Method and apparatus for testing broadband offline partial discharge of generator stator winding

Abstract

A method and apparatus for testing broadband offline partial discharge of a generator stator winding. The method comprises: on the basis of a variable step size policy and a variable cycle delay policy, setting a sampling interval, and initializing an acquisition system; synchronously monitoring phase information of an externally applied power frequency alternating current withstand voltage, starting timing, and performing timing according to a single-cycle sampling interval mechanism and a full-cycle sampling interval mechanism; acquiring a partial discharge signal, using a mother wavelet function to perform synchrosqueezed wavelet transform, and obtaining signals of different frequency components; and restoring an extracted frequency band signal to the time domain, drawing a partial discharge time domain and phase domain result diagram, and outputting same. The method for testing broadband offline partial discharge of a generator stator winding provided by the present method reflects the discharge condition of a high frequency band after aging of a stator insulation system. In view of the narrow signal path and rapid attenuation of a high-frequency signal, the method is suitable for on-site measurement requirements of partial discharge of a stator insulation system of a large synchronous generator unit at a level of 27 kV and below.

Description

A method and apparatus for broadband offline partial discharge testing of generator stator windings

[0001] This application claims priority to Chinese Patent Application No. 202510059467.1, filed on January 15, 2025, entitled "A Broadband Offline Partial Discharge Test Method and Apparatus for Generator Stator Winding", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of offline partial discharge testing technology for generators, specifically a broadband offline partial discharge testing method and apparatus for generator stator windings. Background Technology

[0003] The importance of partial discharge testing for evaluating generator stator insulation systems is well-known in the industry. However, because generators are comprehensive insulated electrical devices, current conventional testing techniques lack threshold-based acceptance criteria, and testing methods lack mature standards. This results in effective offline partial discharge detection of generators relying on large databases and mature human experience, thus being mainly monopolized by companies such as Iris Power and ABB.

[0004] It is understood that, according to current regulations, the guidelines specifically for partial discharge of rotating electrical machines are IEEE 1434 and IEC 60034-27. The national standard GB 20833, "Insulation of Windings of Rotating Electrical Machines," largely adopts the content of IEC 60034-27. IEEE 1434 and IEC 60034-27 agree on calibration or normalization issues related to measurement units and test object types. They limit the permissible acquisition frequency for offline testing to 10kHz to 1MHz, and do not require surface partial discharge testing. Neither provides acceptance criteria for partial discharge amplitude, initiation, or extinction voltage, emphasizing that partial discharge data is only for comparison—observing the trend of partial discharge behavior in a given winding, or comparing a specific coil or winding with a partial discharge database under similar operating conditions to obtain results.

[0005] From a technical perspective, the fault characteristic frequency band of generator stator bars and windings after aging is high; a few hundred pC can develop into breakdown. However, the mica insulation of the generator windings can withstand tens of thousands of pC of discharge for a long time. The corresponding conventional strategy is broadband partial discharge signal detection. Broadband acquisition technology reflects the different levels of expertise among various manufacturers in handling noise interference, transmission distortion, and pattern recognition, and also determines the validity of the measurement results.

[0006] Wideband sampling puts a strain on the performance of components across a wide frequency range. First, the parameters of the partial discharge source and sensor determine the subsequent solution. A processing approach that emphasizes avoiding interference bands will lose information in the time and phase domains, leading to inaccuracies. Second, signal transmission involves attenuation and distortion, and the transmission paths of high-frequency and low-frequency signals are significantly different, strongly correlated with the actual site layout. Finally, after the pulse signals are separated and classified, pattern recognition will be carried out on this basis. The features of different patterns must be unique and separable, and these features can involve information in the time, frequency, and phase domains (power frequency phase).

[0007] In summary, to address the challenges of partial discharge testing of generator stators, a standardized testing method and process are needed to effectively measure test results, facilitate the accumulation of an effective database, and determine the insulation aging status of the equipment. Summary of the Invention

[0008] In view of the aforementioned problems, this application is hereby filed.

[0009] Therefore, the technical problem solved by this application is that existing conventional offline partial discharge hardware solutions are difficult to reflect the internal fault state of the stator insulation system, mainly due to insufficient frequency bandwidth, large partial discharge range, and poor anti-interference capability of high-frequency signal acquisition.

