CN105868522B - Single-phase across the voltage failure current calculation method across three-phase of mixed pressure quadri-circuit lines on the same tower - Google Patents
Single-phase across the voltage failure current calculation method across three-phase of mixed pressure quadri-circuit lines on the same tower Download PDFInfo
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Abstract
A kind of single-phase across the voltage failure current calculation method across three-phase of mixed pressure quadri-circuit lines on the same tower system calculates separately reduction to the positive and negative sequence equiva lent impedance of the two systems of fault point, obtains positive and negative sequence network in the strong magnetic system of light current；The zero-sequence network of two systems is subjected to unified decoupling；The zero sequence impedance of two systems is subjected to unified reduction again；Two zero-sequence networks after reduction are combined into unified compound sequence network, then single-phase fault current when three-phase is across voltage failure calculates.Two parts are superimposed fault current of the forceful electric power weak magnetic system that can be obtained electrical connection when voltage failure by current source two parts that forceful electric power weak magnetic system is divided into the strong magnetic part of light current and transformer is formed.The present invention is suitable for single-phase across the voltage failure calculating across three-phase; it can effectively solve when occurring across voltage failure; it is coupled between two systems complicated; the computationally intensive problem of the excessively high decoupling method of exponent number provides solid theoretical foundation across the relay protection of voltage failure for mixed pressure quadri-circuit lines on the same tower road.
Description
Technical Field
The invention belongs to the field of circuit relay protection, and particularly relates to a fault current calculation method when a single-phase cross three-phase fault occurs in a mixed-voltage same-tower four-circuit system, which provides a solid theoretical basis for relay protection.
Background
The existing fault analysis methods are mostly directed to single-circuit fault analysis, double-circuit fault analysis at the same voltage level and four-circuit fault analysis at the same voltage level, and the only fault analysis method for the mixed-voltage same-tower four-circuit fault is a six-sequence component method using double-circuit. At present, the method adopted in domestic line protection is to ignore mutual inductance between different voltage grades of a mixed voltage tower, roughly perform equivalent on electrical connection, and then perform independent configuration protection on two double-circuit line systems.
When the cross-voltage fault occurs to the mixed-voltage same-tower four-circuit line, the fault characteristics are complex due to mutual inductance among different voltage grades; considering again the electrical connection between the two voltage levels, the analysis method is more complex. The classical fault analysis method can be used for various grounding and phase faults of single lines of single circuit lines and double circuit lines, and comprises the steps of calculating positive, negative and zero sequence network diagrams reduced to a short circuit point, calculating boundary conditions of the fault point, and obtaining a sequence network diagram for fault calculation. When the cross-voltage fault of the weak current strong magnetic system without counting the electrical connection between the two systems is subjected to fault calculation, the positive sequence impedance and the negative sequence impedance which are reduced to a short-circuit point by the two systems are easy to obtain respectively, but the zero sequence impedance between the two systems can not be obtained independently due to mutual inductance between the two voltage levels; meanwhile, the boundary condition is not independent any more, but is related to another system, and a sequential network diagram according to the boundary condition cannot be obtained. After the electrical connection of the two voltage levels is considered, not only the zero sequence network diagram can not be independently calculated, but also the network diagrams of the positive sequence and the negative sequence can not be independently calculated. Therefore, the current domestic line protection adopts a method of neglecting mutual inductance between different voltage levels of a mixed voltage tower, roughly equating electrical connection, and then independently configuring and protecting two double-circuit line systems.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a fault current calculation method during a mixed-voltage same-tower four-circuit single-phase cross three-phase fault. By adopting the technical scheme of the invention, the fault current can be accurately calculated during the cross-voltage fault, and a solid theoretical basis is provided for analyzing relay protection of various principles.
For better understanding of the technical solution of the present invention, the technical terms appearing in the present invention are first described as follows:
mixing and pressing in the same tower: the method is characterized in that power transmission lines with different voltage grades are erected on the same power transmission tower; the invention researches the same tower parts of two transmission lines with different voltage grades, and the power supply and other different tower parts are subjected to thevenin equivalent treatment, so that the power supply and the different tower parts are equivalent to a power supply and outlet impedance form.
