Generator stator winding broadband off-line partial discharge test method and device

Abstract

The invention discloses a generator stator winding broadband off-line partial discharge test method and device, and relates to the technical field of generator partial discharge off-line tests.The generator stator winding broadband off-line partial discharge test method comprises the steps that a sampling interval is set according to a variable step size strategy and a variable period delay strategy, and an acquisition system is initialized; synchronously monitoring phase information of externally applied voltage-withstanding power frequency alternating current, starting timing, and timing according to a single-period sampling interval mechanism and a full-period sampling interval mechanism; acquiring partial discharge signals and performing synchronous extrusion wavelet transform by using a mother wavelet function to obtain signals of different frequency components; and restoring the extracted frequency band signal to a time domain, and drawing and outputting a partial discharge time domain and phase domain result graph. The generator stator winding broadband off-line partial discharge test method provided by the invention reflects the discharge condition of the high frequency band after the stator insulation system is aged. For the facts that a high-frequency signal channel is narrow and attenuation is fast, the device is suitable for on-site measurement of partial discharge of a large-scale synchronous generator set stator insulation system of 27kV and below.

Description

Technical Field

[0001] The invention relates to the technical field of generator partial discharge offline testing, in particular to a generator stator winding broadband offline partial discharge testing method and device. Background Art

[0002] The importance of partial discharge detection for the evaluation of generator stator insulation system is well known in the industry. However, since generators are electrical equipment with comprehensive insulation, the current conventional test technology has no threshold acceptance threshold and the test method has no mature standard. As a result, the effective judgment of generator partial discharge offline detection relies on a large number of databases and mature manual experience, and is mainly monopolized by companies such as Iris Power and ABB.

[0003] It is reported that from the current regulations, the regulations and guidelines specifically used for partial discharge of rotating electrical equipment are IEEE 1434 and IEC 60034-27. The main body of the national standard GB 20833 "Insulation of Rotating Electrical Machine Windings" series of standards accepts the content of IEC 60034-27. IEEE 1434 and IEC 60034-27 have reached an agreement on the calibration or normalization issues related to the measurement unit and the test object type. The allowed acquisition frequency for offline testing is limited to the frequency band of 10kHz~1MHz, and there is no requirement for surface partial discharge testing. Neither of them provides acceptance criteria for partial discharge amplitude, starting or extinction voltage, and emphasizes that partial discharge data is only for comparison - observe the trend of partial discharge behavior of a given winding, or compare a specific coil or winding with a partial discharge database under similar operating conditions to obtain results.

[0004] From a technical perspective, the fault characteristic frequency band of the generator stator bars and windings after aging is high, and hundreds of pC can develop into breakdown, but the mica insulation of the generator windings can withstand tens of thousands of pC of discharge for a long time. The corresponding conventional response strategy is broadband partial discharge signal detection. Broadband acquisition technology reflects the level of each company in dealing with noise interference, transmission process distortion and pattern recognition problems, and also determines the validity of the measurement results.

[0005] Wideband sampling tests the performance of components in a wide frequency range. First, the partial discharge source and sensor parameters determine the subsequent solution. The processing idea of ​​emphasizing avoiding the interference frequency band will lose the information of the signal in the time domain and phase domain, resulting in inaccuracy; secondly, there is attenuation and deformation during signal transmission, and the high-frequency signal path and the low-frequency signal transmission path are obviously different, which has a strong correlation with the actual on-site layout; finally, after the separation and classification of the pulse signal, the pattern recognition task will be carried out on this basis. The feature quantities of different modes must be unique and separable, and the feature quantities can involve time domain, frequency domain and phase domain (power frequency phase) information.

[0006] In summary, in order to address the problems faced by generator stator partial discharge detection, a set of programmed test methods and processes are needed to effectively measure the test results, accumulate an effective database, and determine the insulation aging status of the equipment. Summary of the invention

[0007] In view of the above-mentioned problems, the present invention is proposed.

