Method for evaluating insulation aging state of 10kV XLPE cable based on microwave reflection signal transfer factor

Abstract

The invention discloses a 10kV XLPE cable insulation aging state evaluation method based on a microwave reflection signal transmission factor, and the method comprises the following steps: transmitting high-frequency microwave signals with different frequencies to a to-be-evaluated cable through a high-frequency microwave signal source, and measuring the reflected wave power absolute value and the reflection coefficient of the high-frequency microwave signals after the high-frequency microwave signals are reflected in a cable medium; and respectively calculating a cable distortion coefficient alpha, an electromagnetic disturbance coefficient beta and a microwave reflection signal transmission factor sigma of the to-be-evaluated cable, and evaluating the aging state of cable insulation through the microwave reflection signal transmission factor sigma. The method has the advantages that the high-frequency microwave signal is applied to the XLPE cable, the receiving antenna is used for obtaining the reflected wave, the power absolute value and the reflection coefficient of the reflected wave are detected through the spectrum analyzer, the distortion coefficient and the electromagnetic disturbance coefficient of the cable are calculated, and the microwave reflection signal transmission factor is extracted to evaluate the insulation aging state of the XLPE cable. According to the method, the insulation aging state of the 10kV XLPE cable can be accurately evaluated efficiently and safely, power failure faults caused by serious insulation aging of the cable are reduced, guiding significance can be provided for operation and maintenance personnel to evaluate the service performance of the cable, and safe operation of a power grid is guaranteed.

Description

Technical Field

[0001] The invention relates to the field of XLPE cable insulation aging state assessment, and in particular to a 10kV XLPE cable insulation aging state assessment method based on microwave reflection signal transfer factor. Background Art

[0002] With the rapid development of my country's economic construction, the society's demand for electric energy is growing, and at the same time, the requirements for power quality and power supply reliability are getting higher and higher. Cross-linked polyethylene (XLPE) cable is widely used in power transmission in urban power grids, rail transit and other power systems due to its excellent mechanical and electrical properties, easy installation and high safety. However, as the cable's service life increases, its insulating medium continues to age, which will lead to a decrease in the insulation resistance of the cable and an increase in the leakage current of the insulation layer, seriously affecting the service life of the cable. In addition, if the cable insulation ages severely, it will lead to a large accumulation of local charges, which will cause local discharge, and eventually cause insulation breakdown, resulting in power outages, posing a major hidden danger to the safety and economy of the power system.

[0003] At present, there are few studies on the evaluation of 10kV XLPE cable insulation aging status, and there is no widely promoted and applied detection method. Therefore, an efficient method for evaluating the aging status of 10kV XLPE cable insulation is urgently needed. This method is a 10kV XLPE cable insulation aging status evaluation method based on microwave reflection signal transfer factor. The method is simple to operate and can efficiently and conveniently evaluate the aging status of XLPE cable insulation through the extracted microwave reflection signal transfer factor. It is of great significance to ensure the safe and reliable operation of power cables and improve equipment utilization. Summary of the invention

[0004] The present invention is a 10kV XLPE cable insulation aging state evaluation method based on microwave reflection signal transfer factor, which is used to evaluate the 10kV XLPE cable insulation aging state, and specifically comprises the following steps:

[0005] Step 1: Launch a high-frequency microwave signal to the cable to be evaluated and measure the absolute value of the reflected wave power and the reflection coefficient

[0006] A 10kV XLPE cable with a length of L is selected as the research object. The outer radius of the cable sheath layer, the radius of the cable core, and the outer radius of the cable insulation layer are r w 、r n 、r j; Place the transmitting antenna and the receiving antenna at a distance of 5 cm from the cable to be evaluated, and use a mechanical bracket to keep the two antennas at a fixed angle of 45°. Use a high-frequency microwave signal source to generate microwave signals with frequencies of 20 GHz, 22 GHz, 24 GHz, 26 GHz, 28 GHz, and 30 GHz, respectively. The microwave signal is emitted into the cable through the transmitting antenna, and the reflected wave is obtained by the receiving antenna. Finally, the absolute value of the reflected wave power and the reflection coefficient are detected by a spectrum analyzer. The absolute values ​​of the reflected wave power are recorded as: P dBm1 , P dBm2 , P dBm3 , P dBm4 , P dBm5 , P dBm6 , the reflection coefficients are: S 11 (1) S 11 (2) S 11 (3) S 11 (4) S 11 (5) S 11 (6);

[0007] Step 2: Calculate the cable distortion coefficient α

[0008]

[0009] Among them, P dBmmax is the maximum absolute value of the measured power, P dBmmin is the minimum absolute value of the measured power;

[0010] Step 3: Calculate the electromagnetic disturbance coefficient β

[0011]

[0012] Among them, S 11max is the maximum value of the measured reflection coefficient, S 11min is the minimum value of the measured reflection coefficient;

[0013] Step 4: Calculate the microwave reflection signal transfer factor σ

[0014]

[0015] Step 5: Evaluate the aging state of XLPE cable insulation by microwave reflection signal transfer factor σ

[0016] When σ≤2.158, the target XLPE cable insulation is slightly aged;

[0017] When 2.158<σ≤6.532, the target XLPE cable insulation is moderately aged;

[0018] When σ>6.532, the target XLPE cable insulation is severely aged.

