Oil-immersed transformer overload assessment method and intelligent operation and maintenance system and equipment

Abstract

An oil-immersed transformer overload assessment method and intelligent operation and maintenance system and equipment, comprising the following steps: step S1: obtaining the type, configuration and operating parameters of the transformer; step S2: calculating the relative aging rate V of the insulating paper; step S3: calculating the load rate K under the top oil temperature limit o,lim Load factor K under limit value and hot spot temperature limit h,lim Load rate K under limit value and relative aging rate limit V,lim limit value; Step S4: compare k j With K o,lim Limit value, K h,lim Limit value and K V,lim The relationship between the limit values ​​determines the load type of the transformer; step S5: according to the emergency load type of the transformer, the maximum load factor and the operating time t are calculated. The present invention realizes the evaluation of the overload multiple of the hot spot temperature of the transformer and the overload duration, and accurately evaluates the overload operation state and the duration of the transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of substation operation and maintenance, and in particular to an oil-immersed transformer overload assessment method and an intelligent operation and maintenance system and equipment. Background Art

[0002] As the most important substation equipment, the transformer has complete monitoring measures for grid operation data such as current, voltage, power and temperature. Some substations are also equipped with online detection devices to monitor partial discharge, gas in oil, etc. When the operation mode of the power system changes or another transformer in the substation trips due to a fault, the current transformer will be overloaded. Existing transformers generally allow short-term overload operation, but after a certain period of time, the service life of the transformer will be shortened. However, traditional grid operation data is difficult to fully evaluate the operating status of the transformer, and cannot provide the specific time when the transformer is allowed to operate under overload, which leads to the following problems: first, since the user cannot know the specific time when the transformer is allowed to operate under overload, the user cannot make reasonable arrangements based on this, which brings great inconvenience to practical applications; second, due to the lack of evaluation of the specific time when the transformer is overloaded, the staff can only find that the transformer has been overloaded when the transformer is operating abnormally, which is not conducive to timely handling by the staff and seriously affects the operating life of the transformer. Summary of the invention

[0003] The purpose of the present invention is to overcome the defects of the prior art and provide a reasonable and accurate oil-immersed transformer overload assessment method and an intelligent operation and maintenance system and equipment.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for evaluating overload of an oil-immersed transformer comprises the following steps:

[0006] Step S1: Obtain the type of transformer and the configuration and operating parameters of the transformer;

[0007] Step S2: obtaining the insulation paper type of the transformer according to the configuration and operating parameters of the transformer and calculating the relative aging rate V of the insulation paper;

[0008] Step S3: According to the obtained configuration and operating parameters corresponding to the transformer top oil temperature limit, hot spot temperature limit, relative aging rate V limit and the constraint relationship with the load factor K, calculate the load factor limit value K under the top oil temperature limit o,lim , Load factor limit value K under hot spot temperature limit h,lim , Load factor limit value K under relative aging rate limit V,lim ;

[0009] Step S4: According to the preset load factor vector k and the load factor limit value K under the top oil temperature limit value o,lim , Load factor limit value K under hot spot temperature limit h,lim And the load factor limit value K under the relative aging rate limit V,lim Step S5: when the transformer is judged to be a normal cycle load type, according to K V,lim Get the maximum load factor max K of the transformer;

[0010] When judging the transformer as a long-term emergency load type, according to K o,lim , K h,lim Get the maximum load factor max K;

[0011] When the transformer is judged to be a short-term emergency load type, the maximum load factor max K and the operating time t are calculated based on the configuration and operating parameters.

[0012] Preferably, in step S2, the transformer uses non-thermally modified insulating paper, and the calculation formula of its relative aging rate V is:

[0013]

[0014] The transformer uses thermally modified insulating paper, and the calculation formula for its relative aging rate V is: Among them, θ h The hottest point temperature.

[0015] Preferably, in step S3, according to the configuration and operating parameters of the transformer, a transient equation (I) corresponding to the temperature increase value of the load factor K is established:

[0016]

[0017] Among them, θ o is the top oil temperature, θ h is the transformer hot spot temperature, θ a is the ambient temperature, Δθ oi is the temperature rise of the top layer of oil in the tank at the beginning, Δθ hi is the gradient of the hot spot temperature to the top oil temperature at the beginning, Δθ or is the steady-state temperature rise of the top oil at rated loss, g r is the gradient of the average winding temperature to the average oil temperature at rated current, R is the ratio of load loss to no-load loss at rated current, K is the load factor, H is the hot spot factor, x is the oil index, and y is the exponential power of the current to the winding temperature rise;

