Method and device for judging safety of fully-sealed distribution transformer

Abstract

The invention provides a method and device for judging the safety of a fully-sealed distribution transformer, and the method comprises the steps: monitoring the deformation of wave wings through a sensor, calculating the expansion volume through the deflection, and deducing the descending height of the liquid level of an oil tank. If no oil leakage exists, the transformer is safe; oil leakage is further analyzed, and if the upper end of the iron core is exposed, a breakdown risk exists; if the tap switch is exposed, the potential safety hazard is stored. The method effectively prejudges the safety risk of the transformer by accurately calculating the liquid level height of the oil tank.

Description

Technical Field

[0001] The present application belongs to the field of transformer monitoring, and in particular, relates to a method and device for judging the safety of a fully sealed distribution transformer. Background Art

[0002] Fully sealed distribution transformers play an important role in the power system, and their safety and stability are directly related to the safe operation of the power grid. In order to avoid problems such as oxidation and moisture in the distribution transformer oil, fully sealed designs are widely used. When the ambient air pressure and temperature change, the deformation of the oil tank corrugated fins can effectively adapt to the thermal expansion and contraction of the transformer oil, preventing accidents such as discharge and oil leakage caused by low oil level or excessive pressure inside the oil tank.

[0003] However, there are some potential safety hazards in actual operation. For example, to prevent oil leakage when the oil expands, the oil tank is usually not filled with oil, resulting in part of the structure being exposed to the air, increasing the operational risk. Secondly, when the wave fins shrink due to cooling, if they cannot rebound normally, the oil level will drop excessively, which may cause a discharge accident and pose a serious threat to the safety of power distribution in the power grid.

[0004] Therefore, how to judge the safety of fully sealed distribution transformers has become an issue that needs attention. Summary of the invention

[0005] The purpose of the present application is to overcome the defects in the above-mentioned prior art and provide a method and device for judging the safety of a fully sealed distribution transformer.

[0006] The present application provides a method for determining the safety of a fully sealed distribution transformer, comprising:

[0007] Use sensors to monitor the deformation data of the corrugated fins in the oil tank of the distribution transformer in real time;

[0008] According to the deformation data, the expansion volume of the wave wing is calculated by a deflection calculation formula;

[0009] Calculating the lowering height of the oil tank liquid level according to the expansion volume;

[0010] The safety status of the distribution transformer is judged according to the lowered height, including: judging whether the oil tank is leaking oil; wherein, if the oil tank is not leaking oil, the fully sealed distribution transformer is judged to be safe; if the oil tank is leaking oil, the lowered height is compared with a preset threshold, and the risk type is judged according to the comparison result.

[0011] Optionally, the risk type is determined based on the comparison result, including:

[0012] If the comparison result shows that the lowered height is greater than the first preset threshold value, so that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover;

[0013] If the lowered height is greater than a second preset threshold value, the tap changer of the distribution transformer is exposed to the gas, and there is a risk of creeping discharge.

[0014] Optionally, the deflection calculation formula is:

[0015] △V=2nahf / 3

[0016] f=c0σh 2 / Et(c1 2 +c2 2 ) 0.5

[0017] Among them, n is the number of corrugated ribs of the fuel tank, a is the length of the corrugated plate of the fuel tank, h is the width of the corrugated plate of the fuel tank, c0, c1, c2 are constants related to a and h, σ is the internal stress, E is the elastic modulus, and t is the thickness of the corrugated plate.

[0018] Optionally, according to the deformation data, the expansion volume of the wave fin is calculated by a deflection calculation formula, including:

[0019] The temperature coefficient of the transformer oil is obtained, and the expansion volume is corrected according to the temperature coefficient.

[0020] Optionally, if the comparison result shows that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover, and the power supply of the distribution transformer is cut off.

[0021] The present application also provides a device for judging the safety of a fully sealed distribution transformer, comprising:

[0022] The detection module uses sensors to monitor the deformation data of the corrugated fins in the oil tank of the distribution transformer in real time;

[0023] A calculation module, which calculates the expansion volume of the wave wing according to the deformation data by using a deflection calculation formula;

[0024] A liquid level module, which calculates the lowering height of the liquid level in the oil tank according to the expansion volume;

[0025] A judgment module is provided for judging the safety status of the distribution transformer according to the lowered height, including: judging whether the oil tank is leaking oil; wherein, if the oil tank is not leaking oil, the fully sealed distribution transformer is judged to be safe; if the oil tank is leaking oil, the lowered height is compared with a preset threshold value, and the risk type is judged according to the comparison result.