Weak current strong magnetism transmission system: the electromagnetic connection between the multiple power transmission lines on the same tower is strong, the electrical connection is weak, and a power transmission system which can be ignored compared with the electromagnetic connection is called a weak current strong magnetic system.
Strong and weak magnetism power transmission system: the power transmission system with strong electrical connection among multiple power transmission lines on the same tower and non-negligible power transmission is called as a strong current and weak current system; the mixed-voltage same-tower power transmission system comprises a power transmission line and power systems on two sides, wherein the power systems on one side are connected through a transformer, namely, electrical connection exists among different voltage classes, and the power transmission system is a strong current and weak current power transmission system, and is a weak current and strong current power transmission system in the opposite direction.
A voltage-crossing fault: a cross-line fault between different voltage classes is called a cross-voltage fault, which can be divided into a cross-voltage ground fault and a cross-voltage ungrounded fault.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a mixed-voltage same-tower four-circuit single-phase-to-three-phase-crossing voltage fault current calculation method is characterized in that a mixed-voltage same-tower four-circuit system comprises two double-circuit power transmission systems with different voltage levels, and when no transformer is connected between the two double-circuit power transmission systems with different voltage levels, the mixed-voltage same-tower four-circuit system belongs to a weak-current strong-magnetic power transmission system, and the calculation method comprises the following steps:
step 1: when a single-phase three-phase voltage-crossing fault occurs in a mixed-voltage same-tower four-circuit system, the electromotive force magnitudes and the positive sequence impedance and the negative sequence impedance of two power transmission systems with different voltage levels at a fault point are calculated respectively, wherein the two power transmission systems with different voltage levels are represented by I, II systems respectively, and the electromotive force magnitudes of I, II systems are represented by I, II systems respectivelyPositive sequence impedances are respectively Z1Ψ、Negative sequence impedances respectively of Z2Ψ、The subscript Ψ represents the I system,represents a system II, can represent the A/B/C three-phase of two systems, and 1 and 2 respectively represent positive and negative sequences;
step 2: carrying out unified decoupling on zero sequence networks of two power transmission systems with different voltage levels, sharing buses among circuits with the same voltage level, sharing ground among circuits with different voltage levels, and obtaining a four-circuit zero sequence network after unified decoupling by a parallel double-circuit method;
and step 3: step 2, the zero sequence network of the two power transmission systems with different voltage levels after unified decoupling is enteredThe lines are unified and reduced, the three points of the short circuit points of the ground and the two systems are taken as nodes, the equivalent zero sequence network of the I, II system is unified after other nodes are eliminated, and the equivalent zero sequence network is expressed in a Y form; wherein the zero sequence impedance at the short-circuit point node of the I system is Z0ΨZero sequence impedance at the short circuit point node of the II system isZero sequence impedance at ground node is Z0MAnd 0 in the subscript represents zero sequence.
And 4, step 4: calculating boundary conditions of single-phase cross three-phase cross voltage earth fault and non-earth fault,
II system has three-phase fault, the boundary condition is that the positive sequence voltage and the negative sequence voltage are zero, and
representing a short-circuit point to ground voltage, in which case a ground fault occursRespectively expressed as the positive, negative and zero sequence components of the I system fault current under the weak-current strong-magnetic system,respectively representing the positive, negative and zero sequence components of the I system fault voltage under the weak-current strong-magnetic system;representing the positive, negative and zero sequence components of the II system fault voltage under the weak current strong magnetic system, unifying the electromotive force, the positive and negative sequence networks and the voltage level transmission system according to the step 3The reduced zero sequence networks are combined into a unified composite sequence network;
and 5: on the basis of the composite sequence network diagram obtained in the step 4, the mixed-voltage same-tower four-circuit single-phase cross three-phase fault current under the weak-current strong-magnetic system is calculated according to the following formula,
wherein in the formulaRespectively expressed as the positive, negative and zero sequence components of the I system fault current under the weak-current strong-magnetic system,representing the positive, negative and zero sequence components of the II system fault current under the weak current strong magnetic system; z0M//Z0ΨRepresenting the impedance in parallel.