[0018] Function f1(t) represents the relative increase in the top oil temperature rise when the steady-state value is 1. Function f1(t) is formula (1):

[0019]

[0020] In formula (1), c1 is the thermal model constant, τ o is the average oil time constant;

[0021] The function f2(t) represents the relative increase of the hot spot to the top oil temperature gradient when the steady-state value is 1. The function f2(t) is formula (2):

[0022]

[0023] In formula (2), c2 and c3 are thermal model constants, τ w is the winding time constant;

[0024] Let θ in equation (I) o (t) = F1(K, t), θ h (t) = F2(K, t), and establish the long-term emergency load operation capacity constraint equation (II):

[0025]

[0026] Based on the Newton-Raphson method, equation (II) is used to calculate the load factor limit value K under the top oil temperature limit. o,lim , Load factor limit value K under hot spot temperature limit h,lim , Load factor limit value K under relative aging rate limit V,lim .

[0027] Preferably, in step S4, a load rate vector k is preset, k=[k1, k2, ..., k j , …, k n ], k1<k2<…k j <…<k n ], j, n are positive integers, if k<K V,lim , then it is a normal cycle load type; if k <min(K o,lim , K h,lim ), it is a long-term emergency load type; if K h,lim <k <K o,lim or k>max(K o,lim , K h,lim ), it is a short-term emergency load type.

[0028] Preferably, in step S5, when it is determined that the transformer belongs to the normal cycle load type, the maximum load factor maxK=K V,lim ; When the transformer is judged to be a long-term emergency load type, the maximum load factor max K=min(K o,lim, K h,lim ).

[0029] Preferably, in step S5, when it is determined that the transformer belongs to the short-term emergency load type, the transformer initial load factor K in the configuration and operation parameters is i and transformer initial top oil temperature θ oi , establish the short-term emergency load operation capacity constraint equation (III):

[0030]

[0031] Based on the Newton-Raphson method, equation (III) is used to obtain the load factor limit value K under the top oil temperature limit. O,lim , Load factor limit value K under hot spot temperature limit H,lim , the operating time limit value t under the top oil temperature limit o,lim , operating time limit under hot spot temperature limit t h,lim , then the maximum load factor under the short-term emergency load type max K=min(K O,lim , K H,lim ), maximum running time t=min(t o,lim ,t h,lim ).

[0032] An intelligent operation and maintenance system, used to execute the above-mentioned oil-immersed transformer overload assessment method, characterized in that it includes a parameter configuration module, a data monitoring module, an assessment module, a data statistics module and a visualization module;

[0033] The parameter configuration module is communicatively connected with the evaluation module, and is used to provide the configuration parameters of the transformer to the evaluation module;

[0034] The data monitoring module is in communication connection with the evaluation module, and is used to provide the evaluation module with real-time operation data of the transformer;

[0035] The evaluation module calculates the real-time load capacity of the transformer according to the configuration parameters and real-time operation data of the transformer;

[0036] The data statistics module is in communication connection with the evaluation module, and the data statistics module establishes a state quantity database of the transformer according to the configuration parameters, real-time operation data and the calculated real-time load capacity provided by the evaluation module, and the state quantity database is used to record the historical data and real-time data of the transformer overload operation;

[0037] The visualization module is respectively connected to the evaluation module and the data statistics module for communicating with each other, and is used to present the operating status of the transformer's overload operating capacity.

[0038] Further, the configuration parameters provided by the parameter configuration module to the evaluation module include at least the nameplate information, design parameters, thermal characteristic parameters, routine test data and factory temperature rise test parameters of the transformer;

[0039] The nameplate information includes at least rated capacity, rated capacity, rated voltage, rated current, number of phases, cooling method, load loss, no-load loss and tap range;

[0040] The design parameters include at least the insulation paper type, the top oil rise limit, the winding temperature rise limit and the hot spot temperature limit;

[0041] The thermal characteristic parameters include at least oil index, winding index, thermal model constant, average oil time constant, winding time constant, loss ratio, hot spot coefficient, gradient of average winding temperature to average oil temperature at rated current, and steady-state temperature rise of top oil at rated loss;

[0042] The routine test data at least includes no-load loss measurement and load loss measurement;

[0043] The factory temperature rise test parameters include at least the top oil temperature at rated current, the ambient temperature at rated current, the average winding temperature at the moment of power failure, the average oil temperature at rated current and the hot spot temperature rise.

[0044] Furthermore, the data monitoring module obtains real-time operation data of the transformer, and the real-time operation data of the transformer at least includes real-time load current, real-time top oil temperature, real-time winding temperature and real-time ambient temperature.

