Method for treating overload of transformer in rural power distribution area

Abstract

The invention relates to a rural power distribution area transformer overload treatment method, and belongs to the technical field of power distribution network operation stability, and the method comprises the steps: obtaining photovoltaic installed capacity, transformer rated capacity and historical maximum transformer load rate, and determining equipment data such as energy storage battery rated power needing to be configured; determining equipment data such as energy storage battery rated power required to be configured according to the photovoltaic installed capacity, the transformer rated capacity and the historical maximum transformer load rate of the power distribution area; accounting the real-time load rate of a transformer based on the real-time monitoring data of the power distribution area, and managing the state of charge (SOC) of an energy storage battery according to the real-time load rate of the transformer; and charging and discharging management is performed on the energy storage battery according to the real-time monitoring data of the power distribution area and the real-time load rate of the transformer. The energy storage battery system is accessed to the high-proportion distributed photovoltaic system, and a corresponding energy storage battery charging and discharging management method is provided, so that the heavy overload of the transformer caused by reverse power transmission when the daytime photovoltaic power is greatly generated can be avoided, and the economical efficiency is better.

Description

Technical Field

[0001] The invention belongs to the technical field of distribution network operation stability, and in particular relates to a method for controlling heavy overload of transformers in rural distribution station areas. Background Art

[0002] In June 2021, the National Energy Administration issued a notice on "whole-county distributed photovoltaics". Many provinces and cities across the country issued policies to promote the scale of distributed photovoltaics, and the installed capacity of rural distributed photovoltaics showed explosive growth. However, rural residents have less electricity consumption and a low self-use rate of photovoltaics. When photovoltaics are generated during the day, it is difficult to consume photovoltaic power locally. The excess photovoltaic power needs to be fed back to the 10kV distribution system through the distribution transformer, resulting in heavy overload of the transformer, causing transformer overheating and even transformer burnout accidents, which seriously threatens the safe and stable operation of the distribution network.

[0003] At present, the research on the operational risks caused by the grid-connected photovoltaic power generation mainly focuses on solving the frequency regulation or peak regulation problems in the field of centralized photovoltaic grid-connected power generation. There is little research on the problem of heavy overload of transformers in rural distribution stations with a high proportion of distributed photovoltaic power generation.

[0004] The current solution to the problem of transformer overload in rural distribution areas with a high proportion of distributed photovoltaic power generation is still to apply the transformer capacity increase and transformation method used in the previous single power distribution network, that is, to reduce the transformer load rate by replacing or adding a large-capacity transformer. However, the transformer in rural distribution areas with a high proportion of distributed photovoltaic power generation is only overloaded during the noon period, that is, when the distributed photovoltaic power generation is large. The load rate is low during other periods, and there is even a phenomenon of light load. Therefore, the configuration of a large-capacity transformer is less economical.

[0005] Through the above analysis, the problems and defects of the prior art are as follows:

[0006] (1) Existing technologies are mainly aimed at solving the problems of frequency regulation or peak regulation in the field of centralized photovoltaic grid connection. There is little research on the problem of transformer overload in rural distribution stations with a high proportion of distributed photovoltaics.

[0007] (2) Currently, the method of transformer capacity expansion and transformation is used to deal with the problem of transformer overload in rural distribution areas with a high proportion of distributed photovoltaics.

[0008] The disadvantage is that considering the load nature in rural areas and the characteristics of photovoltaic output, this method will further aggravate the light load operation of the transformer and have poor economic efficiency. Summary of the invention

[0009] The purpose of the present invention is to solve the problem of heavy overload of transformers in rural distribution areas containing a high proportion of distributed photovoltaics, which can make up for the defect of poor economy of the existing method.

