CN113178889B - Security check calculation method for active power distribution network grounding device - Google Patents
Security check calculation method for active power distribution network grounding device Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
- H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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Abstract
The invention relates to a safety check calculation method of an active power distribution network grounding device, which comprises the following steps: acquiring a functional relation diagram of the withstand current of the grounding wire and the protection action time of the circuit switch under the grounding wires with different sectional areas; calculating the maximum short-circuit current of the working point; selecting a grounding wire sectional area meeting the condition from the functional relation graph according to the switch protection action time of the line where the working point is located; calculating single-phase residual voltage and three-phase residual voltage of the working point, and if the single-phase residual voltage and the three-phase residual voltage are lower than the safety voltage of a human body, checking the sectional area of the selected grounding wire through safety; otherwise, the sectional area of the grounding wire is selected again. Based on the current situation of the active power distribution network, the invention provides a checking method of the grounding device, and maintenance personnel can flexibly adjust safety grounding protection measures such as using measures of the grounding wire according to checking conditions of the grounding wire.
Description
Technical Field
The invention relates to a safety check calculation method of an active power distribution network grounding device, and belongs to the field of electric automation.
Background
The distribution network is an intermediate bridge connecting a large power grid with power users, and the reliable and economic operation of the distribution network has an important influence on the stability of the whole power system. The active power distribution network refers to a power distribution network with a large amount of access to distributed power sources and power flowing bidirectionally, and is also called an active power distribution network. At present, a passive power distribution network gradually transits to an active power distribution network, and the grid structure of the power distribution network is changed continuously. And the active power distribution network is subjected to power outage maintenance regularly. Before overhauling, an maintainer needs to additionally install a grounding device on one side of a working point (namely an overhauling point) so as to ensure the safety of the maintainer. The grounding device is a generic term for a ground electrode buried under the ground and a connecting wire from the ground electrode to the equipment, and includes a ground wire, a wire clip, and the like.
However, the existing checking method of the grounding device is not adjusted along with the change of the grid structure of the power distribution network, and the withstand current of the grounding wire is checked according to the principle of no fusing by only using an Audi's formula, so that the sectional area of the grounding wire is selected. The problems of short circuit capacity increase, residual voltage at the working point, bidirectional tide and the like of the power grid are not considered, and certain potential safety hazards exist. Therefore, a method for checking and calculating a grounding device suitable for an active power distribution network is needed.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a safety check calculation method of an active power distribution network grounding device, and provides a checking method of the grounding device based on the current situation of the active power distribution network, so that maintenance personnel can flexibly find the optimal and safest grounding protection measures according to the method.
The technical scheme of the invention is as follows:
a security check calculation method of an active power distribution network grounding device comprises the following steps:
s1, acquiring parameters and a topological structure of an active power distribution network;
s2, calculating to obtain a functional relation between the withstand current of the grounding wire and the protection action time of the circuit switch for the grounding wires with different sectional areas based on an Audi dak formula;
s3, calculating the maximum short-circuit current of the working point according to the topological structure of the active power distribution network;
s4, selecting a grounding wire sectional area meeting the condition according to the switch protection action time of the line where the working point is located by utilizing the functional relation; the condition is that the ground wire withstand current is greater than the maximum short circuit current;
s5, calculating single-phase residual voltage and three-phase residual voltage of the working point according to the parameters and the sectional area of the grounding wire; if the single-phase residual voltage and the three-phase residual voltage are lower than the human body safety voltage, the selected sectional area of the grounding wire passes through safety check; otherwise, the step S4 is skipped, and the sectional area of the grounding wire is selected again.
Further, according to the safety check result of the sectional area of the grounding wire, the using measure of the grounding wire is determined.
Further, the Audi-dak formula is:
wherein S is the sectional area of the grounding wire; i k A withstand current for the ground line; t is the switch protection action time of the line; c is the thermal stability coefficient of the ground wire material.