[0045] Further, the evaluation module calculates the real-time load capacity of the transformer including determining the load type of the transformer, calculating the maximum load multiple and the sustainable operation time;

[0046] The operating status of the transformer overload operating capacity presented by the visualization module at least includes a load status instrument panel, a temperature status meter visual identification, an overload operating capacity trend tracking curve, and operating suggestions.

[0047] A computer device comprises at least one processor, wherein the at least one processor executes the above-mentioned oil-immersed transformer overload assessment method.

[0048] The oil-immersed transformer overload assessment method of the present invention implements the assessment of the transformer hot spot temperature, overload multiple and overload duration based on the obtained transformer configuration and real-time operating parameters, so as to accurately assess the transformer overload operating state and the duration. The user can make reasonable arrangements based on this to avoid the transformer from overtime overload operation and affecting the operating life.

[0049] An intelligent operation and maintenance system and equipment of the present invention realizes the evaluation of the hot spot temperature, overload multiple and overload duration of the transformer through the mutual cooperation between the parameter configuration module, the data monitoring module, the evaluation module and the data statistics module. The visualization module presents the operating status of the transformer's overload operating capacity, so that information such as the transformer's overload operating status and the duration can be accurately grasped.

[0050] In addition, the intelligent operation and maintenance system provides users with a multi-terminal visual data access method based on the industrial Internet platform. Key information such as equipment status data, alarm information, and evaluation reports can be viewed anytime and anywhere through computers and mobile phones, allowing managers to break through time and space limitations and make decisions quickly. It helps users understand the maximum load capacity of transformers and improve operating limits, which plays a very important role in the stable operation of power systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a functional block diagram of the intelligent operation and maintenance system of the present invention;

[0052] Figure 2 is a flow chart of the oil-immersed transformer overload assessment method of the present invention;

[0053] Figure 3 It is the long-term overload capacity trend diagram under different initial load rates and ambient temperatures;

[0054] Figure 4 It is the maximum allowable overload multiple and the temperature change trend with running time under different starting load rates (taking K = 1.22 as an example);

[0055] Figure 5 It is the changing trend of short-term overload capacity under different initial conditions. DETAILED DESCRIPTION

[0056] The following is combined with Figures 1 to 5 The given examples further illustrate the specific implementation of the oil-immersed transformer overload assessment method and intelligent operation and maintenance system of the present invention. The oil-immersed transformer overload assessment method and intelligent operation and maintenance system of the present invention are not limited to the description of the following examples.

[0057] Step S1: Obtain the type of transformer and the configuration and operating parameters of the transformer;

[0058] Step S2: obtaining the insulation paper type of the transformer according to the configuration and operating parameters of the transformer and calculating the relative aging rate V of the insulation paper;

[0059] Step S3: According to the obtained configuration and operating parameters corresponding to the transformer top oil temperature limit, hot spot temperature limit, relative aging rate V limit and the constraint relationship with the load factor K, calculate the load factor limit value K under the top oil temperature limit o,lim , Load factor limit value K under hot spot temperature limit h,lim , Load factor limit value K under relative aging rate limit V,lim ;

[0060] Step S4: According to the preset load rate vector k j The load factor limit value K under the top oil temperature limit o,lim , Load factor limit value K under hot spot temperature limit h,lim And the load factor limit value K under the relative aging rate limit V,lim The comparative relationship between them determines the load type of the transformer;

[0061] Step S5: After determining that the transformer is a normal cycle load type, according to K V,lim Get the maximum load factor max K of the transformer; when judging that the transformer is a long-term emergency load type, according to K o,lim , K h,lim Obtain the maximum load factor max K; when the transformer is judged to be a short-term emergency load type, the maximum load factor max K and the operating time t are calculated according to the configuration and operating parameters.

[0062] The oil-immersed transformer overload assessment method of the present invention implements the assessment of the transformer hot spot temperature, overload multiple and overload duration based on the obtained transformer configuration and operating parameters, and accurately assesses the transformer overload operating state and the duration. The user can make reasonable arrangements based on this to avoid the transformer from overtime overload operation and affecting the operating life.

