A method and system for calculating the action boundary of line differential protection

Abstract

The application discloses a line differential protection action boundary calculation method and system. The method comprises the following steps: determining differential current and braking current according to the current on both sides of the outgoing line, and determining the action criterion of the differential protection; constructing a differential protection action boundary function according to a relationship equation group of the differential current and the braking current; analyzing the change attribute of the differential protection action boundary function, and determining the change rule of the change amount in the differential protection action boundary function; and determining the protection rejection area boundary through the change rule according to the differential protection action boundary function, and evaluating the protection action performance. Thus, the correct action boundary of the differential protection of the outgoing line of the new energy station is determined, and the new energy access capacity range of the safe operation of the power grid is evaluated.

Description

Technical Field

[0001] This invention relates to the field of grid-connected protection technology for new energy power sources, and more specifically, to a method and system for calculating the action boundary of line differential protection. Background Technology

[0002] With the introduction of the "dual-carbon" strategic goal, large-scale grid-connected power generation of new energy sources has become an inevitable development trend in my country's energy and power layout to alleviate the increasingly serious energy crisis and environmental pollution. As of July 2021, the national installed power generation capacity reached 2.27 billion kilowatts, of which wind power capacity was 290 million kilowatts, a year-on-year increase of 34.4%, and solar power capacity was 270 million kilowatts, a year-on-year increase of 23.6%. To initially achieve the "dual-carbon goal," it is projected that by 2030, non-fossil energy will account for about 25% of primary energy consumption, and the total installed capacity of wind and solar power will reach over 1.2 billion kilowatts. However, with the continuous expansion of the proportion of new energy transmission systems, their safe operation also faces severe challenges. The coexistence of AC synchronous power sources and nonlinear controlled power sources, and the topological interconnection of three-phase AC networks and two-phase DC networks, have led to a more prominent time-varying characteristic of system faults, and their distribution characteristics are also undergoing fundamental changes.

[0003] The output of renewable energy sources is characterized by fluctuations and randomness, leading to unstable power frequency fault characteristics. Furthermore, since renewable energy power plants typically use power electronic converters connected to the grid, their short-circuit currents exhibit unique characteristics such as limited amplitude, controlled phase angle, and frequency deviation, which are distinctly different from the fault characteristics of synchronous generators. This, in turn, threatens the reliability and sensitivity of traditional power frequency-based relay protection, even posing risks of false alarms and failures to operate. Therefore, it is necessary to propose a calculation method oriented towards the reliability and sensitivity of relay protection actions. This method clarifies the correct operating boundary of differential protection for renewable energy power plant transmission lines, thereby assessing the renewable energy access capacity range for safe grid operation. This has significant engineering implications for high-proportion renewable energy consumption and safe grid operation. Summary of the Invention

[0004] According to the present invention, a method and system for calculating the operating boundary of line differential protection are provided to address the technical problem in the prior art. Because new energy power plants generally use power electronic converters connected to the grid, their short-circuit currents exhibit unique characteristics such as limited amplitude, controlled phase angle, and frequency deviation, which are drastically different from the fault characteristics of synchronous generators. This leads to a threat to the reliability and sensitivity of traditional relay protection based on power frequency quantities, and even the risk of false alarms or failure to operate.

[0005] According to a first aspect of the present invention, a method for calculating the operating boundary of line differential protection is provided, comprising:

[0006] Based on the current on both sides of the transmission line, determine the differential current and the braking current, and determine the operating criteria for the differential protection.

[0007] Based on the set of equations relating the differential current and the braking current, a boundary function for differential protection operation is constructed.

[0008] Analyze the variation properties of the differential protection action boundary function to determine the variation law of the variation quantity in the differential protection action boundary function;

[0009] Based on the differential protection action boundary function, the boundary of the protection failure zone is determined by the change law, and the protection action performance is evaluated.

[0010] Optionally, the differential current and braking current are determined based on the currents on both sides of the transmitting line, including:

[0011] Determine the differential current I d :I d 2 =I W 2 +I S 2 -2I W I S cos(π-θ C )

[0012] Determine the braking current I r :I r 2 =I W 2 +I S 2 -2I W I S cosθ C

[0013] Where θc represents I W with I S The included angle, I W I represents the phase current on the side of the new energy power station. S This represents the phase current on the system side.

