CN106410784B - Method for calculating sensitivity of active load of transformer substation to regional power grid active network loss - Google Patents
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Abstract
The invention belongs to the technical field of analysis and calculation of power grid network loss in a power system, and particularly relates to a sensitivity calculation method of substation active load to regional power grid active loss in power grid online theoretical loss calculation. The method comprises the following steps: on the basis of a real-time power flow calculation result, firstly, the sensitivity of each bus voltage to the total grid loss of a region is calculated, then, the transformer substation containing low-voltage-side equivalent loads in a regional power grid is calculated, firstly, the sensitivity of the active load of a single equivalent load in the transformer substation to the bus voltage is calculated, the superposition of the sensitivity of the equivalent load and the bus voltage is the sensitivity of the equivalent load to the active grid loss of the regional power grid, and finally, the arithmetic mean value of the sensitivities of all equivalent loads contained in the transformer substation is taken, namely, the active sensitivity of the active load of the transformer substation to the regional power grid. The method can give the sensitivity sequence of the active load of the transformer substation, thereby giving the adjustment direction for reducing the network loss and providing an auxiliary decision for reducing the loss in real time.
Description
Technical Field
The invention belongs to the technical field of analysis and calculation of power grid network loss in a power system, and particularly relates to a sensitivity calculation method of substation active load to regional power grid active loss in power grid online theoretical loss calculation.
Background
The electric energy is a secondary energy obtained by converting a primary energy, and can be converted into mechanical energy, heat energy, magnetic energy and the like. With the development of society, electric energy has become the life line of national economy development, and the application of the electric energy is deeply applied to various fields of production and life. With the rapid increase of the transmission electric quantity of the power grid, the active loss (hereinafter referred to as grid loss) of the power grid is also increased greatly. Taking 2007 as an example, the annual power generation of China is about 3.3 trillion kilowatt hours, the average network loss rate of the power transmission and distribution network is about 7%, only one network loss item, the annual power loss of China reaches 2300 million kilowatt hours, which is equivalent to that 0.9 million tons of standard coal are consumed more, and CO is discharged more2About 2 million tons. How to obtain the maximum economic benefit by the minimum electric energy loss and realize the network loss reduction, energy conservation and emission reduction of the power grid is very significant.
In the process of transmitting and distributing electric energy in a power grid, because power transmission equipment has a resistor, a certain amount of active power loss is generated when current flows, and in a given time period (day, month, season and year), all active electric quantity consumed in each power grid equipment is called grid loss electric quantity and generally comprises active electric quantity consumed by line equipment (line loss for short) and active electric quantity consumed by transformer equipment (variable loss for short). For power grid enterprises managing electric energy transmission, such as provincial and urban power grid companies, although power grids are physically and integrally connected together, the power grids governed by the power grid companies are only a part of the whole power grid, or are divided according to regions or voltage levels, and clear boundary positions are defined between power grid equipment ranges governed by the power grid companies. Similarly, there are well-defined boundaries for the range of grid devices managed by grid enterprises and power generation enterprises. When each power grid company counts and calculates the active power loss of the power grid, only the equipment in the jurisdiction of the company is counted and calculated to cause power loss when transmitting electric energy.
The types of the power grid loss are divided from the calculation mode, and can be divided into two types of statistical loss and theoretical loss. The statistical grid loss is calculated according to the indicated number of the electric energy meter, and is the difference value between the total inflow electric quantity (namely the on-grid electric quantity) and the outflow electric quantity (namely the off-grid electric quantity) of the electric network range participating in the statistical calculation of the grid loss in a given time period. The theoretical grid loss is obtained by calculating the voltage and current of each power transmission device and the corresponding grid loss electric quantity in the jurisdiction range according to the grasped power grid structure parameters and operation parameters by using an electrical engineering principle and an electricity theory, the calculated grid loss is called as the theoretical grid loss, and the theoretical grid loss of the power grid is the sum of the theoretical grid losses of all the electrical devices in the jurisdiction range.