[0063] An intelligent operation and maintenance system for executing the above-mentioned oil-immersed transformer overload assessment method, comprising a parameter configuration module, a data monitoring module, an assessment module, a data statistics module and a visualization module; the parameter configuration module is communicatively connected to the assessment module, and is used to provide the assessment module with the configuration parameters of the transformer; the data monitoring module is communicatively connected to the assessment module, and is used to provide the assessment module with the real-time operation data of the transformer; the assessment module calculates the real-time load capacity of the transformer according to the configuration parameters and real-time operation data of the transformer; the data statistics module is communicatively connected to the assessment module, and the data statistics module establishes a state quantity database of the transformer according to the configuration parameters, real-time operation data and calculation results provided by the assessment module, and the state quantity database is used to record the historical data and real-time data of the transformer overload operation; the visualization module is communicatively connected to the assessment module and the data statistics module, respectively, and is used to present the operating status of the transformer overload operation capacity.

[0064] An intelligent operation and maintenance system of the present invention realizes the evaluation of the hot spot temperature, overload multiple and overload duration of the transformer through the mutual cooperation between the parameter configuration module, the data monitoring module, the evaluation module and the data statistics module. The visualization module presents the operating status of the transformer's overload operating capacity, so that information such as the transformer's overload operating status and the duration can be accurately grasped.

[0065] A method for evaluating overload of an oil-immersed transformer combined with an intelligent operation and maintenance system is provided, which specifically includes the following steps:

[0066] Step S1: The parameter configuration module obtains the configuration parameters of the transformer, the data monitoring module obtains the operating parameters of the transformer when it is in operation, and the evaluation module determines the type of the transformer according to the three-phase maximum rated capacity of the obtained configuration parameters, wherein the three-phase maximum rated capacity SN≤2500kVA belongs to a distribution transformer, the three-phase maximum rated capacity 2500<SN≤100000kVA belongs to a medium-sized transformer, and the three-phase maximum rated capacity SN>100000kVA belongs to a large transformer.

[0067] Step S2: the evaluation module obtains the insulation paper type of the transformer according to the obtained configuration parameters, and calculates the relative aging rate V of the insulation paper;

[0068] When the transformer uses non-thermally modified insulating paper, the calculation formula for its relative aging rate V is: Among them, θ h The hottest point temperature.

[0069] When the insulation paper is thermally modified insulation paper, the calculation formula for its relative aging rate V is: Among them, θ h The hottest point temperature.

[0070] Step S3: The evaluation module calculates the load factor limit value K under the top oil temperature limit value according to the obtained configuration and operating parameters and the transformer top oil temperature limit value, hot spot temperature limit value, relative aging rate V limit value and the relationship between the load factor K. o,lim , Load factor limit value K under hot spot temperature limit h,lim , Load factor limit value K under relative aging rate limit V,lim .

[0071] The specific calculation process is as follows: Since the hot spot temperature of the transformer is equal to the temperature difference between the hot spot temperature in the oil tank and the top oil temperature, the ambient temperature θ a And the sum of the temperature rise of the top oil in the oil tank, and then the relationship between the temperature increase value of the load factor K, the transient equation (I) is established:

[0072]

[0073] Among them, θ o is the top oil temperature, θ h is the transformer hot spot temperature, θ a is the ambient temperature, Δθ oi is the temperature rise of the top layer of oil in the tank at the beginning, Δθ or is the steady-state temperature rise of the top oil at rated loss, g r is the gradient of the average winding temperature to the average oil temperature at rated current, R is the ratio of load loss to no-load loss at rated current, K is the load factor (load current / rated current), H is the hot spot factor, Δθ hi is the gradient of the hot spot temperature to the top oil temperature at the beginning, which is a thermal characteristic parameter, Δθ hi =Hg r K i y , K i is the transformer initial load factor, x is the oil index, and y is the exponential power of the current to the winding temperature rise;

[0074] Function f1(t) represents the relative increase in the top oil temperature rise when the steady-state value is 1. Function f1(t) is formula (1):

[0075]

[0076] In formula (1), c1 is the thermal model constant, τ o is the average oil time constant;

[0077] The function f2(t) represents the relative increase of the hot spot to the top oil temperature gradient when the steady-state value is 1. The function f2(t) is formula (2):

[0078]

[0079] In formula (2), c2 and c3 are thermal model constants, τ w is the winding time constant;

[0080] Let θ in equation (I) o (t) = F1(K, t), θ h (t) = F2(K, t), and establish the long-term emergency load operation capacity constraint equation (II):

[0081]

[0082] Based on the Newton-Raphson method, equation (II) is used to calculate the load factor limit value K under the top oil temperature limit. o,lim , Load factor limit value K under hot spot temperature limit h,lim , Load factor limit value K under relative aging rate limit V,lim .

