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

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

Calculation method of cross-voltage fault current for single-phase cross-three-phase cross-voltage fault current of four-circuit line with mixed voltage on the same tower

technical field

The invention belongs to the field of line relay protection, and in particular relates to a fault current calculation method when a single-phase cross-three-phase fault occurs in a mixed-pressure four-circuit line system on the same tower, and provides a solid theoretical basis for relay protection.

Background technique

Most of the existing fault analysis methods are aimed at the fault analysis of single circuit lines, double circuit lines of the same voltage level and four circuit lines of the same voltage level. The only fault analysis methods for mixed voltage four circuit lines on the same tower are Follow the six-sequence component method of the double circuit. At present, the method adopted in domestic line protection is to ignore the mutual inductance between different voltage levels of the same mixed voltage tower, and roughly equivalent the electrical connection, and then separately configure and protect the two double-circuit line systems.

When a cross-voltage fault occurs on a four-circuit line with mixed voltage on the same tower, due to the mutual inductance between different voltage levels, the fault characteristics are complicated; and considering the electrical connection between two voltage levels, the analysis method is more complicated. The classic fault analysis method can be used for various grounding and phase-to-phase faults of single-circuit lines and double-circuit lines. The steps are to calculate the positive, negative and zero-sequence network diagrams attributed to the short-circuit point, and calculate the boundary conditions of the fault point , to obtain the sequence network diagram for fault calculation. When the fault calculation is performed on the cross-voltage fault of the weak current and strong magnetic system that does not consider the electrical connection between the two systems, the positive and negative sequence impedances of the two systems attributed to the short-circuit point are easy to obtain separately, but due to the difference between the two voltage levels Mutual inductance causes zero-sequence impedance between the two systems, but it can no longer be obtained independently; at the same time, the boundary conditions are no longer independent, but related to another system, and the sequence network diagram based on the boundary conditions cannot be obtained. After considering the electrical connection of the two voltage levels, not only the zero sequence network diagram can no longer be calculated independently, but also the positive and negative sequence network diagrams cannot be calculated independently. Therefore, the current domestic line protection method is to ignore the mutual inductance between different voltage levels of the same mixed voltage tower, roughly equivalent to the electrical connection, and then separately configure the protection method for the two double-circuit line systems.

Contents of the invention

In order to solve the above-mentioned problems existing in the prior art, the present invention proposes a fault current calculation method when a single-phase cross-three-phase fault occurs on a mixed-voltage four-circuit line on the same tower. By adopting the technical scheme of the invention, the fault current can be accurately calculated when a cross-voltage fault occurs, and a solid theoretical basis is provided for analyzing various principles of relay protection.

In order to better understand the technical scheme of the present invention, at first the technical terms appearing in the present invention are described as follows:

Mixed voltage on the same tower: refers to the erection of transmission lines with different voltage levels on the same transmission tower; it should be pointed out that the present invention studies two transmission lines with different voltage levels on the same tower, and the power supply and other parts of different towers are treated as Thevenin equivalents. The power supply and different tower sections are equivalent to the form of power supply and outlet impedance.

Weak current and strong magnetic transmission system: The electromagnetic connection between the multi-circuit transmission lines on the same tower is strong, and the electrical connection is weak. Compared with the electromagnetic connection, the transmission system that can be ignored is called a weak current and strong magnetic system.

Strong current and weak magnetic transmission system: the electrical connection between the multi-circuit transmission lines on the same tower is strong, and the transmission system that cannot be ignored is called a strong current and weak magnetic system; The power supply system has a transformer connection between the power supply systems on one side, that is, there is an electrical connection between different voltage levels, which is a "strong current and weak magnetic power transmission system", and vice versa is a "weak current and strong magnetic power transmission system".

Cross-voltage faults: cross-line faults between different voltage levels are called cross-voltage faults, and cross-voltage faults can be divided into cross-voltage ground faults and cross-voltage non-ground faults.

To achieve the above object, the present invention adopts the following technical solutions:

A cross-voltage fault current calculation method for a single-phase cross-three phase of a mixed-voltage four-circuit line on the same tower. The mixed-voltage four-circuit line system on the same tower includes two double-circuit power transmission systems with different voltage levels, and two different voltage levels When there is no transformer connection between the double-circuit line power transmission systems, the mixed-voltage four-circuit line system on the same tower belongs to the weak current and strong magnetic power transmission system, and it is characterized in that the calculation method includes the following steps:

Step 1: When a single-phase cross-three-phase voltage fault occurs in the mixed-voltage four-circuit line system on the same tower, the electromotive force and the positive and negative sequence impedances of the two different voltage level transmission systems at the fault point are respectively calculated, among which, Two transmission systems with different voltage levels are respectively represented by I and II systems, and the electromotive forces of I and II systems are respectively The positive sequence impedances are Z _1Ψ , The negative sequence impedances are Z _2Ψ , The subscript Ψ represents the I system, Represents the II system, which can represent the A/B/C three-phase of the two systems, and 1 and 2 represent the positive and negative sequences respectively;

