GIS cable terminal interface defect detection method based on ultrasonic method

Abstract

The invention relates to a GIS cable terminal interface defect detection method based on an ultrasonic method. Belongs to the technical field of power transmission and transformation equipment state monitoring. Comprising the steps of arranging a plurality of ultrasonic sensors, transmitting ultrasonic excitation signals, receiving ultrasonic signals, processing the signals and determining defect positions. The device has the advantages that the mode that multiple receivers work synchronously is adopted, comprehensive monitoring on the interface state can be achieved, the multiple ultrasonic sensors are arranged on the surface of the epoxy sleeve, ultrasonic signals propagated through the interface are received from different angles and paths, signals captured by the receivers possibly have different propagation paths and characteristics, and therefore the interface state can be comprehensively monitored. Through comprehensive analysis of signals from a plurality of receivers, the overall condition of the interface can be known more comprehensively, and the design of the plurality of receivers can significantly improve the detection reliability, reduce the blind area possibly existing in a single receiver, and ensure that all potential interface defects can be effectively captured.

Description

Technical Field

[0001] The invention belongs to the technical field of state monitoring of power transmission and transformation equipment, and in particular relates to a method for detecting interface defects of epoxy casings of GIS cable terminals based on an ultrasonic method. Background Art

[0002] Gas-insulated switchgear GIS is a type of switchgear widely used in modern power systems, especially in high-voltage power transmission and distribution systems. GIS equipment integrates high-voltage switches, transformers, voltage transformers, disconnectors, and circuit breakers, and uses SF6 gas as the insulating medium. Due to its small size, reliable operation, good weather resistance, and low maintenance, it is widely used in urban substations, power plants, and power facilities that require high reliability and high safety.

[0003] GIS cable terminals are generally composed of metal conductors, insulation, epoxy sleeves, stress cones, metal inserts and other components. Among them, the silicone rubber material of the stress cone directly matches the cross-linked polyethylene XLPE insulation of the cable, while the epoxy sleeve is directly connected to the outer surface of the stress cone. Therefore, there are two composite interfaces inside the GIS cable terminal: the epoxy resin and silicone rubber interface, and the silicone rubber and XLPE interface. In a low-temperature environment, due to the different expansion rates of metal and epoxy resin, defects are easily generated at the joint surface of the two, resulting in partial discharge and even breakdown failure. In recent years, GIS cable terminal failures have occurred frequently, including cracks in the epoxy sleeve, holes in the stress cone ablation, and breakdown of the cable at the lower end of the stress cone. Especially in cold environments, the probability of GIS cable terminal failure is higher. In order to ensure the safe and stable operation of the power system, the detection of GIS cable terminals is crucial. At present, the detection methods of GIS cable terminals mainly include infrared detection, high-frequency partial discharge detection, and ultra-high frequency partial discharge detection. These methods are based on different sensors and detect physical, chemical or electrical signals when partial discharge occurs to determine whether there are defects. Partial discharge detection is an important means to judge the status of high-voltage cables, but this method is only sensitive to point discharge and suspended discharge in equipment with air as the main insulating medium. It has limitations for other types of defect signals and is not conducive to comprehensive defect judgment. Therefore, it is urgent to take effective measures to detect defects in GIS cable terminals to ensure the safe and stable operation of the equipment.

[0004] In recent years, ultrasonic testing technology has been widely studied and applied in the detection of the operating status of power equipment at home and abroad due to its many advantages. Ultrasonic nondestructive testing is an effective means of defect detection. Ultrasonic waves refer to mechanical waves with a frequency higher than 20kHz, which have good directivity, strong penetration, a wide detection range, efficient detection capabilities and simple equipment. Ultrasonic waves carry a lot of material information, such as material structure, uniformity, internal defects or partial discharge and degradation. Ultrasonic testing methods have the advantages of high detection accuracy and rapid detection, so they are widely used.

[0005] At present, the detection of GIS cable terminals mainly focuses on the internal defects of epoxy casing, and the defects at the interface between epoxy casing and stress cone cannot be effectively observed and detected. Summary of the invention

[0006] The invention provides a method for detecting interface defects of a GIS cable terminal based on an ultrasonic method, so as to solve the problem that interface defects of an epoxy casing and a stress cone at a GIS cable terminal cannot be effectively detected.

[0007] The technical solution adopted by the present invention comprises the following steps: S1: Arrangement of multiple ultrasonic sensors An ultrasonic sensor is installed on the surface of the epoxy casing of the GIS cable terminal, including a transmitter and a receiver. The ultrasonic transmitter and the receiver are arranged at different positions on the surface of the epoxy casing; S2: Transmission of ultrasonic excitation signal An ultrasonic sensor transmits an ultrasonic excitation signal within a certain frequency range, and the excitation signal is a pulse wave, a continuous wave or a modulated waveform; S3: Receiving ultrasonic signals The ultrasonic sensor receives the ultrasonic signal propagating through the interface of the GIS cable terminal, and the ultrasonic signal contains information related to the interface defects; S4: Signal processing and defect location determination The received ultrasonic signal is processed, and the specific location of the interface defect is determined by analyzing the time difference and attenuation between the reflected waves of the processed ultrasonic signal.

