Compound ratio differential verification method and apparatus under multi-distributed new energy connected to feeder line

Abstract

A compound ratio differential verification method and apparatus under multi-distributed new energy connected to a feeder line. The method comprises ratio differential protection speed verification, ratio differential protection reliability and stability verification, and ratio differential protection sensitivity verification; acquiring a transfer error δ caused by CT saturation of a fault branch, if the formula is formula (I), passing the verification, or otherwise, not passing the verification; and acquiring the proportion of a current flowing out of a bus to the total fault current as Ext, if the formula is formula (II), passing the verification, or otherwise, not passing the verification.

Description

Multiple distributed renewable energy access feeder duplex ratio differential calibration method and device Technical Field

[0001] The present invention belongs to the technical field of power system relay protection, and in particular relates to a method and device for duplex ratio differential calibration under feeder access of multiple distributed renewable energy sources. Background Art

[0002] Traditional distribution systems are mostly single-source radial networks. Even if they are structurally closed-loop networks, they often operate in an open-loop mode, with both power flow and fault currents exhibiting unidirectional flow. Therefore, traditional distribution network protection configurations are relatively simple, and three-stage current protection can meet these requirements. However, the integration of distributed generation (DG) has transformed the distribution network structure, transforming it into an active network. In this new active distribution network architecture, the magnitude and direction of power flow and fault currents are uncertain, posing significant challenges to the sensitivity and selectivity of traditional three-stage current protection. In this new landscape, research is urgently needed on new busbar compound ratio differential protection methods tailored to the characteristics of active distribution networks. Compared to other protection principles, current differential protection is more adaptable to complex fault conditions such as power system oscillations and asymmetric short circuits, and is unaffected by voltage transformer disconnections, making it widely used in power systems. In principle, current differential protection offers absolute selectivity and is currently one of the most effective approaches to addressing these emerging protection challenges in active distribution networks.

[0003] When verifying the busbar differential protection ratio on-site, two branches are typically used for a load test. The specific method is: select two branches with the same transformation ratio on busbar I and apply current I1 of equal magnitude and opposite direction to a specific phase. Then, select a branch with the same transformation ratio on busbar II and apply current I2 to a specific phase. The current magnitude is adjusted to activate the busbar II differential protection. The applied current is recorded to verify the maximum differential ratio coefficient. Verifying the busbar differential ratio for multiple branches is challenging for on-site technicians. Under certain conditions, such as in real-world operations, setting up multiple-branch busbar differential ratio verification is time-consuming.

[0004] The existing patent ZL201310038256.7, titled: A high-precision electrical signal measurement device and method, mainly provides the compensation identification and control measurement method of electrical signals, but does not provide the calculation and identification method of busbar compound ratio differential; patent ZL201610945569.4, titled: An arc protection device and its fault diagnosis method, also collects the corresponding voltage and current signals to prepare the arc fault diagnosis method, but does not involve the calculation and identification method of busbar compound ratio differential.

[0005] At present, unbalanced currents often appear in the lines, which makes it difficult to balance the sensitivity, speed and stability of the bus differential protection. At the same time, the bus differential protection logic is highly complex. The existing bus duplex ratio differential protection logic verification is highly complex and prone to errors. For example, for the ratio verification of more than two branches, it is necessary to consider factors such as the primary current balance, secondary current balance and reference ratio conversion of the added branches. On-site test personnel are usually very short of time. If calculations and verifications are not clearly performed, it is often difficult to obtain the correct differential action results, which delays the on-site inspection time, reduces work efficiency and quality, compresses the time for loops, logic and other work, and lays the foundation for potential power grid safety risks.

[0006] Therefore, how to overcome the shortcomings of the existing technology is an urgent problem to be solved in the field of power system relay protection technology.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to solve the shortcomings of the existing technology and overcome the problems of high complexity and easy error in the logic verification of the existing busbar duplex ratio differential protection. A method and device for duplex ratio differential verification under the access of multiple distributed renewable energy feeders is provided to provide on-site technicians with a ratio differential verification method for fast multi-branch access.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] The duplex ratio differential verification method for multiple distributed renewable energy feeders includes the ratio differential protection speed verification, the ratio differential protection reliability and stability verification, and the ratio differential protection sensitivity verification. Specifically:

[0011] Step 1: Calculate the theoretical compound ratio Kr; collect the actual compound ratio setting value Kr';

[0012] Step 2: The speed check of the ratio differential protection is as follows: compare Kr with the actual compound ratio setting value Kr'. If Kr is equal to the actual compound ratio setting value Kr', the speed check is judged to have passed; if Kr is greater than or less than the actual compound ratio setting value Kr', the speed check is judged to have failed.

