CN112698101A - Low-voltage transformer area line impedance measurement system and method based on node current injection mode - Google Patents
Low-voltage transformer area line impedance measurement system and method based on node current injection mode Download PDFInfo
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Abstract
The invention discloses a low-voltage transformer area line impedance measuring system and method based on a node current injection mode, wherein the system comprises a main end module and a slave end module, the main end module is positioned on the wire inlet side of a low-voltage transformer area, and the slave end module is positioned at each node position of a transformer area line; the slave end module comprises a node current sending unit, a voltage acquisition unit and an impedance calculation unit; the node current sending unit is used for sending a node pulse current signal; the voltage acquisition unit is used for acquiring voltage signals of all nodes; the impedance calculation unit is used for obtaining line impedance data information through the voltage signal; and the master end module is used for receiving the impedance data information of each line, describing a line impedance diagram of the whole low-voltage transformer area according to the topological position of each slave end module in the network, and acquiring all line impedance measured values of the low-voltage transformer area. The invention has the advantages of simple measuring process, accurate measurement, high measuring speed and the like.
Description
Technical Field
The invention mainly relates to the technical field of impedance measurement of a power distribution network distribution area line of an electric power low-voltage distribution network, in particular to a low-voltage distribution area line impedance measurement method based on a node injection current mode.
Background
The low-voltage distribution network is used as the tail end of a power grid, is directly oriented to the market, serves the foremost end of customers, and has the characteristics of large size, wide distribution, complex power supply environment, diversified demands and the like.
The 0.4kV power supply network is the last kilometer of power supply, the power consumption quality is directly influenced, the diversity of the access load, the time-varying property and the complexity of a wiring structure in the 0.4kV power supply network bring great difficulty to rapid rush repair of faults of power personnel, and meanwhile, the great influence is caused to the marketing big data acquisition communication.
Because the problems of line aging and wiring disorder exist, hidden troubles are buried for safe and reliable operation of the line. The change of the impedance can reflect whether the line has faults such as short circuit, open circuit and the like. The impedance of the power supply loop is researched, the loop impedance abnormal event is generated in time, the defects of line aging and the like can be found as early as possible, the power failure fault is prevented in time, and the power supply reliability is improved.
In order to further improve the service level of 'taking customers as the center', fault positioning and research and judgment are carried out in a targeted manner on the first-aid repair force, and large data acquisition and application are deepened. Therefore, under the multiple requirements of safety alarms such as 0.4kV power supply network line fault study and judgment, aging early warning analysis, line contact looseness, electrical fire and the like, power failure fault can be prevented in time, power supply reliability is improved, and research on line impedance measurement and corresponding application technology under the 0.4kV power supply network is very important.
At present, there are two main methods for measuring and calculating the line impedance of the low-voltage transformer area:
1. the non-interference method is a mode of establishing a topological model of the whole power distribution network, sampling the voltage and the current of the transformer node and each tail end node at the same time by using a node method, taking multiple values at multiple points and multiple moments, introducing mean square error calculation, and converting the problem into an optimization problem (the multiple values are substituted to obtain a solution meeting the optimal condition) for solving the minimum value. However, this method is complicated, requires a large amount of calculation, and requires the head and tail voltage and current values at the same time to be grasped.
2. The interference method is that a node is established, a harmonic current method is injected into the node by a device, current harmonic waves are injected into a line for multiple times, then the whole low-voltage distribution network model is simplified, only a system power supply, a system impedance, a line impedance and a harmonic source exist in the line, then a plurality of equations are listed by the Thevenin theorem, the system power supply and the system impedance are reduced by adding the equations, and the line impedance is represented by the voltage and the current generated by the multiple times of harmonic power supplies.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the problems in the prior art, the invention provides the low-voltage transformer area line impedance measuring method based on the node injection current mode, which has the advantages of simple process, accurate measurement and high measuring speed.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a low-voltage transformer area line impedance measurement system based on a node current injection mode comprises a main end module and a slave end module, wherein the main end module is positioned on the wire inlet side of a low-voltage transformer area, and the slave end module is positioned at each node position of a transformer area line; the slave end module comprises a node current sending unit, a voltage acquisition unit and an impedance calculation unit;
the node current sending unit is used for actively sending a node pulse current signal, the pulse current signal follows the flow direction of a single-network-level venation structure, the pulse current signal flows from a sending end of the node pulse current signal to a transformer wire outlet end, and a correspondingly flowing line is a line with impedance to be measured;
the voltage acquisition unit is used for acquiring voltage signals of all nodes;
the impedance calculation unit is used for obtaining line impedance data information through the voltage signal;
and the master end module is used for receiving the impedance data information of each line, describing a line impedance diagram of the whole low-voltage transformer area according to the topological position of each slave end module in the network, and acquiring impedance measurement values of all lines in the low-voltage transformer area.
