CN115395494A - High-voltage cable circulating current restraining method for guiding short-circuit current - Google Patents
High-voltage cable circulating current restraining method for guiding short-circuit current Download PDFInfo
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- H—ELECTRICITY
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- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
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Abstract
The invention discloses a high-voltage cable circulating current restraining method for realizing short-circuit current guiding, which comprises the following steps: (1) Aiming at a three-phase cross-interconnected high-voltage cable line, respectively acquiring the induced voltage and impedance of three branches formed by cross-interconnection of a group of three-phase cables, and determining the circulating current size of each branch; (2) Sequencing according to the magnitude of the circulation of each branch in a group of three-phase cables, and determining the maximum circulation branch current I max Second largest circulating branch current I cmax Minimum circulating branch current I min (ii) a 3) Obtaining the transformed impedance Z of the maximum circulating branch max 'Secondary large loop branch's transformation impedance Z cmax '; (4) Series connection improvement of impedance Z in maximum circulating branch max ', serially connecting and reforming impedance Z in secondary and large loop branches cmax ' the smallest circulation branch remains the same. The invention can restrain the circulation under the normal working condition of the cross interconnection grounding system, and the minimum circulation branch guides the fault current under the fault working condition, thereby reducing the induction potential.
Description
Technical Field
The invention relates to the technical field of power transmission and transformation equipment, in particular to a high-voltage cable circulating current restraining method for guiding short-circuit current.
Background
In order to reduce the damage caused by the excessive circulating current of the cable, at present, a series impedance method and a method for additionally installing a return line are mainly used. For example: chinese patent application No. 202111178573.X discloses a method for solving the problem of sudden circulation change of a sheath of a multi-loop high-voltage single-core power cable, namely, a series protection suppressor is additionally arranged at a direct junction of cross interconnection, namely, a proper inductor and a small resistor are respectively connected in series on a three-phase cross interconnection grounding wire. Such series impedance methods reduce the circulating current by increasing the branch impedance directly on all three branches, but will generate higher induced potentials in adjacent loops and other equipment when an earth fault occurs, seriously threatening equipment and personal safety. The method of additionally installing the return line can reduce the fault induced potential, but can not inhibit normal commutation, has huge cost investment and does not meet the actual engineering requirements.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the defects, the invention discloses a high-voltage cable circulating current restraining method for realizing short-circuit current guiding, which can restrain circulating current under the normal working condition of a cross interconnection grounding system and reduce induced potential under the fault working condition.
The technical scheme is as follows: in order to solve the above problems, the present invention provides a method for suppressing the circulating current of a high voltage cable, which realizes the guiding of short circuit current, and comprises the following steps:
respectively acquiring induced voltages and impedances of three branches formed by cross interconnection of a group of three-phase cables aiming at a three-phase cross interconnected high-voltage cable line, and determining the circulating current size of each branch;
(2) Sequencing according to the magnitude of the circulation of each branch in a group of three-phase cables, and determining the maximum circulation branch current I max Second largest circulating branch current I cmax Minimum circulating current branch current I min ；
(3) Obtaining the transformation impedance Z of the maximum circulation branch max 'Secondary large loop branch's transformation impedance Z cmax ', the formula is:
in the formula, Z max ' impedance is reconstructed for the maximum circulation branch; z cmax ' impedance is transformed for a secondary large circulating branch; z is a linear or branched member max Impedance before transformation of the maximum loop current branch; z cmax Impedance before transformation of a secondary large circulating branch is achieved; u shape max The induced voltage of the maximum circulating current branch circuit; u shape cmax The induced voltage of the secondary circulating branch circuit;
(4) Series connection improvement at maximum circulation branchImpedance Z max ', serially connecting and reforming impedance Z in secondary and large loop branches cmax ' the smallest circulation branch remains the same.
Further, the step (1) comprises the following steps:
(1.1) respectively calculating the impedance Z of each branch in a group of three-phase cables i The formulas are as follows:
in the formula, when i is 1, the corresponding branch corresponds to the first branch; when i takes 2, corresponding to a second branch; when i takes 3, corresponding to a third branch; r is a sheath resistor; x is a sheath reactance; l is the length of the sheath of the corresponding branch; ρ is a unit of a gradient S Is the sheath conductivity; a. The S The sectional area of the sheath; alpha is alpha S Is the temperature coefficient of resistance; eta is the ratio of the temperature of the conductor to the temperature of the sheath; t is S The working temperature of the sheath; k 0 Is a constant; s is the conductor axis spacing; d is the average diameter of the shaft sleeve; omega is angular frequency;
(1.2) calculating the induced potential of each branch in a group of three-phase cables, wherein the formula is as follows:
(1.2.1) if the three-phase cable adopts a three-cable parallel straight line laying mode, the induced potential is as follows:
in the formula of U α For side-phase induced voltage, U β Is the intermediate phase induced voltage; r is the average radius of the metal sheath; i is conductor current;
(1.2.2) if the three-phase cable is laid in a delta shape with three cables, the induced voltage is:
in the formula, U is induction voltage;
(2) According to the obtained impedance and faradic electricityThe pressure determines the circulation size I of each branch i The formula is as follows:
in the formula, [ Z ]]＝[Z 1 Z 2 Z 3 ]；
Wherein U is 1 、U 2 、U 3 Taking U according to cable laying mode α 、U β Or U.