[0014] Optionally, the action criteria are determined, including:

[0015] The operating criteria for differential protection are determined based on the starting value, braking coefficient, and braking current.

[0016]

[0017] Among them, I d For differential current, I r For the braking current, respectively satisfy I d =|IW +I S |,I r =|I W –I S |, where I W and I S These are the phase current phasors on the outgoing line station side and the system side, respectively, with the positive direction pointing from the busbar to the line; I op0 is the starting value, and k is the braking coefficient.

[0018] Optionally, based on the relationship equations between the differential current and the braking current, a boundary function for differential protection operation is constructed, including:

[0019] Construct the differential protection action boundary function based on the following formula:

[0020] f(x,θ C ,k)=(1-k 2 )x 2 +(2+2k 2 cosθ C x+(1-k 2 )

[0021] Where x is the phase current I on the power transmission line station side. W and system side phase current I S The short-circuit capacity ratio of the currents on both sides determines the protection operation when the differential protection operation boundary function f(x,θc,k) is greater than zero, and determines the protection failure when the differential protection operation boundary function f(x,θc,k) is less than zero.

[0022] Optionally, the variation properties of the differential protection action boundary function are analyzed to determine the variation law of the variation quantity in the differential protection action boundary function:

[0023] Take the partial derivative of the braking coefficient k of the differential protection action boundary function:

[0024]

[0025] Analysis of the variation law of the braking coefficient k with the differential protection action boundary function: the differential protection action boundary function decreases monotonically as the braking coefficient k increases;

[0026] Take the partial derivative of the angle θc of the differential protection action boundary function:

[0027]

[0028] Analysis of the variation law of variable θc in the differential protection action boundary function: the differential protection action boundary function decreases monotonically as the included angle θc increases.

[0029] Optionally, based on the differential protection action boundary function, the boundary of the protection failure-to-operate region is determined through the variation law, and the protection action performance is evaluated, including:

[0030] Under different braking coefficients k, different possible failure-to-operate boundaries will occur, when the included angle on both sides of the fault phase current satisfies the following equation:

[0031]

[0032] There is a possibility of failure to operate. Based on the short-circuit capacity ratio x, a further verification is performed to determine if failure to operate will occur. The short-circuit capacity ratio will satisfy the following formula:

[0033]

[0034] Within this range, the protection fails to activate;

[0035] When the short-circuit capacity ratio x satisfies the following formula:

[0036]

[0037] Outside this range, the protection system will operate normally and will not refuse to move.

[0038] According to another aspect of the present invention, a line differential protection operation boundary calculation system is also provided, comprising:

[0039] The action criterion module is used to determine the differential current and braking current based on the current on both sides of the transmission line, and to determine the action criteria for the differential protection.

[0040] A boundary function construction module is used to construct the differential protection action boundary function based on the relationship equations between the differential current and the braking current.

[0041] The module for determining the variation pattern is used to analyze the variation attributes of the differential protection action boundary function and determine the variation pattern of the variation quantity in the differential protection action boundary function;

[0042] The performance evaluation module is used to determine the boundary of the protection failure zone based on the variation law of the differential protection action boundary function, and to evaluate the protection action performance.

[0043] Optionally, the action criterion determination module includes:

[0044] The differential current submodule is used to determine the differential current I. d I d 2 =I W 2 +I S 2 -2I WI S cos(π-θ C The braking current submodule is determined for braking current I. r :I r 2 =I W 2 +I S 2 -2I W I S cosθ C

[0045] Where θc represents I W with I S The included angle, I W I represents the phase current on the side of the new energy power station. S This represents the phase current on the system side.

[0046] Optionally, the action criteria are determined, including:

[0047] The action criterion determination submodule is used to determine the action criteria of the differential protection based on the starting value, braking coefficient, and braking current.