[0010] To solve the above-mentioned technical problems, this application provides the following technical solution: a method for broadband offline partial discharge testing of generator stator windings, comprising:

[0011] The sampling interval is set according to the variable step size strategy and the variable period delay strategy, and the acquisition system is initialized.

[0012] Synchronously monitor the phase information of the external withstand voltage power frequency AC and start timing, and perform timing according to the single-cycle sampling interval and full-cycle sampling interval mechanism;

[0013] The partial discharge signal is acquired and synchronous squeezing wavelet transform is performed using the mother wavelet function to obtain signals with different frequency components;

[0014] The extracted frequency band signal is restored to the time domain, and the partial discharge time domain and phase domain results are plotted and output.

[0015] As an optional solution to the broadband offline partial discharge test method for generator stator windings described in this application, the initialization of the acquisition system includes:

[0016] Within a single AC synchronous electrical cycle, the interval for high-speed 1µs partial discharge sampling is a variable step size strategy, and its value is denoted as variable i.

[0017] The strategy for full-cycle acquisition is a variable-period delay strategy. The value of the variable is marked as j. Initialization is completed after setting the two state marker values ​​to 0.

[0018] As an optional scheme of the wideband offline partial discharge test method for generator stator windings described in this application, wherein: the variable step size strategy for single-cycle sampling includes,

[0019] Within the first range of the AC phase, sampling is performed according to the rate I mode, with the sampling interval being the first interval step size;

[0020] Within the second range of the alternating current phase, sampling is performed according to the Rate II mode, with the sampling interval being the second interval step size.

[0021] Within the third range of the alternating current phase, sampling is performed according to the rate III mode, with the sampling interval being the third interval step size.

[0022] As an optional scheme of the wideband offline partial discharge test method for generator stator windings described in this application, the variable period delay strategy includes:

[0023] After the nth sampling, the next single-cycle sampling is performed after a delay of n AC phase cycles, where n ranges from 1 to 10.

[0024] As an optional scheme of the wideband offline partial discharge test method for generator stator windings described in this application, wherein: the acquisition of partial discharge signals includes,

[0025] When the distance between the generator stator bar lead-out and the end cover exceeds 2m, the measurement needs to be taken at the generator stator winding lead-out and neutral point locations respectively.

[0026] In the connection between the test equipment and the test sample, the electrical distance between the coupling capacitor and the test sample must be less than 1m;

[0027] The external construction frequency AC withstand voltage equipment adopts a partial discharge-free device, and the distance between the test source and the coupling capacitor through the high voltage connecting wire must be greater than 3m.

[0028] As an optional scheme of the wideband offline partial discharge test method for generator stator windings described in this application, wherein: obtaining signals with different frequency components includes,

[0029] Let f(t) be a single 1µs data point. Then, use a Morlet-type mother wavelet function Ψ(t) for continuous wavelet transform and calculate its wavelet coefficients W. f (a,b) and instantaneous frequency ω f (a,b);

[0030] Divide the frequency range, if the length of the signal f(t) is n=2L+1 The sampling time interval is Δt, n v Let n be 32. a =Ln v Δω=log2(n / 2) / (n a -1), dividing f(t) into different frequency ranges;

[0031] By squeezing W on the time-frequency surface 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).

[0032] As an optional scheme of the broadband offline partial discharge test method for generator stator windings described in this application, wherein: the continuous wavelet transform is expressed as,

[0033] In the formula, f(t) represents a single 1µs data stream to be processed, t is time; a and b are the frequency scaling factor and time shift factor, respectively; Ψ(t) is the Morlet-type mother wavelet function; W f (a,b) represents the wavelet coefficients;

[0034] The division into different frequency ranges is represented as follows:

[0035] In the formula, ω l ω is the center frequency of the l-th frequency component; l-1 ω l+1 These represent the center frequencies of the (l-1)th and (l+1)th frequency components, respectively.

