A method and system for determining the risk of transformer oil ignition under the action of an air environment electric arc

Abstract

This invention discloses a method and system for determining the ignition risk of transformer oil under the influence of an electric arc in an air environment, belonging to the field of power equipment safety protection technology. The method includes: preparing transformer oil samples with different degrees of aging, measuring the dielectric loss factor and acid value; constructing an experimental device including an adjustable arc igniter; setting experimental parameters and conducting multiple ignition experiments, recording the ignition results; using the Bruceton method to statistically analyze the experimental data, calculating the critical temperature Tc with a 50% ignition probability and the intrinsically safe temperature Ts with a 0.01% ignition probability; and comprehensively determining the ignition risk level based on Tc, Ts, and oil quality parameters. This invention, by simulating real arc faults and coupling multiple factors such as arc energy, oil temperature, and oil aging, proposes a dual-temperature safety index based on probability statistics, achieving accurate and quantitative assessment of transformer oil ignition risk, and providing reliable technical support for the safe operation and maintenance and fire early warning of power equipment.

Description

Technical Field

[0001] This invention relates to the field of power equipment safety protection technology, and more specifically, to a method and system for determining the risk of transformer oil ignition under the influence of an electric arc in an air environment. Background Technology

[0002] As a core hub for power transmission and transformation in a power system, the safe and stable operation of transformers directly impacts the reliability of the power grid and public safety. During long-term service, faults such as bushing leakage, poor tap changer contact, and winding insulation damage can easily trigger localized electric arcs. Transformer oil, as the core insulating and heat dissipation medium within the equipment, is highly susceptible to fire if ignited by an electric arc, as it can quickly spread to the entire system, potentially causing a fire or even an explosion.

[0003] According to statistics from the National Energy Administration's power safety supervision, between 2018 and 2023, a total of 78 major transformer accidents occurred in the national power system. Of these, 35% were caused by electric arcs igniting transformer oil. Each accident resulted in an average direct economic loss exceeding 2 million yuan, accompanied by an average of 4.5 hours of regional power outages, severely impacting industrial production and residents' lives. Therefore, accurately assessing the ignition risk of transformer oil under the influence of electric arcs and identifying potential safety hazards in advance are crucial technical aspects for preventing the escalation of accidents and ensuring the safe operation of the power grid.

[0004] Currently, transformer oil ignition risk assessment technology has the following three significant shortcomings, making it difficult to meet the high-precision requirements of practical engineering protection: Defect 1: Ignition method does not match actual operating conditions. Traditional research often uses open flame ignition methods such as thermal radiation furnaces and alcohol torches, failing to fully consider the core characteristics of electric arcs in actual faults, such as instantaneous high energy and strong plasma impact. Studies have shown that the decomposition efficiency of electric arcs on transformer oil is 8-12 times that of thermal radiation, and the two mechanisms are fundamentally different. This leads to a deviation of 15-25°C between traditional judgments and actual accident conditions, making it impossible to provide accurate basis for on-site prevention and control.

[0005] Defect 2: Lack of quantitative correlation between oil aging degree. Transformer oil undergoes coupled degradation due to thermal aging, oxidative aging, and electrical aging during long-term service, resulting in gradual deterioration of oil quality parameters. However, current technologies only focus on temperature factors and lack a quantitative correlation model between aging degree and ignition risk, making it impossible to accurately assess the safety status of transformer oil at different service years.

[0006] Deficiency 3: Lack of quantitative judgment criteria based on multi-factor coupling. Existing judgment methods have not established ignition critical conditions under the coupling of multiple factors such as arc energy, oil temperature, and aging parameters. The results obtained are mostly qualitative judgments, which are difficult to provide clear quantitative technical basis for setting temperature monitoring thresholds for on-site equipment and determining oil quality replacement cycles. Summary of the Invention

[0007] The present invention aims to address the shortcomings of the prior art by providing a system and method for determining the risk of transformer oil ignition under the action of an electric arc in an air environment, thereby improving the efficiency and accuracy of transformer oil ignition risk assessment.

[0008] The technical solution provided by this invention is, as one aspect of this invention, a method for determining the risk of transformer oil ignition under the action of an electric arc in an air environment, which includes the following steps: Step 1: Prepare transformer oil samples with different aging degrees, and determine the dielectric loss factor tanδ and acid value of each sample; Step 2: Construct an air environment electric arc ignition experimental device, which includes an adjustable electric arc igniter, a temperature-controlled heating plate, an oil container, a temperature measuring instrument, and a video recording device; Step 3: Set experimental parameters, including adding a predetermined volume of transformer oil sample to be tested into the oil container, controlling the distance between the arc igniter and the oil surface, the ignition duration, and the temperature step. Step 4: Change the arc energy and the degree of transformer oil aging, conduct multiple ignition experiments, and record the results of "successful ignition" or "unsuccessful ignition"; Step 5: Use the Bruceton method (also known as the rise and fall method) to statistically analyze the experimental data and calculate the critical temperature Tc with an ignition probability of 50% and the intrinsically safe temperature Ts with an ignition probability of 0.01%. Step 6: Determine the ignition risk level based on the critical temperature Tc, intrinsically safe temperature Ts, and transformer oil aging parameters.

[0009] Preferably, the aging conditions for the transformer oil sample in step 1 are: temperature 90 ℃, humidity 30%, and aging times of 0 h, 72 h, 144 h, 216 h, and 288 h, respectively. In step 2, the output energy gradient of the adjustable arc igniter is 6 J, 9.6 J, 13.8 J, and 20.5 J, corresponding to output voltages of 5 kV, 6.8 kV, 8.1 kV, and 10 kV, respectively.

