Method for calculating abnormal temperature point of internal insulation interface of cable heat-shrink terminal

Abstract

The present application relates to a cable heat shrinkage terminal internal insulation interface abnormal temperature point calculation method, which builds a heat shrinkage terminal simulation model; simulates three working conditions of normal condition, terminal internal insulation interface damp and terminal outer surface contamination; adjusts the load current and the environment temperature, and fits the relationship between the highest insulation temperature and the terminal outer surface highest temperature and the load current and the environment temperature under the three working conditions; calculates the terminal outer surface highest temperature under the three working conditions according to the actual load current and the environment temperature, and selects the working condition of the terminal through the ratio of the terminal outer surface highest temperature under the three working conditions and the terminal outer surface highest temperature under the normal three working conditions and calculates the internal insulation interface highest temperature correspondingly. The present application can know the load current and the environment temperature on site, judge the approximate operation condition of the heat shrinkage terminal according to the measured highest temperature, and obtain the corresponding internal insulation highest temperature, which is convenient for the operation and maintenance personnel to master the cable terminal operation condition.

Description

Technical Field

[0001] This invention belongs to the field of electrical equipment insulation status and fault diagnosis, and in particular to a method for calculating abnormal temperature points at the internal insulation interface of cable heat shrink terminals. Background Technology

[0002] Heat-shrinkable cable terminations are convenient to install, cost-effective, and widely used in power grids. However, with increasing service life, abnormal hot spots often appear on the outer surface of the terminations. Temperature has a significant impact on cable insulation materials; excessively high temperatures can lead to material aging. Therefore, regular temperature monitoring of heat-shrinkable cable terminations is crucial in operation and maintenance. However, current technology can only detect heat on the outer surface of the termination; there is a lack of effective means to determine the temperature of the internal insulation interface, making it difficult to accurately identify the degree of internal heating. This hinders maintenance personnel from accurately formulating the next course of action. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and propose a method for calculating abnormal temperature points at the internal insulation interface of cable heat-shrinkable terminals. This method can infer whether there are defects in the terminal by establishing the temperature relationship between the inner and outer surfaces of the heat-shrinkable terminal and based on the highest abnormal temperature.

[0004] The technical problem solved by this invention is achieved through the following technical solution:

[0005] The method for calculating abnormal temperature points at the internal insulation interface of cable heat-shrinkable terminals includes the following steps:

[0006] Step 1: Build a simulation model of the heat shrink terminal;

[0007] Step 2: Simulate three operating conditions: normal condition, moisture on the internal insulation interface of the terminal, and dirt on the outer surface of the terminal.

[0008] Step 3: By adjusting the load current I and the ambient temperature T, the highest internal insulation temperature T1 and the highest terminal outer surface temperature T2 under three operating conditions are obtained.

[0009] Step 4: Using MATLAB software, linearly fit the relationships between the highest internal insulation temperature T1, the highest external surface temperature T2, the load current I, and the ambient temperature T under the three operating conditions of the terminal.

[0010] Step 5: When applying in the field, adjust the load current I according to the actual load current. f Ambient temperature T f The theoretically calculated maximum surface temperature T during normal operation was obtained. 2n The highest temperature T on the outer surface when the insulation is damp inside. 2i The highest surface temperature T when the outer surface of the insulation is dirty 2o ;

[0011] Step 6: Calculate the measured highest temperature T on the outer surface. 2f Compared with the highest surface temperature T under normal conditions 2n The highest temperature T on the outer surface when the insulation is damp inside. 2i The highest surface temperature T when the outer surface of the insulation is dirty 2o The ratio;

[0012] Step 7: Based on the smallest of the three ratios, select the terminal that may be in the corresponding operating condition;

[0013] Step 8: Based on the determined operating conditions, select the highest temperature relationship of the internal insulation interface under the corresponding conditions to obtain the highest temperature T of the internal insulation interface. 1f .

