Calculation method for distributed photovoltaic access capacity of power distribution network

Abstract

The invention provides a calculation method for distributed photovoltaic access capacity of a power distribution network. The method comprises the following steps: acquiring real-time data of an active power distribution network, including short-circuit voltage, line impedance, bus short-circuit impedance, rated voltage and power factor of a photovoltaic power station; and when a short-circuit fault occurs, calculating the short-circuit current flowing to the bus of the power distribution network from the distributed photovoltaic system by using the data. Then, a quick-break current constant value of the bus is determined according to the short-circuit current; and finally, the accessible capacity is obtained by combining the rated voltage, the power factor and the quick-break current constant value of the distributed photovoltaic system. By accurately calculating the short-circuit current and determining the access capacity, safe and stable operation of the power distribution network is ensured, and powerful support is provided for reliable operation of the power distribution network.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic access to a power grid, and in particular to a method for calculating the capacity of distributed photovoltaic access to a distribution network. Background Art

[0002] With the rapid development of renewable energy, the access of distributed photovoltaic power sources to distribution networks is increasing. The access of distributed photovoltaic power sources not only changes the power flow distribution of the distribution network, but also has a significant impact on its short-circuit current characteristics. Traditional distribution network short-circuit current calculation methods often fail to fully consider the impact of distributed photovoltaic power sources, resulting in deviations in the calculation results, which in turn affects the safe and stable operation of the distribution network.

[0003] In an active distribution network, the access of distributed photovoltaic power sources makes the current characteristics of the distribution network more complicated during a short-circuit fault. When a short-circuit fault occurs in the distribution network, the distributed photovoltaic power source will provide a short-circuit current to the fault point, which increases the magnitude and uncertainty of the short-circuit current of the distribution network. Summary of the invention

[0004] The purpose of this application is to overcome the defects in the above-mentioned prior art and provide a method for calculating the access capacity of distributed photovoltaic power generation in a distribution network.

[0005] The present application provides a method for calculating the access capacity of distributed photovoltaic power generation in a distribution network, including:

[0006] Obtain real-time operating data of the active distribution network, including the short-circuit voltage, line impedance, busbar short-circuit impedance, rated voltage and power factor of the PV power station;

[0007] When a short-circuit fault occurs in the active distribution network, the short-circuit current flowing from the distributed photovoltaic to the distribution network bus is calculated according to the short-circuit voltage, line impedance and bus short-circuit impedance of the photovoltaic power station;

[0008] Determine the quick-break current setting value of the distribution network bus according to the short-circuit current;

[0009] The accessible capacity of distributed photovoltaic is obtained according to the rated voltage, power factor and quick-break current setting of the distributed photovoltaic.

[0010] Optionally, causes of the short circuit fault include line aging, insulation failure, and human operation error.

[0011] Optionally, before obtaining the accessible capacity of distributed photovoltaic power generation, the following steps are also included:

[0012] A short-circuit current simulation analysis is performed on the active power distribution network to verify the accuracy of the short-circuit current calculation.

[0013] Optionally, it also includes:

[0014] According to the access location and access capacity of distributed photovoltaics, the power flow distribution and short-circuit current characteristics of the distribution network are predicted and analyzed.

[0015] Optionally, it also includes:

[0016] After distributed photovoltaics are connected, the distribution network is monitored and protected in real time to ensure the safe and stable operation of the power grid.

[0017] Optionally include:

[0018] A boundary formula is established to describe the change of short-circuit current after distributed photovoltaic access is connected, and the upper limit value and amplitude limit value of the short-circuit current are determined according to the boundary formula.

[0019] Optionally, the derivation process of the boundary formula includes:

[0020] Simplify the fast-break current setting formula;

[0021] Convert short-circuit current form;

[0022] Generate boundary formulas that take into account changes in system impedance after distributed photovoltaic access.

[0023] Optionally, the real-time operation data is obtained by directly measuring parameters such as output voltage, current and power of the photovoltaic power station using sensors and measuring equipment.

[0024] Optionally, it also includes:

[0025] The calculated distributed photovoltaic access capacity is compared with the preset capacity threshold to determine whether the distributed photovoltaic is allowed to access the distribution network.

