Production method of distribution transformer and detection method for over-tolerance of load loss

Abstract

The present invention discloses a production method of a distribution transformer. By setting a specific measurement method, the resistance loss of the transformer body can be determined before the transformer body assembly enters the drying oven, so as to discover in advance the problem of excessive load loss, which facilitates the staff to take corresponding measures in advance to reduce the load loss. Compared with the prior art in which the load loss is measured only after the transformer assembly is completed, a series of time-consuming and laborious operations such as draining oil, lifting the core for the second time, and re-entering the drying oven are not required. The staff can directly weld magnetic isolation electrodes or magnetic isolation pads on the transformer tank cover (when the excessive load loss does not exceed 15 W, weld magnetic isolation electrodes for isolation treatment; when the excessive load loss is greater than 15 W and does not exceed 55 W, weld a whole magnetic isolation pad for non-magnetization treatment), which greatly reduces the labor intensity of the staff and saves labor costs. Correspondingly, the present invention also provides a detection method for excessive load loss of a distribution transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution transformers, and specifically relates to a production method of a distribution transformer and a method for detecting over-tolerance of load loss. Background Art

[0002] A distribution transformer is a static electrical appliance in a distribution system that transforms AC voltage and current according to the law of electromagnetic induction and transmits AC electric energy. Its operating state is directly related to the stable operation of the distribution network. The loss state of a distribution transformer is an important factor affecting the operating state of the transformer. When the loss of the transformer is high, its working temperature will gradually rise, accelerating the aging speed of the internal insulation structure of the transformer and reducing the reliability of the transformer operation. The losses of the transformer can be divided into no-load loss and load loss; among them, the load loss is also called copper loss, which is the loss generated by the internal windings of the transformer under load conditions. Before the transformer leaves the factory, its load loss is measured. In the prior art, after the transformer is assembled, the low-voltage side of the transformer is short-circuited, and the rated current is sent into the high-voltage side, and then the load loss of the transformer is measured. However, the load loss is the load loss at the rated current and the participating temperature, and during the operation of the transformer, the temperature and the load current will change. Therefore, there will be a certain difference between the measured load loss and the standard load loss. When there is an over-tolerance of the load loss, corresponding measures need to be taken to reduce the load loss. Currently, the commonly used treatment method is as follows: if the over-tolerance does not exceed 15W, stainless steel electrodes are welded between the adjacent two low-voltage bushings on the transformer tank cover for magnetic isolation; if the over-tolerance is between 16W and 55W, a whole non-magnetic steel plate is welded at the low-voltage bushing opening on the transformer tank cover. Since the corresponding treatment is carried out on the transformer tank cover, the assembled transformer needs to be disassembled. At this time, a series of operations such as draining oil, secondary core lifting, and re-entering the drying oven are required, which is time-consuming and laborious. Summary of the Invention

[0003] In order to overcome the above problems existing in the prior art, the present invention provides a production method of a distribution transformer. Before the transformer core is assembled and enters the drying oven, its resistance is measured, and the resistance loss is calculated through a specific calculation method to detect the over-tolerance problem of the load loss in advance, so that the staff can take corresponding measures in advance to reduce the load loss. Compared with measuring the load loss after the transformer is assembled in the prior art, a series of time-consuming and laborious operations such as draining oil, secondary core lifting, and re-entering the drying oven are not required, greatly reducing the labor intensity of the staff and saving labor costs. Correspondingly, the present application also provides a method for detecting over-tolerance of load loss of a distribution transformer. Before the transformer core is assembled and enters the drying oven, its resistance is measured and the resistance loss is calculated to detect the over-tolerance problem of the load loss in advance.

[0004] For the production method of a distribution transformer, the present application provides the following technical solutions:

[0005] A production method of a distribution transformer, wherein the high-voltage coil of the transformer is a wire-wound coil and the low-voltage coil is a foil-wound coil; in this production method, before the transformer body assembly is completed and enters the drying oven, its resistance is measured and the resistance loss is calculated to detect in advance the problem of excessive load loss; when there is excessive load loss, corresponding treatment is carried out to reduce the load loss; the specific steps are as follows:

[0006] S1, Select one of the transformer bodies, measure its three-phase high-voltage resistance and three-phase low-voltage resistance at the ambient temperature T1, and calculate the average high-voltage resistance R H1 and the average low-voltage resistance R L1 ; According to the formula P1 = 1.5 * I 2 *R1, where I is the rated current, calculate the high-voltage resistance loss P H1 and the low-voltage resistance loss P L1 respectively, and the total resistance loss P r = P H1 + P L1 ; Then according to the formula P2 = K1 * P1, K1 = (235 + t) / (235 + T1), convert to obtain the high-voltage resistance loss P H2 and the low-voltage resistance loss P L2 at the standard operating temperature t, and the total resistance loss P k1 = P H2 + P L2 ;

[0007] S2, Select a finished transformer after assembly and measure the load loss P s ;

[0008] S3, Calculate the additional loss P f , P f = P s - P k1 ; According to the additional loss, it can be known that the resistance loss of the transformer body at the temperature t must be less than P b - P f = P t , P b is the standard load loss; since the low-voltage coil is a foil-wound coil and the low-voltage resistance loss is basically unchanged and can be ignored, the high-voltage resistance loss P hb at the temperature t = P t - P L2 , and the average high-voltage resistance R Ht must be less than P hb / (1.5 * I 2 ), R Ht = R H1 * K1, with Phb As the standard high - voltage resistance loss;

[0009] S4. At the ambient temperature T2, measure the three - phase high - voltage resistances of the other transformer cores to be detected, and calculate the average high - voltage resistance R H2 ; According to the formula P3 = 1.5 * I 2 * R2, where I is the rated current, calculate the high - voltage resistance loss P H3 ; Then according to the formula P4 = K2 * P3, K2=(235 + t) / (235 + T2), convert to obtain the high - voltage resistance loss P at the temperature t H4 ;

[0010] S5. Compare the high - voltage resistance loss P in step S4 H4 with the standard high - voltage resistance loss P in step S3 hb ; When P H4 - P hb ≤15W, between two adjacent low - voltage bushing mounting holes on the transformer cover, weld magnetic - isolation electrodes for partition treatment; when 15W < P H4 - P hb ≤55W, on the transformer cover, at the position corresponding to the low - voltage bushing mounting holes, weld a whole magnetic - isolation backing plate for non - magnetization treatment.

[0011] The production method of the distribution transformer in this application measures its resistance before the transformer core is assembled and enters the drying oven, and calculates the resistance loss through a specific calculation method to discover the problem of excessive load loss in advance, so that the staff can take corresponding measures in advance to reduce the load loss (when the load loss exceeds the standard by no more than 15W, between two adjacent low - voltage bushing mounting holes on the transformer cover, weld magnetic - isolation electrodes for partition treatment; when the load loss exceeds the standard by 16W - 55W, on the transformer cover, at the position corresponding to the low - voltage bushing mounting holes, weld a whole magnetic - isolation backing plate for non - magnetization treatment); compared with the prior art where the load loss is measured only after the transformer is assembled, it does not require a series of time - consuming and labor - intensive operations such as draining oil, secondary core lifting, and re - entering the drying oven, greatly reducing the labor intensity of the staff and saving labor costs.

[0012] As an optimization, in step S2, the specific measurement process of the load loss P s is as follows:

[0013] Short - circuit the low - voltage side of the transformer finished product, and input more than 50% of the rated current on the high - voltage side; measure the voltage U t , current I t and resistance loss P t at the temperature T1 through a power analyzer; according to the formula P kt = P t*(I / I t ) 2 , calculate the resistance loss P at the rated current kt ; Then according to the formula P s = K1 * P r + (P kt - P r ) / K1, convert to obtain the load loss P at the standard operating temperature t s .

[0014] As an optimization, in step S4, when welding the magnetic isolation electrode, a 4 - mm - wide gap can be opened respectively between adjacent two low - voltage bushing mounting holes on the transformer tank cover first, and then the magnetic isolation electrode is welded into the gap; when welding the magnetic isolation backing plate, a square hole can be opened at the position corresponding to the low - voltage bushing mounting hole on the transformer tank cover first, and then the magnetic isolation backing plate is welded into the square hole; the magnetic isolation electrode and the magnetic isolation backing plate can be made of non - magnetic steel plate; the thickness of the magnetic isolation electrode and the magnetic isolation backing plate can be the same as the thickness of the transformer tank cover. At this time, it is convenient to process, the process difficulty is low, and the performance of the transformer tank cover in terms of power frequency withstand voltage and strength can be guaranteed, ensuring the use stability of the transformer tank cover.

