CN105305433B - Maximum power permeability calculation method for distributed power supply connected to power distribution network - Google Patents
Maximum power permeability calculation method for distributed power supply connected to power distribution network Download PDFInfo
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Abstract
The invention relates to a method for calculating the maximum power permeability of a distributed power supply accessed to a power distribution network, which is characterized by comprising the following steps: 1) for the maximum power permeability of a distributed power supply accessed to a power distribution network, the maximum power permeability of a main transformer power supply area is also considered besides the maximum power permeability of a medium-voltage distribution line; the maximum power permeability of the medium-voltage distribution line refers to the ratio of the maximum total installed capacity of the distributed power supply in the distribution line to the maximum transmission capacity of the distribution line; the permeability of a main transformer power supply area refers to the ratio of installed capacity of a distributed power supply in the main transformer power supply area to rated capacity of a main transformer; 2) and comprehensively considering the restriction of the line shutoff quantity, the restriction of the node voltage and the restriction of the bus short-circuit current. The method and the device respectively compare different positions of different types of distributed power supplies accessed to the power distribution network, further optimize the maximum power permeability of the distributed power supplies accessed to the power distribution network, and provide technical schemes and calculation bases for the distributed power supplies which are wide and a large number of distributed power supplies are accessed to the power distribution network.
Description
Technical Field
The invention relates to a method for calculating the maximum power permeability of a distributed power supply connected to a power distribution network. Belonging to the technical field of permeability algorithm of a distributed power supply connected to a power distribution network.
Background
With the vigorous development of distributed power generation, the support of the distributed power supply to the power distribution network in China is continuously increased. In the future more and more distributed power sources will be directly connected to the medium voltage distribution network. The existing traditional power distribution network is not designed for the access of the distributed power supply, corresponding transformation and upgrading must be carried out after the access of the distributed power supply, wherein the transformation cost of secondary systems such as relay protection, distribution automation and the like is relatively low, the difficulty of construction transformation is also low, and the transformation cost and the transformation implementation difficulty of primary distribution systems such as power transmission lines, buses and the like are relatively high. Therefore, from the perspective of technology and economy, how to fully excavate the access potential of the distributed power supply on the premise of not modifying the existing primary power distribution system so as to meet the access of the distributed power supply and fulfill the index requirements issued by the nation as far as possible is a problem that needs to be solved urgently by all levels of power grid companies at present.
At present, the calculation and analysis of the access capacity limit of the distributed power supply mainly focus on the voltage constraint and the relay protection constraint:
a) in the aspect of considering voltage constraint, an access power optimization calculation model after voltage regulation constraint is mainly considered, and the conditions of an on-load tap changer, a distributed power supply accident outage and a plurality of distributed power supplies can be simulated; or evaluating the influence of the distributed power supply on the quality of the power supply voltage of the power distribution network by using the short circuit ratio and the rigidity ratio; or considering the influence of a tap of the transformer on the bus voltage sensitivity after the distributed power supply is connected, obtaining an access power limit model considering tap oscillation constraint, and not fully considering the constraint of a primary system of the power distribution network; whether the voltage of the power distribution network is suitable for load access and operation is mainly concerned, and the bearing capacity of primary equipment of the power distribution network after the distributed power supply is accessed is not considered.
There are the following disadvantages: the method for calculating the maximum power permeability of the distributed power supply by purely considering voltage constraints comprises the following steps: the limitation of load operation is mainly considered, and the constraint of a primary system of the power distribution network is not fully considered; whether the voltage of the power distribution network is suitable for load access and operation is mainly concerned, and the bearing capacity of primary equipment of the power distribution network after the distributed power supply is accessed is not considered.
b) In the aspect of considering relay protection constraint, mainly aiming at providing an analysis method for DG access capacity considering the influences of power distribution network protection action and distributed power supply short-circuit current attenuation characteristics on the premise of meeting the reliable action of relay protection; or a DG access capacity optimization calculation model considering the interphase protection constraint of the power distribution network calculates and obtains the DG access capacity under the original protection coordination condition; or analyzing the adaptability of the protection setting condition under 2 conditions of the DG power change when the grid-connected position is fixed and the grid-connected position change when the DG capacity is fixed.
There are the following disadvantages: the method for calculating the maximum power permeability of the distributed power supply by purely considering relay protection constraints comprises the following steps: the distributed power supply is connected to the power distribution network, the relay protection of the original traditional power distribution network is generally greatly influenced, the adjustable range of the protection setting value is relatively small due to the poor adaptability of the original relay protection, if the effectiveness of the original relay protection is simply kept, the capacity of the distributed power supply which can be connected is generally small, and the wide and large-scale connection of the distributed power supply is not facilitated; after the distributed power supply is connected to the power distribution network, the power distribution network cannot be correspondingly transformed, at least a secondary power distribution system needs to be transformed, and compared with the transformation of a primary system, the transformation implementation difficulty and transformation investment of the secondary power distribution network system are small, so that relay protection belonging to the secondary system cannot be used as a constraint condition for the access of the distributed power supply in order to adapt to the access of the distributed power supply.
Disclosure of Invention
The invention aims to provide a maximum power permeability calculation method for a distributed power supply to be connected into a power distribution network, aiming at solving the problems that the constraint of a primary system of the power distribution network and the bearing capacity of primary equipment of the power distribution network after the distributed power supply is connected are not fully considered in the calculation method for the maximum power permeability of the distributed power supply in the prior art. The method has the characteristics of providing theoretical calculation basis for the distributed power supply to be connected into the power distribution network and promoting the distributed power supply to be widely and massively connected into the power distribution network.