[0013] Step 3: Ratio differential protection reliability and stability check: obtain the transmission error δ caused by CT saturation of the fault branch, and then perform reliability and stability check. If δ / (2-2δ)≤Kr, the check passes; otherwise, the check fails.

[0014] Step 4: The sensitivity check of the ratio differential protection is as follows: obtain the ratio of the current flowing out of the busbar to the total fault current Ext, and then perform a sensitivity check. If 1 / (Ext) ≤ Kr, the sensitivity check passes; otherwise, the check fails.

[0015] Step 5: If any step fails the verification in the second, third and fourth steps, you need to return to the first step and recalculate the compound ratio Kr. If the second, third and fourth steps all pass the verification, it is considered that the ratio differential verification has passed.

[0016] Furthermore, when verifying the reliability and stability of the ratio differential protection, it is necessary to simulate the fault conditions outside the busbar area. The specific method is as follows:

[0017] 1) Select two branches with the same transformation ratio on the same busbar, and add a phase current to these two branches at the same time. The currents are equal in magnitude but opposite in direction.

[0018] 2) The busbar differential protection should not operate;

[0019] 3) The large differential current and small differential current should be equal to zero.

[0020] Furthermore, when performing sensitivity verification of the ratio differential protection, it is necessary to simulate the fault conditions in the busbar area. The specific method includes the following steps:

[0021] Step (1), verify the differential threshold setting:

[0022] a) Select a branch on the busbar and add a certain current to a phase in this branch. The current value is greater than the differential threshold value;

[0023] b) The busbar differential protection should operate instantaneously, cutting off the busbar coupler and all branches on the busbar where the branch is located, and the busbar differential action signal light should light up;

[0024] Step (2), verify the high value of the differential ratio coefficient:

[0025] a) The busbar tie breaker is closed;

[0026] b) Select any two branches on busbar I with the same transformation ratio and add currents in opposite directions to one phase;

[0027] c) Select a branch with the same transformation ratio on bus II, add current to a phase, and adjust the current to make bus II differential operation;

[0028] d) Record the applied current and verify the high value coefficient of the differential ratio;

[0029] Step (3), verify the low value of the differential ratio coefficient:

[0030] a) The bus tie breaker is disconnected;

[0031] b) Select any two branches on busbar I with the same transformation ratio and add currents in opposite directions to one phase;

[0032] c) Select a branch with the same transformation ratio on bus II, add current to a phase, and adjust the current to make bus II differential operation;

[0033] d) Record the applied current and verify the low value coefficient of the differential ratio;

[0034] Step (4), verify the small difference ratio coefficient:

[0035] a) Select two branches with the same transformation ratio on the same busbar and add currents with opposite directions and different magnitudes to a certain phase;

[0036] b) Fix the current in one branch and adjust the current in the other branch to make the busbar differential operate;

[0037] c) Record the applied current and verify the small difference ratio coefficient.

[0038] Furthermore, in step (2), the specific method for verifying the high value coefficient of the differential ratio is:

[0039] The high value coefficient of the differential ratio is Id is the operating current of the differential protection. At this time, the calculation method of Id is: after the busbar is connected, the sum of the current vectors of all branches except the busbar is equal; I r is the braking current, which is the sum of the absolute values ​​of all branches;

[0040] Among them, S n Indicates L n Current transformer ratio of the branch; I L2 , I L3 , I L4 ...I Ln is the secondary current of each corresponding branch; I Lx The current added to the Lx branch during differential operation; S represents the base transformation ratio;

[0041] If the equation holds, the verification is successful.

[0042] Furthermore, in step (3), the specific method for verifying the low value coefficient of the differential ratio is:

[0043] The low value coefficient of the differential ratio is Id is the operating current of the differential protection. At this time, the calculation method of Id is: after the busbar is disconnected, the sum of the current vectors of all branches on the busbar; I r is the braking current, which is the sum of the absolute values ​​of all branches; If the equation holds, the verification is successful.

[0044] Furthermore, in step (4), the specific method for verifying the small difference ratio coefficient is:

[0045] k x Indicates the small difference ratio coefficient, Id is the operating current of the differential protection; at this time, the calculation method of Id is: the sum of the current vectors of all branches on I bus or II bus, I r is the braking current, which is the sum of the absolute values ​​of all branches of mother I or mother II; If the equation holds, the verification is successful.

[0046] Furthermore, when checking the sensitivity of the ratio differential protection, it is also necessary to simulate the fault conditions in the busbar area during the double busbar switching operation. The specific method is as follows:

[0047] 1) Select any branch on a busbar and close the I and II switches of the branch;

[0048] 2) A single-phase current is loaded in this branch, and the current value is greater than the differential threshold value;

[0049] 3) The busbar differential protection should operate instantaneously to cut off all branches on the busbar and the busbar;

[0050] 4) The I and II mother differential action signal lights are on.

