CN111130109B - Yyn0 low-voltage power distribution network theoretical line loss calculation method and system - Google Patents
Yyn0 low-voltage power distribution network theoretical line loss calculation method and system Download PDFInfo
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- CN111130109B CN111130109B CN202010085898.2A CN202010085898A CN111130109B CN 111130109 B CN111130109 B CN 111130109B CN 202010085898 A CN202010085898 A CN 202010085898A CN 111130109 B CN111130109 B CN 111130109B
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Abstract
A theoretical line loss calculation method and system of Yyn0 low-voltage distribution network, the method includes collecting voltage, current and active electric quantity data of an outlet of the low-voltage distribution network, preprocessing the collected data, and calculating a Yyn0 distribution transformer zero sequence impedance value through the preprocessed data; establishing a three-phase equivalent resistance equation set, and solving the three-phase equivalent resistance of each acquisition point; calculating theoretical loss power of each acquisition point and total power of the low-voltage distribution network; and calculating the theoretical line loss rate of the low-voltage distribution network in a specific statistical period according to the actual statistical period. According to the method, the influence of zero sequence impedance is required to be considered in calculating the three-phase equivalent resistance of the Yyn0 low-voltage distribution network. According to the method and the system for calculating the theoretical line loss of the Yyn0 low-voltage distribution network, provided by the invention, the existing electrical acquisition device of the electric energy meter in the transformer area is fully utilized, no new hardware is needed, and the calculation of the theoretical line loss of the Yyn0 low-voltage distribution network is realized through computer executable program codes.
Description
Technical Field
The invention relates to a theoretical line loss calculation method and system for a Yyn0 low-voltage power distribution network, and belongs to the technical field of power distribution and utilization.
Background
The low-voltage distribution network directly faces customers, loads are high in randomness and unbalance, the high-loss low-voltage lines of the low-voltage distribution network directly influence the power supply quality and the voltage quality of users, and the method has important significance on how to quickly and accurately find out the real high-loss low-voltage lines and scientifically and accurately taking loss reduction measures for power supply enterprises.
At present, the theoretical line loss calculation method of the low-voltage distribution network mainly comprises a voltage loss method, a bamboo joint method, an equivalent resistance method and a station area loss rate method. However, in the conventional low-voltage distribution network theoretical line loss calculation method, the topology relation of the low-voltage distribution network, line parameters and data acquired at the user side are considered, in practical situations, the grid of the low-voltage distribution network is complex, and complete and accurate line parameters and load data are lacked, so that the deviation between the calculation result and the actual value of the conventional low-voltage distribution network theoretical line loss calculation method is larger.
Disclosure of Invention
The invention aims to realize theoretical line loss calculation of a Yyn0 low-voltage power distribution network by only collecting three-phase voltage, current, active and reactive electric quantity at the outlet side of a transformer area under the condition of not considering topological relation of the low-voltage power distribution network, line parameters of the low-voltage power distribution network and electric data at the user side.
According to the technical scheme, the theoretical line loss calculation method of the Yyn0 low-voltage distribution network comprises the steps of collecting voltage, current and active electric quantity data of an outlet of the low-voltage distribution network, preprocessing the collected data, and calculating a Yyn0 distribution transformer zero-sequence impedance value through the preprocessed data; establishing a three-phase equivalent resistance equation set, and solving the three-phase equivalent resistance of each acquisition point; calculating theoretical loss power of each acquisition point and total power of the low-voltage distribution network; and calculating the theoretical line loss rate of the low-voltage distribution network in a specific statistical period according to the actual statistical period.