[0010] Preferably, in step 5, the critical temperature Tc is calculated using the following formula: Tc = T0 + t × [1 / N(0) × ∑(i × ni(0))], Where T0 is the initial temperature of 130 ℃, t is the temperature step size of 5 ℃, N(0) is the total number of successful ignitions, i is the temperature gradient number, and ni(0) is the number of successful ignitions for each temperature gradient. The intrinsically safe temperature Ts is calculated using the following formula: Ts = Tc - 3.89σ, Where σ is the standard deviation, σ = √[∑(ni(0) / N(0) × (T0 + i·t)²) - Tc²].

[0011] Preferably, the risk level determination criteria in step 6 are as follows: Low risk: Transformer oil temperature ≤ Ts, dielectric loss factor < 0.1603%, acid value < 0.008 mgKOH / g; Medium risk: Ts < oil temperature ≤ Tc, or dielectric loss factor between 0.1603% and 0.3056%; High risk: oil temperature > Tc, or dielectric loss factor > 0.3056%, or acid value > 0.014 mgKOH / g.

[0012] Among them, when the arc energy is ≥ 13.8 J, the intrinsically safe temperature Ts is uniformly taken as 124 ℃ as the general judgment threshold.

[0013] Accordingly, as another aspect of the present invention, a system for determining the risk of transformer oil ignition under the influence of an electric arc in an air environment is also provided, comprising: The experimental setup is used to simulate electric arc ignition and collect ignition response data of transformer oil under different arc energies, temperatures, and aging degrees. The data acquisition module is used to obtain experimental results on the dielectric loss factor, acid value, and whether the ignition was successful or not in the transformer oil. The data processing module is used to calculate the critical temperature Tc with a 50% ignition probability and the intrinsically safe temperature Ts with a 0.01% ignition probability based on statistical experimental data from the Bruceton method. The risk assessment module is used to determine the ignition risk level of transformer oil based on the critical temperature Tc, intrinsic safety temperature Ts, and oil quality parameters. The output module is used to output the risk level and corresponding operation and maintenance suggestions.

[0014] Preferably, the experimental apparatus includes: an adjustable electric arc igniter, a temperature-controlled heating plate, an oil container, a temperature measuring instrument, and a video recording device; wherein, the output energy gradient of the adjustable electric arc igniter is 6 J, 9.6 J, 13.8 J, and 20.5 J, corresponding to output voltages of 5 kV, 6.8 kV, 8.1 kV, and 10 kV, respectively.

[0015] Preferably, the data acquisition module includes a dielectric loss tester and an acid value analyzer, which are used to measure the dielectric loss factor tanδ and acid value of transformer oil, respectively.

[0016] Preferably, the calculation formula for the critical temperature Tc in the data processing module is: Tc = T0 + t × [1 / N(0) × ∑(i × ni(0))], and the calculation formula for the intrinsically safe temperature Ts is: Ts = Tc - 3.89σ; where T0 is the initial temperature of 130 ℃, t is the temperature step size of 5 ℃, N(0) is the total number of successful ignitions, i is the temperature gradient number, ni(0) is the number of successful ignitions for each temperature gradient; σ is the standard deviation, σ = √[∑(ni(0) / N(0) × (T0 + i·t)²) - Tc²]; Specifically, when the arc energy is ≥ 13.8 J, the data processing module sets the intrinsically safe temperature Ts to 124 ℃ as a general judgment threshold.

[0017] Preferably, the risk level determination criteria in the risk determination module are as follows: Low risk: Transformer oil temperature ≤ Ts, dielectric loss factor < 0.1603%, acid value < 0.008 mgKOH / g; Medium risk: Ts < oil temperature ≤ Tc, or dielectric loss factor between 0.1603% and 0.3056%; High risk: oil temperature > Tc, or dielectric loss factor > 0.3056%, or acid value > 0.014 mgKOH / g.

[0018] Preferably, the maintenance suggestions output by the output module include: Low risk: Maintain normal operation and maintenance, and conduct periodic re-inspections; Medium risk: Increase the frequency of temperature monitoring and recommend oil filtration treatment; High risk: It is recommended to immediately shut down the machine for inspection or replace the transformer oil.

[0019] Implementing the embodiments of the present invention has the following beneficial effects: This invention provides a method and system for determining the ignition risk of transformer oil under the influence of an electric arc in an air environment. It abandons the traditional methods that rely on thermal radiation or open flame ignition, and innovatively constructs an experimental device including an adjustable electric arc igniter. This device can accurately simulate the instantaneous high energy and strong plasma impact characteristics of an electric arc during a power equipment failure. Experiments have shown that the decomposition efficiency of an electric arc on transformer oil is far higher than that of thermal radiation. By recreating a realistic electric arc ignition scenario, this invention reduces the deviation between the assessment results and actual accident conditions from the traditional 15-25°C range to an acceptable range, significantly improving the reliability of ignition risk assessment.

[0020] This invention breaks through the limitations of existing technologies that only focus on temperature as a single factor, and for the first time establishes a multi-factor coupled ignition risk quantification model that includes arc energy, oil temperature, and oil aging degree (dielectric loss factor, acid value). By preparing oil samples with different aging degrees through accelerated aging tests and measuring their dielectric loss factor and acid value, the safety status of transformer oils with different service years can be accurately assessed, providing a scientific basis for differentiated operation and maintenance of aging equipment.

