, a test sample, and a tripping circuit breaker, characterized in that: The short-circuit power supply is the current source for the direct test of medium-voltage circuit breakers and the synthetic test of high-voltage circuit breakers. The short-circuit transformer realizes the required test voltage through positive and reverse wiring. The phase-selection closing circuit breaker closes at a set moment to generate a delayed zero-crossing test current waveform. The regulating impedance is used to adjust the impedance in the power supply system. The control method for generating a delayed zero-crossing test current based on the power supply system includes the following steps: Select a certain phase A as the test phase for generating a delayed zero-crossing test current, and then close the switch at the zero-crossing point of the line voltage U between this phase A and the adjacent lagging phase B AB of the zero-crossing point; When the adjacent leading phase C closes at an interval of about one-quarter cycle, a delayed zero-crossing test current is generated on phase A. Assume that the per-unit value of the line voltage of selected phase A and the adjacent lagging phase B is If the switching-on time is t = 0, then the expression of the per-unit value of the short-circuit test current of selected phase A is: The DC component I at t = ΔT dc is as follows: In the above formula, ω is the power supply frequency, a is the closing phase angle, is the power factor angle, ΔT is the closing interval time, and τ is the loop time constant.

2. The power supply system for generating a delayed zero-crossing test current according to claim 1, wherein, The short-circuit power supply is a short-circuit generator or a dedicated power line of a substation in a three-phase circuit system. Among them, the voltage level of the dedicated power line of the substation is not less than 220 KV.

3. The power supply system for generating a delayed zero-crossing test current according to claim 1, wherein, It also includes a frequency modulation device, which is connected in parallel with the circuit where the test object is located and is used to adjust the frequency of the current waveform.

4. The power supply system for generating a delayed zero-crossing test current according to claim 1, wherein, The switching action time of the phase-selection closing circuit breaker is 15 - 20 ms, and the closing control accuracy is ±3°.

5. The power supply system for generating a delayed zero-crossing test current according to claim 1, characterized in that, The test object is a switching device or a protection device that needs to perform a delayed zero-crossing short-circuit current interruption.

6. The power supply system for generating a delayed zero-crossing test current according to claim 5, wherein The test object is a single-phase test object or a three-phase test object. When it is a single-phase test object, the test object is connected to the phase where the delayed zero-crossing occurs; when it is a three-phase test object, the test object's test phase is connected to the phase where the delayed zero-crossing occurs.

7. A regulation method for generating a delayed zero-crossing test current, which is implemented based on a power supply system for generating a delayed zero-crossing test current according to any one of claims 1-6, characterized in that, It includes the following steps: Select a certain phase A as the test phase for generating the delayed zero-crossing test current, and then close the switch at the zero-crossing point of the line voltage U between this phase A and the adjacent lagging phase B AB at the zero-crossing point; When the adjacent leading phase C closes at an interval of about one-quarter cycle, a delayed zero-crossing test current is generated on phase A. Assume that the per-unit value of the line voltage of the selected phase A and the adjacent lagging phase B is If the closing time is t = 0, the per-unit value expression of the short-circuit test current of the selected phase A is: The DC component I at the moment t = ΔT dc is as follows: In the above formula, ω is the power supply frequency, a is the closing phase angle, is the power factor angle, ΔT is the closing interval time, and τ is the loop time constant.

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