[0026] Optionally, it is applicable to different types of distribution networks, including: urban distribution network, rural distribution network and industrial distribution network.

[0027] The beneficial effects of this application are:

[0028] The present application provides a method for calculating the access capacity of distributed photovoltaic power generation in a distribution network, including: obtaining real-time operation data of an active distribution network, including the short-circuit voltage, line impedance, bus short-circuit impedance, rated voltage and power factor of a photovoltaic power station; when a short-circuit fault occurs in the active distribution network, the short-circuit current of the distributed photovoltaic power generation flowing to the distribution network bus is calculated according to the short-circuit voltage, line impedance and bus short-circuit impedance of the photovoltaic power station; the quick-break current constant of the distribution network bus is determined according to the short-circuit current; and the accessible capacity of the distributed photovoltaic power generation is obtained according to the rated voltage, power factor and the quick-break current constant of the distributed photovoltaic power generation. The present application obtains the real-time operation data of the active distribution network, accurately calculates the short-circuit current of the distributed photovoltaic power generation flowing to the distribution network bus, and then determines the accessible capacity of the distributed photovoltaic power generation, thereby providing a strong guarantee for the safe and stable operation of the distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of the calculation process of the distributed photovoltaic access capacity of the distribution network in this application;

[0030] Figure 2 This is a schematic diagram of the boundary formula transformation in this application. DETAILED DESCRIPTION

[0031] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that various forms of implementing the present disclosure should not be limited by the embodiments set forth herein. On the contrary, the embodiments are provided to more thoroughly understand the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0032] Please refer to Figure 1 As shown, the present application provides a method for calculating the access capacity of distributed photovoltaic power generation in a distribution network, the steps of the method comprising:

[0033] S101, obtaining real-time operation data of the active distribution network, including short-circuit voltage, line impedance, bus short-circuit impedance, rated voltage and power factor of the photovoltaic power station;

[0034] The active distribution network includes urban distribution network, rural distribution network and industrial distribution network. In the active distribution network, in order to accurately calculate the distributed photovoltaic access capacity, a series of key real-time operation data are first obtained. These data are crucial for subsequent calculations and analysis.

[0035] Short-circuit voltage refers to the voltage that a photovoltaic power station can generate when a short circuit occurs at the output end of the photovoltaic power station. This data is crucial for evaluating the output capacity of a photovoltaic power station and the current contribution under a short-circuit fault.

[0036] Line impedance: Line impedance is an important parameter that describes the relationship between current and voltage in the distribution network. It reflects the resistance encountered by the current when it flows in the line.

[0037] Bus short-circuit impedance: Bus short-circuit impedance refers to the impedance characteristics exhibited when a short circuit occurs at the distribution network bus. It is a key parameter for evaluating the short-circuit current level of the distribution network.

[0038] Rated voltage: Rated voltage describes the voltage value that photovoltaic power plants and distribution network equipment should withstand during normal operation. This data is crucial to ensure the safe operation of the equipment.

[0039] Power factor: The power factor reflects the proportional relationship between active power and apparent power in the power grid. In the active distribution network, the access of distributed photovoltaic power sources will change the power factor, so it is also necessary to collect power factor data in real time.

[0040] Data collection methods and tools

[0041] In order to obtain the above real-time operation data, a variety of methods and tools are used for data collection. For example:

[0042] Use sensors and measuring devices to directly measure parameters such as output voltage, current and power of photovoltaic power plants.

[0043] S102, when a short-circuit fault occurs in the active distribution network, the short-circuit current flowing from the distributed photovoltaic to the distribution network bus is calculated according to the short-circuit voltage, line impedance and bus short-circuit impedance of the photovoltaic power station;

[0044] In an active distribution network, when a short-circuit fault occurs, the distributed photovoltaic power source (such as a photovoltaic power station) will inject a short-circuit current into the distribution network bus. In order to evaluate the magnitude of this short-circuit current, a calculation is performed based on the short-circuit voltage of the photovoltaic power station, the line impedance, and the bus short-circuit impedance.

[0045] The main purpose of short-circuit current calculation is to determine the magnitude of the short-circuit current injected by distributed photovoltaic power sources into the distribution network busbar when a short-circuit fault occurs in the active distribution network. This information is crucial for evaluating the short-circuit current level of the distribution network, designing protection devices, and ensuring the safe and stable operation of the power grid.

