A reliability evaluation method for cable elbow based on real-time electrical and thermal monitoring

Abstract

The present invention discloses a reliability assessment method for cable elbow heads based on real-time electric and thermal monitoring. The reliability assessment method for cable elbow heads based on real-time electric and thermal monitoring can achieve the purpose of measuring and evaluating the operating status and reliability of cable elbow heads used in 10kV ring network cabinets and other places in the power supply section of high-speed railway lines, and avoid problems such as flashover and breakdown caused by degradation of the properties of the cable elbow heads. At the same time, the present invention can also transform the cable elbow heads of the ring network cabinets in field operation, and can also optimize and improve the cable elbow heads when the new ring network cabinets are put into operation. It can monitor the aging process of the cable elbow heads in real time, and provide a basis for field personnel to further explore the service performance of the cable elbow heads through on-site testing and analysis.

Description

Technical Field

[0001] The invention relates to the field of state evaluation of outgoing cables of ring main unit in a power supply section along a high-speed railway, and in particular to a reliability evaluation method of cable elbows based on real-time electrical and thermal monitoring. Background Art

[0002] Along the high-speed railways in my country, there are a large number of power supply sections, which play a role in providing continuous and reliable power supply to the overhead contact system and high-speed trains. In the power supply area, the 10kV ring main unit cable elbow is an important component of the power supply line. Its operating status and failure rate will directly affect the reliability of the railway power supply section. According to the relevant railway power supply system failure statistics, with the increase in the operating years of the 10kV ring main unit related to the high-speed railway lines put into operation earlier, the number of cable elbow failures has increased rapidly, and the impact is very severe, which will cause large-scale power outages in the power supply section, seriously affecting the punctual operation of the high-speed railway, and causing great direct and indirect losses.

[0003] At present, in the actual application process, the insulation state of the cable elbow is easily affected by factors such as construction technology, overload operation, external environment changes and poor grounding. It is difficult to detect and evaluate its operating reliability. With the increase of operating years, the risk of cable elbow failure also increases greatly. There are not many effective monitoring methods available. Therefore, in order to solve the problems of difficult on-site detection and lack of evaluation methods, it is necessary to study the reliability of the operation of the cable elbow of the 10kV ring main unit, and propose a cable elbow reliability evaluation method based on electric-thermal real-time monitoring. Summary of the invention

[0004] The purpose of the invention is to provide a cable elbow reliability assessment method based on electrical-thermal real-time monitoring.

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

[0006] A cable elbow reliability assessment method based on real-time electrical-thermal monitoring is used to achieve the purpose of rapid testing and judgment when the operating status of the outgoing cable of the ring main unit in the power supply section along the high-speed railway line is abnormal, including a ring main unit cable elbow real-time electrical-thermal monitoring system and a cable elbow reliability assessment method based on real-time electrical-thermal monitoring, characterized in that:

[0007] 1. A ring main unit cable elbow electrical-thermal real-time monitoring system, including the following features:

[0008] When the railway traction substation is renovating the 10kV ring main unit cable outlet elbow head electrical-thermal real-time monitoring system in operation or installing the newly put into operation 10kV ring main unit cable outlet elbow head electrical-thermal real-time monitoring system, the following components and the connection relationship between the components are included:

[0009] The components of the monitoring system are support plate (1), A phase cable elbow (2), B phase cable elbow (3), C phase cable elbow (4), A phase elbow grounding hole (5), A phase grounding wire (6), A phase No. 1 temperature sensor (7), A phase No. 2 temperature sensor (8), A phase No. 3 temperature sensor (9), A phase No. 4 temperature sensor (10), A phase cable sheath (11), B phase elbow grounding hole (12), B phase grounding wire (13), B phase No. 1 temperature sensor (14), B phase No. 2 temperature sensor (15), B phase No. 3 temperature sensor (16), B phase No. 4 temperature sensor (17), B phase cable sheath (18), C phase elbow grounding hole (19), C phase grounding wire (20), C phase No. 1 temperature sensor (21), C phase No. 2 temperature sensor (22), C phase No. 3 temperature sensor ( 23), C phase No. 4 temperature sensor (24), C phase cable sheath (25), A phase fluorescent fiber optic sensor (26), A phase photomultiplier tube (27), B phase fluorescent fiber optic sensor (28), B phase photomultiplier tube (29), C phase fluorescent fiber optic sensor (30), C phase photomultiplier tube (31), multi-channel digital oscilloscope (32), computer (33), A phase wireless transmitter (34-a), B phase wireless transmitter (34-b), C phase wireless transmitter (34-c), wireless signal receiver (35), wherein the multi-channel digital oscilloscope (32), computer (33) and wireless signal receiver (35) are located outside the 10kV ring network cabinet (36), and the remaining components are located inside the 10kV ring network cabinet (36), and the 10kV ring network cabinet (36) is always in a closed state when the cable elbow head is operating normally;

