A method for evaluating the current-carrying capacity of oil-immersed transformer bushings

Abstract

The present invention discloses a method for evaluating the current-carrying capacity of an oil-immersed transformer bushing, comprising the following steps: establishing a test platform for evaluating the current-carrying capacity of an oil-immersed transformer bushing, obtaining temperature data and insulation resistance data under different current load factors, and calculating the heat dissipation coefficient K on the outer surface of the bushing under different current load factors s , calculating the internal temperature rise coefficient K of the bushing under different current load factors i‑z , K i‑w , calculating the current-carrying capacity evaluation factor K of the bushing, and evaluating the current-carrying capacity of the oil-immersed transformer bushing under different current load factors. The advantages of the technical solution of the present invention are as follows: aiming at the over-current operation condition of the oil-immersed transformer bushing, a new method for evaluating the current-carrying capacity is proposed, which can accurately evaluate the current-carrying capacity of the oil-immersed transformer bushing and is helpful for the optimized design of the oil-immersed transformer bushing

Description

Technical Field

[0001] The invention relates to the field of online detection and fault diagnosis of electrical insulation, and in particular to a method for evaluating the current-carrying capacity of an oil-immersed transformer bushing. Background Art

[0002] With the rapid development of domestic power grids, the voltage level and capacity of power grids have also increased. Every year, a large number of transformers are put into operation to ensure the stable operation of the power system. Bushings, as key equipment for transformer outlets, are mainly used to connect power transformers and power system busbars. Their safe and stable operation is directly related to the power transformer and even the power supply reliability of the power system.

[0003] For the transformer bushing, its biggest function is to carry current. During operation, a large amount of Joule heat will be generated, which directly affects the aging state of the insulation inside the bushing. Internal overheating may cause insulation failure, greatly increasing the possibility of insulation breakdown, thus causing major accidents. It can be seen that the current carrying capacity of the transformer bushing is directly affected by the temperature rise. During the service of the transformer, it often faces overload operating conditions, which means that the current flowing through the bushing is higher than the rated current, which puts higher requirements on the current carrying capacity of the transformer bushing. Due to the incorrect assessment of the current carrying capacity of the transformer bushing, it operates under overcurrent conditions beyond the tolerance range, causing thermal failure inside the bushing, and ultimately leading to the transformer shutdown accident, which seriously affects the power supply reliability of the power system. Therefore, there is an urgent need for a method that can accurately evaluate the current carrying capacity of the transformer bushing. Summary of the invention

[0004] The present invention provides a method for evaluating the current-carrying capacity of an oil-immersed transformer bushing, which can realize accurate evaluation of the current-carrying capacity of the oil-immersed transformer bushing.

[0005] A method for evaluating the current carrying capacity of an oil-immersed transformer bushing comprises the following steps:

[0006] Step 1: Establish a test platform for evaluating the current carrying capacity of oil-immersed transformer bushings

[0007] The oil-immersed transformer bushing overload capacity evaluation test platform comprises: a constant temperature test chamber (1), a test bushing (2), epoxy impregnated paper (3), a bushing sheath (4), a central current-carrying conductor (5), a constant temperature oil tank (6), transformer oil (7), a middle layer temperature sensor array (8), an outer layer temperature sensor array (9), a sheath surface temperature sensor array (10), a bushing bottom temperature sensor array (11), a transformer oil temperature monitoring sensor (12), an ambient temperature monitoring sensor (13), an insulation resistance tester (14), a grounding point (15), a data processing terminal (16), and an adjustable AC power supply (17);

