New energy transmission line single-ended grounding protection method and system

Abstract

The invention discloses a new energy sending-out line single-terminal grounding protection method and system, and the method comprises the steps: obtaining a voltage instantaneous value and a current instantaneous value at a protection installation part, and the line length of a setting point, calculating the differential of the voltage and zero-sequence current of the setting point, forming a new energy sending-out line single-terminal grounding protection criterion through the calculation of a correlation coefficient, and obtaining a new energy sending-out line single-terminal grounding protection criterion. The judgment module judges whether a fault point is in the area; the new energy sending-out line single-ended grounding protection method and system using the sampling values to form time domain correlation discrimination are not affected by short-circuit current amplitude limitation, non-power-frequency frequency and phase angle control after rapid adjustment of power electronic equipment, and can effectively solve the problem of transient overrun after the new energy sending-out line is grounded through a transition resistor.

Description

Technical Field

[0001] The present invention relates to the field of relay protection for power transmission lines, and more specifically, to a single-ended grounding protection method and system for a new energy transmission line. Background Art

[0002] With the continuous advancement of power technology, the power electronics characteristics of today's power grid are becoming more and more obvious, and the fault characteristics of the protected objects are undergoing fundamental changes. my country's energy cleanliness rate and terminal electrification rate will exceed 50%. With the implementation of my country's clean energy strategy and the rapid promotion of new energy, DC transmission, flexible AC transmission and other technologies, power electronic equipment accounts for an increasingly large proportion in the power grid. The rapid adjustment performance of power electronic equipment makes the AC short-circuit current present new fault characteristics such as limited amplitude, non-power frequency frequency, and controlled phase angle, which brings greater uncertainty to traditional power frequency protection. The sensitivity verification work is complicated, which is a difficult problem that needs to be solved urgently in the field of relay protection.

[0003] Prior art document 1 (CN118472889A) discloses a large-scale new energy AC transmission line protection method and system. This technical document is based on the line protection principle of two-terminal quantities, uses positive-sequence, negative-sequence and zero-sequence currents to form differential protection elements, does not have a phase selection function, and any fault protection three-phase tripping.

[0004] Prior art document 2 (CN116526432A) discloses a time domain distance protection method and system for a new energy transmission line. The document is based on the distance protection principle of ranging type and does not consider the influence of the transition resistance of the fault point. Summary of the invention

[0005] In order to overcome at least one of the defects of the above-mentioned prior art, the present invention provides a single-ended grounding protection method and system for a new energy transmission line. By obtaining the instantaneous voltage and current values ​​at the protection installation location and the line length of the setting point, the setting point voltage u can be calculated. Y , and the differential of the zero-sequence current i'0, by calculating u Y The correlation coefficient of i'0 constitutes the single-ended grounding protection criterion for the new energy transmission line, which is used to determine whether the fault point is within the area.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a single-ended grounding protection method and system for a new energy transmission line, characterized in that it includes the following steps:

[0007] Step 1, obtaining the instantaneous value of three-phase voltage, instantaneous value of current and instantaneous value of zero-sequence current at the protection installation location;

[0008] Step 2, calculating the set point voltage according to the instantaneous values ​​of voltage and current obtained in step 1 and the line length of the set point;

[0009] Step 3, calculating the differential of the zero-sequence current according to the instantaneous value of the zero-sequence current;

[0010] Step 4, calculating the correlation coefficient between the set point voltage and the zero sequence current differential;

[0011] Step 5: determine the fault condition according to whether the correlation coefficient obtained in step 4 satisfies the time domain correlation criterion, and perform protection for the fault.

[0012] Preferably, the set point voltage in step 2 can be expressed by formula (1), which is as follows:

[0013]

[0014] Where: Indicates three phases A, B, and C; is the set point voltage; 3i 0m They are the instantaneous values ​​of phase voltage, phase current and zero-sequence current measured at the protection installation; Len set is the line length of the set point; K L and K R They are the zero-sequence inductance compensation coefficient and the zero-sequence resistance compensation coefficient respectively; L1 is the positive-sequence inductance per unit length; R1 is the positive-sequence resistance per unit length.

