Method for evaluating insulating property and service life of transformer in new energy access lower harbor district

Abstract

The invention discloses a new energy access lower harbor area transformer insulation performance and service life evaluation method, which comprises the following steps: firstly, establishing a wind and light storage AC / DC hybrid micro-grid equivalent simulation model, and quantifying a composite action mechanism of new energy fluctuation and harmonic characteristics on dynamic loss and hot-spot temperature rise of a transformer; analyzing a harmonic loss mechanism of the transformer in different operation modes; secondly, constructing a quay crane and field crane operation simulation model, and analyzing the harmonic characteristics of bridge crane equipment and the influence of the harmonic characteristics on the harmonic distortion rate of the power distribution network; then, on the basis of the data, a transformer hot-spot temperature dynamic calculation model is established in combination with bidirectional power flow characteristics; and finally, calculating transient temperature distribution of the transformer through a flow field-temperature field coupling method, and constructing a multi-physical field coupled insulation aging rate model to realize evaluation of the residual life of the transformer. The method solves the problem that the traditional method cannot quantify the bidirectional power flow and harmonic wave composite aging effect.

Description

Technical Field

[0001] The present invention relates to the field of port area power system and reliability technology, and in particular to a method for evaluating the insulation performance and life of a port area transformer under the condition of new energy access. Background Art

[0002] Against the backdrop of profound changes in the global energy system, the new power system presents typical technical characteristics of a high proportion of new energy access and bidirectional energy flow. As a key energy-intensive infrastructure, the port power supply network promotes low-carbon and electrification through the integration of wind power, photovoltaic power generation units and energy storage systems. The grid connection and reverse transmission of distributed power generation units form a bidirectional energy interaction scenario. However, it is worth noting that the volatility of renewable energy output, the high penetration rate of power electronic equipment and the large-scale application of various types of bridge crane equipment have exacerbated the harmonic pollution problem of the port distribution network. The frequent switching of bidirectional power flows has caused abnormal operation of key power grid equipment, which is manifested in chain reactions such as sudden changes in transformer load direction, dynamic loss accumulation and thermal stress cyclic oscillation.

[0003] As a key node for bidirectional energy transmission in port power systems, transformers are constantly subjected to multi-dimensional disturbances in dynamic load environments. Their insulation structures are subjected to the synergistic impact of alternating electromagnetic and thermomechanical coupled fields, leading to accelerated degradation of material properties. Such operating conditions can cause winding hotspot temperature fluctuations to several times those seen under conventional conditions, leading to nonlinear degradation of transformer life. In port electrification, large-scale loading and unloading equipment such as quay cranes and yard cranes have been widely used due to their high operational efficiency. These quay cranes and yard cranes are high-power nonlinear loads, and their operation can cause significant power fluctuations, increasing harmonic distortion in the distribution network, thereby affecting grid power quality and threatening transformer operational safety. Against this backdrop, in-depth research on the evolution of multi-field coupling effects under bidirectional power flows and the development of equipment condition assessment models adapted to the characteristics of bidirectional power flow have become key technical approaches for improving the operational reliability of new power systems.

[0004] Existing research focuses on unidirectional load or single harmonic source scenarios, ignoring the intermittent output of distributed energy in port microgrids under energy structure transformation, superimposed with impact loads such as shore power systems, quay cranes, and yard cranes. This leads to the frequent "source-load" power imbalance in the system, causing multi-harmonic coupling and bidirectional power mutations. The dynamic thermal-electric coupling mechanism of transformers in bidirectional energy interaction is unclear, and there is a lack of a multi-dimensional transformer insulation performance and life assessment framework that takes into account bidirectional power flow characteristics. This makes it difficult to quantify the cumulative effect of load direction switching on the insulation aging rate.

[0005] Therefore, there is an urgent need to establish a dynamic model of the port area microgrid under bidirectional power flow switching, reveal the multi-physical field interaction degradation mechanism of transformer insulation aging in an environment with a high proportion of new energy access; and construct a transformer insulation performance and life assessment model that integrates magnetic flux density, current harmonic distortion rate, and hot spot temperature rise to provide solutions for enhancing the reliability of port area transformers and improving the efficiency of their full life cycle management. Summary of the Invention

[0006] In response to the above-mentioned deficiencies in the existing technology, the present invention provides a method for evaluating the insulation performance and life of transformers in port areas with the access of new energy. By establishing a new energy-bridge crane multi-harmonic coupling model and a dynamic temperature rise algorithm, combined with fluid-solid coupling temperature field simulation, an accurate evaluation of the insulation status and remaining life of transformers in port areas with a high proportion of new energy access is achieved.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A method for evaluating the insulation performance and life of a transformer in a new energy access area in a lower port area includes the following steps:

[0009] S1. Establish an equivalent simulation model of a wind-solar-storage-AC-DC hybrid microgrid to quantify the combined effect of renewable energy volatility and harmonic characteristics on the dynamic losses and hotspot temperature rise of the port microgrid transformer, and derive the harmonic loss mechanism under different transformer operation modes.