[0021] This invention, based on the Bruceton method, performs probabilistic statistical analysis of experimental data and innovatively defines and calculates two core safety temperatures: the critical temperature Tc (50% ignition probability) and the intrinsically safe temperature Ts (0.01% ignition probability). The intrinsically safe temperature Ts is extended based on the 3.89σ principle of a normal distribution, providing an extreme safety threshold for engineering applications. Furthermore, it clarifies that when the arc energy is ≥13.8 J, Ts is uniformly set at a universal threshold of 124℃, simplifying the application process. A three-tiered risk assessment standard (low / medium / high risk) based on Tc, Ts, and oil quality parameters provides a clear quantitative technical basis for setting temperature monitoring thresholds for on-site equipment and determining oil replacement cycles.

[0022] This invention constructs a complete technical closed loop from "arc ignition experiment, multi-factor data acquisition, probability and statistical calculation, risk level determination, and output of operation and maintenance recommendations." The specific operation and maintenance recommendations output (such as enhanced monitoring, oil filtration, and shutdown maintenance) are all based on quantitative judgment results, which can directly guide the fire early warning and safety protection work of oil-immersed equipment in substations at all levels from 10kV to 500kV, effectively curbing the escalation of accidents caused by transformer oil ignition and ensuring the safe operation of the power grid. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention. Figure 1 This is a schematic diagram of the main process in one embodiment of a method for determining the risk of transformer oil ignition under the action of an electric arc in an air environment provided by the present invention. Figure 2 for Figure 1 A schematic diagram of the experimental setup involved; Figure 3 This is a schematic diagram of the experimental process of electric arc igniting transformer oil in the method provided by the present invention; Figure 4This is a schematic diagram of an embodiment of a system for determining the risk of transformer oil ignition under the action of an electric arc in an air environment, provided by the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] like Figure 1 The diagram shown illustrates the main flow of one embodiment of a method for determining the risk of transformer oil ignition under the influence of an electric arc in an air environment, provided by the present invention; in conjunction with... Figure 2 and Figure 3 As shown, in this embodiment, the determination method includes at least the following steps: Step 1: Prepare transformer oil samples with different aging degrees, and determine the dielectric loss factor tanδ and acid value of each sample; Step 2: Construct an air environment electric arc ignition experimental device, which includes an adjustable electric arc igniter, a temperature-controlled heating plate, an oil container, a temperature measuring instrument, and a video recording device; Step 3: Set experimental parameters, including adding a predetermined volume (e.g., 30ml) of transformer oil sample to be tested into the oil container, controlling the distance between the arc igniter and the oil surface (e.g., 1mm), the ignition duration (e.g., 5 seconds), and the temperature step (5 ℃). Step 4: Change the arc energy and the degree of transformer oil aging, conduct multiple ignition experiments, and record the results of "successful ignition" or "unsuccessful ignition"; Step 5: Use the Bruceton method to statistically analyze the experimental data and calculate the critical temperature Tc with an ignition probability of 50% and the intrinsically safe temperature Ts with an ignition probability of 0.01%. Step 6: Determine the ignition risk level based on the critical temperature Tc, intrinsically safe temperature Ts, and transformer oil aging parameters.

[0026] The following provides a more detailed description of each step.

[0027] In step 1, transformer oil samples are prepared and parameters are tested.

[0028] In a specific example, 25# transformer oil (produced by Jiyang Petrochemical Group, conforming to GB 2536-2011 standard), widely used in the power industry, was selected as the base sample. This type of transformer oil is widely used in core equipment of substations at all levels due to its excellent oxidation resistance and insulation properties. Considering that transformer oil is subject to the combined effects of equipment operating temperature, ambient humidity, and electric field during actual service, undergoing an aging process mainly characterized by oxidation degradation and polymer formation, this invention employs an accelerated aging test method. Thermal aging treatment was performed at 90℃ and 30% humidity (this condition is derived from the Arrhenius equation; 1 hour of accelerated aging is equivalent to approximately 30 days of actual service, effectively simulating the extreme conditions of long-term full-load operation of transformers). A series of aged samples with aging times of 0 h (new oil), 72 h, 144 h, 216 h, and 288 h were obtained. To quantify the degree of oil aging and accurately capture the evolution of oil parameters during the aging process, the following high-precision instruments were used to measure the key physicochemical and insulation parameters of each aged sample: Dielectric loss tester (e.g., BAUR DTL C model from Austria): Samples are heated to 90 °C for measurement, with an accuracy of 1 × 10⁻⁶. -6 ; Acid value analyzer (e.g., Shandong Zhonghui Instruments ZHSZ601A): complies with GB / T264 standard and automatically completes titration analysis; Withstand voltage tester (e.g., Beijing Xingdi Instruments BTS75-3): measures breakdown voltage and verifies the insulation performance of oil.

[0029] The parameters of transformer oil at different aging times are shown in Table 1. The dielectric loss factor (tanδ) reflects the degree of insulation degradation and increases exponentially with aging time. When the aging time reaches 144 hours, the dielectric loss factor increases from 0.001137% in new oil to 0.1603%, an increase of over 140 times. The acid value reflects the degree of oxidative aging of the oil, reaching a critical value of 0.014 mg KOH / g after 216 hours of aging. Volume resistivity and breakdown voltage decrease with aging time, reflecting the decline in the insulation performance of the oil. The evolution of each parameter shows a strong correlation with the ignition characteristics of transformer oil, providing a precise quantitative basis for establishing a correlation model between aging degree and ignition risk. Table 1 Comparison of Aging Time and Transformer Oil Parameters

[0030] The experimental setup constructed in step 2 is as follows: Figure 2 As shown.

