A method for testing space charge performance of direct current cable insulation material and an evaluation system thereof

Abstract

The application discloses a kind of test methods of DC cable insulation material space charge performance and evaluation system thereof, according to the breakdown electric field intensity E 击 With breakdown time t satisfy power index relation E 击 n t=C wherein C is constant, the breakdown time required under different breakdown electric field intensity is different, that is E n ·t1=E n ·t2, determine test electric field intensity E, according to test accuracy and test cost setting test time;Select the temperature of the maximum electric field distortion rate as test temperature, test the maximum value of electric field distortion rate δ of DC cable insulation material under positive and negative test electric field intensity E as the determination test result.The method test electric field intensity, time, temperature and electric field polarity is closer to the operating environment of cable insulation material, and the test result of space charge is more accurate, and the performance of cable insulation material is more reflected;For the selection of cable insulation material, avoid electric field distortion or cable line breakdown to cause safety accident.

Description

Technical Field

[0001] This invention relates to a test of the space charge properties of cable insulation materials, and more particularly to a test method and evaluation system for the space charge properties of DC cable insulation materials. Background Technology

[0002] In recent years, with the rapid development of DC power transmission technology, especially flexible DC power transmission technology, the transmission capacity and voltage levels of DC power transmission have been continuously increasing, placing higher demands on the performance of DC cable insulation materials. Under the influence of a DC electric field, cable insulation materials such as XLPE (cross-linked polyethylene) and PP (polypropylene) easily accumulate space charge, causing distortion of the local electric field. As the space charge accumulates to a certain extent, it can even lead to cable breakdown. Therefore, how to effectively evaluate the space charge performance of DC cable insulation materials has become an urgent problem to be solved.

[0003] The existing national standard GB / T 31489.1-2015 proposes a method for testing space charge performance at room temperature. However, the external test electric field used is the electric field of DC transmission operation, and the test time is only 60 minutes, which differs significantly from the actual operating conditions of DC cables. First, the operating temperature of DC transmission cable insulation materials can reach 70℃ or even 90℃, which is far higher than room temperature. Second, the accumulation of space charge in DC cable insulation materials is not only related to the external electric field, but also has a certain time accumulation effect, and the 60-minute test time is far shorter than the normal operating time of the cable. Third, during power transmission, there are two DC cables, one bearing a positive DC voltage and the other bearing a negative DC voltage. Considering only the space charge performance of the cable insulation material under a DC electric field of one polarity cannot reflect the true performance of the cable insulation material during DC transmission. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to more realistically simulate the environment of cable insulation materials during DC power transmission, accurately and effectively evaluate the space charge performance of DC cable insulation materials during power transmission, and provide a more accurate testing method and evaluation system.

[0005] Technical solution: The method for testing the space charge properties of DC cable insulation materials according to the present invention includes the following steps:

[0006] (a) Based on the breakdown electric field strength E of the DC cable insulation material 击 It has a power-law relationship with the breakdown time t: E 击 n t = C, where C is a constant, and the breakdown time required varies for different breakdown electric field strengths, i.e., E1. n ·t1=E n·t2, the measured electric field strength E is calculated using formula 1:

[0007]

[0008] In the formula, n is the life index of the cable insulation material, t1 is the operating life of the DC cable, E1 is the operating electric field strength of the DC cable, and t2 is the set test time for space charge.

[0009] (b) Determine the temperature that causes the maximum electric field distortion rate δ as the test temperature;

[0010] (c) Based on the test electric field strength E, test time t2, and test temperature determined in steps (a) and (b), detect the electric field distortion rate δ of the DC cable insulation material under positive and negative test electric field strengths E. + and δ - ;

[0011] (d) By comprehensively analyzing and comparing the electric field distortion rate δ under positive and negative test electric field strength E, the larger value of electric field distortion rate δ is taken as the test result.

[0012] Furthermore, the life index n of the DC cable insulation material is 10 to 15, and the operating life t1 of the DC cable is 30 to 40 years. The appropriate values ​​of n and t1 are selected according to the specifications of different DC cable insulation materials.

[0013] Furthermore, the space charge test time t2 is 6h-8h, which balances the accuracy of the test with the time cost of the test.