[0010] Secondly, the A-phase No. 1 temperature sensor (7) is placed near the A-phase elbow head grounding hole (5), in contact with the A-phase grounding wire (6), and connected to the A-phase wireless transmitter (34-a) through a transmission line. The B-phase No. 1 temperature sensor (14) is placed near the B-phase elbow head grounding hole (12), in contact with the B-phase grounding wire (13), and connected to the B-phase wireless transmitter (34-b) through a transmission line. The C-phase No. 1 temperature sensor (21) is placed near the C-phase elbow head grounding hole (19), in contact with the C-phase grounding wire (20), and connected to the C-phase wireless transmitter (34-c) through a transmission line. The A-phase No. 2 temperature sensor (8), the A-phase No. 3 temperature sensor (9), and the A-phase No. 4 temperature sensor (10) are connected to the A-phase wireless transmitter (34-a) at a central angle of 120°. The temperature sensors (15, 16, 17) of the B phase are evenly placed at the junction of the A phase cable elbow (2) and the A phase cable sheath (11) at intervals of 120°, and are all connected to the A phase wireless transmitter (34-a); the temperature sensors (15, 16, 17) of the B phase are evenly placed at the junction of the B phase cable elbow (3) and the B phase cable sheath (18) at intervals of 120° at the center angle, and are all connected to the B phase wireless transmitter (34-b); the temperature sensors (22, 23, 24) of the C phase are evenly placed at the junction of the C phase cable elbow (4) and the C phase cable sheath (25) at intervals of 120° at the center angle, and are all connected to the C phase wireless transmitter (34-c).

[0011] In addition, during the transformation and installation process, the A-phase fluorescent optical fiber sensor (26) and the A-phase photomultiplier tube (27), the B-phase fluorescent optical fiber sensor (28) and the B-phase photomultiplier tube (29), and the C-phase fluorescent optical fiber sensor (30) and the C-phase photomultiplier tube (31) are all connected through common optical fibers, and the two ends of the common optical fibers are respectively provided with an optical fiber coupler and an optical fiber adapter. The A-phase photomultiplier tube (27), the B-phase photomultiplier tube (29), and the C-phase photomultiplier tube (31) are respectively connected to corresponding acquisition channels of a multi-channel digital oscilloscope (32) through communication cables, and the digital oscilloscope (32) and the computer (33) are connected through a data transmission line that meets the IEEE 488.2 protocol; the A-phase wireless transmitter (34-a), the B-phase wireless transmitter (34-b), and the C-phase wireless transmitter (34-c) are all fixed on the inner wall of the 10 kV ring network cabinet (36), so that the wireless signal receiver (35) receives the signals of the above transmitters and transmits the temperature data to the computer (33) in real time through the data transmission line.

[0012] 2. A cable elbow reliability assessment method based on real-time electrical and thermal monitoring, comprising the following steps:

[0013] The first step is to start a multi-channel digital oscilloscope (32), a computer (33), an A-phase wireless transmitter (34-a), a B-phase wireless transmitter (34-b), a C-phase wireless transmitter (34-c) and a wireless signal receiver (35), set the collection time interval of each collection channel, and monitor the temperature information and discharge signal data at the corresponding positions of the A-phase cable elbow head (2), the B-phase cable elbow head (3) and the C-phase cable elbow head (4) in the 10kV ring network cabinet (36) in real time, and the electric-thermal real-time monitoring system starts to work normally.