The invention further comprises the following preferred embodiments:
when two double-circuit transmission lines with different voltage grades in the mixed-voltage same-tower four-circuit system are connected through a transformer, the mixed-voltage same-tower four-circuit system belongs to a strong-current weak-magnetic system, in the calculation of the cross-voltage fault current of the single-phase cross-three-phase of the mixed-voltage same-tower four-circuit under the strong-current weak-magnetic system, the mixed-voltage same-tower four-circuit system under the strong-current weak-magnetic system needs to be divided into a weak-current strong-current transmission system part without counting the transformer and a current source part formed by the transformer, and the single-phase cross-three-phase cross-voltage fault current under the strong-current weak-magnetic system can be obtained by.
When two double-circuit transmission lines with different voltage grades in the mixed-voltage same-tower four-circuit system are connected through a transformer, the mixed-voltage same-tower four-circuit system belongs to a strong-current weak-magnetic system, and the strong-current weak-magnetic mixed-voltage same-tower four-circuit single-phase cross three-phase fault current calculation method further comprises the following steps besides the steps 1-5:
step 6: calculating fault current under single-phase cross three-phase fault formed by current source formed by transformer, according to fault current of transformer part actually measured under single-phase cross three-phase fault type, decomposing current source formed by transformer into positive, negative and zero sequence current source; according to the positive, negative and zero sequence networks of the mixed-voltage same-tower power transmission line when the current source formed by the transformer acts alone, the fault current components provided by the transformer as the current source at two fault points of the system are calculated I, II Wherein,respectively representing the positive, negative and zero sequence components of the fault current of the system I and the positive, negative and zero sequence components of the system II when only partial current sources of the transformer exist.
And 7: respectively superposing the two parts of fault currents calculated in the steps 5 and 6, and enabling the strong current, the weak current and the mixed voltage to have a same-tower four-circuit single-phase cross three-phase fault current valueWherein, the fault current positive sequence, negative sequence and zero sequence values of I, II system are considered when a single-phase cross three-phase fault occurs under a strong current weak magnetic system of the transformer.
The invention has the beneficial effects that: the phase selection method can accurately calculate the fault current when the mixed voltage same-tower single-phase cross three-phase voltage faults occur, gives the fault characteristics when the faults occur, and provides a theoretical basis for the analysis of relay protection of various principles. In addition, the fault analysis method is simple in calculation, and complex calculation of other various high-order decoupling methods is avoided by using positive, negative and zero sequence components for calculation.
Drawings
FIG. 1 is a cross-voltage fault model of a mixed-voltage same-tower four-circuit line with electrical connections;
FIG. 2 is a fault model of the effect of mains electromotive force alone;
FIG. 3 is a fault model of transformer source acting alone;
FIG. 4 is a schematic diagram of a parallel double-circuit zero-sequence network equivalent circuit of a weak electromagnetic system;
FIG. 5 is a schematic diagram of a four-circuit zero-sequence equivalent circuit of the same tower of the weak electromagnetic system;
FIG. 6 is a simplified model diagram of a four-circuit zero-sequence equivalent circuit of the same tower of the weak electromagnetic system;
FIG. 7 is a composite sequence network diagram of a weak current strong magnetic system single-phase cross three-phase earth fault C-abc-g fault;
fig. 8 is a composite sequence network diagram of a weak-current strong-magnetic system single-phase-crossing three-phase ungrounded fault C-abc fault.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
The invention discloses a mixed-voltage same-tower four-circuit single-phase cross three-phase fault current calculation method which divides a mixed-voltage same-tower power transmission system into a weak-current strong-magnetic system and a strong-current weak-magnetic system. The fault calculation of the weak current strong magnetic system comprises the following steps:
step 1: calculating two different voltage level outputs reduced to fault pointThe magnitude of the electromotive force of the electrical system and the positive and negative sequence impedances. Take the abc phase of the C-phase cross-II system of the I system as an example, wherein the specific phase electromotive force of the I system isIn the II system, the electromotive force is as followsPositive sequence impedances are respectively Z1Ψ、Negative sequence impedances respectively of Z2Ψ、
Step 2: and decoupling the zero sequence networks of the two power transmission systems uniformly by using a decoupling method. If buses are shared between circuits with the same voltage class, decoupling is the same as common parallel double loop decoupling as shown in the figure 4, mutual inductance is connected at the common point, mutual inductance is subtracted from zero sequence mutual inductance on the double loops, voltage and current of each node after decoupling are the same, and decoupling between the same voltage classes is carried out in a dotted frame in the figure 5; the decoupling method is similar to the parallel double-loop method, and can also obtain four decoupled loops, as shown in the solid-line box in fig. 5.