[0083] Step S4: Preset the load factor vector k in the evaluation module. The load factor vector k is in array form, which stores [k1, k2, ..., k j， …, k n ], where k1<k2<…k j <…k n , j, n are positive integers, preferably, k n ≤1.8, the evaluation module compares the preset load rate k with the load factor limit value K under the top oil temperature limit o,lim , Load factor limit value K under hot spot temperature limit h,lim And the load factor limit value K under the relative aging rate limit V,lim Compare and judge the load type of the transformer accordingly. If k<K V,lim , then it is a normal cycle load type; if k <min(K o,lim , K h,lim ), it is a long-term emergency load type; if K h,lim <k <K o,lim or k>max(K o,lim , K h,lim ), it is a short-term emergency load type. It should be noted that in the actual comparison process, K o,lim , K o,lim , K h,lim The three types of transformers are determined by comparing the values ​​in the preset load rate vector k.

[0084] Step S5: When the transformer is judged to be of normal cycle load type, its maximum load factor max K=K V,limWhen the transformer is judged as a long-term emergency load type, its maximum load factor max K=min(K o,lim , K h,lim );

[0085] When judging that the transformer is a short-term emergency load type, the transformer initial load factor K in the configuration and operation parameters is used. i and the top oil temperature of the transformer starting oil tank θ oi The maximum load factor max K and the operating time limit t under the top oil temperature limit are calculated. o,lim , operating time limit under hot spot temperature limit t h,lim , according to t o,lim and t h,lim Obtain the maximum sustainable operating time t under the short-term emergency load type.

[0086] The specific calculation process is:

[0087] Establish the short-term emergency load operation capacity constraint equation (III):

[0088]

[0089] Among them, K i is the transformer initial load rate, which is an operating parameter obtained in real time, θ oi is the transformer's initial top oil temperature, and the top oil temperature rise Δθ at the current moment is calculated by the initial load rate and initial ambient temperature oi 、Starting top oil temperatureθ oi 、Hotspot temperature rise Δθ hi Based on the Newton-Raphson method, equation (III) is used to obtain the load factor limit value K under the top oil temperature limit. O,lim , Load factor limit value K under hot spot temperature limit H,lim , operating time limit value t under the top oil temperature limit o,lim , operating time limit under hot spot temperature limit t h,lim , then the maximum sustainable operating time under the short-term emergency load type is t = min (t o,lim ,t h,lim ), maximum load factor max K=min(K O,lim , K H,lim ).

[0090] The intelligent system for executing the above-mentioned calculation process includes a parameter configuration module, a data monitoring module, an evaluation module, a data statistics module and a visualization module, wherein the parameter configuration module, the data monitoring module and the evaluation module are communicatively connected based on the industrial Internet, and the evaluation module is also communicatively connected with the data statistics module and the visualization module based on the industrial Internet.

[0091] Among them, the parameter configuration module is used to provide the configuration parameters of the transformer to the evaluation module, and the configuration parameters include at least the nameplate information, design parameters, thermal characteristic parameters, routine test data and factory temperature rise test parameters of the transformer; the nameplate information includes at least rated capacity, rated capacity, rated voltage, rated current, number of phases, cooling method, load loss, no-load loss and tap range; the design parameters include at least insulation paper type, top oil rise limit, winding temperature rise limit and hot spot temperature limit; the thermal characteristic parameters include at least oil index, winding index, thermal model constant, average oil time constant, winding time constant, loss ratio, hot spot coefficient, gradient of average winding temperature to average oil temperature under rated current and steady-state temperature rise of top oil under rated loss; the routine test data include at least no-load loss measurement and load loss measurement; the factory temperature rise test parameters include at least top oil temperature under rated current, ambient temperature under rated current, average winding temperature at power-off moment, average oil temperature under rated current and hot spot temperature rise.

[0092] The data monitoring module is used to provide the evaluation module with real-time operation data of the transformer. Preferably, the data monitoring module requests the real-time operation data of the transformer through the network interface of the monitoring system or the SCADA system. The real-time operation data of the transformer at least includes real-time load current, real-time top oil temperature, real-time winding temperature and real-time ambient temperature.

[0093] The evaluation module calculates the real-time load capacity of the transformer according to the configuration parameters of the transformer and the real-time operation data, and the real-time load capacity includes the judgment of the load type of the transformer, the calculation of the maximum load rate and the calculation of the sustainable operation time. Preferably, the load type of the transformer mainly includes the normal cycle load type, the long-term overload type and the short-term emergency overload type, among which the normal cycle load type can be considered to be classified as the long-term overload type.

[0094] The data statistics module establishes a transformer state quantity database according to the configuration parameters provided by the evaluation module, the real-time operation data and the calculated real-time load capacity of the transformer, and the state quantity database is used to record the historical data and real-time data of the transformer overload operation.