[0010] S2. Analyze the operating characteristics of the gantry crane equipment and construct a simulation model for the operation of the quay crane and yard crane to analyze the harmonic characteristics of the gantry crane equipment connected to the port distribution network, thereby quantifying the impact of the gantry crane equipment operating status on the harmonic distortion rate of the current at the head-end node of the port distribution network;

[0011] S3. Based on the new energy harmonic loss mechanism output from step S1 and the bridge crane harmonic distortion rate output from step S2, combined with the microgrid implementation monitoring data and transformer design parameters, the bidirectional power flow correction coefficient is used to analyze the combined impact of the bidirectional power flow on the transformer aging process, and a transformer hot spot temperature dynamic model is constructed by improving the IEC354 standard;

[0012] S4. Based on the transformer hotspot temperature dynamic model, the flow field-temperature field coupling method is used to obtain the coupling relationship between the transformer temperature field and the flow field, and then the transient temperature distribution of the transformer is calculated; according to the transient temperature distribution of the transformer, a multi-field coupled transformer insulation aging rate model is constructed to obtain the transformer life assessment result.

[0013] As a preferred solution, in step S1, the different transformer operating modes include: transformer light load mode, transformer heavy load mode, multi-transformer parallel mode and distributed energy grid connection mode; by calculating the harmonic-loss mapping relationship under different operating modes, the harmonic loss mechanism under different transformer operating modes is obtained, including:

[0014] When the transformer is in light load mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic iron loss:

[0015]

[0016] Where, P Fe is the harmonic iron loss, K h is the hysteresis loss coefficient, K e is the eddy current loss coefficient, K a is the additional loss coefficient, f is the operating frequency, V is the core volume, B m is the magnetic flux density amplitude, V h is the hth harmonic voltage, f h is the hth harmonic frequency, N is the number of winding turns, and A is the cross-sectional area of ​​the core;

[0017] When the transformer is in heavy load mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic copper loss:

[0018]

[0019]

[0020] Where, P Cu is the harmonic copper loss, I h is the hth harmonic current, R ac,h is the hth harmonic AC resistance, R dc is the DC resistance, f1 is the fundamental frequency;

[0021] In the multi-transformer parallel mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic resonance loss:

[0022]

[0023] Where, f res,h is the harmonic resonant frequency, L eq is the system equivalent inductance, C eq is the system equivalent capacitance;

[0024] In the distributed energy grid-connected mode, the harmonic loss mechanism of the transformer under different operating modes is obtained by calculating the harmonic superposition loss:

[0025]

[0026] Where, I total,h is the total harmonic current, I inv,h is the inverter hth harmonic current, I bg,h is the background hth harmonic current, θ h is the phase difference.

[0027] As a preferred solution, in step S2, the impact of the operating state of the bridge crane equipment on the harmonic distortion rate of the current at the head-end node of the port area distribution network includes:

[0028] The impact of electrical distance on the harmonic distortion rate of current at the headend node of the port area distribution network: The harmonic distortion rate of current decreases with the increase of the electrical distance from the access point of the bridge crane equipment to the headend node of the distribution network. Among them, the quay crane access shows a quadratic attenuation characteristic, while the yard crane access shows a linear attenuation characteristic.

[0029] Impact of the number of connections on the harmonic distortion rate of the head-end node current: When multiple bridge cranes are connected, the impact of the increase in the number of quay cranes on the harmonic distortion rate of the head-end node current of the port distribution network is greater than the impact of the increase in the number of yard cranes on the harmonic distortion rate of the head-end node current of the port distribution network.

[0030] As a preferred solution, the electrical distance calculation formula is:

[0031] d=R all +ωL all ;

[0032] Where d is the electrical distance from the bridge crane access point to the head end node of the distribution network, R all is the sum of the line resistance from the bridge crane access point to the first end node of the distribution network, L all is the sum of the line inductance from the bridge crane access location to the head end node of the distribution network, and ω is the system angular frequency.

[0033] As a preferred solution, in step S3, the formula of the transformer hot spot temperature dynamic model is:

[0034]

[0035] Where, Indicates the transformer hot spot temperature, Indicates the real-time ambient temperature. Indicates the temperature rise of the top oil temperature over the ambient temperature. It is the temperature rise of the winding hot spot above the top oil temperature.