[0051] Furthermore, in the fourth step, the value range of δ is greater than or equal to 1.5 and less than or equal to 3.

[0052] Furthermore, in the fourth step, δ is set to 2.

[0053] The present invention also provides a multiple-distributed new energy access feeder line compound ratio differential calibration device, which adopts the multiple-distributed new energy access feeder line compound ratio differential calibration method, including:

[0054] The acquisition module is used to collect the actual compound ratio setting value Kr', the transmission error δ caused by the CT saturation of the fault branch, and the ratio of the current flowing out of the bus to the total fault current Ext;

[0055] The first processing module is connected to the acquisition module and is used to calculate the theoretical compound ratio Kr, and then perform a speed check of the ratio differential protection, comparing Kr with the actual compound ratio setting value Kr'. If Kr is equal to the actual compound ratio setting value Kr', it is determined that the speed check has passed; if Kr is greater than or less than the actual compound ratio setting value Kr', it is determined that the speed check has failed;

[0056] The second processing module is connected to the acquisition module and is used to perform reliability and stability verification. If δ / (2-2δ)≤Kr, the verification passes; otherwise, the verification fails.

[0057] The third processing module is connected to the acquisition module and is used to perform sensitivity verification. If 1 / (Ext) ≥ Kr, the sensitivity verification passes; otherwise, the verification fails.

[0058] The display processing module is connected to the acquisition module, the first processing module, the second processing module, and the third processing module respectively, and is used to display the verification results; if any verification fails, it is necessary to return to the acquisition module for collection and re-perform subsequent verification; if all verifications pass, it is considered that the ratio differential verification has passed.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] Typically, on-site verification of bus differential ratios and differential protection involves no more than three branches. In certain environments, multiple branches are required for bus differential element ratio verification, often requiring technicians to spend considerable time calculating. This method, however, first balances the primary current values ​​of each branch and then converts and adds the secondary current values. This approach is clear and less confusing, saving significant verification time. By calculating and verifying the differential current and braking current of multi-branch duplex differential protection, work efficiency is improved, test lines are reduced, and grid security risks are mitigated. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a wiring diagram of a multiple-distributed renewable energy feeder access duplex ratio differential calibration method;

[0062] Figure 2 is a diagram showing the operating characteristics of a compound ratio differential element;

[0063] Figure 3 is a logic diagram of the current in each loop when a branch circuit fails;

[0064] Figure 4 is a logic diagram of the current in each branch when a busbar fails;

[0065] FIG5 is a schematic diagram of the structure of a multiple-distributed new energy access feeder duplex ratio differential calibration device. DETAILED DESCRIPTION

[0066] The present invention is described in further detail below with reference to the embodiments.

[0067] Those skilled in the art will understand that the following examples are intended to illustrate the present invention only and should not be construed as limiting the scope of the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in the art or in the product specifications were used. Materials or equipment used without manufacturer identification are commercially available conventional products.

[0068] Example 1

[0069] The duplex ratio differential verification method for multiple distributed renewable energy feeders includes the ratio differential protection speed verification, the ratio differential protection reliability and stability verification, and the ratio differential protection sensitivity verification. Specifically:

[0070] Step 1: Calculate the theoretical compound ratio Kr; collect the actual compound ratio setting value Kr';

[0071] Step 2: The speed check of the ratio differential protection is as follows: compare Kr with the actual compound ratio setting value Kr'. If Kr is equal to the actual compound ratio setting value Kr', the speed check is judged to have passed; if Kr is greater than or less than the actual compound ratio setting value Kr', the speed check is judged to have failed.

[0072] Step 3: Ratio differential protection reliability and stability check: obtain the transmission error δ caused by CT saturation of the fault branch, and then perform reliability and stability check. If δ / (2-2δ)≤Kr, the check passes; otherwise, the check fails.

[0073] Step 4: The sensitivity check of the ratio differential protection is as follows: obtain the ratio of the current flowing out of the busbar to the total fault current Ext, and then perform a sensitivity check. If 1 / (Ext) ≤ Kr, the sensitivity check passes; otherwise, the check fails.

[0074] Step 5: If any step fails the verification in the second, third and fourth steps, you need to return to the first step and recalculate the compound ratio Kr. If the second, third and fourth steps all pass the verification, it is considered that the ratio differential verification has passed.

[0075] Example 2

[0076] The duplex ratio differential verification method for multiple distributed renewable energy feeders includes the ratio differential protection speed verification, the ratio differential protection reliability and stability verification, and the ratio differential protection sensitivity verification. Specifically:

[0077] Step 1: Calculate the theoretical compound ratio Kr; collect the actual compound ratio setting value Kr';

[0078] Step 2: The speed check of the ratio differential protection is as follows: compare Kr with the actual compound ratio setting value Kr'. If Kr is equal to the actual compound ratio setting value Kr', the speed check is judged to have passed; if Kr is greater than or less than the actual compound ratio setting value Kr', the speed check is judged to have failed.