[0010] To achieve the above objectives, the present invention adopts the following technical measures:

[0011] A method for controlling transformer overload in a rural power distribution area, characterized in that it comprises the following steps:

[0012] S1. Obtain the photovoltaic installed capacity, transformer rated capacity, real-time monitoring data and historical maximum transformer load rate in the rural distribution area;

[0013] S2. Determine the required energy storage battery rated power based on the photovoltaic installed capacity, transformer rated capacity and historical maximum transformer load rate of the distribution station area;

[0014] S3, energy storage battery state of charge SOC management;

[0015] S4, managing the charging and discharging of the energy storage battery based on the real-time monitoring data of the distribution station area;

[0016] Furthermore, the step S1 obtains the photovoltaic installed capacity, transformer rated capacity, real-time monitoring data and transformer historical maximum load rate of the rural distribution station area, where:

[0017] (1) Collect and obtain the sum of all distributed photovoltaic installed capacities in the target area;

[0018] (2) Obtaining the rated capacity of the target transformer and its historical maximum load rate;

[0019] The real-time monitoring data refers to the current value flowing out from the low-voltage side of the transformer in the target substation and the state of charge SOC of the energy storage battery configured in the target substation; when the current value is positive, it means that the photovoltaic output power of the substation is consumed locally and there is no photovoltaic power reverse transmission; when the current value is negative, it means that the photovoltaic output power of the substation is greater than the load power and there is photovoltaic power reverse transmission.

[0020] Furthermore, the step S2 determines the rated power of the energy storage battery to be configured, and the calculation formula of the rated power of the energy storage battery is:

[0021] P ESS =(R max -R0)×P TN

[0022] At the same time, P ESS The following restrictions must also be met:

[0023] 10% × ΣP pv ≤P ESS ≤40%×∑P pv

[0024] If the calculated value P ESSIf the upper limit is exceeded, the upper limit value is taken as 40% × ∑P pv ; If the calculated value P ESS If it exceeds the lower limit, take the lower limit value 10% × ∑P pv .

[0025] Where P ESS , P TN , R max , R0, ∑P pv They represent the rated power of the energy storage battery, the rated capacity of the transformer, the historical maximum load rate of the transformer, the critical value of transformer overload, and the photovoltaic installed capacity of the substation area;

[0026] Furthermore, the transformer overload critical value can be used to determine whether the substation transformer needs to be equipped with an energy storage battery. If the historical maximum load rate of the transformer is greater than the transformer overload critical value, the substation needs to be equipped with an energy storage battery; otherwise, the substation does not need to be equipped with an energy storage battery.

[0027] Furthermore, the energy storage battery state of charge SOC management in step S3 aims to improve the service life of the energy storage battery and avoid overcharging or over-discharging of the battery. It is necessary to manage the state of charge SOC of the energy storage battery and set the distribution range of SOC;

[0028] The SOC distribution range of the energy storage battery during discharge is set to (SOC min , SOC max ), when SOC is less than SOC min The battery is prohibited from discharging.

[0029] According to the transformer load rate, the SOC range of the energy storage battery when charging is set.

[0030] Furthermore, the transformer load factor is

[0031] The transformer load rate calculation formula is:

[0032]

[0033] In the formula, R T They are respectively the current value flowing out of the low-voltage side of the transformer in the target area and the real-time load rate of the transformer.

[0034] Furthermore, the state of charge (SOC) range of the energy storage battery when charging is set according to the transformer load rate, and is divided according to the following standards:

[0035] (a) When the transformer load rate is greater than R0, the photovoltaic output is relatively large, and the state of charge (SOC) distribution range of the energy storage battery is set to (SOC min , SOC max), when SOC is greater than SOC max The battery is prohibited from charging.

[0036] (b) When the transformer load rate is less than R0, the photovoltaic output is relatively small, and the SOC distribution range of the energy storage battery when charging is set to (SOC min , SOC high ), when SOC is greater than SOC high The battery is prohibited from charging.

[0037] Among them, SOC min , SOC max , SOC high They are the lower discharge limit of the energy storage battery, the upper charge limit of the energy storage battery under heavy load of the transformer, and the upper charge limit of the energy storage battery under non-heavy load of the transformer, and set the SOC high Less than SOC max .