Further, the step S3 specifically includes:
calculating three-phase short-circuit current provided by each distributed power supply to a working point in an active power distribution network;
calculating three-phase short-circuit current provided by a large power grid connected with an active power distribution network to a working point;
if the grounding wire is positioned at the upstream of each distributed power supply, taking the sum of three-phase short-circuit currents provided by each distributed power supply to the working point and the maximum value of the three-phase short-circuit currents provided by the large power grid to the working point as the maximum short-circuit current of the working point; if the grounding wire is positioned at the downstream of each distributed power supply, taking the sum of three-phase short-circuit currents provided by each distributed power supply to the working point and the superposition value of the three-phase short-circuit currents provided by the large power grid to the working point as the maximum short-circuit current of the working point.
Further, the calculation formula of the three-phase residual voltage in the step S5 is as follows:
U res3 ＝kU G +I DG (R x +R t )
in U G A power supply voltage for the large power grid; k is a partial pressure coefficient, k is less than 1; i DG A sum of three-phase short-circuit currents provided to the operating points for each distributed power supply; r is R x A cable resistor is short-circuited for a grounding wire; r is R t Is the contact resistance of the wire clip.
Further, the calculation formula of the single-phase residual voltage in the step S5 is as follows:
wherein I is k Representing a single-phase ground current of the ground wire; ρ is the resistivity of the soil; z is Z g The grounding resistor is a grounding wire; x is the distance between the operating point and the ground line.
The invention has the following beneficial effects:
1. according to the invention, the bidirectional tide in the active power distribution network is considered, the maximum value of the three-phase short-circuit current which can be provided for the working point by the upstream and downstream of the working point is selected as the maximum short-circuit current, the reliability of the grounding wire can be effectively ensured, and the safety of maintenance personnel is further ensured.
2. When the sectional area of the grounding wire is checked, the single-phase residual voltage and the three-phase residual voltage of the working point are considered, and the safety of maintenance personnel is effectively ensured.
3. The invention provides a specific calculation method of maximum short-circuit current and residual voltage of working points in an active medium-voltage distribution network and an active low-voltage distribution network, which provides data support for checking grounding devices, ensures that reasonable, reliable and safe grounding devices can be selected and used quickly in actual active distribution network operation and maintenance, and further protects personal safety of maintenance personnel.
4. Based on the current situation of the active power distribution network (bidirectional tide, residual voltage exists at the working point), the invention provides a checking method of the grounding device, and maintenance personnel can flexibly find the optimal and safest grounding protection measures according to the method.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a flow chart of an embodiment;
FIG. 3 is a graph of the withstand current of the ground line as a function of the line switch protection action time for different cross-sectional areas;
fig. 4 is a schematic diagram of the topology of an active medium voltage distribution network;
fig. 5 is a schematic diagram of the topology of an active low voltage distribution network.
Detailed Description
The invention will now be described in detail with reference to the drawings and to specific embodiments.
Example 1
As shown in fig. 1, a security check calculation method for an active power distribution network grounding device includes the following steps:
s1, acquiring a topological structure and parameters of an active power distribution network.
S2, based on an Audi-dak formula, calculating to obtain a functional relation between the withstand current of the grounding wire and the protection action time of the line switch under different sectional areas, and obtaining a functional relation diagram (shown in figure 3). The protection action time of the line switch is a fixed value, and the protection action time of the switch of different lines in the power distribution network is different.
S3, calculating the maximum short-circuit current of the working point according to the topological structure of the active power distribution network;
s4, selecting a cross section area as small as possible from the functional relation diagram according to the switch protection action time of the line where the working point is located under the condition that the withstand current of the grounding wire is larger than the maximum short-circuit current (namely, the principle of no fusing).
S5, calculating single-phase residual voltage and three-phase residual voltage of the working point according to the parameters and the sectional area of the grounding wire, and if the single-phase residual voltage and the three-phase residual voltage are lower than the safety voltage of a human body, checking the sectional area of the selected grounding wire safely; otherwise, the step S4 is skipped, and a larger grounding wire sectional area is selected again until the maximum value of the grounding wire sectional area is selected.