[0079] Step 3: Ratio differential protection reliability and stability check: obtain the transmission error δ caused by CT saturation of the fault branch, and then perform reliability and stability check. If δ / (2-2δ)≤Kr, the check passes; otherwise, the check fails.

[0080] Step 4: The sensitivity check of the ratio differential protection is as follows: obtain the ratio of the current flowing out of the busbar to the total fault current Ext, and then perform a sensitivity check. If 1 / (Ext) ≤ Kr, the sensitivity check passes; otherwise, the check fails.

[0081] Step 5: If any step fails the verification in the second, third and fourth steps, you need to return to the first step and recalculate the compound ratio Kr. If the second, third and fourth steps all pass the verification, it is considered that the ratio differential verification has passed.

[0082] When verifying the reliability and stability of the ratio differential protection, it is necessary to simulate the fault conditions outside the busbar area. The specific method is as follows:

[0083] 1) Select two branches with the same transformation ratio on the same busbar, and add a phase current to these two branches at the same time. The currents are equal in magnitude but opposite in direction.

[0084] 2) The busbar differential protection should not operate;

[0085] 3) The large differential current and small differential current should be equal to zero.

[0086] When checking the sensitivity of the ratio differential protection, it is necessary to simulate the fault conditions in the busbar area. The specific method includes the following steps:

[0087] Step (1), verify the differential threshold setting:

[0088] a) Select a branch on the busbar and add a certain current to a phase in this branch. The current value is greater than the differential threshold value;

[0089] b) The busbar differential protection should operate instantaneously, cutting off the busbar coupler and all branches on the busbar where the branch is located, and the busbar differential action signal light should light up;

[0090] Step (2), verify the high value of the differential ratio coefficient:

[0091] a) The busbar tie breaker is closed;

[0092] b) Select any two branches on busbar I with the same transformation ratio and add currents in opposite directions to one phase;

[0093] c) Select a branch with the same transformation ratio on bus II, add current to a phase, and adjust the current to make bus II differential operation;

[0094] d) Record the applied current and verify the high value coefficient of the differential ratio;

[0095] Step (3), verify the low value of the differential ratio coefficient:

[0096] a) The bus tie breaker is disconnected;

[0097] b) Select any two branches on busbar I with the same transformation ratio and add currents in opposite directions to one phase;

[0098] c) Select a branch with the same transformation ratio on bus II, add current to a phase, and adjust the current to make bus II differential operation;

[0099] d) Record the applied current and verify the low value coefficient of the differential ratio;

[0100] Step (4), verify the small difference ratio coefficient:

[0101] a) Select two branches with the same transformation ratio on the same busbar and add currents with opposite directions and different magnitudes to a certain phase;

[0102] b) Fix the current in one branch and adjust the current in the other branch to make the busbar differential operate;

[0103] c) Record the applied current and verify the small difference ratio coefficient.

[0104] In step (2), the specific method for verifying the high value coefficient of the differential ratio is:

[0105] The high value coefficient of the differential ratio is Id is the operating current of the differential protection. At this time, the calculation method of Id is: after the busbar is connected, the sum of the current vectors of all branches except the busbar is equal; I r is the braking current, which is the sum of the absolute values ​​of all branches;

[0106] Among them, S n Indicates L n Current transformer ratio of the branch; I L2 , I L3 , I L4 ...I Ln is the secondary current of each corresponding branch; I Lx The current added to the Lx branch during differential operation; S represents the base transformation ratio;

[0107] If the equation holds, the verification is successful.

[0108] In step (3), the specific method for verifying the low value coefficient of the differential ratio is:

[0109] The low value coefficient of the differential ratio is Id is the operating current of the differential protection. At this time, the calculation method of Id is: after the busbar is disconnected, the sum of the current vectors of all branches on the busbar; I r is the braking current, which is the sum of the absolute values ​​of all branches; If the equation holds, the verification is successful.

[0110] In step (4), the specific method for verifying the small difference ratio coefficient is:

[0111] k x Indicates the small difference ratio coefficient, Id is the operating current of the differential protection; at this time, the calculation method of Id is: the sum of the current vectors of all branches on I bus or II bus, I r is the braking current, which is the sum of the absolute values ​​of all branches of mother I or mother II; If the equation holds, the verification is successful.