[0014] Furthermore, step (b) includes the following steps:

[0015] (b1) The lowest temperature T during the operation of the DC cable insulation material min and the highest temperature T max Several temperatures were taken in between, and the maximum electric field strength E of the cable insulation material at different temperatures was tested. max ;

[0016] (b2) The maximum electric field strength E obtained from step (b1) max Given the test electric field strength E determined in step (a), calculate the electric field distortion rate δ caused by space charge:

[0017]

[0018] (b3) The temperature at which the electric field distortion rate δ is the largest is taken as the test temperature of the space charge of the DC cable insulation material.

[0019] Furthermore, the T mentioned above max T is the temperature of the inner side of the cable insulation material near the cable conductor. minThis refers to the temperature of the outer side of the cable insulation material.

[0020] Furthermore, the space charge is tested at temperature T. max and T min Choose equal intervals, taking into account factors such as oven temperature control accuracy and number of tests, with a temperature interval of 1-3℃. In the early stages, the smaller the temperature interval, the better, as long as it is convenient to operate.

[0021] Furthermore, the E mentioned above max The performance of space charge in DC cable insulation materials is obtained by testing methods such as electroacoustic pulse method, pressure wave method, or thermal method.

[0022] Furthermore, step (c) calculates the electric field distortion rate δ based on the maximum electric field strength Emax of the cable insulation material at the test temperature:

[0023]

[0024] Furthermore, a space charge performance evaluation system for DC cable insulation materials using the above-mentioned testing method includes a test condition determination module for determining the test electric field strength, test time, and test temperature; a test module for testing the electric field distortion rate under positive and negative electric field strengths; and an evaluation module for comprehensively evaluating the space charge performance of DC cable insulation materials.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The test electric field strength, time and temperature are closer to the service environment of cable insulation materials, and the test results of space charge are more accurate and can better reflect the performance of cable insulation materials; 2. It comprehensively considers the influence of positive and negative electric field polarity on space charge performance during cable operation, and more accurately reflects the real situation of cable insulation materials during operation; 3. It provides a basis for the selection of cable insulation materials and avoids safety accidents caused by electric field distortion or cable breakdown; 4. It provides a theoretical basis and method for evaluating the space charge performance of cable insulation materials. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0028] Taking the space charge performance evaluation of ±535kV DC cable insulation materials as an example, the specific testing and evaluation methods include the following steps:

[0029] (a) Considering both testing accuracy and time cost, the space charge testing time is set to t2 = 8 hours. Based on a ±535kV DC cable with an insulation thickness of 29mm, the operating electric field E1 can be calculated to be 18.4kV / mm. The operating life of the insulation material for this specification of DC cable is approximately 30 years, therefore t1 = 262800 hours, and the lifespan index n = 15. The operating lifespan t1 and n values ​​differ for different cable specifications. According to Formula 1, the test electric field strength E = 36.8kV / mm is calculated.

[0030]

[0031] The E value is much lower than the short-time DC breakdown electric field of DC cable insulation material, which meets the test requirements.

[0032] (b) Determine the test temperature: Test the operating temperature T of the DC cable under full load. min =60℃ and T max =90℃. Considering factors such as oven temperature control accuracy and the number of tests, several temperatures were uniformly selected between 60℃ and 90℃ at 3℃ intervals. For ease of operation in the initial stage, the smaller the temperature interval, the better. The maximum electric field strength E of the cable insulation material at different temperatures was obtained by testing the space charge performance of the DC cable insulation material using the pressure wave method. max According to E max The electric field distortion rate δ at different temperatures is calculated using E, the test electric field strength E determined in step (a), according to Formula 2, as shown in Table 1.

[0033]

[0034] Table 1. Electric field distortion rate δ caused by space charge in DC cable insulation material at different temperatures.

[0035] <![CDATA[E max (kV / mm)]]> 39.8 40.2 40.7 40.6 40.3 40.0 39.7 39.4 39.1 39.0 38.7 δ(%) 8.2 9.3 10.6 10.3 9.5 8.6 7.8 7.1 6.3 6.1 5.2

[0036] As shown in Table 1, when the test temperature is 66℃, the electric field distortion rate δ caused by the space charge of the DC cable insulation material reaches a maximum of 10.6%. Therefore, 66℃ is selected as the reference temperature for space charge testing.