[0026] Optionally, the judgment module judges the risk type according to the comparison result, including:

[0027] If the comparison result shows that the lowered height is greater than the first preset threshold value, so that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover;

[0028] If the lowered height is greater than a second preset threshold value, the tap changer of the distribution transformer is exposed to the gas, and there is a risk of creeping discharge.

[0029] Optionally, the deflection calculation formula is:

[0030] △V=2nahf / 3

[0031] f=c0σh 2 / Et(c1 2 +c2 2 ) 0.5

[0032] Among them, n is the number of corrugated ribs of the fuel tank, a is the length of the corrugated plate of the fuel tank, h is the width of the corrugated plate of the fuel tank, c0, c1, c2 are constants related to a and h, σ is the internal stress, E is the elastic modulus, and t is the thickness of the corrugated plate.

[0033] Optionally, the calculation module calculates the expansion volume of the wave fin according to the deformation data by using a deflection calculation formula, including:

[0034] The temperature coefficient of the transformer oil is obtained, and the expansion volume is corrected according to the temperature coefficient.

[0035] Optionally, the judgment module judges that if the comparison result shows that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover, and cuts off the power supply of the transformer.

[0036] The beneficial effects of this application are:

[0037] The present application provides a method for judging the safety of a fully sealed distribution transformer, including: using a sensor to monitor the deformation data of the wave wing in the oil tank of the distribution transformer in real time; calculating the expansion volume of the wave wing according to the deformation data through the deflection calculation formula; calculating the reduced height of the oil tank liquid level according to the expansion volume; judging the safety status of the distribution transformer according to the reduced height, including: judging whether the oil tank is leaking oil; wherein, if the oil tank is not leaking oil, the fully sealed distribution transformer is judged to be safe; if the oil tank is leaking oil, the reduced height is compared with a preset threshold, and the risk type is judged according to the comparison result. The present application uses the deflection calculation formula and the expansion volume calculation to accurately calculate the reduced height of the oil tank liquid level, thereby accurately judging the safety of the transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of the process of determining the safety of a fully sealed distribution transformer in this application;

[0039] Figure 2 Schematic diagram of the device for judging the safety of a fully sealed distribution transformer in this application. DETAILED DESCRIPTION

[0040] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that various forms of implementing the present disclosure should not be limited by the embodiments set forth herein. On the contrary, the embodiments are provided to more thoroughly understand the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0041] Please refer to Figure 1 As shown, the present application provides a method for determining the safety of a fully sealed distribution transformer, the steps comprising:

[0042] S101. Use sensors to monitor deformation data of corrugated fins in the oil tank of a distribution transformer in real time.

[0043] In order to accurately monitor the deformation data of the wave fins in the oil tank of the distribution transformer, a high-precision and high-sensitivity deformation sensor is selected. The sensor is based on a strain gauge, an optical fiber sensor or other non-contact deformation measurement technology.

[0044] The sensor is installed at a position that can accurately reflect the deformation of the wave fin, such as the apex, inflection point or near the key deformation area of ​​the wave fin.

[0045] The sensor measures the deformation of the wave fin (such as displacement, bending degree, etc.).

[0046] S102. Calculate the expansion volume of the wave wing according to the deformation data using a deflection calculation formula.

[0047] The expansion volume of the wave wing is accurately calculated by using the deformation data of the wave wing generated during the thermal expansion and contraction of the oil (such as the expansion or contraction amount of the wave wing) through the deflection calculation formula.

[0048] The deflection calculation formula is a mathematical formula used to describe the bending or deformation of an object when it is subjected to external forces. In a fully sealed distribution transformer, the expansion or contraction of the corrugated fin can be regarded as the change in deflection under changes in oil pressure and temperature.