[0015] For the detection method of the over - tolerance of the load loss of the distribution transformer, the technical solution of this application is:

[0016] The detection method of the over - tolerance of the load loss of the distribution transformer, which measures its resistance and calculates the resistance loss before the transformer body assembly enters the drying oven to discover the problem of over - tolerance of the load loss in advance. The specific steps are as follows:

[0017] S1, select one of the transformer bodies, measure its three - phase high - voltage resistance and three - phase low - voltage resistance at the ambient temperature T1, and calculate the average high - voltage resistance R H1 and the average low - voltage resistance R L1 ; According to the formula P1 = 1.5 * I 2 * R1, where I is the rated current, calculate the high - voltage resistance loss P H1 and the low - voltage resistance loss P L1 respectively, and the total resistance loss P r = P H1 + P L1 ; Then according to the formula P2 = K1 * P1, K1 = (235 + t) / (235 + T1), convert to obtain the high - voltage resistance loss P H2 and the low - voltage resistance loss P L2 at the standard operating temperature t, and the total resistance loss P k1 = P H2 + P L2 ;

[0018] S2. Select a completed assembled transformer finished product and measure the load loss P s ;

[0019] S3. Calculate the additional loss P f , P f = P s - P k1 ; According to the additional loss, it can be known that the resistance loss of the transformer body at temperature t must be less than P b - P f = P t , P b is the standard load loss; Since the low - voltage resistance loss is basically unchanged and can be ignored, then the high - voltage resistance loss P hb = P t - P L2 , and the average value of the high - voltage resistance R Ht must be less than P hb / (1.5 * I 2 ), R Ht = R H1 * K1, taking P hb as the standard high - voltage resistance loss;

[0020] S4. At the ambient temperature T2, measure the three - phase high - voltage resistance of the other transformer bodies to be detected, and calculate the average value of the high - voltage resistance R H2 ; According to the formula P3 = 1.5 * I 2 * R2, where I is the rated current, calculate the high - voltage resistance loss P H3 ; Then according to the formula P4 = K2 * P3, K2 = (235 + t) / (235 + T2), convert to obtain the high - voltage resistance loss P H4 at temperature t;

[0021] S5. Compare the high - voltage resistance loss P H4 in step S4 with the standard high - voltage resistance loss P hb in step S3; When P H4 is greater than P hb , it indicates that there is an over - tolerance of the load loss. On the contrary, it indicates that there is no over - tolerance of the load loss.

[0022] Compared with the prior art, the method for detecting over - tolerance of the load loss of the distribution transformer in this application selects one of the transformer bodies before the transformer body is assembled and enters the drying oven, measures its three - phase high - voltage resistance and three - phase low - voltage resistance, and obtains a standard high - voltage resistance loss value according to a specific calculation method. Then measure the high - voltage resistance of the other transformer bodies to be detected and calculate the high - voltage resistance loss value, and compare it with the standard high - voltage resistance loss value to discover the problem of over - tolerance of the load loss in advance. The operation is simple, convenient, and highly reliable.

[0023] As an optimization, in step S2, the load loss P s is measured as follows:

[0024] Short-circuit the low-voltage side of the finished transformer, and send a rated current of more than 50% to the high-voltage side; measure the voltage U t , current I t and resistance loss P t at temperature T1 through a power analyzer; according to the formula P kt = P t *(I / I t ), calculate the resistance loss P 2 under the rated current; then according to the formula P kt = K1 * P s + (P r - P kt ) / K r ), convert to obtain the load loss P t at the standard operating temperature t. s Description of the Drawings

[0025] Figure 1 is a flowchart of the method for detecting over-tolerance of the load loss of the distribution transformer in this application;

[0026] Figure 2 is a schematic diagram of the measurement principle of the load loss of the finished transformer in this application;

[0027] Figure 3 is a schematic diagram of the transformer cover after welding the magnetic isolation electrode;

[0028] Figure 4 is a schematic diagram of the transformer cover after welding the magnetic isolation backing plate.

[0029] The reference signs in the drawings are: 1 - transformer cover, 101 - low-voltage bushing mounting hole; 2 - magnetic isolation electrode; 3 - magnetic isolation backing plate; 4 - hot-rolled flat steel. Specific Embodiments

[0030] The following further describes this application in conjunction with the drawings and embodiments, but it is not used as a basis for limiting this application.