[0038] Furthermore, the step S4 is about energy storage battery charge and discharge management, and the management process is as follows:

[0039] According to the current value flowing out from the low-voltage side of the target transformer Determine the charging and discharging mode of energy storage batteries:

[0040] when When SOC≤SOC min , set the energy storage battery discharge power P ess =0, if SOC>SOC min , set the energy storage battery discharge power P ess =αP ESS ;

[0041] when When the target substation sends power back to the grid, the photovoltaic power generation power of the substation exceeds the load power of the substation, and the energy storage battery needs to be charged. According to the load rate of the transformer, the following two charging management modes are adopted:

[0042] (a) When the transformer load rate is greater than the transformer overload critical value, that is, R T >R0, the photovoltaic output is large and the transformer is heavily overloaded; if SOC ≥ SOC max , set the energy storage battery discharge power P ess =0; if SOC <SOC max , set the energy storage battery discharge power P ess =-P ESS ;

[0043] (b) When the transformer load rate is less than the transformer overload critical value, that is, R T When <R0, the photovoltaic output is small and the transformer operates normally; if SOC≥SOC high , set the energy storage battery discharge power P ess =0; if SOC <SOC high , set the energy storage battery discharge power P ess =-αP ESS ;

[0044] In the formula, α, P ess They are respectively the charge and discharge coefficient of the energy storage battery and the charge and discharge power reference value of the energy storage battery.

[0045] In order to ensure the health of the energy storage battery, the energy storage battery is charged and discharged at a lower power in both non-emergency situations of discharge or non-heavy load charging. Therefore, it is necessary to set the size of the energy storage battery charge and discharge coefficient α.

[0046] Furthermore, the energy storage battery charge and discharge coefficient α is set to a value less than 1.

[0047] Furthermore, a device applicable to the method for treating heavy overload of transformer in a rural distribution station area comprises a metering device, an energy storage battery, a control device and a computer;

[0048] The metering device is installed in the transformer low-voltage distribution cabinet to monitor the current value flowing out of the transformer low-voltage side in real time, and calculate the real-time load rate of the transformer based on this;

[0049] The energy storage battery is configured at a line switch of a low-voltage distribution cabinet of a transformer in a target substation. The control device is connected to the energy storage battery at one end and to a computer at the other end. The computer runs the collected relevant parameters and runs the relevant algorithms to obtain the optimization results. The energy storage battery is managed by SOC and charge and discharge through the control device.

[0050] Working principle:

[0051] The present invention configures an energy storage battery system for rural distribution stations with a high proportion of distributed photovoltaic access, and provides a corresponding energy storage battery charge and discharge management method to avoid transformer overload caused by power reverse transmission during daytime photovoltaic power generation. It mainly includes: first, obtaining the photovoltaic installed capacity, transformer rated capacity, real-time monitoring data and historical maximum transformer load rate of the target distribution station; secondly, determining the required energy storage battery rated power based on the photovoltaic installed capacity, transformer rated capacity and historical maximum transformer load rate of the distribution station; then, calculating the real-time load rate of the transformer based on the real-time monitoring data of the distribution station, and managing the energy storage battery state of charge SOC according to the real-time load rate of the transformer; finally, based on the real-time monitoring data of the distribution station and the real-time load rate of the transformer, the energy storage battery is charged and discharged, including when photovoltaic power is reversed to the power grid, the energy storage battery charges and stores this part of the photovoltaic power, and when the photovoltaic power generation is small, the energy storage battery discharges to make up for this part of the load power shortage, so as to avoid the distribution transformer from being overloaded.

[0052] Beneficial effects of the present invention:

[0053] The present invention configures energy storage batteries and control devices for rural distribution stations with a high proportion of distributed photovoltaic access, and provides a corresponding energy storage battery management method, which can avoid heavy transformer overload caused by power reverse transmission during daytime photovoltaic power generation. Compared with the currently used transformer capacity increase and transformation method, this method can, on the one hand, avoid further aggravation of the transformer light load rate when photovoltaic power is not output, and on the other hand, the energy storage battery supplies power to the grid when the photovoltaic output cannot meet the load of the station area, which can effectively smooth the peak of electricity consumption in the evening and is more economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A diagram of the system for managing severe overload in rural distribution stations;

[0055] Figure 2 Classify the state of charge of energy storage batteries into ranges. DETAILED DESCRIPTION