[0014] Furthermore, the specific implementation method of step 4 is as follows:

[0015] When the terminal is running normally:

[0016] T1=-105.5741+0.282*I+1.2661*T

[0017] T2=-100.7055+0.26899*I+1.2539*T

[0018] When the internal insulation interface of the terminal is damp:

[0019] T1=-102.2017+0.28098*I+1.2651*T

[0020] T2=-98.1389+0.26863*I+1.2536*T

[0021] When the outer surface of the terminal is dirty:

[0022] T1=-96.4048+0.27919*I+1.2633*T

[0023] T2=-85.4795+0.26554*I+1.2502*T.

[0024] Furthermore, the specific implementation method of step 5 is as follows:

[0025] T 2n =-100.7055+0.26899*I+1.2539*T

[0026] T 2i =-98.1389+0.26863*I+1.2536*T

[0027] T 2o =-85.4795+0.26554*I+1.2502*T.

[0028] Furthermore, the specific implementation method of step 6 is as follows:

[0029] ratio1 = abs(T) 2f -T 2n ) / T 2n

[0030] ratio2=abs(T 2f -T 2i ) / T 2i

[0031] ratio3=abs(T 2f -T 2o ) / T 2o .

[0032] The advantages and positive effects of this invention are:

[0033] This invention constructs a simulation model of a heat-shrinkable terminal; simulating three operating conditions: normal operation, a damp internal insulation interface, and a dirty external surface. By adjusting the load current and ambient temperature, the maximum internal insulation temperature and the maximum external surface temperature under these three conditions are obtained, and the relationship between these temperatures and the load current and ambient temperature is fitted. Based on the actual load current and ambient temperature, the theoretical maximum external surface temperature under the three operating conditions is calculated. The ratio of the theoretical maximum external surface temperature to the normal maximum external surface temperature is used to select the terminal's operating condition and calculate the corresponding maximum internal insulation interface temperature. This invention allows for the determination of the approximate operating condition of the heat-shrinkable terminal based on the measured maximum temperature, given the load current and ambient temperature on-site, and provides the corresponding maximum internal insulation temperature. This facilitates maintenance personnel in understanding the cable terminal's operating status and has potential engineering application value. Attached Figure Description

[0034] Figure 1 This is a flowchart of the present invention;

[0035] Figure 2 This is a schematic diagram of the simulation model of the heat-shrinkable terminal of the present invention. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the accompanying drawings.

[0037] Methods for calculating abnormal temperature points at the internal insulation interface of cable heat-shrinkable terminals, such as... Figure 1 As shown, it includes the following steps:

[0038] Step 1: Build a simulation model of the heat shrink terminal.

[0039] Considering that the internal insulation interface temperature of actual cable heat-shrinkable terminals is difficult to measure, and that simulating various defects and faults in practice is extremely challenging, a geometric model of a 35kV heat-shrinkable cable terminal was established using COMSOL, such as... Figure 2 As shown, the simulation depicts the temperature distribution under normal conditions, assuming the internal insulation interface of the cable is damp and the external surface is dirty. The simulation considers the current magnitude I under different cable loads and the ambient temperature T. The results show the highest internal insulation interface temperature T1 and the highest external surface temperature T2 under different I and T values ​​for the three states of the cable heat-shrinkable terminal.

[0040] Step 2: Simulate three operating conditions: normal condition, moisture on the internal insulation interface of the terminal, and dirt on the outer surface of the terminal.

[0041] Step 3: By adjusting the load current I and the ambient temperature T, the highest internal insulation temperature T1 and the highest terminal outer surface temperature T2 under three operating conditions are obtained.

[0042] Step 4: Using MATLAB software, linearly fit the relationships between the highest internal insulation temperature T1, the highest external surface temperature T2, the load current I, and the ambient temperature T under the three operating conditions of the terminal.

[0043] When the terminal is running normally:

[0044] T1=-105.5741+0.282*I+1.2661*T

[0045] T2=-100.7055+0.26899*I+1.2539*T

[0046] When the internal insulation interface of the terminal is damp:

[0047] T1=-102.2017+0.28098*I+1.2651*T

[0048] T2=-98.1389+0.26863*I+1.2536*T

[0049] When the outer surface of the terminal is dirty:

[0050] T1=-96.4048+0.27919*I+1.2633*T

[0051] T2=-85.4795+0.26554*I+1.2502*T.