[0008] On the right side of the constant temperature test chamber (1), three ambient temperature monitoring sensors (13) connected to the data processing terminal (16) are installed to monitor the internal temperature of the constant temperature test chamber (1) in real time; inside the test bushing (2), a middle layer temperature sensor array (8) and an outer layer temperature sensor array (9) connected to the data processing terminal (16) are arranged to respectively monitor the surface temperature of the central current-carrying conductor (5) and the surface temperature of the epoxy impregnated paper (3) in real time. The number of sensors included in both the middle layer temperature sensor array (8) and the outer layer temperature sensor array (9) is M, and they are numbered 1, 2, 3, …, m from bottom to top, where m ∈ [1, M]; on the surface of the bushing sheath petticoat (4), a petticoat surface temperature sensor array (10) connected to the data processing terminal (16) is installed to monitor the surface temperature of the bushing sheath petticoat (4) in real time. The number of petticoat pieces included in the bushing sheath petticoat (4) is N, and correspondingly, the number of sensors included in the petticoat surface temperature sensor array (10) is also N, and they are numbered 1, 2, 3, …, n from bottom to top, where n ∈ [1, N]; the constant temperature oil tank (6) is filled with transformer oil (7). To monitor the temperature of the transformer oil (7) in real time, three transformer oil temperature monitoring sensors (12) connected to the data processing terminal (16) are installed in the constant temperature oil tank (6); the bottom of the test bushing (2) is immersed in the transformer oil (7), and a bushing bottom temperature sensor array (11) connected to the data processing terminal (16) is installed at the bottom of the test bushing (2). The bushing bottom temperature sensor array (11) includes H sensors, which are numbered 1, 2, 3, …, h from bottom to top, where h ∈ [1, H]; one end of the insulation resistance tester (14) is connected to the central current-carrying conductor (5) of the test bushing (2), and the other end is connected to the ground point (15) to measure the conductor-to-ground insulation resistance of the test bushing (2); the adjustable AC power supply (17) is used to supply power to the test bushing (2), the insulation resistance tester (14) and the data processing terminal (16).

[0009] Step 2: Obtain the temperature data and insulation resistance data under different load factors

[0010] Set the temperature of the constant temperature test chamber (1) to T A , in units of K. When the temperature difference between any two of the three ambient temperature monitoring sensors (13) is less than 1 K, it is considered that the internal temperature of the constant temperature test chamber (1) has reached stability; set the temperature of the constant temperature oil tank (6) to T B , in units of K. When the temperature difference between any two of the three transformer oil temperature monitoring sensors (12) is less than 1 K, it is considered that the internal temperature of the constant temperature oil tank (6) has reached stability; after the internal temperatures of both the constant temperature test chamber (1) and the constant temperature oil tank (6) have reached stability, turn on the insulation resistance tester (14) to measure the conductor-to-ground insulation resistance of the test bushing (2), and record it as R f , in units of 1013 Ω·m, immediately cut off the power supply of the insulation resistance tester (14) after the data recording is completed;

[0011] After completing the above operations, sequentially set the effective value of the output current of the adjustable AC power supply (17) to I 1.0 、I 1.1 、I 1.2 …I 1.9 、I 2.0 , with the unit of A, corresponding to the current load factors a = 1.0, 1.1, 1.2…1.9, 2.0 in sequence, where I 1.0 is the rated current of the test bushing (2);

[0012] The test bushing (2) operates at I a . When the fluctuation range of the temperature values obtained by the middle layer temperature sensor array (8), the outer layer temperature sensor array (9), the petticoat surface temperature sensor array (10) and the bushing bottom temperature sensor array (11) is less than 0.5 K, it is considered that the test bushing (2) has reached a stable state, and record the time taken for the test bushing (2) to reach the stable state from startup, recorded as t a , with the unit of hour; record the temperature data obtained by the middle layer temperature sensor array (8), and record them sequentially from bottom to top as T z-a-1 、T z-a-2 、T z-a-3 …T z-a-m , and the maximum value is recorded as T z-a-max ; record the temperature data obtained by the outer layer temperature sensor array (9), and record them sequentially from bottom to top as T w-a-1 、T w-a-2 、T w-a-3 …T w-a-m , and the maximum value is recorded as T w-a-max ; record the temperature data obtained by the petticoat surface temperature sensor array (10), and record them sequentially from bottom to top as T s-a-1 、T s-a-2 、T s-a-3 …T s-a-n , and the maximum value is recorded as T s-a-max ; record the temperature data obtained by the bushing bottom temperature sensor array (11), and record them sequentially from bottom to top as T d-a-1 、T d-a-2 、T d-a-3 …T d-a-h , and the maximum value is recorded as T d-a-max ; after recording the above data, cut off the power supply of the test bushing (2), and then turn on the insulation resistance tester (14) to measure the conductor-to-ground insulation resistance of the test bushing (2), recorded as R a ;