[0008] The ultrasonic sensor in step S1 of the present invention selects a common ultrasonic sensor, which is responsible for both transmitting ultrasonic excitation signals and receiving ultrasonic signals reflected from the interface.

[0009] The ultrasonic sensor of the present invention adopts a piezoelectric patch sensor, which is closely attached to the surface of the epoxy casing of the GIS cable terminal, arranged at intervals in the circumferential direction of the casing, and surrounds the casing to form multi-point coverage.

[0010] The ultrasonic transmitter and receiver of the present invention are arranged in an area close to the interface where defects may occur, so as to ensure that the signal propagation path covers all possible defective parts.

[0011] The frequency range of the ultrasonic excitation signal in step S2 of the present invention is adjusted according to the detection requirements, and an ultrasonic excitation signal in the range of 20 kHz to 500 kHz is selected to take into account both the penetration depth and the resolution of the detection.

[0012] The ultrasonic excitation signal selected by the present invention is a sine wave signal modulated by a Hanning window with a frequency of 50 kHz.

[0013] The ultrasonic signal in step S3 of the present invention includes reflection, attenuation and delay characteristics of the signal, and multiple receivers work synchronously to capture signals on different propagation paths.

[0014] The ultrasonic signal processing in step S4 of the present invention includes the following steps: Filtering: Use a bandpass filter to remove background noise and improve the signal-to-noise ratio; Delay calculation: Compare the time delay between the transmitted signal and the received signal to infer the propagation time difference of the signal through the interface and locate whether there are interface defects; Feature extraction: Extract key features of ultrasonic signals, including signal amplitude, attenuation rate, and phase change characteristics, to indicate whether there are defects on the interface and the nature and severity of the defects.

[0015] The advantages of the present invention are: it adopts a multi-receiver synchronous working mode to realize comprehensive monitoring of the interface state, and arranges multiple ultrasonic sensors on the surface of the epoxy sleeve to receive ultrasonic signals propagating through the interface from different angles and paths. The signal captured by each receiver may have different propagation paths and characteristics. By comprehensively analyzing the signals from multiple receivers, the overall condition of the interface can be more comprehensively understood. The design of multiple receivers can significantly improve the reliability of detection, reduce the blind spots that may exist in a single receiver, and ensure that all potential interface defects can be effectively captured.

[0016] The present invention uses an ultrasonic method to detect interface defects between the epoxy casing and the stress cone of the GIS cable terminal, effectively identifying various defects that may exist on the interface, including cracks, air gaps, voids and other defects, and can accurately locate the defects. It uses multiple sensors for detection to improve the coverage of detection defects. Traditional live detection methods often make it difficult to perform non-destructive detection of potential defects in GIS cable terminals after the cable terminal is assembled and before the GIS equipment is assembled, especially minor defects caused by improper installation process or material stress. Through the application of this method, the problem that defects generated during the installation process cannot be effectively detected after the GIS cable terminal is assembled is solved. The invention can ensure the safe operation level of the equipment, reduce the probability of failure, and provide a strong guarantee for the safe operation of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a flow chart of the present invention; Figure 2 It is a schematic diagram of the installation position of the ultrasonic sensor of the present invention; Figure 3 It is a waveform diagram of the transmission signal of the present invention; Figure 4 It is a waveform diagram of the received signal of the present invention. DETAILED DESCRIPTION

[0018] The following steps are involved: S1: Arrangement of multiple ultrasonic sensors. Ultrasonic sensors, including transmitters and receivers, are installed on the surface of the epoxy casing of the GIS cable terminal. The ultrasonic transmitter and receiver are arranged at different positions on the surface of the epoxy casing, preferably close to the area where defects may occur on the interface, to ensure that the signal propagation path covers all possible defective parts; S2: Transmission of ultrasonic excitation signal An ultrasonic sensor transmits an ultrasonic excitation signal within a certain frequency range, and the excitation signal is a pulse wave, a continuous wave or a modulated waveform; S3: Receiving ultrasonic signals The ultrasonic sensor receives the ultrasonic signal propagating through the GIS cable terminal interface. The received signal contains information related to the interface defects, including the reflection, attenuation and delay characteristics of the signal. Multiple receivers work synchronously to capture the signals on different propagation paths, so as to monitor the interface status more comprehensively. S4: Signal processing and defect location determination The received ultrasonic signal is processed, including the following steps: Filtering: Use a bandpass filter to remove background noise and improve the signal-to-noise ratio; Delay calculation: By comparing the time delay between the transmitted signal and the received signal, the propagation time difference of the signal through the interface can be inferred, and the presence of interface defects can be located; Feature extraction: Extract key features of ultrasonic signals, including signal amplitude, attenuation rate, and phase change characteristics. These features can indicate whether there are defects on the interface and the nature and severity of the defects. Based on the signal received by the receiver, the specific location of the interface defect is determined by analyzing the time difference and attenuation between the reflected waves of the ultrasonic signal, and the severity of the defect and its potential impact on the operation of the equipment are judged.

