Method for zero sequence resistance current differential protection of interconnection line between stations of small resistance grounding system

Abstract

The application discloses a kind of small resistance grounding system interconnection line zero sequence resistance current differential protection methods, comprising the following steps: 1) the three-phase current of interconnection line sending end current transformer is collected and the zero sequence voltage of interconnection line sending end power station bus is collected, the three-phase current of interconnection line receiving end current transformer is collected and the zero sequence voltage of interconnection line receiving end power station bus is collected 2) according to the three-phase current of interconnection line sending end current transformer and calculate interconnection line sending end resistance zero sequence current 3) according to the three-phase current of interconnection line receiving end current transformer and calculate interconnection line receiving end resistance zero sequence current 4) according to interconnection line sending end resistance zero sequence current and interconnection line receiving end resistance zero sequence current, calculate zero sequence resistance differential current and braking current 5) when or, then, zero sequence differential protection action, the method can accurately and timely judge that single-phase grounding fault occurs in grounding interconnection line, and timely removes fault.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, and relates to a method for zero-sequence resistive current differential protection of inter-station tie lines in low-resistance grounding systems. Background Technology

[0002] As the scale of new energy continues to expand, there are more and more wind power, photovoltaic and energy storage power stations distributed in a decentralized manner. After multiple power stations are connected by interconnection lines, they are connected to the power grid through a power station.

[0003] Currently, single-phase grounding protection for tie lines uses full-current zero-sequence differential protection. When a single-phase grounding fault occurs outside the tie line zone, the differential current on both sides of the line includes the capacitive current of the tie line to ground, which is detrimental to the selectivity of the single-phase differential protection and reduces its reliability. When a single-phase grounding fault occurs within the tie line zone, the capacitive current of the tie line to ground results in a differential current close to zero on both sides of the line, having no effect on increasing the differential operating current. Furthermore, the amplitude of the capacitive differential current depends on the capacitive current to ground of the substations on both sides, meaning the amplitude of the capacitive differential current is affected by the operating mode of the substations.

[0004] In substations with resistive grounding, single-phase grounding protection of tie lines employs resistive current zero-sequence differential protection. When the grounding resistances on both sides of the tie line are effectively engaged, the adverse effects of capacitive current during single-phase grounding can be overcome. It is unaffected by the large unbalanced current caused by excessively long tie lines, nor by the substation's operating mode. Using resistive current zero-sequence differential protection, when a single-phase grounding occurs on the tie line, the zero-sequence differential current is the vector difference of the resistive current flowing through the current transformers on both sides of the tie line. This invention utilizes the characteristics of the zero-sequence current in the tie line and employs a relay protection method based on the principle of resistive current zero-sequence differential protection to accurately and promptly determine when a single-phase grounding has occurred on the grounded tie line and disconnect the faulty tie line. The principle of this invention is clear and reliable, conforming to the basic principles of relay protection: reliability, sensitivity, selectivity, and speed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for zero-sequence resistive current differential protection of inter-station tie lines in low-resistance grounding systems. This method can accurately and promptly determine the occurrence of a single-phase grounding fault in the grounding tie line and promptly clear the fault.

[0006] To achieve the above objectives, the zero-sequence resistive current differential protection method for inter-station tie lines in a low-resistance grounding system according to the present invention includes the following steps:

[0007] 1) Collect the three-phase current from the three-phase current transformer at the sending end of the tie line. and Collect the zero-sequence voltage of the power station bus at the sending end of the interconnection line. Collect the three-phase current of the three-phase current transformer at the receiving end of the tie line. and Collect the zero-sequence voltage of the receiving-end substation bus of the tie line.

[0008] 2) Based on the three-phase current of the three-phase current transformer at the sending end of the tie line. and Calculate the resistive zero-sequence current at the sending end of the tie line.

[0009] 3) Based on the three-phase current of the three-phase current transformer at the receiving end of the tie line. and Calculate the zero-sequence current of the tie-line with resistance at the receiving end.

[0010] 4) Based on the resistive zero-sequence current at the sending end of the tie line and the resistive zero-sequence current at the receiving end of the tie line Calculate the zero-sequence resistive differential current and braking current

[0011] 5) When or When this happens, the zero-sequence differential protection will operate, in which case, K is the zero-sequence differential starting current, and K is the zero-sequence differential braking coefficient.

[0012] Zero-sequence resistive current at the sending end of the tie line for:

[0013]

[0014] Where, θ is and included angle This is the three-phase current vector at the sending end of the tie line.

[0015] Three-phase current vector at the sending end of the tie line for:

[0016]

[0017] Zero-sequence current at the receiving end of the tie line for:

[0018]

[0019] in, for and included angle This is the three-phase current vector at the receiving end of the tie line.