[0049] According to the material properties of the wave fin (such as elastic modulus, Poisson's ratio, etc.), structural dimensions (such as length, width, thickness, etc.) and deformation data (such as the bending amount and inclination angle of the wave fin), select the appropriate deflection calculation formula for calculation. The specific expression is as follows:

[0050] V=2nahf / 3

[0051] f=c0σh 2 / Et(c12 +c2 2 ) 0.5

[0052] Among them, n is the number of corrugated ribs of the fuel tank, a is the length of the corrugated plate of the fuel tank, h is the width of the corrugated plate of the fuel tank, c0, c1, c2 are constants related to a and h, σ is the internal stress, E is the elastic modulus, and t is the thickness of the corrugated plate.

[0053] S103, calculating the lowering height of the oil tank liquid level according to the expansion volume.

[0054] The calculation results will directly reflect the expansion volume of the wave fin, and this volume change further reflects the decrease or increase of the oil level in the transformer tank.

[0055] The expansion volume change of the wave fin is obtained from step S102. The lowering height of the oil level in the oil tank is calculated by the ratio of the expansion volume of the wave fin to the cross-sectional area of ​​the oil tank.

[0056] If the lowering height is abnormal, an early warning signal will be issued, indicating that the transformer may be in an unsafe operating state.

[0057] S104. Determine the safety status of the distribution transformer according to the lowered height, including: determining whether the oil tank is leaking oil; if the oil tank is not leaking oil, determining that the fully sealed distribution transformer is safe; if the oil tank is leaking oil, comparing the lowered height with a preset threshold, and determining the risk type according to the comparison result.

[0058] If the comparison result shows that the lowered height is greater than the first preset threshold value, so that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover;

[0059] If the lowered height is greater than a second preset threshold value, the tap changer of the distribution transformer is exposed to the gas, and there is a risk of creeping discharge.

[0060] In the finite element simulation software, the top structure inside the oil tank of the 10kV distribution transformer was accurately modeled. The model describes the internal structure of the distribution transformer in detail, including some cores, fixtures, high-voltage leads, low-voltage leads, tap changers and their leads, neutral point leads, lead fixtures, high-voltage bushings and low-voltage bushings and other key components. This model sets the relative dielectric constants of different materials (4.5 for insulation wood, 6.0 for bushing material, 2.5 for transformer oil, 1.0 for air gap, and infinite (10^8) for metal materials) to truly restore the internal electric field environment of the transformer.

[0061] The research object is the Yyn cascade distribution transformer. The ideal situation of voltage balance is considered in the simulation. The neutral terminal is set to 0 potential, the core, clamps and shell are grounded, and the low-voltage winding and high-voltage winding are converted and set according to 380V and 10kV three-phase line voltages respectively.

[0062] The mesh is divided into free tetrahedrons and the size is extremely refined to ensure the accuracy of the simulation results. The model is solved by separation iteration and finally the steady-state solution is obtained.

[0063] The simulation simulates the following four working conditions:

[0064] No oil leakage:

[0065] In the full oil state, the maximum value of the surface electric field is 0.81kV / mm, which appears at the interface between the phase B high-voltage lead and the fixed insulator; the maximum value of the spatial electric field is 2.04kV / mm, which appears inside the phase B high-voltage bushing. At this time, since the transformer is full of oil, the electric field strength does not pose a threat.

[0066] Oil leakage:

[0067] The oil level is below the bottom of the high-voltage bushing: the maximum value of the surface electric field is still 0.81kV / mm, and the position remains unchanged; the maximum value of the spatial electric field increases to 2.25kV / mm, appearing inside the high-voltage bushing of phase B. At this time, the insulation inside the bushing of phase B changes from oil to air gap insulation, and there is a risk of breakdown.

[0068] The bottom of the high-voltage bushing is exposed: the maximum value of the surface electric field remains at 0.81 kV / mm; the maximum value of the spatial electric field is 2.09 kV / mm, which also appears inside the high-voltage bushing of phase B. At this time, the inside of the bushing of phase B is still insulated by gas, which poses a potential threat.

[0069] The upper end surface of the core is exposed: the maximum value of the surface electric field is still 0.81kV / mm; the maximum value of the space electric field is 1.97kV / mm, which appears inside the high-voltage bushing of phase B. At this time, the surface of the bushing and the lead clamp of phase B are exposed to the air, and there is a serious threat of breakdown and flashover (the breakdown field strength in air is about 3kV / mm, and the surface flashover field strength in air is about 1.2kV / mm).