[0095] The visualization module is respectively connected to the evaluation module and the data statistics module for communicating and presenting the operating status of the transformer overload operating capacity. The operating status of the transformer overload operating capacity presented by the visualization module at least includes a load status instrument panel, a temperature status meter visual identification (i.e., a graphical display of the temperature status by the meter), an overload operating capacity trend tracking curve, and operating suggestions. The visualization module is a mobile phone, a computer, or a display screen.

[0096] Combination Figure 1-5 As well as Tables 1-4, provide an embodiment of a method for evaluating overload of an oil-immersed transformer using an intelligent operation and maintenance system at a 35kV substation.

[0097] The configuration parameters of the on-site transformer are obtained through the configuration parameter module in the intelligent operation and maintenance system. The nameplate information mainly includes: model SWZ11-125000 / 35, three-phase three-winding, oil-immersed self-cooling; the design parameters mainly include: non-thermally modified insulation paper type, top oil rise limit value θ o，lim =105℃, hot spot temperature limitθ h，lim =140℃; thermal characteristic parameters are shown in Table 1, routine test data (i.e. loss measurement test) are shown in Table 2 and Table 3, factory temperature rise test parameters and calculation data are shown in Table 4. The temperature rise test adopts the short-circuit method, high-to-low pressure, high voltage 7 taps, test stabilization time 3 hours, temperature change per hour does not exceed 1K, the total loss that should be applied during the test is 75.28kW, the actual total loss applied is 75.28kW, and then the rated current is applied for 1 hour, the winding thermal resistance is measured, and the winding temperature rise is calculated.

[0098] Table 1 Transformer thermal characteristic parameters

[0099]

[0100] Table 2 No-load loss measurement

[0101]

[0102] Table 3 Load loss measurement

[0103]

[0104] Table 4 Temperature rise test measurement and calculation data results

[0105]

[0106] The data monitoring module requests the real-time operation data of the transformer through the network interface of the substation monitoring system. The operation data includes operation parameters such as load current and ambient temperature.

[0107] The evaluation module calculates the real-time load capacity of the transformer according to the configuration parameters and real-time operating parameters provided by the data monitoring module and the configuration parameter module, based on the oil-immersed transformer overload evaluation method. The load types mainly include long-term emergency load types (considering that the normal cycle load types are classified as long-term overload types) and short-term emergency load types.

[0108] Long-term emergency load is caused by the long-term out-of-service of some transformers in the system, which will accelerate the aging of the operating transformer, but will not directly endanger the safety of insulation. Long-term emergency load may last for weeks or months. It is recommended to minimize the chance of this operation mode. When it must be used, try to shorten the time of over-rated current operation, reduce the multiple of over-rated current, and put in standby coolers according to the manufacturer's regulations when conditions permit. If the transformer has serious defects (such as abnormal cooling system, serious oil leakage, local overheating, abnormal analysis results of dissolved gas in oil, etc.) or insulation has weaknesses, it is not suitable to operate with over-rated current.

[0109] When the transformer is operated in a long-term load type, under different initial load rates, the relationship between the maximum allowable load factor of the transformer and the ambient temperature is as follows: Figure 3 As shown by Figure 3 It can be seen that the maximum allowable load factor under the hot spot temperature limit is always smaller than the maximum load factor evaluated by the top oil temperature limit, which shows that the long-term overload capacity of the transformer depends on the constraint of the hot spot temperature limit; when the ambient temperature is constant, the maximum allowable load factor is independent of the starting load rate of the transformer; and when the starting load rate is constant, the maximum allowable load factor decreases with the increase of ambient temperature.

[0110] K i =0.5,θ a =40℃, for example, K is calculated based on equation (II) constraints. o,lim =1.24, K h,lim =1.22, select the smaller value as the maximum allowable load load max K = 1.22, the maximum allowable load factor (taking K = 1.22 as an example) and the trend of the hot spot temperature and top oil temperature of the transformer with the running time under different starting load rates are as follows Figure 2 As shown by Figure 2 It can be seen that when the transformer is in long-term emergency load operation conditions, after long-term operation for about 500 minutes, the hot spot temperature approaches the limit value, while the top oil temperature has not yet reached the limit value, indicating that the temperature limit of the transformer is mainly limited by the hot spot temperature.

