A Wide-Frequency Offline Partial Discharge Test Method and Device for Generator Stator Windings

Abstract

The present invention discloses a wide-frequency off-line partial discharge test method and device for a generator stator winding, which relates to the technical field of off-line partial discharge tests of generators, and includes: setting a sampling interval according to a variable step size strategy and a variable cycle delay strategy, and initializing an acquisition system; synchronously monitoring the phase information of the applied withstand voltage power frequency alternating current and starting timing, and timing according to the single-cycle sampling interval and the full-cycle sampling interval mechanism; acquiring partial discharge signals and performing synchrosqueezing wavelet transform using a mother wavelet function to obtain signals of different frequency components; restoring the extracted frequency band signals to the time domain, drawing partial discharge time domain and phase domain result diagrams and outputting them. The wide-frequency off-line partial discharge test method for a generator stator winding provided by the present invention reflects the discharge situation in the high-frequency band after the aging of the stator insulation system. Facing the fact that the high-frequency signal path is narrow and the attenuation is fast, it meets the requirements for on-site measurement of partial discharge of the stator insulation system of large synchronous generator sets with a voltage class of 27 kV and below.

Description

Technical Field

[0001] The present invention relates to the technical field of off-line partial discharge testing of generators, and specifically to a method and device for wide-frequency off-line partial discharge testing of generator stator windings. Background Art

[0002] The importance of partial discharge detection for the evaluation of the generator stator insulation system is well-known in the industry. However, since generators are electrical equipment with comprehensive insulation, the current conventional test technologies have no threshold acceptance criteria, and the test methods have no mature standards. As a result, the effective discrimination of off-line partial discharge detection of generators depends on a large number of databases and mature manual experience, and thus is mainly monopolized by companies such as Iris Power and ABB.

[0003] It is reported that from the perspective of the current regulations, the regulation guidelines specifically for partial discharge of rotating electrical machine equipment are IEEE 1434 and IEC 60034-27. The national standard GB 20833 "Insulation of Rotating Machine Windings" series standards mainly accept 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. The limited frequency band for the allowable acquisition frequency of off-line testing is 10 kHz to 1 MHz, and there is no requirement for surface partial discharge testing. Also, neither of them provides acceptance criteria for partial discharge amplitude, inception or extinction voltage, emphasizing that partial discharge data is only for comparison - observing the trend of partial discharge behavior of a given winding, or comparing 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 generator stator bars and windings is high after aging, and hundreds of pC can develop into breakdown. However, the mica insulation of generator windings can withstand a discharge amount of tens of thousands of pC for a long time. The corresponding conventional countermeasure is wide-band partial discharge signal detection. The wide-frequency acquisition technology reflects the level of each company in dealing with noise interference, distortion during transmission, and pattern recognition problems, and also determines the effectiveness of the measurement results.

[0005] Wide-frequency sampling poses a test on the performance of components in the wide-frequency range. First, the parameters of the partial discharge source and the sensor determine the subsequent scheme. The processing idea of emphasizing avoiding the interference frequency band will lose information in the time domain and phase domain of the signal, leading to inaccuracy. Second, there is attenuation and distortion during signal transmission, and the high-frequency signal path and the low-frequency signal transmission path are significantly different, which has a strong correlation with the actual on-site layout. Finally, after the separation and classification of pulse signals, the pattern recognition task will be carried out on this basis. The characteristic quantities of different patterns must be unique and separable, and the characteristic quantities can involve information in the time domain, frequency domain, and phase domain (power frequency phase).

[0006] In summary, in view of the problems faced by the partial discharge detection of the generator stator, a set of programmed test methods and processes are needed to effectively obtain test results, facilitate the accumulation of an effective database, and determine the insulation aging state of the equipment. Summary of the Invention

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

[0008] Therefore, the technical problem solved by the present invention is that the existing conventional off-line partial discharge hardware solutions are difficult to reflect the internal fault state of the stator insulation system, mainly due to insufficient frequency bandwidth, a large range of partial discharge measurement ranges, and poor anti-interference ability for high-frequency signal acquisition.