[0031] In the production method of the distribution transformer of this application, the high-voltage coil of the transformer is a wire-wound coil, and the low-voltage coil is a foil-wound coil; in this production method, before entering the drying oven after the transformer body assembly is completed, measure its resistance and calculate the resistance loss to detect the problem of over-tolerance of the load loss in advance; when there is over-tolerance of the load loss (exceeding the tolerance range specified in the product standard), perform corresponding processing (see the flowchart Figure 1 ), to reduce the load loss, and the specific steps are as follows:

[0032] S1. Select one transformer core and measure its three-phase high-voltage resistance and three-phase low-voltage resistance at the ambient temperature T1, and calculate the average high-voltage resistance R H1 and the average low-voltage resistance R L1 ; According to the formula P1 = 1.5 * I 2 * R1, where I is the rated current, calculate the high-voltage resistance loss P H1 and the low-voltage resistance loss P L1 , and the total resistance loss P r = P H1 + P L1 ; Then, according to the formula P2 = K1 * P1, where K1 = (235 + t) / (235 + T1), convert to obtain the high-voltage resistance loss P H2 and the low-voltage resistance loss P L2 at the standard operating temperature t, and the total resistance loss P k1 = P H2 + P L2 ;

[0033] S2. Select a finished transformer after assembly and measure the load loss P s ; The specific measurement process of the load loss P s is as follows:

[0034] Short-circuit the low-voltage side of the finished transformer and apply more than 50% of the rated current to the high-voltage side; Measure the voltage U t , current I t and resistance loss P t (see the measurement schematic diagram in Figure 2 ); According to the formula P kt = P t *(I / I t ), calculate the resistance loss P 2 at the rated current; Then, according to the formula P kt = K1 * P s +(P r - P kt - P r ) / K1, convert to obtain the load loss P s at the temperature t (the load loss P s shall not be greater than the standard load loss P b );

[0035] S3. Calculate the additional loss P f , P f = P s - P k1 ; According to the additional loss, the resistance loss of the transformer core at the temperature t must be less than P b - Pf = P t , P b is the standard load loss; since the low-voltage coil is a foil-wound coil and the low-voltage resistance loss is basically unchanged and negligible, the high-voltage resistance loss P at temperature t hb = P t - P L2 , and the average value of the high-voltage resistance R Ht must be less than P hb / (1.5 * I 2 ), R Ht = R H1 * K1, taking P hb as the standard high-voltage resistance loss (if the average value of the high-voltage resistance R Ht is greater than P hb / (1.5 * I 2 ), then at the position corresponding to the low-voltage bushing mounting hole 101 on the transformer tank cover 1, weld a whole piece of magnetic isolation backing plate 3 for non-magnetization treatment, and at the same time re-select a transformer core and repeat steps S1 - S3);

[0036] S4. Measure the three-phase high-voltage resistance of the transformer core to be tested at the ambient temperature T2, and calculate the average value of the high-voltage resistance R H2 ; According to the formula P3 = 1.5 * I 2 * R2, where I is the rated current, calculate the high-voltage resistance loss P H3 ; Then according to the formula P4 = K2 * P3, K2 = (235 + t) / (235 + T2), convert to obtain the high-voltage resistance loss P at temperature t H4 ;

[0037] S5. Compare the high-voltage resistance loss P H4 in step S4 with the standard high-voltage resistance loss P hb in step S3; When P H4 is greater than P hb (according to the product standard regulations, positive deviation is not allowed), it indicates that there is an over-limit load loss. On the contrary, it indicates that there is no over-limit load loss (load loss = resistance loss + additional loss; therefore, when the measured resistance loss value is greater than the standard resistance loss value, it can prove that there is an over-limit load loss); When P H4 - P hb ≤ 15W, weld a magnetic isolation electrode 2 between two adjacent low-voltage bushing mounting holes 101 on the transformer tank cover 1 for isolation treatment (see Figure 3 ); When 15W < P H4 - P hb ≤ 55W, at the position corresponding to the low-voltage bushing mounting hole 101 on the transformer tank cover 1, weld a whole piece of magnetic isolation backing plate 3 for non-magnetization treatment (see Figure 4)。These two processing methods can reduce the probability of magnetic flux leakage in the low-voltage bushing, thereby reducing the load loss.