As a further improvement of the above technical solution:
and the master end module and the slave end module are communicated in a 485 or carrier mode.
The invention also discloses a measuring method of the low-voltage transformer area line impedance measuring system based on the node injection current mode, which comprises the following steps:
1) the node current sending unit actively sends a node pulse current signal, the pulse current signal follows the flow direction of a single-network-level venation structure, the pulse current signal flows from a sending end of the node pulse current signal to a transformer wire outlet end, and a correspondingly flowing line is a line with impedance to be measured;
2) the voltage acquisition unit acquires voltage signals of all nodes;
3) the impedance calculation unit obtains line impedance data information through the voltage signal;
4) and the master end module receives the impedance data information of each line, describes a line impedance diagram of the whole low-voltage distribution area according to the topological position of each slave end module in the network, and acquires all line impedance measured values of the low-voltage distribution area.
As a further improvement of the above technical solution:
in the step 4), the specific process is as follows:
listing the impedance relationship equivalent circuit of the slave end module in the platform area, the following equation is obtained:
Ug(s)＝Iline×(Zg+Zline)+Ua(s) (1)
Iline(s)＝Iload(s)+Ivsc(s) (2)
the following can be deduced from (1) and (2):
converting the (4) into a time domain state equation, and then simultaneously solving:
in the formula (5), ZgThe constant value can be obtained by the voltage percentage of the short-circuit impedance of the transformer, the rated power and the rated voltage:
wherein U isg(s) -nominal voltage of the transformer (voltage source) at time s; i isline(s) -measuring the current on the branch at time s; zg-the internal resistance of the transformer (voltage source); zline-measuring the impedance on the branch; u shapea(s) -the voltage at node a at time s; i isload(s) -s current flowing through the load branch at time; i isvscPulsed injection current at time(s) -s; u shapeg(1) -nominal voltage of the transformer (voltage source) at time 1; u shapeg(2) Time 2, the rated voltage of the transformer (voltage source); u shapea(1) -the voltage of node a at time 1; u shapea(2) -the voltage of node a at time 2; i isload(1) -time instant 1, the current flowing through the load branch; i isload(2) -time 2, the current flowing through the load branch; i isvsc(1) -time 1, pulsed injection current; i isvsc(2) Time instant 2, pulsed injection current;
wherein U isg(S) as a constant voltage source, invariant in the time domain S; u shapea(S) the values in the time domain S can be measured directly by the slave module; i isvsc(S) is a pulsed current signal injected from the slave end module, the values in the time domain S being directly measurable by the slave end module; i isload(S) is the value of the load in the time domain S, which cannot be measured directly;
in the very short range of the time domain S, the load cannot be suddenly changed, and the load current cannot be suddenly changed, so that the load current can be regarded as Iload(1)＝Iload(2) Then, equation (5) can be simplified to:
the line impedance Z can be determinedline。
The line impedance is obtained by carrying out value calculation for multiple times in a preset time when the load current is relatively unchanged.
Before step 1), dividing the whole low-voltage transformer area circuit into 4 layers, namely a 4-layer structure of 'variable-line-table-household'; wherein the transformer is arranged at the part from the line side to the line side, and the part comprises equipment with a main end module; the part from the back of the 'line' of the transformer main outgoing line switch to the branch box sequentially comprises the outgoing line switch, the branch circuit, the branch switch and the incoming line circuit of the branch box, and the layer can be subdivided into one layer or two layers according to the existence of the outgoing line switch; the meter, namely the part from the branch box to the line of the user load meter box, comprises the user load meter box and a meter box outlet line; the 'household' is the household incoming line, the household electric meter and the household switch of each household; through the four-layer division, the line topological structure of a low-voltage distribution station area is completely displayed so as to divide line impedance measuring points and determine measured values.