The zero sequence impedance calculation method comprises the following steps:
(1) Subtracting the minimum value from the maximum value of the three-phase current of each acquisition point at the outlet of the platform region to obtain the current difference delta i of the acquisition point t ：
Δi t ＝(max(i at ,i bt ,i ct )-min(i at ,i bt ,i ct ))×CT
Wherein: i.e at 、i bt 、i ct A, b and c three phases at t moment respectively pass through current mutual inductanceThe secondary outlet current value after the conversion is converted by the converter, and CT is the electrorheological ratio;
(2) Subtracting the minimum value from the maximum value of the three-phase voltage at each acquisition point of the distribution transformer to obtain the voltage difference delta u at the acquisition point t ：
Δu t ＝max(u at ,u bt ,u ct )-min(u at ,u bt ,u ct )
Wherein u is at 、u bt 、u ct The three-phase outlet voltage values of a, b and c are respectively the t;
(3) The unitary linear equation is adopted for the difference delta i of the passing current t After formula processing, a current difference sequence delta i and a voltage difference sequence delta u are formed for fitting, and the fitting formula is as follows:
y＝a 0 +a 1 x
wherein: x and y are independent variable and dependent variable respectively, a 0 、a 1 Fitting parameters respectively;
giving a current difference sequence delta i and a voltage difference sequence delta u to obtain an error function:
to minimize the error function, the following condition is satisfied:
obtaining fitting parameters a according to the above 0 、a 1 The method comprises the steps of carrying out a first treatment on the surface of the Zero sequence impedance R 0 I.e. equal to a 0 。
The equivalent resistance is solved as follows:
establishing an equivalent resistance formula for calculating theoretical line loss according to the preprocessed outlet three-phase voltage and current data, wherein the influence of zero sequence impedance is required to be considered in calculating the three-phase equivalent resistance of the Yyn0 low-voltage distribution network; the set of equations for calculating the equivalent resistance is as follows:
wherein: i at 、I bt 、I ct The output current values at the moment t of the three phases are A, B, C respectively; u (U) at 、U at 、U at The output voltage values of the three phases t are A, B, C respectively; r is R at 、R at 、R at The equivalent resistance values are A, B, C three-phase t time points and are used for calculating theoretical line loss values; r is R 0 Is zero sequence impedance;
the equation set of the equivalent resistance has a solution, and the formula
Calculating an equivalent resistance value for calculating the theoretical line loss value at the moment t; when the above equation is equal to zero, the equation set of equivalent resistance is not solved, and the theoretical line loss is not calculated and deleted at the moment.
The utility model provides a Yyn0 low voltage distribution network theory line loss calculation system, includes electric energy meter collection device and computer equipment, the computer equipment includes memory, treater and stores on the memory and can the computer program of running on the treater, its characterized in that, the treater is when carrying out the procedure realizes following steps:
(1) Preprocessing three-phase voltage, current and active electric quantity data acquired at the power supply outlet side of the Yyn0 low-voltage distribution network;
(2) Judging a power supply wiring mode according to the three-phase current sequence of the Yyn0 low-voltage power distribution network;
(3) Judging the connection group of the distribution transformer according to the three-phase voltage sequence of the Yyn0 low-voltage distribution network;
(4) Calculating the zero sequence impedance of the Yyn0 distribution transformer;
(5) Establishing an equivalent resistance formula for calculating theoretical line loss according to the preprocessed outlet three-phase voltage and current data, and calculating the three-phase equivalent resistance of the Yyn0 low-voltage power distribution network;
(6) And calculating the theoretical line loss and the theoretical line loss rate of the Yyn0 low-voltage power distribution network.
Compared with the conventional equivalent resistance method, the equivalent resistance calculation formula provided by the invention has the beneficial effects that the topological relation, the circuit parameters and the user side electrical data of the low-voltage distribution circuit are not required to be considered, so that the practical requirements are met; different from the Dyn11 low-voltage power distribution network, the method for calculating the three-phase equivalent resistance of the Yyn0 low-voltage power distribution network needs to consider the influence of zero-sequence impedance, and improves the accuracy of the three-phase equivalent resistance calculation result.
According to the method and the system for calculating the theoretical line loss of the Yyn0 low-voltage distribution network, provided by the invention, the existing electrical acquisition device of the electric energy meter in the transformer area is fully utilized, no new hardware is needed, and the calculation of the theoretical line loss of the Yyn0 low-voltage distribution network is realized through computer executable program codes. The Yyn0 low-voltage distribution network theoretical line loss calculation method and system are applicable to the conditions of three-phase load unbalance and three-phase load balance
Drawings
Fig. 1 is a flow chart of a theoretical line loss calculation method of a Yyn0 low-voltage power distribution network;
fig. 2 shows a star connection of the current transformer.