[0009] To solve the above technical problems, the present invention provides the following technical solution: A wide-frequency off-line partial discharge test method for a generator stator winding, including:

[0010] Set the sampling interval according to the variable step size strategy and variable cycle delay strategy, and initialize the acquisition system;

[0011] Synchronously monitor the phase information of the applied withstand voltage power frequency alternating current and start timing, and perform timing according to the single-cycle sampling interval and full-cycle sampling interval mechanism;

[0012] Collect partial discharge signals and perform synchrosqueezing wavelet transform using the mother wavelet function to obtain signals of different frequency components;

[0013] Restore the extracted frequency band signals to the time domain, draw the partial discharge time domain and phase domain result diagrams and output them.

[0014] As a preferred scheme of the wide-frequency off-line partial discharge test method for the generator stator winding of the present invention, wherein: the initialization of the acquisition system includes,

[0015] Within a single alternating current synchronous electrical cycle, the interval of high-speed 1us partial discharge sampling is the variable step size strategy, and its value is marked as variable i;

[0016] The strategy for full-cycle acquisition is the variable cycle delay strategy, and its value is marked as variable j. After setting the two status marker values to 0, the initialization is completed.

[0017] As a preferred scheme of the wide-frequency off-line partial discharge test method for the generator stator winding of the present invention, wherein: the variable step size strategy for single-cycle sampling includes,

[0018] Within the first range interval of the alternating current phase, sample according to the rate I mode, and the sampling interval is the first interval step size;

[0019] Within the second range interval of the alternating current phase, sample according to the rate II mode, and the sampling interval is the second interval step size;

[0020] In the third range interval of the AC power phase, sampling is performed according to the rate III mode, and the sampling interval is the third interval step size.

[0021] As a preferred solution of the wide-frequency off-line partial discharge test method for the generator stator winding described in the present invention, wherein: the variable-period delay strategy includes

[0022] After the nth sampling, delay for n AC power phase periods for the next single-period sampling, where n ranges from 1 to 10.

[0023] As a preferred solution of the wide-frequency off-line partial discharge test method for the generator stator winding described in the present invention, wherein: the acquisition of partial discharge signals includes

[0024] When the distance between the lead wire of the generator stator bar and the end cover exceeds 2 m, measurements need to be taken at the outlet part and the neutral point part of the generator stator winding respectively;

[0025] In the connection between the test equipment and the test object, the electrical layout distance between the coupling capacitor and the test object needs to be less than 1 m;

[0026] The external power frequency AC withstand voltage equipment uses partial discharge-free equipment, and the distance between the test source and the coupling capacitor through the high-voltage connection wire needs to be greater than 3 m.

[0027] As a preferred solution of the wide-frequency off-line partial discharge test method for the generator stator winding described in the present invention, wherein: the obtaining of signals with different frequency components includes

[0028] Record the single 1 μs data as f(t), select the Morlet mother wavelet function Ψ(t) for continuous wavelet transform, and calculate its wavelet coefficient W f (a, b) and the instantaneous frequency ω f (a, b);

[0029] Divide the frequency interval. If the length of the signal f(t) is n = 2 L+1 , the sampling time interval is Δt, and n v is taken as 32. Let n a = Ln v , Δω = log2(n / 2) / (n a –1), and divide f(t) into different frequency intervals;

[0030] By squeezing the value of W f (a, b) in the interval near the center frequency ω l , calculate the synchrosqueezed wavelet coefficient T l (a, b). f (a, b).

[0031] As a preferred embodiment of the wide-band off-line partial discharge test method for the generator stator winding according to the present invention, where: the continuous wavelet transform is expressed as

[0032]

[0033] In the formula, 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-type mother wavelet function; W f (a, b) represents the wavelet coefficient;

[0034] The division into different frequency intervals is expressed as

[0035]

[0036] In the formula, ω l is the center frequency of the l-th frequency component; ω l-1、 ω l+1 represent the center frequencies of the (l - 1)-th and (l + 1)-th frequency components respectively;

[0037] The synchrosqueezed wavelet coefficient is expressed as

[0038]

[0039] In the formula, T f (a, b) is the synchrosqueezed wavelet coefficient; is the conjugate Fourier transform of the wavelet function; a i is the scale factor of the i-th satisfying the squeezing frequency band; Δa i is the discretized scale factor;

[0040] The restoration of the extracted band signal to the time domain is expressed as

[0041]

[0042] In the formula, T f (ω l , t) is the wavelet coefficient after the extracted synchrosqueezed wavelet coefficient T f (a, b) is restored to the time domain.