[0031] This device achieves integrated functionality of "operating condition simulation - parameter acquisition - process recording" through modular design, accurately simulating fault arc conditions of transformers at different voltage levels and the actual service temperature environment of transformer oil. The selection and parameter settings of each core component are optimized and matched based on actual engineering needs, ensuring the synergy of the overall system performance and the reliability of the test results. In one example, the specific parameters and functions are as follows: The adjustable arc igniter (KTGD-B type) includes an arc controller 11 and an arc conductive rod 10. Its input voltage range is 90~220 V, and its output energy gradients are 6 J, 9.6 J, 13.8 J, and 20.5 J, corresponding to output voltages of 5 kV, 6.8 kV, 8.1 kV, and 10 kV, respectively. This energy gradient covers the typical fault arc energy range of 10 kV distribution transformers to 110 kV main grid transformers, enabling accurate simulation of operating conditions for equipment at different voltage levels. Temperature-controlled heating plate (DB-1 type) 12: Temperature control range 20~450 ℃, temperature control accuracy ±5 ℃. This temperature control range not only covers the normal operating temperature of transformer oil (40~80 ℃), but also includes the temperature range of abnormal temperature rise (80~150 ℃) and fire precursor (150~200 ℃), etc. The temperature control accuracy of ±5 ℃ can ensure the accuracy of the ignition critical temperature test; it is controlled by temperature controller 14.

[0032] Oil container 13: 120 mm in diameter, with a volume suitable for 30 mL of transformer oil. Preliminary experiments have verified that this size can avoid oil splashing caused by electric arc shock waves, while ensuring the repeatability of ignition experiments. Portable thermocouple temperature measuring instrument 15: Its measuring point is located directly below the ignition rod head, with a measurement accuracy of ±0.5 ℃, and it monitors the oil surface temperature in real time; Camera equipment (camera) 16: Frame rate ≥ 30 frames / s, records the entire ignition process, used to verify the determination of whether ignition is successful.

[0033] Meanwhile, a smoke exhaust fan 17 is installed at the top of the experimental device.

[0034] In step 3, sample loading and parameter settings are performed: 30 mL of transformer oil to be tested is accurately added to the oil container using a pipette, with the error controlled within ±0.5 mL; the oil container is placed in the center of the heating plate, and the positioning scale is used for calibration to ensure that the center of the oil container, the center of the heating plate, and the center of the ignition rod are collinear, so as to avoid uneven temperature distribution or ignition failure due to positional deviation; The distance between the arc igniter and the oil surface was set to 1 mm, the ignition duration to 5 s, the temperature step to 5 ℃, and the initial temperature to 130 ℃. Temperature control: Turn on the heating plate and heat up according to the preset temperature program. The heating rate is set to 5 ℃ / min to avoid local overheating of the oil sample due to excessive heating. After the oil temperature reaches the set temperature, it is kept stable for 3 seconds. This stabilization time has been verified in the early stage to ensure that the temperature uniformity error between the upper and lower layers of the oil sample is ≤0.5 ℃. Then, the real-time oil temperature is recorded by thermocouples, and the recording accuracy is retained to one decimal place. Arc ignition: Adjust the distance between the arc igniter and the oil surface to 1 mm, start the arc and perform an ignition operation for 5 seconds, during which the phenomenon is recorded by video equipment.

[0035] In step 4, the arc energy and transformer oil aging degree are varied to conduct multiple ignition experiments, recording the results of "successful ignition" or "failed ignition"; (Refer to...) Figure 2 The image shown is a schematic diagram illustrating an example of an experiment where an electric arc ignites transformer oil in air.

[0036] Referring to the ignition criteria in GB / T 21615-2008 "Determination of Flash Point of Flammable Liquids in Closed Cup", if a flash or stable combustion phenomenon lasting ≥3 seconds occurs during the experiment, it is judged as "successfully ignited"; if only a momentary spark or no combustion phenomenon occurs, it is judged as "unignited"; at the same time, the judgment results are double-checked in conjunction with the video recording equipment to avoid misjudgment. In step 5, the Bruceton method is used to statistically analyze the experimental data and calculate the critical temperature Tc with an ignition probability of 50% and the intrinsically safe temperature Ts with an ignition probability of 0.01%.

[0037] To accurately obtain the ignition critical conditions of transformer oil, this invention employs the internationally recognized Bruceton method (step method) statistical experimental results. Compared to traditional single-point testing methods, this method has advantages such as small sample size requirements, high testing efficiency, and high statistical accuracy. It can efficiently obtain probabilistic statistical characteristics with small sample sizes by iteratively adjusting experimental conditions between adjacent temperature gradients, making it particularly suitable for determining critical parameters with random uncertainty, such as ignition. Based on this method, this invention innovatively defines and calculates two core safety temperature parameters: first, the critical temperature Tc (ignition probability 50%), which reflects the characteristic threshold of the oil's flammability and is a core indicator for assessing the oil's ignition risk; second, the intrinsically safe temperature Ts (ignition probability 0.01%), which corresponds to the extreme safety threshold in engineering applications. Based on the normal distribution 3σ principle extension, it ensures that when the equipment operates below this temperature, the ignition risk is at an acceptablely low level. The specific calculation logic is as follows: The critical temperature Tc is calculated using the following formula: Tc = T0 + t × [1 / N(0) × ∑(i × ni(0))], Where T0 is the initial temperature of 130 ℃, t is the temperature step size of 5 ℃, N(0) is the total number of successful ignitions, i is the temperature gradient number, and ni(0) is the number of successful ignitions for each temperature gradient. The intrinsically safe temperature Ts is calculated using the following formula: Ts = Tc - 3.89σ, Where σ is the standard deviation, σ = √[∑(ni(0) / N(0) × (T0 + i·t)²) - Tc²].