[0036] The synchronous compression wavelet coefficients are expressed as follows:

[0037] In the formula, T f (a,b) are the synchronous squeezing wavelet coefficients; It is the conjugate Fourier transform of the wavelet function; a i Let Δa be the scale factor for the i-th frequency band that satisfies the compression band. i The scale factor after discretization;

[0038] The process of restoring the extracted frequency band signal to the time domain is expressed as follows:

[0039] In the formula, T f (ω l After extraction, the wavelet coefficients T are simultaneously squeezed. f (a,b) Wavelet coefficients restored to the time domain.

[0040] Another objective of this application is to provide a wideband offline partial discharge test device for generator stator windings. By constructing such a device, the insulation of large generators can be correctly and effectively identified, and life extension assessment can be achieved, thereby enabling power generation companies to reduce costs and increase efficiency, and ensuring the safe and stable operation of the power system.

[0041] To solve the above-mentioned technical problems, this application provides the following technical solution: a wideband offline partial discharge test device for generator stator windings, comprising: a signal acquisition unit, used to set the sampling interval and initialize the acquisition system according to a variable step size strategy and a variable period delay strategy, the signal acquisition unit including a coupling capacitor, used to connect to an external withstand voltage device and couple the signal to the test object, the coupling capacitor being 82pF and having a voltage rating of 60kV; a synchronous voltage monitoring unit, used to synchronously monitor the phase information of the external withstand voltage power frequency AC and start timing; and a signal processing unit, used to receive the acquired partial discharge signal and perform synchronous compression using a mother wavelet function. Wavelet transform is used to obtain signals with different frequency components. The signal processing unit includes a partial discharge instrument, equipped with a 5V, 12-bit high-speed AD converter with a range of 20nC and a measurement resolution of 10pC, an operational amplifier, a digital signal processor, and a memory, responsible for processing and analyzing the acquired partial discharge signals; a frequency band signal restoration unit is used to restore the extracted frequency band signals to the time domain, plot the partial discharge time domain and phase domain results, and output them; a detection impedance box is used to detect the partial discharge signal, 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.

[0042] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the wideband offline partial discharge test method for generator stator windings as described above.

[0043] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the wideband offline partial discharge test method for generator stator windings as described above.

[0044] The beneficial effects of this application are as follows: The wideband offline partial discharge test method for generator stator windings provided in this application offers a processing method for extracting the true value of partial discharge signals, specifically reflecting the high-frequency discharge situation after the stator insulation system has aged. Simultaneously, addressing the narrow and rapid attenuation of high-frequency signals, this application provides key operational steps for on-site testing. This method is convenient to operate, reliable in principle, and suitable for on-site measurement requirements 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, facilitating its widespread application in the field. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments 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.

[0046] Figure 1 is a hardware schematic diagram of a broadband offline partial discharge test method for generator stator windings provided in this application.

[0047] Figure 2 is a schematic diagram of the test site connection of a broadband offline partial discharge test method for generator stator windings provided in an embodiment of this application.

[0048] Figure 3 is a flowchart of the partial discharge signal truth extraction method of a generator stator winding broadband offline partial discharge test method provided in an embodiment of this application.

[0049] Figure 4 is a schematic diagram of the principle of variable step size acquisition of partial discharge signal based on synchronous AC phase information in a wideband offline partial discharge test method for generator stator windings provided in an embodiment of this application.

[0050] Figure 5 is a diagram showing the original partial discharge signal acquisition results of a broadband offline partial discharge test method for generator stator windings provided in an embodiment of this application.

[0051] Figure 6 shows the time-domain truth extraction result of a partial discharge signal in a wideband offline partial discharge test method for generator stator windings provided in an embodiment of this application. Detailed Implementation

[0052] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort should fall within the scope of protection of this application.

[0053] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0054] Example 1

[0055] Referring to Figures 1 and 2, an embodiment of this application provides a wideband offline partial discharge test equipment and system for generator stator windings, including:

[0056] Step 1: Fabricate a coupling capacitor, denoted as Cp. According to the patent requirements, this capacitor should be 82pF and have a voltage rating of 60kV.

[0057] Step 2: Fabricate the impedance detection box. The internal circuit principle of the impedance detection box is shown in Figure 1, consisting of a detection resistor R, a clamping diode D1, and a shielding capacitor Cx. According to the patent requirements, R is 2.7kΩ. This example uses a surface-mount resistor, which is more suitable for high-frequency electronic environments. As per the patent requirements, the clamping diode D1 is a bidirectional transient diode with a clamping voltage of 5V. The shielding capacitor Cx is 100nF.