[0036] As a preferred solution, in step S4, the formula for the coupling relationship between the transformer temperature field and the flow field is expressed as:

[0037]

[0038] Where ρ is the transformer oil density, c is the transformer specific heat capacity, T is the temperature length, u, v, w represent the components of the oil tassel in the x, y, z directions respectively, k is the thermal conductivity, Q is the heat generated by the microelement, is the harmonic operator.

[0039] As a preferred solution, in step S4, the formula of the multi-field coupled transformer insulation aging rate model is expressed as:

[0040]

[0041] Where r(T) is the transformer aging rate at the instantaneous hot spot temperature T, A is the pre-factor, and E a is the activation energy, and R is the gas constant.

[0042] As a preferred solution, in step S4, the transformer life assessment result is obtained by assessing the transformer's remaining life calculated based on the accumulated insulation aging of the transformer;

[0043] The formula for the remaining life of the transformer is expressed as:

[0044]

[0045] Where L is the remaining life of the transformer, L0 is the initial life of the transformer, T(t) is the hot spot temperature of the transformer at time t, r(T(t)) is the insulation aging rate of the transformer at time t, is the cumulative insulation aging of the transformer at time t.

[0046] As a preferred solution, in step S4, before obtaining the transformer life assessment result, the multi-field coupled transformer insulation aging rate model is further corrected by the transformer accelerated aging factor;

[0047] The formula for the transformer accelerated aging factor is expressed as:

[0048]

[0049] Where, F AA is the transformer accelerated aging factor, is the reference value of the hot spot temperature, and C1 and C2 are acceleration factor constants.

[0050] Compared with the prior art, the present invention has the following technical effects:

[0051] 1. The present invention establishes an equivalent simulation model of a wind-solar-storage-AC-DC hybrid microgrid to quantify the combined effect of the fluctuating output of new energy and harmonic characteristics on the dynamic loss and hotspot temperature rise of the port microgrid transformer, analyzes the harmonic loss mechanism of the transformer under different operating modes of light load, heavy load, parallel connection and energy grid connection, and completely reveals the coupling mechanism of new energy harmonics and bridge crane load harmonics, solving the technical problem that traditional evaluation methods cannot quantify the superposition effect of multiple harmonic sources; by establishing a hotspot stability dynamic model including bidirectional flow correction, it breaks through the limitations of the traditional analysis framework based on steady-state or unidirectional flow assumptions in dynamic load evaluation, improves the calculation accuracy, and provides theoretical support for transformer insulation performance analysis and remaining life evaluation.

[0052] 2. The present invention obtains a simulation model of the operation of quay cranes and yard cranes by analyzing the operating characteristics of the bridge crane equipment. The analysis shows that when large-scale logistics loading and unloading equipment (bridge crane equipment) is connected to the port distribution network, the pulse load characteristics of the bridge crane equipment will induce a time-varying response of the power grid parameters, which is manifested as a sudden change in load power and a transient offset in the current phase, resulting in a significant increase in the harmonic impact of the system; through the mapping relationship between the harmonic distortion rate and the life of the transformer, the influence of the bridge crane access position, number and operating status on the harmonic distortion rate of the head node of the distribution network and the life of the transformer is quantified, providing decision support for the port power infrastructure operation and maintenance personnel to optimize the harmonic control strategy and build a preventive maintenance mechanism.

[0053] 3. Based on the new energy harmonic loss mechanism and the harmonic distortion rate of the bridge crane, the present invention combines the microgrid implementation monitoring data and the transformer design parameters, analyzes the impact of bidirectional power flow on the aging of port transformers, and establishes a dynamic model of transformer hotspot temperature in combination with the improved IEC354 standard; proposes a transformer hotspot temperature dynamic mapping method based on flow field-temperature field coupling, constructs a multi-field coupled transformer insulation aging rate model, and obtains the transformer life assessment result. In this way, the problem of the lack of transformer status methods adapted to the electrification and low-carbon port scenarios in the existing technology is solved, and the problem of the lack of dynamic assessment methods adapted to the port scenarios in the existing technology is solved, which helps to improve the safety and economy of port transformer operation and enhance the reliability and full life cycle management efficiency of the port power infrastructure. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to make the purpose, technical solutions and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0055] Figure 1 This is a flow chart of the insulation performance and life evaluation method for the new energy access transformer in the Xiagang area disclosed in the present invention;

[0056] Figure 2 This is a structural diagram of the equivalent simulation model of the wind-solar-storage-AC-DC hybrid microgrid in the present invention;