[0048]

[0049] Among them, I d For differential current, I r For the braking current, respectively satisfy I d =|I W +I S |,I r =|I W –I S |, where I W and I S These are the phase current phasors on the outgoing line station side and the system side, respectively, with the positive direction pointing from the busbar to the line; I op0 is the starting value, and k is the braking coefficient.

[0050] Optionally, a boundary function module is constructed, including:

[0051] Construct a boundary function submodule to build the differential protection action boundary function according to the following formula:

[0052] f(x,θ C ,k)=(1-k 2 )x 2 +(2+2k 2 cosθ C x+(1-k 2 )

[0053] Where x is the phase current I on the power transmission line station side.W and system side phase current I S The short-circuit capacity ratio of the currents on both sides determines the protection operation when the differential protection operation boundary function f(x,θc,k) is greater than zero, and determines the protection failure when the differential protection operation boundary function f(x,θc,k) is less than zero.

[0054] Optionally, the module for determining the pattern of change includes:

[0055] The derivative braking coefficient submodule is used to calculate the partial derivative of the braking coefficient k of the differential protection action boundary function:

[0056]

[0057] The braking coefficient analysis submodule is used to analyze the variation law of the braking coefficient k with the differential protection action boundary function: the differential protection action boundary function decreases monotonically as the braking coefficient k increases;

[0058] The derivative angle submodule is used to calculate the partial derivative of the angle θc between the differential protection action boundary functions:

[0059]

[0060] An angle analysis submodule is used to analyze the variation law of the included angle θc in the differential protection action boundary function: the differential protection action boundary function monotonically decreases as the included angle θc increases. Optionally, an action performance evaluation module includes:

[0061] The included angle condition submodule is used to determine the possible failure-to-operate boundaries under different braking coefficients k, when the included angle on both sides of the fault phase current satisfies the following formula:

[0062]

[0063] The short-circuit capacity ratio condition-satisfying submodule is used to verify whether there is a possibility of failure to operate, based on the short-circuit capacity ratio x. The short-circuit capacity ratio satisfies the following formula:

[0064]

[0065] The protection failure-to-operate submodule is used to prevent the protection from failing to operate within this range.

[0066] When the short-circuit capacity ratio x satisfies the following formula:

[0067]

[0068] The protection action submodule is used to protect normal actions when outside this range, preventing them from failing to operate.

[0069] Therefore, the operating boundary can be calculated using the formula proposed in this paper, clarifying the correct operating boundary of the differential protection for the transmission lines of renewable energy power plants, and thus assessing the renewable energy access capacity range for safe grid operation. This has significant engineering implications for high-proportion renewable energy consumption and safe grid operation. Attached Figure Description

[0070] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0071] Figure 1 This is a schematic diagram of a method for calculating the operating boundary of line differential protection according to this embodiment;

[0072] Figure 2 This is a schematic diagram illustrating the relationship between differential current and braking current according to this embodiment;

[0073] Figure 3 This is a schematic diagram illustrating the variation law of the variable in the differential protection action boundary function according to this embodiment;

[0074] Figures 4(a) and 4(b) are schematic diagrams of the protection operation and phase angle under different short-circuit capacity ratios according to this embodiment;

[0075] Figure 5 This is a schematic diagram of a line differential protection operation boundary calculation system according to this embodiment. Detailed Implementation

[0076] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0077] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0078] According to a first aspect of the present invention, a method 100 for calculating the operating boundary of line differential protection is provided, with reference to... Figure 1 As shown, the method 100 includes:

[0079] S101: Determine the differential current and braking current based on the current on both sides of the transmission line, and determine the operating criteria for the differential protection.

[0080] S102: Construct the differential protection action boundary function based on the relationship equations between the differential current and the braking current;

[0081] S103: Analyze the changing properties of the differential protection action boundary function, and determine the changing pattern of the changing quantity in the differential protection action boundary function;

[0082] S104: Based on the differential protection action boundary function, determine the protection failure zone boundary through the change law, and evaluate the protection action performance.

[0083] Specifically, the method includes the following steps:

[0084] Step 1: Referring to the differential protection's operating equations, construct a set of equations relating operating and braking based on the parallelogram method;

[0085] Step 2: Derive the equations relating action and braking, and construct the boundary functions for differential protection action;

[0086] Step 3: Analyze the changing properties of the function and clarify the changing patterns of the quantities within the function;

[0087] Step 4: Substitute the protection settings into the function to clarify the boundary of the protection failure zone and evaluate the protection action performance.