[0014] Step 2: Test and estimate the hot spot temperature inside the cable elbow

[0015] According to the temperature information at the corresponding positions of the A-phase cable elbow (2), the B-phase cable elbow (3), and the C-phase cable elbow (4) in the 10 kV ring network cabinet (36) monitored in the second step, the collected Celsius temperature information of the A-phase cable elbow (2) is recorded as T A1 、T A2 、T A3 、T A4 The collected temperature information of the B-phase cable elbow (3) is T B1 、T B2 、T B3 、T B4 The collected temperature information of the elbow head (4) of the C-phase cable is T C1 、T C2 、T C3 、T C4 ;

[0016] Using the temperature information of the above cable elbows, the hot spot temperature inside the elbow is estimated. A1 、T A2 、T A3 、T A4 Substituting into formula (1), we can get the maximum hot spot temperature T of the A-phase cable elbow (2): AM for:

[0017]

[0018] Where, T 0 is the external environment temperature. It is recommended to take the temperature inside the 10kV ring network cabinet where the cable elbow to be monitored is located. At the same time, B1 、T B2 、T B3 、T B4 and T C1 、T C2 、T C3 、T C4Substituting into equations (3) and (4), we can obtain the maximum hot spot temperature T inside the B-phase cable elbow (3) and the C-phase cable elbow (4), respectively. BM 、T CM :

[0019]

[0020] In the above formula, T 0 It is also the external ambient temperature. It is still recommended to take the temperature inside the 10kV ring main unit where the cable elbow to be monitored is located.

[0021] Step 3: Calculate the temperature difference ratio of the hot spot inside the cable elbow

[0022] According to the maximum internal hot spot temperatures of the A, B, and C phase cable elbows estimated in the second step, calculate the difference ratio δ of the hot spot temperatures of the different phase cable elbows. i , i takes A, B, C respectively,

[0023]

[0024] Where, T M is the calculated average value of the hot spot temperature inside the three-phase cable elbow.

[0025] Step 4: Operating status characteristic index γ i Estimate and compare

[0026] Compare the temperature difference ratio of the hot spot inside the cable elbow calculated in the third step to δ A ,δ B ,δ C , select its maximum value δ Max Make a judgment,

[0027] 4.1 When δ Max When ≤1.3, it can be determined that the elbows of each phase cable are in normal operation, and the monitoring can be stopped to wait for the next set of transmission data;

[0028] 4.2 When δ Max When the temperature difference of the hot spot inside the cable elbow is greater than 1.3, the cable elbow with the largest temperature difference may have an operation problem. Then, the discharge information on the A-phase photomultiplier tube (27), the B-phase photomultiplier tube (29), and the C-phase photomultiplier tube (31) is collected by a computer (33) and a digital oscilloscope (32), and the collected single pulse signal voltage peak value is recorded as u A、 u B、 u C , whose unit is V, and the pulse width is t A、 t B、 t C , its unit is μs;

[0029] According to formula (6), the operating state characteristic index γ i The judgment of i is A, B, C respectively.

[0030]

[0031] In the formula, γ i The value is γ A , γ B , γ C , respectively represent the operating status characteristic indexes of the A-phase cable elbow (2), the B-phase cable elbow (3), and the C-phase cable elbow (4); for γ A , γ B , γ C Sort and select the maximum value γ Max .

[0032] Step 5: Evaluation of the reliability of the cable elbow of the ring main unit

[0033] According to the calculation and judgment in the above steps, the reliability of the cable elbow of the ring main unit is evaluated:

[0034] 5.1 Comparison of the maximum value of the hot spot temperature difference inside the cable elbow Max and the maximum value of the characteristic index of the operating state γ Max , determine whether it is the same cable elbow;

[0035] 5.2 If it is finally determined to be the same cable elbow, it can be determined that the cable elbow is in a defective operating state and needs to be shut down for inspection or maintenance as soon as possible;

[0036] If the comparison result shows that the cable elbow is not the same, only the maximum value of the internal hot spot temperature difference δ Max and the maximum value of the characteristic index of the operating state γ Max Repeat the third to fifth steps for the corresponding two cable elbows, and finally identify the cable elbow that is in operation with a defect;

[0037] If after repeating steps 2 to 4 several times, the comparison results still show that they are not the same cable elbow, then it is determined that the two cable elbows are operating with defects and need to be paid special attention or repaired immediately.