Detailed Description
An embodiment of the present invention is shown in fig. 1.
The Yyn0 low-voltage power distribution network in the embodiment refers to a 0.4kV low-voltage power distribution network with Yyn0 power supply distribution transformer connection group.
The theoretical line loss calculation method of the Yyn0 low-voltage power distribution network comprises the following steps:
(1) Data acquisition
The embodiment utilizes the low-voltage distribution network gateway electric energy meter device to collect three-phase voltage and current values at the outlet side of the low-voltage distribution network, the sampling interval is generally 15 minutes or 30 minutes, a voltage transformer is not additionally arranged on the voltage, the electric energy meter directly collects the three-phase voltage values at the outlet, conversion is not carried out through the voltage transformer, the current transformer adopts a star connection method, the electric energy meter collects current secondary values after three-phase current conversion, and the standard wiring of the current transformer is shown in figure 2.
(2) Data preprocessing
Aligning the acquired outlet three-phase voltage and current data sequences according to time, and deleting all acquired values at a certain acquisition time if at least one item has an abnormal value (the current value is more than 1000A or the voltage value is more than 480A is judged to be the abnormal value); if a missing value exists at a certain acquisition time, the missing value is set to be 0.
(3) Power supply wiring mode determination
Judging a power supply wiring mode according to the three-phase current sequence, judging two-phase power supply of the power supply mode if only one phase current is constant at 0A, judging two-phase power supply of the power supply mode if two-phase currents are constant at 0A, and judging that a station area is not put into operation if three-phase currents are constant at 0A; if the three-phase current is not constant at 0A, the three-phase power supply is judged.
(4) Link group determination
Judging the connection group of the distribution transformer according to the three-phase voltage sequence, taking 48 or 96 collection points A phase and B phase, B phase and C phase, and the minimum value of the correlation coefficient of the three voltage sequences of the A phase and the C phase, setting a correlation coefficient threshold value (default value 0.9), judging the connection group to be Dyn11 when the correlation coefficient threshold value is larger than the threshold value, and judging the connection group to be Yyn0 when the correlation coefficient threshold value is smaller than the threshold value, wherein the correlation coefficient threshold value is shown in the formula (1):
wherein: u (u) a 、u b 、u c For a three-phase voltage sequence of a certain day of the outlet voltage of the low-voltage distribution network, corr (x, y) represents calculating correlation coefficients of two sequences, min () is a minimum function, and a calculation formula of the correlation coefficients is shown as a formula (2):
wherein: x is x i ，y i For which the point voltage values are taken at the moment i of the two phases,
mean value of x sequence, +.>
The average value of y sequences, n being the sequence length.
In the embodiment, theoretical line loss calculation is performed on the low-voltage power distribution network with the connection group judged to be Yyn0, and the theoretical line loss calculation of the Dyn11 low-voltage power distribution network is not involved.
(5) Zero sequence impedance determination
Different from the Dyn11 distribution transformer, the Yyn0 distribution transformer has a larger influence on the outlet voltage, and the zero-sequence impedance is required to be considered in the step (6) of calculating the three-phase equivalent resistance, and the zero-sequence impedance calculation processing steps are as follows:
1) Subtracting the minimum value from the maximum value of the three-phase current of each acquisition point at the outlet of the platform region to obtain the current difference delta i of the acquisition point t ：
Δi t ＝(max(i at ,i bt ,i ct )-min(i at ,i bt ,i ct ))×CT (3)
Wherein: i.e at 、i bt 、i ct And the three phases a, b and c at the moment t are respectively converted into secondary outlet current values by a current transformer, and CT is the current ratio.
2) Subtracting the minimum value from the maximum value of the three-phase voltage at each acquisition point of the distribution transformer to obtain the voltage difference delta u at the acquisition point t ：
Δu t ＝max(u at ,u bt ,u ct )-min(u at ,u bt ,u ct ) (4)
Wherein: u (u) at 、u bt 、u ct The three-phase outlet voltage values of a, b and c are respectively the t.