[0008] Therefore, the technical problem solved by the present invention is that the existing conventional offline partial discharge hardware solution is difficult to reflect the internal fault state of the stator insulation system, mainly because the frequency bandwidth is insufficient, the partial discharge range is large, and the high-frequency signal acquisition anti-interference ability is poor.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions: a wide-band offline partial discharge test method for a generator stator winding, comprising: Set the sampling interval according to the variable step size strategy and the variable period delay strategy, and initialize the acquisition system; Synchronously monitor the phase information of the external withstand voltage power frequency AC power and start timing, and perform timing according to the single-cycle sampling interval and full-cycle sampling interval mechanisms; Collect partial discharge signals and use mother wavelet function to perform synchronous squeezed wavelet transform to obtain signals of different frequency components; The extracted frequency band signal is restored to the time domain, and the partial discharge time domain and phase domain result diagrams are plotted and output.

[0010] As a preferred solution of the generator stator winding broadband offline partial discharge test method of the present invention, the initialization of the acquisition system includes: In a single AC synchronous power cycle, the high-speed 1us partial discharge sampling interval is a variable step size strategy, and its value is marked as variable i; The strategy for full-cycle acquisition is a variable-cycle delay strategy, and its value is marked as variable j. The initialization is completed after the two state mark values ​​are set to 0.

[0011] As a preferred solution of the wide-band offline partial discharge test method for the stator winding of a generator described in the present invention, the variable step-size strategy of single-cycle sampling includes: In a first range of the AC phase, sampling is performed according to the rate I mode, and the sampling interval is a first interval step length; In the second range of the AC phase, sampling is performed according to the rate II mode, and the sampling interval is the second interval step length; In the third range of the AC phase, sampling is performed according to the rate III mode, and the sampling interval is the third interval step.

[0012] As a preferred solution of the wide-band offline partial discharge test method for the stator winding of a generator described in the present invention, the variable-cycle delay strategy includes: After the nth sampling, the next single-cycle sampling is performed after a delay of n AC phase cycles, wherein the value of n is 1 to 10.

[0013] As a preferred solution of the wide-band offline partial discharge test method for the generator stator winding of the present invention, the collecting of partial discharge signals includes: When the distance between the generator stator bar lead wire and the end cover exceeds 2m, the measurement needs to be made at the generator stator winding lead wire location and the neutral point location respectively; In the connection between the test equipment and the test product, the electrical layout distance between the coupling capacitor and the test product must be less than 1m; The external construction frequency AC withstand voltage equipment uses non-partial discharge equipment, and the distance between the test source and the coupling capacitor through the high-voltage connecting wire must be greater than 3m.

[0014] As a preferred solution of the wide-band offline partial discharge test method for stator windings of a generator according to the present invention, the signals of different frequency components are obtained, including: The single 1us data is recorded as f(t), and the Morlet mother wavelet function Ψ(t) is selected for continuous wavelet transform to calculate its wavelet coefficient W f (a, b) and instantaneous frequency ω f (a, b); Divide the frequency interval, if the signal f(t) length is n=2 L+1 , the sampling time interval is Δt,n v Take it as 32, let n a =Ln v , Δω=log2(n / 2) / (n a –1), divide f(t) into different frequency intervals; By squeezing the time-frequency surface W f (a,b) at the center frequency ω l Nearby interval W l The value of the synchronous squeezing wavelet coefficient T is calculated f (a,b).

[0015] As a preferred solution of the generator stator winding broadband offline partial discharge test method described in the present invention, the continuous wavelet transform is expressed as: , Where f(t) is the single 1us data to be processed, t is time; a and b are the frequency scale factor and time translation factor respectively; Ψ(t) is the selected Morlet mother wavelet function; W f(a, b) represents wavelet coefficients; The division into different frequency intervals is expressed as, , In the formula, ω l is the center frequency of the lth frequency component; ω l-1、 ω l+1 Respectively represent the center frequencies of the l-1th and l+1th frequency components; The synchronous squeezing wavelet coefficients are expressed as, , Where, T f (a, b) are synchronous squeezing wavelet coefficients; ; is the conjugate Fourier transform of the wavelet function; a i is the scale factor of the i-th frequency band that satisfies the squeeze frequency; Δa i is the discretized scale factor; The extracted frequency band signal is restored to the time domain, which is expressed as: , Where, T f (ω l ,t) Extract the post-synchronous extrusion wavelet coefficients T f (a,b) Wavelet coefficients restored to the time domain.