[0015] Preferably, the zero-sequence inductance compensation coefficient K L It can be expressed by formula (2), as follows:

[0016] K L =(L0-L1) / 3L1 (2)

[0017] Where: L0 is the zero-sequence inductance per unit length, and L1 is the positive-sequence inductance per unit length.

[0018] Preferably, the zero-sequence resistance compensation coefficient K R It can be expressed by formula (3), as follows:

[0019] K R =(R0-R1) / 3R1 (3)

[0020] Where R0 is the zero-sequence resistance per unit length, and R1 is the positive-sequence resistance per unit length.

[0021] Preferably, the differential of the zero-sequence current in step 3 can be expressed by equation (4), as follows:

[0022]

[0023] Wherein: i'0 is the zero-sequence current differential value; i0 is the zero-sequence current obtained in step S1.

[0024] In step 4, the correlation coefficient between the set point voltage and the zero-sequence current differential can be expressed by equation (5), as follows:

[0025]

[0026] Where: ρ is the correlation coefficient, u Yi is the set point voltage at the i-th point; i' 0i is the differential value of the zero-sequence current at the i-th point; δ is the safety margin.

[0027] Preferably, in step 5, judging the fault condition according to whether the correlation coefficient satisfies the time domain correlation criterion is specifically:

[0028] If the time domain correlation criterion is met, it is determined that an in-zone fault has occurred and the protection device is activated.

[0029] Preferably, if the time domain correlation criterion is not met, it is determined that an out-of-zone fault has occurred, the protection device does not operate, and the backup protection is activated.

[0030] Preferably, the time domain correlation criterion in step 5 can be expressed by formula (7), which is as follows:

[0031] ρ<-sinδ (7)

[0032] Where ρ is the correlation coefficient and δ is the safety margin.

[0033] Compared with the prior art, the present invention has the following characteristics: the technical solution of the present invention is different from the power frequency vector protection principle widely used in the prior art. Instead, the voltage u of the set point can be calculated by obtaining the instantaneous value of the voltage and current at the protection installation location and the line length of the set point. Y , using the differential of zero-sequence current i'0, by calculating u Y The correlation coefficient of i'0 constitutes the single-ended grounding protection criterion for the new energy transmission line, which is used to determine whether the fault point is within the area;

[0034] The present invention utilizes instantaneous values ​​of voltage and current to form a single-ended grounding protection method and system for new energy transmission lines for time domain correlation judgment. The method and system are not affected by the limited amplitude of short-circuit current after rapid adjustment of power electronic equipment, the non-industrial frequency, and the controlled phase angle, and can effectively solve the transient overrun problem of the new energy transmission line after grounding through a transition resistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of a circuit system in an embodiment of the present invention;

[0036] Figure 2 Schematic diagram of the method flow in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0038] Figure 1 Schematic diagram of the line system in an embodiment of the present invention. Taking the case where the protection device is installed on the M side as an example, F1 is an in-zone fault, K is a setting point, and F2 is an out-of-zone fault protected by the M side.

[0039] The first embodiment of the present invention provides a single-ended grounding protection method and system for a new energy transmission line. Figure 2 As shown, the following steps are included:

[0040] Step 1: Obtain the instantaneous values ​​of three-phase voltage, current and zero-sequence current at the protection installation location;

[0041] Step 2: Calculate the set point voltage based on the instantaneous values ​​of voltage and current obtained in step 1 and the line length of the set point. The set point voltage equation can be expressed by formula (1), as follows:

[0042]

[0043] Where: Indicates three phases A, B, and C; is the set point voltage; 3i 0m They are the instantaneous values ​​of phase voltage, phase current and zero-sequence current measured at the protection installation; Len set is the line length of the set point; K L , K R is the zero-sequence compensation coefficient; L1 is the positive-sequence inductance per unit length; R1 is the positive-sequence resistance per unit length.