S6, determining the using measure of the grounding wire according to the checking result of the sectional area.
The formulas for calculating the single-phase residual voltage and the three-phase residual voltage show that the single-phase residual voltage and the three-phase residual voltage are respectively increased along with the increase of the short-circuit cable resistance and the wire clamp contact resistance of the grounding wire. The short-circuit cable resistance and the wire clamp contact resistance are reduced along with the increase of the sectional area of the grounding wire, and the sectional area is 16mm according to the DL-T879-2004 technology in the power industry 2 ，25mm 2 ，35mm 2 ，50mm 2 ，70mm 2 ，95mm 2 ，120mm 2 The average resistance value per meter should be less than 1.24mΩ,0.79mΩ,0.56mΩ,0.40mΩ,0.28mΩ,0.21mΩ,0.16mΩ, respectively. Therefore, a large enough cross-sectional area is required to be selected to ensure that the single-phase residual voltage and the three-phase residual voltage are lower than the safe voltage of the human body.
In individual cases (e.g. overhauling at the outlet end of the distribution transformer), even if the sectional area of the selected ground wire reaches the maximum value (e.g. 120 mm) under its construction specification 2 ) The cross-sectional area still cannot pass the safety check. The maintenance personnel can use the grounding wire in parallel or in a plurality of ways such as connecting multiple grounding wiresMeasures are taken to ensure safety.
Based on the current situation of the active power distribution network, the invention provides a checking method of the grounding device, and a maintainer can flexibly find the optimal and safest grounding protection measures (namely the sectional area of the grounding wire and the using measure of the grounding wire) according to the method. Meanwhile, when the sectional area of the grounding wire is checked, the single-phase residual voltage and the three-phase residual voltage of the working point are considered, and the safety of maintenance personnel is effectively ensured.
Example two
Further, the step S3 specifically includes:
and calculating three-phase short-circuit current provided by each distributed power supply to the working point in the active power distribution network.
And calculating three-phase short-circuit current provided by a large power grid connected with the active power distribution network to the working point.
If the grounding wire is positioned at the upstream of each distributed power supply, taking the sum of three-phase short-circuit currents provided by each distributed power supply to the working point and the maximum value of the three-phase short-circuit currents provided by the large power grid to the working point as the maximum short-circuit current of the working point.
If the grounding wire is positioned at the downstream of each distributed power supply, taking the sum of three-phase short-circuit currents provided by each distributed power supply to the working point and the superposition value of the three-phase short-circuit currents provided by the large power grid to the working point as the maximum short-circuit current of the working point.
Due to the fact that a plurality of distributed power supplies are connected, bidirectional power flow occurs in the active power distribution network, namely, the power can be supplied in the upstream and downstream directions of the working point. The embodiment has the advantages that the bidirectional power flow in the active power distribution network is considered, the maximum value of the three-phase short-circuit current which can be provided for the working point by the upstream and the downstream of the working point is selected as the maximum short-circuit current, the reliability of the grounding wire can be effectively ensured, and the safety of maintenance personnel is further ensured.
Example III
Referring to fig. 2, a security check calculation method for an active power distribution network grounding device includes the following steps:
s1, acquiring a topological structure and parameters of an active power distribution network. The topology structure comprises various power devices (such as a distributed power supply and the like) connected in the active power distribution network, a connection mode among the various power devices and the like. The parameters include short-circuit capacity (the short-circuit capacity characterizes the power supply capacity of a power system and is used for calculating the impedance of the large power grid) of the large power grid connected with the active power distribution network, a neutral point grounding mode (the power grid system with the neutral point directly grounded is a small current grounding system, the power grid system with the neutral point grounded through a small resistor is a large current grounding system), line parameters (the length and the type (the impedance and the capacitance resistance of each type of line are different) of the line in the active power distribution network), distributed power supply parameters, the switching protection action time of the line and the like.