[0016] Another object of the present invention is to provide a generator stator winding broadband offline partial discharge test device, which can realize the correct and effective identification of large-scale generator insulation and achieve the purpose of life extension assessment by constructing a generator stator winding broadband offline partial discharge test device, thereby prompting power generation companies to reduce costs and increase efficiency and ensure safe and stable operation of the power system.

[0017] In order to solve the above technical problems, the present invention provides the following technical solutions: a wide-band offline partial discharge test device for a generator stator winding, comprising: a signal acquisition unit, used to set a sampling interval according to a variable step size strategy and a variable period delay strategy and initialize the acquisition system, the signal acquisition unit comprising a coupling capacitor, used to connect to an external withstand voltage device and couple the signal to the test product, the coupling capacitor is 82pF, and the voltage level is 60kV; a synchronous voltage monitoring unit, used to synchronously monitor the phase information of the external withstand voltage power frequency alternating current and start timing; a signal processing unit, used to receive the collected partial discharge signal and use the mother wavelet function for synchronous extrusion Wavelet transform is used to obtain signals of different frequency components. The signal processing unit includes a partial discharge instrument, which is equipped with a 5V, 12-bit high-speed AD converter with a range of 20nC, a measurement resolution of 10pC, an operational amplifier, a digital signal processor and a memory, and is responsible for processing and analyzing the collected partial discharge signals; a frequency band signal restoration unit is used to restore the extracted frequency band signal to the time domain, draw the partial discharge time domain and phase domain result diagrams and output them; a detection impedance box is used to detect the partial discharge signal, and the detection impedance box includes a resistor R with a value of 2.7kΩ; a clamping diode D1 with a clamping voltage of 5V; and a shielding capacitor Cx with a value of 100nF.

[0018] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above-mentioned method for broadband offline partial discharge testing of a generator stator winding when executing the computer program.

[0019] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the above-mentioned method for broadband offline partial discharge testing of a generator stator winding.

[0020] Beneficial effects of the present invention: The wide-band offline partial discharge test method for the generator stator winding provided by the present invention provides a processing method for extracting the true value of the partial discharge signal, which specifically reflects the discharge situation in the high-frequency band after the stator insulation system is aged. At the same time, facing the fact that the high-frequency signal path is narrow and decays quickly, the present invention provides key operating steps for field tests. This method is easy to operate and has a reliable principle. It is suitable for the requirements of on-site measurement of partial discharge in the stator insulation system of large synchronous generator sets of 27kV and below. The test technology has high versatility and safety, and is easy to promote and use on site. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0022] Figure 1 A hardware schematic diagram of a wide-frequency off-line partial discharge test method for a generator stator winding provided by the present invention.

[0023] Figure 2 A test site connection schematic diagram of a wide-band offline partial discharge test method for a generator stator winding is provided in accordance with an embodiment of the present invention.

[0024] Figure 3 A flow chart of partial discharge signal true value extraction for a wide-band offline partial discharge test method for a generator stator winding is provided in accordance with an embodiment of the present invention.

[0025] Figure 4 A schematic diagram of the principle of variable step length acquisition of partial discharge signals according to synchronous alternating current phase information in a wide-band offline partial discharge test method for a generator stator winding provided by an embodiment of the present invention.

[0026] Figure 5 A diagram showing the original partial discharge signal acquisition results of a wide-band offline partial discharge test method for a generator stator winding provided by an embodiment of the present invention.

[0027] Figure 6 A diagram showing the time domain true value extraction results of a partial discharge signal in a wide-band offline partial discharge test method for a generator stator winding provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0029] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0030] Example 1 Reference Figure 1 and Figure 2 , which is an embodiment of the present invention, provides a generator stator winding broadband offline partial discharge test equipment and system, including: Step 1: Make a coupling capacitor, denoted as Cp. According to the patent content requirements, the capacitor is 82pF and the operating voltage level is 60kV; Step 2: Make a detection impedance box. The internal circuit principle of the detection impedance box is as follows: Figure 1 As shown, it consists of a detection resistor R, a clamping diode D1, and a shielding capacitor Cx. According to the requirements of the patent content, R is 2.7kΩ. This example uses a chip resistor process that is more suitable for high-frequency electronic use environments. According to the requirements of the patent content, the clamping diode D1 selects a bidirectional transient diode with a clamping voltage of 5V. The shielding capacitor Cx is 100nF.