[0058] Step 3: Construct the partial discharge signal processing system—the partial discharge analyzer. Following the patent requirements, a 5V, 12-bit high-speed AD converter is selected. Operational amplifiers, DSPs, and memory are configured using standard electronic components. As per the patent requirements, the partial discharge signal range is 20nC, and the measurement resolution is 10pC. In this example, ports A and B are connected to the signal from the impedance detection box, and port C is connected to an externally applied AC withstand voltage synchronization signal.

[0059] The coupling capacitor in step 1 has the following characteristics: it adopts a circular arc high-voltage contact surface as the hardware architecture, uses a multilayer ceramic material with high dielectric properties, and the electrolyte and electrode contact layer adopts a gapless sintering process, which can maintain a stable rated capacitance value within 10GHz.

[0060] The impedance detection box in step 2 has the following characteristics: it uses a metal shielded shell and is equipped with a dedicated shielded signal cable. In the impedance detection circuit, a surface-mount resistor is used as the carrier for extracting the high-pass signal voltage. The clamping diode D1 is a bidirectional transient diode to ensure transient conduction performance. The detection resistor R, clamping diode D1, and shielding capacitor Cx are arranged and connected on a specially designed high-frequency circuit board.

[0061] The partial discharge signal processing system in step 3—the partial discharge instrument—has the following characteristics, as shown in Figure 2. It receives analog partial discharge voltage signals from the detection impedance box via ports A and B, with a channel range of -5V to +5V. Port C receives an externally applied AC withstand voltage synchronization signal, with a channel range of -100V to +100V. The externally applied AC withstand voltage synchronization signal primarily extracts its phase information and, after analog-to-digital conversion, maintains normal sampling at a low-frequency sampling rate of 50kHz. The partial discharge voltage signals received at ports A and B are processed by a dedicated high-speed AD converter and operational amplifier before being sent to the DSP for processing. The dedicated module supports a 1000MHz sampling rate and initiates high-speed sampling according to the software instructions of the partial discharge instrument, extracting 1µs of data each time. The sampling behavior is a variable-step, intermittent sampling.

[0062] Specifically, the electrical circuit components of a partial discharge signal acquisition system include: coupling capacitors; clamping diodes; resistors; and non-polarized capacitors.

[0063] The main signal circuit components of the partial discharge signal processing system include: high-speed AD converter, operational amplifier, DSP, memory, etc., and the signal terminals include: impedance detection dual-port connection terminal and external AC synchronous signal terminal.

[0064] As an optional embodiment of the hardware system described in this application, the detection impedance composed of the clamping diode, resistor, and non-polarized capacitor is used for high-frequency discharge signal acquisition in the range of 1MHz-300MHz, as shown in Figure 1. The 1MHz cutoff frequency is high-pass filtered by the designed detection impedance circuit; the 300MHz high-frequency value is taken from the database values ​​of epoxy overheating material aging test samples and obtained by processing the data using the hardware resolution and algorithm of the acquisition system.

[0065] Therefore, the hardware features of this application are as follows: 1) The coupling capacitor Cp is 82pF, which has an insulation withstand voltage of not less than 60kV; 2) The sensing resistor R is 2.7kΩ, and surface mount resistor technology is used as much as possible for high-frequency applications. The shielding capacitor Cx is 100nF, and the clamping diode D1 is a bidirectional transient diode with a clamping voltage of 5V. The sensing resistor R, shielding capacitor Cx, clamping diode D1, and their internal connecting wires together form an impedance box; 3) Considering anti-interference performance, a ±5V, 12-bit high-speed AD converter is selected, resulting in a data resolution of 2.44mV. Following conventional electronic component configurations such as operational amplifiers, DSPs, and memory, and selecting 20nC as the range for the generator stator partial discharge signal, the measurement resolution of this scheme is approximately 10pC.

