Double-pole fault line selection and type identification method for double-circuit direct-current lines on same tower

Abstract

The invention relates to the technical field of high-voltage direct-current power transmission, and discloses a same-tower double-circuit direct-current line bipolar fault line selection and type identification method, which comprises the following steps of: decoupling differential current of each pole line to obtain modulus current of each pole line, and identifying a fault line according to a ratio between moduli; bipolar fault line selection can be carried out only by collecting the current of each polar line, and the result is accurate and reliable. Compared with a conventional fault line selection method, a criterion adopts a ratio mode, a setting value is larger, and the influence of transition resistance is small; whether the fault type is a line touch fault can be identified according to the voltage variation of the fault line selection; compared with an existing fault line selection method, the fault line selection method not only can identify whether a bipolar line fault occurs, but also can further identify whether the fault type is a single-circuit direct current bipolar line fault or a double-circuit direct current touch line fault. According to the method, a same-tower double-circuit direct current line protection system is supplemented and perfected, the problem of same-tower double-circuit direct current line collision fault identification is solved, and reliable operation of same-tower double-circuit direct current is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of high-voltage direct current transmission, and in particular to a method for selecting and identifying bipolar fault lines and types of double-circuit direct current lines on the same tower. Background Art

[0002] High-voltage direct current transmission technology is widely used in large-capacity transmission projects due to its advantages such as long transmission distance, low transmission loss and convenient control. With the increasing demand for electricity, the transmission capacity of the power system is constantly increasing, and the land for transmission lines is becoming increasingly tight. Limited by the resources of the transmission corridor, many projects use multiple DC lines on the same tower. Compared with conventional single-circuit lines, multiple DC lines on the same tower can greatly reduce the land occupation area and save transmission corridors, improve the utilization rate of line channels, and reduce construction costs.

[0003] As an important part of the DC transmission system, DC lines frequently fail due to long distances, high voltage levels, and harsh transmission environments. The installation of double-circuit DC lines on the same tower increases the complexity of the transmission line, resulting in an increase in the probability of failure and an increase in the number of fault types. In addition to conventional single-circuit DC line faults, the electrical distance between the conductors installed on the same tower is small. Under the influence of external factors such as strong wind disturbances and short circuits of foreign objects, line-touching faults between the two DC lines may also occur, causing a strong impact on the system. Therefore, it is necessary to study the fault characteristics and protection algorithms of double-circuit DC lines on the same tower to ensure the safe and reliable operation of the system. At present, the DC line fault selection criterion can only identify single-circuit DC line faults, and cannot reliably distinguish between single-circuit DC bipolar faults and double-circuit DC line-touching faults. Therefore, it is urgent to propose a line selection and identification method for bipolar faults in double-circuit DC lines on the same tower. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a method for selecting and identifying bipolar fault lines in a double-circuit DC line on the same tower, which can quickly and reliably identify single-circuit DC bipolar faults and double-circuit DC line-touching faults, and solve the existing fault line selection problem of double-circuit lines on the same tower. The technical solution is as follows: A method for selecting and identifying bipolar fault lines and types of double-circuit DC lines on the same tower comprises the following steps: Step 1: Obtain the rectifier-side current and inverter-side current of the quadrupole line in the double-circuit DC line on the same tower; Step 2: Calculate the differential current of each pole line, that is, subtract the inverter side current from the rectifier side current to obtain the differential current of each pole line; Step 3: Decouple and transform the differential current of each pole line to obtain the mode components of the differential current of each pole line, including the ground mode component, the first line mode component, the second line mode component and the third line mode component; Step 4: Calculate the ratios of the first line mode component, the second line mode component and the third line mode component to the ground mode component respectively; Step 5: Take the extreme value of the ratio of each modulus component within the time interval and multiply it by the reliability coefficient Obtaining fault characteristic quantities, and constructing a criterion according to the values ​​of the fault characteristic quantities to identify the faulty line; Step 6: According to the fault line selection result, calculate the absolute value of the voltage change of the corresponding fault line, and determine the fault type according to the absolute value of the voltage change.

[0005] Furthermore, in step 1, the four-pole circuits are represented by 1P, 1N, 2P and 2N, respectively, 1P and 1N are the positive and negative poles of the first circuit, 2P and 2N are the positive and negative poles of the second circuit, respectively; the currents at both ends are represented by subscripts and express, Represents the rectifier side, represents the inverter side; the current on the rectifier side of the four-pole line is expressed as: , , and , the inverter side current is expressed as: , , and ; The differential current of each pole line in step 2 is expressed as , , and ; ; In step 3, the ground mode component, the first line mode component, the second line mode component and the third line mode component are respectively , , and Indicates; specifically: ; The ratio of each modulus component in step 4 is: ; In step 5, multiply the reliability coefficient The fault characteristics obtained are: , and ; According to the value of the fault characteristic quantity, the judgment criteria for identifying the faulty line are as follows: like K 2m >1. K 3m <-1 and -1< K 1m <1, then 1N2P fault; like K 2m >1. K 3m >1 and -1< K 1m <1, then 1P2N fault; like K 2m >1. K 1m >1 and -1< K 3m <1, then 1P1N fault; like K 2m >1. K 1m <-1 and -1< K 3m <1, then 2P2N fault; like K 3m >1. K 1m >1 and -1< K 2m <1, then 1P2P fault; like K 3m <-1, K 1m >1 and -1< K 2m <1, then 1N2N fault.