[0057] Figure 3 The structural diagram of the quay crane simulation model in the present invention;

[0058] Figure 4 This is a structural diagram of the field bridge simulation model proposed in the present invention;

[0059] Figure 5 This is a diagram showing the relationship between the access location of the bridge crane equipment and the harmonic distortion rate of the current at the head end node of the distribution network in the present invention;

[0060] Figure 6 This is a diagram showing the relationship between the number of bridge crane devices stacked and the harmonic distortion rate of the current at the head-end node of the distribution network in the present invention;

[0061] Figure 7 The transformer life span changes with time under different operating conditions in the present invention;

[0062] Figure 8 This is a graph showing the change in the average life of the transformer under different working conditions in the transformer life assessment of the present invention. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but only represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0064] The present invention will be described in further detail below with reference to the accompanying drawings.

[0065] In the existing technology, the insulation performance and life assessment of port area transformers cannot adapt to the harmonic effects and multi-physical field coupling effects under the condition of high proportion of new energy access, frequent power flow switching, bridge crane equipment access status, and the effect of multi-physical field coupling, resulting in the inability to accurately assess the actual insulation performance and remaining life of port area transformers. In response to the above problems, the present invention provides a method for assessing the insulation performance and life of port area transformers under new energy access. By establishing an equivalent simulation model of a wind, solar, AC, and DC hybrid microgrid, the combined effects of the fluctuating output of new energy and the harmonic characteristics on the dynamic loss and hot spot temperature rise of the port area microgrid transformer are quantified, the harmonic loss mechanism of the transformer under different operating modes is analyzed, and a multi-field coupled transformer insulation aging rate model is constructed to evaluate the transformer life, thereby ensuring the reliable operation and optimized management of the transformer in the port area power system.

[0066] like Figure 1 As shown, the present invention discloses a method for evaluating the insulation performance and life of a transformer in the lower port area connected to new energy:

[0067] S1. Establish an equivalent simulation model of a wind-solar-storage-AC-DC hybrid microgrid to quantify the combined effect of renewable energy volatility and harmonic characteristics on the dynamic losses and hotspot temperature rise of the port microgrid transformer, and derive the harmonic loss mechanism under different transformer operation modes.

[0068] S2. Analyze the operating characteristics of the gantry crane equipment and construct a simulation model for the operation of the quay crane and yard crane to analyze the harmonic characteristics of the gantry crane equipment connected to the port distribution network, thereby quantifying the impact of the gantry crane equipment operating status on the harmonic distortion rate of the current at the head-end node of the port distribution network;

[0069] S3. Based on the new energy harmonic loss mechanism output from step S1 and the bridge crane harmonic distortion rate output from step S2, combined with the microgrid implementation monitoring data and transformer design parameters, the bidirectional power flow correction coefficient is used to analyze the combined impact of the bidirectional power flow on the transformer aging process, and a transformer hot spot temperature dynamic model is constructed by improving the IEC354 standard;

[0070] S4. Based on the transformer hotspot temperature dynamic model, the flow field-temperature field coupling method is used to obtain the coupling relationship between the transformer temperature field and the flow field, and then the transient temperature distribution of the transformer is calculated; according to the transient temperature distribution of the transformer, a multi-field coupled transformer insulation aging rate model is constructed to obtain the transformer life assessment result.

[0071] The present invention proposes a method for evaluating the insulation performance and life of transformers in port areas with new energy access. First, an equivalent simulation model of a wind, solar and storage microgrid is established to study the combined effects of new energy power generation fluctuations and grid harmonics on transformer loss and heat generation, and analyze the harmonic loss laws under different working modes; then, a simulation model is constructed for the port's unique bridge crane equipment to determine the impact of the harmonics generated when the bridge crane is working on the grid; then, the analysis results of the previous two steps are combined, considering the characteristics of bidirectional current flow, and the existing temperature calculation standard is improved through a preset bidirectional power flow correction coefficient obtained by calibrating the transformer cooling system characteristics to obtain a more accurate dynamic temperature rise model; finally, the dynamic temperature rise model is used to calculate the temperature changes inside the transformer, and combined with the material aging law, the remaining life of the transformer is accurately predicted.

[0072] For step S1, in this embodiment, the equivalent simulation model of the wind-solar-storage-AC-DC hybrid microgrid is established as follows: Figure 2 As shown in the figure, the microgrid includes wind power generation units, photovoltaic power generation units and energy storage units. Based on this model, the impact of the fluctuating output and harmonic characteristics of renewable energy on the dynamic loss and hot spot temperature rise of the port area microgrid transformer is analyzed, and the impact of harmonics in the system on the transformer under different transformer operation modes is compared.