[0070] In the finite element simulation software, a detailed model of the tap switch inside the oil tank is constructed. The model includes key components such as the outer porcelain sleeve, epoxy fasteners, tap contact fingers and screws, rotating springs and screws, and truly restores the internal structure of the distribution transformer.

[0071] The relative dielectric constants of the components in the model are defined, including the outer porcelain sleeve (6.0), epoxy fasteners (4.0), transformer oil (2.5), air gap (1.0), and metal material (taken as infinity, i.e. 10^8).

[0072] A Dyn cascade distribution transformer was selected, and its tap changer has three gears, namely 0% and ±2.5%.

[0073] The three-phase voltages were set to the peak values ​​of their respective voltages to ground to simulate actual operating conditions.

[0074] Free tetrahedral mesh is used for meshing, and the size is set to be extremely fine to ensure the accuracy of the simulation.

[0075] The model is solved by a separated iteration method to obtain the steady-state electric field distribution results.

[0076] Four different simulations were performed:

[0077] No oil leakage: The maximum electric field appears at the triple junction formed by the metal spring near the shaft, the ceramic hardware, and the insulating oil, with an amplitude of 3.335kV / mm. At the same time, the electric field along the extended contact finger and the insulating clamp is about 0.87kV / mm. Since these locations are all in the oil, they will not pose an insulation threat.

[0078] Oil leakage:

[0079] The oil level does not cover the metal connection point: Under this condition, the maximum electric field still appears at the triple junction, but the amplitude is slightly reduced to 3.303kV / mm. The surface electric field of the extended contact finger and the insulating clamp also remains relatively stable. Although the oil level has dropped, the key parts are still covered by oil, so the insulation performance is not significantly affected.

[0080] Flush with the terminal block: Since this part of the information does not directly provide the specific electric field distribution data or description under this working condition, it can be inferred that as the oil level continues to drop, the electric field strength near the terminal block and its surrounding areas may change, and specific simulation results are needed to evaluate its insulation safety.

[0081] The tap changer is completely exposed to the gas: In this extreme condition, the tap changer is completely exposed to the air, which will cause a significant change in the electric field distribution. Since the dielectric strength of air is much lower than that of transformer oil, the tap changer and its surrounding areas are subject to a higher insulation risk. Special attention needs to be paid to the electric field strength and possible insulation failure under this condition.

[0082] Please refer to Figure 2 As shown, the present application also provides a device for judging the safety of a fully sealed distribution transformer, comprising:

[0083] The detection module 201 uses sensors to monitor the deformation data of the wave fins in the oil tank of the distribution transformer in real time;

[0084] A calculation module 202 calculates the expansion volume of the wave wing according to the deformation data using a deflection calculation formula;

[0085] A liquid level module 203 calculates the lowering height of the liquid level in the oil tank according to the expansion volume;

[0086] The judgment module 204 judges the safety status of the distribution transformer according to the lowered height, including: judging whether the oil tank is leaking oil; if the oil tank is not leaking oil, judging that the fully sealed distribution transformer is safe; if the oil tank is leaking oil, comparing the lowered height with a preset threshold, and judging the risk type according to the comparison result.

[0087] If the comparison result shows that the lowered height is greater than the first preset threshold value, so that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover;

[0088] If the lowered height is greater than a second preset threshold value, the tap changer of the distribution transformer is exposed to the gas, and there is a risk of creeping discharge.

[0089] Wherein, the deflection calculation formula is:

[0090] △V=2nahf / 3

[0091] f=c0σh 2 / Et(c1 2 +c2 2 ) 0.5

[0092] Among them, n is the number of corrugated ribs of the fuel tank, a is the length of the corrugated plate of the fuel tank, h is the width of the corrugated plate of the fuel tank, c0, c1, c2 are constants related to a and h, σ is the internal stress, E is the elastic modulus, and t is the thickness of the corrugated plate.

[0093] The detection module uses sensors to monitor the deformation data of the wave fins in the oil tank of the distribution transformer in real time, including: if the deformation data is abnormal, triggering an alarm.

[0094] The calculation module calculates the expansion volume of the wave fin according to the deformation data by using a deflection calculation formula, including: obtaining a temperature coefficient of transformer oil, and correcting the expansion volume according to the temperature coefficient.