[0046] Steps for short-circuit current calculation

[0047] Get key parameters:

[0048] Short-circuit voltage (Epv) of a photovoltaic power station: This is the voltage that a photovoltaic power station can generate under short-circuit conditions. It reflects the output capacity of the photovoltaic power station and the current contribution under short-circuit faults.

[0049] Line impedance (Z line): This is an important parameter that describes the relationship between current and voltage in the distribution network. It reflects the resistance encountered by the current when it flows in the line.

[0050] Bus short-circuit impedance (Zbus): This describes the impedance characteristics exhibited when a short circuit occurs at the distribution network bus. It is a key parameter for evaluating the short-circuit current level of the distribution network.

[0051] Apply the short-circuit current calculation formula:

[0052] The calculation formula for short-circuit current is:

[0053]

[0054] Among them, I sc Indicates short-circuit current, E pv is the short-circuit voltage of the photovoltaic power station, Z line is the line impedance, Z bus is the busbar short-circuit impedance.

[0055] According to the short-circuit current value calculated by the formula, the impact of distributed photovoltaic power generation on the distribution network busbar in the event of a short-circuit fault is evaluated. If the short-circuit current is too large, it will pose a threat to the safe and stable operation of the power grid, so corresponding protection measures are taken.

[0056] Ensure that the acquired short-circuit voltage, line impedance, busbar short-circuit impedance and other parameters are accurate. The accuracy of these parameters directly affects the calculation results of short-circuit current.

[0057] S103, determining a fast-break current constant of a distribution network bus according to the short-circuit current;

[0058] The setting of the quick-break current setting (also called the instantaneous overcurrent protection setting) is crucial to ensure the safe and stable operation of the power grid. Especially in the distribution network containing distributed photovoltaic (DPV) systems, the access of photovoltaic power sources will have an impact on the short-circuit current, which is the so-called boosting effect.

[0059] When a short circuit occurs somewhere in the distribution network, the current flows through the fault point. The magnitude of the short circuit current depends on the voltage, impedance of the system and the location of the fault point. A current threshold is set to protect the equipment in the distribution network from damage by short circuit current. When the actual current exceeds this threshold, the protection device will act quickly to cut off the fault circuit.

[0060] Reliability coefficient (k): It is used to ensure that the instantaneous current setting has a certain safety margin (reliability coefficient k) to cope with the uncertainty factors in actual operation. The reliability coefficient value range is usually 1.3 to 1.5.

[0061] After considering the boosting effect of distributed photovoltaics, the calculation formula for the quick-break current constant is:

[0062] I set = k * I sc

[0063] Among them, I set It is the quick-break current setting, i.e. the operating current of the protection device. K, the reliability factor, is used to improve the reliability and sensitivity of the protection. The value range is 1.3 to 1.5, and the specific value needs to be determined according to the actual situation of the system and the protection requirements.

[0064] Measure or calculate the short-circuit current value in the distribution network. Use professional power system analysis software or conduct field measurements. In the calculation process, the impact of distributed photovoltaic access on the short-circuit current should be fully considered. According to the actual situation of the system and the protection requirements, select the reliability coefficient k. The selection of the reliability coefficient should ensure that the quick-break current setting has a certain safety margin while avoiding false operations. Multiply the measured or calculated short-circuit current value by the reliability coefficient k to obtain the quick-break current setting I set .

[0065] The calculated instantaneous current constant I set Set it in the corresponding protection device to ensure that when a short circuit occurs, the protection device can act quickly and cut off the fault circuit.

[0066] S104: Obtain the accessible capacity of distributed photovoltaics according to the rated voltage, power factor and quick-break current setting of the distributed photovoltaics.

[0067] In order to determine the upper limit and amplitude limit of the short-circuit current, a boundary formula describing the change of short-circuit current after distributed photovoltaic access is first established.

[0068] When deriving the specific form of the boundary formula, the simplified quick-break current constant formula and the cosine theorem are combined, and the change of system impedance after distributed photovoltaic access is considered.

[0069] Boundary formula derivation process:

[0070] S201, simplified quick-break current constant formula.