[0073] Specifically, in step S1, the combined effect of renewable energy volatility and harmonic characteristics on the dynamic loss and hotspot temperature rise of the port microgrid transformer is quantified in the following way:

[0074] During transformer operation, no-load losses are relatively stable, while hotspot temperature rise is primarily influenced by load losses. Load losses include winding resistance losses, eddy current losses, and stray losses caused by magnetic flux leakage. The former two directly affect winding temperature, while the latter causes transformer oil temperature to rise through magnetic flux leakage. The large-scale integration of renewable energy often leads to system overload, harmonic distortion, and frequent short-circuit failures, significantly increasing load losses.

[0075] In other words, due to the cumulative effect of heat, when the additional losses generated by harmonics and overload prevent heat from dissipating quickly, the hotspot temperature continues to rise, which in turn accelerates the aging of the insulation material. In a compound mechanism, the increased losses caused by harmonics increase the winding resistance, further increasing losses. High temperatures also reduce oil viscosity, reducing cooling capacity and further increasing temperatures, forming a positive feedback loop.

[0076] Specifically:

[0077] (1) Under overload conditions, the load current surges, causing the winding hotspot temperature to rise nonlinearly;

[0078] (2) Harmonic components induce additional eddy current losses;

[0079] (3) The short-circuit current shock causes the winding temperature rise rate to increase sharply, resulting in a heat accumulation effect in a short period of time.

[0080] It can be seen that the access of new energy will lead to a compound strengthening trend of transformer load loss and its associated thermal effects.

[0081] In specific implementation, in step S1, the different transformer operating modes include: transformer light load mode, transformer heavy load mode, multi-transformer parallel mode and distributed energy grid connection mode; by calculating the harmonic-loss mapping relationship under different operating modes, the harmonic loss mechanism under different transformer operating modes is obtained, including:

[0082] When the transformer is in light load mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic iron loss:

[0083]

[0084] Where, P Fe is the harmonic iron loss, K h is the hysteresis loss coefficient, K e is the eddy current loss coefficient, K a is the additional loss coefficient, f is the operating frequency, V is the core volume, B m is the magnetic flux density amplitude, V h is the hth harmonic voltage, f h is the hth harmonic frequency, N is the number of winding turns, and A is the cross-sectional area of ​​the core;

[0085] When the transformer is in heavy load mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic copper loss:

[0086]

[0087] Where, P Cu is the harmonic copper loss, I h is the hth harmonic current, R ac,h is the hth harmonic AC resistance, R dc is the DC resistance, f1 is the fundamental frequency;

[0088] In the multi-transformer parallel mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic resonance loss:

[0089]

[0090] Where, f res,h is the harmonic resonant frequency, L eq is the system equivalent inductance, C eq is the system equivalent capacitance;

[0091] In the distributed energy grid-connected mode, the harmonic loss mechanism of the transformer under different operating modes is obtained by calculating the harmonic superposition loss:

[0092]

[0093] Where, I total,h is the total harmonic current, I inv,h is the inverter hth harmonic current, I bg,h is the background hth harmonic current, θ h is the phase difference.

[0094] Regarding step S2, in this embodiment, the constructed quay crane and yard crane simulation model is as follows: Figure 3 and Figure 4 As shown in the figure, the model is based on the Simulink asynchronous motor simulation module. By controlling the electromagnetic torque value, it accurately reproduces and studies the operating characteristics of the bridge crane equipment, simulates the power consumption during actual operation, and analyzes the harmonic characteristics of this type of port logistics loading and unloading equipment. It then quantifies the impact of different operating conditions of the bridge crane on the harmonic current distortion rate of the common node at the head end of the distribution network and the life of the port transformer.

[0095] In specific implementation, the impact of the operating status of the bridge crane equipment on the harmonic distortion rate of the current at the head-end node of the port area distribution network includes:

[0096] The influence of electrical distance on the harmonic distortion rate of the current at the head end node of the port area distribution network: Figure 5 As shown in the figure, the current harmonic distortion rate decays with the increase of the electrical distance from the access location of the bridge crane equipment to the head node of the distribution network; specifically, with the increase of the electrical distance, the harmonic distortion rate shows a downward trend; in the case of quay crane access, the relationship between the harmonic distortion rate and the electrical distance is a quadratic relationship, that is, with the increase of the electrical distance, the rate of decrease of the harmonic distortion rate gradually slows down; in the case of field bridge access, it shows a linear relationship, that is, with the increase of the electrical distance, the harmonic distortion rate decreases at a constant rate.