[0056] The following will be combined with the accompanying drawings of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] As attached Figure 1-2 , we carried out transformer overload control in a typical rural distribution station area. The transformer overload control system in the station area is as follows: Figure 1As shown, the transformer ratio of this area is 10kV / 400V, the high-voltage side is connected to the 10kV distribution network, and the low-voltage side is connected to the low-voltage distribution cabinet. The low-voltage distribution cabinet has two outgoing lines, one of which is connected to the 400V line. Multiple loads and rooftop distributed photovoltaic PV are connected in parallel on this line. The energy storage battery ESS is connected to the other outgoing line of the transformer low-voltage distribution cabinet. The energy storage battery can charge and discharge to the grid according to real-time monitoring data, and store the photovoltaic excess power that is difficult to absorb in this area, thereby avoiding reverse heavy overload of the transformer. The process is as follows:

[0058] 1) Obtain the photovoltaic installed capacity, transformer rated capacity, real-time monitoring data and historical maximum transformer load rate of the rural distribution station area;

[0059] The electrical data of this area include: transformer rated capacity P TN The transformer has a historical maximum load factor of 400kW, R max 100%, photovoltaic installed capacity in the area ∑P pv It is 380kW.

[0060] Real-time monitoring data include: the current value flowing out from the low-voltage side of the transformer in the target area, and the state of charge (SOC) of the energy storage battery configured in the target area. When the current value is positive, it means that the photovoltaic output power of the area is consumed locally, and there is no photovoltaic power reverse transmission; when the current value is negative, it means that the photovoltaic output power of the area is greater than the load power, and there is photovoltaic power reverse transmission;

[0061] 2) Determine the required energy storage battery rated power based on the photovoltaic installed capacity, transformer rated capacity and historical maximum transformer load rate of the distribution station area;

[0062] Energy storage battery rated power P ESS The calculation formula is:

[0063] P ESS =(R max -R0)×P TN

[0064] P ESS The following restrictions must also be met:

[0065] 10%×yP pv ≤P ESS ≤40%×yP pv

[0066] If the calculated value P ESS If the upper limit is exceeded, the upper limit value is taken as 40% × ΣP pv ; If the calculated value P ESS If the lower limit is exceeded, the lower limit value is taken as 10% × ΣP pv .

[0067] It is usually assumed that if the transformer load rate is greater than 80%, the transformer is overloaded; if the load rate is greater than 100%, the transformer is overloaded. For this reason, the transformer overload threshold R0 is defined as 80%. Based on the above information, it can be obtained that P ESS It is 80kW.

[0068] 3) Energy storage battery state of charge SOC management

[0069] In order to increase the operating life of the energy storage battery and avoid overcharging / overdischarging of the battery, it is necessary to manage the state of charge (SOC) of the energy storage battery. The SOC distribution range is shown in the attached figure. Figure 2 The state of charge (SOC) distribution range of the energy storage battery during discharge is set to (5%, 95%), and when the SOC is less than 5%, the battery is prohibited from discharging.

[0070] The transformer load rate calculation formula is:

[0071]

[0072] In the formula, R T They are respectively the current value flowing out of the low-voltage side of the transformer in the target area and the real-time load rate of the transformer.

[0073] According to the transformer load rate, the energy storage battery state of charge SOC is divided into the following two ranges:

[0074] (a) When the transformer load rate is greater than 80%, the photovoltaic output is large, and the state of charge (SOC) distribution range of the energy storage battery is set to (5%, 95%). When the SOC is greater than 95%, the battery is prohibited from charging.

[0075] (b) When the transformer load rate is less than 80%, the photovoltaic output is relatively small, and the state of charge (SOC) distribution range of the energy storage battery is set to (5%, 80%). When the SOC is greater than 80%, the battery is prohibited from charging;

[0076] 4) managing the charging and discharging of the energy storage battery based on the real-time monitoring data of the distribution station area;

[0077] Determine the charging and discharging mode of the energy storage battery based on the current value flowing out from the low-voltage side of the target transformer:

[0078] when When , it indicates that the power grid supplies power to the target area, that is, the photovoltaic power generation power of the area is lower than the load power of the area, and the energy storage battery needs to be discharged. If SOC≤5%, set the energy storage battery discharge power P ess =0, if SOC>5%, set the energy storage battery discharge power P ess =0.5P ESS ;