[0052] Step 5: When applying in the field, adjust the load current I according to the actual load current. f (A) Ambient temperature T f (°C) The theoretically calculated maximum surface temperature T during normal operation is obtained. 2nThe highest temperature T on the outer surface when the insulation is damp inside. 2i The highest surface temperature T when the outer surface of the insulation is dirty 2o .

[0053] T 2n =-100.7055+0.26899*I+1.2539*T

[0054] T 2i =-98.1389+0.26863*I+1.2536*T

[0055] T 2o =-85.4795+0.26554*I+1.2502*T.

[0056] Step 6: Calculate the measured highest temperature T on the outer surface. 2f (°C) and the highest temperature of the outer surface under normal conditions (T) 2n The highest temperature T on the outer surface when the insulation is damp inside. 2i The highest surface temperature T when the outer surface of the insulation is dirty 2o The ratio of .

[0057] ratio1 = abs(T) 2f -T 2n ) / T 2n

[0058] ratio2=abs(T 2f -T 2i ) / T 2i

[0059] ratio3=abs(T 2f -T 2o ) / T 2o .

[0060] When ratio1 is the smallest, it is inferred that the terminal is not abnormal; when ratio2 is the smallest, it is inferred that the internal insulation interface of the terminal may be damp; when ratio3 is the smallest, it is inferred that there may be dirt on the outer surface of the terminal.

[0061] Step 7: Select the terminal that may be in the corresponding operating condition based on the smallest of the three ratios.

[0062] Step 8: Based on the determined operating conditions, select the highest temperature relationship of the internal insulation interface under the corresponding conditions to obtain the highest temperature T of the internal insulation interface. 1f .

[0063] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.

Claims

1. A method for calculating abnormal temperature points at the internal insulation interface of a cable heat-shrinkable terminal, characterized in that: Includes the following steps: Step 1: Build a simulation model of the heat shrink terminal; Step 2: Simulate three operating conditions: normal condition, moisture on the internal insulation interface of the terminal, and dirt on the outer surface of the terminal. Step 3: By adjusting the load current I and the ambient temperature T, the highest internal insulation temperature T1 and the highest terminal outer surface temperature T2 under three operating conditions are obtained. Step 4: Using MATLAB software, linearly fit the relationships between the highest internal insulation temperature T1, the highest external surface temperature T2, the load current I, and the ambient temperature T under the three operating conditions of the terminal. When the terminal is running normally: T1 = -105.5741 + 0.282 * I + 1.2661 * T T2 = -100.7055 + 0.26899 * I + 1.2539 * T When the internal insulation interface of the terminal is damp: T1 = -102.2017 + 0.28098 * I + 1.2651 * T T2 = -98.1389 + 0.26863 * I + 1.2536 * T When the outer surface of the terminal is dirty: T1 = -96.4048 + 0.27919 * I + 1.2633 * T T2 = -85.4795 + 0.26554 * I + 1.2502 * T Step 5: When applying in the field, adjust the load current I according to the actual load current. f Ambient temperature T f The theoretically calculated maximum surface temperature T during normal operation was obtained. 2n The highest temperature T on the outer surface when the insulation is damp inside. 2i The highest surface temperature T when the outer surface of the insulation is dirty 2o ; T 2n = -100.7055 + 0.26899 * I + 1.2539 * T T 2i = -98.1389 + 0.26863 * I + 1.2536 * T T 2o = -85.4795 + 0.26554 * I + 1.2502 * T; Step 6: Calculate the measured highest temperature T on the outer surface. 2f Compared with the highest surface temperature T under normal conditions 2n The highest temperature T on the outer surface when the insulation is damp inside. 2i The highest surface temperature T when the outer surface of the insulation is dirty 2o The ratio; ratio1 = abs(T 2f - T 2n ) / T 2n ratio2 = abs(T 2f - T 2i ) / T 2i ratio3 = abs(T 2f - T 2o ) / T 2o Step 7: Based on the smallest of the three ratios, select the terminal that may be in the corresponding operating condition; Step 8: Based on the determined operating conditions, select the highest temperature relationship of the internal insulation interface under the corresponding conditions to obtain the highest temperature T of the internal insulation interface. 1f .

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