[0071] The known quick-break current constant formula is I set = k*I sc , where k is the reliability coefficient, ranging from 1.3 to 1.5, I sc is the short circuit current.

[0072] Short circuit current I sc Represented as I sc =ZV, where V is the system voltage and Z is the system impedance.

[0073] Therefore, the simplified quick-break current constant formula is expressed as:

[0074] I set =(1.3~1.5)×ZV

[0075] S202, convert the short-circuit current form.

[0076] When distributed photovoltaics are connected to the power system, the system impedance Z will change. Use the cosine theorem to describe this change. Assume that the original system impedance is Z sys , the impedance of distributed photovoltaic is Z dpv , the angle between them is φ, then the new system impedance Z new It is expressed as:

[0077]

[0078] Since we are concerned about the change of short-circuit current, we convert the above formula into the form of short-circuit current:

[0079]

[0080] In order to ensure that the quick-break protection can operate correctly when a short-circuit fault occurs and avoid false operation, an inequality or equation is written about parameters such as distributed photovoltaic access capacity, access location, system impedance and quick-break protection setting.

[0081] S203: Generate boundary formula.

[0082] Considering the setting value I of the quick-break protection set Greater than or equal to the new short-circuit current I sc_new The minimum value of (to ensure reliable action) and less than or equal to a certain threshold (to avoid false action) can be obtained as follows:

[0083]

[0084] By solving these boundary formulas through mathematical methods (such as numerical solution, iteration method, etc.), the upper limit and amplitude limit of the short-circuit current are obtained. These values ​​represent the maximum short-circuit current and its variation range that distributed photovoltaics may generate under different conditions.

[0085] According to the boundary formula and the upper limit of the short-circuit current, the short-circuit current generated by the distributed photovoltaic system when a short-circuit fault occurs is determined.

[0086] Based on the relationship between short-circuit current and rated current, the accessible capacity boundary of distributed photovoltaic is determined. This refers to the maximum capacity of distributed photovoltaic access without exceeding the system's tolerance.

[0087] The calculation formula for the accessible capacity of distributed photovoltaics is:

[0088]

[0089] Among them, I sc_max is the upper limit of the short-circuit current, U n is the rated voltage and cosφ is the power factor.

[0090] Through this formula, the maximum capacity of distributed photovoltaic access can be calculated while ensuring safe and stable operation of the system.

[0091] Before formally calculating the accessible capacity of distributed photovoltaics, it is necessary to first perform a short-circuit current simulation analysis on the active distribution network in order to ensure the accuracy and reliability of subsequent steps.

[0092] Short-circuit current simulation analysis is a simulation calculation based on power system simulation software or tools. By inputting the actual parameters of the active distribution network, such as line impedance, transformer parameters, load conditions, etc., as well as key information such as the access location and capacity of the distributed photovoltaic power station, the simulation software can simulate the short-circuit current injected by the distributed photovoltaic power station into the distribution network bus under different short-circuit fault conditions.

[0093] Specifically, the main steps of short-circuit current simulation analysis include:

[0094] Model establishment: First, it is necessary to establish an accurate power system simulation model based on the actual structure and parameters of the active distribution network. This model should be able to accurately reflect key information such as the topology of the distribution network, line parameters, transformer parameters, and load distribution.

[0095] Parameter setting: After the model is established, you need to set the simulation parameters, including the type of short-circuit fault (such as three-phase short circuit, single-phase ground short circuit, etc.), the location of the short-circuit fault (such as the end of the line, transformer outlet, etc.) and the access status of the distributed photovoltaic power station (such as access capacity, access location, etc.).

[0096] Simulation calculation: After setting the parameters, you can start the simulation software to calculate the short-circuit current. The simulation software will calculate the short-circuit current injected by the distributed photovoltaic power station into the distribution network busbar when a short-circuit fault occurs based on the input parameters and model.

[0097] Result verification: After the simulation calculation is completed, the result needs to be verified. This can be achieved by comparing with the actual measurement data or comparing with the theoretical calculation results. If the simulation results are consistent with the actual situation or the theoretical calculation results, then it can be considered that the calculation of the short-circuit current is accurate, so that the calculation of the accessible capacity of distributed photovoltaics can be further performed.