3) Fitting the current difference sequence delta i and the voltage difference sequence delta u which are processed by the formula (3) by adopting a unitary linear equation, wherein the fitting formula is shown as the formula (5):
y＝a 0 +a 1 x (5)
wherein: x and y are independent variable and dependent variable respectively, a 0 、a 1 Parameters were fitted separately.
Given the current difference sequence Δi and the voltage difference sequence Δu, an error function is derived according to equation (6):
to minimize the error function, the condition of equation (7) is satisfied:
wherein:
A T is the transposed matrix of a.
Obtaining fitting parameters a according to a formula (7) 0 、a 1 Zero sequence impedance R 0 I.e. equal to a 0 。
(6) Calculating equivalent resistance
According to the preprocessed outlet three-phase voltage and current data, an equivalent resistance formula for calculating theoretical line loss is established, and different from a Dyn11 low-voltage distribution network, the influence of zero sequence impedance is considered in calculating the three-phase equivalent resistance of the Yyn0 low-voltage distribution network, and an equation set is shown as a formula (8):
wherein: i at 、I bt 、I ct Respectively A, B, C three-phase outlet current values at t time, U at 、U at 、U at Respectively A, B, C three-phase t-moment outlet voltage value, R at 、R at 、R at Equivalent resistance values for calculating theoretical line loss values at A, B, C three-phase t moments respectively, R 0 Zero sequence impedance calculated for equation (7).
If the formula (9) is not equal to 0, the equation set formula (8) has a solution, an equivalent resistance value for calculating a theoretical line loss value at the time t is calculated, and if the formula (9) is equal to 0, the equation set formula (8) has no solution, and the theoretical line loss is not calculated and deleted at the time.
(7) Theoretical line loss calculation
Three-phase equivalent resistance value R calculated according to each acquisition point at 、R at 、R at And the three-phase outlet current and the outlet voltage value, the theoretical line loss value P at the acquisition time can be calculated xst And low voltage distribution network output power P t As shown in the formula (10) and the formula (11):
P xst ＝U at I at +U bt I bt +U ct I ct (11)
further, the theoretical line loss rate P corresponding to the statistical period can be obtained xst % as shown in formula (12):
wherein: p (P) xst Calculating a theoretical line loss value at the moment t and P for the formula (10) t And obtaining the outlet power of the low-voltage distribution network at the moment t for the acquisition device, wherein n is the number of sequential acquisitions.
And n is optionally taken, so that the theoretical line loss value and the theoretical line loss rate of the low-voltage power distribution network in different statistical periods can be obtained.
(8) Example verification
In order to verify the effectiveness of the theoretical line loss calculation method of the Yyn0 low-voltage distribution network in this embodiment, theoretical line loss calculation of a medium-voltage distribution line 2019 of a certain company in Jiangxi is taken as an example, and the calculation results are shown in table 1.
The actual theoretical line loss rate is calculated based on the accurate topological relation, line parameters and distribution transformer parameters, and as can be seen from table 1, the maximum deviation between the theoretical line loss rate calculated in this embodiment and the actual theoretical line loss rate is not more than +/-10%, so as to meet the practical engineering requirements.
Table 1 comparison table of theoretical line loss and actual theoretical line loss calculated in this example
According to the method for calculating the theoretical line loss of the Yyn0 low-voltage power distribution network, existing electrical acquisition devices of the electric energy meter in the transformer area are fully utilized, new hardware is not needed, and the calculation of the theoretical line loss of the Yyn0 low-voltage power distribution network is realized through executable program codes of computer equipment.