Step 2: Unify the zero-sequence networks of two different voltage level transmission systems for unified decoupling, share the bus between the same voltage level lines, and share the common ground between different voltage level lines, and use the method of parallel double circuit lines to obtain unified decoupling The four-circuit zero-sequence network;

Step 3: Unify the zero-sequence networks of the two different voltage level transmission systems after the unified decoupling in step 2, take the ground and the short-circuit point of the two systems as nodes, and unify I and II after eliminating other nodes The equivalent zero-sequence network of the system is expressed in the form of Y; where the zero-sequence impedance at the short-circuit point node of the I system is Z _0Ψ , and the zero-sequence impedance at the short-circuit point node of the II system is The zero-sequence impedance at the ground node is Z _0M , and 0 in the subscript represents zero-sequence.

Step 4: Calculate the boundary conditions for single-phase cross-three-phase voltage-to-ground faults and non-ground faults,

When a three-phase fault occurs in the II system, the boundary condition is that the positive and negative sequence voltages are zero, and

Represents the short-circuit point-to-ground voltage, where a ground fault occurs when Respectively expressed as the positive, negative and zero-sequence components of the I system fault current under the weak current and strong magnetic system, Represent the positive, negative and zero-sequence components of the I system fault voltage under the weak current and strong magnetic system respectively; It represents the positive, negative and zero-sequence components of the fault voltage of the II system under the weak current and strong magnetic system. According to the above, the electromotive force, positive and negative sequence networks of the two voltage level transmission systems, and the zero sequence network after step 3 are uniformly reduced combined into a unified composite sequence network;

Step 5: On the basis of the composite sequence network diagram obtained in step 4, calculate the single-phase cross-three-phase fault current of the mixed-voltage four-circuit line on the same tower under the weak current and strong magnetic system according to the following formula,

Among them, in the formula Respectively expressed as the positive, negative and zero-sequence components of the I system fault current under the weak current and strong magnetic system, It represents the positive, negative and zero-sequence components of the II system fault current under the weak current and strong magnetic system; Z _0M //Z _0Ψ represents the parallel connection of impedance.

The present invention further includes the following preferred solutions:

When two double-circuit transmission lines with different voltage levels in the mixed-voltage four-circuit system on the same tower are connected through a transformer, the mixed-voltage four-circuit system on the same tower belongs to a strong current and weak magnetic system. In the calculation of cross-voltage fault current of single-phase cross-three-phase cross-voltage fault current of mixed-voltage four-circuit line on the same tower under the magnetic system, it is necessary to divide the mixed-voltage four-circuit system on the same tower under the strong current and weak magnetic system into a weak current and strong magnetic transmission system without transformers Part, and the current source part formed by the transformer, the fault current components of the two parts are superimposed to obtain the single-phase cross-three-phase cross-voltage fault current under the strong current and weak magnetic field system.

When two double-circuit transmission lines with different voltage levels in the mixed-voltage four-circuit system on the same tower are connected through a transformer, the mixed-voltage four-circuit system on the same tower belongs to a strong current and weak magnetic system, and the strong current In addition to the aforementioned steps 1-5, the calculation method for the single-phase cross-three-phase fault current of the four-circuit line with weak magnetic field and mixed voltage on the same tower also includes the following steps:

Step 6: Calculate the fault current under the single-phase cross-three-phase fault formed by the current source formed by the transformer, and decompose the current source formed by the transformer into positive, negative, Zero-sequence current source; according to the positive, negative, and zero-sequence networks of the mixed voltage transmission line on the same tower when the current source formed by the transformer acts alone, calculate the fault current components provided by the transformer as the current source at the two fault points of the I and II systems in, Respectively represent the positive, negative and zero-sequence components of the I system fault current and the positive, negative and zero-sequence components of the II system when there is only part of the transformer current source.

Step 7: Superimpose the two parts of the fault current calculated in steps 5 and 6 respectively, and the fault current value of the single-phase cross-three-phase fault current of the four-circuit line with strong current and weak magnetic pressure on the same tower in, It is the fault current positive sequence, negative sequence and zero sequence values of the I and II systems when the single-phase cross-three-phase fault is considered in the strong current and weak magnetic system of the transformer.

The beneficial effects of the present invention are: the phase selection method of the present invention can accurately calculate the fault current when the mixed-voltage single-phase cross-three-phase voltage fault occurs on the same tower, and the fault characteristics of this type of fault are given. The analysis of conservation provides the rationale. Moreover, the fault analysis method of the present invention is simple to calculate, using positive, negative and zero-sequence components for calculation, which avoids complex calculations of various other high-order decoupling methods.

