A method for evaluating dynamic load capacity of an oil-immersed power transformer

Abstract

The application discloses a kind of oil-immersed power transformer dynamic load capacity evaluation method, establishes transformer dynamic load capacity evaluation model, considers the operating condition of transformer, in combination with the threshold of various constraint conditions, determine the dynamic load capacity of corresponding operating condition;Again, the mathematical model of dynamic load capacity evaluation including hot spot temperature, ambient temperature, load rate and other parameters is established, the threshold of hot spot temperature, top layer oil temperature, life loss and other constraint conditions is determined according to operating condition, then 24 h load curve and ambient temperature curve corresponding to operating condition are obtained, after the overall multiplication or reduction of load curve, the corresponding hot spot temperature, top layer oil temperature, life loss value are calculated, and whether threshold is reached is judged, if any threshold is reached, then the corresponding load curve is the final dynamic load curve.Through the method of the application, transformer dynamic load curve can be more accurately determined, and the most sensitive constraint limiting load is obtained.

Description

Technical Field

[0001] This invention relates to the field of dynamic load capacity technology for transformers, and in particular to a method for evaluating the dynamic load capacity of oil-immersed power transformers. Background Technology

[0002] With the rapid growth of electricity load, the peak-to-valley difference has been widening year by year. In 2017, Beijing's peak-to-valley difference reached a maximum of 47.03%, Tianjin's reached 40.85%, and Guangzhou's reached 46.91% in 2019. This fluctuating load characteristic has led to a decrease in the overall utilization rate of power equipment. Simultaneously, the deepening of my country's power market reform and the continuous increase in medium- and long-term market trading volume have made transmission congestion an urgent problem to be solved. Transmission congestion generally occurs during peak hours or under special operating conditions. Blindly expanding the network cannot fully utilize the equipment's transmission capacity, and the contradiction between the safe operation of power system equipment and huge equipment investments is becoming increasingly prominent. While mitigating system investment and ensuring safety, maximizing the rational utilization of the transmission capacity of existing power circuits is crucial. As a key power equipment in the power system, transformers require comprehensive dynamic load capacity assessment. This assessment, while ensuring system stability and equipment safety, allows for adjustments to transformer load capacity to maximize their load capacity, improve transformer utilization, and ensure the safe and stable operation of the system. This is a key issue currently of concern in the power system and has an urgent engineering need.

[0003] Regarding the dynamic load capacity assessment of transformers:

[0004] Chinese patent CN201310697510.4 provides a dynamic capacity expansion method for oil-immersed transformers. It simplifies the heat conduction process inside the transformer into a circuit model and calculates the winding hot spot temperature, top oil temperature, average oil temperature, and average winding temperature of the transformer under the current load conditions. The winding hot spot temperature is limited to no more than 140°C. If the internal temperature of the transformer may exceed the limit value of the short-term emergency load, the time to reach the limit value and the last reached steady-state temperature are calculated as an alarm signal.

[0005] Chinese patent CN202110624626.X describes a dynamic capacity expansion system for transformers based on transformer monitoring. The system is characterized in that when the transformer winding hotspot temperature is not greater than a winding hotspot temperature threshold, the transformer surface infrared imaging temperature is not greater than a transformer surface temperature threshold, and the gas content in the transformer oil is not greater than a gas content threshold, the server does not generate an alarm signal and increases the transformer load. Conversely, if the conditions are not met, the server generates an alarm signal and transmits the alarm signal type to the monitoring terminal.

[0006] Chinese patent CN201711078950.6 comprehensively analyzes the factors affecting transformer hot spot temperature, incorporating the influence of solar radiation power and comprehensively considering the changes in load loss and oil viscosity with temperature to establish a hot spot temperature calculation model, further improving the accuracy of the hot spot temperature calculation results. Using transformer hot spot temperature, relative loss life, and auxiliary equipment capacity level as constraints on load capacity, the load capacity of the transformer is accurately assessed based on its safe and stable operation.

[0007] Chinese patents CN202111499876.1, CN201120420823.1, and CN202210073268.2, among other invention or utility model patents, all provide different schemes for evaluating transformer load capacity.