[0013] Step 3: Calculate the heat dissipation coefficient K on the outer surface of the bushing under different current load factors s

[0014]

[0015] If T d-a-h = T B , then the test data of this time is invalid, and it is necessary to check and retest until T d-a-h ≠ T B ;

[0016] Step 4: Calculate the temperature rise coefficient K inside the bushing under different current load factors i-z , K i-w

[0017]

[0018] If R a = R f , then the test data of this time is invalid, and it is necessary to check and retest until R a ≠ R f ;

[0019] Step 5: Calculate the current-carrying capacity evaluation factor K of the bushing

[0020]

[0021] Step 6: Evaluate the current-carrying capacity of the oil-immersed transformer bushing under different current load factors

[0022] If 0 ≤ K < 0.5, it indicates that the transformer bushing can operate short-term under the overload condition with the current load factor of a; if θ ≥ 0.5, it indicates that the transformer bushing cannot operate under the overload condition with the current load factor of a

[0023] The advantage of the technical solution of the present invention is that for the over-current operation condition of the oil-immersed transformer bushing, a brand-new current-carrying capacity evaluation method is proposed, which can accurately evaluate the current-carrying capacity of the oil-immersed transformer bushing and contribute to the optimized design of the oil-immersed transformer bushing Brief Description of the Drawings

[0024] Figure 1 is a flow chart of a method for evaluating the current-carrying capacity of an oil-immersed transformer bushing involved in the present invention

[0025] Figure 2 is a structural schematic diagram of a test platform for evaluating the current-carrying capacity of an oil-immersed transformer bushing involved in the present invention Detailed Embodiments

[0026] The implementation process of the present invention will be further described in detail below with reference to the accompanying drawings. It should be emphasized that the specific implementation cases described herein are only used to explain the present invention and do not limit the scope of the inventive concept and its claims.

[0027] Step 1: Establish an evaluation test platform for the current-carrying capacity of oil-immersed transformer bushings

[0028] The evaluation test platform for the overload capacity of oil-immersed transformer bushings includes: a constant-temperature test chamber (1), a test bushing (2), epoxy-impregnated paper (3), bushing sheath petticoats (4), a central current-carrying conductor (5), a constant-temperature oil tank (6), transformer oil (7), a middle-layer temperature sensor array (8), an outer-layer temperature sensor array (9), a petticoat surface temperature sensor array (10), a bushing bottom temperature sensor array (11), a transformer oil temperature monitoring sensor (12), an ambient temperature monitoring sensor (13), an insulation resistance tester (14), a grounding point (15), a data processing terminal (16), and an adjustable AC power supply (17);

[0029] On the right side of the constant temperature test chamber (1), there are 3 environmental temperature monitoring sensors (13) connected to the data processing terminal (16) to monitor the internal temperature of the constant temperature test chamber (1) in real time; inside the test sleeve (2), there is a middle layer temperature sensor array (8) and an outer layer temperature sensor array (9) connected to the data processing terminal (16) to respectively monitor the surface temperature of the central current-carrying conductor (5) and the surface temperature of the epoxy-impregnated paper (3) in real time. The number of sensors included in both the middle layer temperature sensor array (8) and the outer layer temperature sensor array (9) is M = 36, and they are numbered 1, 2, 3, …, m from bottom to top, where m ∈ [1, M]; on the surface of the sleeve sheath umbrella skirt (4), there is an umbrella skirt surface temperature sensor array (10) connected to the data processing terminal (16) to monitor the surface temperature of the sleeve sheath umbrella skirt (4) in real time. The number of umbrella skirt pieces included in the sleeve sheath umbrella skirt (4) is N = 20, corresponding to the number of sensors included in the umbrella skirt surface temperature sensor array (10) also being N, and they are numbered 1, 2, 3, …, n from bottom to top, where n ∈ [1, N]; the constant temperature oil tank (6) is filled with transformer oil (7). To achieve real-time monitoring of the temperature of the transformer oil (7), 3 transformer oil temperature monitoring sensors (12) connected to the data processing terminal (16) are installed in the constant temperature oil tank (6); the bottom of the test sleeve (2) is immersed in the transformer oil (7), and a sleeve bottom temperature sensor array (11) connected to the data processing terminal (16) is installed at the bottom of the test sleeve (2). The sleeve bottom temperature sensor array (11) includes H = 11 sensors, numbered 1, 2, 3, …, h from bottom to top, where h ∈ [1, H]; one end of the insulation resistance tester (14) is connected to the central current-carrying conductor (5) of the test sleeve (2), and the other end is connected to the ground point (15) to measure the conductor-to-ground insulation resistance of the test sleeve (2); the adjustable AC power supply (17) is used to supply power to the test sleeve (2), the insulation resistance tester (14), and the data processing terminal (16).