The purpose of the invention can be achieved by adopting the following technical scheme:
the method for calculating the maximum power permeability of the distributed power supply connected to the power distribution network is characterized by comprising the following steps:
1) for the maximum power permeability of a distributed power supply accessed to a power distribution network, in addition to the maximum power permeability of a medium-voltage distribution line, when different distributed power supplies are accessed to a plurality of lines and the lines are all accessed to the same main transformer, the maximum power permeability of a power supply area of the main transformer is also considered; the maximum power permeability of the medium-voltage distribution line refers to a ratio of the maximum total installed capacity of the distributed power supply in the distribution line to the maximum transmission capacity of the distribution line; the permeability of the main transformer power supply area refers to the ratio of the installed capacity of a distributed power supply in the main transformer power supply area to the rated capacity of the main transformer;
2) the method for calculating the maximum power permeability of the medium-voltage distribution line comprehensively considers the current-carrying capacity constraint of the line, the node voltage constraint and the short-circuit current constraint of the bus; the calculation model is as follows:
in the formula, PrlmaxIn order to comprehensively consider the maximum power permeability of the medium-voltage distribution line with various constraints,maximum power penetration of a line, P, to account for line ampacity constraintsrlmax(V)To account for the line maximum power penetration constrained by the node voltage,maximum line power penetration, P, to account for bus short circuit current constraintsrlmaxGetPrlmax(V)Andminimum value of (d); equations (102) - (103) are node active and reactive balance equations, where PGiAnd QGiRespectively representing active and reactive power output, P, of the distributed power supply on the node iDiAnd QDiLoad active and reactive power, Q, respectively, on node ii(V, theta) is node reactive power, Pi(V, theta) are active power of the node, and V and theta respectively represent voltage and phase angle vectors; sLAndthe actual transmission capacity and the rated transmission capacity of the line are respectively; viThe node voltage is Vmin, the lower limit of the node voltage is Vmin, and the upper limit of the node voltage is Vmax; i isBjAndthe method comprises the following steps of respectively setting an actual short-circuit current value and a rated value of the three-phase short-circuit current of a 10kV bus j on a distribution line; s.t. represents a constraint.
Under special conditions, the maximum power permeability of the distributed power supply in the main transformer power supply area meets the voltage constraint of each line node and the bus short-circuit current constraint in the main transformer power supply area, and the main transformer capacity constraint is also considered.
Further, the calculation model of the maximum power permeability of the medium-voltage distribution line is solved by an enumeration method, and the specific steps are as follows:
1) the installed capacity of the distributed power supply is given as the rated transmission capacity of the line, so that the current-carrying capacity of the line is not out of limit;
2) respectively checking whether node voltage and bus short-circuit current meet constraints through load flow calculation and three-phase short-circuit calculation, and if any constraint requirement cannot be met, performing load flow calculation and three-phase short-circuit calculation again after the installed capacity of the distributed power supply is reduced until the requirements of the formula (105) and the formula (106) are met;
3) and respectively considering the maximum power permeability of the three constraint conditions for comparison, and taking a smaller value as the maximum power permeability of the distributed power supply comprehensively considering the multiple constraints.
Further, the constraint considered by the medium-voltage distribution line maximum power permeability calculation method is specifically as follows:
1) the current-carrying capacity of the line is constrained, the local load is 0 and is used as a boundary condition for calculating the maximum power permeability, and if the current-carrying capacity of the line is only examined independently, the maximum value of the permeability of the distribution line is 100 percent; if the requirement of distribution network scheduling on the operation margin is considered at the same time, multiplying the requirement by the percentage value of the corresponding margin on the basis of independently considering the maximum power permeability of the line current-carrying capacity constraint;
2) node voltage constraint, mainly considering the condition that a distributed power supply is far away from a main transformer low-voltage side 10kV bus (4), and under the conditions that the current-carrying capacity of a circuit is not out of limit and the local load is 0, evaluating the influence of the distributed power supply on the node voltage quality by load flow calculation so as to determine the permeability index of the distributed power supply on the premise that the current-carrying capacity of the circuit is not out of limit and the node voltage quality is not over standard; under the condition that the line lengths are the same, the influence of reactive injection of the distributed power supply on the node voltage is mainly considered, the power factor when the reactive injection is the most is taken as a simulation parameter, and the maximum power permeability of the distributed power supply is analyzed;
3) bus short-circuit current constraint, taking the transmission capacity of a distribution line as the upper limit, analyzing the short-circuit current values of all levels of buses when the inversion type distributed power supply or the rotary type distributed power supply with different capacities is accessed to a user side 10kV bus (6) and a main transformer low-voltage side 10kV bus (4), determining the access capacity limit of the corresponding inversion type distributed power supply or the rotary type distributed power supply according to the bus current level specified in the planning technical guidance principle of the existing medium-voltage distribution network, when the distributed power supply accessed in the power distribution network simultaneously comprises a rotating type and an inversion type, the maximum power permeability considering the constraint of the short-circuit current of the bus is positioned between the maximum power permeability values of the distributed power supply which is only considered for the inversion type and the rotating type, and the specific numerical value is determined according to the specific parameters and the installed capacity proportion of the inversion type distributed power supply and the rotating type distributed power supply.
Further, the constraint considered by the calculation method of the maximum power permeability of the power supply area of the main transformer is specifically as follows:
1) node voltage constraint, because voltage distribution has locality, for a distributed power supply with a certain total capacity, if access point distribution is more dispersed and uniform, the influence on the lifting of each level of bus voltage is smaller, otherwise, the voltage of the access point is in a certain variation range, and if the distributed power supply is more dispersed and uniform in access, the capacity of the accessible distributed power supply is larger;
2) the method comprises the steps that bus short-circuit current is restricted, when a certain group of buses in a power distribution network are in three-phase short circuit, short-circuit current is provided by a main transformer and all distributed power supplies respectively, and the short-circuit current value is the sum of vectors of the short-circuit current provided by each power supply point and the superposition characteristic of the short-circuit current, so that the capacity of the accessible distributed power supplies in a main transformer power supply area is the same as the capacity of the accessible distributed power supplies of a single-circuit line; the method comprises the steps that the influence of distributed power sources on the maximum power permeability of a main transformer power supply area is considered in a rotating mode and an inversion mode respectively, when various distributed power sources are connected into the main transformer power supply area, the maximum power permeability of the main transformer power supply area is an intermediate value of the maximum power permeability when the access of the rotating distributed power sources is considered independently and the access of the inversion distributed power sources is considered independently, and specific numerical values are determined according to specific parameters and installed capacity proportions of the inversion distributed power sources and the rotating distributed power sources;
3) main transformer capacity constraint, wherein the total capacity of a distributed power supply connected with a main transformer low-voltage side 10kV bus (4) does not exceed the rated capacity of the main transformer, and the maximum power permeability of the main transformer capacity constraint is considered independently at the moment and is 100%; and if the requirement of distribution network scheduling on the operation margin is considered, multiplying the maximum power permeability value of the main transformer capacity constraint by the corresponding margin requirement percentage on the basis of independent consideration.