[0019] In the arrangement of ultrasonic sensors in step S1 described in the present invention, a common ultrasonic sensor is responsible for both emitting ultrasonic excitation signals and receiving ultrasonic signals reflected from the interface; a piezoelectric patch sensor is used, which is in close contact with the surface of the epoxy casing of the GIS cable terminal, and multiple sensors are used, which are arranged at intervals in the circumferential direction of the casing, surrounding the casing to form multi-point coverage. This surrounding arrangement ensures that the ultrasonic signal can be transmitted to the cable terminal interface from different angles and paths, covering the entire detection area, thereby improving the comprehensiveness of the detection.

[0020] In step S2 of the present invention, the frequency range of the signal is adjusted according to the detection requirements, and an ultrasonic signal in the range of 20kHz to 500kHz is selected to take into account the penetration depth and resolution of the detection. The ultrasonic excitation signal is a sine wave signal modulated by a Hanning window with a frequency of 50kHz. The frequency of 50kHz can not only provide good penetration, but also maintain sufficient resolution to ensure effective identification of smaller interface defects. The sinusoidal excitation signal modulated by the Hanning window has good signal focusing and noise suppression capabilities, which can effectively reduce spectrum leakage, reduce sidelobe effects, and concentrate signal energy on the main lobe, thereby improving the frequency resolution of the ultrasonic signal. In this way, clearer echo signal characteristics can be obtained during the detection process, and in the case of multiple reflections, noise interference can be effectively reduced, which is convenient for accurate analysis of interface defects.

[0021] In steps S3 and S4, the ultrasonic sensor arranged on the surface of the epoxy casing receives the signal reflected by the ultrasonic wave after passing through the interface, and the received ultrasonic signal is processed by a bandpass filter to improve the signal-to-noise ratio. The received signal contains a wealth of information related to interface defects, mainly including characteristics such as signal reflection, attenuation and delay, which can help accurately evaluate the health status of the interface and detect potential defects. If there are defects such as cracks at the interface between the epoxy casing of the GIS cable terminal and the stress cone, the ultrasonic signal will experience significant energy attenuation when penetrating these defects, and the echo signal time will be advanced. By measuring the delay difference of the signal, the size of the defect can be determined, and the defect can be evaluated.

[0022] By adopting the above technical solution, the ultrasonic method is used to detect the interface defects of the GIS cable terminal and evaluate its defects, thereby solving the problem that the interface defects between the epoxy casing and the stress cone of the GIS cable terminal cannot be effectively detected.

[0023] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings: This embodiment is implemented based on the technical solution of the invention, and a detailed implementation method and process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0024] See also Figure 1 , including the following steps: S1: Arrangement of multiple ultrasonic sensors. Eight piezoelectric patch ultrasonic sensors are used. They are close to the surface of the epoxy casing of the GIS cable terminal. The air gap between the sensor and the surface of the object being measured is eliminated through the silicone grease coupling agent to improve the detection accuracy. The ultrasonic sensors are 100 mm away from the upper end of the epoxy casing and are arranged at intervals along the circumferential direction to form multi-point coverage. Figure 2 As shown; S2: Transmission of ultrasonic excitation signal. The selected transmission signal is a sine signal modulated by a 5-fold Hanning window, with a center frequency of 50kHz and a cycle number of 5. The signal function is shown in the following formula and the waveform is as follows: Figure 3 As shown;