Step 3, carrying out unified reduction on zero sequence networks of two different power transmission systems, taking three points of a ground, a short circuit point of the two systems and the like as nodes as shown in figure 5, and eliminating other nodes by respectively using Y/△ transformation, series-parallel connection and other effective methods to obtain an equivalent zero sequence network of the two systems, as shown in figure 6, the zero sequence impedance at the short circuit point node of the system I is represented in a Y form, wherein the zero sequence impedance at the short circuit point node of the system I is Z0ΨZero sequence impedance at the short circuit point node of the II system isZero sequence impedance at a site node is Z0M0 in the subscript represents zero sequence。
The step is a voltage-crossing fault current calculation method for single-phase crossing of three phases of four circuit lines on the same tower under the condition of weak electric and strong magnetic mixed voltage. The cross-voltage fault model of the strong-current weak-current mixed-voltage same-tower four-circuit system with electrical connection is shown in the attached figure 1; for a strong current and weak magnetic system with a cross-voltage fault, a superposition method is used, and a power supply for providing fault current for a fault point is divided into a power supply part of the weak current and strong magnetic system without electrical connection and a current source part formed by a transformer, as shown in figures 1-3. According to the above thought, the fault currents provided by the two parts of power supplies can be respectively solved, and then the two parts of currents are superposed to obtain the result of the fault current. The calculation of the fault current of the weak current and strong magnetic part is the same as the steps, and the current superposition part comprises the following steps:
step 6: calculating fault current under single-phase cross three-phase fault formed by current source formed by transformer, decomposing into positive, negative and zero sequence current source according to the fault current of measured transformer part; respectively drawing the positive sequence network topological diagram, the negative sequence network topological diagram and the zero sequence network topological diagram of the network of FIG. 3, and easily respectively calculating the fault current provided by the part of current sources at two fault points in the topological structure according to the theory of the electric networkThe fault current positive, negative and zero sequence components of the system I and the system II under the action of partial current source of the transformer are respectively shown.
And 7: respectively superposing the two parts of fault currents calculated in the steps 5 and 6,othersPart of the same can be obtained by analogyNamely, the fault current of I, II system is obtained when the single-phase cross three-phase fault of the electrically connected strong and weak magnetic system is taken into account.
The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (3)
1. A mixed-voltage same-tower four-circuit single-phase-to-three-phase-crossing voltage fault current calculation method is characterized in that a mixed-voltage same-tower four-circuit system comprises two double-circuit power transmission systems with different voltage levels, and when no transformer is connected between the two double-circuit power transmission systems with different voltage levels, the mixed-voltage same-tower four-circuit system belongs to a weak-current strong-magnetic power transmission system, and the calculation method comprises the following steps:
step 1: when the mixed voltage same-tower four-circuit system has single-phase and three-phase voltage faults, two different electricity at the fault point are calculated and reduced respectivelyThe electromotive force of the voltage class power transmission system and the positive sequence impedance and the negative sequence impedance are respectively represented by I, II systems, and the electromotive force of I, II systems is respectively represented byPositive sequence impedances are respectively Z1Ψ、Negative sequence impedances respectively of Z2Ψ、The subscript Ψ represents the I system,represents a system II, can represent the A/B/C three-phase of two systems, and 1 and 2 respectively represent positive and negative sequences;
step 2: carrying out unified decoupling on zero sequence networks of two power transmission systems with different voltage levels, sharing buses among circuits with the same voltage level, sharing ground among circuits with different voltage levels, and obtaining a four-circuit zero sequence network after unified decoupling by a parallel double-circuit method;
and step 3: carrying out unified reduction on the zero sequence networks of the two power transmission systems with different voltage levels after unified decoupling in the step 2, taking the three points of the short circuit points of the ground and the two systems as nodes, eliminating other nodes, and then unifying I, II equivalent zero sequence networks of the systems, and expressing the equivalent zero sequence networks in a Y form; wherein the zero sequence impedance at the short-circuit point node of the I system is Z0ΨZero sequence impedance at the short circuit point node of the II system isZero sequence impedance at ground node is Z0M0 in the subscript represents zero sequence;
