Method for researching PD law of suspended water drops in oil-immersed transformer

Abstract

The invention discloses a method for researching a PD law of suspended water drops in an oil-immersed transformer. The test method comprises the following steps: analyzing a basic rule when partial discharge (PD for short) of suspended water drops in the oil-immersed transformer occurs in a laminar flow (Reynolds number is less than 2300) state; the method comprises the following steps of: drawing a three-dimensional (Phase Resolution Partial Discharge, referred to as PRPD) atlas under the conditions of different step-up voltages and different flow velocities by Python, and drawing the three-dimensional (Phase Resolution Partial Discharge, referred to as PRPD) atlas under the conditions of different step-up voltages and different flow velocities; and finding out a repeatable and regular step-up voltage controllable point dominated by migration, aggregation or electric field distortion of the suspended water drops, drawing a PRPD atlas under the voltage, and analyzing the PD rule of the suspended water drops in the oil-immersed transformer under different laminar flow states.

Description

Technical Field

[0001] The present invention relates to the technical field of research on the law of PD occurrence of suspended water droplets in oil-immersed transformers under flowing conditions, and in particular to a method for studying the PD law of suspended water droplets in oil-immersed transformers. Background Art

[0002] With the large-scale construction of UHV power transmission and transformation projects, transformers, as the core hub equipment for power conversion, face severe challenges in terms of insulation reliability. In recent years, insulation defects have become the primary cause of high-voltage equipment accidents. Fault analysis of oil-immersed transformers shows that the existing forms of moisture in insulating oil mainly include dissolved state, suspended state, and deposited state. Among them, the dissolved state and deposited state have little impact on PD (Partial Discharge). In areas with significant day-night temperature differences, the thermal expansion and contraction effect will cause periodic changes in suspended water droplets.

[0003] The main paths of moisture intrusion include: moisture generated by the cracking of oil molecules caused by PD in insulating oil; penetration of external moisture in the transformer; phase change of dissolved / deposited moisture caused by oil temperature fluctuations. It should be noted that the PD of suspended water droplets in oil-immersed transformers presents unique laws. The traditional "small bridge" conduction mechanism is difficult to reasonably explain the PD behavior of micron-sized water droplets under flowing conditions. Existing research mostly focuses on static oil liquid systems, and has not systematically revealed the regulation mechanism of the coupling effect of circulating oil flow and suspended water droplets on PD, which has become the key theoretical bottleneck restricting the development of transformer intelligent diagnosis technology. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention solves the problem of supplementing the research on the PD law of suspended water droplets in oil-immersed transformers and supplementing the discharge theory in transformer oil containing suspended water droplets.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A research method for the PD law of suspended water droplets in oil-immersed transformers, including a transformer discharge defect system, an AC boosting platform, and a digital partial discharge detection system. Among them, the laminar flow range is determined in the developed transformer discharge defect system, and the voltage is boosted through the AC boosting platform under different laminar flow (Reynolds number less than 2300) states. The PD signals are collected by a pulse current sensor recommended by IEC60270 standard, and the signals when PD occurs in the suspended water droplets in the oil are transmitted to the digital partial discharge detection system. Then, Python is used to draw the three-dimensional partial discharge phase distribution PRPD maps under different step-up voltages and different flow rates. Finally, the repeatable and regular step-up voltage controllable points dominated by the migration, aggregation or electric field distortion of the suspended water droplets are found. The PRPD maps are drawn at this voltage, and the PD law of the suspended water droplets in the oil-immersed transformer under different laminar flow states is analyzed.

[0007] Preferably, the basic law of PD occurrence in the suspended water droplets in the oil-immersed transformer is analyzed under the laminar flow (Reynolds number less than 2300) state;

[0008] Preferably, the three-dimensional PRPD maps under different step-up voltages and different flow rates are drawn by Python;

[0009] Preferably, the repeatable and regular step-up voltage controllable points dominated by the migration, aggregation or electric field distortion of the suspended water droplets are found.

[0010] The beneficial effects of the present invention:

[0011] (1) The present invention proposes a research method for the PD law of suspended water droplets in oil-immersed transformers, analyzes the basic law of PD occurrence in the suspended water droplets in the oil-immersed transformer under the laminar flow state, and prevents the irregular discharge caused by the movement disorder of the suspended water droplets in the turbulent flow state.

[0012] (2) The three-dimensional PRPD maps under different step-up voltages and different flow rates are drawn by Python, which is easier to explore the internal PD law of the suspended water droplets compared with two-dimensional maps such as phase-discharge quantity, step-up voltage-discharge quantity, and flow rate-discharge quantity.

[0013] (3) The repeatable and regular step-up voltage controllable points dominated by the migration, aggregation or electric field distortion of the suspended water droplets are found. This step-up voltage is a sign of the start of regular PD behavior (such as stable discharge quantity distribution, phase concentration, etc.). The selection of this voltage takes into account both scientific rigor and engineering practicality, and provides key experimental support for the insulation design and condition assessment of transformers. Description of the drawings

[0014] Figure 1 It is the flow chart of the method of the present invention;

[0015] Figure 2 This is the laminar flow range diagram of the present invention;

[0016] Figure 2 Among them: In the developed transformer discharge defect system, the laminar flow range is determined. The points below the black solid line belong to the laminar flow state, avoiding the irregular discharge caused by the movement disorder of the suspended moving water droplets in the turbulent flow state, and thus it is difficult to analyze the PD law of the suspended moving water droplets.