[0066] Example 2

[0067] Referring to Figures 3-6, an embodiment of this application provides a signal processing algorithm flow for a wideband offline partial discharge test system for generator stator windings, which is calculated according to the following steps:

[0068] As shown in Figure 3, Step 1: Initialization settings of the acquisition system. This is divided into single-cycle sampling interval and full-cycle sampling interval mechanisms. Within a single AC synchronous electrical cycle, the high-speed 1µs partial discharge sampling interval uses a variable step size strategy, and its value is marked as variable i; the full-cycle acquisition strategy uses a variable period delay strategy, and its value is marked as variable j. Initialization is completed by setting both state markers to 0.

[0069] Step 2: Monitor the phase information of the externally applied withstand voltage power frequency AC current and start timing. Timing is performed according to the single-cycle sampling interval and full-cycle sampling interval mechanism.

[0070] Step 3: Acquire the impedance box signal terminal voltage signal within a 1µs short time window, denoted as the sequence f(t), and process this data segment according to the synchronous squeezing wavelet algorithm to obtain the multi-band signal g(t).

[0071] Step 4: Complete one partial discharge measurement according to the single-cycle variable step size high-speed sampling strategy and the variable-cycle delay full-cycle sampling strategy, output the results, and draw the time-domain partial discharge result diagram and the phase-domain partial discharge result diagram.

[0072] The specific features of step 1 are as follows: As shown in Figure 4, within a single AC synchronous cycle, before the partial discharge signal appears at the onset and extinction voltage stages, the acquisition interval is in rate I mode, at which time the interval is the largest, as shown in the dashed box 5 in Figure 4, generally appearing in the AC phase range of 0°~20° and 160°~180°; during the development of the onset and extinction of partial discharge, the acquisition interval step size needs to be slightly faster, which is rate II mode, as shown in the dashed box 4 in Figure 4, generally appearing in the AC phase range of 20°~50° and 130°~160°; during the process of more active partial discharge activity, the acquisition interval is the fastest, which is rate III mode, as shown in the dashed box 3 in Figure 4, generally appearing in the AC phase range of 50°~90° and 90°~130°. The number of times the high-speed 1µs partial discharge acquisition occurs within a single cycle is denoted as i. Full-cycle acquisition is performed repeatedly within a single cycle using a variable-cycle delay method. The variable-step delay strategy is as follows: after completing one single-cycle partial discharge acquisition, delay by one AC phase cycle (0.02s in this example) and increment the marker value by 1, at which point j = 1; after the second single-cycle acquisition, delay by two AC phase cycles (0.04s), j = 2; ..., and so on. After 10 single-cycle acquisitions, a full-cycle partial discharge acquisition is completed when j = 10, taking approximately 1.1s to display a full-cycle partial discharge result graph.

[0073] The specific feature of step 2 is that it is always necessary to strictly capture the phase information of the synchronous AC power, and each partial discharge acquisition behavior always starts at the 0° phase point of the AC power with applied withstand voltage.

[0074] The specific feature of step 3 is that synchronous squeezing wavelet transform is started at 200-300MHz, 150-200MHz, and 80-120MHz respectively to obtain a signal with a specific frequency component g(t) for partial discharge truth extraction.

[0075] (1) Denote a single 1µs data point as f(t), perform continuous wavelet transform using the Morlet-type mother wavelet function Ψ(t), and calculate its wavelet coefficients W. f (a,b) and instantaneous frequency ω f (a,b):

[0076] In the formula, f(t) represents a single 1µs data stream to be processed, t is time; a and b are the frequency scaling factor and time shift factor, respectively; Ψ(t) is the Morlet-type mother wavelet function; W f (a,b) represents the wavelet coefficients;

[0077] (2) Further divide the frequency range: If the length of the signal f(t) is n = 2 L+1 Where L is a calculation parameter, referring to the format where any data length is written as 2 to the power of L+1, the sampling time interval is Δt, and n v Let n be 32. a =Ln v Δω=log2(n / 2) / (n a -1), divide f(t) into different frequency ranges.

[0078] As shown below:

[0079] In the formula, ω l ω is the center frequency of the l-th frequency component; l-1、 ω l+1 These represent the center frequencies of the (l-1)th and (l+1)th frequency components, respectively.