Further, when node voltage constraint is considered independently, a calculation model of the maximum access capacity of the distributed power supply in the main transformer power supply area is as follows:
SGTmax＝min(ST110,SGTsum) （ 107 ）
in the formula, SGTmaxMaximum capacity, S, accessible to distributed power supplies in the main transformer power supply areaGTsumSum of capacities, S, of distributed power supplies accessible to a main transformer power supply areaT110Is a main transformer capacity, wherein SGTmaxShould be the main transformer capacity ST110And SGTsumMinimum value of (1); pGiFor the active power output of the distributed power supply on node i,QGifor distributed power supply reactive power output, Q, on node ii(V, theta) is node reactive power, Pi(V, theta) is the active power of the node, V is the voltage, and theta is the phase angle vector; viIs the node voltage, VminIs the lower limit of the node voltage, VmaxIs the upper limit of the node voltage; sGmaxThe maximum distributed power capacity average value which can be accessed on each loop line is represented by SLjmax which is the rated transmission capacity of the line, and N is the number of the loop lines; s.t. represents a constraint.
Further, the expression of the maximum power penetration of the medium-voltage distribution line is as follows:
in the above formula SGLFor the maximum capacity, S, of the accessible distributed power supply in the distribution lineLmaxThe maximum transmission capacity of the distribution line;
the main transformer power supply region permeability expression is as follows:
in the above formula SGsumIs the sum of the installed capacity S of the distributed power supply connected to the outgoing line of the main transformer low-voltage side 10kV bus (4)TThe rated capacity of the main transformer is 110kV or 220 kV.
Further, the maximum power permeability of the distributed power supply of the single-circuit distribution line is the maximum power permeability of the standard wiring.
The invention has the following outstanding advantages:
1. the maximum power permeability of a distributed power supply accessed to a power distribution network needs to consider the maximum power permeability of a medium-voltage distribution line and also needs to consider the maximum power permeability of a main transformer power supply area; the maximum power permeability of the medium-voltage distribution line refers to a ratio of the maximum total installed capacity of the distributed power supply in the distribution line to the maximum transmission capacity of the distribution line; the permeability of the power supply area of the main transformer is the ratio of the installed capacity of the distributed power supply of the power supply area of the main transformer to the rated capacity of the main transformer, so that the problems that the constraint of a primary system of a power distribution network and the bearing capacity of primary equipment of the power distribution network after the distributed power supply is accessed are not fully considered in the calculation method of the maximum power permeability of the distributed power supply in the prior art can be solved, the theoretical calculation basis is provided for the distributed power supply to be accessed into the power distribution network, and the outstanding beneficial effects that the distributed power supply is widely and massi.
2. The invention provides a comprehensive calculation method for maximum power permeability of a distributed power supply based on comprehensive consideration of transmission capacity constraint of a distribution line, main transformer capacity constraint, node voltage constraint and bus short-circuit current constraint of the conventional distribution network in China, which analyzes the maximum power permeability level of the distributed power supply which can be accessed in the distribution line and the whole main transformer power supply area of different types of distributed power supplies in different access modes, thereby obtaining the maximum capacity which can be accessed by the distributed power supply in the distribution line and the main transformer power supply area and the access condition requirement of the maximum capacity on the premise of not transforming the distribution primary system, and the comprehensive calculation method has the advantages of providing theoretical calculation basis for accessing the distributed power supply to the distribution network, promoting wide and large-scale access of the distributed power supply to the distribution network and the like.
Drawings
Fig. 1 is a calculation flow chart of a method for calculating maximum power permeability of a medium-voltage distribution line.
Fig. 2 is a simulation model diagram of a distributed power access distribution network, taking a city distribution network as an example.
FIG. 3 is a simulation model diagram of the primary access locations taking into account the effect of the distributed power supply on the node voltage.
FIG. 4 is a simulation model diagram of a 10kV bus when a distributed power supply access point is far away from the low voltage of a transformer substation.
FIG. 5 is a simulation model diagram of a 10kV bus of a distributed power supply access point adjacent to a low voltage of a transformer substation.
FIG. 6 is a schematic diagram of considering node voltage constraints.
Fig. 7 is a schematic diagram of considering bus short circuit current constraints.
FIG. 8 is a graph illustrating the variation trend of the node voltage deviation rate in the simulation example.
Fig. 9 is a bus short-circuit current variation trend chart taking photovoltaic as an example.
Fig. 10 is a trend chart of the change of the bus short-circuit current by taking a synchronous machine as an example.
In the figure: 1-external power grid, 2-110 kV bus, 3-110/10 kV main transformer, 4-main transformer low-voltage side 10kV bus, 5-10 kV cable, 6-user side 10kV bus, 7-load, 8-photovoltaic and 9-synchronous machine.
Detailed Description
The invention is described in further detail below with reference to the following figures and examples:
specific example 1:
the invention discloses a method for calculating the maximum power permeability of a distributed power supply accessed to a power distribution network, which is characterized by comprising the following steps:
1) for the maximum power permeability of a distributed power supply accessed to a power distribution network, in addition to the maximum power permeability of a medium-voltage distribution line, when different distributed power supplies are accessed to a plurality of lines and the lines are all accessed to the same main transformer, the maximum power permeability of a power supply area of the main transformer is also considered; the maximum power permeability of the medium-voltage distribution line refers to a ratio of the maximum total installed capacity of the distributed power supply in the distribution line to the maximum transmission capacity of the distribution line; the permeability of the main transformer power supply area refers to the ratio of the installed capacity of a distributed power supply in the main transformer power supply area to the rated capacity of the main transformer;
2) the method for calculating the maximum power permeability of the medium-voltage distribution line comprehensively considers the current-carrying capacity constraint of the line, the node voltage constraint and the short-circuit current constraint of the bus; the calculation model is as follows:
in the formula, PrlmaxIn order to comprehensively consider the maximum power permeability of the medium-voltage distribution line with various constraints,maximum power penetration of a line, P, to account for line ampacity constraintsrlmax(V)To account for the line maximum power penetration constrained by the node voltage,maximum line power penetration, P, to account for bus short circuit current constraintsrlmaxGetPrlmax(V)Andminimum value of (d); equations (102) - (103) are node active and reactive balance equations, where PGiAnd QGiRespectively representing active and reactive power output, P, of the distributed power supply on the node iDiAnd QDiLoad active and reactive power, Q, respectively, on node ii(V, theta) is node reactive power, Pi(V, theta) are active power of the node, and V and theta respectively represent voltage and phase angle vectors; sLAndthe actual transmission capacity and the rated transmission capacity of the line are respectively; viIs the node voltage, VminIs the lower limit of the node voltage, VmaxIs the upper limit of the node voltage; i isBjAndthe method comprises the following steps of respectively setting an actual short-circuit current value and a rated value of the three-phase short-circuit current of a 10kV bus j on a distribution line; s.t. represents a constraint;
under special conditions, the maximum power permeability of the distributed power supply in the main transformer power supply area meets the voltage constraint of each line node and the bus short-circuit current constraint in the main transformer power supply area, and the main transformer capacity constraint is also considered.