[0038] The beneficial effects of the present invention are:

[0039] 1. The cable elbow reliability assessment method based on real-time electric-thermal monitoring of the present invention can efficiently, accurately, in real time and conveniently measure and evaluate the operating status and reliability of the cable elbow used in the 10kV ring network cabinet in the power supply section of the high-speed railway line, avoid flashover, breakdown and other problems caused by abnormal operating status of the cable elbow, and realize reliable operation of the railway power supply section.

[0040] 2. The cable elbow head reliability assessment method based on electric-thermal real-time monitoring of the present invention can monitor the aging process of the cable elbow head in real time, and provide a basis for on-site personnel to further explore the service performance of the cable elbow head through on-site testing and analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a structural schematic diagram of the electrical-thermal real-time monitoring system of the cable elbow of the ring main unit of the present invention; DETAILED DESCRIPTION

[0042] The present invention will be further described below in conjunction with the accompanying drawings.

[0043] Figure 1 This is a schematic diagram of the structure of the real-time monitoring system for the electric-thermal elbow of the cable of the ring main unit of the present invention, which is used to achieve the purpose of rapid testing and judgment when the operating status of the outgoing cable of the ring main unit in the power supply section along the high-speed railway line is abnormal. Its structure and use method include the following contents:

[0044] The proposed ring main unit cable elbow electrical-thermal real-time monitoring system includes the following features:

[0045] When the railway traction substation is renovating the electric-thermal real-time monitoring system of the 10kV ring main unit cable outlet elbow head in operation or installing the new electric-thermal real-time monitoring system of the 10kV ring main unit cable outlet elbow head in operation, the following components and the connection relationship between the components are mainly included: the components of the monitoring system are support plate (1), A phase cable elbow head (2), B phase cable elbow head (3), C phase cable elbow head (4), A phase elbow head grounding hole (5), A phase grounding wire (6), A phase No. Temperature sensor (7), A phase No. 2 temperature sensor (8), A phase No. 3 temperature sensor (9), A phase No. 4 temperature sensor (10), A phase cable sheath (11), B phase elbow grounding hole (12), B phase grounding wire (13), B phase No. 1 temperature sensor (14), B phase No. 2 temperature sensor (15), B phase No. 3 temperature sensor (16), B phase No. 4 temperature sensor (17), B phase cable sheath (18), C phase elbow grounding hole (19), C phase grounding wire Ground wire (20), C phase No. 1 temperature sensor (21), C phase No. 2 temperature sensor (22), C phase No. 3 temperature sensor (23), C phase No. 4 temperature sensor (24), C phase cable sheath (25), A phase fluorescent fiber optic sensor (26), A phase photomultiplier tube (27), B phase fluorescent fiber optic sensor (28), B phase photomultiplier tube (29), C phase fluorescent fiber optic sensor (30), C phase photomultiplier tube (31), multi-channel digital oscilloscope (32), A computer (33), an A-phase wireless transmitter (34-a), a B-phase wireless transmitter (34-b), a C-phase wireless transmitter (34-c), and a wireless signal receiver (35), wherein the multi-channel digital oscilloscope (32), the computer (33), and the wireless signal receiver (35) are located outside the 10kV ring network cabinet (36), and the remaining components are located inside the 10kV ring network cabinet (36), and the 10kV ring network cabinet (36) is always in a closed state when the cable elbow is operating normally;

[0046] Secondly, the A-phase No. 1 temperature sensor (7) is placed near the A-phase elbow head grounding hole (5), in contact with the A-phase grounding wire (6), and connected to the A-phase wireless transmitter (34-a) through a transmission line. The B-phase No. 1 temperature sensor (14) is placed near the B-phase elbow head grounding hole (12), in contact with the B-phase grounding wire (13), and connected to the B-phase wireless transmitter (34-b) through a transmission line. The C-phase No. 1 temperature sensor (21) is placed near the C-phase elbow head grounding hole (19), in contact with the C-phase grounding wire (20), and connected to the C-phase wireless transmitter (34-c) through a transmission line. The A-phase No. 2 temperature sensor (8), the A-phase No. 3 temperature sensor (9), and the A-phase No. 4 temperature sensor (10) are connected to the A-phase wireless transmitter (34-a) at a central angle of 120°. The temperature sensors (15, 16, 17) of the B phase are evenly placed at the junction of the A phase cable elbow (2) and the A phase cable sheath (11) at intervals of 120°, and are all connected to the A phase wireless transmitter (34-a); the temperature sensors (15, 16, 17) of the B phase are evenly placed at the junction of the B phase cable elbow (3) and the B phase cable sheath (18) at intervals of 120° at the center angle, and are all connected to the B phase wireless transmitter (34-b); the temperature sensors (22, 23, 24) of the C phase are evenly placed at the junction of the C phase cable elbow (4) and the C phase cable sheath (25) at intervals of 120° at the center angle, and are all connected to the C phase wireless transmitter (34-c).

