A Method for Evaluating the Aging State of 10kV XLPE Cables Based on the Electromagnetic Wave Propagation Factor in the Medium

Abstract

The present invention discloses a method for evaluating the aging state of 10 kV XLPE cables based on the electromagnetic wave transfer factor in the medium, comprising the following steps: measuring the waveform amplitude and time after the transmission of high-frequency pulses in the cross-linked polyethylene cable, calculating the rapid change coefficient α of the cable to be evaluated, calculating the amplitude change factor β of the cable to be evaluated, calculating the electromagnetic wave transfer factor γ, and determining the aging state of the cable through the electromagnetic wave transfer factor γ. The beneficial effects of the present invention are as follows: by applying a high-frequency pulse waveform to the XLPE cable, collecting the time required for the pulse wave to be transmitted in the cable and the pulse amplitude after transmission, calculating the rapid change factor and the amplitude change factor, and extracting the electromagnetic wave transfer factor to evaluate the aging state of the XLPE cable. This method is efficient and convenient for evaluation, can evaluate the insulation state of the XLPE cable well, and reduce power outage faults by replacing the cables with severe aging states in a timely manner, ensuring the safe and reliable operation of the power grid.

Description

Technical Field

[0001] The present invention belongs to the field of XLPE cable insulation aging state evaluation, and particularly relates to a method for evaluating the aging state of 10 kV XLPE cables based on the electromagnetic wave transfer factor in the medium. Background Art

[0002] Cross-linked polyethylene cables are widely used in power transmission and distribution systems due to a series of advantages such as relatively simple structure, large current-carrying capacity, and good conductivity. As the service life of the cable increases, its insulating medium ages continuously. The aging of the insulating medium will lead to phenomena such as a decrease in the insulation resistance of the cable and an increase in the leakage current of the insulating layer, seriously affecting the service life of the cable.

[0003] In order to ensure the stable operation of the cable and improve the reliability of power supply capacity, there is an urgent need for a convenient and reliable method for evaluating the aging state of 10 kV distribution network cables. This method is an XLPE cable aging state evaluation method based on the electromagnetic wave transfer factor in the medium. This method is simple to operate and can efficiently and conveniently evaluate the aging state of the cable through the extracted electromagnetic wave transfer factor. Summary of the Invention

[0004] The present invention is a method for evaluating the aging state of 10 kV XLPE cables based on the electromagnetic wave transfer factor in the medium, and is used to evaluate the insulation aging state of XLPE cables operating in the distribution network for a long time.

[0005] The technical solution of the present invention is as follows:

[0006] The first step: Measure the waveform amplitude and time after the high-frequency pulse is transmitted in the cross-linked polyethylene cable;

[0007] Inject square wave pulses with frequencies of 10 MHz, 20 MHz, 30 MHz, 40 MHz, 50 MHz, and 60 MHz and an amplitude of 100 V into the cable cores at one end of the cable to be evaluated, and record the input frequencies as: f1, f2, f3, f4, f5, f6; Connect an oscilloscope externally at the other end of the cable where the waveform is injected, and detect the transmission time of the pulse wave inside the cable and the waveform voltage amplitude at the end through the oscilloscope, and record the transmission time as t1, t2, t3, t4, t5, t6, and the waveform amplitude as V1, V2, V3, V4, V5, V6;

[0008] The second step: Calculate the rapid change coefficient α of the cable to be evaluated, and the calculation process is as follows:

[0009]

[0010] In the formula, L is the length of the cable to be evaluated, t max is the maximum value of the detected transmission time, t minTo detect the minimum transfer time, c is the speed of light;

[0011] Step 3: Calculate the amplitude change factor β of the cable to be evaluated. The calculation process is as follows:

[0012]

[0013] In the formula, V max is the maximum value of the waveform amplitude, and V min is the minimum value of the waveform amplitude;

[0014] Step 4: Calculate the electromagnetic wave transfer factor γ. The calculation process is as follows:

[0015]

[0016] Step 6: Determine the aging state of the cable through the electromagnetic wave transfer factor γ:

[0017] If γ < 4.136, the insulation of the target cross-linked polyethylene cable is slightly aged;

[0018] If 4.136 ≤ γ < 10.27, the insulation of the target cross-linked polyethylene cable is moderately aged;

[0019] If 10.27 ≤ γ, the insulation of the target cross-linked polyethylene cable is severely aged.