[0088] The specific process of step 1 is as follows: For common ratio-controlled current differential protection, its typical operating criterion is as follows:

[0089]

[0090] In the formula: I d For differential current, I r For the braking current, respectively satisfy I d =|I W +I S |,I r =|I W –I S |, where I W and I S These are the phase currents of the same name at the protection installation points on the outgoing line substation side and the system side, respectively, with the positive direction pointing from the busbar to the line; I op0 is the starting value, and k is the braking coefficient, typically ranging from 0.5 to 0.8.

[0091] It is worth noting that I op0 =kI set I setThis is a "start-up" threshold for differential protection, and this value can be set manually. According to the regulations, in zero-sequence differential protection, I... op0 The sensitivity to clearing high-resistance grounding faults should be no less than 1.5; if there is no zero-sequence differential protection, the low-value section I of the phase-current differential protection should be used. op0 The sensitivity to clearing high-resistance grounding faults should be no less than 1.3. If zero-sequence differential protection is available, the low-value segment I of the phase-current differential protection should be provided. op0 The sensitivity for clearing high-resistance grounding faults is not less than 1; simultaneously, the high-value section I of the phase-separated current differential protection... op0 It should reliably avoid the steady-state capacitive current of the line (reliability factor not less than 4).

[0092] After the differential protection "start" threshold is met, i.e., I d >I op0 The formula is true and satisfies the sensitivity requirement, see reference. Figure 2 As shown, according to the parallelogram law, if the sum of two phasors with an included angle greater than 90 degrees is less than their difference, meaning the differential current is less than the braking current, then there is a possibility of failure to operate. Therefore, based on the parallelogram law, the differential current and braking current are expressed using the cosine theorem, where θc represents I. W with I S The included angle. That is:

[0093] I d 2 =I W 2 +I S 2 -2I W I S cos(π-θ C )

[0094] I r 2 =I W 2 +I S 2 -2I W I S cosθ C (2)

[0095] Substituting formula (2) into the protective action equation I of formula (1) d >kI r In this case, assuming the short-circuit capacity ratio of the currents on both sides is 1:x, that is, I... S =xI W The formula holds true; therefore, the protection can operate correctly if the following conditions are met:

[0096]

[0097] The specific process of step 2 is as follows: Substitute formula (2) from step 1 into formula (3), simplify it, and let it be a function with multiple variables, that is:

[0098] f(x,θ C ,k)=(1-k 2 )x 2 +(2+2k 2 cosθ C x+(1-k 2 (4)

[0099] According to formula (4), when the function f(x,θc,k) is greater than 0, it represents protection action; conversely, when f(x,θc,k) is less than zero, it represents protection failure.

[0100] The specific process of step 3 is as follows: Since the short-circuit capacity ratio x is always greater than 0, k∈[0.6,0.8] is always greater than 0, and θc∈(90,180) leads to cosθc∈(0,-1), we take the partial derivative of the function f(x,θc,k) with respect to k, and mainly analyze the effect of variable k on the function:

[0101]

[0102] From formula (5), we can conclude that the function after partial derivative is less than 0, meaning that the function decreases monotonically as k increases. (Refer to...) Figure 3 As shown.

[0103] Similarly, taking the partial derivative of the function f(x,θc,k) with respect to θc, we mainly analyze the effect of the variable θc on the function:

[0104]

[0105] From formula (5), we can conclude that the function after partial derivative is less than 0, meaning that the function decreases monotonically as θc increases. (Refer to...) Figure 3 As shown.

[0106] The specific process of step 4 is as follows: In order to maximize the obtained protection failure area, the braking coefficient k is taken as 0.8 and θc = 180 degrees is substituted into the function to obtain the maximum area of ​​f(x,θc,k)<0, which is the maximum false operation area of ​​the protection. At this time, x = 9, that is, the short-circuit capacity ratio is 1:9. Therefore, it can be known that when the short-circuit capacity ratio is greater than 1:9, the function f(x,θc,k)>0, that is, the protection can definitely operate correctly.