[0043] Another object of the present invention is to provide a wide-band off-line partial discharge test device for the generator stator winding, which can realize the correct and effective identification of the insulation of large generators and achieve the purpose of life extension assessment by constructing a wide-band off-line partial discharge test device for the generator stator winding, promote cost reduction and efficiency increase of power generation enterprises, and ensure the safe and stable operation of the power system.

[0044] To solve the above technical problems, the present invention provides the following technical solutions: A wide-frequency off-line partial discharge test device for a generator stator winding, comprising: a signal acquisition unit, configured to set a sampling interval according to a variable step size strategy and a variable cycle delay strategy and initialize the acquisition system. The signal acquisition unit includes a coupling capacitor for connecting to an applied voltage withstand device and coupling signals to the test object. The coupling capacitor is 82 pF and the voltage level is 60 kV; a synchronous voltage monitoring unit, configured to synchronously monitor the phase information of the applied voltage power frequency alternating current and start timing; a signal processing unit, configured to receive the acquired partial discharge signals and perform synchrosqueezing wavelet transform using a mother wavelet function to obtain signals of different frequency components. The signal processing unit includes a partial discharge detector equipped with a 5V, 12-bit high-speed AD converter, with a measurement range of 20 nC, a measurement resolution of 10 pC, 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, configured to restore the extracted frequency band signals to the time domain, draw partial discharge time domain and phase domain result diagrams and output them; a detection impedance box, configured 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 5V; and a shielding capacitor Cx with a value of 100 nF.

[0045] A computer device includes a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the above-mentioned wide-frequency off-line partial discharge test method for a generator stator winding are implemented.

[0046] A computer-readable storage medium stores a computer program thereon. When the computer program is executed by a processor, the steps of the above-mentioned wide-frequency off-line partial discharge test method for a generator stator winding are implemented.

[0047] Advantages of the present invention: The wide-frequency off-line partial discharge test method provided by the present invention provides a processing method for extracting the true value of partial discharge signals, which specifically reflects the discharge conditions in the high-frequency band after the aging of the stator insulation system. At the same time, in view of the fact that the high-frequency signal path is narrow and the attenuation is fast, the present invention provides the key operation steps for on-site tests. This method is convenient to operate and reliable in principle, meeting the requirements for on-site measurement of partial discharges in the stator insulation systems of large synchronous generator sets with a voltage level of 27 kV and below. The test technology has high versatility and safety, and is convenient for on-site popularization and use. Description of the Drawings

[0048] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0049] Figure 1 This is the hardware schematic diagram of a wide - band off - line partial discharge test method for the generator stator winding provided by the present invention.

[0050] Figure 2 This is the schematic diagram of on - site connection for a wide - band off - line partial discharge test method for the generator stator winding provided by an embodiment of the present invention.

[0051] Figure 3 This is the flow chart for extracting the true value of the partial discharge signal in a wide - band off - line partial discharge test method for the generator stator winding provided by an embodiment of the present invention.

[0052] Figure 4 This is the schematic diagram of the variable - step - size acquisition principle of the partial discharge signal according to the synchronous alternating - current phase information in a wide - band off - line partial discharge test method for the generator stator winding provided by an embodiment of the present invention.

[0053] Figure 5 This is the acquisition result diagram of the original partial discharge signal in a wide - band off - line partial discharge test method for the generator stator winding provided by an embodiment of the present invention.

[0054] Figure 6 This is the time - domain true - value extraction result diagram of a certain partial discharge signal in a wide - band off - line partial discharge test method for the generator stator winding provided by an embodiment of the present invention. Detailed implementation manners

[0055] To make the above - mentioned objects, features and advantages of the present invention more obvious and understandable, the following will describe the detailed implementation manners of the present invention with reference to the accompanying drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0057] Embodiment 1

[0058] Refer to Figure 1 and Figure 2 , which is an embodiment of the present invention, providing a wide - band off - line partial discharge test equipment and system for the generator stator winding, including:

[0059] Step 1: Fabricate a coupling capacitor, denoted as Cp. According to the requirements of the patent content, the capacitor is 82 pF and the operating voltage level is 60 kV;

[0060] Step 2: Fabricate a detection impedance box. The internal circuit principle of the detection impedance box is as Figure 1 shown, which 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 2.7 kΩ. In this example, the surface mount resistor process is adopted to better suit the high-frequency electronic usage environment. According to the requirements of the patent content, the clamping diode D1 is selected as a bidirectional transient diode with a clamping voltage of 5 V. The shielding capacitor Cx is 100 nF.