Compared with the prior art, the invention has the advantages that:
the method comprises the steps of sending pulse current signals from each node through a node current sending unit, obtaining voltage signals of each node through a voltage collecting unit, obtaining line impedance data information through an impedance calculating unit, describing a line impedance diagram of the whole low-voltage transformer area through a main end module according to the line impedance data information and the topological position of each slave end module in a network, and obtaining all line impedance measured values of the low-voltage transformer area; the whole process is simple, other interferences can be eliminated, and the method has the characteristics of accurate measurement, quick output result, less occupied resources and the like.
Drawings
FIG. 1 is an equivalent circuit diagram of a measurement system of the present invention in a particular application;
fig. 2 is a diagram of the arrangement of the measuring system of the invention in the low-pressure area.
FIG. 3 is a flow chart of the measurement method of the present invention in a specific application.
Detailed Description
The invention is further described below with reference to the figures and the specific embodiments of the description.
As shown in fig. 1 and fig. 2, the impedance measuring system for a low-voltage transformer area line based on a node injection current mode in this embodiment includes a master end module and a slave end module, wherein the master end module is located at a line incoming side of the low-voltage transformer area, and the slave end module is located at each node position of the transformer area line; the slave end module comprises a node current sending unit, a voltage acquisition unit and an impedance calculation unit; the node current sending unit is used for actively sending a node pulse current signal, the pulse current signal follows the flow direction of a single-network-level venation structure, the pulse current signal flows from a sending end of the node pulse current signal to a transformer wire outlet end, and a correspondingly flowing line is a line with impedance to be measured; the voltage acquisition unit is used for acquiring voltage signals of all nodes; the impedance calculation unit is used for obtaining line impedance data information through the voltage signal; and the master end module is used for receiving the impedance data information of each line, describing a line impedance diagram of the whole low-voltage transformer area according to the topological position of each slave end module in the network, and acquiring all line impedance measured values of the low-voltage transformer area.
The method comprises the steps of sending pulse current signals from each node through a node current sending unit, obtaining voltage signals of each node through a voltage collecting unit, obtaining line impedance data information through an impedance calculating unit, describing a line impedance diagram of the whole low-voltage transformer area through a main end module according to the line impedance data information and the topological position of each slave end module in a network, and obtaining all line impedance measured values of the low-voltage transformer area; the whole process is simple, other interferences can be eliminated, and the method has the characteristics of accurate calculation, quick output result, less occupied resources and the like.
In one embodiment, the system divides the entire low-voltage distribution transformer area line into 4 layers, namely a 4-layer structure of 'transformer-line-table-user'. The transformer is arranged at the line side of the transformer, and the part of the transformer from the line side to the line comprises equipment with main end equipment; the part from the back of the 'line', namely a main outgoing line switch of the transformer, to the branch box comprises the outgoing line switch, a branch line, the branch switch and the incoming line circuit of the branch box, and the layer can be subdivided into one layer or two layers according to the existence of the outgoing line switch; the meter, namely the part from the branch box to the line of the user load meter box, comprises the user load meter box and a meter box outlet line; the 'household' is the service entrance line, the service electricity meter and the service switch of each household. Through the 4-layer division, the line topological structure of a low-voltage distribution station area can be completely displayed, and the division of line impedance measuring points and the determination of measured values are facilitated. As shown in fig. 2.
In a specific embodiment, the master module and the slave module are provided with communication units, and the master module and the slave module communicate with each other in a 485 or carrier mode.
As shown in fig. 3, the present invention also discloses a method for measuring the line impedance of the low voltage transformer area based on the node injection current mode, which comprises the following steps:
1) the node current sending unit actively sends a node pulse current signal, the pulse current signal follows the flow direction of a single-network-level venation structure, the pulse current signal flows from a sending end of the node pulse current signal to a transformer wire outlet end, and a correspondingly flowing line is a line with impedance to be measured;
2) the voltage acquisition unit acquires voltage signals of all nodes;
3) the impedance calculation unit obtains line impedance data information through the voltage signal;
4) the master end module receives impedance data information of each line, describes a line impedance diagram of the whole low-voltage distribution area according to the topological position of each slave end module in the network, and obtains impedance measured values of all lines in the low-voltage distribution area.