[0107] During application, the braking coefficient k of different protection devices may vary. Therefore, to evaluate the operating performance of the protection device, it is necessary to substitute the actual k value of the device to be estimated into function (4). At this time, function (4) is the relationship between the short-circuit capacity ratio and the phase angle difference. Then, substitute the actual short-circuit capacity ratio into the function to obtain the value of the phase angle difference. Finally, determine whether the protection will fail to operate. The specific expression is as follows:

[0108] Under different braking coefficients k, different possible failure-to-operate boundaries will occur, when the phase angle difference on both sides of the fault phase current satisfies the following equation:

[0109]

[0110] At this point, there is a possibility of failure to operate, and it is necessary to verify again whether failure to operate will occur based on the actual short-circuit capacity ratio x. The short-circuit capacity ratio satisfies the following formula:

[0111]

[0112] That is, within this range, the protection will fail to activate.

[0113] When the short-circuit capacity ratio satisfies the following formula:

[0114]

[0115] That is, outside this range, the protection can operate normally and will not fail to operate. Taking a new energy transmission system as an example, the proposed method is verified.

[0116] Referring to Figure 4(a), which shows the operation and phase angle when the short-circuit capacity ratio is 1:1.28 and k = 0.8, theoretical calculations show that substituting the short-circuit capacity ratio boundary of 1:1.28 and k = 0.8 into the proposed function yields an angle of 103 degrees. It can be seen that the phase angle difference between the fault currents on both sides of fault phase B is approximately 50 degrees, less than 103 degrees, meaning it will not fail to operate; the phase angle difference between the fault currents on both sides of fault phase C is approximately 114.6 degrees, greater than 103 degrees, meaning the protection will fail to operate. Conversely, according to theoretical calculations, the short-circuit capacity ratio boundary at 114.6 degrees is 1:3.5, while the short-circuit capacity ratio at this time is 1:1.28, which is less than 1:3.5. Therefore, it will fail to operate, consistent with the theoretical analysis.

[0117] Referring to Figure 4(b), which shows the operation and phase angle when the short-circuit capacity ratio is 1:12.7 and k = 0.8, the phase angle difference of the fault current on both sides of fault phase B is approximately 42 degrees, which is less than 103 degrees, meaning it will not fail to operate. The phase angle difference of the fault current on both sides of fault phase C is approximately 104 degrees, which is greater than 103 degrees, but since the short-circuit capacity ratio is 1:12.7 and 12.7 is greater than 9, it will not fail to operate, consistent with the theoretical analysis.

[0118] Therefore, the operating boundary can be calculated using the formula proposed in this paper, clarifying the correct operating boundary of the differential protection for the transmission lines of renewable energy power plants, and thus assessing the renewable energy access capacity range for safe grid operation. This has significant engineering implications for high-proportion renewable energy consumption and safe grid operation.

[0119] Optionally, the differential current and braking current are determined based on the currents on both sides of the transmitting line, including:

[0120] Determine the differential current I d :I d 2 =I W 2 +I S 2 -2I W I S cos(π-θ C )

[0121] Determine the braking current I r :I r 2 =I W 2 +I S 2 -2I W I S cosθ C

[0122] Where θc represents I W with I S The included angle, I W I represents the phase current on the side of the new energy power station. S This represents the phase current on the system side.

[0123] Optionally, the action criteria are determined, including:

[0124] The operating criteria for differential protection are determined based on the starting value, braking coefficient, and braking current.

[0125]

[0126] Among them, I d For differential current, I r For the braking current, respectively satisfy I d =|I W +I S |,I r =|I W –I S |, where I W and I S These are the phase current phasors on the outgoing line station side and the system side, respectively, with the positive direction pointing from the busbar to the line; Iop0 is the starting value, and k is the braking coefficient.