[0008] However, the above methods all have the following shortcomings when evaluating the dynamic load capacity of transformers:

[0009] The dynamic load capacity of transformers is categorized into different scenarios, such as system planning, seasonal peak electricity consumption, and emergency support for nearby equipment failures, corresponding to different time scales. The methods mentioned above do not consider temperature and load fluctuations when assessing the dynamic load capacity of transformers, usually assuming that the load and ambient temperature are constant values, resulting in a margin in the assessment results. However, the constraints in the dynamic load process of transformers are usually based on hot spot temperature. But top oil temperature, insulation life loss, etc., may also become constraints that limit the dynamic current carrying capacity of transformers. Using only the hot spot temperature not exceeding the threshold as a constraint cannot accurately determine the bottleneck point that limits the transformer load. Therefore, when assessing the dynamic load capacity of transformers, it is necessary to fully consider hot spot temperature, top oil temperature, insulation life loss, etc.

[0010] Therefore, a method for evaluating the dynamic load capacity of oil-immersed power transformers is needed. Summary of the Invention

[0011] This invention provides a method for evaluating the dynamic load capacity of an oil-immersed power transformer, thereby addressing at least the technical problem of inaccurate evaluation of the dynamic load capacity of transformers in related technologies.

[0012] According to one aspect of the present invention, a method for evaluating the dynamic load capacity of an oil-immersed power transformer is provided, comprising:

[0013] Step 1: Establish a dynamic load capacity assessment model for transformers;

[0014] Step 2: Set the basic parameters of the transformer dynamic load capacity assessment model;

[0015] Step 3: Based on the transformer's operating conditions, determine the time range for dynamic load capacity assessment, life loss, and threshold values ​​for top oil temperature and hot spot temperature.

[0016] Step 4: Set the initial iteration factor for the typical load curve in Step 2, and generate a new load curve;

[0017] Step 5: Set the initial top oil temperature rise and hot spot temperature rise values, and input the new load curve into the transformer hot spot temperature estimation model, top oil temperature estimation model, and insulation life loss estimation model for calculation to obtain the real-time transformer top oil temperature, hot spot temperature, and insulation life loss.

[0018] Step 6: Determine whether the real-time transformer top oil temperature, hot spot temperature, and insulation life loss exceed the corresponding threshold. If any one of them exceeds the corresponding threshold, the loop iteration factor is reduced and the process proceeds to step 4 for recalculation; otherwise, proceed to step 7.

[0019] Step 7: Determine whether the transformer top oil temperature, hot spot temperature, and insulation life loss are equal to any threshold. If any of the transformer top oil temperature, hot spot temperature, and insulation life loss are equal to the corresponding threshold, the loop iteration stops, and the dynamic load curve, hot spot temperature curve, top oil temperature curve, life loss curve, maximum load rate, and threshold load factors are output. Otherwise, the loop iteration factor increases and the process enters step 4 for recalculation.

[0020] Optionally, the basic parameters of the transformer dynamic load capacity assessment model include: a set of typical load and ambient temperature curves of the transformer, the transformer oil time constant, the winding time constant, and the temperature rise of the top oil and hot spots of the transformer under rated operating conditions.

[0021] Optionally, the typical load and ambient temperature curves are 24-hour load and ambient temperature curves.

[0022] Optionally, establishing a transformer dynamic load capacity assessment model includes establishing the objective function and constraints of the transformer dynamic load capacity assessment model.

[0023] Optionally, forming a new load curve includes multiplying the initial cycle iteration factor L of the typical load curve with the 24-hour typical load curve data to obtain a new load curve.

[0024] Optionally, the expression for the transformer dynamic load capacity assessment model is:

[0025] max K

[0026]

[0027] In the above formula, K is the load factor, and θh For hotspot temperature, θ o For top oil temperature, L tot θ represents the transformer insulation life loss within the corresponding time range. hlim For hotspot temperature threshold, θ tlim For the top oil temperature threshold, L lim This is the threshold for insulation life loss.

[0028] Optionally, the loop iteration factor is reduced by 0.1.

[0029] Optionally, the loop iteration factor is increased by 0.1.