[0097] The electrical distance calculation formula is:

[0098] d=R all +ωL all ;

[0099] Where d is the electrical distance from the bridge crane access point to the head end node of the distribution network, R all is the sum of the line resistance from the bridge crane access point to the first end node of the distribution network, L all is the sum of the line inductance from the bridge crane access point to the head end node of the distribution network, and ω is the system angular frequency;

[0100] The impact of the number of connections on the harmonic distortion rate of the head-end node current: Figure 6 As shown in the figure, under the condition that both the quay crane and the yard crane are connected at the head-end node, when multiple cranes are connected, the effect of the increase in the number of quay cranes on the harmonic distortion rate of the head-end node current of the port distribution network is greater than the effect of the increase in the number of yard cranes on the harmonic distortion rate of the head-end node current of the port distribution network, that is, the superimposed connection of the quay cranes has a significant positive impact on the harmonic distortion rate of the head-end node, and the increase in the number of yard cranes has little effect on the harmonic distortion rate.

[0101] For step S3, in this embodiment, by analyzing the changes in the transformer current load, additional loss and cooling capacity under bidirectional power flow, the influence of bidirectional power flow on the transformer aging process is analyzed, and the influence of harmonic current is taken into account. The hot spot temperature estimation formula in the IEC354 standard is improved, and based on the improved IEC354 standard, a transformer hot spot temperature calculation model is given, which can accurately calculate the transformer hot spot temperature and provide important theoretical support for evaluating the remaining life of the transformer.

[0102] In specific implementation, the formula of the transformer hot spot temperature dynamic model is:

[0103]

[0104] Where, Indicates the transformer hot spot temperature, Indicates the real-time ambient temperature. Indicates the temperature rise of the top oil temperature over the ambient temperature. It is the temperature rise of the winding hot spot above the top oil temperature.

[0105] in, and Calculated by the following formula:

[0106]

[0107] Where, and They represent the initial and final temperature rises of the transformer winding hot spot relative to the top oil within the time interval t; τ h Indicates the winding time constant, which is only related to the material structure of the transformer winding; and They represent the initial and final temperature rises of the top oil relative to the environment within the time interval t; τ to represents the top oil time constant;

[0108] τ to The calculation formula is:

[0109]

[0110] Where, τ to,R represents the top oil time constant under rated load; n∈[0.8,1] represents the transformer top oil temperature rise calculation index, and when n=1, τ to =τ to,R ; is the rated temperature rise of the top oil relative to the environment.

[0111] and and satisfy:

[0112]

[0113] Where, P R is the resistance loss; P EC is the eddy current loss; P NL is the no-load loss; P LL is the load loss, and R is the rated value of the corresponding variable.

[0114] The calculation formulas for various types of losses are:

[0115]

[0116] P EC =F EC k EC P R ;

[0117] P OSL =F B F OSL k OSL P R ;

[0118]

[0119] P LL =P R +P EC +P OSL ;

[0120] Where, P OSL is the stray loss; I T is the effective value of the fundamental component phase current of the load current flowing through the transformer; R T is the transformer resistance parameter; k EC ∈[0.05,0.15] is the eddy current loss coefficient; k OSL ∈[0.05,0.2] is the stray loss coefficient; B Tm is the maximum value of transformer magnetic flux density; δ h , δ e are the hysteresis loss and eddy current loss coefficients in the transformer core respectively; f RThe rated frequency of the transformer; F R 、F EC 、F OSL are the harmonic loss calculation factors for resistance loss, eddy current loss, and stray loss respectively; F B is the magnetic density variation compensation coefficient.

[0121] For step S4, in this embodiment, a dynamic mapping method of the transformer hot spot temperature of the fluid-solid coupling temperature field is proposed based on the heating and heat dissipation characteristics of the transformer. Based on the evolution law of the transformer operating state obtained based on the multi-physical field coupling effect, a multi-field coupled transformer insulation aging rate model is constructed, and the transformer life is evaluated based on this model.

[0122] In specific implementation, in step S4, the formula for the coupling relationship between the transformer temperature field and the flow field is expressed as:

[0123]

[0124] Where ρ is the transformer oil density, c is the transformer specific heat capacity, T is the temperature length, u, v, w represent the components of the oil tassel in the x, y, z directions respectively, k is the thermal conductivity, Q is the heat generated by the microelement, is the harmonic operator.

[0125] In specific implementation, in step S4, the formula of the multi-field coupled transformer insulation aging rate model is expressed as:

[0126]

[0127] Where r(T) is the transformer aging rate at the instantaneous hot spot temperature T, A is the pre-factor, and E a is the activation energy, and R is the gas constant.