Furthermore, two ends of a three-phase cable in the three-phase cross-interconnected high-voltage cable line are directly grounded, and the cross-interconnected section inside the three-phase cable is grounded through the parallel sheath protector.
Further, the three-phase cross-connected high-voltage cable line is a single-loop line or a multi-loop line.
Furthermore, the three-phase cables in the three-phase cross-interconnected high-voltage cable line are all high-voltage single-core cables adopting an aluminum sheath structure.
Has the beneficial effects that: compared with the prior art, the method for restraining the circulation of the high-voltage cable for guiding the short-circuit current has the advantages that 1, impedance is improved through design, the corresponding improved impedance is connected in series to the maximum circulation branch and the secondary circulation branch in the three-phase cable, and the circulation restraining cost of the whole cross interconnection line is reduced compared with the existing three-phase cable series impedance mode while the cross interconnection line restrains the circulation under the normal working condition; 2. when a single-phase earth fault occurs in the cross interconnection line, the fault current leads the current to flow back to a neutral point through the minimum circulating current branch, and the fault induction voltage is reduced, so that the safety of surrounding equipment and personnel is protected.
Drawings
FIG. 1 is a flow chart of the method of the present invention;
fig. 2 shows a connection mode before cross-connection modification of a single-loop high-voltage single-core cable in the embodiment;
fig. 3 shows a connection mode of the single-loop high-voltage single-core cable after cross-connection modification in this embodiment.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings.
As shown in fig. 1, the present invention provides a method for suppressing a circulating current of a high voltage cable to achieve short circuit current guiding, which comprises the following steps:
step one, aiming at a three-phase cross-interconnected high-voltage cable line, selecting a single-loop branch in the embodiment; respectively obtaining the induced voltage and impedance of three branches formed by the cross interconnection of a group of three-phase cables, and determining the circulating current size of each branch.
Specifically, as shown in fig. 2, in the embodiment, three cables in the single-circuit line are respectively cross-connected through a cross-connection grounding box to form three branches; branch one respectively: A1-B2-C3 cross-connection section and a second branch: B1-C2-A3 cross-connection section and branch III: C1-A2-B3 cross-connect segments. Two ends of the three cables are grounded in parallel, and the middle of the cross interconnection section is grounded through the parallel sheath protector.
(1) Calculating the induction voltage and the impedance of each branch, wherein the specific formula is as follows:
(1.1) respectively calculating the impedance Z of each branch in a group of three-phase cables i The formulas are as follows:
in the formula, when i is 1, the corresponding branch I is obtained; when i is taken as 2, corresponding to the branch II; when i is taken as 3, corresponding to the branch III; r is a sheath resistor; x is a sheath reactance; l is the length of the sheath of the corresponding branch; ρ is a unit of a gradient S Is the sheath conductivity; a. The S The sectional area of the sheath; alpha (alpha) ("alpha") S Is the temperature coefficient of resistance; eta is the conductor temperature ratio corresponding to the sheath temperature; t is a unit of S The working temperature of the sheath; k 0 Is a constant; s is the conductor axis spacing; d is the average diameter of the shaft sleeve; omega is angular frequency;
(1.2) calculating the induced potential of each branch in a group of three-phase cables, wherein the formula is as follows:
(1.2.1) if the three-phase cable adopts a parallel straight-line laying mode of three cables, the induced potential is as follows:
in the formula of U α For side-phase induced voltage, U β Is the intermediate phase induced voltage; r is the average radius of the metal sheath; i is conductor current;
(1.2.2) if the three-phase cable is laid in a delta shape with three cables, the induced voltage is:
in the formula, U is induction voltage;
(2) Determining the circulation magnitude I of each branch circuit according to the obtained impedance and the induction voltage of each branch circuit i The formula is as follows:
in the formula, [ Z ]]＝[Z 1 Z 2 Z 3 ]；
Wherein, when three cables adopt a parallel straight line laying mode, the voltage U of the first branch circuit 1 Voltage U to branch three 3 All values are U α Voltage U of branch two 2 Value is U β (ii) a When three cables are laid in a delta shape, the voltage U of the branch circuit I 1 Voltage U of branch two 2 Voltage U of branch three 3 The values are all U.