[0020] The beneficial effect of the present invention is that by applying a high-frequency pulse waveform to the XLPE cable, collecting the time required for the pulse wave to transfer in the cable and the pulse amplitude after transfer, calculating the velocity change factor and the amplitude change factor, and extracting the electromagnetic wave transfer factor to evaluate the aging state of the XLPE cable. This evaluation method is simple, efficient, and convenient, and can better evaluate the insulation state of the XLPE cable. Description of the Drawings

[0021] Figure 1 is a flowchart of an XLPE cable aging state evaluation method based on the electromagnetic wave transfer factor in the medium involved in the present invention; Detailed Embodiments

[0022] The present invention will be further described below in conjunction with the drawings and specific implementation processes.

[0023] Step 1: Measure the waveform amplitude and time after the high-frequency pulse is transferred in the cross-linked polyethylene cable;

[0024] Inject square wave pulses with amplitudes of 100V and frequencies of 10MHz, 20MHz, 30MHz, 40MHz, 50MHz, and 60MHz into the cable cores at one end of the cable to be evaluated. Denote the input frequencies as: f1, f2, f3, f4, f5, f6; Connect an oscilloscope externally at the other end of the injected waveform of the cable. Record the transmission times of the pulse waves inside the cable detected by the oscilloscope as t1, t2, t3, t4, t5, t6, and record the waveform voltage amplitudes at the end as V1, V2, V3, V4, V5, V6;

[0025] Step 2: Calculate the velocity change coefficient α of the cable to be evaluated. The calculation process is as follows:

[0026]

[0027] In the formula, L is the length of the cable to be evaluated, t max is the maximum detected transmission time, t min is the minimum detected transmission time, and c is the speed of light;

[0028] Step 3: Calculate the amplitude change factor β of the cable to be evaluated. The calculation process is as follows:

[0029]

[0030] In the formula, V max is the maximum value of the waveform amplitude, and V min is the minimum value of the waveform amplitude;

[0031] Step 4: Calculate the electromagnetic wave transmission factor γ. The calculation process is as follows:

[0032]

[0033] Step 6: Determine the aging state of the cable through the electromagnetic wave transmission factor γ:

[0034] If γ < 4.136, the insulation of the target cross-linked polyethylene cable is slightly aged;

[0035] If 4.136 ≤ γ < 10.27, the insulation of the target cross-linked polyethylene cable is moderately aged;

[0036] If 10.27 ≤ γ, the insulation of the target cross-linked polyethylene cable is severely aged.

Claims

1. A method for evaluating the aging state of 10 kV XLPE cables based on the electromagnetic wave transfer factor in the medium, characterized in that, It includes the following steps: Step 1: Inject square wave pulses with amplitudes of 100 V and frequencies of 10 MHz, 20 MHz, 30 MHz, 40 MHz, 50 MHz, and 60 MHz into the cable cores at one end of the cable to be evaluated. Denote the input frequencies as: f1, f2, f3, f4, f5, f6; Connect an oscilloscope externally at the other end of the cable where the waveform is injected. Detect the transmission time of the pulse wave inside the cable through the oscilloscope and denote it as t1, t2, t3, t4, t5, t6, and detect the waveform voltage amplitude at the end as V1, V2, V3, V4, V5, V6; Step 2: Calculate the rapid change coefficient α of the cable to be evaluated. The calculation process is as follows: where L is the length of the cable to be evaluated, t max is the maximum propagation time detected, t min is the minimum propagation time detected, and c is the speed of light; Step 3: Calculate the amplitude change factor β of the cable to be evaluated. The calculation process is as follows: where V max is the maximum value of the waveform amplitude, and V min is the minimum value of the waveform amplitude; Step 4: Calculate the electromagnetic wave transmission factor γ. The calculation process is as follows: Step 5: Evaluate the aging state of the cable through the electromagnetic wave transmission factor γ.

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