[0128] In a specific implementation, in step S4, the transformer life assessment result is obtained by assessing the remaining life of the transformer calculated based on the accumulated insulation aging of the transformer;

[0129] The formula for the remaining life of the transformer is expressed as:

[0130]

[0131] Where L is the remaining life of the transformer, L0 is the initial life of the transformer, T(t) is the hot spot temperature of the transformer at time t, r(T(t)) is the insulation aging rate of the transformer at time t, is the cumulative insulation aging of the transformer at time t, and (T+273) is the absolute temperature converted from temperature.

[0132] In specific implementation, in step S4, before obtaining the transformer life assessment result, the multi-field coupled transformer insulation aging rate model is also corrected by the transformer accelerated aging factor;

[0133] The formula for the transformer accelerated aging factor is expressed as:

[0134]

[0135] Where, F AA is the transformer accelerated aging factor; The reference value of hot spot temperature is 110℃, which is recommended by IEEE. However, for transformers designed according to GB1094 series standard for power transformers, the commonly used reference value of hot spot temperature is 98℃ under rated load and normal ambient temperature. C1 and C2 are both acceleration factor constants. According to IEEE concept, C1=1.31×10 9 , C2=16158.

[0136] Figure 7 The curve of transformer life changing with time under different operating conditions is shown in Figure 2. Figure 7 It can be seen that when the ambient temperature, load disturbance and cooling conditions are random or fluctuate slightly every day, the transformer life consumption obtained by simulation based on the transformer aging model changes over time. Figure 7 Each line in the figure corresponds to a complete simulation process. The results reflect the differences in transformer life consumption caused by small perturbations in initial conditions and the randomness of the operating environment, and also reflect the discrete characteristics of the transformer aging process in the actual operating environment.

[0137] In order to verify the effectiveness of the transformer life assessment in this embodiment, this embodiment evaluates the average life of the transformer under different simulation conditions. The results are as follows: Figure 8 As shown, it can be seen Figure 8 The model simulates the change in transformer lifespan over time under six simulation conditions: load factors (50%, 80%, and 100%), cooling capacities (normal, 30% reduction, and 20% increase), and ambient temperatures (normal and 40°C). The results for all six conditions demonstrate a linear increase in transformer lifespan over time. However, due to the differences in operating conditions, the degree of transformer aging varies, validating the practical engineering applicability of this lifespan assessment model.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described with reference to the preferred embodiments of the present invention, it should be understood by those skilled in the art that various changes can be made in form and details without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A method for evaluating the insulation performance and life of transformers in the lower port area with new energy access, characterized in that: The steps include: S1. Establish an equivalent simulation model of a wind-solar-storage-AC-DC hybrid microgrid to quantify the combined effect of renewable energy volatility and harmonic characteristics on the dynamic losses and hotspot temperature rise of the port microgrid transformer, and derive the harmonic loss mechanism under different transformer operation modes. S2. Analyze the operating characteristics of the gantry crane equipment and construct a simulation model for the operation of the quay crane and yard crane to analyze the harmonic characteristics of the gantry crane equipment connected to the port distribution network, thereby quantifying the impact of the gantry crane equipment operating status on the harmonic distortion rate of the current at the head-end node of the port distribution network; S3. Based on the new energy harmonic loss mechanism output from step S1 and the bridge crane harmonic distortion rate output from step S2, combined with the microgrid implementation monitoring data and transformer design parameters, the bidirectional power flow correction coefficient is used to analyze the combined impact of the bidirectional power flow on the transformer aging process, and a transformer hot spot temperature dynamic model is constructed by improving the IEC354 standard; S4. Based on the transformer hotspot temperature dynamic model, the flow field-temperature field coupling method is used to obtain the coupling relationship between the transformer temperature field and the flow field, and then the transient temperature distribution of the transformer is calculated; according to the transient temperature distribution of the transformer, a multi-field coupled transformer insulation aging rate model is constructed to obtain the transformer life assessment result.