Description of drawings

Figure 1 is a cross-voltage fault model of a mixed-voltage four-circuit line on the same tower with electrical connections;

Figure 2 is the fault model of the power electromotive force acting alone;

Figure 3 is the fault model of the transformer source acting alone;

Fig. 4 is a schematic diagram of the equivalent circuit of the zero-sequence network of the parallel double-circuit line of the weak current and strong magnetic system;

Figure 5 is a schematic diagram of the zero-sequence equivalent circuit of the four-circuit line on the same tower in the weak current and strong magnetic system;

Figure 6 is a schematic diagram of a simplified model of the zero-sequence equivalent circuit of the four-circuit line on the same tower in the weak current and strong magnetic system;

Figure 7 is a composite sequence network diagram of a single-phase cross-three-phase ground fault C-abc-g fault in a weak current and strong magnetic system;

Figure 8 is a composite sequence network diagram of a single-phase cross-three-phase ungrounded fault C-abc fault in a weak current and strong magnetic system.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation methods.

The invention discloses a single-phase cross-three-phase fault current calculation method of a four-circuit line with mixed voltage on the same tower, which divides the power transmission system of mixed voltage on the same tower into a weak current and strong magnetic system and a strong current and weak magnetic system. The fault calculation of the weak current and strong magnetic system includes the following steps:

Step 1: Calculate the electromotive force and positive and negative sequence impedances of two different voltage level transmission systems attributed to the fault point. Taking phase C of system I across phase abc of system II as an example, the electromotive force of the special phase of system I is In the II system, taking phase a as an example, the magnitude of the electromotive force is The positive sequence impedances are Z _1Ψ , The negative sequence impedances are Z _2Ψ ,

Step 2: Use the decoupling method to uniformly decouple the zero-sequence networks of the two transmission systems. Lines with the same voltage level share the same busbar, so the decoupling is the same as the decoupling of general parallel double-circuit lines. After decoupling, the voltage and current of each node are the same, and the dotted line box in Figure 5 is the decoupling between the same voltage levels; the lines of different voltage levels share the same ground, and the decoupling method is similar to the method of parallel double-circuit lines. The decoupled four-loop line can be obtained, as shown in the solid line box in Fig. 5 .

Step 3: Unify the zero-sequence networks of two different transmission systems, as shown in Figure 5. Taking the ground and the short-circuit point of the two systems as nodes, use Y/△ transformation, series-parallel connection and other equivalent methods to eliminate other nodes to obtain an equivalent zero-sequence network that unifies the two systems, as shown in Figure 6. Expressed in the form of Y. Among them, the zero-sequence impedance at the short-circuit point node of system I is Z _0Ψ , and the zero-sequence impedance at the short-circuit point node of system II is The zero-sequence impedance at the site node is Z _0M , and 0 in the subscript represents zero-sequence.

The above steps are the calculation method for the cross-voltage fault current of the single-phase cross-three phase of the four-circuit line with weak current and strong magnetic mixed voltage on the same tower. For the strong current and weak magnetic mixed voltage four-circuit line system on the same tower with electrical connections, the cross-voltage fault model is shown in Figure 1; for the strong current and weak magnetic system with cross-voltage faults, the superposition method will provide fault current The power supply is divided into the power supply part of the weak current and strong magnetic system regardless of the electrical connection, and the current source part formed by the transformer, as shown in Figure 1-3. According to the above ideas, the fault current provided by the two parts of the power supply can be solved separately, and then the result of the fault current can be obtained by superimposing the two parts of the current. The fault current calculation of the weak current and strong magnetic part is the same as the above steps, and the steps of the current superposition part are as follows:

Step 6: Calculate the fault current under a single-phase cross-three-phase fault formed by the current source formed by the transformer, and decompose it into positive, negative, and zero-sequence current sources according to the measured fault current of the transformer; draw the positive and negative current sources of the network in Figure 3 respectively. , negative, and zero-sequence network topology diagrams, in this topology structure, it is easy to calculate the fault current provided by this part of the current source at the two fault points according to the electrical network theory Respectively represent the positive, negative and zero-sequence components of the I system fault current and the positive, negative and zero-sequence components of the II system under the action of the partial current source of the transformer.

Step 7: Superimpose the two parts of the fault current calculated in steps 5 and 6 respectively, Other parts can be obtained by analogy That is to find out the fault current of I and II systems when the single-phase cross-three-phase fault of the strong current and weak magnetic system of the electrical connection is taken into account.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone familiar with the technology can easily think of changes or replacements within the technical scope disclosed in the present invention. , should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by 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 Z_1Ψ、Negative sequence impedances respectively of Z_2Ψ、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 Z_0ΨZero sequence impedance at the short circuit point node of the II system isZero sequence impedance at ground node is Z_0M0 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; z_0M//Z_0ΨRepresenting 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.