The statistical network loss is based on an electric quantity data acquisition system, and generally, in view of cost saving, a power grid company only installs an electric energy meter at boundary equipment in a power grid range under jurisdiction, so that the statistical network loss only can give a total network loss value, and the network loss of each element in a power grid cannot be calculated and analyzed respectively. The theoretical network loss calculation and analysis can provide the accurate network loss and network loss distribution condition of each element in the power grid range under jurisdiction, and if the online theoretical network loss analysis and calculation is realized by combining the real-time operation mode of the power grid, the defect of network loss statistics can be well made up.
The network loss calculation is a more complex part in the power flow calculation of the power system. In the traditional network loss optimization system, various different sensitivity calculation schemes need to be specified manually, and then the selection of the loss reduction scheme is carried out under the guidance of the experience of an analyst. Due to the fact that the topology of the power transmission network is complex, the data volume is large, the state space of the obtained sensitivity scheme is increased in a geometric series proportion, and the working efficiency of an analyst is greatly reduced.
The method has the advantages that the sensitivity of the active load of the transformer substation to the active network loss of the regional power grid is calculated, the method has great significance for a power grid company to make a scheduling decision for reducing the network loss, the active load of the transformer substation can be sequenced to the sensitivity of the network loss, and the active load of the transformer substation is adjusted, so that the network loss of the power grid is effectively reduced.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a method for calculating the active sensitivity of the active load of a transformer substation to a regional power grid. On the basis of a real-time power flow calculation result, firstly, the sensitivity of each bus voltage to the total grid loss of a region is calculated, then, the transformer substation containing low-voltage-side equivalent loads in a regional power grid is calculated, firstly, the sensitivity of the active load of a single equivalent load in the transformer substation to the bus voltage is calculated, the superposition of the sensitivity of the equivalent load and the bus voltage is the sensitivity of the equivalent load to the active grid loss of the regional power grid, and finally, the arithmetic mean value of the sensitivities of all equivalent loads contained in the transformer substation is taken, namely, the active sensitivity of the active load of the transformer substation to the regional power grid. The method can give the sensitivity sequence of the active load of the transformer substation, thereby giving the adjustment direction for reducing the network loss and providing an auxiliary decision for reducing the loss in real time.
A method for calculating the sensitivity of active load of a transformer substation to the active network loss of a regional power grid comprises the following steps:
1) calculating the sensitivity of the bus voltage to the active network loss of the regional power grid,
1.1) determining the influence range of the bus voltage on the regional power grid active power grid loss;
the influence of the bus i on the grid loss of the power grid is mainly expressed as the grid loss of a branch connected with the bus, and can be written as follows:
wherein Pij and Pji are active power flows flowing through a branch connecting the bus i and the adjacent bus j, Pij represents a power flow flowing from the bus i to the bus j, and Pji represents a power flow flowing from the bus j to the bus j. In grid loss analysis, the object of the study is a manually defined regional grid, which is a subset of the complete grid. Thus, equation (1-1) is modified to:
wherein the set LA represents the bus included in the manually specified regional power grid.
1.2) calculating the sensitivity of the bus voltage to the active network loss of the regional power grid:
according to equation (1-1), the sensitivity of the net loss affected by the bus i to the bus corrected voltage is calculated as:
wherein ViIs the amplitude of the bus i voltage, θiIs the phase angle of the bus i voltage. According to the branch flow equation, the following can be obtained:
wherein g isijFor conductance of the branch connecting bus i and bus j, bijIs the susceptance of that branch. From formulae (1-4) to (1-7), taking into account (1-2):
the sensitivity of the voltage (amplitude phase angle) of the ith bus to the active network loss of the regional power grid is given by the formulas (1-8) and (1-9). In the calculation, V obtained by current power grid load flow calculationi、VjAnd thetaijIn the substituted type, the sensitivity of the bus i voltage to the regional power grid active power grid loss in the current state can be obtained.
2) Calculating the network loss sensitivity of each equivalent load active load in the transformer substation containing the low-voltage side equivalent load to the regional power grid
2.1) calculating the sensitivity of an equivalent load active load to the bus voltage in the substation
In newton's method load flow calculation, the linearized correction equation can be written as:
wherein
Is a jacobian matrix. The jacobian matrix describes the effect of the active reactive power being injected on the bus voltage. And forming a constant Jacobian matrix by using the current power flow calculation result, and constructing a linear equation of the variation of the injection power flow and the variation of the bus voltage as shown in (2-1).