[0079] when When the target area is feeding back electricity to the grid, the photovoltaic power generation power of the area exceeds the load power of the area, and the energy storage battery needs to be charged. According to the load rate of the transformer, the following two charging management modes are adopted:

[0080] (a) When the transformer load rate is greater than the transformer overload critical value, that is, R T >80%, the photovoltaic output is high and the transformer is overloaded. If SOC≥95%, set the energy storage battery discharge power P ess =0; if SOC<95%, set the energy storage battery discharge power P ess =-P ESS ;

[0081] (b) When the transformer load rate is less than the transformer overload critical value, that is, R T <80%, the photovoltaic output is low and the transformer operates normally. If SOC≥80%, set the energy storage battery discharge power P ess =0; if SOC<80%, set the energy storage battery discharge power P ess =-0.5P ESS ;

[0082] Among them, P ess It is the reference value of the energy storage battery discharge power in the target area.

[0083] A device applicable to the method for treating heavy overload of transformer in a rural distribution station area, comprising a metering device, an energy storage battery and a control device thereof, and a computer;

[0084] The metering device is installed in the transformer low-voltage distribution cabinet to monitor the current value flowing out of the transformer low-voltage side in real time, and calculate the real-time load rate of the transformer based on this;

[0085] The energy storage battery is configured at a line switch of a low-voltage distribution cabinet of a transformer in a target substation. The control device is connected to the energy storage battery at one end and to a computer at the other end. The computer runs the collected relevant parameters and runs the relevant algorithms to obtain the optimization results. The energy storage battery is managed by SOC and charge and discharge through the control device.

Claims

1. A method for treating heavy overload of transformer in rural distribution area, characterized in that: The following steps are involved: S1. Obtain the photovoltaic installed capacity, transformer rated capacity, real-time monitoring data and historical maximum transformer load rate in the rural distribution area; S2. Determine the required energy storage battery rated power based on the photovoltaic installed capacity, transformer rated capacity and historical maximum transformer load rate of the distribution station area; S3, energy storage battery state of charge SOC management; S4. Perform charge and discharge management of the energy storage battery based on the real-time monitoring data of the distribution station area.

2. A method for treating heavy overload of transformer in rural distribution area as claimed in claim 1, characterized in that: The step S1 obtains the photovoltaic installed capacity, transformer rated capacity, real-time monitoring data and transformer historical maximum load rate of the rural distribution station area, where: (1) Collect and obtain the sum of all distributed photovoltaic installed capacities in the target area; (2) Obtaining the rated capacity of the target transformer and its historical maximum load rate; The real-time monitoring data refers to the current value flowing out from the low-voltage side of the transformer in the target substation and the state of charge SOC of the energy storage battery configured in the target substation; when the current value is positive, it means that the photovoltaic output power of the substation is consumed locally and there is no photovoltaic power reverse transmission; when the current value is negative, it means that the photovoltaic output power of the substation is greater than the load power and there is photovoltaic power reverse transmission.

3. A method for treating heavy overload of transformer in rural distribution area as claimed in claim 1, characterized in that: The step S2 determines the rated power of the energy storage battery to be configured, and the calculation formula of the rated power of the energy storage battery is: P ESS =(R max -R0)×P TN At the same time, P ESS The following restrictions must also be met: 10%×ΣP pv ≤P ESS ≤40%×ΣP pv If the calculated value P ESS If the upper limit is exceeded, the upper limit value is taken as 40% × ΣP pv ; If the calculated value P ESS If it exceeds the lower limit, take the lower limit value 10% × ∑P pv . Where P ESS , P TN , R max , R0, ∑P pv They respectively represent the rated power of the energy storage battery, the rated capacity of the transformer, the historical maximum load rate of the transformer, the overload critical value of the transformer, and the photovoltaic installed capacity of the substation.

4. A method for treating heavy overload of transformer in rural distribution area as claimed in claim 3, characterized in that: The transformer overload critical value can be used to determine whether the transformer in the substation needs to be equipped with an energy storage battery. If the historical maximum load rate of the transformer is greater than the transformer overload critical value, the substation needs to be equipped with an energy storage battery; otherwise, the substation does not need to be equipped with an energy storage battery.