[0127] Optionally, based on the relationship equations between the differential current and the braking current, a boundary function for differential protection operation is constructed, including:

[0128] Construct the differential protection action boundary function based on the following formula:

[0129] f(x,θ C ,k)=(1-k 2 )x 2 +(2+2k 2 cosθ C x+(1-k 2 )

[0130] Where x is the phase current I on the power transmission line station side. W and system side phase current I S The short-circuit capacity ratio of the currents on both sides determines the protection operation when the differential protection operation boundary function f(x,θc,k) is greater than zero, and determines the protection failure when the differential protection operation boundary function f(x,θc,k) is less than zero.

[0131] Optionally, the variation properties of the differential protection action boundary function are analyzed to determine the variation law of the variation quantity in the differential protection action boundary function:

[0132] Take the partial derivative of the braking coefficient k of the differential protection action boundary function:

[0133]

[0134] Analysis of the variation law of the braking coefficient k with the differential protection action boundary function: the differential protection action boundary function decreases monotonically as the braking coefficient k increases;

[0135] Take the partial derivative of the angle θc of the differential protection action boundary function:

[0136]

[0137] Analysis of the variation law of variable θc in the differential protection action boundary function: the differential protection action boundary function decreases monotonically as the included angle θc increases.

[0138] Optionally, based on the differential protection action boundary function, the boundary of the protection failure-to-operate region is determined through the variation law, and the protection action performance is evaluated, including:

[0139] Under different braking coefficients k, different possible failure-to-operate boundaries will occur, when the included angle on both sides of the fault phase current satisfies the following equation:

[0140]

[0141] There is a possibility of failure to operate. Based on the short-circuit capacity ratio x, a further verification is performed to determine if failure to operate will occur. The short-circuit capacity ratio will satisfy the following formula:

[0142]

[0143] Within this range, the protection fails to activate;

[0144] When the short-circuit capacity ratio x satisfies the following formula:

[0145]

[0146] Outside this range, the protection system will operate normally and will not refuse to move.

[0147] Therefore, the operating boundary can be calculated using the formula proposed in this paper, clarifying the correct operating boundary of the differential protection for the transmission lines of renewable energy power plants, and thus assessing the renewable energy access capacity range for safe grid operation. This has significant engineering implications for high-proportion renewable energy consumption and safe grid operation.

[0148] According to another aspect of the invention, reference Figure 5 As shown, a line differential protection operation boundary calculation system 500 is also provided, which includes:

[0149] The action criterion module 510 is used to determine the differential current and braking current based on the current on both sides of the transmission line, and to determine the action criterion of the differential protection.

[0150] The boundary function construction module 520 is used to construct the differential protection action boundary function based on the relationship equations between the differential current and the braking current.

[0151] The module 530 for determining the change pattern is used to analyze the change attributes of the differential protection action boundary function and determine the change pattern of the change quantity in the differential protection action boundary function.

[0152] The performance evaluation module 540 is used to determine the boundary of the protection failure zone based on the variation law of the differential protection action boundary function, and to evaluate the protection action performance.

[0153] Optionally, the action determination criterion module 510 includes:

[0154] The differential current submodule is used to determine the differential current I. d I d 2 =I W 2 +I S 2 -2IW I S cos(π-θ C )

[0155] Determine the braking current submodule, used for braking current I r :I r 2 =I W 2 +I S 2 -2I W I S cosθ C

[0156] Where θc represents I W with I S The included angle, I W I represents the phase current on the side of the new energy power station. S This represents the phase current on the system side.

[0157] Optionally, the action determination criterion module 510 includes:

[0158] The action criterion determination submodule is used to determine the action criteria of the differential protection based on the starting value, braking coefficient, and braking current.

[0159]

[0160] Among them, I d For differential current, I r For the braking current, respectively satisfy I d =|I W +I S |,I r =|I W –I S |, where I W and I S These are the phase current phasors on the outgoing line station side and the system side, respectively, with the positive direction pointing from the busbar to the line; I op0 is the starting value, and k is the braking coefficient.

[0161] Optionally, the boundary function module 520 is constructed, including:

[0162] Construct a boundary function submodule to build the differential protection action boundary function according to the following formula:

[0163] f(x,θ C ,k)=(1-k 2 )x 2 +(2+2k 2 cosθ C x+(1-k 2 )

[0164] Where x is the phase current I on the power transmission line station side. W and system side phase current I S The short-circuit capacity ratio of the currents on both sides determines the protection operation when the differential protection operation boundary function f(x,θc,k) is greater than zero, and determines the protection failure when the differential protection operation boundary function f(x,θc,k) is less than zero.