Calculating the sensitivity of an active load of an equivalent load to each bus voltage of the power grid, setting the equivalent load to be connected to a bus j, and setting the right vector of the equation (2-1) as:
wherein Δ Pj-1; namely, except the unit variation of the injected active power on the jth bus, which is the unit 1 of the active power increase of the load, and all other variations are 0, the equation (2-1) is solved, and the sensitivity delta theta of the equivalent load active power load to the voltage of the bus i in the power grid can be obtainedi、ΔUi。
2.2) calculating the sensitivity of an equivalent load active load to the grid loss of the regional power grid
Calculating the substations of 110kV and 35 substations in the regional power grid, which contain equivalent loads on the low-voltage side, by using the calculation results obtained in the steps 1.2 and 2.1, and determining the sensitivity of the active load of an equivalent load k to the active network loss of the regional power grid as follows:
the subscript i corresponds to buses contained in the manually specified regional power grid, and N is the number of the buses.
2.3) returning to the step 2.1), and continuing to calculate the next equivalent load of the transformer substation until all the equivalent loads in the transformer substation are calculated.
3) Calculating sensitivity of active load of transformer substation to active network loss of regional power grid
Setting K equivalent loads in a transformer substation, wherein the sensitivity of the transformer substation active load to the regional power grid active network loss is the arithmetic average value of all equivalent load sensitivities:
the invention has the technical characteristics and effects that:
the method is different from the traditional method and has the obvious characteristic that the method for calculating the sensitivity of the active load of the transformer substation to the active network loss of the regional power grid is provided. According to the method, the sensitivity of the active load of the transformer substation to the active network loss of the regional power grid can be sequenced, and the network loss reduction, energy conservation and emission reduction of the power grid can be realized.
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Fig. 1 is a schematic diagram of a method for calculating the sensitivity of the active load of the transformer substation to the active network loss of the regional power grid according to the invention.
Detailed Description
The method for calculating the sensitivity of the active load of the transformer substation to the active network loss of the regional power grid, which is provided by the invention, is explained in detail by combining with the embodiment as follows:
the power flow calculation of the power system is a calculation for researching the steady-state operation condition of the power system, calculates the voltage of a bus, the power of each element and the network loss according to given data, and evaluates the operation states of all parts of a power grid. And then, the operation of the power grid system is monitored and optimized according to the calculated data, so that the rationality, reliability and economy of a power supply scheme or an operation mode are improved. For the running power system, whether parameters such as the voltage of a bus, the power of a branch circuit and the like in the current system exceed limits can be evaluated through load flow calculation; if the abnormality occurs, measures are taken to adjust the operation mode.
The grid flow equation in polar coordinates can be expressed as:
wherein V isiIs the amplitude of the bus i voltage, θiIs the phase angle, V, of the bus i voltagejIs the magnitude of the bus j voltage, θjThe phase angle of the voltage of the bus j, I represents a set of the bus j connected with the bus I through a branch; gijFor conductance of the branch connecting bus i and bus j, bijIs the susceptance of the branch. PGiFor active power generation on bus i, PDiFor active load on bus i, QGiFor reactive power generation of bus i, QDiIs the reactive load on bus i.
The branch power flow calculation expression can be further obtained from the power flow mode as follows:
wherein P isijFor active power flow, P, flowing in a branch connecting a busbar i and its adjacent busbar jijRepresenting the flow of current, P, from bus i to bus jjiRepresents the current flowing from bus j to bus j; the branch comprises a line or transformer winding connecting the bus bars. QijFor branch reactive power flow, ycRepresenting the half admittance of the line.
The power flow calculation can determine the steady-state operation state of the power grid under the condition of the determination of the power grid structure parameters. Nodes in the power grid can be divided into PQ nodes, PV nodes and V theta nodes according to given variables, and power grid state variables, namely node voltage amplitude and phase angle, are calculated. The power flow equation is a group of high-order nonlinear algebraic equations and needs to be solved by an iterative method. The Newton-Raphson power flow algorithm is a power flow algorithm with second-order convergence, and therefore the Newton-Raphson power flow algorithm is widely applied. However, since the jacobian matrix of the method is a state variable function to be solved, the jacobian matrix is formed again in the iteration process and solved by a gaussian elimination method, and the calculated amount of each iteration is large. Because the method is the basis of various power flow calculation methods, the method has an important position in power grid analysis.