The expression of the maximum power penetration of the medium-voltage distribution line is as follows:
in the above formula SGLFor the maximum capacity, S, of the accessible distributed power supply in the distribution lineLmaxThe maximum transmission capacity of the distribution line; for the standard type wiring in the power distribution network, if the maximum capacity of the distributed power supply which can be accessed to each circuit is the same, the maximum power permeability of the distributed power supply of the single-circuit distribution circuit is the maximum power permeability of the group of standard type wiring.
The main transformer power supply region permeability expression is as follows:
in the above formula SGsumThe sum of installed capacities S of distributed power supplies connected to the outgoing line of a main transformer low-voltage side 10kV bus 4TThe rated capacity of the main transformer is 110kV or 220 kV.
Referring to fig. 1, the calculation model of maximum power permeability of the medium-voltage distribution line is solved by an enumeration method, and the specific steps are as follows:
1) the installed capacity of the distributed power supply is given as the rated transmission capacity of the line, so that the current-carrying capacity of the line is not out of limit;
2) respectively checking whether node voltage and bus short-circuit current meet constraints through load flow calculation and three-phase short-circuit calculation, and if any constraint requirement cannot be met, performing load flow calculation or short-circuit current calculation again after the installed capacity of the distributed power supply is reduced until the requirements of the formula (105) and the formula (106) are met;
3) and respectively considering the maximum power permeability of the three constraint conditions for comparison, and taking a smaller value as the maximum power permeability of the distributed power supply comprehensively considering the multiple constraints.
Referring to fig. 2, the maximum power permeability value of a distributed power supply accessing a typical distribution network composed of a 110kV substation, a 10kV cable and a ring main unit is analyzed and calculated by taking a city distribution network as an example. In the figure, an external power grid 1 is connected to a 110kV bus 2 at the high-voltage side of an 110/10kV main transformer 3, and a 10kV bus 6 at a user side is represented as a 10kV ring main unit bus. According to the main access mode of the distributed power supply, the short-circuit current of each 10kV bus is considered to be the sum of short-circuit current vectors provided by the transformer substation and each distributed power supply, so that the distributed power supply and the load 7 connected to each 10kV cable 5 can be equalized to the 10kV bus 6 on the user side shown in the figure, the access situation of a single distributed power supply can be simulated, the scattered access situation of a plurality of distributed power supplies can be examined, and meanwhile, the access situation of the distributed power supply adjacent to the transformer substation can be simulated and the limit situation when the tail end of the 10kV cable 5 is accessed can be simulated by setting the length of the 10kV cable 5.
The method for calculating the maximum power permeability of the medium-voltage distribution line comprehensively considers the following three constraints:
1) line shutoff volume constraint; because the distributed power supply is connected to the power distribution network and mainly consumed on site, the transmission power of the distributed power supply is firstly provided for the local load 7, so that the occupancy rate of the 10kV cable 5 is reduced, but when the maximum power permeability of the distributed power supply is considered, the condition that the output of the distributed power supply is completely transmitted is considered, namely the local load 7 is 0. Taking local load as 0 as a boundary condition for calculating the maximum power permeability, and independently checking the current-carrying capacity of the line, wherein the maximum value of the permeability of the distribution line is 100%; if the requirement of distribution network scheduling on the operation margin is considered at the same time, multiplying the requirement by the percentage value of the corresponding margin on the basis of independently considering the maximum power permeability of the line current-carrying capacity constraint;
2) node voltage constraints; referring to fig. 3, because medium voltage and low voltage distribution network often are resistive, therefore the reactive power and the active power injected by the distributed power supply can both affect the distribution network voltage, and especially, great effect is generated on the distributed power supply access point, but the capacity of the distributed power supply accessible on the single loop is relatively small, if the distributed power supply access point is adjacent to the main transformer low voltage side 10kV bus 4, then the distributed power supply is equivalent to directly accessing the large system, the distributed power supply will be less obvious in the lifting of the access point voltage, and this phenomenon can also be analyzed by the voltage fluctuation formula:
in the above formula, Δ Q is the incorporated reactive increment, SkFor the short-circuit capacity of the grid-connected point of the distributed power supply, because the short-circuit capacity of the main transformer low-voltage side bus is larger, when the same reactive increment is injected, the distributed power supply connected to the main transformer low-voltage side 10kV bus 4 has smaller influence on the voltage change of the access point, so that the condition that the distributed power supply is far away from the main transformer low-voltage side 10kV bus can be mainly considered when the influence of the distributed power supply on the voltage of the node is considered.
The distributed power supply is mainly consumed on site, the voltage of access points of the distributed power supply is reduced when the local load 7 is put into operation, the voltage of the access points is reduced more when the put local load 7 is larger, and in order to effectively check the maximum power permeability of a medium-voltage distribution line, when the constraint of the node voltage on the permeability of the distributed power supply is considered, the influence of the distributed power supply on the quality of the node voltage is checked by load flow calculation under the conditions that the line shutoff quantity is not out of limit and the local load 7 is 0, so that the permeability index of the distributed power supply under the conditions that the line shutoff quantity is not out of limit and the quality of the node voltage is not over standard is determined.
Under the condition that the line lengths are the same, the influence of reactive injection of the distributed power supplies on the node voltage is mainly considered, so that only the power factors of the distributed power supplies need to be concerned, and the types of the distributed power supplies do not need to be concerned. According to the relevant standard, the power factors of the synchronous machine 9 and the photovoltaic 8 are continuously adjustable within the range of 0.95 (leading) to 0.95 (lagging), and as the higher the power factor is, the less reactive power is emitted by the distributed energy source, and the less obvious the voltage rise of the access point is, the maximum power permeability of the medium-voltage distribution line is, when the constraint of the node voltage on the permeability of the distributed power supply is considered, the power factor when the reactive power is injected at most is taken as a simulation parameter, and the maximum power permeability of the distributed power supply is analyzed.