5. A method for treating heavy overload of transformer in rural distribution area as claimed in claim 1, characterized in that: The energy storage battery state of charge (SOC) management in step S3 aims to improve the service life of the energy storage battery and avoid overcharging or over-discharging of the battery. It is necessary to manage the state of charge (SOC) of the energy storage battery and set the distribution range of SOC. The SOC distribution range of the energy storage battery during discharge is set to (SOC min , SOC max ), when SOC is less than SOC min The battery is prohibited from discharging; According to the transformer load rate, the SOC range of the energy storage battery when charging is set.

6. A method for treating heavy overload of transformer in rural distribution area as claimed in claim 5, characterized in that: The transformer load factor, The transformer load rate calculation formula is: In the formula, R T They are respectively the current value flowing out of the low-voltage side of the transformer in the target area and the real-time load rate of the transformer.

7. A method for treating severe overload of transformer in rural distribution area as claimed in claim 5, characterized in that: The state of charge (SOC) range of the energy storage battery when charging is set according to the transformer load rate, and is divided according to the following standards: (a) When the transformer load rate is greater than R0, the photovoltaic output is relatively large, and the SOC distribution range of the energy storage battery when charging is set to (SOC min , SOC max ), when SOC is greater than SOC max When the load rate of the transformer is less than R0, the battery is prohibited from charging; (b) When the load rate of the transformer is less than R0, the photovoltaic output is relatively small, and the state of charge SOC distribution range of the energy storage battery when charging is set to (SOC min , SOC high ), when SOC is greater than SOC high The battery is prohibited from charging; Among them, SOC min , SOC max , SOC high They are the lower discharge limit of the energy storage battery, the upper charge limit of the energy storage battery under heavy load of the transformer, and the upper charge limit of the energy storage battery under non-heavy load of the transformer, and set the SOC high Less than SOC max .

8. A method for treating heavy overload of transformer in rural distribution area as claimed in claim 1, characterized in that: The step S4 energy storage battery charge and discharge management, the management process is as follows: According to the current value flowing out from the low-voltage side of the target transformer Determine the charging and discharging mode of energy storage batteries: when When SOC≤SOC min , set the energy storage battery discharge power P ess =0, if SOC>SOC min , set the energy storage battery discharge power P ess =αP ESS ; when When the target area is feeding back electricity to the grid, the photovoltaic power generation power of the area exceeds the load power of the area, and the energy storage battery needs to be charged. According to the load rate of the transformer, the following two charging management modes are adopted: (a) When the transformer load rate is greater than the transformer overload critical value, that is, R T >R0, the photovoltaic output is large and the transformer is heavily overloaded; if SOC ≥ SOC max , set the energy storage battery discharge power P ess =0; if SOC <SOC max , set the energy storage battery discharge power P ess =-P ESS ; (b) When the transformer load rate is less than the transformer overload critical value, that is, R T When <R0, the photovoltaic output is small and the transformer operates normally; if SOC≥SOC high , set the energy storage battery discharge power P ess =0; if SOC <SOC high , set the energy storage battery discharge power P ess =-αP ESS ; In the formula, α, P ess They are respectively the energy storage battery charge and discharge coefficient and the energy storage battery charge and discharge power reference value; In order to ensure the health of the energy storage battery, the energy storage battery is charged and discharged at a lower power in both non-emergency situations of discharge or non-heavy load charging. Therefore, it is necessary to set the size of the energy storage battery charge and discharge coefficient α.

9. A method for treating heavy overload of transformer in rural distribution area as claimed in claim 7, characterized in that: The energy storage battery charge and discharge coefficient α is set to a value less than 1.

10. The device for treating overload of transformer in rural distribution area according to claim 1 is characterized in that: Includes metering device, energy storage battery, control device and computer; The metering device is installed in the transformer low-voltage distribution cabinet to monitor the current value flowing out of the transformer low-voltage side in real time, and calculate the real-time load rate of the transformer based on this; The energy storage battery is configured at a first-line outgoing switch of the low-voltage distribution cabinet of the target area transformer. One end of the control device is connected to the energy storage battery, and the other end is connected to a computer. The control device is used to perform SOC management and charge and discharge management on the energy storage battery.

Images