[0019] The beneficial effects of the present invention are: by applying a high-frequency microwave signal to the XLPE cable, using a receiving antenna to obtain a reflected wave, and detecting the absolute value of the reflected wave power and the reflection coefficient through a spectrum analyzer, the cable distortion coefficient and the electromagnetic disturbance coefficient are calculated, and the microwave reflection signal transmission factor is extracted to evaluate the insulation aging state of the XLPE cable. The method can efficiently and safely accurately evaluate the insulation aging state of a 10kV XLPE cable, reduce power outages caused by severe cable insulation aging, and provide guidance for operation and maintenance personnel to evaluate the service performance of the cable, thereby ensuring the safe operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation processes.

[0022] Figure 1 The flowchart of a method for evaluating the insulation aging state of a 10kV XLPE cable based on a microwave reflection signal transfer factor is shown, which includes the following steps:

[0023] Step 1: Launch a high-frequency microwave signal to the cable to be evaluated and measure the absolute value of the reflected wave power and the reflection coefficient

[0024] A 10kV XLPE cable with a length of L is selected as the research object. The outer radius of the cable sheath layer, the radius of the cable core, and the outer radius of the cable insulation layer are r w 、r n 、r j ; Place the transmitting antenna and the receiving antenna at a distance of 5 cm from the cable to be evaluated, and use a mechanical bracket to keep the two antennas at a fixed angle of 45°. Use a high-frequency microwave signal source to generate microwave signals with frequencies of 20 GHz, 22 GHz, 24 GHz, 26 GHz, 28 GHz, and 30 GHz, respectively. The microwave signal is emitted into the cable through the transmitting antenna, and the reflected wave is obtained by the receiving antenna. Finally, the absolute value of the reflected wave power and the reflection coefficient are detected by a spectrum analyzer. The absolute values ​​of the reflected wave power are recorded as: P dBm1 , P dBm2 , P dBm3 , P dBm4 , P dBm5 , P dBm6 , the reflection coefficients are: S 11 (1) S 11 (2) S 11 (3) S 11 (4) S 11 (5) S11 (6);

[0025] Step 2: Calculate the cable distortion coefficient α

[0026]

[0027] Among them, P dBmmax is the maximum absolute value of the measured power, P dBmmin is the minimum absolute value of the measured power;

[0028] Step 3: Calculate the electromagnetic disturbance coefficient β

[0029]

[0030] Among them, S 11max is the maximum value of the measured reflection coefficient, S 11min is the minimum value of the measured reflection coefficient;

[0031] Step 4: Calculate the microwave reflection signal transfer factor σ

[0032]

[0033] Step 5: Evaluate the aging state of the XLPE cable insulation by the microwave reflection signal transfer factor σ. When σ≤2.158, the target XLPE cable insulation is slightly aged;

[0034] When 2.158<σ≤6.532, the target XLPE cable insulation is moderately aged; when σ>6.532, the target XLPE cable insulation is severely aged.

Claims

1. A method for evaluating the insulation aging status of 10kV XLPE cable based on microwave reflection signal transfer factor, characterized in that: Step 1: Launch a high-frequency microwave signal to the cable to be evaluated and measure the absolute value of the reflected wave power and the reflection coefficient A 10kV XLPE cable with a length of L is selected as the research object. The outer radius of the cable sheath layer, the radius of the cable core, and the outer radius of the cable insulation layer are r and w 、r n 、r j ; Place the transmitting antenna and the receiving antenna at a distance of 5 cm from the cable to be evaluated, and use a mechanical bracket to keep the two antennas at a fixed angle of 45°. Use a high-frequency microwave signal source to generate microwave signals with frequencies of 20 GHz, 22 GHz, 24 GHz, 26 GHz, 28 GHz, and 30 GHz, respectively. The microwave signal is emitted into the cable through the transmitting antenna, and the reflected wave is obtained by the receiving antenna. Finally, the absolute value of the reflected wave power and the reflection coefficient are detected by a spectrum analyzer. The absolute values ​​of the reflected wave power are recorded as: P dBm1 , P dBm2 , P dBm3 , P dBm4 , P dBm5 , P dBm6 , the reflection coefficients are: S 11 (1) S 11 (2) S 11 (3) S 11 (4) S 11 (5) S 11 (6); Step 2: Calculate the cable distortion coefficient α Among them, P dBmmax is the maximum absolute value of the measured power, P dBmmin is the minimum absolute value of the measured power; Step 3: Calculate the electromagnetic disturbance coefficient β Among them, S 11max is the maximum value of the measured reflection coefficient, S 11min is the minimum value of the measured reflection coefficient; Step 4: Calculate the microwave reflection signal transfer factor σ Step 5: Evaluate the insulation aging state of XLPE cable by microwave reflection signal transfer factor σ.

Images