3) Bus short circuit current constraint; because the length of the 10kV cable 5 is closely related to the short-circuit impedance, the maximum power permeability of the medium-voltage distribution line should consider the following two situations respectively under the condition that the length of the 10kV cable 5 is determined when considering the constraint of the bus short-circuit current on the permeability of the distributed power supply:
the first situation is as follows: referring to fig. 4, a distributed power supply is connected to a user side 10kV bus 6, and the situation when the distributed power supply access point is far away from a main transformer low voltage side 10kV bus 4 is mainly simulated;
case two: referring to fig. 5, when the distributed power supply is directly connected to the main transformer low-voltage side 10kV bus 4, the influence on the short-circuit current of each level of bus is mainly used for simulating the situation when the distributed power supply access point is adjacent to the main transformer low-voltage side 10kV bus 4.
Due to the fact that short-circuit currents generated by different types of distributed power supplies are different, the maximum power permeability of the medium-voltage distribution line is calculated, and when constraint of bus short-circuit currents on the permeability of the distributed power supplies is considered, maximum power permeability values of the inverter type distributed power supplies and the rotary type distributed power supplies far away from the transformer substation and the adjacent transformer substation can be analyzed by taking the photovoltaic 8 and the synchronous machine 9 as examples.
When specific simulation calculation is carried out, the short-circuit current values of all levels of buses when photovoltaic 8 or synchronous machines 9 with different capacities are accessed to a user side 10kV bus 6 and a main transformer low-voltage side 10kV bus 4 are analyzed by taking the transmission capacity of a distribution line as an upper limit; and determining the limitation of the access capacity of the photovoltaic 8 or the synchronous machine 9 by referring to the bus current level specified in the existing medium-voltage distribution network planning technical guidance principle, thereby determining the maximum power permeability value of the distributed power supply.
As is clear from actual tests, the short-circuit current generated by the inverter-type distributed power supply represented by the photovoltaic system 8 is small, and the short-circuit current generated by the rotary-type distributed power supply represented by the synchronous machine 9 is large. When various distributed power supplies are accessed, the maximum power permeability of the medium-voltage distribution line considering short-circuit current constraint is between the maximum power permeability of the distributed power supplies only considering inversion and only considering rotation type access, and the specific numerical value is determined mainly according to the specific parameters and installed capacity proportion of the inversion distributed power supplies and the rotation type distributed power supplies.
When different distributed power supplies are connected into a plurality of lines and the lines are connected into the same main transformer, the maximum power permeability of a power supply area of the main transformer is also considered; the constraint condition that the maximum power permeability of the main transformer power supply area should be considered is further analyzed as follows:
1) node voltage constraint: referring to fig. 6, when the main transformer low voltage has multiple circuits of access, it is assumed that the capacity of the distributed power source accessed at the point a is SGAWhen the voltage amplitude deviation of the point a is just enabled to reach the upper limit of the national standard by the access of the point a, if there is distributed energy on other return lines of the low-voltage side of the main transformer (for example, the point B is accessed to another distributed energy in the figure), the voltage deviation at the point a bus is likely to exceed the standard, and the maximum value of the permeability of the 110kV main transformer power supply area is as follows:
if the distributed power supply capacity respectively connected to the point A and the point B is S'GAAnd S'GBAnd has S'GA＝S'GBIf the voltage amplitudes of the access points all reach the upper limit of the national standard, the more distributed and uniform the access of the distributed power supplies, the sum S 'of the capacities of the distributed power supplies accessed to the points A and B'GA+S'GB＞SGAAt this time, the maximum permeability value of the 110kV main transformer power supply area is as follows:
from the above analysis, P'rt＞PrtAnd by analogy, when the distributed power supply can be uniformly connected to all outgoing lines of the low-voltage side of the main transformer, the obtained permeability of the distributed power supply of the main transformer power supply area is the maximum.
Therefore, when the constraint of the node voltage deviation on the maximum power permeability of the main transformer power supply area is considered, the access point voltage is within a certain variation range, and the more distributed and uniform the distributed power supply access is, the larger the accessible capacity of the distributed power supply is.
2) And (3) bus short circuit current constraint: referring to fig. 7, there are two loops of 10kV outgoing lines on the low-voltage side of the main transformer, and it is assumed that the distributed power supply is accessed in two situations:
the first situation is as follows: only the point a is connected to the distributed power supply (the synchronous machine 9), when the three-phase short circuit occurs on the user side 10kV bus 6, the short circuit current is provided by the main transformer and the synchronous machine 9, and it is assumed that the short circuit current of the user side 10kV bus 6 just reaches the specified limit value in this case.
Case two: on the basis of the first situation, when a distributed power supply (a synchronous machine 9) is connected to a point B, if a three-phase short circuit occurs again on a user side 10kV bus 6, because a power distribution network containing the distributed power supply belongs to an active bidirectional power supply network, when a certain group of buses in the power distribution network have a three-phase short circuit, short-circuit currents are respectively provided by a main transformer and all distributed power supplies, and the short-circuit current value is the sum of vectors of the short-circuit currents provided by all power supply points, the short-circuit current of the user side 10kV bus 6 is provided by the synchronous machine 9-1, the synchronous machine 9-2 and the main transformer, and because of the superposition characteristic of the short-circuit currents, the short-circuit current of the 10kV bus 1 exceeds.
The two situations represent the situation of considering the single-circuit line and the main transformer power supply area respectively, and therefore when the constraint of the bus short-circuit current is considered, the capacity of the distributed power supply which can be accessed by the main transformer power supply area is the same as the capacity of the distributed power supply which can be accessed by the single-circuit line.
The distributed power source connected to the power distribution network shown in fig. 7 is a synchronous machine 9 type, and since the short-circuit currents generated by different types of distributed power sources are different, when analyzing the bus short-circuit current constraint of the main transformer power supply area, the influence of the inverter type distributed power source and the rotary type distributed power source on the permeability of the main transformer power supply area should be considered separately.
When the constraint of bus short-circuit current on the maximum power permeability of a main transformer power supply area is considered, when various distributed power supplies are connected into the main transformer power supply area, the maximum power permeability of the main transformer power supply area is an intermediate value of the maximum power permeability when photovoltaic 8 access and synchronous machine 9 access are considered independently, and the specific numerical value is determined mainly according to specific parameters and installed capacity proportion of an inverter distributed power supply and a rotary distributed power supply.