[0031] Step 3: Make a partial discharge signal processing system - partial discharge instrument. According to the requirements of the patent content, select a 5V, 12-bit high-speed AD converter. Configure operational amplifiers, DSPs, and memory according to conventional electronic components. According to the requirements of the patent content, the range of partial discharge signals is 20nC, and the measurement resolution is 10pC. In this example, ports A and B are connected to the signal of the detection impedance box, and port C is connected to the synchronous electrical signal of the external AC withstand voltage.

[0032] The coupling capacitor of step 1 has the following characteristics: it uses an arc ring high-voltage contact surface as the hardware architecture, uses a ceramic multilayer material with high dielectric properties, and uses a gap-free firing process for the electrolyte and electrode contact layers, and can maintain a stable rated capacitance value within 10 GHz.

[0033] The detection impedance box of step 2 has the following characteristics: a metal shielding shell is used, and the connecting wire is equipped with a dedicated shielded signal wire. In the detection impedance circuit, a detection resistor using a patch process is used as an extraction carrier for the high-pass signal voltage. The clamping diode D1 selects a bidirectional transient diode to ensure transient conduction performance. The detection resistor R, the clamping diode D1, and the shielding capacitor Cx are arranged and connected on a special high-frequency circuit board.

[0034] The partial discharge signal processing system in step 3, the partial discharge instrument, has the following characteristics: Figure 2 As shown, the analog partial discharge voltage signal sent by the detection impedance box is connected through ports A and B, and the channel range is -5V~+5V. Port C is connected to the synchronous electrical signal of the external AC withstand voltage, and the channel range is -100V~+100V. The synchronous electrical signal of the external AC withstand voltage mainly extracts its phase information, and maintains normal sampling at a low-frequency sampling rate of 50kHz after analog-to-digital conversion. The partial discharge voltage signal connected to ports A and B is processed by a dedicated high-speed AD converter and operational amplifier, and then sent to the DSP for processing. The dedicated module supports a sampling rate of 1000MHz, and the high-speed sampling behavior is started according to the software instructions of the partial discharge instrument. 1us data points are extracted each time, and the sampling behavior is variable step-length intermittent sampling.

[0035] Specifically, the electrical circuit components of the partial discharge signal acquisition system include: coupling capacitor; clamping diode; resistor; non-polarized capacitor; The main signal circuit components of the partial discharge signal processing system include: high-speed AD converter, operational amplifier, DSP, memory, etc. The signal terminals include: detection impedance dual-port connection terminal and external AC synchronous signal terminal.

[0036] As a preferred solution of the hardware system described in the present invention, the detection impedance composed of the clamping diode, the resistor, and the non-polar capacitor is used for collecting high-frequency discharge signals of 1MHz-300MHz. Figure 1 The cut-off frequency of 1MHz is high-pass filtered by the designed detection impedance circuit; the high frequency value of 300MHz is taken from the database value of the epoxy overheat material aging test sample, and is obtained by using the hardware resolution and algorithm processing of the acquisition system.

[0037] To this end, the hardware features of the present invention are: 1) the coupling capacitor Cp is 82pF, which has an insulation withstand voltage level of no less than 60kV; 2) the detection resistor R is 2.7kΩ, and the chip resistor process is used as much as possible in consideration of high-frequency application scenarios. The shielding capacitor Cx is 100nF, and the clamping diode D1 selects a bidirectional transient diode, and the clamping voltage is 5V. The detection resistor R, the shielding capacitor Cx, the clamping diode D1 and their internal connecting wires together form an impedance box; 3) After considering the anti-interference performance, a ±5V, 12-bit high-speed AD converter is selected, and the data rate is 2.44mV. According to the conventional electronic components, the operational amplifier, DSP and memory are configured, and 20nC is selected as the range of the generator stator partial discharge signal. The measurement resolution of this solution is about 10pC.