[0112] When checking the sensitivity of the ratio differential protection, it is also necessary to simulate the fault conditions in the busbar area during the double busbar switching operation. The specific method is as follows:

[0113] 1) Select any branch on a busbar and close the I and II switches of the branch;

[0114] 2) A single-phase current is loaded in this branch, and the current value is greater than the differential threshold value;

[0115] 3) The busbar differential protection should operate instantaneously to cut off all branches on the busbar and the busbar;

[0116] 4) The I and II mother differential action signal lights are on.

[0117] Example 3

[0118] The duplex ratio differential verification method for multiple distributed renewable energy feeders includes the ratio differential protection speed verification, the ratio differential protection reliability and stability verification, and the ratio differential protection sensitivity verification. Specifically:

[0119] Step 1: Calculate the theoretical compound ratio Kr; collect the actual compound ratio setting value Kr';

[0120] Step 2: The speed check of the ratio differential protection is as follows: compare Kr with the actual compound ratio setting value Kr'. If Kr is equal to the actual compound ratio setting value Kr', the speed check is judged to have passed; if Kr is greater than or less than the actual compound ratio setting value Kr', the speed check is judged to have failed.

[0121] Step 3: Ratio differential protection reliability and stability check: obtain the transmission error δ caused by CT saturation of the fault branch, and then perform reliability and stability check. If δ / (2-2δ)≤Kr, the check passes; otherwise, the check fails.

[0122] Step 4: The sensitivity check of the ratio differential protection is as follows: obtain the ratio of the current flowing out of the busbar to the total fault current Ext, and then perform a sensitivity check. If 1 / (Ex)t≤K, the sensitivity check passes; otherwise, the check fails.

[0123] Step 5: If any step fails the verification in the second, third and fourth steps, you need to return to the first step and recalculate the compound ratio Kr. If the second, third and fourth steps all pass the verification, it is considered that the ratio differential verification has passed.

[0124] When verifying the reliability and stability of the ratio differential protection, it is necessary to simulate the fault conditions outside the busbar area. The specific method is as follows:

[0125] 1) Select two branches with the same transformation ratio on the same busbar, and add a phase current to these two branches at the same time. The currents are equal in magnitude but opposite in direction.

[0126] 2) The busbar differential protection should not operate;

[0127] 3) The large differential current and small differential current should be equal to zero.

[0128] When checking the sensitivity of the ratio differential protection, it is necessary to simulate the fault conditions in the busbar area. The specific method includes the following steps:

[0129] Step (1), verify the differential threshold setting:

[0130] a) Select a branch on the busbar and add a certain current to a phase in this branch. The current value is greater than the differential threshold value;

[0131] b) The busbar differential protection should operate instantaneously, cutting off the busbar coupler and all branches on the busbar where the branch is located, and the busbar differential action signal light should light up;

[0132] Step (2), verify the high value of the differential ratio coefficient:

[0133] a) The busbar tie breaker is closed;

[0134] b) Select any two branches on busbar I with the same transformation ratio and add currents in opposite directions to one phase;

[0135] c) Select a branch with the same transformation ratio on bus II, add current to a phase, and adjust the current to make bus II differential operation;

[0136] d) Record the applied current and verify the high value coefficient of the differential ratio;

[0137] Step (3), verify the low value of the differential ratio coefficient:

[0138] a) The bus tie breaker is disconnected;

[0139] b) Select any two branches on busbar I with the same transformation ratio and add currents in opposite directions to one phase;

[0140] c) Select a branch with the same transformation ratio on bus II, add current to a phase, and adjust the current to make bus II differential operation;

[0141] d) Record the applied current and verify the low value coefficient of the differential ratio;

[0142] Step (4), verify the small difference ratio coefficient:

[0143] a) Select two branches with the same transformation ratio on the same busbar and add currents with opposite directions and different magnitudes to a certain phase;

[0144] b) Fix the current in one branch and adjust the current in the other branch to make the busbar differential operate;

[0145] c) Record the applied current and verify the small difference ratio coefficient.

[0146] In step (2), the specific method for verifying the high value coefficient of the differential ratio is:

[0147] The high value coefficient of the differential ratio is Id is the operating current of the differential protection. At this time, the calculation method of Id is: after the busbar is connected, the sum of the current vectors of all branches except the busbar is equal; I r is the braking current, which is the sum of the absolute values ​​of all branches;

[0148] Among them, S n Indicates the current transformer ratio of the Ln branch; I L2 , I L3 , I L4 ...I Ln is the secondary current of each corresponding branch; I Lx The current added to the Lx branch during differential operation; S represents the base transformation ratio;

[0149] If the equation holds, the verification is successful.

[0150] In step (3), the specific method for verifying the low value coefficient of the differential ratio is:

[0151] The low value coefficient of the differential ratio is Id is the operating current of the differential protection. At this time, the calculation method of Id is: after the busbar is disconnected, the sum of the current vectors of all branches on the busbar; I r is the braking current, which is the sum of the absolute values ​​of all branches; If the equation holds, the verification is successful.