[0061] Step 3: Fabricate a partial discharge signal processing system - a partial discharge detector. According to the requirements of the patent content, a 5 V, 12-bit high-speed AD converter is selected. Operational amplifiers, DSPs, memories, etc. are configured according to conventional electronic components. According to the requirements of the patent content, the range of the partial discharge signal is 20 nC, and the measurement resolution is 10 pC. In this example, signals from the detection impedance box are connected to ports A and B, and a synchronous electrical signal of the applied AC withstand voltage is connected to port C.

[0062] The coupling capacitor in Step 1 has the following characteristics: it adopts an arc-ring high-voltage contact surface as the hardware architecture, uses a ceramic multi-layer material with high dielectric properties, and the electrolyte and electrode contact layer adopts a voidless firing process, which can maintain a stable rated capacitance value within 10 GHz.

[0063] The detection impedance box in Step 2 has the following characteristics: it adopts a metal shielding shell, and the connecting wire is a special shielding signal wire. In the detection impedance circuit, a surface mount detection resistor is used as the extraction carrier for the high-pass signal voltage. The clamping diode D1 is selected as a bidirectional transient diode to ensure the 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.

[0064] The partial discharge signal processing system - the partial discharge detector in Step 3 has the following characteristics, as Figure 2 shown. Analog partial discharge voltage signals sent from the detection impedance box are connected through ports A and B, and the range of the channel is -5 V to +5 V. A synchronous electrical signal of the applied AC withstand voltage is connected to port C, and the range of the channel is -100 V to +100 V. The phase information of the synchronous electrical signal of the applied AC withstand voltage is mainly extracted, and after analog-to-digital conversion, it is sampled regularly at a low-frequency sampling rate of 50 kHz. The partial discharge voltage signals connected to ports A and B are processed by a special high-speed AD converter and an operational amplifier and then sent to the DSP for processing. The special module supports a sampling rate of 1000 MHz, starts high-speed sampling according to the software instructions of the partial discharge detector, extracts 1 us data points each time, and the sampling behavior is variable-step intermittent sampling.

[0065] Specifically, the electrical circuit components of the partial discharge signal acquisition system include: coupling capacitors; clamping diodes; resistors; non-polar capacitors;

[0066] The main signal circuit components of the partial discharge signal processing system include: high-speed AD converters, operational amplifiers, DSPs, memories, etc. The signal terminals include: detection impedance two-port connection terminals, and external AC synchronous signal terminals.

[0067] As a preferred solution of the hardware system of the present invention, among them: the detection impedance composed of the clamping diode, resistor, and non-polar capacitor is used for high-frequency discharge signal acquisition in the range of 1 MHz - 300 MHz, as Figure 1 shown. The cut-off frequency of 1 MHz is achieved by the designed detection impedance circuit for high-pass filtering; the high frequency value of 300 MHz is taken from the database value of the epoxy overheating material aging test sample and obtained by using the hardware resolution and algorithm processing of the acquisition system.

[0068] Therefore, the hardware features of the present invention are as follows: 1) The coupling capacitor Cp is 82 pF, and this capacitor has an insulation withstand voltage level of not less than 60 kV; 2) The detection resistor R is 2.7 kΩ. Considering the high-frequency application scenario, the chip resistor process is preferably used. The shielding capacitor Cx is 100 nF, and the clamping diode D1 is selected as a bidirectional transient diode with a clamping voltage of 5 V. The detection resistor R, shielding capacitor Cx, clamping diode D1, and their internal connection wires together form an impedance box; 3) After considering the anti-interference performance, a high-speed AD converter of ±5 V, 12-bit is selected, and the data resolution is 2.44 mV. According to the configuration of conventional electronic components, operational amplifiers, DSPs, memories, etc. are selected. If 20 nC is selected as the range of the generator stator partial discharge signal, the measurement resolution of this solution is about 10 pC.