[0038] Furthermore, in step S4, when welding the magnetic isolation electrode 2, first, a 4-mm-wide gap is respectively opened on the transformer tank cover 1 between two adjacent low-voltage bushing mounting holes 101, and then the magnetic isolation electrode 2 is welded into the gap, and the upper surface of the magnetic isolation electrode 2 is flush with the upper surface of the tank cover 1; when welding the magnetic isolation backing plate 3, first, a square hole is opened at the position corresponding to the low-voltage bushing mounting hole 101 on the transformer tank cover 1, and then the magnetic isolation backing plate 3 is welded into the square hole, and the upper surface of the magnetic isolation backing plate 3 is flush with the upper surface of the tank cover 1; both the magnetic isolation electrode 2 and the magnetic isolation backing plate 3 are made of non-magnetic steel plate; the thicknesses of the magnetic isolation electrode 2 and the magnetic isolation backing plate 3 are the same as the thickness of the transformer tank cover 1. At this time, it is convenient to process, the process difficulty is low, and the performance of the transformer tank cover 1 in terms of power frequency withstand voltage and strength can be ensured, and the use stability of the transformer tank cover 1 can be guaranteed. Inside the transformer tank cover 1, corresponding to the position of each low-voltage bushing mounting hole 101, a hot-rolled flat steel 4 is respectively provided to fix the position of the low-voltage bushing and prevent the low-voltage bushing from shifting.

[0039] Implementation case:

[0040] In this case, the production method of the distribution transformer of the present application described above is adopted to measure whether there is an overload loss in the S13-400 / 10 transformer (the high-voltage coil is wound with copper wire, and the low-voltage coil is wound with copper foil). Among them, the standard load loss P b : 3615 W; rated voltage U(H / L): 10 / 0.4 kV; rated current I(H / L): 23.1 / 577.4 A; standard operating temperature t: 75 °C (when calculating the load loss of the transformer, it should be corrected to the reference temperature; the reference temperature of oil-immersed transformers stipulated in the national standard is 75 °C).

[0041] First, at the ambient temperature T1 (26 °C in this embodiment), select one of the transformer bodies to be tested that has not entered the drying oven after assembly, and measure that the three-phase high-voltage resistance and three-phase low-voltage resistance values are respectively: R AB = 1.865 Ω, R BC = 1.868 Ω, R CA = 1.866 Ω; R ab = 0.002612 Ω, R bc = 0.002605 Ω, R ca = 0.002631 Ω; temperature coefficient K1 = (235 + 75) / (235 + 26) ≈ 1.188;

[0042] Calculate the average high-voltage resistance R H1 ≈1.866 Ω, average low-voltage resistance RL1 = 0.002616 Ω; The high - voltage resistance loss P H1 = 1.5 * 23.1 * 23.1 * 1.866 = 1494 W; The low - voltage resistance loss P L1 = 1.5 * 577.4 * 577.4 * 0.002616 = 1308 W; Then convert to the high - voltage resistance loss P at 75 °C H2 = 1494 * 1.188 ≈ 1775 W; Convert to the low - voltage resistance loss P at 75 °C L2 = 1308 * 1.188 ≈ 1554 W; Then the total resistance loss P at 26 °C r = 1494 + 1308 = 2802 W; Calculate the total resistance loss P at 75 °C after conversion K1 = 1775 + 1554 = 3329 W;

[0043] Then select a completed transformer product (a transformer product without problems after testing), short - circuit the low - voltage side of the transformer product, and input more than 50% of the rated current on the high - voltage side; at a temperature of 26 °C, measured by a power analyzer: U t = 380 V, I t = 21.93 A, P t = 2805 W;

[0044] Calculate the load loss P under the rated current kt = 2805 * (23.1 / 21.93) 2 = 3112 W; Calculate the load loss P at a temperature of 75 °C after conversion s = 1.188 * 2802+(3112 - 2802) / 1.188 = 3590 W (less than the standard load loss);

[0045] Then, the additional loss P f = 3590 - 3329 = 261 W; According to the additional loss, the 75 °C resistance loss must be < 3615 - 261 = 3354 W; Since the low - voltage coil is wound with copper foil and there is no wire stretching, the resistance loss is basically unchanged and can be ignored. Then the high - voltage resistance loss at 75 °C should be P hb = 3354 - 1554 = 1800 W; Then the average value of the high - voltage resistance at 75 °C must be less than 1800 / (1.5 * 23.1 * 23.1)=2.249 Ω; The average value of the high - voltage resistance R at 75 °C Ht = 1.866 * 1.188 ≈ 2.217 Ω < 2.249 Ω; In subsequent measurements, use 1800 W as a standard high - voltage resistance loss value, measure and calculate the high - voltage resistance loss values of other transformer bodies to be detected, and then compare with this standard value to see if there is a problem of over - tolerance of the load loss.