[0038] The calculation results for different arc energies and aging times are shown in Table 2 below (selected for arc energies of 13.8 J and 20.5 J): Table 2 Calculation results under different arc energies and aging times

[0039] To enhance the engineering applicability of the method, this invention statistically analyzed full experimental data at four arc energies: 6 J, 9.6 J, 13.8 J, and 20.5 J. The analysis revealed that when the arc energy was <13.8 J, the intrinsically safe temperature (Ts) decreased significantly with increasing energy, fluctuating by 8-10 °C. When the arc energy was ≥13.8 J (corresponding to transformer voltage levels of 8.1 kV and above), the fluctuation range of the intrinsically safe temperature (Ts) was less than 3 °C, indicating a stable trend. A weighted average of the Ts values ​​from samples with different aging times under this condition was calculated, yielding an average value of 124 °C, which was used as a general safety threshold. This threshold covers over 85% of the arc fault conditions in medium and high voltage transformers in my country's power grid, eliminating the need for separate testing for different voltage levels and significantly improving the method's engineering adaptability and application efficiency.

[0040] In a specific example, the risk level determination criteria in step 6 are as follows: Low risk: Transformer oil temperature ≤ Ts, dielectric loss factor < 0.1603%, acid value < 0.008 mgKOH / g; Medium risk: Ts < oil temperature ≤ Tc, or dielectric loss factor between 0.1603% and 0.3056%; High risk: oil temperature > Tc, or dielectric loss factor > 0.3056%, or acid value > 0.014 mgKOH / g.

[0041] Among them, when the arc energy is ≥ 13.8 J, the intrinsically safe temperature Ts is uniformly taken as 124 ℃ as the general judgment threshold.

[0042] To further understand the principles and more details of the method provided by this invention, the determination method of this invention will be described in detail below with reference to specific engineering cases.

[0043] This embodiment uses the No. 25 transformer oil of a 110 kV urban core substation that has been in service for 10 years as an example. This substation is responsible for supplying power to three surrounding industrial parks and two residential communities. The transformer operating load has been maintained at a high level of 75%-85% for a long time, and the oil quality ages faster than that of ordinary substations. It has typical characteristics of old and heavily loaded equipment. This case study fully demonstrates the practicality and reliability of the method of the present invention.

[0044] 1. Implementation Preparation (1) Sample collection: Strictly follow the DL / T 429.7-2010 standard "Sampling Methods for Oil and Gas in Power Plants" to collect 500 mL of 25# transformer oil sample from the bottom oil port of the transformer in the target substation. Before sampling, rinse the sampling bottle with the oil to be collected 3 times. During the sampling process, control the flow rate at 50 mL / s to avoid generating air bubbles. After sampling, immediately seal the sampling bottle, affix a label containing the equipment number, sampling time, and ambient temperature, and place it in an insulated box (temperature controlled at 20-25 ℃) for rapid testing. Avoid secondary oxidation caused by prolonged contact between the oil sample and air throughout the process. (2) Experimental equipment: The experimental device described in this invention is selected, wherein the adjustable arc igniter is set to an energy gradient of 13.8 J (corresponding to an 8.1 kV voltage, matching the 110 kV transformer fault arc condition), and the temperature-controlled heating plate, oil container and other equipment are calibrated according to the parameters. (3) Auxiliary instruments: The dielectric loss tester, acid value tester, etc. are all preheated and calibrated to ensure that the test accuracy meets the requirements.

[0045] 2. Implementation Steps Step 1: Oil quality parameter testing The dielectric loss factor was measured by heating the oil sample to 90 °C using a BAUR DTL C-type dielectric loss tester from Austria; the acid value was determined using a ZHSZ601A acid value tester from Shandong Zhonghui Instruments, following the GB / T264 standard. Test results: Dielectric loss factor 0.2150%, acid value 0.012 mg KOH / g.

[0046] Step 2: Ignition Experiment (1) Sample loading: Add 30 mL of the collected oil sample to the oil container and place it in the center of the heating plate, ensuring that the thermocouple measuring point is 5 mm below the center of the oil surface; (2) Parameter settings: The distance between the arc igniter and the oil surface is adjusted to 1 mm, the ignition duration is 5 s, the temperature step is 5℃, and the initial temperature is 130℃; (3) Experimental iteration: The experiment was carried out according to the Bruceton method. The initial experimental temperature was 130 ℃, and "not ignited" was recorded. The temperature was increased to 135 ℃, and "not ignited" was recorded. The temperature was increased to 140 ℃, and "ignition successful" was recorded. Then the temperature was reduced to 137.5 ℃ (the temperature step size was adjusted to 2.5 ℃ to improve accuracy), and "ignition successful" was recorded. This condition was repeated 20 times, and the number of successful times was counted as 12.