[0030] Compared with existing technologies, the present invention has the following advantages:

[0031] This invention provides a method for evaluating the dynamic load capacity of oil-immersed power transformers. It establishes a dynamic load capacity evaluation model for the transformer, considering its operating conditions and incorporating threshold values ​​for various constraints to determine the dynamic load capacity for each condition. A mathematical model for dynamic load capacity evaluation, including parameters such as hot spot temperature, ambient temperature, and load rate, is then established. Threshold values ​​for constraints such as hot spot temperature, top oil temperature, and lifespan loss are determined based on the operating conditions. Next, the 24-hour load curve and ambient temperature curve for the corresponding operating conditions are obtained. After doubling or subtracting the load curve, the corresponding hot spot temperature, top oil temperature, and lifespan loss values ​​are calculated, and it is determined whether any threshold value is reached. If any threshold value is reached, the corresponding load curve is the final dynamic load curve. This method enables more accurate determination of the transformer's dynamic load curve and the identification of the most sensitive constraints limiting the load. Attached Figure Description

[0032] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart of a method for evaluating the dynamic load capacity of an oil-immersed power transformer according to an embodiment of the present invention. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0036] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0037] According to an embodiment of the present invention, an embodiment of a method for evaluating the dynamic load capacity of an oil-immersed power transformer is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0038] like Figure 1 This is a flowchart of a dynamic load capacity assessment method for an oil-immersed power transformer according to an embodiment of the present invention, as shown below. Figure 1 As shown, the method includes the following steps:

[0039] Step 1: Establish a dynamic load capacity assessment model for transformers, including establishing the objective function and constraints of the dynamic load capacity assessment model for transformers.

[0040] The expression for the transformer dynamic load capacity assessment model is as follows:

[0041]

[0042] In the above formula, K is the load factor, and θ h For hotspot temperature, θ o For top oil temperature, L tot θ represents the insulation life loss of the transformer within the corresponding time range. hlim For hotspot temperature threshold, θ tlim For the top oil temperature threshold, L limThis is the threshold for insulation life loss.

[0043] The formula for calculating insulation life loss is:

[0044]

[0045] in:

[0046]

[0047] In the above formula, N represents the number of time intervals in that period, and V... n and t n These represent the relative aging rate of the insulation and the time within the nth time interval, respectively, where V is the relative aging rate and n is the number of time intervals.

[0048] The formula for estimating the top oil temperature is:

[0049]

[0050] In the above formula, R is the ratio of load loss to no-load loss under rated current; x is the transformer oil index; Δθ or The temperature rise of the transformer top oil under rated losses; k 11 τ is a constant; t is the running time in minutes; τ is the running time in minutes. o θ is the transformer average oil time constant, in minutes; a The ambient temperature is expressed in °C.

[0051] The formula for calculating the temperature rise of hotspots is:

[0052] Δθ h =Δθ h1 -Δθ h2 (5)

[0053] Where, Δθ h1 , Δθ h2 Let K be the temperature gradient reduction value of the hot spot on the top oil corresponding to the loading rate K, expressed by the following formula:

[0054]

[0055]

[0056] In the above formula, k 21 k 22 Δθ is a constant; hi τ represents the initial gradient between the transformer hot spot temperature and the top oil temperature; W is the time constant of the hot spot location in the transformer winding, in minutes; y is the winding index.

[0057] The formula for calculating the hotspot temperature is:

[0058] θ h =θ o +Δθ h (8)

[0059] Step 2: Set the basic parameters of the transformer dynamic load capacity assessment model.

[0060] Specifically, the basic parameters of the transformer dynamic load capacity assessment model include: a set of typical load and ambient temperature curves for the transformer, the transformer oil time constant, the winding time constant, and the temperature rise of the top oil and hot spots under rated operating conditions. The typical load and ambient temperature curves are 24-hour load and ambient temperature curves.

[0061] Step 3: Based on the transformer's operating conditions, determine the time range for dynamic load capacity assessment, life loss, and threshold values ​​for top oil temperature and hot spot temperature.

[0062] Step 4: Set the initial iteration factor L of the typical load curve in Step 2, usually set to 1, and multiply the typical load curve with the 24h typical load curve data to form a new load curve.

[0063] Step 5: Set the initial top oil temperature rise and hot spot temperature rise values, and input the new load curve into the transformer hot spot temperature estimation model, top oil temperature estimation model, and insulation life loss estimation model for calculation to obtain the transformer top oil temperature, hot spot temperature, and insulation life loss.

[0064] Step 6: Determine whether the transformer top oil temperature, hot spot temperature, and insulation life loss exceed the corresponding threshold. If any one of them exceeds the corresponding threshold, the loop iteration factor L is reduced by 0.1, and the process proceeds to step 4 for recalculation. If no threshold is exceeded, proceed to step 7.