S2, according to an Audi dak formula, calculating a function relation diagram of withstand current of the grounding wire with each section area grade of 16mm2, 25mm2, 35mm2 and the like and the protection action time of the circuit switch, and the function diagram is shown in fig. 3.
The Audi-dak formula is:
wherein S is the sectional area of the grounding wire; i k Is tolerant of current (i.e., short circuit current value flowing through the ground); t is the switch protection action time of the line; c is the thermal stability coefficient of the material used for the grounding wire.
S3, calculating the maximum short-circuit current of the working point according to the topological structure of the active power distribution network:
calculating three-phase short-circuit current of each distributed power supply in the active power distribution network:
the distributed power sources may be roughly classified into a rotary motor type distributed power source and an inverter type distributed power source according to a grid-connected manner different from the power distribution network.
The three-phase short-circuit current calculation formula that rotary motor type distributed power supply provided to operating point:
in U N 、X d "exit voltage and sub-transient impedance of the rotary motor type distributed power supply, respectively.
The three-phase short-circuit current calculation formula provided by the inverse distributed power supply to the working point comprises the following steps:
wherein S is DG 、U DG The rated capacity and the rated voltage of the inversion type distributed power supply are respectively.
The three-phase short-circuit current provided by the active power distribution network, which is connected with the large power grid and is supplied to the working point, is calculated, and because the current flowing equipment in the active medium-voltage power distribution network and the active low-voltage power distribution network are different (the active medium-voltage power distribution network can be regarded as a part of the active low-voltage power distribution network, and the active low-voltage power distribution network further comprises a part after the current flows through a distribution transformer), the three-phase short-circuit current is divided into the following two conditions:
in an active medium-voltage distribution network, three-phase short-circuit current I provided by a large power grid to a working point is calculated f0 The formula of (2) is as follows:
wherein; z is Z xi For rotary motor type distributed power supply xi The impedance value of the line to its upstream previous node; z is Z nj Is an inversion type distributed power supply ni The impedance value of the line to its upstream previous node; z is Z f1 The impedance value of the line between the working point and the upstream previous node; x is X s Impedance of a large power grid; i B Is the reference current of the active medium voltage distribution network.
When the active low-voltage distribution network is overhauled, as the current wrongly sent by a large power grid and a distributed power supply is converted by a distribution transformer (when the active medium-voltage distribution network is overhauled, the wrongly sent current does not pass through the distribution transformer before reaching a working point), the three-phase short-circuit current I provided by the large power grid to the working point is calculated f0 The distribution transformer is considered (i.e. the impedance, transformation ratio, grounding resistance, etc. of the distribution transformer are considered), and the formula is as follows:
wherein Z is xi For rotary motor type distributed power supply xi The impedance value of the line to its upstream previous node; z is Z nj Is an inversion type distributed power supply ni The impedance value of the line to its upstream previous node; z is Z f2 An impedance value for a line between the distribution transformer and an upstream previous node; z is Z f3 A line impedance value for a line between the operating point and the distribution transformer; x is X s Impedance of a large power grid; z is Z T 、U 2N /U 1N The impedance and transformation ratio of the distribution transformer are respectively.
Wherein, the impedance X of the large power grid s The calculation formula is as follows:
wherein: u (U) G Is the power supply voltage of a large power grid, S c Is the short-circuit capacity of a large power grid.
If the grounding wire is positioned at the upstream of each distributed power supply, taking the sum of three-phase short-circuit currents provided by each distributed power supply to the working point and the maximum value of the three-phase short-circuit currents provided by the large power grid to the working point as the maximum short-circuit current of the working point.
If the grounding wire is positioned at the downstream of each distributed power supply, taking the sum of three-phase short-circuit currents provided by each distributed power supply to the working point and the superposition value of the three-phase short-circuit currents provided by the large power grid to the working point as the maximum short-circuit current of the working point.