[0038] Example 2 Reference Figure 3-Figure 6 , is an embodiment of the present invention, and provides a signal processing algorithm flow of a generator stator winding broadband offline partial discharge test system, and the calculation is performed according to the following steps: like Figure 3 As shown, step 1: initialization setting of the acquisition system. It is divided into single-cycle sampling interval and full-cycle sampling interval mechanism. In a single AC synchronous power cycle, the interval of high-speed 1us partial discharge sampling is a variable step length strategy, and its value is marked as variable i; the strategy of full-cycle acquisition is a variable cycle delay strategy, and its value is marked as variable j. After setting the two state mark values ​​to 0, the initialization is completed.

[0039] Step 2: Monitor the phase information of the AC power of the external withstand voltage and start timing. The timing is performed according to the single-cycle sampling interval and full-cycle sampling interval mechanism.

[0040] Step 3: Collect the voltage signal at the signal end of the impedance box in a short time window of 1us, record it as a series f(t), and process the data according to the synchronous squeezing wavelet algorithm to obtain the signal g(t) in multiple frequency bands.

[0041] Step 4: According to the single-cycle variable step-size high-speed sampling strategy and the full-cycle sampling strategy with variable cycle delay, complete a partial discharge measurement, output the results, and draw the time domain partial discharge result diagram and the phase domain partial discharge result diagram.

[0042] The specific features of step 1 are: Figure 4 As shown in the half cycle shown, in a single AC synchronous power cycle, before the partial discharge signal appears in the starting and extinction voltage stages, the acquisition interval is rate I mode, at this time the interval is the largest, as shown in Figure 4 The dotted line frame 5 position generally appears in the range of 0°~20° and 160°~180° of the AC phase. During the development of the initial partial discharge and the extinction of the partial discharge, the acquisition interval step needs to be slightly faster, which is the rate II mode, such as Figure 4 The dotted box 4 position generally appears in the range of 20°~50° and 130°~160° of the AC phase. In the process of more active partial discharge activity, the acquisition interval is the fastest, which is the rate III mode, such as Figure 4 The dotted box 3 shown in the figure generally appears in the range of 50°~90° and 90°~130° of the AC phase. The number of times the high-speed 1us partial discharge acquisition behavior occurs in a single cycle is recorded as i; the full-cycle acquisition repeats the partial discharge acquisition in a single cycle in a variable cycle delay mode, and the variable step delay strategy is: after completing a single-cycle partial discharge acquisition, delay 1 AC phase cycle, which is 0.02s in this example, and make the marker value +1, at this time j=1; after the second single-cycle acquisition, delay 2 AC phase cycles, that is, delay 0.04s, j=2; ..., and so on. After 10 single-cycle acquisition behaviors occur, when j=10, a full-cycle partial discharge acquisition is completed, and it takes about 1.1s to display a full-cycle partial discharge result diagram.

[0043] The specific characteristics of step 2 are: it is always necessary to strictly capture the phase information of the synchronous AC power, and each time the partial discharge acquisition behavior starts, it always starts at the 0° point of the AC power phase of the external withstand voltage.

[0044] The specific feature of step 3 is: starting synchronous squeezing wavelet transform at 200-300 MHz, 150-200 MHz, and 80-120 MHz respectively, and obtaining a signal of a specific frequency component g(t) for partial discharge true value extraction.

[0045] (1) Record the single 1us data as f(t), select the Morlet mother wavelet function Ψ(t) for continuous wavelet transform, and calculate That Wavelet coefficients W f (a, b) and instantaneous frequency ω f (a,b): (1) Where f(t) is the single 1us data to be processed, t is time; a and b are the frequency scale factor and time translation factor respectively; Ψ(t) is the selected Morlet mother wavelet function; W f (a, b) represents wavelet coefficients; (2) Divide the frequency interval again: If the length of the signal f(t) is n=2 L+1 , where L is a calculation parameter, which means that any data length is written in the format of 2 to the power of L+1, and the sampling time interval is Δt, n v Take it as 32, let n a =Ln v , Δω=log2(n / 2) / (n a –1), divide f(t) into different frequency intervals, As shown below: (2) In the formula, ω l is the center frequency of the lth frequency component; ω l-1、 ω l+1 Represent the center frequencies of the l-1th and l+1th frequency components respectively.