[0046] At an ambient temperature T2 (25°C in this embodiment), the three-phase high-voltage resistances of the body of another transformer to be tested are measured as: R AB = 1.933 Ω, R BC = 1.941 Ω, R CA = 1.929 Ω; the temperature coefficient K2 = (235 + 75) / (235 + 25) ≈ 1.192;

[0047] The average value of the high-voltage resistance R H2 ≈ 1.934 Ω is calculated; the high-voltage resistance loss P H3 = 1.5 * 23.1 * 23.1 * 1.934 ≈ 1548 W; and then it is converted to the high-voltage resistance loss P H4 = 1548 * 1.192 ≈ 1845 W at 75°C;

[0048] P H4 is compared with P hb , and it is found that P H4 - P hb = 1845 - 1800 = 45 W, indicating that there is an over-tolerance in the load loss; at this time, a whole-piece magnetic isolation backing plate 3 needs to be welded at the position corresponding to the low-voltage bushing mounting hole 101 on the transformer cover 1 for non-magnetization treatment.

[0049] In this application, the ambient temperatures T1 and T2 are the room temperatures, and these two temperatures can be the same or different; since the room temperature is constantly changing, the room temperature at the time of measurement is what T1 and T2 are.

[0050] The above general description of the invention involved in this application and the description of its specific implementation manners should not be understood as a limitation on the technical solution of the invention. Those skilled in the art can, based on the disclosure of this application, without departing from the constituent elements of the involved invention, add, subtract, or combine the disclosed technical features in the above general description or / and specific implementation manners (including embodiments) to form other technical solutions that fall within the protection scope of this application.

Claims

1. A production method of a distribution transformer, characterized in that, The high-voltage coil of the transformer is a wire-wound coil, and the low-voltage coil is a foil-wound coil; in this production method, before the transformer body assembly enters the drying oven, its resistance is measured and the resistance loss is calculated to detect the problem of excessive load loss in advance; when there is an excessive load loss, corresponding treatment is carried out to reduce the load loss; the specific steps are as follows: S1. Select one transformer core, measure its three-phase high-voltage resistance and three-phase low-voltage resistance at the ambient temperature T1, and calculate the average high-voltage resistance R H1 and the average low-voltage resistance R L1 ; According to the formula P1 = 1.5 * I 2 * R1, where I is the rated current, calculate the high-voltage resistance loss P H1 and the low-voltage resistance loss P L1 , and the total resistance loss P r = P H1 + P L1 ; Then, according to the formula P2 = K1 * P1, where K1 = (235 + t) / (235 + T1), convert to obtain the high-voltage resistance loss P H2 and the low-voltage resistance loss P L2 at the standard operating temperature t, and the total resistance loss P k1 = P H2 + P L2 ; S2. Select a finished assembled transformer and measure the load loss P s ; S3, calculate the additional loss P f , P f = P s - P k1 ; According to the additional loss, the resistance loss of the transformer body at temperature t must be less than P b - P f = P t , P b is the standard load loss; Since the low-voltage coil is a foil-wound coil and the low-voltage resistance loss is basically unchanged and negligible, the high-voltage resistance loss P hb = P t - P L2 , and the average high-voltage resistance R Ht must be less than P hb / (1.5 * I 2 ), R Ht = R H1 * K1, taking P hb as the standard high-voltage resistance loss; S4. Measure the three-phase high-voltage resistance of the transformer body to be detected at the ambient temperature T2, and calculate the average high-voltage resistance value R H2 ; According to the formula P3 = 1.5 * I 2 * R2, where I is the rated current, calculate the high-voltage resistance loss P H3 ; Then, according to the formula P4 = K2 * P3, where K2 = (235 + t) / (235 + T2), convert to obtain the high-voltage resistance loss P at the temperature t H4 ; S5. Compare the high-voltage resistance loss P in step S4 H4 with the standard high-voltage resistance loss P in step S3 hb ; when P H4 -P hb ≤ 15 W, between two adjacent low-voltage bushing mounting holes (101) on the transformer cover (1), weld the magnetic isolation electrode (2) for isolation treatment; When 15W < P H4 - P hb ≤ 55W, on the transformer cover (1), at the position corresponding to the low-voltage bushing mounting hole (101), a whole magnetic isolation pad (3) is welded for non-magnetization treatment.