[0006] Furthermore, in step 6, the absolute value of the voltage change of each fault line is calculated as follows: ; in, is the absolute value of the voltage change of each fault line, X =1 or 2, Y = P or N ; is the instantaneous value of the voltage of each fault line at time t; That is the time of voltage change; If the voltage change , it is a positive and negative line contact fault; If the voltage change , it is a same-pole contact fault; If the voltage change , it is a non-line-touching bipolar fault.

[0007] The beneficial effects of the present invention are: 1. The present invention decouples the differential current of each pole line to obtain the modulus current of each pole line, and identifies the fault line according to the ratio between the moduli.

[0008] 2. The present invention only needs to collect the current of each pole line to perform bipolar fault line selection, and the result is accurate and reliable.

[0009] 3. Compared with the conventional fault line selection method, the present invention adopts a ratio method as the criterion, has a larger setting value, and is less affected by the transition resistance.

[0010] 4. The present invention identifies whether the fault type is a line-touching fault based on the voltage change of the fault line selection. Compared with the existing fault line selection method, it can not only identify whether a bipolar fault occurs, but also further identify whether the fault type is a single-circuit DC bipolar line fault or a double-circuit DC line-touching fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a topological diagram of a double-circuit DC line on the same tower provided by an embodiment of the present invention, where SVG (Static Var Generator) is a static var generator.

[0012] Figure 2 This is a diagram showing the arrangement of double-circuit DC lines on the same tower provided in an embodiment of the present invention.

[0013] Figure 3 A flow chart of a method for bipolar fault line selection and type identification for a double-circuit DC line on the same tower provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0015] like Figure 1 Taking the topology diagram of the double-circuit DC line on the same tower (transmission system) as an example, simulation and verification are performed on PSCAD. According to the fault line selection method provided by the present invention, a fault line selection criterion model is built. It includes a differential current calculation module, a differential current modulus component calculation module, and a differential current modulus component ratio module. Set any two-pole lines in the double-circuit DC to have a ground fault or a line-touching fault, and record the results output by the fault line selection model.

[0016] like Figure 2 The figure shows the arrangement diagram of the double-circuit DC lines on the same tower provided by the present invention. The arrangement of the two-circuit DC lines takes into account the ideal rectangular balanced arrangement, and the decoupling transformation is performed through the decoupling matrix of the parallel four-wire system. The decoupling transformation matrix is ​​as follows: .

[0017] like Figure 3The figure shows a flow chart of a method for selecting and identifying bipolar fault lines and types of double-circuit DC lines on the same tower proposed by the present invention, comprising: (1) Obtain the rectifier-side current and inverter-side current of the four-pole line in the double-circuit DC line on the same tower.

[0018] The four-pole circuits are represented by 1P, 1N, 2P and 2N, 1P and 1N are the positive and negative poles of the first circuit, 2P and 2N are the positive and negative poles of the second circuit, respectively; the currents at both ends are represented by subscripts and express, Represents the rectifier side, represents the inverter side; the current on the rectifier side of the four-pole line is expressed as: , , and , the inverter side current is expressed as: , , and .

[0019] (2) Calculate the differential current of each pole line, that is, subtract the inverter side current from the rectifier side current to obtain the differential current of each pole line. The differential current of the four pole lines is expressed as , , and : .

[0020] (3) Decouple the differential current of each pole line and calculate the modulus component of the differential current of each pole line. Each modulus component is expressed as , , and The subscripts 0, 1, 2, and 3 correspond to the ground mode component, the first line mode component, the second line mode component, and the third line mode component, respectively: .

[0021] (4) Calculate the ratios of the first line mode component, the second line mode component and the third line mode component to the ground mode component respectively: ; in, K 1 is the ratio of the absolute value of the first line mode component to the ground mode component, K 2 is the ratio of the absolute value of the second line mode component to the ground mode component, K 3 It is the ratio of the absolute value of the third line mode component to the ground mode component.

[0022] (5) Take the extreme value of the modulus component ratio within the time interval and multiply it by the reliability coefficient The fault characteristic quantity is obtained and the fault line is identified according to the calculation result.

[0023] To avoid measurement errors that may cause the ratio of the corresponding modulus components of the non-fault line to be much greater than the set value, resulting in malfunction, the ratio result is multiplied by the reliability coefficient , in this embodiment, 0.8 is taken to ensure the reliability of the action.

[0024] K 2m >1. K 3m <-1 and -1< K 1m <1: 1N2P fault; K 2m >1. K 3m >1 and -1< K 1m <1, then 1P2N fault; K 2m >1. K 1m >1 and -1< K 3m <1, then 1P1N fault; K 2m >1. K 1m <-1 and -1< K 3m <1, then 2P2N fault; K 3m >1. K 1m >1 and -1< K 2m <1, then 1P2P fault; K 3m <-1, K 1m >1 and -1< K 2m <1, then 1N2N fault.