In a specific embodiment, the specific process of step 4) is:
listing the impedance relationship equivalent circuit of the slave end module in the platform area, the following equation is obtained:
Ug(s)＝Iline×(Zg+Zline)+Ua(s) (1)
Iline(s)＝Iload(s)+Ivsc(s) (2)
the following can be deduced from (1) and (2):
converting the (4) into a time domain state equation, and then simultaneously solving:
in the formula (5), ZgThe constant value can be obtained by the voltage percentage of the short-circuit impedance of the transformer, the rated power and the rated voltage:
Ug(s) -nominal voltage of the transformer (voltage source) at time s; i isline(s) -measuring the current on the branch at time s; zg-the internal resistance of the transformer (voltage source); zline-measuring the impedance on the branch; u shapea(s) -the voltage at node a at time s; i isload(s) -s current flowing through the load branch at time; i isvscPulsed injection current at time(s) -s; u shapeg(1) -nominal voltage of the transformer (voltage source) at time 1; u shapeg(2) Time 2, the rated voltage of the transformer (voltage source); u shapea(1) -the voltage of node a at time 1; u shapea(2) -the voltage of node a at time 2; i isload(1) -time instant 1, the current flowing through the load branch; i isload(2) -time 2, the current flowing through the load branch; i isvsc(1) -time 1, pulsed injection current; i isvsc(2) Time instant 2, pulsed injection current;
wherein U isg(S) as a constant voltage source, invariant in the time domain S; u shapea(S) the values in the time domain S can be measured directly by the slave module; i isvsc(S) is a pulsed current signal injected from the slave end module, the values in the time domain S being directly measurable by the slave end module; i isload(S) is the value of the load in the time domain S, which cannot be measured directly;
if the load cannot be suddenly changed and the load current cannot be suddenly changed even in a very short range of the time domain S, it can be considered as Iload(1)＝Iload(2) Then, equation (5) can be simplifiedThe composition is as follows:
the line impedance Z can be determinedline(ii) a Wherein the line impedance is obtained by carrying out value calculation for a plurality of times within a preset time when the load current is relatively unchanged.
In a specific embodiment, before step 1), the whole low-voltage distribution area line is divided into 4 layers, namely a 4-layer structure of 'change-line-table-user'; wherein the transformer is arranged at the part from the line side to the line side, and the part comprises equipment with a main end module; the part from the back of the 'line' of the transformer main outgoing line switch to the branch box sequentially comprises the outgoing line switch, the branch circuit, the branch switch and the incoming line circuit of the branch box, and the layer can be subdivided into one layer or two layers according to the existence of the outgoing line switch; the meter, namely the part from the branch box to the line of the user load meter box, comprises the user load meter box and a meter box outlet line; the 'household' is the household incoming line, the household electric meter and the household switch of each household; through the four-layer division, the line topological structure of a low-voltage distribution station area is completely displayed so as to divide line impedance measuring points and determine measured values.
The above invention is described in its entirety with reference to a complete embodiment:
the realization principle of the measuring system is as follows: the node pulse current injection type signal line impedance technology is adopted, namely a set of measuring system of main end line impedance data receiving equipment (namely a main end module) and slave end node current transmitting, voltage collecting and impedance calculating equipment (namely a slave end module) is constructed, the slave end module is positioned at each node position (branch or tail end) of a line of a distribution room, the main end module is positioned at the incoming line side (initial end) of a low-voltage distribution room, and the slave end module is provided with a node current transmitting unit, a voltage collecting unit, an impedance calculating unit and a data transmitting unit; the main end module is provided with a data receiving unit. The node current sending unit actively sends a node pulse current signal, the pulse current signal follows the flow direction of a single-network-level venation structure, the pulse current signal flows from a sending end (slave end equipment) of the pulse current to a transformer wire outlet end, and a line passing through the middle is a line to be measured in impedance. The slave end module obtains line impedance data information through measurement sampling and data analysis and calculation, and then sends the line impedance data information to the master end module through carrier wave signals; the low-voltage distribution area system is in a tree network state, and by analogy, all the slave end modules can calculate the line impedance data between the slave end modules and the master end module and sequentially send the line impedance data to the master end module, and the master end module can describe the line impedance diagram of the whole low-voltage distribution area according to the topological positions of all the slave end modules in the network, so that the aim of obtaining all the line impedance measured values of the low-voltage distribution area is fulfilled. As shown in fig. 1.