[0095] The judgment module judges that if the comparison result shows that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover, and cuts off the power supply of the transformer.

Claims

1. A method for judging the safety of a fully sealed distribution transformer, characterized in that: include: Use sensors to monitor the deformation data of the corrugated fins in the oil tank of the distribution transformer in real time; According to the deformation data, the expansion volume of the wave wing is calculated by a deflection calculation formula; Calculating the lowering height of the oil tank liquid level according to the expansion volume; The safety status of the distribution transformer is judged according to the lowered height, including: judging whether the oil tank is leaking oil; wherein, if the oil tank is not leaking oil, the fully sealed distribution transformer is judged to be safe; if the oil tank is leaking oil, the lowered height is compared with a preset threshold, and the risk type is judged according to the comparison result.

2. A method for judging the safety of a fully sealed distribution transformer according to claim 1, characterized in that: Determine the risk type based on the comparison results, including: If the comparison result shows that the lowered height is greater than the first preset threshold value, so that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover; If the lowered height is greater than a second preset threshold value, the tap changer of the distribution transformer is exposed to the gas, and there is a risk of creeping discharge.

3. A method for judging the safety of a fully sealed distribution transformer according to claim 1, characterized in that: The deflection calculation formula is: △V=2nahf / 3 f=c0σh 2 / And(t1 2 +c2 2 ) 0.5 Among them, n is the number of corrugated ribs of the fuel tank, a is the length of the corrugated plate of the fuel tank, h is the width of the corrugated plate of the fuel tank, c0, c1, c2 are constants related to a and h, σ is the internal stress, E is the elastic modulus, and t is the thickness of the corrugated plate.

4. A method for judging the safety of a fully sealed distribution transformer according to claim 1, characterized in that: According to the deformation data, the expansion volume of the wave wing is calculated by the deflection calculation formula, including: The temperature coefficient of the transformer oil is obtained, and the expansion volume is corrected according to the temperature coefficient.

5. A method for judging the safety of a fully sealed distribution transformer according to claim 1, characterized in that: If the comparison result shows that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover, and the power supply of the distribution transformer is cut off.

6. A device for judging the safety of a fully sealed distribution transformer, characterized in that: include: The detection module uses sensors to monitor the deformation data of the corrugated fins in the oil tank of the distribution transformer in real time; A calculation module, which calculates the expansion volume of the wave wing according to the deformation data by using a deflection calculation formula; A liquid level module, which calculates the lowering height of the liquid level in the oil tank according to the expansion volume; A judgment module is provided for judging the safety status of the distribution transformer according to the lowered height, including: judging whether the oil tank is leaking oil; wherein, if the oil tank is not leaking oil, the fully sealed distribution transformer is judged to be safe; if the oil tank is leaking oil, the lowered height is compared with a preset threshold value, and the risk type is judged according to the comparison result.

7. A device for judging the safety of a fully sealed distribution transformer according to claim 6, characterized in that: The judgment module judges the risk type according to the comparison result, including: If the comparison result shows that the lowered height is greater than the first preset threshold value, so that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover; If the lowered height is greater than a second preset threshold value, the tap changer of the distribution transformer is exposed to the gas, and there is a risk of creeping discharge.

8. A device for judging the safety of a fully sealed distribution transformer according to claim 6, characterized in that: The deflection calculation formula is: △V=2nahf / 3 f=c0σh 2 / Et(c1 2 +c2 2 ) 0.5 Among them, n is the number of corrugated ribs of the fuel tank, a is the length of the corrugated plate of the fuel tank, h is the width of the corrugated plate of the fuel tank, c0, c1, c2 are constants related to a and h, σ is the internal stress, E is the elastic modulus, and t is the thickness of the corrugated plate.

9. A device for judging the safety of a fully sealed distribution transformer according to claim 6, characterized in that: The calculation module calculates the expansion volume of the wave wing according to the deformation data by using a deflection calculation formula, including: The temperature coefficient of the transformer oil is obtained, and the expansion volume is corrected according to the temperature coefficient.

10. A device for judging the safety of a fully sealed distribution transformer according to claim 6, characterized in that: The judgment module judges that if the comparison result shows that the upper end surface of the core of the distribution transformer is exposed, there is a risk of breakdown and flashover, and cuts off the power supply of the transformer.

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