[0047] Step 3: Data Calculation Based on experimental data, the core parameters are calculated step-by-step according to the formula of this invention to ensure the traceability and accuracy of the calculation process: 1. Basic data compilation: The total number of successful ignitions N(0) = 12. The temperature gradient is set with 135℃ as the base (denoted as i=0), 140℃ as the +1 gradient, and 137.5℃ as the -0.5 gradient, corresponding to 8 successful ignitions ni(0) (i=+1) and 4 successful ignitions (i=-0.5) respectively. 2. Calculation of critical temperature Tc: Tc = T0 + t×[1 / N(0)×∑(i×ni(0))] = 130 + 5×[1 / 12×(1×8 + (-0.5)×4)]= 130 + 5×(6 / 12) = 133.33 ℃; 3. Calculation of standard deviation σ: First, calculate the weighted average temperature of each temperature gradient, then substitute it into the formula to calculate the standard deviation: σ = √[(8 / 12×140² + 4 / 12×137.5²) - 133.33²] = √[(12880 + 6328.125) -17776.8889] = √[19208.125 - 17776.8889] ≈ √1431.2361 ≈ 1.85 ℃; 4. Intrinsic safety temperature Ts calculation: Ts = Tc - 3.89×σ = 133.33 - 3.89×1.85 ≈133.33 - 7.3965 ≈ 126.0 ℃.

[0048] Step 4: Risk Level Determination Based on the oil quality parameters and calculation results, the following assessments were made: the dielectric loss factor of 0.2150% falls within the range of 0.1603% to 0.3056%; the acid value is 0.012 mgKOH / g < 0.014 mgKOH / g; and the current transformer operating oil temperature is 85 ℃, below Ts (126.0 ℃). The overall assessment classifies this as a medium-risk situation, with the primary risk source being the excessive dielectric loss factor caused by oil aging.

[0049] 3. Application of Implementation Results Based on the assessment results, and considering the substation's operating load characteristics and equipment aging status, targeted operation and maintenance recommendations were formulated. All recommendations are derived from the quantitative data of this invention to ensure scientific validity and operability. (1) Strengthen temperature monitoring: Increase the frequency of transformer oil temperature monitoring from once a day to once every 2 hours, use intelligent temperature measurement terminals to collect data in real time and upload it to the operation and maintenance platform; set the oil temperature warning threshold to 120 ℃ (based on Ts=126.0℃, a safety margin of 6 ℃ is reserved, which can cover the instantaneous temperature rise caused by equipment load fluctuations), and automatically trigger an alarm when the oil temperature reaches the warning threshold; (2) Oil treatment: The transformer oil is treated with a ZLY-100 vacuum oil filter. The oil filtration temperature is controlled at 60-70 ℃, the vacuum degree is ≤60 Pa, and the oil flow rate is 80 L / h. Impurities, moisture and aging products in the oil are removed by three-stage filtration. After treatment, the oil is retested according to the method of this invention to ensure that the oil quality parameters meet the standards. (3) Periodic re-inspection: Set a re-inspection cycle of 3 months. During the re-inspection, the dielectric loss factor, acid value and ignition characteristic parameters of the oil sample are collected simultaneously to form an oil quality status change curve. If the dielectric loss factor still does not drop below 0.1603%, it indicates that the oil quality has entered the irreversible deterioration stage and new oil must be replaced immediately to avoid escalation of risks.

[0050] Subsequent retest results: After vacuum filtration, oil samples were collected again for testing. The dielectric loss factor of the oil sample decreased to 0.1230% (<0.1603%), and the acid value was 0.007 mg KOH / g (<0.008 mg KOH / g). The ignition experiment was re-conducted and calculated according to the method of this invention, yielding Tc=138.5 ℃ and Ts=128.5 ℃. The current transformer operating oil temperature is 85 ℃, far below Ts, and the overall risk is determined to be low. This retest result verifies the accuracy of the determination method of this invention and demonstrates that the operation and maintenance measures formulated based on the determination results have significant effects, fully reflecting the guiding value of this invention for on-site operation and maintenance work.

[0051] It is understood that the method provided by this invention, which is a technology for determining the ignition risk of transformer oil under the action of electric arc in an air environment, can be directly applied to the oil quality safety detection and fire early warning scenarios of oil-containing power equipment such as oil-immersed transformers, reactors, and instrument transformers in substations of 10 kV to 500 kV levels.

[0052] This technology provides precise technical support for the operation and maintenance of key equipment in the power system by establishing a quantitative correlation between arc energy, oil aging degree and ignition critical conditions. It is especially suitable for core links such as oil condition assessment of old substations, safety verification before commissioning of new equipment and risk tracing after failure.

[0053] like Figure 4 The diagram shows a schematic representation of an embodiment of a system for determining the risk of transformer oil ignition under the influence of an electric arc in an air environment, provided by the present invention. In this embodiment, the determination system includes at least: Experimental apparatus 1 is used to simulate electric arc ignition and collect ignition response data of transformer oil under different arc energies, temperatures and aging degrees; Data acquisition module 2 is used to obtain experimental results of transformer oil dielectric loss factor, acid value, and whether ignition was successful; Data processing module 3 is used to calculate the critical temperature Tc with an ignition probability of 50% and the intrinsically safe temperature Ts with an ignition probability of 0.01% based on statistical experimental data from the Bruceton method. Risk assessment module 4 is used to determine the ignition risk level of transformer oil based on critical temperature Tc, intrinsic safety temperature Ts, and oil quality parameters. Output module 5 is used to output the risk level and corresponding operation and maintenance suggestions.