Before the test system is realized, the circuit layered architecture of the low-voltage transformer area is designed as follows: the system divides the whole low-voltage distribution transformer area line into 4 layers, namely a 4-layer structure of 'transformer-line-table-household'. The transformer is arranged at the line side of the transformer, and the part of the transformer from the line side to the line comprises equipment with main end equipment; the part from the back of the 'line', namely a main outgoing line switch of the transformer, to the branch box comprises the outgoing line switch, a branch line, the branch switch and the incoming line circuit of the branch box, and the layer can be subdivided into one layer or two layers according to the existence of the outgoing line switch; the meter, namely the part from the branch box to the line of the user load meter box, comprises the user load meter box and a meter box outlet line; the 'household' is the service entrance line, the service electricity meter and the service switch of each household. Through the 4-layer division, the line topological structure of a low-voltage distribution station area can be completely displayed, and the division of line impedance measuring points and the determination of measured values are facilitated. As shown in fig. 2.
Specifically, in conjunction with fig. 1 and 2, the following configuration may be made in one particular project implementation; firstly, dividing the whole low-voltage distribution transformer area into 4 layers, namely a 4-layer structure of 'transformer-line-meter-house', each layer is provided with a corresponding line, and if the lines from a meter box to a house are very close and are temporarily ignored, the lines can be divided into 3 layers, such as L1, L1.A.1, L1.A.1.1 and the like, as shown in FIG. 2;
the first layer "L1" represents the line between the transformer low voltage outgoing line side and the first-level branch device, and the outgoing line side of this layer of transformer is attached with 1 main terminal for receiving the line impedance measurement data sent by all the slave devices in the whole transformer area after analysis and calculation, and analyzing and calculating the line layered impedance data of the whole transformer area, and finally automatically generating a transformer area line impedance relation diagram, as shown in fig. 2;
the middle layer 'L1. A.1', namely the line from the outlet side of the first-stage branch box to the inlet line of the second-stage branch box, the second-stage branch box is branched, so that the middle layer can be classified into different lines such as 'L1. A.1' and 'L1. A.2', and the like, as shown in FIG. 2;
a section of line from a meter box layer meter, namely a secondary branch box outgoing line to a slave end device (namely a meter box monitoring terminal) is denoted by 'l 1. a.1.1', and 1 meter box monitoring terminal, namely a slave end device, is attached to the incoming line side of each meter box and is used for sending a pulse current signal of a node of the meter box, as shown in fig. 2;
the last floor "house" is the switch from the outgoing line of each house of the meter box to the load of the user entering the house, each house is 1 end node, because the distance from the meter box to the house is very close, the impedance of the circuit at this section is negligible, as shown in fig. 2;
after the equipment assignment of the whole platform area is completed, a pulse current signal is sent from bottom to top, for example; the method is characterized in that a meter box monitoring terminal in a meter box, which is a slave end device belonging to the tail end of a line 'L1. A.1.1', sends a pulse current address signal, and because only 1 current source (transformer) exists in a low-voltage distribution area, the flowing direction of a current signal is unidirectional, namely the current signal reaches the transformer from bottom to top, therefore, lines on the same layer but different nodes are pulse current signals which cannot flow through other nodes on the same layer, namely the pulse current signals only alternate along the lines 'L1. A.1.1', 'L1. A.1', 'L1. A' and 'L1', and finally reach a line outlet end of a corresponding transformer. Therefore, the line impedance calculated by the endmost slave device of "l 1. a.1.1" is the route of the line impedance. By analogy, the single line impedance calculated by the tail-end slave device at different positions can be determined, and the suffix name of each stage is the same, so that the lines from the stage to the head end are overlapped, and the line impedance of each stage is analyzed step by step.
Specifically, as shown in fig. 2, from bottom to top, the slave end module with the meter box terminal at the rearmost end is used for injecting a pulse current signal into the tail end line, and meanwhile, the calculated impedance information of the line can be sent to the master end module through 485 or carrier waves; the main end module is the highest layer of the whole low-voltage distribution transformer area, receives impedance line measured values sent by all the slave end modules, collects all impedance measured value information, adds topological address information of the whole area, analyzes the common line segment and the branch line segment, and finally generates a complete line impedance calculation graph of the area and uploads the complete line impedance calculation graph to the main station. As shown in fig. 2.