[0152] In step (4), the specific method for verifying the small difference ratio coefficient is:

[0153] k xIndicates the small difference ratio coefficient, Id is the operating current of the differential protection; at this time, the calculation method of Id is: the sum of the current vectors of all branches on I bus or II bus, I r is the braking current, which is the sum of the absolute values ​​of all branches of mother I or mother II; If the equation holds, the verification is successful.

[0154] In the fourth step, the value range of δ is greater than or equal to 1.5 and less than or equal to 3. Preferably, the value of δ is 2.

[0155] As shown in FIG5 , a multiple-distributed renewable energy access feeder duplex ratio differential calibration device adopts the multiple-distributed renewable energy access feeder duplex ratio differential calibration method described above, including:

[0156] The acquisition module 101 is used to collect the actual compound ratio setting value Kr', the transmission error δ caused by the CT saturation of the fault branch, and the ratio of the current flowing out of the bus to the total fault current Ext;

[0157] The first processing module 102 is connected to the acquisition module 101 and is used to calculate the theoretical compound ratio Kr and then perform a speed check of the ratio differential protection. The calculation result is compared with the actual compound ratio setting value Kr'. If Kr is equal to the actual compound ratio setting value Kr', the speed check is judged to have passed. If Kr is greater than or less than the actual compound ratio setting value Kr', the speed check is judged to have failed.

[0158] The second processing module 103 is connected to the acquisition module 101 and is used to perform reliability and stability verification. If δ / (2-2δ)≤Kr, the verification passes; otherwise, the verification fails.

[0159] The third processing module 104 is connected to the acquisition module 101 and is used to perform sensitivity verification. If 1 / (Ex)t≥K, the sensitivity verification passes; otherwise, the verification fails.

[0160] The display processing module 105 is connected to the acquisition module 101, the first processing module 102, the second processing module 103, and the third processing module 104 respectively, and is used to display the verification results. If any verification fails, it is necessary to return to the acquisition module 101 for collection and re-perform subsequent verification. If all the verifications pass, it is considered that the ratio differential verification has passed.

[0161] Example 4

[0162] The present invention provides a compound ratio differential verification method for multiple distributed renewable energy feeder accesses. The method mainly verifies the four properties of the protection device: selectivity, sensitivity, reliability and stability, and speed. Since differential protection is inherently selective and has been achieved by existing technologies, the verification method proposed in the present invention has three key indicators: verification of the compound ratio (the slope Kr of the boundary line between the action zone and the braking zone, as shown in Figure 2, which assesses the speed of the ratio differential protection), avoidance of the transmission error δ caused by saturation of the fault branch CT (i.e., reliability and stability verification of the ratio differential protection), and the ratio of the outgoing bus fault current to the total bus current Ext (i.e., sensitivity verification of the ratio differential protection).

[0163] The following is a detailed introduction to the verification methods for these three key indicators:

[0164] A. Calculation of multi-branch compound ratio braking ratio:

[0165] For the verification of the large difference ratio of the multi-branch busbar compound ratio differential, select one of the two busbar branches Lx as the differential branch with an initial current value of 0A. Then, take all the remaining branches on the two busbars, the branch flowing out of the busbar as a whole as Im, and the branch flowing into the busbar as a whole as In, and make the secondary current amplitudes of the outflowing Im and In equal. Finally, add the secondary current to the Lx branch until the protection differential action light lights up. At this time, the secondary current added is the action current Id of the differential protection, and |Im|+|In|+|Ix| is used as the secondary braking current Ir of the differential protection. Among them, Ix represents the newly added current value of a phase. This current value is a vector. The large difference ratio can be calculated by the secondary current value added to Lx. If the large difference ratio is known, the secondary current value that should be added to Lx can also be calculated, as follows:

[0166] 1) As shown in Figure 1, assuming that the branch current flowing out of the bus is positive, that is, 0 degrees; the branch current flowing into the bus is negative, that is, 180 degrees, when Ix is not applied. The bus-coupled branch current flows from I bus to II bus, and the secondary current value of each branch before conversion satisfies formula (1). When Ix is applied. The bus-coupled branch current flows from I bus to II bus, and the secondary current value of each branch before conversion satisfies formula (2), as follows: I m ∠0°=I n ∠180° (1)

[0167] Where:

[0168] Branch L1 is a double busbar connection line, and branches L2, L3, L4, and Ln are feeder branches for distributed photovoltaic access. Branch Lx is the branch for test application. L2, I L3 , I L4 ...I Ln is the secondary current of each corresponding branch;

[0169] 1) Assume L X The initial branch current is 0A, the current amplitudes of branches L2, L1 and L4+L5+L6...Ln are the same, and the phases of L2 and L4+L5+L6...Ln are opposite.