[0037] (c) Testing the electric field distortion rate δ of the DC cable insulation material under a positive test electric field strength E: Based on steps (a) and (b), determine the test time t2 = 8h, the test electric field E = 36.8kV / mm, and the test temperature T = 66℃. Test the space charge properties of the DC cable insulation material under a positive electric field E = 36.8kV / mm. max = 41.3 kV / mm. The electric field distortion rate δ can be calculated. + =12.2%.

[0038] Testing the electric field distortion rate of DC cable insulation material under a negative test electric field strength E: Based on steps (a) and (b), determine the test time t2 = 8h, the test electric field E = -36.8kV / mm, and the test temperature T = 66℃. Test the space charge properties of the DC cable insulation material under a negative electric field E = -36.8kV / mm. max =40.7kV / mm. The calculated electric field distortion rate δ- = 10.6%.

[0039] (d) By comprehensively analyzing and comparing the electric field distortion rate δ under positive and negative test electric field intensities E, the larger value of electric field distortion rate δ is selected. + =12.1% is the test result for the space charge performance of ±535kV DC cable insulation materials. Based on the space charge performance of cable insulation materials, more precise selection of transmission cable materials can be made to prevent safety accidents caused by electric field distortion or cable breakdown.

Claims

1. A method for testing the space charge properties of DC cable insulation materials, characterized in that, Includes the following steps: (a) According to the power-law relationship between the operating electric field strength and the service life of a DC cable, the service life of a DC cable varies under different operating electric field strengths, i.e., E1. n •t1=E n •t2, the measured electric field strength E is calculated using the formula: In the formula, n is the life index of the cable insulation material, t1 is the operating life of the DC cable, E1 is the operating electric field strength of the DC cable, and t2 is the set test time for space charge. (b) Determine the temperature that causes the maximum electric field distortion rate δ as the test temperature; (c) Based on the test electric field strength E, test time t2 and test temperature determined in steps (a) and (b), detect the electric field distortion rate δ of the DC cable insulation material under positive and negative test electric field strength E; (d) By comprehensively analyzing and comparing the electric field distortion rate δ under positive and negative test electric field strength E, the larger value of electric field distortion rate δ is taken as the test result; Step (b) includes the following steps: (b1) The lowest temperature T under the operating conditions of DC cable insulation material min and the highest temperature T max Several temperatures were taken in between, and the maximum electric field strength E of the cable insulation material at different temperatures was tested. max ; (b2) The maximum electric field strength E obtained according to step (b1) max Given the test electric field strength E determined in step (a), calculate the electric field distortion rate δ caused by space charge: ； (b3) The temperature at which the electric field distortion rate is the highest is taken as the test temperature of the space charge of the DC cable insulation material; Wherein, the T max T is the temperature of the inner side of the cable insulation material near the cable conductor. min This refers to the temperature of the outer side of the cable insulation material.

2. The method for testing the space charge properties of DC cable insulation materials according to claim 1, characterized in that, The life index n of the cable insulation material is 10~15.

3. The method for testing the space charge properties of DC cable insulation materials according to claim 1, characterized in that, The service life t1 of the DC cable is 30-40 years.

4. The method for testing the space charge properties of DC cable insulation materials according to claim 1, characterized in that, The space charge test time t2 is 6-8 hours.

5. The method for testing the space charge properties of DC cable insulation materials according to claim 1, characterized in that, The space charge test temperature is at T max and T min Select the temperature at equal intervals, with a test temperature interval of 1-3℃.

6. The method for testing the space charge properties of DC cable insulation materials according to claim 1, characterized in that, The E mentioned max The performance of space charge in DC cable insulation materials is obtained by testing the electroacoustic pulse method, pressure wave method, or thermal method.

7. A system for evaluating the space charge performance of DC cable insulation materials using the test method described in any one of claims 1-6, characterized in that, It includes a test condition determination module for determining the test electric field strength, test time, and test temperature; a test module for testing the electric field distortion rate under positive and negative electric field strengths; and an evaluation module for comprehensively evaluating the space charge performance of DC cable insulation materials.

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