[0080] By squeezing W on the time-frequency surface 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) are shown below:

[0081] In the formula, T f (a,b) are the synchronous squeezing wavelet coefficients; It is the conjugate Fourier transform of the wavelet function; a i Let Δa be the scale factor for the i-th frequency band that satisfies the compression band. i The scale factor is the discretized value.

[0082] (3) Then extract the synchronously squeezed wavelet coefficients T f (a,b) are restored to the time domain to obtain a g(t) signal of a specific frequency:

[0083] In the formula, T f (ω l After extraction, the wavelet coefficients T are simultaneously squeezed. f (a,b) Wavelet coefficients restored to the time domain.

[0084] Finally, g(t)∈[g1(t),g2(t),g3(t)] was obtained, which respectively refer to the time-domain signals obtained after synchronous compression processing at 200~300MHz, 150~200MHz, and 80~120MHz.

[0085] The specific features of step 4 are as follows: Following the single-cycle variable step-size high-speed sampling strategy and the variable-cycle delay full-cycle sampling strategy described in step 1), a complete partial discharge signal sampling process is performed. Time-domain partial discharge result diagrams and phase-domain partial discharge result diagrams are plotted, and the result diagrams are output.

[0086] Then, depending on actual needs, multiple trials can be conducted in other scenarios.

[0087] Referring to Figures 5 and 6, an embodiment of this application illustrates the implementation effect of a signal processing algorithm for a wideband offline partial discharge test system for generator stator windings:

[0088] In Figure 5, the thick lines represent data derived from simulated stator partial discharge signals, while the thin lines represent the noisy full signal acquired from the actual physical channel. The signal duration is 1 µs, the sampling rate is 1 GHz, and the effective data length is 1000 points.

[0089] Using this raw data as single-point sampling data within a single period, and employing the method described in step 3), the time-domain signals obtained after synchronous compression processing at 200–300MHz, 150–200MHz, and 80–120MHz for g(t)∈[g1(t),g2(t),g3(t)] are shown in Figure 6. It is easy to see that the partial discharge signals appearing at 0.1µs and 0.7µs can always be identified independently or in combination within the three extraction frequency bands. During operation, with the aid of a suitable human-computer interaction interface, results from different frequency bands can be flexibly retrieved, and the results of partial discharge signal extraction can be observed.

[0090] The results show that the signal extraction method described in this application can be used for the true value extraction of generator stator partial discharge signals. Compared with conventional methods, this method is more suitable for the evaluation and discrimination of stator insulation systems due to its wideband detection capability. The principle is fixed and the results are reliable.

[0091] Example 3

[0092] One embodiment of this application differs from the previous two embodiments in that, for the purpose of more accurately determining the degree of degradation of the generator stator insulation system, this application also specifies points of particular concern in the field testing method under existing equipment. Its characteristics are as follows:

[0093] 1) When the distance between the generator stator bar lead-out and the end cover exceeds 2m, the measurement needs to be taken at the generator stator winding lead-out and neutral point locations respectively;

[0094] 2) In the connection between the test equipment and the test specimen, the coupling capacitor should be as close as possible to the test specimen in terms of electrical distance, and the arrangement distance should be less than 1m;

[0095] 3) The AC withstand voltage equipment for external construction frequency must be a partial discharge-free device, and the distance between the test source and the coupling capacitor through the high voltage connecting wire must be greater than 3m.

[0096] This example simulates an offline partial discharge test on the stator of a 27kV, 660MVA water-hydrogen-hydrogen generator. Using the partial discharge detection equipment, apparatus, and system described in this application, the on-site setup shown in Figure 2 is established. Given the on-site equipment installation conditions, the distance between the generator stator lead wires and the end cover is approximately 3m or more, and the high-voltage cable connecting the coupling capacitor and the stator lead wires is approximately 1m (i.e., "Cable 1" in Figure 2). The high-voltage cable between the test source and the coupling capacitor is greater than 3m (i.e., "Cable 2" in Figure 2).

[0097] Therefore, the test procedure in this embodiment is as follows: Remove the generator neutral grounding wire, short-circuit the non-test phases to ground, and leave the neutral point of the test phase suspended; at the outgoing end, short-circuit the non-test phases, and connect the test phases to the partial discharge detection system and the external AC withstand voltage system as shown in Figure 2. Perform three partial discharge tests sequentially according to the phase sequence. Then, move the partial discharge detection system and the external AC withstand voltage system to the neutral point and repeat the three partial discharge tests, with the wiring method as shown above.