The newton-raphson power flow algorithm is described in "advanced power network analysis" (published by the university of qinghua, 1996, page 190-:
wherein each element of the jacobian matrix is
To find these partial derivatives, P can be calculatedi、QiRespectively unfolded as follows
And a meter
When j ≠ i, since for a particular j, only δ for that particular nodejThus specifying δij＝δi-δjIs a variable, can
Similarly, since for a particular j, only the U of that particular nodejIs a variable, can
When j is equal to i, the value is deltaiIs a variable, all deltaij＝δi-δjAre all variable, can
Similarly, due to UiIs a variable, can
According to formulas (5) - (8), when Ui、UjWhen known, each element of the Jacobian matrix in the formula (1) can be calculated to form a well-known Jacobian matrix.
The network loss calculation is a more complex part in the power flow calculation of the power system. In the traditional network loss optimization system, various different sensitivity calculation schemes need to be specified manually, and then the selection of the loss reduction scheme is carried out under the guidance of the experience of an analyst. Due to the fact that the topology of the power transmission network is complex, the data volume is large, the state space of the obtained sensitivity scheme is increased in a geometric series proportion, and the working efficiency of an analyst is greatly reduced.
The method has the advantages that the sensitivity of the active load of the transformer substation to the active network loss of the regional power grid is calculated, the method has great significance for a power grid company to make a scheduling decision for reducing the network loss, the active load of the transformer substation can be sequenced to the sensitivity of the network loss, and the active load of the transformer substation is adjusted, so that the network loss of the power grid is effectively reduced.
As shown in fig. 1, a schematic diagram of a method for calculating the sensitivity of the active load of the transformer substation to the active network loss of the regional power grid according to the present invention is shown, the method of the present invention includes:
1) calculating the sensitivity of the bus voltage to the active network loss of the regional power grid,
1.1) determining the influence range of the bus voltage on the regional power grid active power grid loss;
the influence of the bus i on the grid loss of the power grid is mainly expressed as the grid loss of a branch connected with the bus, and can be written as follows:
wherein Pij and Pji are active power flows flowing through a branch connecting the bus i and the adjacent bus j, Pij represents a power flow flowing from the bus i to the bus j, and Pji represents a power flow flowing from the bus j to the bus j. In grid loss analysis, the object of the study is a manually defined regional grid, which is a subset of the complete grid. Thus, equation (1-1) is modified to:
wherein the set LA represents the bus included in the manually specified regional power grid.
1.2) calculating the sensitivity of the bus voltage to the active network loss of the regional power grid:
according to equation (1-1), the sensitivity of the net loss affected by the bus i to the bus corrected voltage is calculated as:
wherein ViIs the amplitude of the bus i voltage, θiIs the phase angle of the bus i voltage. According to the branch flow equation, the following can be obtained:
wherein g isijFor conductance of the branch connecting bus i and bus j, bijIs the susceptance of that branch. From formulae (1-4) to (1-7), taking into account (1-2):
the sensitivity of the voltage (amplitude phase angle) of the ith bus to the active network loss of the regional power grid is given by the formulas (1-8) and (1-9). In the calculation, V obtained by current power grid load flow calculationi、VjAnd thetaijIn the substituted type, the sensitivity of the bus i voltage to the regional power grid active power grid loss in the current state can be obtained.
In the embodiment of the invention, a typical power grid composed of 5 stations is considered, and specific connection relations are shown as accessories, wherein the stations 1-4 are in a grid loss area, the station 5 is not in a regional grid loss area (namely loss of a branch Y15 is not counted in the grid loss area), the station 1 is a transformer substation, hereinafter referred to as a transformer substation _1, and a low-voltage bus of the transformer substation _1 is connected with two equivalent loads. The procedure of the sensitivity calculation is analyzed by a specific example below.