[0054] Among them, such as Figure 2 As shown, the experimental apparatus 1 includes: an adjustable arc igniter, a temperature-controlled heating plate 12, an oil container 13, a temperature measuring instrument 15, and a video recording device 15. The adjustable arc igniter includes an arc controller 11 and an arc conductive rod 10. The temperature-controlled heating plate 12 is connected to a temperature controller 14. The output energy gradient of the adjustable arc igniter is 6 J, 9.6 J, 13.8 J, and 20.5 J, corresponding to output voltages of 5 kV, 6.8 kV, 8.1 kV, and 10 kV, respectively.

[0055] The data acquisition module 2 includes a dielectric loss tester and an acid value tester, which are used to measure the dielectric loss factor tanδ and acid value of transformer oil, respectively.

[0056] The calculation formula for the critical temperature Tc in the data processing module 3 is: Tc = T0 + t × [1 / N(0)× ∑(i × ni(0))], and the calculation formula for the intrinsically safe temperature Ts is: Ts = Tc - 3.89σ; where T0 is the initial temperature of 130 ℃, t is the temperature step size of 5 ℃, N(0) is the total number of successful ignitions, i is the temperature gradient number, ni(0) is the number of successful ignitions for each temperature gradient, and σ is the standard deviation, σ = √[∑(ni(0) / N(0) × (T0 + i·t)²) - Tc²]; Specifically, when the arc energy is ≥ 13.8 J, the data processing module sets the intrinsically safe temperature Ts to 124 ℃ as a general judgment threshold.

[0057] The risk level determination criteria in the risk determination module 4 are as follows: Low risk: Transformer oil temperature ≤ Ts, dielectric loss factor < 0.1603%, acid value < 0.008 mgKOH / g; Medium risk: Ts < oil temperature ≤ Tc, or dielectric loss factor between 0.1603% and 0.3056%; High risk: oil temperature > Tc, or dielectric loss factor > 0.3056%, or acid value > 0.014 mgKOH / g.

[0058] The maintenance suggestions output by the output module 5 include: Low risk: Maintain normal operation and maintenance, and conduct periodic re-inspections; Medium risk: Increase the frequency of temperature monitoring and recommend oil filtration treatment; High risk: It is recommended to immediately shut down the machine for inspection or replace the transformer oil.

[0059] For more details, please refer to and combine with the above. Figures 1 to 3 The description of that will not be repeated here.

[0060] Implementing the embodiments of the present invention has the following beneficial effects: This invention provides a method and system for determining the ignition risk of transformer oil under the influence of an electric arc in an air environment. It abandons the traditional methods that rely on thermal radiation or open flame ignition, and innovatively constructs an experimental device including an adjustable electric arc igniter. This device can accurately simulate the instantaneous high energy and strong plasma impact characteristics of an electric arc during a power equipment failure. Experiments have shown that the decomposition efficiency of an electric arc on transformer oil is far higher than that of thermal radiation. By recreating a realistic electric arc ignition scenario, this invention reduces the deviation between the assessment results and actual accident conditions from the traditional 15-25°C range to an acceptable range, significantly improving the reliability of ignition risk assessment.

[0061] This invention breaks through the limitations of existing technologies that only focus on temperature as a single factor, and for the first time establishes a multi-factor coupled ignition risk quantification model that includes arc energy, oil temperature, and oil aging degree (dielectric loss factor, acid value). By preparing oil samples with different aging degrees through accelerated aging tests and measuring their dielectric loss factor and acid value, the safety status of transformer oils with different service years can be accurately assessed, providing a scientific basis for differentiated operation and maintenance of aging equipment.

[0062] This invention, based on the Bruceton method, performs probabilistic statistical analysis of experimental data and innovatively defines and calculates two core safety temperatures: the critical temperature Tc (50% ignition probability) and the intrinsically safe temperature Ts (0.01% ignition probability). The intrinsically safe temperature Ts is extended based on the 3.89σ principle of a normal distribution, providing an extreme safety threshold for engineering applications. Furthermore, it clarifies that when the arc energy is ≥13.8 J, Ts is uniformly set at a universal threshold of 124℃, simplifying the application process. A three-tiered risk assessment standard (low / medium / high risk) based on Tc, Ts, and oil quality parameters provides a clear quantitative technical basis for setting temperature monitoring thresholds for on-site equipment and determining oil replacement cycles.

[0063] This invention constructs a complete technical closed loop from "arc ignition experiment, multi-factor data acquisition, probability and statistical calculation, risk level determination, and output of operation and maintenance recommendations." The specific operation and maintenance recommendations output (such as enhanced monitoring, oil filtration, and shutdown maintenance) are all based on quantitative judgment results, which can directly guide the fire early warning and safety protection work of oil-immersed equipment in substations at all levels from 10kV to 500kV, effectively curbing the escalation of accidents caused by transformer oil ignition and ensuring the safe operation of the power grid.

[0064] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 Units that specify functions within one or more boxes.