and 4, step 4: calculating boundary conditions of single-phase cross three-phase cross voltage earth fault and non-earth fault,
the I system has single-phase fault with the boundary condition of
II system has three-phase fault, the boundary condition is that the positive sequence voltage and the negative sequence voltage are zero, and
representing a short-circuit point to ground voltage, in which case a ground fault occurs Respectively expressed as the positive, negative and zero sequence components of the I system fault current under the weak-current strong-magnetic system,respectively representing the positive, negative and zero sequence components of the I system fault voltage under the weak-current strong-magnetic system;representing the positive, negative and zero sequence components of the II system fault voltage under the weak-current strong-magnetic system, and combining the electromotive forces, positive and negative sequence networks of the two power transmission systems with different voltage levels and the zero sequence network uniformly calculated in the step 3 into a uniform composite sequence network;
and 5: on the basis of the composite sequence network diagram obtained in the step 4, the mixed-voltage same-tower four-circuit single-phase cross three-phase fault current under the weak-current strong-magnetic system is calculated according to the following formula,
the fault current at ground fault is
Fault current at ungrounded fault of
Wherein in the formulaRespectively expressed as the positive, negative and zero sequence components of the I system fault current under the weak-current strong-magnetic system,representing the positive, negative and zero sequence components of the II system fault current under the weak current strong magnetic system; z0M//Z0ΨRepresenting the impedance in parallel.
2. The method for calculating the cross-voltage fault current of the mixed-voltage same-tower four-circuit single-phase cross three-phase cross, which is characterized in that:
when two double-circuit transmission lines with different voltage grades in the mixed-voltage same-tower four-circuit system are connected through a transformer, the mixed-voltage same-tower four-circuit system belongs to a strong-current weak-magnetic system, in the calculation of the cross-voltage fault current of the single-phase cross-three-phase of the mixed-voltage same-tower four-circuit under the strong-current weak-magnetic system, the mixed-voltage same-tower four-circuit system under the strong-current weak-magnetic system needs to be divided into a weak-current strong-current transmission system part without counting the transformer and a current source part formed by the transformer, and the single-phase cross-three-phase cross-voltage fault current under the strong-current weak-magnetic system can be obtained by.
3. The method for calculating the cross-voltage fault current of the mixed-voltage same-tower four-circuit single-phase cross three-phase cross, which is characterized in that:
when two double-circuit transmission lines with different voltage grades in the mixed-voltage same-tower four-circuit system are connected through a transformer, the mixed-voltage same-tower four-circuit system belongs to a strong-current weak-magnetic system, and the strong-current weak-magnetic mixed-voltage same-tower four-circuit single-phase cross three-phase fault current calculation method further comprises the following steps besides the steps 1-5:
step 6: calculating fault current under single-phase cross three-phase fault formed by current source formed by transformer, according to fault current of transformer part actually measured under single-phase cross three-phase fault type, decomposing current source formed by transformer into positive, negative and zero sequence current source; according to the positive, negative and zero sequence networks of the mixed-voltage same-tower power transmission line when the current source formed by the transformer acts alone, the fault current components provided by the transformer as the current source at two fault points of the system are calculated I, II Wherein,respectively representing the positive, negative and zero sequence components of the fault current of the system I and the positive, negative and zero sequence components of the system II when only partial current sources of the transformer exist;
and 7: respectively superposing the two parts of fault currents calculated in the steps 5 and 6, and enabling the strong current, the weak current and the mixed voltage to have a same-tower four-circuit single-phase cross three-phase fault current valueWherein, the fault current positive sequence, negative sequence and zero sequence values of I, II system are considered when a single-phase cross three-phase fault occurs under a strong current weak magnetic system of the transformer.
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| CN104049180A (en) * | 2014-07-04 | 2014-09-17 | 国家电网公司 | Double-circuit line non-in-phase jumper wire earth fault single-end distance measurement method |
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| CN104049180A (en) * | 2014-07-04 | 2014-09-17 | 国家电网公司 | Double-circuit line non-in-phase jumper wire earth fault single-end distance measurement method |
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