[0044] The zero sequence compensation coefficient K L , K R It can be expressed by formula (2) and formula (3), as follows:

[0045] K L =(L0-L1) / 3L1 (2)

[0046] K R =(R0-R1) / 3R1 (3)

[0047] Where: L0 is the zero-sequence inductance per unit length, L1 is the positive-sequence inductance per unit length, R0 is the zero-sequence resistance per unit length, and R1 is the positive-sequence resistance per unit length.

[0048] As a prominent substantive feature of the present invention and one of the significant advances it brings to the prior art, the present invention takes into account the influence of the transition resistance at the fault point and effectively solves the transient overrun problem of the new energy transmission line after being grounded through the transition resistance.

[0049] Step 3, calculate the differential of the zero-sequence current according to the instantaneous value of the zero-sequence current. The calculated differential value of the zero-sequence current can be expressed by formula (4), as follows:

[0050]

[0051] Where: i'0 is the zero-sequence current differential value; i0 is the zero-sequence current obtained in step 1.

[0052] In this embodiment, the differential is replaced by the difference.

[0053] Step 4, calculate the correlation coefficient between the set point voltage and the zero sequence current differential, and judge whether the action condition is met according to the correlation coefficient; the correlation coefficient between the set point voltage and the zero sequence current differential can be expressed by formula (5), as follows:

[0054]

[0055] Where: ρ is the correlation coefficient, u Yi is the set point voltage at the i-th point; i' 0i is the differential value of the zero-sequence current at the i-th point; n is the number of sampling points.

[0056] The number of sampling points n can be expressed by formula (6), as follows:

[0057] n=fT (6)

[0058] Where: f is the sampling rate, T is the sampling time.

[0059] Step 5, determine whether the correlation coefficient obtained in step 4 meets the time domain correlation criterion. If it does, it is determined that an internal fault has occurred and the protection device is activated. If it does not, it is determined that an external fault has occurred, the protection device does not operate, and the backup protection is activated. The time domain correlation criterion can be expressed by formula (7), as follows:

[0060] ρ<-sinδ (7)

[0061] Where δ is the safety margin and ρ is the correlation coefficient.

[0062] In the present invention, the sampling rate can be 1200 Hz, the sampling time T can be 0.01S or 0.02S, n can be 12 or 24, Δt when calculating the differential is 0.000833S, the nth point is the current sampling point, n-1 is the previous point of the current sampling point, and so on. The safety margin δ can be 12°.

[0063] by Figure 1 For example, the protection is installed on the M side, K is the setting point, when a fault occurs at point F1, the correlation coefficient ρ satisfies the formula in step 4, and the protection device is activated; when a fault occurs at point F2, the correlation coefficient does not satisfy the formula in step 4, the protection device does not operate, and the backup protection is activated.

[0064] As one of the outstanding substantive features of the present invention and a significant improvement over the prior art, the instantaneous values ​​of voltage and current are used to form a single-ended grounding protection for new energy transmission lines for time domain correlation judgment, phase calculation, and phase selection function. In addition, the present invention uses single-ended data to form protection criteria, without the need for a communication channel.

[0065] A second embodiment of the present invention provides a single-ended grounding protection system for a new energy transmission line, comprising:

[0066] Data acquisition module, used to obtain the instantaneous values ​​of three-phase voltage, current and zero-sequence current at the protection installation;

[0067] A set point voltage calculation module is used to calculate the set point voltage;

[0068] Current differential module, used to calculate the differential value of zero-sequence current;

[0069] A correlation coefficient calculation module is used to calculate the correlation coefficient according to the set point voltage and zero sequence current differential;

[0070] The fault protection module is used to determine the fault type and perform protection according to the correlation coefficient criterion.