[0030] Step 2: Obtain temperature data and insulation resistance data under different load factors

[0031] Set the temperature of the constant temperature test chamber (1) to T A = 300K. When the temperature difference between any two of the 3 environmental temperature monitoring sensors (13) is less than 1K, it is considered that the internal temperature of the constant temperature test chamber (1) has reached stability; set the temperature of the constant temperature oil tank (6) to T B = 350K. When the temperature difference between any two of the 3 transformer oil temperature monitoring sensors (12) is less than 1K, it is considered that the internal temperature of the constant temperature oil tank (6) has reached stability; after the internal temperatures of both the constant temperature test chamber (1) and the constant temperature oil tank (6) have reached stability, turn on the insulation resistance tester (14) to measure the conductor-to-ground insulation resistance of the test sleeve (2) and record it as R f in units of 1013 Ω·m, immediately disconnect the power supply of the insulation resistance tester (14) after the data recording is completed;

[0032] After completing the above operations, sequentially set the effective value of the output current of the adjustable AC power supply (17) to I 1.0 、I 1.1 、I 1.2 …I 1.9 、I 2.0 , with the unit of A, corresponding to the current load factors a = 1.0, 1.1, 1.2…1.9, 2.0 in sequence, where I 1.0 is the rated current of the test bushing (2);

[0033] The test bushing (2) operates at I 1.5 . When the fluctuation range of the temperature values obtained by the middle layer temperature sensor array (8), the outer layer temperature sensor array (9), the petticoat surface temperature sensor array (10) and the bushing bottom temperature sensor array (11) is less than 0.5K, it is considered that the test bushing (2) has reached a stable state, and record the time taken for the test bushing (2) to reach the stable state from startup, recorded as t 1.5 , with the unit of hour; record the temperature data obtained by the middle layer temperature sensor array (8), and record them sequentially from bottom to top as T z-1.5-1 、T z-1.5-2 、T z-1.5-3 …T z-1.5-36 , and the maximum value is recorded as T z-1.5-max ; record the temperature data obtained by the outer layer temperature sensor array (9), and record them sequentially from bottom to top as T w-1.5-1 、T w-1.5-2 、T w-1.5-3 …T w-1.5-36 , and the maximum value is recorded as T w-1.5-max ; record the temperature data obtained by the petticoat surface temperature sensor array (10), and record them sequentially from bottom to top as T s-1.5-1 、T s-1.5-2 、T s-1.5-3 …T s-1.5-20 , and the maximum value is recorded as T s-1.5-max ; record the temperature data obtained by the bushing bottom temperature sensor array (11), and record them sequentially from bottom to top as T d-1.5-1 、T d-1.5-2 、T d-1.5-3 …T d-1.5-11 , and the maximum value is recorded as T d-1.5-max ; after recording the above data, disconnect the power supply of the test bushing (2), and then turn on the insulation resistance tester (14) to measure the conductor - ground insulation resistance of the test bushing (2), recorded as R 1.5 ;

[0034] Step 3: Calculate the heat dissipation coefficient K of the outer surface of the bushing under different current load factors s