[0047] In addition, during the transformation and installation process, the A-phase fluorescent optical fiber sensor (26) and the A-phase photomultiplier tube (27), the B-phase fluorescent optical fiber sensor (28) and the B-phase photomultiplier tube (29), and the C-phase fluorescent optical fiber sensor (30) and the C-phase photomultiplier tube (31) are all connected through common optical fibers, and the two ends of the common optical fibers are respectively provided with an optical fiber coupler and an optical fiber adapter. The A-phase photomultiplier tube (27), the B-phase photomultiplier tube (29), and the C-phase photomultiplier tube (31) are respectively connected to corresponding acquisition channels of a multi-channel digital oscilloscope (32) through communication cables, and the digital oscilloscope (32) and the computer (33) are connected through a data transmission line (satisfying the IEEE 488.2 protocol); the A-phase wireless transmitter (34-a), the B-phase wireless transmitter (34-b), and the C-phase wireless transmitter (34-c) are all fixed on the inner wall of the 10 kV ring network cabinet (36), so that the wireless signal receiver (35) receives the signals of the above transmitters and can transmit the temperature data to the computer (33) in real time through the data transmission line.

[0048] The following is an evaluation conducted on the installed ring main unit cable elbow electrical-thermal real-time monitoring system:

[0049] The first step is to start a multi-channel digital oscilloscope (32), a computer (33), an A-phase wireless transmitter (34-a), a B-phase wireless transmitter (34-b), a C-phase wireless transmitter (34-c) and a wireless signal receiver (35), set the collection time interval of each collection channel, and monitor the temperature information and discharge signal data at the corresponding positions of the A-phase cable elbow head (2), the B-phase cable elbow head (3) and the C-phase cable elbow head (4) in the 10kV ring network cabinet (36) in real time, and the electric-thermal real-time monitoring system starts to work normally.

[0050] Step 2: Test and estimate the hot spot temperature inside the cable elbow

[0051] According to the temperature information at the corresponding positions of the A-phase cable elbow (2), the B-phase cable elbow (3), and the C-phase cable elbow (4) in the 10 kV ring network cabinet (36) monitored in the previous step, the collected temperature information of the A-phase cable elbow (2) is recorded as T A1 、T A2 、T A3 、T A4 (Celsius), the temperature information of the B-phase cable elbow (3) collected is T B1 、T B2 、T B3 、T B4 (Celsius), the temperature information of the elbow head (4) of the C-phase cable collected is T C1 、T C2 、T C3 、T C4 (Celsius);

[0052] Using the temperature information of the above cable elbows, the hot spot temperature inside the elbow is estimated. A1 、T A2 、T A3 、T A4 Substituting into formula (1), we can get the maximum hot spot temperature T of the A-phase cable elbow (2): AM for:

[0053]

[0054] Where, T 0 is the external environment temperature. It is recommended to take the temperature inside the 10kV ring network cabinet where the cable elbow to be monitored is located. At the same time, B1 、T B2 、T B3 、T B4 and T C1 、T C2 、T C3 、T C4Substituting into equations (3) and (4), we can obtain the maximum hot spot temperature T inside the B-phase cable elbow (3) and the C-phase cable elbow (4), respectively. BM 、T CM :

[0055]

[0056] In the above formula, T 0 It is also the external ambient temperature. It is still recommended to take the temperature inside the 10kV ring main unit where the cable elbow to be monitored is located.