[0069] Embodiment 2

[0070] Referring to Figures 3 - 6 , as an embodiment of the present invention, a signal processing algorithm flow of a wide-frequency off-line partial discharge test system for a generator stator winding is provided, and the calculation is carried out according to the following steps:

[0071] As Figure 3 shown, Step 1: Initialization settings of the acquisition system. It is divided into a single-cycle sampling interval and a full-cycle sampling interval mechanism. Within a single AC synchronous electrical cycle, the interval of high-speed 1 us partial discharge sampling is a variable step size 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 marker values to 0, the initialization is completed.

[0072] Step 2: Monitor the power frequency AC phase information of the applied voltage withstand test and start timing. The timing is carried out according to the single-cycle sampling interval and full-cycle sampling interval mechanisms.

[0073] Step 3: Collect the voltage signal at the impedance box signal terminal within a 1us short time window, denoted as the sequence f(t), and process this section of data according to the synchrosqueezing wavelet algorithm to obtain the signal g(t) in multiple frequency bands.

[0074] Step 4: Complete a partial discharge measurement according to the single-cycle variable step-size high-speed sampling strategy and the full-cycle sampling strategy with variable-cycle delay, output the results, and draw the time-domain partial discharge result graph and the phase-domain partial discharge result graph.

[0075] The specific feature of the above-mentioned Step 1 is as follows: Figure 4 As shown within the half cycle as indicated, within a single AC synchronous electrical cycle, before the start and extinction voltage stages of the partial discharge signal appear, the sampling interval is the rate I mode, and this time interval is the largest. As Figure 4 shown at the position of the dashed box 5 in the schematic diagram, it generally appears in the range of 0° - 20°, 160° - 180° of the AC phase; during the development process of the initial partial discharge and extinction partial discharge, the sampling interval step size needs to be slightly faster, which is the rate II mode. As Figure 4 shown at the position of the dashed box 4 in the schematic diagram, it generally appears in the range of 20° - 50°, 130° - 160° of the AC phase; during the process where the partial discharge activity is relatively active, the sampling interval is the fastest, which is the rate III mode. As Figure 4 shown at the position of the dashed box 3 in the schematic diagram, it generally appears in the range of 50° - 90°, 90° - 130° of the AC phase. The value marking the number of occurrences of the high-speed 1us partial discharge acquisition behavior within a single cycle is denoted as i; the full-cycle acquisition repeats the partial discharge acquisition within a single cycle in a variable-cycle delay manner. The variable step-size delay strategy is: after completing a single-cycle partial discharge acquisition, delay by 1 AC phase cycle, which is 0.02s in this example, and increment the marking value by 1. At this time, j = 1; after the second single-cycle acquisition, delay by 2 AC phase cycles, that is, delay by 0.04s, and j = 2;... and so on. After 10 single-cycle acquisition behaviors occur, when j = 10, the partial discharge acquisition of a full cycle is completed, and it takes about 1.1s to display a full-cycle partial discharge result graph.

[0076] The specific feature of the above-mentioned Step 2 is that it is always necessary to strictly capture the phase information of the synchronous alternating current, and each time the partial discharge acquisition behavior starts at the 0° point of the AC phase of the applied voltage withstand test.

[0077] The specific feature of the above-mentioned Step 3 is that synchrosqueezing wavelet transforms are respectively started at 200 - 300 MHz, 150 - 200 MHz, and 80 - 120 MHz to obtain the signals of specific frequency components g(t) for partial discharge true value extraction.

[0078] (1) Record the single 1us data as f(t), select the Morlet mother wavelet function Ψ(t) for continuous wavelet transform, and calculate its wavelet coefficient W f (a, b) and instantaneous frequency ω f (a,b):

[0079]

[0080] 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 Morlet mother wavelet function; W f (a, b) represents wavelet coefficients;

[0081] (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,

[0082] As shown below:

[0083]

[0084] 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.

[0085] 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:

[0086]

[0087] 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.