Step two, sequencing according to the current magnitude of each branch in a group of three-phase cables, and determining the maximum circulating branch current I max Second largest circulating branch current I cmax Minimum circulating branch current I min 。
In this embodiment, the current magnitudes of the three branches are ordered as follows: I.C. A 3 >I 2 >I 1 . Therefore, the first branch is the minimum circular current branch, the second branch is the second largest circular current branch, and the third branch is the largest circular current branch.
And step three, calculating and obtaining the transformation impedance of the maximum circulating branch and the secondary circulating branch according to the induced voltage and the impedance of the three branches in the current circuit. The concrete formula is as follows:
in the formula, Z max ' is the modified impedance of the largest circulating branch; z cmax ' is the modified impedance of the secondary large loop branch; z is a linear or branched member max The impedance before the maximum circulation branch is transformed is taken as Z 3 ；Z cmax The impedance before the secondary large circulating branch is transformed is taken as Z 2 ；U max The induced voltage of the maximum circulating current branch is U 3 ；U cmax Is the induced voltage of the secondary circulating branch and takes the value of U 2 。
Step four, serially connecting the maximum circulating branch, namely the branch III to modify the impedance Z max ' in the secondary large branch, i.e. branch two, the impedance Z is series-connected and reformed cmax ' the smallest circulation branch, i.e. branch, remains the same.
As shown in fig. 3, impedance Z is measured max ' value is Z 3 ' the impedance is connected to the junction of the section C1 and the section A2 in the cross-connection section C1-A2-B3 in series; impedance Z cmax ' value is Z 2 ' is connected in series to the junction of section B1 and section C2 in the cross-connect section of sections B1-C2-A3.
Therefore, when the circuit works normally, the impedance of the branch circuit is increased due to the serially connected impedance, and the magnitude of the circulating current is restrained. When a single-phase earth fault occurs in a group of three-phase cables, compared with the prior art that three cross interconnection branches formed by cross interconnection of the three-phase cables are all connected in series with equal impedance, the fault current is guided to flow back through the minimum circulating current branch due to the fact that one branch is not connected in series with the impedance. Therefore, when fault current is generated, the series connection mode adopted by the application can not generate voltage drop on impedance and cause each branch circuit to bear the fault current to damage the whole circuit, and the voltage drop generated by the minimum branch circuit impedance is far smaller than the voltage drop generated in the prior art.
Specifically, the impedance is connected in series in the prior art by directly connecting equal impedances in series in all three cross-connected branches to connect 2 Ω fault current I in series k For example at 20 kA: the fault current returns to the neutral point through three branches, and the voltage drop generated by each impedance is 13.33kV; the specific calculation formula is as follows:
wherein k is the number of branches, I k Is a fault current;
in the embodiment, because the branch circuits are not connected in series with the impedance, the sheath in the first branch circuit is used as a return line, and the fault current returns to the neutral point through the first branch circuit; taking the sheath resistivity of the first branch as 2.83 × 10-8 Ω/m and the length as 300m as an example, the voltage drop generated by the current guiding branch is 0.1698V, and the formula is as follows:
ΔU＝I k ·γ·l＝20×2.83×300×10 -5 ＝0.1698V
wherein γ is the sheath resistivity; l is the sheath length;
comparing the two conditions, the invention can reduce the fault induction voltage and protect the series-connected current-suppressing device under the fault working condition.
Similarly, the method of the invention is also suitable for multi-loop cable transmission systems. The multi-loop cable transmission system is provided with a plurality of groups of three-phase cables, each group of three-phase cables and external electrical components form a single loop, and each single loop is respectively connected with the impedance of the structure in series by adopting the method, so that the loop current is restrained under the normal working condition, and the induced voltage is reduced under the fault working condition.
Claims (5)
1. A high-voltage cable circulating current restraining method for guiding short-circuit current is characterized by comprising the following steps:
(1) Aiming at a three-phase cross-interconnected high-voltage cable line, respectively acquiring the induced voltage and impedance of three branches formed by cross-interconnection of a group of three-phase cables, and determining the circulating current size of each branch;
(2) Sequencing according to the magnitude of the circulation of each branch in a group of three-phase cables, and determining the maximum circulation branch current I max Second largest circulating branch current I cmax Minimum circulating branch current I min ；
(3) Obtaining the transformed impedance Z of the maximum circulating branch max 'secondary large loop branch' improved impedance Z cmax ', the formula is:
in the formula, Z max ' impedance is transformed for the maximum circulating branch; z is a linear or branched member cmax ' impedance is transformed for the secondary large loop branch; z max Impedance before transformation of the maximum loop current branch; z cmax Impedance before transformation of a secondary large circulating branch is achieved; u shape max The induced voltage of the maximum circulating current branch circuit; u shape cmax The induced voltage of the secondary circulating branch circuit;
(4) Series connection improvement of impedance Z in maximum circulating branch max ' in the secondary large loop branch, the impedance Z is series-connected and reformed cmax ', the minimum circulation branch is kept as it is.