[0046] By squeezing the time-frequency surface W f (a,b) at the center frequency ω l Nearby interval W l The value of the synchronous squeezing wavelet coefficient T is calculated f (a,b) is as follows: (3) Where, T f (a, b) are synchronous squeezing wavelet coefficients; ; is the conjugate Fourier transform of the wavelet function; a i is the scale factor of the i-th frequency band that satisfies the squeeze frequency; Δa i is the discretized scale factor.

[0047] (3) Then extract the synchronously squeezed wavelet coefficients T f (a,b) is restored to the time domain to obtain the g(t) signal of a specific frequency: (4) Where, T f (ω l ,t) Extract the post-synchronous extrusion wavelet coefficients T f (a,b) Wavelet coefficients restored to the time domain.

[0048] Finally, g(t)∈[g1(t),g2(t),g3(t)] is obtained, which refer to the time domain signals obtained after synchronous squeezing processing at 200~300MHz, 150~200MHz, and 80~120MHz, respectively.

[0049] The specific features of step 4 are: perform a complete partial discharge signal sampling process according to the single-cycle variable step-size high-speed sampling strategy and the full-cycle sampling strategy with variable cycle delay described in the specific features of step 1). Draw a time domain partial discharge result diagram and a phase domain partial discharge result diagram, and output the result diagram.

[0050] Then, according to actual needs, multiple tests can be performed in other set scenarios.

[0051] Reference Figure 5~Figure 6 , which is an embodiment of the present invention, illustrates the implementation effect of a signal processing algorithm of a wide-band offline partial discharge test system for a generator stator winding: Figure 5 The data in the thick line is derived from the simulated stator partial discharge signal, and the thin line is the full signal with noise collected by the actual physical channel. The signal time length is 1us, the sampling rate is 1GHz, and the effective data length is 1000 points.

[0052] The original data is taken as the single-point sampling data in a single cycle, and the time domain signals obtained after synchronous extrusion processing at 200~300MHz, 150~200MHz, and 80~120MHz are as follows: Figure 6 As shown. It is not difficult to see that the partial discharge signals appearing at 0.1us and 0.7us can always be identified in the three extraction frequency bands in an independent and combined manner. During operation, with certain human-computer interaction interface settings, the results of different frequency bands can be flexibly retrieved and the results of partial discharge signal extraction can be observed.

[0053] The results show that the signal extraction method described in the present invention can be used for true value extraction of generator stator partial discharge signals. Compared with conventional methods, the broadband detection involved in this method is more suitable for the evaluation and discrimination of stator insulation systems, with a fixed principle and reliable results.

[0054] Example 3 An embodiment of the present invention is different from the previous two embodiments in that, in order to more accurately determine the degree of deterioration of the stator insulation system of the generator, the present invention also specifies the points of special concern in the field test method under the existing device. Its characteristics are: 1) When the distance between the generator stator bar lead wire and the end cover exceeds 2m, the measurement needs to be made at the generator stator winding lead wire location and the neutral point location respectively; 2) When connecting the test equipment to the test product, the coupling capacitor needs to be as close to the test product as possible in terms of electrical distance, with a layout distance of less than 1m; 3) External construction frequency AC withstand voltage equipment must use non-partial discharge equipment, and the distance between the test source and the coupling capacitor through the high-voltage connecting wire must be greater than 3m.

[0055] This example simulates an offline partial discharge test on a 27kV, 660MVA water-hydrogen-hydrogen generator stator. Figure 2 The on-site arrangement effect is shown. Considering the on-site equipment installation and arrangement conditions, the distance between the generator stator bar lead wire and the end cover is about 3m or more, and the high-voltage cable connecting the coupling capacitor and the stator bar lead wire end is about 1m, that is, Figure 2 The "cable 1" in the test source and the coupling capacitor has a high voltage cable greater than 3m, that is Figure 2 Cable 2 in the

[0056] Therefore, the test process of this embodiment is as follows: remove the neutral point grounding wire of the generator, short-circuit the non-test phase to ground, and leave the neutral point of the test phase suspended; at the end of the outgoing line, short-circuit the non-test phase, and connect the test phase according to Figure 2 The schematic diagram shown is connected with the partial discharge detection system and the external AC withstand voltage system. Perform 3 partial discharge tests in sequence according to the phase sequence. Then, move the partial discharge detection system and the AC external withstand voltage system to the neutral point and repeat the partial discharge test 3 times. The wiring is based on the above method.