[0057] Step 3: Calculate the temperature difference ratio of the hot spot inside the cable elbow

[0058] According to the maximum internal hot spot temperatures of the A, B, and C phase cable elbows estimated in the second step, calculate the difference ratio δ of the hot spot temperatures of the different phase cable elbows. i , i takes A, B, C respectively,

[0059]

[0060] Where, T M is the calculated average value of the hot spot temperature inside the three-phase cable elbow.

[0061] Step 4: Operating status characteristic index γ i Estimate and compare

[0062] Compare the temperature difference ratio of the hot spot inside the cable elbow calculated in the third step to δ A ,δ B ,δ C , select its maximum value δ Max Make a judgment,

[0063] 4.1 When δ Max When ≤1.3, it can be determined that the elbows of each phase cable are in normal operation, and the monitoring can be stopped to wait for the next set of transmission data;

[0064] At this time, the obtained δ Max The value is 1.85, which corresponds to the A-phase cable elbow (2), so continue with the following steps.

[0065] 4.2 When δ Max When the temperature difference of the hot spot inside the cable elbow is greater than 1.3, the cable elbow with the largest temperature difference may have an operation problem. Then, the discharge information on the A-phase photomultiplier tube (27), the B-phase photomultiplier tube (29), and the C-phase photomultiplier tube (31) is collected by a computer (33) and a digital oscilloscope (32), and the collected single pulse signal voltage peak value is recorded as u A、 u B、 uC , whose unit is V, and the pulse width is t A、 t B、 t C , its unit is μs;

[0066] According to formula (6), the operating state characteristic index γ i The judgment of i is A, B, C respectively.

[0067]

[0068] In the formula, γ i The value is γ A , γ B , γ C , respectively represent the operating status characteristic indexes of the A-phase cable elbow (2), the B-phase cable elbow (3), and the C-phase cable elbow (4); for γ A , γ B , γ C Sort and select the maximum value γ Max .

[0069] At this time, the maximum value γ is obtained Max The corresponding one is the A-phase cable elbow.

[0070] Step 5: Evaluation of the reliability of the cable elbow of the ring main unit

[0071] According to the calculation and judgment in the above steps, the reliability of the cable elbow of the ring main unit is evaluated:

[0072] 5.1 Comparison of the maximum value of the hot spot temperature difference inside the cable elbow Max and the maximum value of the characteristic index of the operating state γ Max , determine whether it is the same cable elbow;

[0073] 5.2 If it is finally determined to be the same cable elbow, it can be determined that the cable elbow is in a defective operating state and needs to be shut down for inspection or maintenance as soon as possible;

[0074] If the comparison result shows that they are not the same cable elbows, repeat the second to fourth steps only for the two cable elbows, and finally determine the cable elbow that is running with a defect;

[0075] If after repeating steps 2 to 4 several times, the comparison results still show that they are not the same cable elbow, then it is determined that the two cable elbows are operating with defects and need to be paid special attention or repaired immediately.

[0076] At this time, by comparison, the internal hot spot temperature difference is greater than the maximum value δ Max and the maximum value of the characteristic index of the operating state γMax They all correspond to the A-phase cable elbows, so it is determined that the A-phase cable elbow (2) is in a defective operating state and needs to be repaired as soon as possible.