The data of the bus _1 and the branch of the substation _1 are obtained through load flow calculation as follows:
i＝1 j＝2 V1＝1.002276 V2＝0.998736 g12＝29.762905 θ12＝0.004401
i＝1 j＝3 V1＝1.002276 V3＝0.991473 g13＝5.736257 θ13＝0.051120
i＝1 j＝4 V1＝1.002276 V4＝1.002766 g14＝14.826341 θ14＝0.020143
i＝1 j＝5 V1＝1.002276 V5＝1.005152 g15＝10.432392 θ15＝0.014018
considering that the formula 2-1, the branch Y15 is not in the region of regional grid loss statistics, so that the branch is excluded when calculating the voltage-to-grid loss sensitivity, and other three groups of data are substituted into the formula 1-7, so that the sensitivity of the bus-1 voltage to the grid loss can be obtained
The sensitivity of the bus-1 voltage to the network loss can be obtained by substituting the data into the formulas 1 to 8
According to the above calculation method, the sensitivity of all bus voltages in the area to the area grid loss can be calculated.
TABLE 1-1 sensitivity of bus Voltage to area losses
2) Calculating the network loss sensitivity of each equivalent load active load in the transformer substation containing the low-voltage side equivalent load to the regional power grid
2.1) calculating the sensitivity of an equivalent load active load to the bus voltage in the substation
In newton's method load flow calculation, the linearized correction equation can be written as:
wherein
Is a jacobian matrix. Yaya (elegant)The comparable matrix describes the effect of active reactive power being injected on the bus voltage. And forming a constant Jacobian matrix by using the current power flow calculation result, and constructing a linear equation of the variation of the injection power flow and the variation of the bus voltage as shown in (2-1).
Calculating the sensitivity of an active load of an equivalent load to each bus voltage of the power grid, setting the equivalent load to be connected to a bus j, and setting the right vector of the equation (2-1) as:
wherein Δ Pj-1; namely, except the unit variation of the injected active power on the jth bus, the variation is the unit 1 of the load active power increase, the other variations are all 0, the equation (2-1) is solved, and the sensitivity delta theta of the equivalent load active power load to the bus i voltage in the power grid can be obtainedi、ΔUi。
The following table gives the sensitivity of the connected equivalent load _1 injected unit active of the substation bus _1 to 5 bus voltages:
| numbering | Name (R) | Δθi | ΔUi |
| 1 | Bus-bar _1 | 0.009 | 0 |
| 2 | Bus-bar _2 | 0.008 | 0 |
| 3 | Bus-bar _3 | 0.008 | 0 |
| 4 | Bus-bar _4 | 0.008 | 0 |
| 5 | Bus-bar _5 | 0.007 | 0 |
TABLE 2-1 sensitivity of equivalent load _1 to bus voltage
The following table gives the sensitivity of the connected equivalent load _2 injection unit real power of the substation bus _1 to 5 bus voltages:
| numbering | Name (R) | Δθi | ΔUi |
| 1 | Bus-bar _1 | 0.009 | 0 |
| 2 | Bus-bar _2 | 0.008 | 0 |
| 3 | Bus-bar _3 | 0.008 | 0 |
| 4 | Bus-bar _4 | 0.008 | 0 |
| 5 | Bus-bar _5 | 0.007 | 0 |
TABLE 2-2 sensitivity of equivalent load _2 to bus voltage
2.2) calculating the sensitivity of an equivalent load active load to the grid loss of the regional power grid
Calculating the substations of 110kV and 35 substations in the regional power grid, which contain equivalent loads on the low-voltage side, by using the calculation results obtained in the steps 1.2 and 2.1, and determining the sensitivity of the active load of an equivalent load k to the active network loss of the regional power grid as follows:
the subscript i corresponds to buses contained in the manually specified regional power grid, and N is the number of the buses.
2.3) returning to the step 2.1), and continuing to calculate the next equivalent load of the transformer substation until all the equivalent loads in the transformer substation are calculated.