3) And (3) main transformer capacity constraint: when the local load of the main transformer low-voltage side 10kV cable 5 is 0, the maximum capacity of the distributed power supply which can be accessed to each 10kV cable 5 is the maximum transmission capacity S of the lineLmaxFor a 110kV main transformer, if a low-voltage side 10kV outgoing line has N loops, theoretically, the maximum accessible capacity of a power supply area of the main transformer is;
SGsum＝SLmax×N
at present, the capacity S of a 110kV main transformer in ChinaT110Mainly 40MVA, 50MVA and 63MVA, taking the main transformers of 50MVA and 63MVA as an example, the number of 10kV actual outgoing lines is generally 12-16. Supposing that the number of 10kV outgoing lines on the low-voltage side of a 63MVA main transformer is 12, and the rated current-carrying capacity of a 10kV cable 5 is generally 0.441kA, theoretically, the maximum capacity of a distributed power supply which can be accessed to a power supply area of the main transformer is SGsum91.656MVA, S is visibleGsum＞ST110When all the local loads 7 are 0 and the rated output of the distributed power supply is obtained, the uplink power exceeds the main transformer capacity value, and the calculation result is not allowed.
Therefore, if the main transformer capacity constraint is considered separately, the maximum capacity of the distributed power supply accessible to the main transformer power supply area should be a main transformer rated capacity value, and at this time, the maximum power permeability value of the main transformer power supply area is 100%, and if the requirement of distribution network scheduling on the operation margin is considered, the maximum power permeability value of the main transformer capacity constraint is considered separately and then multiplied by a corresponding margin requirement percentage value, so that the maximum power permeability value of the main transformer capacity constraint is considered separately.
The method for calculating the maximum power permeability of the distributed power supply accessed to the power distribution network is further analyzed by combining a simulation example as follows:
the invention adopts the power simulation software PowerFactory14.0 of the German DIgSILENT company as a simulation calculation tool to carry out the simulation calculation of the maximum power permeability of the distributed power supply aiming at the models shown in figures 2 to 6. In the figure, the 110/10kV main transformer capacity is 63MVA, the high-voltage side voltage is 110kV, the low-voltage side voltage is 10.5kV, the short-circuit impedance is 16%, and the outgoing line number of a main transformer low-voltage side 10kV bus 4 is 16. In order to better analyze the influence of the short-circuit current of the distributed power supply on each 10kV bus, when no distributed power supply is connected, the short-circuit current of the low-voltage side bus 4 of the transformer substation is limited to be 18kA, namely the short-circuit capacity of an external system is 2127.218 MVA. The rated current-carrying capacity of the 10kV cable 5 is 0.441kA, the length of the line is 3km, the alternating current resistance of the line is 0.0795 omega/km, and the reactance is 0.0898 omega/km.
Taking the synchronous machine 9 and the photovoltaic 8 as an example, analyzing the influence of the distributed power supply on the power grid, wherein simulation parameters of the synchronous machine 9 and the photovoltaic 8 are shown in table 1:
TABLE 1
Under the condition that the full output of the distributed energy sources is considered and all the distributed energy sources are sent upwards (the local load 7 is 0), in order to ensure that the current-carrying capacity of the line is not out of limit, the maximum installed capacity of the distributed energy sources connected to each circuit is 7.638MVA of total line transmission capacity; according to the regulation in GB/T12325-2008 power quality supply voltage deviation, the three-phase supply voltage deviation of 20kV and below is +/-7% of the nominal voltage; according to the relevant requirements of national power grids and southern power grids in the technical guidance principle of medium-voltage distribution network planning, the short-circuit current of a 110kV bus 2 is set to be not more than 40kA, and the short-circuit current of 10kV and 20kV buses is set to be not more than 20 kA.
Referring to fig. 8, the installed capacity of the distributed power supply is gradually reduced by taking the rated transmission capacity of the line as an initial value, the voltage deviation rate of a node (a point) is obtained through load flow calculation after each capacity reduction, and the capacity ratio in the graph is the ratio of the capacity of the distributed power supply to the rated transmission capacity of the line; as can be seen from fig. 8, the voltage deviation of the access point meets the standard only when the access capacity of the distributed power source is 70% or less of the rated transmission capacity of the line, so if it is required to ensure that the current-carrying capacity of the line does not exceed the limit and the node voltage deviation meets the national standard, the maximum value of the permeability of the distributed energy source is 70%, and the corresponding maximum access capacity of the distributed energy source is 5.35 MVA.
Referring to fig. 6, if the distributed power supplies are uniformly distributed on the 16 loops of the 110kV main transformer power supply area, through optimization calculation, when the capacity of the distributed energy accessed on each loop is 1.312MVA, the voltage deviation of each level of bus meets the requirement, and at this time, the maximum value of the permeability of the 110kV main transformer power supply area is 33.3%.
Referring to fig. 9, an inverter type distributed power supply represented by a photovoltaic 8 is connected to a power distribution network, a rated transmission capacity of a line is used as an initial value, when the photovoltaic 8 is connected to a 10kV bus 6 on a user side, installed capacity of the photovoltaic 8 is gradually reduced, and a short-circuit current value of each level of bus is obtained through three-phase short-circuit calculation after each capacity reduction.
Referring to fig. 9, when the capacity ratio of the photovoltaic 8 changes from 0 to 1, the short-circuit currents of the buses at all levels do not exceed the standard, and it can be seen that the short-circuit current provided by the inverter-type distributed power supply is small, and the influence of the access of the inverter-type distributed power supply on the short-circuit currents of the buses at all levels is small. If the photovoltaic 8 with different capacities is directly connected to the main transformer low-voltage side 10kV bus 4, simulation shows that the short-circuit current of each level of bus still does not exceed the level specified in the distribution network planning guidance principle, and the maximum permeability values of the photovoltaic 8 connected to the user side 10kV bus 6 and the photovoltaic 8 directly connected to the main transformer low-voltage side 10kV bus 4 are both 100% under the condition that the transmission capacity of a cable line is not out of limit. In addition, simulation calculation also shows that when the installed capacity of the photovoltaic 8 on a single loop does not exceed the rated transmission capacity of the line and the total installed capacity of the photovoltaic 8 on multiple loops does not exceed the main transformer capacity, the short circuit level of each level of bus does not exceed the standard, and the maximum value of the permeability of the photovoltaic 8 in the power supply area of the main transformer is 100% when only the short circuit constraint of each level of bus is considered.