2. The method for restraining the circulation of the high-voltage cable for realizing the short-circuit current guiding according to claim 1, wherein the step (1) comprises the following steps:
(1.1) respectively calculating the impedance Z of each branch in a group of three-phase cables i The formulas are as follows:
in the formula, when i is 1, the corresponding branch corresponds to the first branch; when i takes 2, corresponding to a second branch; when i takes 3, corresponding to a third branch; r is a sheath resistor; x is a sheath reactance; l is the length of the sheath of the corresponding branch; rho S Is the sheath conductivity; a. The S The sectional area of the sheath; alpha (alpha) ("alpha") S Is the temperature coefficient of resistance; eta is the conductor temperature ratio corresponding to the sheath temperature; t is S The working temperature of the sheath; k 0 Is a constant; s is the conductor axis spacing; d is the average diameter of the shaft sleeve; omega is angular frequency;
(1.2) calculating the induced potential of each branch in a group of three-phase cables, wherein the formula is as follows:
(1.2.1) if the three-phase cable adopts a three-cable parallel straight line laying mode, the induced potential is as follows:
in the formula of U α Is a side-phase induced voltage, U β Is the intermediate phase induced voltage; r is the average radius of the metal sheath; i is conductor current;
(1.2.2) if the three-phase cable is laid in a delta shape with three cables, the induced voltage is:
in the formula, U is induction voltage;
(2) Determining the circulating current size I of each branch circuit according to the obtained impedance and the induction voltage i The formula is as follows:
in the formula (2)Z]＝[Z 1 Z 2 Z 3 ]；
Wherein, U 1 、U 2 、U 3 Taking U according to cable laying mode α 、U β Or U.
3. The method for restraining the circulation of the high-voltage cable for guiding the short-circuit current according to claim 1, wherein the three-phase cables are all high-voltage single-core cables adopting an aluminum sheath structure.
4. The method as claimed in claim 1, wherein the two ends of the three-phase cable in the three-phase cross-connected high-voltage cable line are directly grounded, and the cross-connected sections inside the three-phase cable are grounded through the parallel sheath protector.
5. The method as claimed in claim 1, wherein the three-phase cross-connected high-voltage cable lines are single-loop lines or multi-loop lines.
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Citations (6)
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|---|---|---|---|---|
| TW220017B (en) * | 1992-07-17 | 1994-02-01 | Tay-Her Yang | Differential speed and parallel operated circuit for the commutator motor |
| JP2008125197A (en) * | 2006-11-09 | 2008-05-29 | Toshiba Corp | Short circuit protection system and method of distribution system |
| CN102411074A (en) * | 2011-08-03 | 2012-04-11 | 广东威特真空电子制造有限公司 | High power waveguide impedance transformer |
| CN105470994A (en) * | 2016-01-29 | 2016-04-06 | 中南大学 | Microgrid inverter control method having circulating current suppression and harmonic suppression capability |
| CN110504850A (en) * | 2018-05-17 | 2019-11-26 | 株洲中车时代电气股份有限公司 | A kind of fairing and its circulation inhibition method |
| CN112100829A (en) * | 2020-08-31 | 2020-12-18 | 浙江大学 | Sheath induced voltage and circulation calculation method of cable system laid along bridge |
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Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TW220017B (en) * | 1992-07-17 | 1994-02-01 | Tay-Her Yang | Differential speed and parallel operated circuit for the commutator motor |
| JP2008125197A (en) * | 2006-11-09 | 2008-05-29 | Toshiba Corp | Short circuit protection system and method of distribution system |
| CN102411074A (en) * | 2011-08-03 | 2012-04-11 | 广东威特真空电子制造有限公司 | High power waveguide impedance transformer |
| CN105470994A (en) * | 2016-01-29 | 2016-04-06 | 中南大学 | Microgrid inverter control method having circulating current suppression and harmonic suppression capability |
| CN110504850A (en) * | 2018-05-17 | 2019-11-26 | 株洲中车时代电气股份有限公司 | A kind of fairing and its circulation inhibition method |
| CN112100829A (en) * | 2020-08-31 | 2020-12-18 | 浙江大学 | Sheath induced voltage and circulation calculation method of cable system laid along bridge |
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