[0017] Figure 3 This is the PRPD map of the embodiment of the present invention at a temperature of 40°C, with different three-dimensional step-up voltages and a flow rate of 0m 3 / h;

[0018] Figure 4 This is the PRPD map of the embodiment of the present invention at a temperature of 40°C, with different three-dimensional step-up voltages and a flow rate of 0.3m 3 / h;

[0019] Figure 5 This is the PRPD map of the embodiment of the present invention at a temperature of 40°C, with different three-dimensional step-up voltages and a flow rate of 0.6m 3 / h;

[0020] Figure 6 This is the PRPD map of the embodiment of the present invention at a temperature of 40°C, with different three-dimensional step-up voltages and a flow rate of 0.9m 3 / h;

[0021] Figures 3 to 6 Among them: The PRPD maps of different three-dimensional step-up voltages and different flow rates are drawn by Python, which is easier to explore the internal PD law of the suspended moving water droplets compared with two-dimensional maps such as phase-discharge amount, step-up voltage-discharge amount, and flow rate-discharge amount.

[0022] Figure 7 This is the PRPD map at a flow rate of 0m / h under a step-up voltage of 32 kV at a temperature of 40°C in the embodiment; 3 / h;

[0023] Figure 8 This is the PRPD map at a flow rate of 0.3m / h under a step-up voltage of 32 kV at a temperature of 40°C in the embodiment; 3 / h;

[0024] Figure 9 This is the PRPD map at a flow rate of 0.6m / h under a step-up voltage of 32 kV at a temperature of 40°C in the embodiment; 3 / h;

[0025] Figure 10 This is the PRPD map at a flow rate of 0.9m / h under a step-up voltage of 32 kV at a temperature of 40°C in the embodiment; 3 / h;

[0026] Figures 7 to 10 Among them: Determine the repeatable and regular step-up voltage controllable points dominated by the migration, aggregation or electric field distortion of suspended water droplets. This step-up voltage is a sign of the beginning of regular PD behavior (such as stable discharge quantity distribution, phase concentration, etc.). The selection of this voltage takes into account both scientific rigor and engineering practicability, providing key experimental support for the insulation design and condition assessment of transformers. Specific implementation mode

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0028] Refer to Figure 1 , a research method for the PD law of suspended water droplets in oil-immersed transformers, including the following steps:

[0029] S1: Determine the laminar flow range in the developed transformer discharge defect system;

[0030] S2: Boost the voltage through an AC voltage booster at different laminar flow (Reynolds number less than 2300) states;

[0031] S3: Collect PD signals according to the pulse current sensor recommended by IEC60270 standard;

[0032] S4: Transmit the signals when PD occurs in suspended water droplets in oil to a digital partial discharge detection system;

[0033] S5: Then use Python to draw PRPD maps under different step-up voltages and different flow velocity states in three dimensions;

[0034] S6: Finally, find the repeatable and regular step-up voltage controllable points dominated by the migration, aggregation or electric field distortion of suspended water droplets;

[0035] S7: Draw PRPD maps at this voltage and analyze the PD laws of suspended water droplets in oil-immersed transformers under different laminar flow states.

[0036] Keep the temperature at 40°C and the frequency at 50HZ unchanged. In the transformer discharge defect system, when the flow velocities are 0, 0.3, 0.6, 0.9 m 3 / h (all in laminar flow states), as Figure 2 shown, the points below the black solid line belong to the laminar flow state. Collect PD signals through a pulse current sensor and transmit them to a digital partial discharge detection system. Use Python to draw PRPD maps under different step-up voltages and different flow velocity states in three dimensions, as Figure 3As shown, in the static state: the phases corresponding to the overall discharge amount are distributed in the ranges of 5 - 60°, 150 - 260°, and 230 - 360°, showing the characteristics of wide-phase-band discharge. The high discharge amount (red area) is concentrated at high voltages (greater than 35 kV). The main reason is that the local electric field around the suspended water droplets in the oil-immersed transformer is concentrated or the surface charges of the water droplets accumulate due to the static insulation medium, resulting in continuous discharge. In the flowing state: the phase distribution area corresponding to the overall discharge amount is significantly reduced, and the red area is concentrated at voltages greater than 40 kV, indicating that in the flowing state, the transformer oil shortens the residence time of the surface charges of the suspended water droplets between the upper and lower plates, reducing the local electric field distortion between the plates, thereby suppressing the discharge.