Referring to fig. 10, when a rotary distributed power supply represented by a synchronous machine 9 is connected to a 10kV bus 6 on a user side of a distribution network, it can be known that when the connection capacity of the synchronous machine 9 is 90% or less of the rated transmission capacity of a line, the short-circuit current of each bus does not exceed the short-circuit level specified by the distribution network planning guidance principle; when the synchronous machine 9 is directly connected to the main transformer low-voltage side 10kV bus, the short-circuit current of each bus does not exceed the short-circuit level specified in the distribution network planning guidance principle only when the connection capacity of the synchronous machine 9 is 81% or less of the rated capacity of the line, and the main reason is that the short-circuit impedance is reduced by directly connecting to the main transformer low-voltage side bus, and the short-circuit current injected into the bus is increased.
The maximum capacity of the distributed power supply which can be accessed in the main transformer power supply area is basically the same as the maximum capacity of the distributed power supply which can be accessed in a single-circuit line. In order to ensure a certain margin, the maximum capacity of the distributed power supply when the distributed power supply is directly connected to a low-voltage side bus of a transformer substation can be taken as the maximum access capacity of the synchronous machine 9 in a main transformer power supply area, so that the maximum permeability of the corresponding synchronous machine 9 in a 110kV main transformer power supply area is 9.82%.
Through the simulation, maximum values of permeability of the distribution line are obtained by considering the current-carrying capacity constraint of the line, the node voltage quality constraint and the bus short-circuit current constraint, and when the maximum values of permeability of the distribution line with various constraints are comprehensively considered, the maximum values of permeability of the distribution line should be the minimum value of the two maximum values of permeability. Due to the fact thatPrlmax(V)＝70％，The values of (A) are as follows: 100% when only the photovoltaic 8 is accessed; when the synchronous machine 9 is connected to the 10kV bus 6 at the user side, the voltage is 90 percent; when the synchronous machine 9 is connected to the main transformer low-voltage side 10kV bus 4, the connection rate is 81 percent. Thus, it is known that Prlmax70%, that is, when the permeability of the distributed power supply on the line is 70% or less, the current-carrying capacity of the line, the node voltage quality and the constraint of the bus short-circuit current can all meet the requirements.
According to the permeability definition of the main transformer power supply area and the simulation analysis, obtaining the maximum permeability index value respectively considering the node voltage quality constraint and the bus short-circuit current constraint, wherein if the maximum permeability of the main transformer power supply area comprehensively considering various constraints is PrtmaxAnd the maximum power permeability of a main transformer power supply area considering node voltage constraint is Prtmax(V)The maximum power permeability of a main transformer power supply area considering the constraint of bus short circuit current isThen P isrtmaxShould get Prtmax(V)Andthe smaller of these. PrtmaxThe values of (A) are as follows: (1) when only the photovoltaic cells 8 are accessed by multiple loops, Prtmax(V)The content of the active carbon is 33.3 percent,is 100%, then Prtmax33.3 percent; (2) when only the synchronizer 9 is accessed through multiple loops, Prtmax(V)The content of the active carbon is 33.3 percent,9.82%%, then Prtmax9.82%; (3) when various distributed power supplies are accessed through multiple loops, the maximum value of the permeability of the main transformer power supply area is between the maximum value of the permeability when only the photovoltaic 8 is accessed and the maximum value of the permeability when only the synchronous machine 9 is accessed, namely, P is more than or equal to 9.82 percentrtmax≤33.3％。
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the embodiments, and those skilled in the art can make equivalent substitutions and changes within the scope of the present invention without departing from the spirit or the inventive concept.
Claims (7)
1. The method for calculating the maximum power permeability of the distributed power supply connected to the power distribution network is characterized by comprising the following steps:
1) for the maximum power permeability of a distributed power supply accessed to a power distribution network, in addition to considering the maximum power permeability of medium-voltage distribution lines, when different distributed power supplies are accessed to a plurality of lines and the lines are all accessed to the same main transformer, the maximum power permeability of a power supply area of the main transformer is also considered; the maximum power permeability of the medium-voltage distribution line refers to a ratio of the maximum total installed capacity of the distributed power supply in the distribution line to the maximum transmission capacity of the distribution line; the permeability of the main transformer power supply area refers to the ratio of the installed capacity of a distributed power supply in the main transformer power supply area to the rated capacity of the main transformer;
2) the method for calculating the maximum power permeability of the medium-voltage distribution line comprehensively considers the current-carrying capacity constraint of the line, the node voltage constraint and the short-circuit current constraint of the bus; the calculation model is as follows:
in the formula, PrlmaxIn order to comprehensively consider the maximum power permeability of the medium-voltage distribution line with various constraints,maximum power penetration of a line, P, to account for line ampacity constraintsrlmax(V)To account for the line maximum power penetration constrained by the node voltage,maximum line power penetration, P, to account for bus short circuit current constraintsrlmaxGetPrlmax(V)Andminimum value of (d); equations (102) - (103) are node active and reactive balance equations, where PGiAnd QGiRespectively representing active and reactive power output, P, of the distributed power supply on the node iDiAnd QDiLoad active and reactive power on node i respectivelyRate, Qi(V, theta) is node reactive power, Pi(V, theta) are active power of the node, and V and theta respectively represent voltage and phase angle vectors; sLAndthe actual transmission capacity and the rated transmission capacity of the line are respectively; viIs the node voltage, VminIs the lower limit of the node voltage, VmaxIs the upper limit of the node voltage; i isBjAndthe method comprises the following steps of respectively setting an actual short-circuit current value and a rated value of the three-phase short-circuit current of a 10kV bus j on a distribution line; s.t. represents a constraint.
2. The method for calculating the maximum power penetration rate of the distributed power supply accessed to the power distribution network according to claim 1, wherein the method comprises the following steps: the calculation model of the maximum power permeability of the medium-voltage distribution line is solved by an enumeration method, and the calculation method comprises the following specific steps:
1) the installed capacity of the distributed power supply is given as the rated transmission capacity of the line, so that the current-carrying capacity of the line is not out of limit;
2) respectively checking whether node voltage and bus short-circuit current meet constraints through load flow calculation and three-phase short-circuit calculation, and if any constraint requirement cannot be met, performing load flow calculation and three-phase short-circuit calculation again after the installed capacity of the distributed power supply is reduced until the requirements of the formula (105) and the formula (106) are met;
3) and respectively considering the maximum power permeability of the constraint conditions for comparison, and taking a smaller value as the maximum power permeability of the distributed power supply comprehensively considering the multiple constraints.