And S4, determining a point (namely a red point in the graph) in the functional relation graph (figure 3) according to the maximum short-circuit current and the switch protection action time of the line where the working point is located. And selecting the cross section area as small as possible under the condition that the withstand current of the grounding wire is larger than the maximum short-circuit current. If the red dot is located between the 35mm2 cross-sectional area line and the 50mm2 cross-sectional area line in the figure, the cross-sectional area of the ground line is selected to be 50mm2.
S5, calculating single-phase residual voltage and three-phase residual voltage of the working point according to the parameters and the sectional area of the grounding wire:
according to the technical rule of consulting DL-T879-2004 of the electric industry of the sectional area of the grounding wire, the clamp contact resistance R of the grounding wire is obtained x Short-circuit cable resistor R of grounding wire t 。
The three-phase residual voltage at the working point is calculated as follows:
U res3 ＝kU G +I DG (R x +R t )
in U G The power supply voltage of a large power grid connected with the active power distribution network; k is a partial pressure coefficient of the large power grid to the working point, and k is smaller than 1; i DG A sum of three-phase short-circuit currents provided to the operating points for each distributed power supply; r is R x A cable resistor is short-circuited for a grounding wire; r is R t Is the contact resistance of the wire clip.
Calculating the single-phase residual voltage of the working point, wherein the formula is as follows:
wherein I is k Representing a single-phase ground current of the ground wire; ρ is the resistivity of the soil; z is Z g The grounding resistor is a grounding wire; x is the distance between the operating point and the ground line.
Wherein, single-phase grounding current I k The calculation mode of (a) is as follows:
if the active power distribution network is a high-current grounding system, namely, the neutral point is grounded through a small resistor, then
In the method, in the process of the invention,
open circuit voltage for ground, +.>
Is an equivalent voltage source of a distributed power supply, Z ∑(1) 、Z ∑(2) 、Z ∑(0) Equivalent positive sequence, negative sequence and zero sequence impedance of active power distribution network, I B Is the reference current of the active distribution network.
If the active distribution network is a low-current grounding system, i.e. the neutral point is directly grounded, then
In U Φ Phase voltage of active distribution network, C ∑ The total capacitance of the power transmission line in the active power distribution network is L, and the L is arc suppression coil inductance.
If the single-phase residual voltage and the three-phase residual voltage are smaller than the human body safety voltage, the selected sectional area passes through safety check; otherwise, the step S4 is skipped to select a larger cross-sectional area again.
And determining using measures of the grounding wire, such as multiple grounding wires, according to the checking result of the sectional area to reduce short circuit current and residual voltage of the working point.
The method has the beneficial effects that a specific calculation method for the maximum short-circuit current and the residual voltage of the working points in the active medium-voltage distribution network and the active low-voltage distribution network is provided, a checking calculation method is provided for the grounding device, the grounding device which is reasonable, reliable and safe can be selected and used quickly in the actual operation and maintenance of the active distribution network, and the personal safety of maintenance personnel is further protected. When the three-phase short-circuit current is calculated, the increase of the short-circuit capacity of the system caused by the access of the distributed power supply is considered, and the calculation accuracy of the maximum short-circuit current of the working point is improved.
Example IV
As shown in fig. 4, the active medium voltage distribution network is overhauled, and the active medium voltage distribution network comprises a large power grid G 1 M+n rotary motor type distributed power supply l xi； (i is more than or equal to 0 and less than or equal to m+n), and p+q inversion type distributed power supplies l nj (j is more than or equal to 0 and less than or equal to p+q), and a distribution transformer. Wherein Z is xi Representation l xi The impedance value of the line to the previous node upstream thereof (as Z in FIG. 4 x2 Representation l x2 To l x1 Resistance of the line betweenResistance value); z is Z nj Representation l nj The impedance value of the line to the previous node upstream thereof (as Z in FIG. 4 n2 Representation l n2 To l n1 Impedance value of the line between them); z is Z f1 An impedance value of a line between the operating point and a previous node upstream thereof; kf 1 、Kf 2 Is a switch.