[0111] Short-term emergency load means that due to an accident in the system, the transformer is severely overloaded in a short period of time. The hot spot temperature of the transformer winding may reach a dangerous level and may cause a temporary decrease in insulation strength. Under this type of load operation, it is recommended to put all coolers, including spare ones, into use (unless otherwise specified by the manufacturer), and try to compress the load and reduce the time. The load duration generally does not exceed 0.5h.

[0112] When the ambient temperature remains unchanged, the short-term emergency overload capacity of the transformer under different starting conditions is evaluated. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that the maximum sustainable operation time allowed by the transformer for short-term emergency operation decreases as the initial load rate and the top oil temperature increase. i =0.5,θ oi =52℃ initial state, the critical load rate point of the transformer in short-term emergency operation is 1.35pu, and the maximum sustainable operation time is 158min. When the maximum load rate is 1.8pu, the maximum sustainable operation time is only 21min. i =0.8,θ oi =66.29℃, the critical load rate of the transformer in the short-term emergency operation state is 1.35pu, and the maximum sustainable operation time is 133min. When the maximum load rate is 1.8pu, the maximum sustainable operation time is only 16min. i =1.0,θ oi =78.3℃ initial state, the critical load rate point of the transformer entering short-term emergency operation state is 1.35pu, and the maximum sustainable operation time is 97min. When the corresponding maximum load rate is 1.8pu, the longest sustainable operation time allowed is only 11min. The results show that the higher the load rate, the shorter the maximum sustainable operation time.

[0113] The present invention also provides a computer device, comprising at least one processor, wherein the at least one processor executes the oil-immersed transformer overload assessment method of the present invention. The computer device is installed with a program for implementing the oil-immersed transformer overload assessment method to implement the oil-immersed transformer overload assessment and intelligent operation and maintenance system.

[0114] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for evaluating overload of an oil-immersed transformer, characterized in that: The following steps are included: Step S1: Obtain the type of transformer and the configuration and operating parameters of the transformer; Step S2: obtaining the insulation paper type of the transformer according to the configuration and operating parameters of the transformer and calculating the relative aging rate V of the insulation paper; Step S3: According to the obtained configuration and operating parameters corresponding to the transformer top oil temperature limit, hot spot temperature limit, relative aging rate V limit and the constraint relationship with the load factor K, calculate the load factor limit value K under the top oil temperature limit o,lim , Load factor limit value K under hot spot temperature limit h,lim , Load factor limit value K under relative aging rate limit V,lim ; Step S4: According to the preset load factor vector k and the load factor limit value K under the top oil temperature limit value o,lim , Load factor limit value K under hot spot temperature limit h,lim And the load factor limit value K under the relative aging rate limit V,lim The comparative relationship between them determines the load type of the transformer; Step S5: When the transformer is judged to be of normal cycle load type, according to K V,lim Get the maximum load factor max K of the transformer; When judging the transformer as a long-term emergency load type, according to K o,lim , K h,lim Get the maximum load factor max K; When the transformer is judged to be a short-term emergency load type, the maximum load factor max K and the operating time t are calculated based on the configuration and operating parameters; In step S3, according to the configuration and operating parameters of the transformer, a transient equation (I) corresponding to the temperature increase value of the load factor K is established: Among them, θ o is the top oil temperature, θ h is the transformer hot spot temperature, θ a is the ambient temperature, Δθ oi is the temperature rise of the top layer of oil in the tank at the beginning, Δθ hi is the gradient of the hot spot temperature to the top oil temperature at the beginning, Δθ or is the steady-state temperature rise of the top oil at rated loss, g r is the gradient of the average winding temperature to the average oil temperature at rated current, R is the ratio of load loss to no-load loss at rated current, K is the load factor, H is the hot spot factor, x is the oil index, and y is the exponential power of the current to the winding temperature rise; Function f1(t) represents the relative increase in the top oil temperature rise when the steady-state value is 1. Function f1(t) is formula (1): In formula (1), c1 is the thermal model constant, τ o is the average oil time constant; The function f2(t) represents the relative increase of the hot spot to the top oil temperature gradient when the steady-state value is 1. The function f2(t) is formula (2): In formula (2), c2 and c3 are thermal model constants, τ w is the winding time constant; Let θ in equation (I) o (t) = F1(K, t), θ h (t) = F2(K, t), and establish the long-term emergency load operation capacity constraint equation (II): Based on the Newton-Raphson method, equation (II) is used to calculate the load factor limit value K under the top oil temperature limit. o,lim , Load factor limit value K under hot spot temperature limit h,lim , Load factor limit value K under relative aging rate limit V,lim .