[0035] Substitute the temperature data of the umbrella skirt surface temperature sensor and the insulation resistance data obtained in the second step into the following formula to calculate the heat dissipation coefficient K of the outer surface of the bushing s , when the current load factor a = 1.5, calculate to obtain K s = 2.6232;

[0036]

[0037] Step 4: Calculate the temperature rise coefficient K of the inside of the bushing under different current load factors i-z 、K i-w

[0038] Substitute the temperature data of the middle layer temperature sensor and the outer layer temperature sensor obtained in the second step into the following formula to calculate the temperature rise coefficient K of the inside of the bushing i-z 、K i-w , when the current load factor a = 1.5, calculate to obtain K i-z = 35.1065、K i-w = 29.7525;

[0039]

[0040] Step 5: Calculate the current-carrying capacity evaluation factor K of the bushing

[0041] Substitute the heat dissipation coefficient K of the outer surface of the bushing calculated in the third step s and the temperature rise coefficient K of the inside of the bushing calculated in the fourth step i-z 、K i-w into the following formula to calculate the current-carrying capacity evaluation factor K of the bushing, and obtain K = 0.3198;

[0042]

[0043] Step 6: Evaluate the current-carrying capacity of the oil-immersed transformer bushing under different current load factors. When the current load factor a = 1.5, the calculated current-carrying capacity evaluation factor of the bushing is 0 ≤ K < 0.5, indicating that the transformer bushing can operate short-term under the overload condition with the current load factor a

[0044] The above examples are only for the introduction and explanation of the present invention and do not cover all its protection scope. Any non-creative modifications, improvements, etc. based on the present invention fall within the protection scope of its claims