2. The production method of a distribution transformer according to claim 1, characterized in that, In step S2, the load loss P s is measured as follows: Short-circuit the low-voltage side of the finished transformer and feed more than 50% of the rated current into the high-voltage side; measure the voltage U at temperature T1 using a power analyzer. t 、Current I t and resistance loss P t According to the formula P kt =P t *(I / I t ) 2 , calculate the resistance loss P at rated current kt ; Then according to the formula P s =K1*P r +(P kt -P r ) / K1, converted to load loss P at standard operating temperature t s .

3. The production method of a distribution transformer according to claim 1, characterized in that: In step S4, when welding the magnetic isolation electrode bar (2), first open a 4-mm-wide gap between two adjacent low-voltage bushing mounting holes (101) on the transformer cover (1), and then weld the magnetic isolation electrode bar (2) in the gap; when welding the magnetic isolation backing plate (3), first open a square hole at the position on the transformer cover (1) corresponding to the low-voltage bushing mounting hole (101), and then weld the magnetic isolation backing plate (3) in the square hole.

4. The production method of a distribution transformer according to claim 3, characterized in that: Both the magnetic isolation electrode bar (2) and the magnetic isolation backing plate (3) are made of non-magnetic steel plate.

5. The production method of a distribution transformer according to claim 4, characterized in that: The thicknesses of the magnetic isolation electrode bar (2) and the magnetic isolation backing plate (3) are the same as the thickness of the transformer cover (1).

6. A detection method for over - tolerance of load loss of a distribution transformer, characterized in that, Before the transformer body assembly enters the drying oven, this method measures its resistance and calculates the resistance loss to detect the problem of excessive load loss in advance. The specific steps are as follows: S1. Select the core of one of the transformers, measure its three-phase high-voltage resistance and three-phase low-voltage resistance at the ambient temperature T1, and calculate the average high-voltage resistance R H1 and the average low-voltage resistance R L1 ; According to the formula P1 = 1.5 * I 2 * R1, where I is the rated current, calculate the high-voltage resistance loss P H1 and the low-voltage resistance loss P L1 , and the total resistance loss P r = P H1 + P L1 ; Then, according to the formula P2 = K1 * P1, where K1 = (235 + t) / (235 + T1), convert to obtain the high-voltage resistance loss P H2 and the low-voltage resistance loss P L2 at the standard operating temperature t, and the total resistance loss P k1 = P H2 + P L2 ; S2. Select a completed assembled transformer finished product and measure the load loss P s ; S3, calculate the additional loss P f , P f = P s - P k1 ; According to the additional loss, the resistance loss of the transformer body at temperature t must be less than P b - P f = P t , P b is the standard load loss; Since the low - voltage resistance loss is basically unchanged and can be ignored, the high - voltage resistance loss P hb = P t - P L2 , and the average value of the high - voltage resistance R Ht must be less than P hb / (1.5 * I 2 ), R Ht = R H1 * K1, taking P hb as the standard high - voltage resistance loss; S4. Measure the three-phase high-voltage resistance of the transformer body to be detected at the ambient temperature T2, and calculate the average high-voltage resistance value R H2 ; According to the formula P3 = 1.5 * I 2 * R2, where I is the rated current, calculate the high-voltage resistance loss P H3 ; Then, according to the formula P4 = K2 * P3, where K2 = (235 + t) / (235 + T2), convert to obtain the high-voltage resistance loss P at the temperature t H4 ; S5. Compare the high-voltage resistance loss P in step S4 H4 with the standard high-voltage resistance loss P in step S3 hb ; when P H4 is greater than P hb , it indicates that there is an out-of-tolerance load loss.

7. The detection method for over - tolerance of load loss of a distribution transformer according to claim 6, characterized in that, In step S2, the load loss P s is measured as follows: Short-circuit the low-voltage side of the finished transformer and input more than 50% of the rated current on the high-voltage side; measure the voltage U t , current I t and resistance loss P t at temperature T1 with a power analyzer; according to the formula P kt =P t *(I / I t ), calculate the resistance loss P 2 under the rated current; then according to the formula P kt =K1*P s +(P r -P kt ) / K1, convert to obtain the load loss P r at the standard operating temperature t s .

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