[0057] The benefit of this example is that since high-frequency signals always decay rapidly and easily form paths through stray capacitance on exposed high-voltage wire rods, the constraint on "cable 1" ensures that most partial discharge signals can be effectively monitored. Similarly, the constraint on "cable 2" ensures that the high-frequency interference signals of most test sources can be weakened. In addition, the inevitable attenuation of high-frequency signals makes the effective detection range more easily affected the farther the sensor is from the object being detected. Therefore, repeating the test at the beginning and end of the stator winding can reduce the detection blind area and more realistically reflect the correctness of the partial discharge results.

[0058] Example 4 One embodiment of the present invention provides a generator stator winding broadband offline partial discharge test device, comprising: A signal acquisition unit, used to set the sampling interval according to the variable step size strategy and the variable period delay strategy and initialize the acquisition system, the signal acquisition unit includes a coupling capacitor, used to connect to the external withstand voltage device and couple the signal to the test product, the coupling capacitor is 82pF, and the voltage level is 60kV; A synchronous voltage monitoring unit, used to synchronously monitor the phase information of the external withstand voltage power frequency AC power and start timing; A signal processing unit, used for receiving the collected partial discharge signal and performing synchronous squeezed wavelet transform using a mother wavelet function to obtain signals of different frequency components, wherein the signal processing unit includes a partial discharge instrument, equipped with a 5V, 12-bit high-speed AD converter, a range of 20nC, a measurement resolution of 10pC, an operational amplifier, a digital signal processor and a memory, and is responsible for processing and analyzing the collected partial discharge signal; A frequency band signal restoration unit, used to restore the extracted frequency band signal to the time domain, draw the partial discharge time domain and phase domain result diagrams and output them; The detection impedance box is used to detect the partial discharge signal. The detection impedance box includes a resistor R with a value of 2.7 kΩ; a clamping diode D1 with a clamping voltage of 5 V; and a shielding capacitor Cx with a value of 100 nF.

[0059] Example 5 An embodiment of the present invention is different from the first four embodiments in that: If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions to enable a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0060] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0061] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0062] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one or combination of the following technologies known in the art: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0063] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A broadband offline partial discharge test method for a generator stator winding, characterized in that: include: Set the sampling interval according to the variable step size strategy and the variable period delay strategy, and initialize the acquisition system; Synchronously monitor the phase information of the external withstand voltage power frequency AC power and start timing, and perform timing according to the single-cycle sampling interval and full-cycle sampling interval mechanisms; Collect partial discharge signals and use mother wavelet function to perform synchronous squeezed wavelet transform to obtain signals of different frequency components; The extracted frequency band signal is restored to the time domain, and the partial discharge time domain and phase domain result diagrams are plotted and output.

2. The method for broadband off-line partial discharge testing of generator stator windings according to claim 1, characterized in that: The initialization of the acquisition system includes: In a single AC synchronous power cycle, the high-speed 1us partial discharge sampling interval is a variable step size strategy, and its value is marked as variable i; The strategy for full-cycle acquisition is a variable-cycle delay strategy, and its value is marked as variable j. The initialization is completed after the two state mark values ​​are set to 0.

3. The method for broadband off-line partial discharge testing of generator stator windings according to claim 2, characterized in that: The variable step size strategy of the single-cycle sampling includes: In a first range of the AC phase, sampling is performed according to the rate I mode, and the sampling interval is a first interval step length; In the second range of the AC phase, sampling is performed according to the rate II mode, and the sampling interval is the second interval step length; In the third range of the AC phase, sampling is performed according to the rate III mode, and the sampling interval is the third interval step.