[0025] The modulus ratios and fault line selection results are shown in Table 1.

[0026] Table 1 Fault line selection criteria and fault line selection results .

[0027] (6) Based on the fault line selection results, calculate the absolute value of the fault line voltage change : ; in, is the absolute value of the voltage change of each fault line, X =1 or 2, Y = P or N ; is the instantaneous value of the voltage of each fault line at time t; That is, the time of voltage change; in this embodiment Take 10ms, that is, the voltage change is the current voltage minus the voltage 10 milliseconds ago.

[0028] According to the absolute value of the voltage change of the fault line Determine the fault type: If the selected lines all meet the absolute value of the voltage change , positive and negative line touching fault; If the selected lines all meet the absolute value of the voltage change , same-pole contact fault; If the selected lines all meet the absolute value of the voltage change , non-touch-line bipolar fault; Among them, pu is the unit of per unit value and is dimensionless.

[0029] According to the fault line selection and similar identification method provided by the present invention, a line contact fault and an inter-pole short circuit fault are set, and the results of the fault pole selection and type identification model output are recorded, as shown in Table 2 below.

[0030] Table 2 Results of fault selection and type identification model output .

[0031] In summary, the bipolar fault line selection and type identification method for the double-circuit DC line on the same tower provided by the present invention obtains the modulus current of each pole line by decoupling the differential current of each pole line, and identifies the fault line according to the ratio between each modulus. Only by collecting the current of each pole line, bipolar fault line selection can be performed, and the result is accurate and reliable. Compared with the existing fault line selection method, it can not only identify whether a bipolar fault occurs, but also further identify whether the fault type is a single-circuit DC bipolar line fault or a double-circuit DC line-touching fault.

Claims

1. A method for selecting and identifying bipolar fault lines and types of double-circuit DC lines on the same tower, characterized in that: The following steps are involved: Step 1: Obtain the rectifier-side current and inverter-side current of the quadrupole line in the double-circuit DC line on the same tower; Step 2: Calculate the differential current of each pole line, that is, subtract the inverter side current from the rectifier side current to obtain the differential current of each pole line; Step 3: Decouple and transform the differential current of each pole line to obtain the mode components of the differential current of each pole line, including the ground mode component, the first line mode component, the second line mode component and the third line mode component; Step 4: Calculate the ratios of the first line mode component, the second line mode component and the third line mode component to the ground mode component respectively; Step 5: Take the extreme value of the ratio of each modulus component within the time interval and multiply it by the reliability coefficient Obtaining fault characteristic quantities, and constructing a criterion according to the values ​​of the fault characteristic quantities to identify the faulty line; Step 6: According to the fault line selection result, calculate the absolute value of the voltage change of the corresponding fault line, and determine the fault type according to the absolute value of the voltage change.

2. A method for selecting and identifying bipolar fault lines and types of double-circuit DC lines on the same tower according to claim 1, characterized in that: In step 1, the four-pole circuits are represented by 1P, 1N, 2P and 2N, respectively. 1P and 1N are the positive and negative poles of the first circuit, respectively, and 2P and 2N are the positive and negative poles of the second circuit, respectively. The currents at both ends are represented by subscripts and express, Represents the rectifier side, represents the inverter side; the current on the rectifier side of the four-pole line is expressed as: , , and , the inverter side current is expressed as: , , and ; In step 2, the differential current of each pole line is expressed as , , and ; ； In step 3, the ground mode component, the first line mode component, the second line mode component and the third line mode component are respectively , , and Indicates; specifically: ； In step 4, the ratio of each mode component is: ； In step 5, multiply by the reliability coefficient The fault characteristics obtained are: K 1m , K 2m and K 3m ; According to the value of the fault characteristic quantity, the judgment criteria for identifying the faulty line are as follows: like K 2m >1. K 3m <-1 and -1< K 1m <1, then 1N2P fault; like K 2m >1. K 3m >1 and -1< K 1m <1, then 1P2N fault; like K 2m >1. K 1m >1 and -1< K 3m <1, then 1P1N fault; like K 2m >1. K 1m <-1 and -1< K 3m <1, then 2P2N fault; like K 3m >1. K 1m >1 and -1< K 2m <1, then 1P2P fault; like K 3m <-1, K 1m >1 and -1< K 2m <1, then 1N2N fault.

3. The method for selecting and identifying bipolar fault lines and types of double-circuit DC lines on the same tower according to claim 1 is characterized in that: In step 6, the absolute value of the voltage change of each fault line is calculated as follows: ； in, is the absolute value of the voltage change of each fault line, X =1 or 2, Y = P or N ; is the instantaneous value of the voltage of each fault line at time t; That is the time of voltage change; If the voltage change , it is a positive and negative line contact fault; If the voltage change , it is a same-pole contact fault; If the voltage change , it is a non-line-touching bipolar fault.

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