[0020] Three-phase current vector at the receiving end of the tie line for:

[0021]

[0022] Zero-sequence resistive differential current for:

[0023]

[0024] Braking current for:

[0025]

[0026] The present invention has the following beneficial effects:

[0027] In practical operation, the zero-sequence resistive current differential protection method for inter-station tie lines in low-resistance grounding systems described in this invention calculates the zero-sequence resistive differential current. and braking current Based on zero-sequence resistive differential current and braking current This invention determines whether a single-phase ground fault has occurred and, if so, promptly disconnects the fault. When the grounding resistance on both sides of the tie line is effectively engaged, it overcomes the adverse effects of capacitive current during a single-phase ground fault, is unaffected by the large unbalanced current caused by excessively long tie lines outside the fault zone, and is also unaffected by the power station's operating mode. Resistive current zero-sequence differential protection is employed; when a single-phase ground fault occurs on the tie line, the zero-sequence differential current is the vector difference of the resistive current flowing through the current transformers on both sides of the tie line. This invention utilizes the characteristics of the zero-sequence current in the tie line and employs a relay protection method based on the principle of resistive current zero-sequence differential protection to accurately and promptly determine if a single-phase ground fault has occurred on the grounded tie line and disconnect the faulty tie line. The principle is clear and reliable, conforming to the basic principles of relay protection: reliability, sensitivity, selectivity, and speed. Attached Figure Description

[0028] Figure 1 A schematic diagram of a single-phase ground fault current in an inter-station tie line with resistive grounding.

[0029] Figure 2 This is a vector diagram of the present invention. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0031] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0032] refer to Figure 1 and Figure 2 The zero-sequence resistive current differential protection method for inter-station tie lines in a low-resistance grounding system according to the present invention includes the following steps:

[0033] 1) Collect the three-phase current from the three-phase current transformer at the sending end of the tie line. and Collect the zero-sequence voltage of the power station bus at the sending end of the interconnection line. Collect the three-phase current of the three-phase current transformer at the receiving end of the tie line. and Collect the zero-sequence voltage of the receiving-end substation bus of the tie line.

[0034] 2) Based on the three-phase current of the three-phase current transformer at the sending end of the tie line. and Calculate the resistive zero-sequence current at the sending end of the tie line.

[0035]

[0036]

[0037] Where, θ is and included angle The three-phase current vector at the sending end of the tie line;

[0038] 3) Based on the three-phase current of the three-phase current transformer at the receiving end of the tie line. and Calculate the zero-sequence current of the tie-line with resistance at the receiving end.

[0039]

[0040]

[0041] in for and included angle The three-phase current vector at the receiving end of the tie line;

[0042] 4) Based on the resistive zero-sequence current at the sending end of the tie line and the resistive zero-sequence current at the receiving end of the tie line Calculate the zero-sequence resistive differential current and braking current

[0043]

[0044]

[0045] 5) When or When this happens, the zero-sequence differential protection will operate, in which case, K is the zero-sequence differential starting current, and K is the zero-sequence differential braking coefficient.

[0046] The operating conditions for zero-sequence differential protection also include:

[0047] The tie-line zero-sequence resistive current differential zero-sequence protection hard plate is activated;

[0048] The tie-line zero-sequence resistive current differential zero-sequence protection soft pressure plate is activated;

[0049] The grounding transformer circuit breaker at the sending end of the connecting line is closed.

[0050] The grounding transformer circuit breaker at the receiving end of the connecting line is closed.

[0051] The grounding transformer zero-sequence differential protection output delay is 0.1s to 20s, where the specific set value is less than the backup set value time of the neutral point zero-sequence overcurrent system.

[0052] This invention is applicable to single-phase grounding protection of lines using tie lines, employing resistive current zero-sequence differential protection. It achieves single-phase grounding protection of tie lines by modifying the protection logic and calculating the differential current. This invention provides accurate fault location with short delay, prevents single-phase grounding from evolving into phase-to-phase faults, and isolates the faulty circuit. Its principle is simple and reliable, conforming to the basic principles of relay protection: reliability, sensitivity, selectivity, and speed.

Claims

1. A method for differential protection of zero-sequence resistive current in inter-station tie lines of a low-resistance grounding system, characterized in that, Includes the following steps: 1) Collect the three-phase current from the three-phase current transformer at the sending end of the tie line. Collect the zero-sequence voltage of the power station bus at the sending end of the interconnection line. Collect the three-phase current of the three-phase current transformer at the receiving end of the tie line. Collect the zero-sequence voltage of the receiving-end substation bus of the interconnection line. ; 2) Based on the three-phase current of the three-phase current transformer at the sending end of the tie line. Calculate the resistive zero-sequence current at the sending end of the tie line. ; 3) Based on the three-phase current of the three-phase current transformer at the receiving end of the tie line. Calculate the zero-sequence current of the tie-line with resistance at the receiving end. ; 4) Based on the resistive zero-sequence current at the sending end of the tie line and the resistive zero-sequence current at the receiving end of the tie line Calculate the zero-sequence resistive differential current and braking current ; 5) When > or > When this happens, the zero-sequence differential protection will operate, in which case, This is the zero-sequence differential starting current. K The zero-sequence differential braking coefficient; Zero-sequence resistive current at the sending end of the tie line for: in, for and included angle The three-phase current vector at the sending end of the tie line; Three-phase current vector at the sending end of the tie line for: Zero-sequence current at the receiving end of the tie line for: in, for and included angle The three-phase current vector at the receiving end of the tie line; Three-phase current vector at the receiving end of the tie line for: Zero-sequence resistive differential current for: Braking current for: 。

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