[0170] 2) Add currents of equal amplitude and opposite phase to branch L3 and branches L4+L5+L6...Ln.

[0171] Except for the bus tie branch, on busbars I and II, the primary current flowing into busbars L2 and L3 is equal to the primary current flowing out of busbars L4, L5, L6...Ln, satisfying the formula: S2I L2 ∠180°+S3I L3 ∠180°=S4I L4 ∠0°+S5I L5 ∠0°+…S n I Ln ∠0° (4)

[0172] That is, the bus differential protection current is zero at this time. S2 represents the current transformer ratio of the feeder L2 branch, S3 represents the current transformer ratio of the feeder L3 branch, and so on. n It represents the current transformer ratio of the feeder Ln branch, and S represents the reference ratio.

[0173] 3) On the Lx branch, the initial secondary current is 0A, the step size is set to 0.01A, and the current is gradually increased until the protection device is operated with a large differential. At this time, the current added by Lx is the differential operation value I Lx .

[0174] 4) The braking current Ir of the busbar large difference is the sum of the absolute value of the secondary current of each branch on busbars I and II except the busbar branch after conversion by the reference transformation ratio.

[0175] From 2)-4), we know that the secondary current flowing into the busbar L2 and L3 branches is equal to the current flowing out of the busbar L4, L5, L6...Ln branches, that is,

[0176] I r is the braking current; S2 S3...S n 、S x is the current transformer ratio corresponding to each branch; S is the base ratio of the current transformer; I L2 , IL3 , I L4 ...I Ln is the secondary current corresponding to each branch. I Lx Id is the current added to the Lx branch during differential operation; Id is the operating current;

[0177] 5) Thus we can get:

[0178] in, is the high value coefficient of the differential ratio, indicating the high value ratio of the large difference; Id is the operating current of the differential protection; at this time, the calculation method of Id is: after the busbar is connected, the sum of the current vectors of all branches except the busbar; I r is the braking current, which is the sum of the absolute values ​​of all branches;

[0179] in, is the low-value coefficient of the differential ratio, indicating the low-value ratio of the large difference; Id is the operating current of the differential protection; in this case, the calculation method of Id is: after the busbar is disconnected, the sum of the current vectors of all branches on the single busbar; I r is the braking current, which is the sum of the absolute values ​​of all branches;

[0180] Among them, k x is the small difference ratio coefficient, Id is the operating current of the differential protection; at this time, the calculation method of Id is: the sum of the current vectors of all branches on the busbar and the single busbar, I r is the braking current, which is the sum of the absolute values ​​of all branches; k x Depending on the calculation of I mother or II mother, the operating current Id is different, so the calculation formula will not be used to explain it.

[0181] B Considering the transmission error δ (%) caused by CT saturation of the fault branch when the fault occurs inside or outside the busbar area

[0182] If the transmission error caused by CT saturation of the faulty branch is δ when the fault occurs outside the zone, and the CT errors of the other branches are negligible, then Id=|1-δ-1|=δ, I r =|1-δ-1|+|1|=2-δ Therefore Id / (I r -Id)=δ / (2-2δ). As shown in FIG3 , when the busbar inflow current is 1, the differential current loop current is δ, and the fault branch current is 1-δ.

[0183] According to the action criterion of compound ratio differential relay, in order to ensure that the differential relay does not malfunction when there is a fault outside the zone, the Id / (I r-Id)<Kr, that is, δ / (2-2δ) <Kr (9)

[0184] Under normal circumstances, the secondary wiring of the busbar compound ratio differential protection is connected to a dedicated protection level winding, namely 5P level protection winding and 10P level protection winding. The transmission error limit caused by saturation of the 5P level protection winding is 5%.

[0185] That is, δ=5%, Kr>0.05 / (2-0.10)=2.63%;

[0186] The transmission error limit caused by saturation of the 10P level protection winding is 10%.

[0187] That is, δ=10%, Kr>0.1 / (2-0.20)=5.56%.

[0188] C. When considering the fault in the zone, the ratio of the outgoing bus fault current to the total bus current Ext (%)

[0189] If the proportion of the current flowing out of the busbar to the total fault current during an internal fault is Ext, and Id = 1, then Ir = 1 + Ext; as shown in Figure 4, when a fault occurs on the busbar, if the total current of the busbar fault difference loop is 1, and the current flowing out of a branch of the busbar is Ext, then the current flowing into the remaining branches is 1 + Ext.