Claims (3)
1. A theoretical line loss calculation method of a Yyn0 low-voltage distribution network comprises the steps of collecting three-phase voltage and current values at an outlet of the low-voltage distribution network, and preprocessing the collected data, and is characterized in that the zero-sequence impedance value of the Yyn0 distribution transformer is calculated through the preprocessed data; establishing a three-phase equivalent resistance equation set, and solving the three-phase equivalent resistance of each acquisition point; calculating theoretical loss power of each acquisition point and total power of the low-voltage distribution network; calculating the theoretical line loss rate of the low-voltage distribution network in a specific statistical period according to the actual statistical period;
the zero sequence impedance calculation method comprises the following steps:
(1) Subtracting the minimum value from the maximum value of the three-phase current of each acquisition point at the outlet of the platform region to obtain the current difference delta i of the acquisition point t ：
Δi t ＝(max(i at ,i bt ,i ct )-min(i at ,i bt ,i ct ))×CT
Wherein: i.e at 、i bt 、i ct A, b and c three phases at the moment t are respectively converted into two phases by a current transformerSecondary outlet current value, CT is electrorheological ratio;
(2) Subtracting the minimum value from the maximum value of the three-phase voltage at each acquisition point of the distribution transformer to obtain the voltage difference delta u at the acquisition point t ：
Δu t ＝max(u at ,u bt ,u ct )-min(u at ,u bt ,u ct )
Wherein u is at 、u bt 、u ct The three-phase outlet voltage values of a, b and c are respectively the t;
(3) Fitting the current difference sequence delta i and the voltage difference sequence delta u by adopting a unitary linear equation, wherein the fitting formula is as follows:
y＝a 0 +a 1 x
wherein: x and y are independent variable and dependent variable respectively, a 0 、a 1 Fitting parameters are respectively adopted;
giving a current difference sequence delta i and a voltage difference sequence delta u to obtain an error function:
wherein n represents the number of acquisition points;
to minimize the error function, the following condition is satisfied:
obtaining fitting parameters a according to the above 0 、a 1 The method comprises the steps of carrying out a first treatment on the surface of the Zero sequence impedance R 0 I.e. equalAt a 0 。
2. The method for calculating theoretical line loss of a Yyn0 low-voltage power distribution network according to claim 1, wherein the equivalent resistance is solved as follows:
considering the influence of neutral point offset caused by three-phase imbalance of the zero-sequence impedance of the Yyn0 distribution transformer, establishing an equivalent resistance formula for calculating theoretical line loss according to the preprocessed outlet three-phase voltage and current data, and calculating the influence of the zero-sequence impedance of the three-phase equivalent resistance of the Yyn0 low-voltage distribution network; the set of equations for calculating the equivalent resistance is as follows:
wherein: i at 、I bt 、I ct The output current values at the moment t of the three phases are A, B, C respectively; u (U) at 、U at 、U at The output voltage values of the three phases t are A, B, C respectively; r is R at 、R at 、R at The equivalent resistance values are A, B, C three-phase t time points and are used for calculating theoretical line loss values; r is R 0 Is zero sequence impedance;
the equation set of the equivalent resistance has a solution, and the formula
Calculating an equivalent resistance value for calculating the theoretical line loss value at the moment t; when the above equation is equal to zero, the equation set of equivalent resistance is not solved, and the theoretical line loss is not calculated and deleted at the moment.
3. A system for implementing the Yyn0 low-voltage distribution network theoretical line loss calculation method according to any one of claims 1-2, comprising an electric energy meter acquisition device and a computer device, the computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the processor implements the following steps when executing the program:
(1) Preprocessing three-phase voltage, current and active electric quantity data acquired at the power supply outlet side of the Yyn0 low-voltage distribution network;
(2) Judging a power supply wiring mode according to the three-phase current sequence of the Yyn0 low-voltage power distribution network;
(3) Judging the connection group of the distribution transformer according to the three-phase voltage sequence of the Yyn0 low-voltage distribution network;
(4) Solving zero sequence impedance of the distribution transformer;
(5) Establishing an equivalent resistance formula for calculating theoretical line loss according to the preprocessed outlet three-phase voltage and current data, and solving a three-phase equivalent resistance equation set;
(6) Calculating theoretical line loss power of the Yyn0 low-voltage power distribution network;
(7) According to actual needs, the theoretical line loss rate of each acquisition point in the sun and moon can be calculated, and the theoretical line loss rate under different statistical periods is calculated.
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