A Method for Evaluating the Damage State of 10kV XLPE Cable Sheaths

Abstract

The present invention discloses a method for evaluating the damage state of the sheath of a 10 kV XLPE cable, which includes the steps of injecting a linear swept frequency modulated signal into the cable to be measured and collecting the reflected signal, performing one-dimensional continuous wavelet transform, calculating the characterization parameters of the damage state of the cable sheath, and using the characterization parameters to evaluate the damage state of the XLPE cable sheath. The beneficial effects of the present invention are as follows: it can efficiently and safely detect and evaluate the damage degree of the outer sheath of a 10 kV XLPE cable, avoid eddy current and local overheating caused by serious damage to the cable outer sheath, reduce the operation safety risk of power cables; provide a basis and reference for operation and maintenance personnel to timely evaluate the service performance of the cable, effectively ensure the reliability of the cable line operation, improve the utilization rate of equipment assets, and have high economic significance and social significance.

Description

Technical Field

[0001] The present invention relates to the field of cable sheath damage assessment, and particularly to a method for assessing the damage state of a 10 kV XLPE cable sheath. Background Art

[0002] With the rapid development of China's economic construction, power facilities are constantly being built and upgraded. The social demand for electric energy is increasing day by day, and at the same time, the requirements for power quality and power supply reliability are also getting higher and higher. The basic task of the power system is to produce, transmit, and distribute electric energy safely, reliably, and with high quality. Due to its excellent mechanical properties and electrical properties, XLPE cables are widely used in the power transmission of electrical systems such as urban power grids and rail transit because they are convenient for laying and installation, do not occupy space when buried underground, and have high safety. They play an irreplaceable role in the normal operation of the entire electrical system. However, the laying and operating environment of power cables is relatively complex, and their outer sheaths are often damaged due to reasons such as puncture scratches and termite erosion. During service, the induced electromotive force on the metal shielding layer of the cable will be unbalanced, resulting in eddy currents and local overheating, seriously affecting the long-term life and short-term operating safety of the cable, and bringing great hidden dangers to the safe and stable operation of the power system.

[0003] At present, there is little research on the damage state assessment of 10 kV XLPE cable sheaths, and there is no detection method that has been widely promoted and applied. Therefore, it is urgent to find an efficient method for assessing the damage state of 10 kV XLPE cable sheaths, which provides a basis for maintenance personnel to timely assess the service performance of the cable after fault location, and is of great significance for ensuring the safe and reliable operation of power cables and improving the utilization rate of equipment assets. Summary of the Invention

[0004] The present invention is a method for assessing the damage state of a 10 kV XLPE cable sheath, which is used to evaluate the degree of fault damage of the outer sheath of a 10 kV XLPE cable, and specifically includes the following steps:

[0005] Step 1: Inject a linear swept-frequency and frequency-modulated signal into the cable to be measured and collect the reflected signal:

[0006] Generate a short-time linear swept-frequency and frequency-modulated signal with a Gaussian envelope through a signal generator, set the center frequency to 70 MHz, the frequency bandwidth to 100 MHz, and the duration to 100 ns; externally attach electrodes to the head end of the outer sheath of the XLPE cable to be evaluated, and then connect it to the signal generator and oscilloscope through a T-type probe to inject the frequency-modulated signal and collect the reflected signal;

[0007] Step 2: Perform one-dimensional continuous wavelet transform:

[0008] Starting from the time point corresponding to the first peak of the reflected signal, 500 consecutive sampling points are intercepted for one-dimensional continuous wavelet transform. The transform scales α are taken as 2, 4, 6, 8, and 10 respectively, and the coefficient matrix A after wavelet transform is recorded.

[0009] Step 3: Calculate the cable sheath damage state characterization parameter γ:

[0010]

[0011] In the formula, N is the number of transform scales of continuous wavelet transform, taking N = 5; M is the number of sampling points of the intercepted signal, taking M = 500; a (i,j) is the element in the i-th row and j-th column of the coefficient matrix A, i ∈ [1, N], j ∈ [1, M], and both i and j are taken as integers;

[0012] Step 4: Use the characterization parameter γ to evaluate the damage state of the XLPE cable sheath:

[0013] When γ ≤ 1.21, the XLPE cable sheath is slightly damaged;

[0014] When 1.21 < γ ≤ 1.45, the XLPE cable sheath is moderately damaged;

[0015] When γ > 1.45, the XLPE cable sheath is severely damaged.