[0098] The advantage of this example is that, since high-frequency signals always attenuate rapidly and easily form circuits through stray capacitance on exposed high-voltage conductors, the constraint on "cable 1" ensures that most partial discharge signals can be effectively monitored. Similarly, the constraint on "cable 2" ensures that most high-frequency interference signals from the test source can be attenuated. Furthermore, the unavoidable attenuation of high-frequency signals means that the effective detection range is more easily affected the farther the sensor is from the object being tested. Therefore, repeating the test at both ends of the stator winding can reduce the detection blind zone and more accurately reflect the correctness of the partial discharge results.

[0099] Example 4

[0100] One embodiment of this application provides a wideband offline partial discharge test device for generator stator windings, comprising:

[0101] The signal acquisition unit is used to set the sampling interval and initialize the acquisition system according to the variable step size strategy and the variable period delay strategy. The signal acquisition unit includes a coupling capacitor for connecting to the external withstand voltage device and coupling the signal to the test sample. The coupling capacitor is 82pF and has a voltage rating of 60kV.

[0102] Synchronous voltage monitoring unit is used to synchronously monitor the phase information of the external withstand voltage power frequency AC and start timing;

[0103] The signal processing unit is used to receive the acquired partial discharge signal and perform synchronous squeeze wavelet transform using the mother wavelet function to obtain signals with different frequency components. The signal processing unit includes a partial discharge instrument, equipped with a 5V, 12-bit high-speed AD converter with a range of 20nC and a measurement resolution of 10pC, an operational amplifier, a digital signal processor, and a memory, and is responsible for processing and analyzing the acquired partial discharge signal.

[0104] The frequency band signal restoration unit is used to restore the extracted frequency band signal to the time domain, plot the partial discharge time domain and phase domain results and output them;

[0105] The impedance detection box is used to detect partial discharge signals. The impedance detection 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.

[0106] Example 5

[0107] One embodiment of this application differs from the previous four embodiments in that:

[0108] If the aforementioned functions are implemented as 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 this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0109] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device.

[0110] More specific examples of computer-readable media (a non-exhaustive list) include: electrical connections (electronic devices) having one or more wires, portable computer disk drives (magnetic devices), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0111] It should be understood that various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0112] It should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application, and all such modifications and substitutions should be covered within the scope of the claims of this application.

Claims

1. A method for broadband offline partial discharge testing of generator stator windings, characterized in that, include: The sampling interval is set according to the variable step size strategy and the variable period delay strategy, and the acquisition system is initialized. Synchronously monitor the phase information of the external withstand voltage power frequency AC and start timing, and perform timing according to the single-cycle sampling interval and full-cycle sampling interval mechanism; The partial discharge signal is acquired and synchronous squeezing wavelet transform is performed using the mother wavelet function to obtain signals with different frequency components; The extracted frequency band signal is restored to the time domain, and the partial discharge time domain and phase domain results are plotted and output.

2. The method for broadband offline partial discharge test of generator stator winding as described in claim 1, characterized in that: The initialization of the acquisition system includes, Within a single AC synchronous electrical cycle, the interval for high-speed 1µs partial discharge sampling is a variable step size strategy, and its value is denoted as variable i. The strategy for full-cycle acquisition is a variable-period delay strategy. The value of the variable is marked as j. Initialization is completed after setting the two state marker values ​​to 0.

3. The broadband offline partial discharge test method for generator stator windings as described in claim 2, characterized in that: The variable step size strategy for single-cycle sampling includes, Within the first range of the AC phase, sampling is performed according to the rate I mode, with the sampling interval being the first interval step size; Within the second range of the alternating current phase, sampling is performed according to the Rate II mode, with the sampling interval being the second interval step size. Within the third range of the alternating current phase, sampling is performed according to the rate III mode, with the sampling interval being the third interval step size.

4. The broadband offline partial discharge test method for generator stator windings as described in 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, where n ranges from 1 to 10.