2. The method for evaluating the insulation performance and life of transformers in the lower port area connected to new energy according to claim 1 is characterized in that: In step S1, the different operating modes of the transformer include: transformer light load mode, transformer heavy load mode, multi-transformer parallel mode and distributed energy grid connection mode; by calculating the harmonic-loss mapping relationship under different operating modes, the harmonic loss mechanism under different operating modes of the transformer is obtained, including: When the transformer is in light load mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic iron loss: Where, P Fe is the harmonic iron loss, K h is the hysteresis loss coefficient, K e is the eddy current loss coefficient, K a is the additional loss coefficient, f is the operating frequency, V is the core volume, B m is the magnetic flux density amplitude, V h is the hth harmonic voltage, f h is the hth harmonic frequency, N is the number of winding turns, and A is the cross-sectional area of ​​the core; When the transformer is in heavy load mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic copper loss: Where, P Cu is the harmonic copper loss, I h is the hth harmonic current, R ac,h is the hth harmonic AC resistance, R dc is the DC resistance, f1 is the fundamental frequency; In the multi-transformer parallel mode, the harmonic loss mechanism of the transformer in different operating modes is obtained by calculating the harmonic resonance loss: Where, f res,h is the harmonic resonant frequency, L eq is the system equivalent inductance, C eq is the system equivalent capacitance; In the distributed energy grid-connected mode, the harmonic loss mechanism of the transformer under different operating modes is obtained by calculating the harmonic superposition loss: Where, I total,h is the total harmonic current, I inv,h is the inverter hth harmonic current, I bg,h is the background hth harmonic current, θ h is the phase difference.

3. The insulation performance and life evaluation method of the new energy access transformer in the lower port area according to claim 1 is characterized in that: In step S2, the impact of the operating status of the bridge crane equipment on the harmonic distortion rate of the current at the head-end node of the port area distribution network includes: The impact of electrical distance on the harmonic distortion rate of current at the headend node of the port area distribution network: The harmonic distortion rate of current decreases with the increase of the electrical distance from the access point of the bridge crane equipment to the headend node of the distribution network. Among them, the quay crane access shows a quadratic attenuation characteristic, while the yard crane access shows a linear attenuation characteristic. Impact of the number of connections on the harmonic distortion rate of the head-end node current: When multiple bridge cranes are connected, the impact of the increase in the number of quay cranes on the harmonic distortion rate of the head-end node current of the port distribution network is greater than the impact of the increase in the number of yard cranes on the harmonic distortion rate of the head-end node current of the port distribution network.

4. The method for evaluating the insulation performance and life of transformers in the lower port area connected to new energy according to claim 3 is characterized in that: The electrical distance calculation formula is: d=R all +ωL all ; Where d is the electrical distance from the bridge crane access point to the head end node of the distribution network, R all is the sum of the line resistance from the bridge crane access point to the first end node of the distribution network, L all is the sum of the line inductance from the bridge crane access location to the head end node of the distribution network, and ω is the system angular frequency.

5. The method for evaluating the insulation performance and life of transformers in the lower port area connected to new energy according to claim 1 is characterized in that: In step S3, the transformer hotspot temperature dynamic model is expressed as follows: Where, Indicates the transformer hot spot temperature, Indicates the real-time ambient temperature. Indicates the temperature rise of the top oil temperature over the ambient temperature. It is the temperature rise of the winding hot spot above the top oil temperature.

6. The method for evaluating the insulation performance and life of transformers in the lower port area connected to new energy according to claim 1 is characterized in that: In step S4, the formula for the coupling relationship between the transformer temperature field and the flow field is expressed as: Where ρ is the transformer oil density, c is the transformer specific heat capacity, T is the temperature length, u, v, w represent the components of the oil tassel in the x, y, z directions respectively, k is the thermal conductivity, Q is the heat generated by the microelement, is the harmonic operator.

7. The method for evaluating the insulation performance and life of transformers in the lower port area connected to new energy according to claim 6 is characterized in that: In step S4, the formula of the multi-field coupled transformer insulation aging rate model is expressed as: Where r(T) is the transformer aging rate at the instantaneous hot spot temperature T, A is the pre-factor, and E a is the activation energy, and R is the gas constant.

8. The method for evaluating the insulation performance and life of transformers in the lower port area connected to new energy according to claim 7 is characterized in that: In step S4, the transformer life assessment result is obtained by assessing the transformer's remaining life calculated based on the accumulated insulation aging of the transformer; The formula for the remaining life of the transformer is expressed as: Where L is the remaining life of the transformer, L0 is the initial life of the transformer, T(t) is the hot spot temperature of the transformer at time t, r(T(t)) is the insulation aging rate of the transformer at time t, is the cumulative insulation aging of the transformer at time t.

9. The method for evaluating the insulation performance and life of transformers in the lower port area connected to new energy according to claim 7 is characterized in that: In step S4, before obtaining the transformer life assessment result, the multi-field coupled transformer insulation aging rate model is corrected by the transformer accelerated aging factor; The formula for the transformer accelerated aging factor is expressed as: Where, F AA is the transformer accelerated aging factor, θ h is the reference value of the hot spot temperature, and C1 and C2 are acceleration factor constants.

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