[0065] Step 7: Determine whether the transformer top oil temperature, hot spot temperature, and insulation life loss are equal to any threshold. If any of the transformer top oil temperature, hot spot temperature, and insulation life loss are equal to the corresponding threshold, the loop iteration stops, and the dynamic load curve, hot spot temperature curve, top oil temperature curve, life loss curve, maximum load rate, and threshold load factors are output. Otherwise, if none of them reach the threshold, the loop iteration factor L is increased by 0.1, and the process proceeds to step 4 for recalculation.

[0066] Step 8: Determine the load curve and maximum load capacity of the transformer based on the dynamic load curve and maximum load rate obtained in Step 7.

[0067] This invention establishes a dynamic load capacity assessment model for oil-immersed power transformers. Using typical 24-hour load and ambient temperature as inputs, it can assess the dynamic load capacity of transformers under different operating conditions. In addition to hot spot temperature constraints, it fully considers risk factors such as insulation life loss and top oil temperature in dynamic load capacity assessment. Based on this, it determines the maximum load capacity of the transformer, ensuring safety while maximizing the transformer's load capacity.

[0068] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating the dynamic load capacity of an oil-immersed power transformer, characterized in that, include: Step 1: Establish a dynamic load capacity assessment model for transformers; Step 2: Set the basic parameters of the transformer dynamic load capacity assessment model; Step 3: Based on the transformer's operating conditions, determine the time range for dynamic load capacity assessment, life loss, and threshold values ​​for top oil temperature and hot spot temperature. Step 4: Set the initial cycle iteration factor of the typical load curve in Step 2 and form a new load curve; forming a new load curve includes: multiplying the initial cycle iteration factor L of the typical load curve with the 24h typical load curve data to obtain a new load curve; Step 5: Set the initial top oil temperature rise and hot spot temperature rise values, and input the new load curve into the transformer hot spot temperature estimation model, top oil temperature estimation model, and insulation life loss estimation model for calculation to obtain the real-time transformer top oil temperature, hot spot temperature, and insulation life loss. Step 6: Determine whether the real-time transformer top oil temperature, hot spot temperature, and insulation life loss exceed the corresponding threshold. If any one of them exceeds the corresponding threshold, the loop iteration factor is reduced and the process proceeds to step 4 for recalculation; otherwise, proceed to step 7. Step 7: Determine whether the transformer top oil temperature, hot spot temperature, and insulation life loss are equal to any threshold. If any of the transformer top oil temperature, hot spot temperature, and insulation life loss are equal to the corresponding threshold, the loop iteration stops, and the dynamic load curve, hot spot temperature curve, top oil temperature curve, life loss curve, maximum load rate, and threshold load factors are output. Otherwise, the loop iteration factor increases and the process enters step 4 for recalculation.

2. The method for evaluating the dynamic load capacity of an oil-immersed power transformer according to claim 1, characterized in that, The basic parameters of the transformer dynamic load capacity assessment model include: a set of typical load and ambient temperature curves of the transformer, the transformer oil time constant, the winding time constant, and the temperature rise of the top oil and hot spots of the transformer under rated operating conditions.

3. The method for evaluating the dynamic load capacity of an oil-immersed power transformer according to claim 2, characterized in that, The typical load and ambient temperature curves are based on 24-hour load and ambient temperature curves.

4. The method for evaluating the dynamic load capacity of an oil-immersed power transformer according to claim 1, characterized in that, Establishing a dynamic load capacity assessment model for transformers includes establishing the objective function and constraints of the model.

5. The method for evaluating the dynamic load capacity of an oil-immersed power transformer according to claim 1, characterized in that, The expression for the transformer dynamic load capacity assessment model is as follows: In the above formula, K For load rate θ h Hotspot temperature θ o Top oil temperature 、L tot This refers to the transformer insulation life loss within the corresponding time range. θ hlim For hotspot temperature threshold, θ tlim For the top oil temperature threshold, L lim This is the threshold for insulation life loss.

6. The method for evaluating the dynamic load capacity of an oil-immersed power transformer according to claim 1, characterized in that, The iteration factor is reduced by 0.

1.

7. The method for evaluating the dynamic load capacity of an oil-immersed power transformer according to claim 1, characterized in that, The loop iteration factor is increased by 0.1.

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