When measurement is carried out, the node current sending unit actively sends a node pulse current signal, the pulse current signal follows the flow direction of a single-network-level venation structure, the pulse current signal flows from a sending end of the node pulse current signal to a wire outlet end of the transformer, and a correspondingly flowing line is a line with impedance to be measured;
the voltage acquisition unit acquires voltage signals of all nodes;
the impedance calculation unit obtains line impedance data information through the voltage signal;
the master end module receives impedance data information of each line, describes a line impedance diagram of the whole low-voltage distribution area according to the topological position of each slave end module in the network, and obtains impedance measured values of all lines in the low-voltage distribution area.
Specifically, the specific calculation process of the line impedance measurement is shown in fig. 3:
from fig. 1, the following equation can be derived;
Ug(s)＝Iline×(Zg+Zline)+Ua(s) (1)
Iline(s)＝Iload(s)+Ivsc(s) (2)
can be derived from (1) and (2);
converting the (4) into a time domain state equation, and then performing simultaneous solution;
(5) in the formula, ZgThe method is a fixed value, and can be obtained by the voltage percentage of the short-circuit impedance of the transformer (marked by a transformer nameplate), the rated power and the rated voltage:
Ug(s) -nominal voltage of the transformer (voltage source) at time s; i isline(s) -measuring the current on the branch at time s; zg-the internal resistance of the transformer (voltage source); zline-measuring the impedance on the branch; u shapea(s) -the voltage at node a at time s; i isload(s) -s current flowing through the load branch at time; i isvscPulsed injection current at time(s) -s; u shapeg(1) -nominal voltage of the transformer (voltage source) at time 1; u shapeg(2) Time 2, the rated voltage of the transformer (voltage source); u shapea(1) -the voltage of node a at time 1; u shapea(2) -the voltage of node a at time 2; i isload(1) -time instant 1, the current flowing through the load branch; i isload(2) -time 2, the current flowing through the load branch; i isvsc(1) -time 1, pulsed injection current; i isvsc(2) Time instant 2, pulsed injection current;
Ug(S) can be seen as a constant voltage source, constant in the time domain S, in the specific example, UgAnd(s) outputting a power supply for the transformer side system, namely a voltage value measured by the main-end equipment. In the case of a certain period of very small load, such as early morning hours, and a very short instance calculation time, such as within 5 seconds, the system power supply can be approximately treated as constant. U shapea(S) in the example, the voltage value of the position where the slave end equipment is located, namely the voltage value monitored by the meter box monitoring terminal, the value in the time domain S can be directly measured by the meter box monitoring terminal,assuming that S is 5 seconds, Ivsc(s) is the pulse current from the end module, the values in 5 seconds are all measured directly from the end module, Iload(s) is a value of the load within 5 seconds, and cannot be directly measured by the slave device. However, the following design can be made, in the case that the load cannot change suddenly and the load current cannot change suddenly under the condition that the specific load is in a very small time period, such as early morning and the example calculation time is only 5 seconds which is very short, I can be regarded asload(1)＝Iload(2) Then, equation (5) can be simplified to:
at the initial time of 5 seconds, the meter box monitoring device sends out pulse current Ivsc(1) While monitoring and recording the voltage Ua(1) (ii) a At the end time of 5 seconds, the meter box monitoring device sends out pulse current Ivsc(2) While monitoring and recording the voltage Ua(2) (ii) a The transformer-power supply parameters in the local transformer area are investigated in advance, and Z is calculatedgThen, according to the formula (7), Z can be obtainedlineThe practical limitation condition is that the value calculation must be performed several times in a very short time when the load current is relatively constant.
Assuming that the initial time of 5 seconds is time S1, the end time of 5 seconds is time S2, and the transformer is 800kVA, the u% is 6.18 u-400S obtained by the name plate of the transformere800000, Z is obtained from equation (6)g0.01236, the meter box monitoring device sends out pulse current I at S1vsc(1) When U is measured at 13Aa(1) 223V; s2 moment meter box monitoring device sends out pulse current Ivsc(1) When U is measured at 10Aa(1) When 224V is obtained, Z can be obtained from equation (7)line0.3209, the results were in agreement with theory according to multisim12 simulation analysis.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.