[0065] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for determining the risk of transformer oil ignition under the influence of an electric arc in an air environment, characterized in that, Includes the following steps: Step 1: Prepare transformer oil samples with different aging degrees, and determine the dielectric loss factor tanδ and acid value of each sample; Step 2: Construct an air environment electric arc ignition experimental device, which includes an adjustable electric arc igniter, a temperature-controlled heating plate, an oil container, a temperature measuring instrument, and a video recording device; Step 3: Set experimental parameters, including adding a predetermined volume of transformer oil sample to be tested into the oil container, controlling the distance between the arc igniter and the oil surface, the ignition duration, and the temperature step. Step 4: Change the arc energy and the degree of transformer oil aging, conduct multiple ignition experiments, and record the results of "successful ignition" or "failed ignition"; Step 5: Use the Bruceton method to statistically analyze the experimental data and calculate the critical temperature Tc with an ignition probability of 50% and the intrinsically safe temperature Ts with an ignition probability of 0.01%. Step 6: Determine the ignition risk level based on the critical temperature Tc, intrinsically safe temperature Ts, and transformer oil aging parameters.

2. The determination method according to claim 1, characterized in that, The aging conditions for the transformer oil samples in step 1 were: temperature 90 ℃, humidity 30%, and aging times of 0 h, 72 h, 144 h, 216 h, and 288 h, respectively. In step 2, the output energy gradient of the adjustable arc igniter is 6 J, 9.6 J, 13.8 J, and 20.5 J, corresponding to output voltages of 5 kV, 6.8 kV, 8.1 kV, and 10 kV, respectively.

3. The determination method according to claim 2, characterized in that, In step 5, the critical temperature Tc is calculated using the following formula: Tc = T0 + t × [1 / N(0) × ∑(i × ni(0))], Where T0 is the initial temperature of 130 ℃, t is the temperature step size of 5 ℃, N(0) is the total number of successful ignitions, i is the temperature gradient number, and ni(0) is the number of successful ignitions for each temperature gradient. The intrinsically safe temperature Ts is calculated using the following formula: Ts = Tc - 3.89σ, Where σ is the standard deviation, σ = √[∑(ni(0) / N(0) × (T0 + i·t)²) - Tc²].

4. The determination method according to any one of claims 1 to 3, characterized in that, The risk level determination criteria in step 6 are as follows: Low risk: Transformer oil temperature ≤ Ts, dielectric loss factor < 0.1603%, acid value < 0.008 mgKOH / g; Medium risk: Ts < oil temperature ≤ Tc, or dielectric loss factor between 0.1603% and 0.3056%; High risk: oil temperature > Tc, or dielectric loss factor > 0.3056%, or acid value > 0.014 mgKOH / g. Among them, when the arc energy is ≥ 13.8 J, the intrinsically safe temperature Ts is uniformly taken as 124 ℃ as the general judgment threshold.

5. A system for determining the risk of transformer oil ignition under the influence of an electric arc in an air environment, characterized in that, include: The experimental setup is used to simulate electric arc ignition and collect ignition response data of transformer oil under different arc energies, temperatures, and aging degrees. The data acquisition module is used to obtain experimental results on the dielectric loss factor, acid value, and whether the ignition was successful or not in the transformer oil. The data processing module is used to calculate the critical temperature Tc with a 50% ignition probability and the intrinsically safe temperature Ts with a 0.01% ignition probability based on statistical experimental data from the Bruceton method. The risk assessment module is used to determine the ignition risk level of transformer oil based on the critical temperature Tc, intrinsic safety temperature Ts, and oil quality parameters. The output module is used to output the risk level and corresponding operation and maintenance suggestions.

6. The determination system according to claim 5, characterized in that, The experimental setup includes: an adjustable electric arc igniter, a temperature-controlled heating plate, an oil container, a temperature measuring instrument, and a video recording device; wherein, the output energy gradient of the adjustable electric arc igniter is 6 J, 9.6 J, 13.8 J, and 20.5 J, corresponding to output voltages of 5 kV, 6.8 kV, 8.1 kV, and 10 kV, respectively.

7. The determination system according to claim 6, characterized in that, The data acquisition module includes a dielectric loss tester and an acid value analyzer, which are used to measure the dielectric loss factor tanδ and acid value of transformer oil, respectively.

8. The determination system according to claim 7, characterized in that, The formula for calculating the critical temperature Tc in the data processing module is: Tc = T0 + t × [1 / N(0) × ∑(i × ni(0))], and the formula for calculating the intrinsically safe temperature Ts is: Ts = Tc - 3.89σ; where T0 is the initial temperature of 130 ℃, t is the temperature step size of 5 ℃, N(0) is the total number of successful ignitions, i is the temperature gradient number, ni(0) is the number of successful ignitions for each temperature gradient; σ is the standard deviation, σ = √[∑(ni(0) / N(0) × (T0 + i·t)²) - Tc²]; Specifically, when the arc energy is ≥ 13.8 J, the data processing module sets the intrinsically safe temperature Ts to 124℃ as a universal judgment threshold.

9. The determination system according to claim 8, characterized in that, The risk level determination criteria in the risk assessment module are as follows: Low risk: Transformer oil temperature ≤ Ts, dielectric loss factor < 0.1603%, acid value < 0.008 mgKOH / g; Medium risk: Ts < oil temperature ≤ Tc, or dielectric loss factor between 0.1603% and 0.3056%; High risk: oil temperature > Tc, or dielectric loss factor > 0.3056%, or acid value > 0.014 mgKOH / g.

10. The determination system according to any one of claims 5 to 9, characterized in that, The operation and maintenance suggestions output by the output module include: Low risk: Maintain normal operation and maintenance, and conduct periodic re-inspections; Medium risk: Increase the frequency of temperature monitoring and recommend oil filtration treatment; High risk: It is recommended to immediately shut down the machine for inspection or replace the transformer oil.

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