3. The method for calculating the maximum power penetration rate of the distributed power supply accessed to the power distribution network according to claim 1, wherein the method comprises the following steps: the constraint considered by the medium-voltage distribution line maximum power permeability calculation method is specifically as follows:
1) the current-carrying capacity of the line is constrained, the local load is 0 and is used as a boundary condition for calculating the maximum power permeability, and if the current-carrying capacity of the line is only examined independently, the maximum value of the permeability of the distribution line is 100 percent; if the requirement of distribution network scheduling on the operation margin is considered at the same time, multiplying the requirement by the percentage value of the corresponding margin on the basis of independently considering the maximum power permeability of the line current-carrying capacity constraint;
2) node voltage constraint, mainly considering the condition that a distributed power supply is far away from a main transformer low-voltage side 10kV bus, and under the conditions that the circuit current-carrying capacity is not out of limit and the local load is 0, checking the influence of the distributed power supply on the node voltage quality by load flow calculation to determine the permeability index of the distributed power supply on the premise that the circuit current-carrying capacity is not out of limit and the node voltage quality is not out of limit; under the condition that the line lengths are the same, the influence of reactive injection of the distributed power supply on the node voltage is mainly considered, the power factor when the reactive injection is the most is taken as a simulation parameter, and the maximum power permeability of the distributed power supply is analyzed;
3) bus short-circuit current constraint, taking the transmission capacity of a distribution line as the upper limit, analyzing the short-circuit current values of all levels of buses when the inversion type distributed power supply or the rotary type distributed power supply with different capacities is accessed to a user side 10kV bus and a main transformer low-voltage side 10kV bus (4), determining the access capacity limit of the corresponding inversion type distributed power supply or rotary type distributed power supply according to the bus current level specified in the prior medium-voltage distribution network planning technical guidance principle, when the distributed power supply accessed in the power distribution network simultaneously comprises a rotating type and an inversion type, the maximum power permeability considering the constraint of the short-circuit current of the bus is positioned between the maximum power permeability values of the distributed power supply which is only considered for the inversion type and the rotating type, and the specific numerical value is determined according to the specific parameters and the installed capacity proportion of the inversion type distributed power supply and the rotating type distributed power supply.
4. The method for calculating the maximum power penetration rate of the distributed power supply accessed to the power distribution network according to claim 1, wherein the method comprises the following steps: the constraint considered by the calculation method of the maximum power permeability of the power supply area of the main transformer is specifically as follows:
1) node voltage constraint, because voltage distribution has locality, for a distributed power supply with a certain total capacity, if access point distribution is more dispersed and uniform, the influence on the lifting of each level of bus voltage is smaller, otherwise, the voltage of the access point is in a certain variation range, and if the distributed power supply is more dispersed and uniform in access, the capacity of the accessible distributed power supply is larger;
2) the method comprises the steps that bus short-circuit current is restricted, when a certain group of buses in a power distribution network are in three-phase short circuit, short-circuit current is provided by a main transformer and all distributed power supplies respectively, and the short-circuit current value is the sum of vectors of the short-circuit current provided by each power supply point and the superposition characteristic of the short-circuit current, so that the capacity of the accessible distributed power supplies in a main transformer power supply area is the same as the capacity of the accessible distributed power supplies of a single-circuit line; the method comprises the steps that the influence of distributed power sources on the maximum power permeability of a main transformer power supply area is considered in a rotating mode and an inversion mode respectively, when various distributed power sources are connected into the main transformer power supply area, the maximum power permeability of the main transformer power supply area is an intermediate value of the maximum power permeability when the access of the rotating distributed power sources is considered independently and the access of the inversion distributed power sources is considered independently, and specific numerical values are determined according to specific parameters and installed capacity proportions of the inversion distributed power sources and the rotating distributed power sources;
3) main transformer capacity constraint, wherein the total capacity of a distributed power supply connected with a main transformer low-voltage side 10kV bus (4) does not exceed the rated capacity of the main transformer, and the maximum power permeability of the main transformer capacity constraint is considered independently at the moment and is 100%; and if the requirement of distribution network scheduling on the operation margin is considered, multiplying the maximum power permeability value of the main transformer capacity constraint by the corresponding margin requirement percentage on the basis of independent consideration.
5. The method for calculating the maximum power penetration rate of the distributed power supply accessed to the power distribution network according to claim 4, wherein the method comprises the following steps: when node voltage constraint is considered independently, a calculation model of the maximum access capacity of the distributed power supply in the main transformer power supply area is as follows:
SGTmax＝min(ST110,SGTsum) （ 107 ）
in the formula, SGTmaxMaximum capacity, S, accessible to distributed power supplies in the main transformer power supply areaGTsumSum of capacities, S, of distributed power supplies accessible to a main transformer power supply areaT110Is a main transformer capacity, wherein SGTmaxShould be the main transformer capacity ST110And SGTsumMinimum value of (1); pGiFor distributed power supply active power output, Q, on node iGiFor distributed power supply reactive power output, Q, on node ii(V, theta) is node reactive power, Pi(V, theta) is the active power of the node, V is the voltage, and theta is the phase angle vector; viIs the node voltage, VminIs the lower limit of the node voltage, VmaxIs the upper limit of the node voltage; sGmaxThe maximum distributed power capacity average value which can be accessed on each loop line is represented by SLjmax which is the rated transmission capacity of the line, and N is the number of the loop lines; s.t. represents a constraint.
6. The method for calculating the maximum power penetration rate of the distributed power supply accessed to the power distribution network according to claim 1, wherein the method comprises the following steps:
the expression of the maximum power penetration of the medium-voltage distribution line is as follows:
in the above formula SGLFor the maximum capacity, S, of the accessible distributed power supply in the distribution lineLmaxThe maximum transmission capacity of the distribution line;
the main transformer power supply region permeability expression is as follows:
in the above formula SGsumThe sum of installed capacities S of distributed power supplies connected to the outgoing line of a main transformer low-voltage side 10kV busTIs 110kVOr the rated capacity of a 220kV main transformer.
7. The method for calculating the maximum power penetration rate of the distributed power supply accessed to the power distribution network according to claim 6, wherein the method comprises the following steps: and the maximum power permeability of the distributed power supply of the single-circuit distribution line is the maximum power permeability of the standard wiring.
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