2. The oil-immersed transformer overload assessment method according to claim 1, characterized in that: In step S2, the transformer uses non-thermally modified insulating paper, and the calculation formula of its relative aging rate V is: The transformer uses thermally modified insulating paper, and the calculation formula for its relative aging rate V is: Among them, θ h The hottest point temperature.

3. The oil-immersed transformer overload assessment method according to claim 1, characterized in that: In step S4, a load factor vector k is preset, where k = [k1, k2, ..., k j ,…,k n ], k1<k2<…k j <…<k n ], j, n are positive integers, if k<K V,lim , then it is a normal cycle load type; if k <min(K o,lim , K h,lim ), it is a long-term emergency load type; if K h,lim <k <K o,lim or k>max(K o,lim , K h,lim ), it is a short-term emergency load type.

4. The oil-immersed transformer overload assessment method according to claim 3, characterized in that: In step S5, when it is determined that the transformer belongs to the normal cycle load type, the maximum load factor max K = K V,lim ; When the transformer is judged to be a long-term emergency load type, the maximum load factor max K=min(K o,lim , K h,lim ).

5. The oil-immersed transformer overload assessment method according to claim 3, characterized in that: In step S5, after determining that the transformer belongs to the short-term emergency load type, the transformer initial load factor K in the configuration and operation parameters is i and transformer initial top oil temperature θ oi , establish the short-term emergency load operation capacity constraint equation (III): Based on the Newton-Raphson method, equation (III) is used to obtain the load factor limit value K under the top oil temperature limit. O,lim , Load factor limit value K under hot spot temperature limit H,lim , the operating time limit value t under the top oil temperature limit o,lim , operating time limit under hot spot temperature limit t h,lim , then the maximum load factor under the short-term emergency load type max K=min(K O,lim , K H,lim ), maximum running time t=min(t o,lim ,t h,lim ).

6. An intelligent operation and maintenance system, used to execute the oil-immersed transformer overload assessment method according to any one of claims 1 to 5, characterized in that: It includes parameter configuration module, data monitoring module, evaluation module, data statistics module and visualization module; The parameter configuration module is communicatively connected with the evaluation module, and is used to provide the configuration parameters of the transformer to the evaluation module; The data monitoring module is in communication connection with the evaluation module, and is used to provide the evaluation module with real-time operation data of the transformer; The evaluation module calculates the real-time load capacity of the transformer according to the configuration parameters and real-time operation data of the transformer; The data statistics module is in communication connection with the evaluation module, and the data statistics module establishes a state quantity database of the transformer according to the configuration parameters, real-time operation data and the calculated real-time load capacity provided by the evaluation module, and the state quantity database is used to record the historical data and real-time data of the transformer overload operation; The visualization module is respectively connected to the evaluation module and the data statistics module for communicating with each other, and is used to present the operating status of the transformer's overload operating capacity.

7. The intelligent operation and maintenance system according to claim 6, characterized in that: The configuration parameters provided by the parameter configuration module to the evaluation module include at least the nameplate information, design parameters, thermal characteristic parameters, routine test data and factory temperature rise test parameters of the transformer; The nameplate information includes at least rated capacity, rated capacity, rated voltage, rated current, number of phases, cooling method, load loss, no-load loss and tap range; The design parameters include at least the insulation paper type, the top oil rise limit, the winding temperature rise limit and the hot spot temperature limit; The thermal characteristic parameters include at least oil index, winding index, thermal model constant, average oil time constant, winding time constant, loss ratio, hot spot coefficient, gradient of average winding temperature to average oil temperature at rated current, and steady-state temperature rise of top oil at rated loss; The routine test data at least includes no-load loss measurement and load loss measurement; The factory temperature rise test parameters include at least the top oil temperature at rated current, the ambient temperature at rated current, the average winding temperature at the moment of power failure, the average oil temperature at rated current and the hot spot temperature rise.

8. The intelligent operation and maintenance system according to claim 6, characterized in that: The data monitoring module obtains real-time operation data of the transformer, and the real-time operation data of the transformer at least includes real-time load current, real-time top oil temperature, real-time winding temperature and real-time ambient temperature.

9. The intelligent operation and maintenance system according to claim 6, characterized in that: The evaluation module calculates the real-time load capacity of the transformer, including determining the load type of the transformer, calculating the maximum load multiple and the sustainable operation time; The operating status of the transformer overload operating capacity presented by the visualization module at least includes a load status instrument panel, a temperature status meter visual identification, an overload operating capacity trend tracking curve, and operating suggestions.

10. A computer device comprising at least one processor, characterized in that: The at least one processor executes the oil-immersed transformer overload assessment method according to any one of claims 1-5.

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