At working point f 1 If Kf, the grounding wire 1 is hung at the short distance 1 False action (Kf) 1 Malfunction indicates: during maintenance, switch Kf 1 Due to misoperation of the device, people and the like, the power supply suddenly transmits power by mistake, and the safety of maintenance personnel is endangered), the working point f 1 Upstream (i.e. G) 1 、l xi (0≤i≤m)、l nj (0.ltoreq.j.ltoreq.p)) three-phase short-circuit current I f∑up The calculation is as follows:
wherein I is f0 Three-phase short-circuit current provided to the working point for a large power grid; i fxi Three-phase short-circuit current provided to the operating point for a rotary motor type distributed power supply; i fnj Three-phase short-circuit current provided to the working point for the inversion type distributed power supply; z is Z xi For rotary motor type distributed power supply xi The impedance value of the line to its upstream previous node; z is Z nj Is an inversion type distributed power supply nj The impedance value of the line to its upstream previous node; z is Z f1 To the working pointThe impedance value of the line between the nodes upstream of the impedance value; x is X s Is a large power grid G 1 Impedance of I B The reference current is the reference current of the active power distribution network; u (U) N 、X d "exit voltage, sub-transient impedance of the rotary motor type distributed power supply, respectively; s is S DG 、U DG Is rated capacity and rated voltage of the inversion type distributed power supply.
If K f2 False operation, working point f 1 Downstream (l) xi 、l nj (m≤i≤m+n)、l nj (p.ltoreq.j.ltoreq.p+q)) three-phase short-circuit current I f∑down The calculation is as follows:
wherein I is fxi Three-phase short-circuit current provided to the operating point for a rotary motor type distributed power supply; i fnj Three-phase short-circuit current provided to the working point for the inversion type distributed power supply; z is Z xi 、Z nj 、Z f1 、Z c Respectively rotary motor type distributed power supply xi Inversion type distributed power supply l nj Impedance values of the line between the distribution transformer, the line end and the upstream previous node; x is X s The system impedance of the large power grid; i B The reference current is the reference current of the active power distribution network; u (U) N 、X d "exit voltage, sub-transient impedance, S for a distributed power supply of the rotary motor type respectively DG 、U DG The rated capacity and the rated voltage of the inversion type distributed power supply are respectively.
In the present embodiment, assuming that the sectional area of a single ground wire cannot pass the safety check, at the working point f 1 One side hangingA ground line 1 and a ground line 2. And assume K f1 The three-phase short-circuit current on the grounding wire 1 and the grounding wire 2 is calculated as follows:
wherein R is x1 、R t1 The short-circuit cable resistance and the wire clamp contact resistance of the grounding wire 1 are respectively; r is R x2 、R t2 The short-circuit cable resistance and the wire clamp contact resistance of the grounding wire 2 are respectively; z is Z 12 I is the line impedance between the ground line 1 and the ground line 2 f∑up For working point f 1 Upstream three-phase short-circuit current.
Calculating single-phase residual voltage as follows:
wherein Z is g2 The ground resistance of the ground wire 2; z is Z g1 The ground resistance of the ground wire 1; z is Z 12 Representing the line impedance between two ground lines; i k Representing single phase ground current at ground line 1; ρ is the resistivity of the soil; x is the distance between the working point and the ground line.
The improvement of the embodiment is that under the condition that a single grounding wire cannot pass the verification, maintenance personnel can finish the grounding protection by using methods of hooking multiple grounding wires and the like, and the residual voltage calculation method is utilized to verify again, so that the residual voltage of a working point is ensured to be lower than the safety voltage of a human body, and the safety of the maintenance personnel is ensured.