[0025] S3: Receiving ultrasonic signals The ultrasonic sensor receives the ultrasonic signal propagating through the GIS cable terminal interface, and the excitation signal can be sequentially transmitted through a single sensor, and the ultrasonic sensor transmitting the excitation signal and two nearby sensors receive the signal together; The received signal contains information related to the interface defects, including characteristics such as signal reflection, attenuation and delay. Multiple receivers can work synchronously to capture signals on different propagation paths, thereby more comprehensively monitoring the interface status; S4: Signal processing and defect assessment The received signal is first processed by a bandpass filter to remove background noise and retain valid signals within the preset frequency range; the lower limit frequency of the passband range is set to 48kHz, the upper limit frequency is set to 52kHz, the stopband cutoff frequency is set to 47kHz and 53kHz, the sampling frequency is set to 120kHz, the passband ripple is set to 1dB, and the stopband attenuation is set to 60dB; the FIR bandpass filter designed by the window function method is used to filter the received signal. The signals received with and without defects on the interface are as follows: Figure 4As shown, it can be found that when there are defects in the interface, the received echo is advanced. This phenomenon is because when the ultrasonic wave encounters a defect, the signal will be reflected at the discontinuity of the interface, and the propagation distance of the reflected signal is relatively short, so the delay of the received signal is small; in contrast, when the interface is complete and defect-free, the ultrasonic signal will continue to propagate and be reflected back at a farther uniform interface, resulting in a later delay in the received echo signal. The propagation delay of the ultrasonic signal is directly related to the distance of the signal propagation path. Therefore, by analyzing the advance amount of the echo signal, it can be inferred whether the signal has encountered an abnormal reflection point during the propagation process, that is, an interface defect.

[0026] The difference between ultrasonic signals with and without defects on the interface is mainly reflected in the delay and amplitude of the received signal. By analyzing the advance of the echo signal, it is possible to effectively determine whether there are defects on the GIS cable terminal interface, and locate the specific location of the defect through the delay difference and amplitude change. This detection method provides a reliable guarantee for the assembly quality of the cable terminal, and also solves the problem that hidden defects that may occur during the assembly process cannot be effectively detected.

[0027] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting interface defects of GIS cable terminals based on ultrasonic method, characterized in that: The following steps are involved: S1: Arrangement of multiple ultrasonic sensors An ultrasonic sensor is installed on the surface of the epoxy casing of the GIS cable terminal, including a transmitter and a receiver. The ultrasonic transmitter and the receiver are arranged at different positions on the surface of the epoxy casing; S2: Transmission of ultrasonic excitation signal An ultrasonic sensor transmits an ultrasonic excitation signal within a certain frequency range, and the excitation signal is a pulse wave, a continuous wave or a modulated waveform; S3: Receiving ultrasonic signals The ultrasonic sensor receives the ultrasonic signal propagating through the interface of the GIS cable terminal, and the ultrasonic signal contains information related to the interface defects; S4: Signal processing and defect location determination The received ultrasonic signal is processed, and the specific location of the interface defect is determined by analyzing the time difference and attenuation between the reflected waves of the processed ultrasonic signal.

2. The method for detecting interface defects of GIS cable terminals based on ultrasonic method according to claim 1 is characterized in that: The ultrasonic sensor in step S1 selects a common ultrasonic sensor, which is responsible for both transmitting ultrasonic excitation signals and receiving ultrasonic signals reflected from the interface.

3. The method for detecting interface defects of GIS cable terminals based on ultrasonic method according to claim 2 is characterized in that: The ultrasonic sensor adopts a piezoelectric patch sensor, which is closely attached to the surface of the epoxy casing of the GIS cable terminal, arranged at intervals in the circumferential direction of the casing, and surrounds the casing to form multi-point coverage.

4. The method for detecting interface defects of GIS cable terminals based on ultrasonic method according to claim 3 is characterized in that: The ultrasonic transmitter and receiver are arranged in areas close to the interface where defects may occur, so as to ensure that the signal propagation path covers all possible defective parts.

5. The method for detecting interface defects of GIS cable terminals based on ultrasonic method according to claim 1 is characterized in that: The frequency range of the ultrasonic excitation signal in step S2 is adjusted according to the detection requirements, and an ultrasonic excitation signal in the range of 20 kHz to 500 kHz is selected to take into account both the penetration depth and the resolution of the detection.

6. The method for detecting interface defects of GIS cable terminals based on ultrasonic method according to claim 5 is characterized in that: The ultrasonic excitation signal is a sine wave signal modulated by a Hanning window with a frequency of 50kHz.

7. The method for detecting interface defects of GIS cable terminals based on ultrasonic method according to claim 1 is characterized in that: The ultrasonic signal in step S3 includes reflection, attenuation and delay characteristics of the signal, and multiple receivers work synchronously to capture signals on different propagation paths.

8. The method for detecting interface defects of GIS cable terminals based on ultrasonic method according to claim 1 is characterized in that: In step S4, the ultrasonic signal processing The following steps are involved: Filtering: Use a bandpass filter to remove background noise and improve the signal-to-noise ratio; Delay calculation: Compare the time delay between the transmitted signal and the received signal to infer the propagation time difference of the signal through the interface and locate whether there are interface defects; Feature extraction: Extract key features of ultrasonic signals, including signal amplitude, attenuation rate, and phase change characteristics, to indicate whether there are defects on the interface and the nature and severity of the defects.

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