The data in the tables 1-1 and 2-1 are substituted into a formula, and the sensitivity of the equivalent load _1 in the transformer substation _1 to the active work of the regional power grid can be calculated to be Sc10.0114, the sensitivity of the equivalent load _2 to the active power of the regional power grid is Sc2＝0.0114。
3) Calculating sensitivity of active load of transformer substation to active network loss of regional power grid
Setting K equivalent loads in a transformer substation, wherein the sensitivity of the transformer substation active load to the regional power grid active network loss is the arithmetic average value of all equivalent load sensitivities:
the sensitivity of the power load of the transformer substation _1 to the active power of the regional power grid can be calculated by substituting the data into the formula (3-1)
Claims (1)
1. The method for calculating the sensitivity of the active load of the transformer substation to the active network loss of the regional power grid is characterized by comprising the following steps of: the method comprises the following steps:
1) calculating the sensitivity of the bus voltage to the active network loss of the regional power grid,
1.1) determining the influence range of the bus voltage on the regional power grid active power grid loss;
the influence of the bus i on the grid loss of the power grid is mainly expressed as the grid loss of a branch connected with the bus, and can be written as follows:
wherein Pij and Pji are active power flows flowing on a branch circuit connecting a bus i and an adjacent bus j, Pij represents a power flow flowing from the bus i to the bus j, and Pji represents a power flow flowing from the bus j to the bus j, in the network loss analysis, an object to be researched is an artificially defined regional power grid which is a subset of a complete power grid, so that the formula (1-1) is modified as follows:
the set LA represents a bus included in the manually specified regional power grid;
1.2) calculating the sensitivity of the bus voltage to the active network loss of the regional power grid:
according to equation (1-1), the sensitivity of the net loss affected by bus i to the bus voltage is calculated as:
wherein ViIs the amplitude of the bus i voltage, θiFor the phase angle of the voltage of the bus i, according to the branch flow equation, the following can be obtained:
wherein g isijFor conductance of the branch connecting bus i and bus j, bijFor the susceptance of this branch, it can be obtained from the formulae (1-4) to (1-7) in consideration of (1-2):
the sensitivity of the voltage amplitude phase angle of the ith bus to the active network loss of the regional power grid is given by the formulas (1-8) and (1-9), and in the calculation, V is calculated according to the current power grid load flowi、VjAnd thetaijIn the substitution type, the sensitivity of the bus i voltage to the regional power grid active power grid loss in the current state can be obtained;
2) calculating the network loss sensitivity of each equivalent load active load in the transformer substation containing the low-voltage side equivalent load to the regional power grid
2.1) calculating the sensitivity of an equivalent load active load in a transformer substation to bus voltage in Newton method load flow calculation, a linearized correction equation can be written as:
wherein
The method is a Jacobian matrix, the Jacobian matrix describes the influence of active and reactive power injected on the bus voltage, a constant Jacobian matrix is formed by using the current power flow calculation result, a linear equation of the variation of the injected power flow and the variation of the bus voltage is constructed as shown in (2-1),
calculating the sensitivity of an active load of an equivalent load to each bus voltage of the power grid, setting the equivalent load to be connected to a bus j, and setting the right vector of the equation (2-1) as:
wherein Δ Pj-1; namely, except the unit variation of the injected active power on the jth bus, the variation is the unit 1 of the load active power increase, the other variations are all 0, the equation (2-1) is solved, and the sensitivity delta theta of the equivalent load active power load to the bus i voltage in the power grid can be obtainedi、ΔUi；
2.2) calculating the sensitivity of an equivalent load active load to the grid loss of the regional power grid
Calculating the substations of 110kV and 35kV substations in the regional power grid, which contain equivalent loads on a low-voltage side, by using the calculation results obtained in the steps 1.2) and 2.1), and determining the sensitivity of the active load of an equivalent load k to the active network loss of the regional power grid as follows:
the subscript i corresponds to buses contained in the manually specified regional power grid, and N is the number of the buses;
2.3) returning to the step 2.1), and continuing to calculate the next equivalent load of the transformer substation until all the equivalent loads in the transformer substation are calculated;
3) calculating sensitivity of active load of transformer substation to active network loss of regional power grid
Setting K equivalent loads in a transformer substation, wherein the sensitivity of the transformer substation active load to the regional power grid active network loss is the arithmetic average value of all equivalent load sensitivities:
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| CN103269069A (en) * | 2013-03-18 | 2013-08-28 | 国家电网公司 | Method for reconstructing low-voltage power transmission system |
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