Example five
As shown in fig. 5: overhauling an active low-voltage distribution network, and at a working point f 2 Overhauling the non-remote grounding wire 3, assuming K f1 The three-phase short-circuit current on the grounding wire 3 is calculated as follows:
wherein Z is xi For rotary motor type distributed power supply xi The impedance value of the line to its upstream previous node; z is Z nj Is an inversion type distributed power supply ni The impedance value of the line to its upstream previous node; z is Z f2 An impedance value for a line between the distribution transformer and an upstream previous node; z is Z f3 Line impedance values from the operating point to the distribution transformer; x is X s Impedance of a large power grid; z is Z T 、U 2N /U 1N The impedance and the transformation ratio of the distribution transformer are respectively; u (U) N 、X d "exit voltage, sub-transient impedance of the rotary motor type distributed power supply, respectively; s is S DG 、U DG Is rated capacity and rated voltage of the inversion type distributed power supply.
The foregoing description is only illustrative of the present invention and is not intended to limit the scope of the invention, and all equivalent structures or equivalent processes or direct or indirect application in other related technical fields are included in the scope of the present invention.
Claims (4)
1. The safety check calculation method of the grounding device of the active power distribution network is characterized by comprising the following steps of:
s1, acquiring parameters and a topological structure of an active power distribution network;
s2, calculating to obtain a functional relation between the withstand current of the grounding wire and the protection action time of the circuit switch for the grounding wires with different sectional areas based on an Audi dak formula;
s3, calculating the maximum short-circuit current of the working point according to the topological structure of the active power distribution network;
s4, selecting a grounding wire sectional area meeting the condition according to the switch protection action time of the line where the working point is located by utilizing the functional relation; the condition is that the ground wire withstand current is greater than the maximum short circuit current;
s5, calculating single-phase residual voltage and three-phase residual voltage of the working point according to the parameters and the sectional area of the grounding wire; if the single-phase residual voltage and the three-phase residual voltage are lower than the human body safety voltage, the selected sectional area of the grounding wire passes through safety check; otherwise, jumping to the step S4, and re-selecting the sectional area of the grounding wire;
the calculation formula of the three-phase residual voltage in the step S5 is as follows:
U res3 ＝kU G +I DG (R x +R t )
in U G The power supply voltage of the large power grid; k is a partial pressure coefficient, k is less than 1; i DG A sum of three-phase short-circuit currents provided to the operating points for each distributed power supply; r is R x A cable resistor is short-circuited for a grounding wire; r is R t The contact resistance of the wire clamp;
the calculation formula of the single-phase residual voltage in the step S5 is as follows:
wherein I is k Representing a single-phase ground current of the ground wire; ρ is the resistivity of the soil; z is Z g The grounding resistor is a grounding wire; x is the distance between the working point and the grounding wire;
in U Φ Phase voltage of active distribution network, C ∑ The total capacitance of the power transmission line in the active power distribution network is L, and the L is arc suppression coil inductance.
2. The method for computing security check of an active power distribution network grounding device of claim 1, further comprising: and determining the using measure of the grounding wire according to the safety checking result of the sectional area of the grounding wire.
3. The method for computing the security check of the grounding device of the active power distribution network according to claim 1, wherein the audi dak formula is:
wherein S is the sectional area of the grounding wire; i k A withstand current for the ground line; t is the switch protection action time of the line; c is the thermal stability coefficient of the ground wire material.
4. The method for security check calculation of an active power distribution network grounding device according to claim 3, wherein the step S3 specifically comprises:
calculating three-phase short-circuit current provided by each distributed power supply to a working point in an active power distribution network;
calculating three-phase short-circuit current provided by a large power grid connected with an active power distribution network to a working point;
if the grounding wire is positioned at the upstream of each distributed power supply, taking the sum of three-phase short-circuit currents provided by each distributed power supply to the working point and the maximum value of the three-phase short-circuit currents provided by the large power grid to the working point as the maximum short-circuit current of the working point; if the grounding wire is positioned at the downstream of each distributed power supply, taking the sum of three-phase short-circuit currents provided by each distributed power supply to the working point and the superposition value of the three-phase short-circuit currents provided by the large power grid to the working point as the maximum short-circuit current of the working point.
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| WO2019007348A1 (en) * | 2017-07-06 | 2019-01-10 | 长沙理工大学 | Safe processing method for active voltage reduction of ground fault phase of non-effective grounding system |
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