Claims (6)
1.A low-voltage transformer area line impedance measurement system based on a node current injection mode is characterized by comprising a main end module and a slave end module, wherein the main end module is positioned on the wire inlet side of a low-voltage transformer area, and the slave end module is positioned at each node position of a transformer area line; the slave end module comprises a node current sending unit, a voltage acquisition unit and an impedance calculation unit; the node current sending unit is used for actively sending a node pulse current signal, the pulse current signal follows the flow direction of a single-network-level venation structure, the pulse current signal flows from a sending end of the node pulse current signal to a transformer wire outlet end, and a correspondingly flowing line is a line with impedance to be measured; the voltage acquisition unit is used for acquiring voltage signals of all nodes; the impedance calculation unit is used for obtaining line impedance data information through the voltage signal; and the master end module is used for receiving the impedance data information of each line, describing a line impedance diagram of the whole low-voltage transformer area according to the topological position of each slave end module in the network, and acquiring impedance measurement values of all lines in the low-voltage transformer area.
2. The system of claim 1, wherein the master module and the slave module communicate with each other via 485 or carrier.
3. A method for measuring the impedance of the line in the low-voltage transformer area based on the node injection current mode as claimed in claim 1 or 2, comprising the steps of:
1) the node current sending unit actively sends a node pulse current signal, the pulse current signal follows the flow direction of a single-network-level venation structure, the pulse current signal flows from a sending end of the node pulse current signal to a transformer wire outlet end, and a correspondingly flowing line is a line with impedance to be measured;
2) the voltage acquisition unit acquires voltage signals of all nodes;
3) the impedance calculation unit obtains line impedance data information through the voltage signal;
4) and the master end module receives the impedance data information of each line, describes a line impedance diagram of the whole low-voltage distribution area according to the topological position of each slave end module in the network, and acquires all line impedance measured values of the low-voltage distribution area.
4. The measurement method according to claim 3, wherein in step 4), the specific process is as follows:
listing the impedance relationship equivalent circuit of the slave end module in the platform area, the following equation is obtained:
Ug(s)＝Iline(s)×(Zg+Zline)+Ua(s) (1)
Iline(s)＝Iload(s)+Ivsc(s) (2)
the following can be deduced from (1) and (2):
converting the (4) into a time domain state equation, and then simultaneously solving:
in the formula (5), ZgThe constant value can be obtained by the voltage percentage of the short-circuit impedance of the transformer, the rated power and the rated voltage:
wherein U isg(s) -nominal voltage of the transformer (voltage source) at time s; i isline(s) -measuring the current on the branch at time s; zg-the internal resistance of the transformer (voltage source); zline-measuring the impedance on the branch; u shapea(s) -the voltage at node a at time s; i isload(s) -s current flowing through the load branch at time; i isvscPulsed injection current at time(s) -s; u shapeg(1) -nominal voltage of the transformer (voltage source) at time 1; u shapeg(2) Time 2, the rated voltage of the transformer (voltage source); u shapea(1) -the voltage of node a at time 1; u shapea(2) -the voltage of node a at time 2; i isload(1) -time instant 1, the current flowing through the load branch; i isload(2) -time 2, the current flowing through the load branch; i isvsc(1) -time 1, pulsed injection current; i isvsc(2) Time instant 2, pulsed injection current;
wherein U isg(S) as a constant voltage source, invariant in the time domain S; u shapea(S) the values in the time domain S can be measured directly by the slave module; i isvsc(S) is a pulsed current signal injected from the slave end module, the values in the time domain S being directly measurable by the slave end module; i isload(S) is the value of the load in the time domain S, which cannot be measured directly;
in the very short range of the time domain S, the load cannot be suddenly changed, and the load current cannot be suddenly changed, so that the load current can be regarded as Iload(1)＝Iload(2) Then, equation (5) can be simplified to:
the line impedance Z can be determinedline。
5. A method as claimed in claim 4, in which the line impedance is calculated over a predetermined period of time in which the load current is relatively constant.
6. The measurement method according to claim 4, characterized in that, before step 1), the whole low-voltage platform area line is divided into 4 layers, namely a 'variable-line-table-user' 4-layer structure; wherein the transformer is arranged at the part from the line side to the line side, and the part comprises equipment with a main end module; the part from the back of the 'line' of the transformer main outgoing line switch to the branch box sequentially comprises the outgoing line switch, the branch circuit, the branch switch and the incoming line circuit of the branch box, and the layer can be subdivided into one layer or two layers according to the existence of the outgoing line switch; the meter, namely the part from the branch box to the line of the user load meter box, comprises the user load meter box and a meter box outlet line; the 'household' is the household incoming line, the household electric meter and the household switch of each household; through the four-layer division, the line topological structure of a low-voltage distribution station area is completely displayed so as to divide line impedance measuring points and determine measured values.
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