4. The method for broadband off-line partial discharge testing of generator stator windings according to claim 3, characterized in that: The variable period delay strategy, include, After the nth sampling, the next single-cycle sampling is performed after a delay of n AC phase cycles, wherein the value of n is 1 to 10.

5. The method for broadband off-line partial discharge testing of generator stator windings according to claim 4, characterized in that: The collecting partial discharge signal, include, When the distance between the generator stator bar lead wire and the end cover exceeds 2m, the measurement needs to be made at the generator stator winding lead wire location and the neutral point location respectively; In the connection between the test equipment and the test product, the electrical layout distance between the coupling capacitor and the test product must be less than 1m; The external construction frequency AC withstand voltage equipment uses non-partial discharge equipment, and the distance between the test source and the coupling capacitor through the high-voltage connecting wire must be greater than 3m.

6. The method for broadband off-line partial discharge testing of generator stator windings according to claim 5, characterized in that: The obtaining of signals with different frequency components comprises: The single 1us data is recorded as f(t), and the Morlet mother wavelet function Ψ(t) is selected for continuous wavelet transform to calculate its wavelet coefficient W f (a, b) and instantaneous frequency ω f (a, b); Divide the frequency interval, if the signal f(t) length is n=2 L+1 , the sampling time interval is Δt,n v Take it as 32, let n a =Ln v , Δω=log2(n / 2) / (n a –1), divide f(t) into different frequency intervals; By squeezing the time-frequency surface W f (a,b) at the center frequency ω l Nearby interval W l The value of the synchronous squeezing wavelet coefficient T is calculated f (a,b).

7. The method for broadband off-line partial discharge testing of generator stator windings according to claim 6, characterized in that: The continuous wavelet transform is expressed as, ， Where f(t) is the single 1us data to be processed, t is time; a and b are the frequency scale factor and time translation factor respectively; Ψ(t) is the selected Morlet mother wavelet function; W f (a, b) represents wavelet coefficients; The division into different frequency intervals is expressed as, ， In the formula, ω l is the center frequency of the lth frequency component; ω l-1、 ω l+1 Respectively represent the center frequencies of the l-1th and l+1th frequency components; The synchronous squeezing wavelet coefficients are expressed as, ， Where, T f (a, b) are synchronous squeezing wavelet coefficients; ; is the conjugate Fourier transform of the wavelet function; a i is the scale factor of the i-th frequency band that satisfies the squeeze frequency; Δa i is the discretized scale factor; The extracted frequency band signal is restored to the time domain, which is expressed as: ， Where, T f (ω l ,t) Extract the post-synchronous extrusion wavelet coefficients T f (a,b) Wavelet coefficients restored to the time domain.

8. A device using the generator stator winding broadband offline partial discharge test method as claimed in any one of claims 1 to 7, characterized in that: include: A signal acquisition unit, used to set the sampling interval according to the variable step size strategy and the variable period delay strategy and initialize the acquisition system, the signal acquisition unit includes a coupling capacitor, used to connect to the external withstand voltage device and couple the signal to the test product, the coupling capacitor is 82pF, and the voltage level is 60kV; A synchronous voltage monitoring unit, used to synchronously monitor the phase information of the external withstand voltage power frequency AC power and start timing; A signal processing unit, used for receiving the collected partial discharge signal and performing synchronous squeezed wavelet transform using a mother wavelet function to obtain signals of different frequency components, wherein the signal processing unit includes a partial discharge instrument, equipped with a 5V, 12-bit high-speed AD converter, a range of 20nC, a measurement resolution of 10pC, an operational amplifier, a digital signal processor and a memory, and is responsible for processing and analyzing the collected partial discharge signal; A frequency band signal restoration unit, used to restore the extracted frequency band signal to the time domain, draw the partial discharge time domain and phase domain result diagrams and output them; as well as, A detection impedance box is used to detect partial discharge signals. The detection impedance box includes a resistor R with a value of 2.7 kΩ; a clamping diode D1 with a clamping voltage of 5 V; Shielding capacitor Cx, value is 100nF.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the generator stator winding broadband offline partial discharge test method according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the generator stator winding broadband offline partial discharge test method according to any one of claims 1 to 7 are implemented.

Images