5. The broadband offline partial discharge test method for generator stator windings as described in claim 4, characterized in that: The acquired partial discharge signal include, When the distance between the generator stator bar lead-out and the end cover exceeds 2m, the measurement needs to be taken at the generator stator winding lead-out and neutral point locations respectively. In the connection between the test equipment and the test sample, the electrical distance between the coupling capacitor and the test sample must be less than 1m; The external construction frequency AC withstand voltage equipment adopts a partial discharge-free device, and the distance between the test source and the coupling capacitor through the high voltage connecting wire must be greater than 3m.

6. The broadband offline partial discharge test method for generator stator windings as described in claim 5, characterized in that: The acquisition of signals with different frequency components includes, Let f(t) be a single 1µs data point. Then, use a Morlet-type mother wavelet function Ψ(t) for continuous wavelet transform and calculate its wavelet coefficients W. f (a,b) and instantaneous frequency ω f (a,b); Divide the frequency range, if the length of the signal f(t) is n=2 L+1 The sampling time interval is Δt, n v Let n be 32. a =Ln v Δω=log2(n / 2) / (n a -1), dividing f(t) into different frequency ranges; By squeezing W on the time-frequency surface 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 broadband offline partial discharge test method for generator stator windings as described in claim 6, characterized in that: The continuous wavelet transform is expressed as follows: In the formula, f(t) represents a single 1µs data stream to be processed, and t represents time. a and b are the frequency scaling factor and time shift factor, respectively; Ψ(t) uses a Morlet-type mother wavelet function; W f (a,b) represents the wavelet coefficients; The division into different frequency ranges is represented as follows: In the formula, ω l ω is the center frequency of the l-th frequency component; l-1 ω l+1 These represent the center frequencies of the (l-1)th and (l+1)th frequency components, respectively. The synchronous compression wavelet coefficients are expressed as follows: In the formula, T f (a,b) are the synchronous squeezing wavelet coefficients; It is the conjugate Fourier transform of the wavelet function; a i Let Δa be the scale factor for the i-th frequency band that satisfies the compression band. i The scale factor after discretization; The process of restoring the extracted frequency band signal to the time domain is expressed as follows: In the formula, T f (ω l After extraction, the wavelet coefficients T are simultaneously squeezed. f (a,b) Wavelet coefficients restored to the time domain.

8. The generator stator winding broadband offline partial discharge test method as described in claim 1, the method further includes: The detection impedance is composed of a clamping diode, a resistor, and a non-polarized capacitor; the clamping diode is connected in parallel with the series branch formed by the resistor and the non-polarized capacitor. The detection impedance is used for high-frequency discharge signal acquisition in the 1MHz-300MHz range; The different frequency components are 200–300 MHz, 150–200 MHz, and 80–120 MHz.

9. An apparatus employing the broadband offline partial discharge test method for generator stator windings as described in any one of claims 1 to 8, characterized in that, include: The signal acquisition unit is used to set the sampling interval and initialize the acquisition system according to the variable step size strategy and the variable period delay strategy. The signal acquisition unit includes a coupling capacitor for connecting to the external withstand voltage device and coupling the signal to the test sample. The coupling capacitor is 82pF and has a voltage rating of 60kV. Synchronous voltage monitoring unit is used to synchronously monitor the phase information of the external withstand voltage power frequency AC and start timing; The signal processing unit is used to receive the acquired partial discharge signal and perform synchronous squeeze wavelet transform using the mother wavelet function to obtain signals with different frequency components. The signal processing unit includes a partial discharge instrument, equipped with a 5V, 12-bit high-speed AD converter with a range of 20nC and a measurement resolution of 10pC, an operational amplifier, a digital signal processor, and a memory, and is responsible for processing and analyzing the acquired partial discharge signal. The frequency band signal restoration unit is used to restore the extracted frequency band signal to the time domain, plot the partial discharge time domain and phase domain results and output them; as well as, The detection impedance box is used to detect partial discharge signals. The detection impedance box includes a resistor R with a value of 2.7kΩ and a clamping diode D1 with a clamping voltage of 5V. The shielding capacitor Cx has a value of 100nF.

10. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the generator stator winding broadband offline partial discharge test method according to any one of claims 1 to 8.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the broadband offline partial discharge test method for generator stator windings as described in any one of claims 1 to 8.

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