Claims

1. A method for evaluating the current-carrying capacity of an oil-immersed transformer bushing, characterized in that, The steps include the following: Step 1: Establish a test platform for evaluating the current-carrying capacity of oil-immersed transformer bushings The test platform for evaluating the overload capacity of oil-immersed transformer bushings includes: a constant-temperature test chamber (1), a test bushing (2), epoxy-impregnated paper (3), bushing sheath umbrella skirts (4), a central current-carrying conductor (5), a constant-temperature oil tank (6), transformer oil (7), a middle-layer temperature sensor array (8), an outer-layer temperature sensor array (9), an umbrella skirt surface temperature sensor array (10), a bushing bottom temperature sensor array (11), a transformer oil temperature monitoring sensor (12), an ambient temperature monitoring sensor (13), an insulation resistance tester (14), a grounding point (15), a data processing terminal (16), and an adjustable AC power supply (17); On the right side of the constant-temperature test chamber (1), there are 3 ambient temperature monitoring sensors (13) connected to the data processing terminal (16) for real-time monitoring of the internal temperature of the constant-temperature test chamber (1); inside the test bushing (2), there are a middle-layer temperature sensor array (8) and an outer-layer temperature sensor array (9) connected to the data processing terminal (16) to respectively achieve real-time monitoring of the surface temperature of the central current-carrying conductor (5) and the epoxy-impregnated paper (3). The number of sensors in both the middle-layer temperature sensor array (8) and the outer-layer temperature sensor array (9) is M, numbered from bottom to top as 1, 2, 3, …, m, where m ∈ [1, M]; on the surface of the bushing sheath umbrella skirts (4), there is an umbrella skirt surface temperature sensor array (10) connected to the data processing terminal (16) to achieve real-time monitoring of the surface temperature of the bushing sheath umbrella skirts (4). The number of umbrella skirt pieces in the bushing sheath umbrella skirts (4) is N, corresponding to the number of sensors in the umbrella skirt surface temperature sensor array (10) also being N, numbered from bottom to top as 1, 2, 3, …, n, where n ∈ [1, N]; the constant-temperature oil tank (6) is filled with transformer oil (7). To achieve real-time monitoring of the temperature of the transformer oil (7), there are 3 transformer oil temperature monitoring sensors (12) installed in the constant-temperature oil tank (6) and connected to the data processing terminal (16); the bottom of the test bushing (2) is immersed in the transformer oil (7), and a bushing bottom temperature sensor array (11) connected to the data processing terminal (16) is installed at the bottom of the test bushing (2). The bushing bottom temperature sensor array (11) contains H sensors, numbered from bottom to top as 1, 2, 3, …, h, where h ∈ [1, H]; one end of the insulation resistance tester (14) is connected to the central current-carrying conductor (5) of the test bushing (2), and the other end is connected to the grounding point (15) for measuring the conductor-to-ground insulation resistance of the test bushing (2); the adjustable AC power supply (17) is used to supply power to the test bushing (2), the insulation resistance tester (14), and the data processing terminal (16); Step 2: Obtain temperature data and insulation resistance data under different load factors Set the temperature of the constant temperature test chamber (1) to T A , in units of K. When the temperature difference between any two of the three ambient temperature monitoring sensors (13) is less than 1K, it is considered that the internal temperature of the constant temperature test chamber (1) has reached stability; set the temperature of the constant temperature oil tank (6) to T B , in units of K. When the temperature difference between any two of the three transformer oil temperature monitoring sensors (12) is less than 1K, it is considered that the internal temperature of the constant temperature oil tank (6) has reached stability; after the internal temperatures of both the constant temperature test chamber (1) and the constant temperature oil tank (6) have stabilized, turn on the insulation resistance tester (14) to measure the conductor-to-ground insulation resistance of the test bushing (2), and record it as R f , in units of 10 13 Ω·m. Immediately disconnect the power supply of the insulation resistance tester (14) after the data recording is completed; After the above operations are completed, the effective value of the output current of the adjustable AC power supply (17) is set to I 1.0 , I 1.1 , I 1.2 … I 1.9 , I 2.0 , in units of A, corresponding to the current load factors a = 1.0, 1.1, 1.2… 1.9, 2.0 in sequence, where I 1.0 is the rated current of the test bushing (2); The test casing (2) operates in I a When the temperature value fluctuation ranges obtained by the middle layer temperature sensor array (8), the outer layer temperature sensor array (9), the petticoat surface temperature sensor array (10) and the casing bottom temperature sensor array (11) are less than 0.5 K, it is considered that the test casing (2) has reached a stable state, and the time taken for the test casing (2) to reach the stable state from startup is recorded, denoted as t a , in hours; Record the temperature data obtained by the middle layer temperature sensor array (8), and record them sequentially from bottom to top as T z-a-1 、T z-a-2 、T z-a-3 …T z-a-m , and the maximum value is denoted as T z-a-max ; Record the temperature data obtained by the outer layer temperature sensor array (9), and record them sequentially from bottom to top as T w-a-1 、T w-a-2 、T w-a-3 …T w-a-m , and the maximum value is denoted as T w-a-max ; Record the temperature data obtained by the surface temperature sensor array (10) of the umbrella skirt, and record them as T successively from bottom to top s-a-1 , T s-a-2 , T s-a-3 …T s-a-n , and record the maximum value as T s-a-max ; Record the temperature data obtained by the bottom temperature sensor array (11) of the bushing, and record them as T successively from bottom to top d-a-1 , T d-a-2 , T d-a-3 …T d-a-h , and record the maximum value as T d-a-max ; After recording the above data, disconnect the power supply of the test bushing (2), and then turn on the insulation resistance tester (14) to measure the insulation resistance between the conductor and the ground of the test bushing (2), and record it as R a ; Step 3: Calculate the heat dissipation coefficient K on the outer surface of the casing under different current load factors s If T d-a-h = T B , then the data of this test is invalid, and it is necessary to check and retest until T d-a-h ≠ T B ; Step 4: Calculate the internal temperature rise coefficient K of the bushing under different current load factors i-z , K i-w If R a = R f , the data of this test is invalid, and it is necessary to check and retest until R a ≠ R f ; Step 5: Calculate the bushing current-carrying capacity evaluation factor K Step 6: Evaluate the current-carrying capacity of oil-immersed transformer bushings under different current load factors If 0 ≤ K < 0.5, it indicates that the transformer bushing can operate short-term under the overload condition with a current load factor of a; if θ ≥ 0.5, it indicates that the transformer bushing cannot operate under the overload condition with a current load factor of a.

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