Claims

1. A cable elbow reliability assessment method based on real-time electrical and thermal monitoring, characterized in that: The steps include: Step 1: Laying the elbow head of the ring main unit cable to monitor the electrical and thermal real-time relationship When the railway traction substation is renovating the 10kV ring main unit cable outlet elbow head electrical-thermal real-time monitoring system in operation or installing the newly put into operation 10kV ring main unit cable outlet elbow head electrical-thermal real-time monitoring system, the following components and the connection relationship between the components are included: The components of the monitoring system are support plate (1), A phase cable elbow (2), B phase cable elbow (3), C phase cable elbow (4), A phase elbow grounding hole (5), A phase grounding wire (6), A phase No. 1 temperature sensor (7), A phase No. 2 temperature sensor (8), A phase No. 3 temperature sensor (9), A phase No. 4 temperature sensor (10), A phase cable sheath (11), B phase elbow grounding hole (12), B phase grounding wire (13), B phase No. 1 temperature sensor (14), B phase No. 2 temperature sensor (15), B phase No. 3 temperature sensor (16), B phase No. 4 temperature sensor (17), B phase cable sheath (18), C phase elbow grounding hole (19), C phase grounding wire (20), C phase No. 1 temperature sensor (21), C phase No. 2 temperature sensor (22), C phase No. 3 temperature sensor ( 23), C phase No. 4 temperature sensor (24), C phase cable sheath (25), A phase fluorescent fiber optic sensor (26), A phase photomultiplier tube (27), B phase fluorescent fiber optic sensor (28), B phase photomultiplier tube (29), C phase fluorescent fiber optic sensor (30), C phase photomultiplier tube (31), multi-channel digital oscilloscope (32), computer (33), A phase wireless transmitter (34-a), B phase wireless transmitter (34-b), C phase wireless transmitter (34-c), wireless signal receiver (35), wherein the multi-channel digital oscilloscope (32), computer (33) and wireless signal receiver (35) are located outside the 10kV ring network cabinet (36), and the remaining components are located inside the 10kV ring network cabinet (36), and the 10kV ring network cabinet (36) is always in a closed state when the cable elbow head is operating normally; Secondly, the A-phase No. 1 temperature sensor (7) is placed near the A-phase elbow head grounding hole (5), in contact with the A-phase grounding wire (6), and connected to the A-phase wireless transmitter (34-a) through a transmission line. The B-phase No. 1 temperature sensor (14) is placed near the B-phase elbow head grounding hole (12), in contact with the B-phase grounding wire (13), and connected to the B-phase wireless transmitter (34-b) through a transmission line. The C-phase No. 1 temperature sensor (21) is placed near the C-phase elbow head grounding hole (19), in contact with the C-phase grounding wire (20), and connected to the C-phase wireless transmitter (34-c) through a transmission line. The A-phase No. 2 temperature sensor (8), the A-phase No. 3 temperature sensor (9), and the A-phase No. 4 temperature sensor (10) are connected to the A-phase wireless transmitter (34-a) at a central angle of 120°. The temperature sensors (15, 16, 17) of the B phase are evenly placed at the junction of the A phase cable elbow (2) and the A phase cable sheath (11) at intervals of 120°, and are all connected to the A phase wireless transmitter (34-a); the temperature sensors (15, 16, 17) of the B phase are evenly placed at the junction of the B phase cable elbow (3) and the B phase cable sheath (18) at intervals of 120° at the center angle, and are all connected to the B phase wireless transmitter (34-b); the temperature sensors (22, 23, 24) of the C phase are evenly placed at the junction of the C phase cable elbow (4) and the C phase cable sheath (25) at intervals of 120° at the center angle, and are all connected to the C phase wireless transmitter (34-c); In addition, during the transformation and installation process, the A-phase fluorescent optical fiber sensor (26) and the A-phase photomultiplier tube (27), the B-phase fluorescent optical fiber sensor (28) and the B-phase photomultiplier tube (29), and the C-phase fluorescent optical fiber sensor (30) and the C-phase photomultiplier tube (31) are all connected through common optical fibers, and the two ends of the common optical fibers are respectively provided with an optical fiber coupler and an optical fiber adapter. The A-phase photomultiplier tube (27), the B-phase photomultiplier tube (29), and the C-phase photomultiplier tube (31) are respectively connected to corresponding acquisition channels of a multi-channel digital oscilloscope (32) through communication cables, and the digital oscilloscope (32) and the computer (33) are connected through a data transmission line that meets the IEEE 488.2 protocol; the A-phase wireless transmitter (34-a), the B-phase wireless transmitter (34-b), and the C-phase wireless transmitter (34-c) are all fixed on the inner wall of the 10 kV ring network cabinet (36), so that the wireless signal receiver (35) receives the signals of the above transmitters and transmits the temperature data to the computer (33) in real time through