[0088] (3) Then synchronously squeeze the extracted wavelet coefficients \(T_{(a,b)}\) again f (a,b) and restore them to the time domain to obtain the \(g(t)\) signal of a specific frequency:

[0089]

[0090] where \(T_{(a,b)}\) f (\(\omega\) l ,t) is the synchronously squeezed wavelet coefficient \(T_{(a,b)}\) after extraction f restored to the time domain.

[0091] Finally, \(g(t)\in[g_1(t),g_2(t),g_3(t)]\) is obtained, which respectively refer to the time domain signals obtained after synchronous squeezing processing at 200 - 300 MHz, 150 - 200 MHz, and 80 - 120 MHz.

[0092] The specific feature of step 4 is as follows: 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), perform a complete partial discharge signal sampling process. Draw the time - domain partial discharge result graph and the phase - domain partial discharge result graph, and output the result graph.

[0093] Then, according to actual requirements, multiple tests can be carried out in other set scenarios.

[0094] Referring to Figures 5 - 6 , as an embodiment of the present invention, it illustrates the implementation effect of the signal processing algorithm of a wide - band off - line partial discharge test system for generator stator windings:

[0095] Figure 5 The thick - line data in it is 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 1 μs, the sampling rate is 1 GHz, and the effective data length is 1000 points.

[0096] Taking this original data as the single - point sampling data within a single cycle, using the method described in step 3), the obtained \(g(t)\in[g_1(t),g_2(t),g_3(t)]\), the time - domain signals obtained after synchronous squeezing processing at 200 - 300 MHz, 150 - 200 MHz, and 80 - 120 MHz are as Figure 6 shown. It is not difficult to see that the partial discharge signals occurring at 0.1 μs and 0.7 μs can always be identified through independent and combined methods in the three extraction frequency bands. During operation, with the cooperation of a certain man - machine interaction interface setting, different frequency - band results can be flexibly retrieved and the results of partial discharge signal extraction can be observed.

[0097] The results show that the signal extraction method described in the present invention can be used for extracting the true value of the partial discharge signal of the generator stator. Compared with the conventional method, the broadband detection involved in this method is more applicable to the evaluation and discrimination of the stator insulation system, with a fixed principle and reliable results.

[0098] Embodiment 3

[0099] An embodiment of the present invention, which is different from the previous two embodiments, is that, considering the need to more accurately discriminate the degree of deterioration of the generator stator insulation system, the present invention also stipulates the points that need special attention in the on-site test method under the existing device. Its characteristics are as follows:

[0100] 1) When the distance between the lead wire of the generator stator bar and the end cover exceeds 2 m, the measurement needs to be carried out at the outlet part and the neutral point part of the generator stator winding respectively;

[0101] 2) In the connection between the test equipment and the test object, the coupling capacitor needs to be as close as possible to the test object in terms of electrical distance, and the layout distance is less than 1 m;

[0102] 3) The external power frequency AC withstand voltage equipment needs to use partial discharge-free equipment, and the distance between the test source and the coupling capacitor through the high-voltage connection wire needs to be greater than 3 m.

[0103] This example simulates an off-line partial discharge test on the stator of a 27 kV, 660 MVA water-hydrogen-hydrogen type generator. Using the partial discharge detection equipment, device and system described in the present invention, the on-site layout effect as shown in Figure 2 is established. Considering the on-site equipment installation and layout conditions, the distance between the lead wire of the generator stator bar and the end cover is about 3 m or more, and the high-voltage cable connecting the coupling capacitor and the outlet end of the stator bar is about 1 m, that is, Figure 2 "Cable 1" in Figure 2 , and the high-voltage cable between the test source and the coupling capacitor is greater than 3 m, that is,

[0104] "Cable 2" in Figure 2 . Therefore, the test process of this embodiment is as follows: Remove the grounding wire of the generator neutral point, short-circuit and ground the non-test phase, and leave the neutral point of the test phase suspended; at the outlet end, short-circuit the non-test phase, and connect the test phase to the partial discharge detection system and the external AC withstand voltage system according to the schematic diagram shown in Figure 2 . Conduct 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 3 partial discharge tests. The wiring should aim high.