[0098] In the process of connecting distributed photovoltaic (DPV) to the distribution network, its connection location and connection capacity are two crucial factors, which directly determine the changes in the power flow distribution and short-circuit current characteristics of the distribution network. Therefore, when planning, designing or adjusting the distribution network, the power flow distribution and short-circuit current characteristics of the distribution network are predicted and analyzed based on the connection location and connection capacity of distributed photovoltaic.

[0099] Flow distribution refers to the distribution of voltage at each node and power at each branch in the power system. After distributed photovoltaics are connected to the distribution network, the flow distribution of the distribution network will change due to the differences in the power generation power and access location of the photovoltaic power station.

[0100] When distributed photovoltaics are connected to the end of the distribution network, it will reduce the transmission pressure of the upstream lines and reduce line losses, but it may also cause the terminal voltage to increase and affect the voltage quality.

[0101] When distributed photovoltaics are connected to the middle of the distribution network or close to a substation, it may have a significant impact on the power flow distribution of the entire distribution network, and its impact on the stability of the grid needs to be comprehensively considered.

[0102] The larger the access capacity of distributed photovoltaic power generation, the more significant its impact on the power flow distribution of the distribution network. After the access of large-capacity photovoltaic power stations, the power flow direction of the distribution network may be changed, and even reverse power flow may be caused in some cases.

[0103] Reverse power flow will pose challenges to the protection devices and automation equipment of the distribution network, and corresponding measures need to be taken to adapt and transform them.

[0104] Short-circuit current refers to the current that flows when a short-circuit fault occurs in the power system. After distributed photovoltaics are connected to the distribution network, their short-circuit current characteristics will also change.

[0105] Different locations of distributed photovoltaic access will cause changes in the distribution and size of short-circuit current. In particular, when a short-circuit fault occurs near a photovoltaic power station, the size of the short-circuit current may increase significantly due to the short-circuit current provided by the photovoltaic power station.

[0106] This places higher demands on the protection devices of the distribution network, ensuring that they can correctly identify and act on short-circuit faults.

[0107] The larger the access capacity of distributed photovoltaics, the greater the short-circuit current it provides. This may cause the short-circuit current level of the distribution network to exceed the rated value of the original protection device, which needs to be upgraded or modified.

[0108] At the same time, after the large-capacity photovoltaic power station is connected, it may also affect the short-circuit current distribution of the distribution network, causing the short-circuit current level in some areas to increase or decrease.

[0109] In order to accurately predict the changes in power flow distribution and short-circuit current characteristics of the distribution network after distributed photovoltaic access, the following methods can be used:

[0110] 1. Use power system simulation software (such as PSASP, ETAP, etc.) to establish a simulation model of the distribution network, and input parameters such as the access location and access capacity of distributed photovoltaics. Through simulation calculations, the changes in the power flow distribution and short-circuit current characteristics of the distribution network can be obtained.

[0111] 2. For simple distribution network structures, analytical methods can be used for calculation. By establishing a mathematical model, the calculation formulas for the power flow distribution and short-circuit current characteristics of the distribution network after distributed photovoltaic access are derived, and calculations and analyses are performed.

[0112] 3. Based on the existing experience and data, establish the empirical formula for the power distribution and short-circuit current characteristics of the distribution network after the distributed photovoltaic access. This method is simple and easy, but the accuracy may be limited to a certain extent.

[0113] After distributed photovoltaic (DPV) is connected to the distribution network, in order to ensure the safe and stable operation of the power grid, the distribution network is monitored and protected in real time.

[0114] By installing sensors and measuring equipment, key parameters of the distribution network such as voltage, current, power factor, active power, reactive power, etc. can be collected in real time. These parameters can reflect the operating status of the distribution network and provide data support for subsequent protection and control.

[0115] Sensors and measuring equipment are used to collect parameters such as voltage and current at each node of the distribution network in real time. These parameters can be transmitted to the data center or monitoring platform via wired or wireless means.

[0116] The collected data is processed and analyzed, including data verification, filtering, transformation, etc. Through data processing, more accurate and reliable power grid operation status information can be obtained.

[0117] Based on the processed data, the operating status of the distribution network is monitored in real time, including voltage fluctuations, current overloads, power factor anomalies, etc. Once an abnormality is found, the alarm mechanism is triggered immediately.