the data transmission line; Step 2: Start the multi-channel digital oscilloscope (32), the computer (33), the A-phase wireless transmitter (34-a), the B-phase wireless transmitter (34-b), the C-phase wireless transmitter (34-c) and the wireless signal receiver (35), set the acquisition time interval of each acquisition channel, and monitor the temperature information and discharge signal data at the corresponding positions of the A-phase cable elbow head (2), the B-phase cable elbow head (3) and the C-phase cable elbow head (4) in the 10kV ring network cabinet (36) in real time, and the electric-thermal real-time monitoring system starts to work normally; Step 3: Test and estimate the hot spot temperature inside the cable elbow According to the temperature information at the corresponding positions of the A-phase cable elbow (2), the B-phase cable elbow (3), and the C-phase cable elbow (4) in the 10 kV ring network cabinet (36) monitored in the second step, the collected Celsius temperature information of the A-phase cable elbow (2) is recorded as T A1 , T A2 , T A3 , T A4 The collected temperature information of the B-phase cable elbow (3) is T B1 , T B2 , T B3 , T B4 The collected temperature information of the elbow head (4) of the C-phase cable is T C1 , T C2 , T C3 , T C4 ; Using the temperature information of the above cable elbows, the hot spot temperature inside the elbow is estimated. A1 , T A2 , T A3 , T A4 Substituting into formula (1), we can get the maximum hot spot temperature T of the A-phase cable elbow (2): AM for: Where T0 is the external environment temperature, which is the temperature inside the 10kV ring main unit where the cable elbow to be monitored is located; at the same time, T B1 , T B2 , T B3 , T B4 and T C1 , T C2 , T C3 , T C4 Substituting into equations (2) and (3), we can obtain the maximum hot spot temperature T inside the B-phase cable elbow (3) and the C-phase cable elbow (4) respectively. BM , T CM : In the above formula, T0 is also the external environment temperature, which is the temperature inside the 10kV ring main unit where the cable elbow to be monitored is located; Step 4: Calculate the temperature difference ratio of the hot spot inside the cable elbow According to the maximum internal hot spot temperatures of the A, B, and C phase cable elbows estimated in the third step, calculate the difference ratio δ of the hot spot temperatures of the different phase cable elbows. i , i takes A, B, C respectively, Where, T M is the calculated average value of the hot spot temperature inside the three-phase cable elbow; Step 5: Operating status characteristic index γ i Estimate and compare Compare the temperature difference ratio of the hot spot inside the cable elbow calculated in step 4 to δ A ,δ B ,δ C , select its maximum value δ Max Make a judgment, 5.1 When δ Max When ≤1.3, it is determined that the elbows of each phase cable are in normal operation, and the monitoring is stopped to wait for the next set of transmission data; 5.2 When δ Max When the temperature difference of the hot spot inside the cable elbow is greater than 1.3, the cable elbow with the largest temperature difference may have an operation problem. Then, the discharge information on the A-phase photomultiplier tube (27), the B-phase photomultiplier tube (29), and the C-phase photomultiplier tube (31) is collected by a computer (33) and a digital oscilloscope (32), and the collected single pulse signal voltage peak value is recorded as u A、 u B、 u C , the unit is V, the pulse width is t A、 t B、 t C , unit is μs; According to formula (6), the operating state characteristic index γ i The judgment of i is A, B, C respectively. In the formula, γ i The value is γ A , γ B , γ C , respectively represent the operating status characteristic indexes of the A-phase cable elbow (2), the B-phase cable elbow (3), and the C-phase cable elbow (4); for γ A , γ B , γ C Sort and select the maximum value γ Max ; Step 6: Evaluation of the reliability of the cable elbow of the ring main unit According to the calculation and judgment in the above steps, the reliability of the cable elbow of the ring main unit is evaluated: 6.1 Comparison of the maximum value of the hot spot temperature difference inside the cable elbow Max and the maximum value of the characteristic index of the operating state γ Max , determine whether it is the same cable elbow; 6.2 If it is finally determined to be the same cable elbow, it can be determined that the cable elbow is in a defective operating state and needs to be shut down for inspection or maintenance as soon as possible; If the comparison result shows that the cable elbow is not the same, only the maximum value of the internal hot spot temperature difference δ Max and the maximum value of the operating state characteristic index γ Max Repeat the third to fifth steps for the corresponding two cable elbows, and finally identify the cable elbow that is in operation with a defect; If after repeating steps 3 to 5 several times, the comparison results still show that they are not the same cable elbow, then it is determined that both cable elbows are operating with defects and need to be paid special attention or repaired immediately.

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