[0165] Optionally, the module 530 for determining the pattern of change includes:

[0166] The derivative braking coefficient submodule is used to calculate the partial derivative of the braking coefficient k of the differential protection action boundary function:

[0167]

[0168] The braking coefficient analysis submodule is used to analyze the variation law of the braking coefficient k with the differential protection action boundary function: the differential protection action boundary function decreases monotonically as the braking coefficient k increases;

[0169] The derivative angle submodule is used to calculate the partial derivative of the angle θc between the differential protection action boundary functions:

[0170]

[0171] The angle analysis submodule is used to analyze the variation law of the included angle θc in the differential protection action boundary function: the differential protection action boundary function decreases monotonically as the included angle θc increases.

[0172] Optionally, the motion performance evaluation module 540 includes:

[0173] The included angle condition submodule is used to determine the possible failure-to-operate boundaries under different braking coefficients k, when the included angle on both sides of the fault phase current satisfies the following formula:

[0174]

[0175] The short-circuit capacity ratio condition-satisfying submodule is used to verify whether there is a possibility of failure to operate, based on the short-circuit capacity ratio x. The short-circuit capacity ratio satisfies the following formula:

[0176]

[0177] The protection failure-to-operate submodule is used to prevent the protection from failing to operate within this range.

[0178] When the short-circuit capacity ratio x satisfies the following formula:

[0179]

[0180] The protection action submodule is used to protect normal actions when outside this range, preventing them from failing to operate.

[0181] The line differential protection action boundary calculation system 500 of one embodiment of the present invention corresponds to the line differential protection action boundary calculation method 100 of another embodiment of the present invention, and will not be described again here.

[0182] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0183] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0184] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0185] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1The steps of the function specified in one or more boxes.

[0186] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0187] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A method for calculating the operating boundary of line differential protection, characterized in that, include: Based on the current on both sides of the transmission line, determine the differential current and the braking current, and determine the operating criteria for the differential protection. Based on the set of equations relating the differential current and the braking current, a boundary function for differential protection operation is constructed. Analyze the variation properties of the differential protection action boundary function to determine the variation law of the variation quantity in the differential protection action boundary function; Based on the differential protection action boundary function, the boundary of the protection failure-to-operate region is determined through the change law, and the protection action performance is evaluated; characterized in that, based on the current on both sides of the sending line, the differential current and the braking current are determined, including: Determine the differential current I d : Determine the braking current I r : in, θc express I W and I S The included angle, I W This indicates the phase current on the side of the new energy power station. I S Indicates the phase current on the system side; Based on the relationship equations between the differential current and the braking current, the differential protection operation boundary function is constructed, including: Construct the differential protection action boundary function based on the following formula: in, x For the phase current of the sending line station side I W and system-side phase current I S The short-circuit capacity ratio of the currents on both sides, when the differential protection operates within the boundary function... f ( x,θc , k When the value is greater than zero, the protection action is determined. When the boundary function of the differential protection action is greater than zero, the protection action is determined. f ( x,θc , k When the value is less than zero, protection is deemed to be inactive.

2. The method according to claim 1, characterized in that, Determine the action criteria, including: The operating criteria for differential protection are determined based on the starting value, braking coefficient, and braking current. in, I d For differential current, I r For the braking current, respectively satisfy the following conditions: I d =| I W + I S |, I r =| I W – I S |, among which I W and I S These are the phase current phasors on the sending line and the system side, respectively, with the positive direction pointing from the bus to the line. I op0 This is the starting value. k This is the braking coefficient.