[0118] Based on real-time monitoring, effective protection strategies need to be formulated to ensure the safe and stable operation of the power grid after the access of distributed photovoltaics.

[0119] When the current in the distribution network exceeds the set value, the overcurrent protection device will immediately operate to cut off the fault circuit and prevent the current from continuing to increase, thereby protecting the power grid equipment from damage.

[0120] After distributed photovoltaics are connected, the voltage at some nodes may increase. When the voltage exceeds the set value, the overvoltage protection device will be activated to reduce the voltage or cut off the circuit to protect the grid equipment.

[0121] When the voltage drops due to insufficient distributed photovoltaic power generation or a grid fault, the undervoltage protection device will operate to ensure that the grid equipment operates within a safe voltage range.

[0122] When a ground fault occurs in the distribution network, the ground fault protection device will act quickly to cut off the fault circuit and prevent the fault from expanding.

[0123] After distributed photovoltaics are connected, if a grid failure causes some areas to be disconnected from the main grid, forming an island grid, the island protection device will be activated to ensure the safe operation of equipment in the island grid or timely disconnection.

[0124] Furthermore, the calculated accessible capacity of distributed photovoltaics is compared with a preset capacity threshold to determine whether the distributed photovoltaics are allowed to access the distribution network.

Claims

1. A method for calculating the access capacity of distributed photovoltaic power generation in a distribution network, characterized in that: include: Obtain real-time operating data of the active distribution network, including the short-circuit voltage, line impedance, busbar short-circuit impedance, rated voltage and power factor of the PV power station; When a short-circuit fault occurs in the active distribution network, the short-circuit current flowing from the distributed photovoltaic to the distribution network bus is calculated according to the short-circuit voltage, line impedance and bus short-circuit impedance of the photovoltaic power station; Determine the quick-break current setting value of the distribution network bus according to the short-circuit current; The accessible capacity of distributed photovoltaic is obtained according to the rated voltage, power factor and quick-break current setting of the distributed photovoltaic.

2. A method for calculating the capacity of distributed photovoltaic access to a distribution network according to claim 1, characterized in that: The causes of the short circuit failure include line aging, insulation failure, and human operating errors.

3. The method for calculating the distributed photovoltaic access capacity of a distribution network according to claim 1, characterized in that: Before obtaining the accessible capacity of distributed photovoltaics, it also includes: A short-circuit current simulation analysis is performed on the active power distribution network to verify the accuracy of the short-circuit current calculation.

4. A method for calculating the capacity of distributed photovoltaic access to a distribution network according to claim 1, characterized in that: Also includes: According to the access location and access capacity of distributed photovoltaics, the power flow distribution and short-circuit current characteristics of the distribution network are predicted and analyzed.

5. The method for calculating the distributed photovoltaic access capacity of a distribution network according to claim 1, characterized in that: Also includes: After distributed photovoltaics are connected, the distribution network is monitored and protected in real time to ensure the safe and stable operation of the power grid.

6. A method for calculating the capacity of distributed photovoltaic access to a distribution network according to claim 1, characterized in that: include: A boundary formula is established to describe the change of short-circuit current after distributed photovoltaic access is connected, and the upper limit value and amplitude limit value of the short-circuit current are determined according to the boundary formula.

7. A method for calculating the capacity of distributed photovoltaic access to a distribution network according to claim 6, characterized in that: The derivation process of the boundary formula includes: Simplify the fast-break current setting formula; Convert short-circuit current form; Generate boundary formulas that take into account changes in system impedance after distributed photovoltaic access.

8. A method for calculating the capacity of distributed photovoltaic access to a distribution network according to claim 1, characterized in that: The real-time operation data is obtained by directly measuring the output voltage, current and power of the photovoltaic power station using sensors and measuring equipment.

9. A method for calculating the capacity of distributed photovoltaic access to a distribution network according to claim 1, characterized in that: Also includes: The calculated distributed photovoltaic access capacity is compared with the preset capacity threshold to determine whether the distributed photovoltaic is allowed to access the distribution network.

10. A method for calculating the access capacity of distributed photovoltaic power generation in a distribution network according to any one of claims 1 to 9, characterized in that: Applicable to different types of distribution networks, including urban distribution networks, rural distribution networks and industrial distribution networks.

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