[0105] The benefits of this example are as follows: Since high-frequency signals always attenuate rapidly and are prone to forming a path through stray capacitance on the exposed high-voltage bars, 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 weakened. Additionally, the inevitable attenuation of high-frequency signals makes the effective detection range more susceptible to being affected as the distance between the sensor and the object to be detected increases. Therefore, repeating the test at the head and tail ends of the stator winding can reduce the detection blind area and more truly reflect the correctness of the partial discharge results.

[0106] Embodiment 4

[0107] An embodiment of the present invention provides a wide-band off-line partial discharge test device for a generator stator winding, including:

[0108] A signal acquisition unit, configured to set the sampling interval according to a variable step size strategy and a variable cycle delay strategy and initialize the acquisition system. The signal acquisition unit includes a coupling capacitor, which is used to connect to an applied voltage withstand device and couple signals to the test object. The coupling capacitor is 82 pF and the voltage level is 60 kV;

[0109] A synchronous voltage monitoring unit, configured to synchronously monitor the phase information of the applied voltage withstand power frequency alternating current and start timing;

[0110] A signal processing unit, configured to receive the acquired partial discharge signals and perform synchrosqueezing wavelet transform using a mother wavelet function to obtain signals of different frequency components. The signal processing unit includes a partial discharge instrument, equipped with a 5 V, 12-bit high-speed AD converter, with a range of 20 nC, a measurement resolution of 10 pC, an operational amplifier, a digital signal processor, and a memory, responsible for processing and analyzing the acquired partial discharge signals;

[0111] A frequency band signal restoration unit, configured to restore the extracted frequency band signals to the time domain, draw partial discharge time domain and phase domain result diagrams and output them;

[0112] A detection impedance box, configured 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; and a shielding capacitor Cx with a value of 100 nF.

[0113] Embodiment 5

[0114] An embodiment of the present invention, different from the previous four embodiments, is:

[0115] If the above-described 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, in essence, or the part that contributes to the prior art, or a part of this 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 for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage medium includes: USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs, etc., which can store program codes of various kinds.

[0116] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a definite sequence list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch instructions from the instruction execution system, apparatus, or device and execute the instructions), or in combination with these instruction execution systems, apparatuses, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by or in combination with an instruction execution system, apparatus, or device.

[0117] More specific examples (non-exhaustive list) of computer-readable media include the following: electrical connection parts with one or more wirings (electronic devices), portable computer disk cartridges (magnetic devices), random access memories (RAMs), read-only memories (ROMs), erasable programmable read-only memories (EPROMs or flash memories), fiber optic devices, and portable compact disc read-only memories (CDROMs). Additionally, the computer-readable medium 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 media, then editing, interpreting, or otherwise processing it as necessary, and then storing it in a computer memory.

[0118] It should be understood that various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above 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, any one or combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0119] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A broadband offline partial discharge test method for generator stator windings, 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; The detection impedance is formed by a clamping diode, a resistor, and a non-polar capacitor; The clamping diode is connected in parallel with a series branch consisting of a resistor and a non-polarized capacitor; The detection impedance is used for collecting 1MHz-300MHz high-frequency discharge signals; The different frequency components are 200-300 MHz, 150-200 MHz, and 80-120 MHz; 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 a variable q; 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 setting the two state mark values ​​of variable q and variable j to 0; The variable period delay strategy, include, After the kth sampling, the next single-cycle sampling is performed after a delay of k AC phase cycles, wherein the value of k is 1 to 10.

2. The method for broadband off-line partial discharge testing of generator stator windings according to claim 1, characterized in that: The variable step size strategy 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.

3. The method for broadband off-line partial discharge testing of generator stator windings according to claim 2, 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.

4. The method for broadband off-line partial discharge testing of generator stator windings according to claim 3, 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).

5. The method for broadband off-line partial discharge testing of generator stator windings according to claim 4, 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 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) Extraction and subsequent synchronous extrusion of wavelet coefficients T f (a,b) Wavelet coefficients restored to the time domain.

6. A device using the generator stator winding broadband offline partial discharge test method as claimed in any one of claims 1 to 5, 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.

7. 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, the steps of the generator stator winding broadband offline partial discharge test method according to any one of claims 1 to 5 are implemented.

8. 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 5 are implemented.

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