3. According to the method described in claim 1, analyze the changing properties of the differential protection action boundary function to determine the changing pattern of the variable in the differential protection action boundary function: Braking coefficient of the differential protection action boundary function k Find the partial derivative: Analysis of braking coefficient k The variation law of the differential protection action boundary function: The differential protection action boundary function changes with the braking coefficient. k The increase of is monotonically decreasing; The angle between the differential protection action boundary function and the angle between the differential protection action boundary function and the differential protection action boundary function. θc Find the partial derivative: Analysis variables θc The variation law of the differential protection action boundary function: the differential protection action boundary function changes with the included angle θc The increase is monotonically decreasing.

4. The method according to claim 1, characterized in that, Based on the differential protection action boundary function, the boundary of the protection failure zone is determined through the variation law, and the protection action performance is evaluated, including: At different braking coefficients k Different possible failure-to-operate boundaries will occur when the angle between the two sides of the fault phase current satisfies the following formula: There is a possibility of failure to operate, based on the aforementioned short-circuit capacity ratio. x The verification of whether it will fail to operate is performed again, and the short-circuit capacity ratio satisfies the following formula: Within this range, the protection fails to activate; When the short-circuit capacity ratio x Satisfy the following formula: Outside this range, the protection system will operate normally and will not refuse to move.

5. A line differential protection operation boundary calculation system, characterized in that, include: The action criterion module is used to determine the differential current and braking current based on the current on both sides of the transmission line, and to determine the action criteria for the differential protection. A boundary function construction module is used to construct the differential protection action boundary function based on the relationship equations between the differential current and the braking current. The module for determining the variation pattern is used to analyze the variation attributes of the differential protection action boundary function and determine the variation pattern of the variation quantity in the differential protection action boundary function; The performance evaluation module is used to determine the boundary of the protection failure zone based on the differential protection action boundary function and the change law, and to evaluate the protection action performance. The action criterion determination module includes: The differential current submodule is used to determine the differential current. I d Determine the braking current submodule, used for braking current. I r : in, θc express I W and I S The included angle, I W This indicates the phase current on the side of the new energy power station. I S Indicates the phase current on the system side; The boundary function module is constructed, including: Construct a boundary function submodule to build the differential protection action boundary function according to the following formula: in, x For the phase current of the sending line station side I W and system-side phase current I S The short-circuit capacity ratio of the currents on both sides, when the differential protection operates within the boundary function... f ( x,θc , k When the value is greater than zero, the protection action is determined. When the boundary function of the differential protection action is greater than zero, the protection action is determined. f ( x,θc , k When the value is less than zero, protection is deemed to be inactive.

6. The system according to claim 5, the action determination criterion module includes: The action criterion determination submodule is used to determine the action criteria of the differential protection based on the starting value, braking coefficient, and braking current. in, I d For differential current, I r For the braking current, respectively satisfy the following conditions: I d =| I W + I S |, I r =| I W – I S |, among which I W and I S These are the phase current phasors on the sending line and the system side, respectively, with the positive direction pointing from the bus to the line. I op0 This is the starting value. k This is the braking coefficient.

7. The system according to claim 6, characterized in that, The module for determining the pattern of change includes: The derivative braking coefficient submodule is used to calculate the braking coefficient of the differential protection action boundary function. k Find the partial derivative: The braking coefficient analysis submodule is used to analyze the braking coefficient. k The variation law of the differential protection action boundary function: The differential protection action boundary function changes with the braking coefficient. k The increase of is monotonically decreasing; The derivative angle submodule is used to calculate the angle of the differential protection action boundary function. θc Find the partial derivative: The included angle analysis submodule is used to analyze included angles. θc The variation law of the differential protection action boundary function: the differential protection action boundary function changes with the included angle θc The increase is monotonically decreasing.

8. The system according to claim 7, characterized in that, The motion performance evaluation module includes: The included angle condition submodule is used to determine the possible failure-to-operate boundaries under different braking coefficients k, when the included angle on both sides of the fault phase current satisfies the following formula: The short-circuit capacity ratio condition-satisfying submodule is used to verify whether there is a possibility of failure to operate, based on the short-circuit capacity ratio x. The short-circuit capacity ratio satisfies the following formula: The protection failure-to-operate submodule is used to prevent the protection from failing to operate within this range. When the short-circuit capacity ratio x satisfies the following formula: The protection action submodule is used to protect normal actions when outside this range, preventing them from failing to operate.

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