[0071] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A single-ended grounding protection method for a new energy transmission line, characterized in that: The following steps are included: Step 1, obtaining the instantaneous value of three-phase voltage, instantaneous value of current and instantaneous value of zero-sequence current at the protection installation location; Step 2, calculating the set point voltage according to the instantaneous values ​​of voltage and current obtained in step 1 and the line length of the set point; Step 3, calculating the differential of the zero-sequence current according to the instantaneous value of the zero-sequence current; Step 4, calculating the correlation coefficient between the set point voltage and the zero sequence current differential; Step 5: determine the fault condition according to whether the correlation coefficient obtained in step 4 satisfies the time domain correlation criterion, and perform protection for the fault.

2. A single-ended grounding protection method for a new energy transmission line according to claim 1, characterized in that: The set point voltage in step 2 can be expressed by formula (1), as follows: Where: Indicates three phases A, B, and C; is the set point voltage; 3i 0m They are the instantaneous values ​​of phase voltage, phase current and zero-sequence current measured at the protection installation; Len set is the line length of the set point; K L and K R They are the zero-sequence inductance compensation coefficient and the zero-sequence resistance compensation coefficient respectively; L1 is the positive-sequence inductance per unit length; R1 is the positive-sequence resistance per unit length.

3. A single-ended grounding protection method for a new energy transmission line according to claim 2, characterized in that: Zero-sequence inductance compensation coefficient K L It can be expressed by formula (2), as follows: K L =(L0-L1) / 3L1 (2) Where: L0 is the zero-sequence inductance per unit length, L1 is the positive-sequence inductance per unit length.

4. A single-ended grounding protection method for a new energy transmission line according to claim 2, characterized in that: Zero sequence resistance compensation coefficient K R It can be expressed by formula (3), as follows: K R =(R0-R1) / 3R1 (3) Where R0 is the zero-sequence resistance per unit length, and R1 is the positive-sequence resistance per unit length.

5. A single-ended grounding protection method for a new energy transmission line according to claim 1, characterized in that: The differential of the zero-sequence current in step 3 can be expressed by equation (4), as follows: Where: i'0 is the zero-sequence current differential value; i0 is the zero-sequence current obtained in step 1.

6. A single-ended grounding protection method for a new energy transmission line according to claim 1, characterized in that: The correlation coefficient in step 4 can be expressed by formula (5), as follows: Where: ρ is the correlation coefficient, u Yi is the set point voltage at the i-th point; i' 0i is the differential value of the zero-sequence current at the i-th point, and n is the number of sampling points.

7. A single-ended grounding protection method for a new energy transmission line according to claim 1, characterized in that: In step 5, the fault condition is judged according to whether the correlation coefficient meets the time domain correlation criterion: If the correlation coefficient meets the time domain correlation criterion, it is judged that an in-zone fault has occurred and the protection device is activated.

8. A single-ended grounding protection method for a new energy transmission line according to claim 7, characterized in that: If the correlation coefficient does not meet the time domain correlation criterion, it is judged that an out-of-zone fault has occurred, the protection device does not operate, and the backup protection is activated.

9. A single-ended grounding protection method for a new energy transmission line according to claim 7, characterized in that: The time domain correlation criterion in step 5 can be expressed by equation (7), as follows: ρ<-sinδ (7) Where ρ is the correlation coefficient and δ is the safety margin.

10. A single-ended grounding protection system for a new energy transmission line, operating a single-ended grounding protection method for a new energy transmission line as claimed in any one of claims 1 to 9, characterized in that: include: Data acquisition module, used to obtain the instantaneous values ​​of three-phase voltage, current and zero-sequence current at the protection installation; A set point voltage calculation module is used to calculate the set point voltage; Current differential module, used to calculate the differential value of zero-sequence current; A correlation coefficient calculation module is used to calculate the correlation coefficient according to the set point voltage and zero sequence current differential; The fault protection module is used to determine the fault type and perform protection according to the correlation coefficient criterion.

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