[0037] As Figure 4 shown, at low flow rates (0 - 0.3 m 3 / h), the discharge shows a continuous type. The main reason is the stable discharge channel triggered by the gradual accumulation of the surface charges of the suspended water droplets. As Figure 5 shown, at high flow rates (0.6 - 0.9 m 3 / h), the discharge changes to an intermittent pulse type (phase concentration, increased voltage threshold). In the flowing state, the transformer oil causes the charges to not accumulate continuously, and the PD is only triggered when the externally applied voltage instantaneously exceeds the critical value.

[0038] As Figure 6 shown, as the externally applied step-up voltage increases, the phase distribution of the high-density PD region shows a regular shift. The core aggregation area gradually migrates from the initial 240° to 150°. This migration trend is significantly present under the four flow rate conditions (0 - 0.9 m 3 / h) and has a strong correlation with the voltage amplitude.

[0039] The above experimental data show that when the external electric field intensity on the suspended water droplets in the oil-immersed transformer reaches 32 kV, regular PD behaviors (such as stable discharge amount distribution, phase concentration, etc.) begin to appear, which can trigger a repeatable discharge mode dominated by water droplet migration, aggregation, or electric field distortion, providing a controllable starting point for studying the influence of laminar flow state on the dynamic characteristics of PD. 32 kV meets the recommended voltage range for initial PD detection in the transformer insulation state assessment standard of IEEE C57.104. The selection of this voltage takes into account both scientific rigor and engineering practicality, providing key experimental support for transformer insulation design and state assessment.

[0040] Keep the temperature at 40 °C, the frequency at 50 HZ, and the step-up voltage at 32 kV unchanged, and draw the overall PRPD maps of the suspended water droplets at flow rates of 0, 0.3, 0.6, and 0.9 m 3 / h, as Figures 7 to 10As shown in the figure, the envelope of the PRPD spectrum at all flow rates is an acute triangle. The envelope of the positive half cycle of the PRPD spectrum is smooth and has low volatility, indicating that the positive polarity discharge is less affected by the flow rate disturbance; the envelope of the negative half cycle is sharp and the discharge concentration phase is 190-300°, reflecting that the field strength distortion of the suspended water droplets at the upper and lower plates in the negative half cycle is more likely to trigger PD, and the smaller the flow rate, the higher the triangle. The main reason is that in the stage of suspended water droplets migrating to the high-voltage electrode in the negative half cycle, the charge separation at the dielectric interface aggravates the local field strength distortion and triggers PD near the phase of 200°.

[0041] Low flow rate (v<0.6m 3 / h), the number of discharge points in the whole cycle is large and the distribution is sparse, but the discharge amount near 200° in the negative half cycle is significantly higher than that in other areas; at high flow rate (v≥0.6m 3 / h), the discharge point density decreases and the flowing transformer oil forces the suspended water droplets to reach the critical field strength in a specific phase interval (200°~240°), which appears as a band-shaped point cluster. Under static conditions, the surface charge of the suspended water droplets continues to accumulate, triggering a high-amplitude discharge in a wide phase domain. The high envelope of the spectrum is due to the matching of the charge relaxation time and the power frequency period; under the flowing state, the fluid shear force strips off the charge, suppresses the electric field distortion, and leads to a decrease in the discharge amount and a concentrated phase.

[0042] The process of this experimental method can supplement the study of the PD law of suspended water droplets in oil-immersed transformers and the discharge theory in transformer oil containing suspended water droplets. By analyzing the basic law of PD of suspended water droplets in oil-immersed transformers under laminar flow (Reynolds number less than 2300), the collected PD signals are plotted by Python in three dimensions under different step-up voltages and different flow rates. Finally, the repeatable and regular step-up voltage controllable points dominated by the migration, aggregation or electric field distortion of suspended water droplets are found, which further provides ideas for the real-time charged detection of PD of suspended water droplets in oil-immersed transformers.

[0043] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

Claims

1. A research method for the PD law of suspended moving water droplets in oil-immersed transformers, characterized in that, It includes the following steps: (S1) Determine the laminar flow range in the developed transformer discharge defect system; (S2) Boost the voltage through an AC voltage booster under different laminar flow states; (S3) Collect partial discharge PD signals according to the pulse current sensor recommended by industry standards; (S4) Transmit the signals when partial discharge PD occurs in the suspended water droplets in oil to the digital partial discharge detection system; (S5) Draw the PRPD diagrams under different step-up voltages and different flow velocity states in three dimensions; (S6) Finally, find the controllable points of step-up voltage; (S7) Draw the PRPD diagram at this voltage and analyze the PD laws of the suspended water droplets in the oil-immersed transformer under different laminar flow states.

2. The research method for the PD law of suspended moving water droplets in an oil-immersed transformer according to claim 1, wherein In (S2), the laminar flow means that the Reynolds number is less than 2300.

3. The research method for the PD law of suspended moving water droplets in an oil-immersed transformer according to claim 1, characterized in that, (S5) Use Python to draw the PRPD diagram.

4. A method for studying the PD law of suspended moving water droplets in an oil-immersed transformer according to claim 1, characterized in that, (S6) Find the repeatable and regular controllable points of step-up voltage dominated by the migration, aggregation or electric field distortion of the suspended water droplets.

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