[0016] The beneficial effects of the present invention are as follows: It can efficiently and safely detect and evaluate the damage degree of the outer sheath of 10kV XLPE cables, avoid eddy currents and local overheating caused by severe damage to the cable outer sheath, reduce the operation safety risks of power cables; provide a basis and reference for maintenance personnel to timely evaluate the service performance of cables, effectively ensure the reliability of cable line operation, improve the utilization rate of equipment assets, and have high economic and social significance. Description of the Drawings

[0017] Figure 1 is the flow chart of the present invention. Detailed Embodiments

[0018] The present invention will be further described below in conjunction with the drawings and specific implementation processes.

[0019] Figure 1 As shown is the flow chart of a method for evaluating the damage state of the 10kV XLPE cable sheath, including the following steps:

[0020] Step 1: Inject a linear swept frequency modulated signal into the cable to be measured and collect the reflected signal:

[0021] First, a short-time linearly swept frequency chirp signal with a Gaussian envelope is generated by a signal generator, with the center frequency set at 70 MHz, the frequency bandwidth at 100 MHz, and the duration at 100 ns. Then, an external electrode is attached to the head end of the outer sheath of the XLPE cable to be evaluated, and it is connected to the signal generator and the oscilloscope through a T-type probe to inject the frequency-modulated signal and collect the reflected signal.

[0022] Step 2: Perform one-dimensional continuous wavelet transform:

[0023] Starting from the time point corresponding to the first peak of the reflected signal, 500 consecutive sampling points are intercepted for one-dimensional continuous wavelet transform. The wavelet transform scales α are taken as 2, 4, 6, 8, and 10 respectively, and the coefficient matrix A after wavelet transform is recorded.

[0024] Step 3: Calculate the characterization parameter γ of the cable sheath damage state:

[0025]

[0026] In the formula, N is the number of wavelet transform scales for one-dimensional continuous wavelet transform, and N = 5 is taken; M is the number of sampling points of the intercepted signal, and M = 500 is taken; a (i,j) is the element in the i-th row and j-th column of the coefficient matrix A, where i ∈ [1, N], j ∈ [1, M], and both i and j are integers.

[0027] Step 4: Use the characterization parameter γ to evaluate the damage state of the XLPE cable sheath:

[0028] When γ ≤ 1.21, the XLPE cable sheath has minor damage;

[0029] When 1.21 < γ ≤ 1.45, the XLPE cable sheath has moderate damage;

[0030] When γ > 1.45, the XLPE cable sheath has severe damage.

Claims

1. A method for evaluating the damage state of the sheath of a 10kV XLPE cable, characterized in that it includes the following steps: Step 1: Inject a linear swept frequency modulated signal into the cable to be measured and collect the reflected signal: Generate a short-time linear swept frequency modulated signal with a Gaussian envelope through a signal generator, set the center frequency to 70MHz, the frequency bandwidth to 100MHz, and the duration to 100ns; externally attach an electrode to the head end of the outer sheath of the XLPE cable to be evaluated, and then connect it to the signal generator and oscilloscope through a T-type probe, inject the frequency modulated signal and collect the reflected signal; Step 2: Perform one-dimensional continuous wavelet transform: Starting from the time point corresponding to the first peak of the reflected signal, intercept 500 consecutive sampling points, perform one-dimensional continuous wavelet transform, and take the wavelet transform scales α as 2, 4, 6, 8, 10 respectively, and record the coefficient matrix A after wavelet transform; Step 3: Calculate the cable sheath damage state characterization parameter γ: where N is the number of transform scales of the continuous wavelet transform, and N = 5 is taken; M is the number of sampling points of the intercepted signal, and M = 500 is taken; a (i,j) is the element at the i-th row and j-th column in the coefficient matrix A, i ∈ [1, N], j ∈ [1, M], and both i and j are taken as integers; Step 4: Use the characterization parameter γ to evaluate the damage state of the XLPE cable sheath: When γ ≤ 1.21, the sheath of the XLPE cable is slightly damaged; When 1.21 < γ ≤ 1.45, the sheath of the XLPE cable is moderately damaged; When γ > 1.45, the sheath of the XLPE cable is severely damaged.

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