[0190] According to the action criterion of compound ratio differential relay, to ensure differential action when fault occurs in the zone, Id / (I r -Id)≤Kr, that is, 1 / (1+Ext)-1≤, that is, 1 / (Ext)≤Kr (10)

[0191] Under normal circumstances, the secondary wiring of the busbar compound ratio differential protection is correctly connected to the corresponding junction box. The compound busbar compound ratio differential protection requires high sensitivity. The ratio of the existing outflow busbar fault current to the total busbar current Ext is generally greater than or equal to 10% and less than or equal to 15%, that is, 10% ≤ Ext ≤ 15%, that is, 3.33 ≤ Kr ≤ 5;

[0192] This factor does not need to be considered when considering faults outside the busbar area.

[0193] The calculation and value selection methods of the three key indicators discussed above are shown in formulas (6)-(10). When checking for faults within the busbar duplex ratio differential zone, formulas (6)-(10) must be considered simultaneously. When checking for faults outside the busbar duplex ratio differential zone, formulas (6)-(9) must be considered simultaneously.

[0194] Application Examples

[0195] Five branches are selected as examples, as shown in Figure 1.

[0196] Given: Assuming the branch current flowing into the busbar is negative and the branch current flowing out of the busbar is positive, the branch ratios are: L1 = 2000 / 5; L2 = 2000 / 5; L3 = 1000 / 5; L4 = 2500 / 5; Lx = 2500 / 5; and the base ratio is 2500 / 5. If the secondary currents of L2 and L4 are the same current Y, and the secondary current value of branch L3 is Z, then in order to balance the currents of branches L2, L3, and L4, the primary current values ​​of the three branches must first be balanced, that is, according to the formula S2I L2 ∠180°+S3I L3 ∠180°=S4I L4 ∠0°

[0197] We get 400Y+200Z=500Y, that is, Y=2Z;

[0198] At this time, the secondary current added to the L2 branch is 1A, and the secondary current of the L4 branch is also 1A. From the previous analysis, we know that I Lx =X, X is the independent variable;

[0199] I r =2+X, according to the ratio formula

[0200] At the same time, according to the different accuracy levels of the CT protection winding and the different sensitivities of the busbar differential protection, by selecting appropriate δ and Ext, the three key indicators can be quickly calibrated.

[0201] Test soft and hard pressure plates and control words

[0202] 1) Test the impact of soft and hard pressure plates and control words on protection

[0203] Technical requirements: The protection will only be activated when both the soft and hard pressure plates and the control words are put into operation.

[0204] Test method:

[0205] Apply the differential soft and hard pressure plates, along with the control word, and increase the amount until the differential protection action conditions are met. Observe the device's operation. Remove the soft and hard pressure plates, along with the control word, and observe whether the protection operates. (If the result differs from the theoretical result, modify the X value and recalculate. Continue calculating until the condition is met.)

[0206] The test records are shown in Table 1.

[0207] Table 1

[0208] 2) Bus differential complex ratio differential threshold value check

[0209] Technical requirements: The action value error does not exceed 3%

[0210] Test method:

[0211] Set the set value Idset to 0.1In (In is the rated current, 0.1In means 0.1 times the rated current), the xth interval is located in the Ⅰ mother, add the x-interval single-phase current 0.95*Idset, and continuously increase the current value. The maximum current is 1.05*Idset. Observe the action of the ratio differential to see if it operates within (0.97-1.03)*Idset. If it operates, it means that the action value error does not exceed 3%, otherwise it does not meet the error requirement.

[0212] If we analyze the differential ratio, we know that when K = 1, the differential protection activates as long as the current in branch X is greater than 2A. When K = 0.5, the differential protection activates as long as the current in branch X is greater than 1A. Similarly, this allows us to quickly and efficiently determine the current value to be added to branch X. If the differential ratio is unknown, we can gradually add secondary current to branch X, substituting the current value at which the differential action occurs into the ratio formula to quickly determine the ratio value for the differential element.

[0213] Busbar differential protection verification and debugging process:

[0214] 1. Simulate fault conditions outside the busbar area: no voltage is applied to make the "lock open" light on

[0215] 1) Select two branches with the same transformation ratio on the same busbar, and add A-phase (or B-phase or C-phase) current to these two branches at the same time. The currents are equal in magnitude (1-10A) and opposite in direction.

[0216] 2) The busbar differential protection should not operate;

[0217] 3) Observe the panel display: the large differential current and the small differential current should be equal to zero.

[0218] 2. Simulate fault conditions in the busbar area: Do not apply voltage to make the "Locked Open" light on.

[0219] 1) Verify the differential threshold setting:

[0220] a) Select any branch on the busbar and add the B-phase current to this branch. The current value must be greater than the differential threshold value.

[0221] b) The busbar differential protection should operate instantaneously, cutting off the busbar coupler and all branches on the busbar where the branch is located, and the busbar differential action signal light should light up;

[0222] 2) Verify the high value of the differential ratio coefficient:

[0223] a) The bus tie breaker is closed (only the normally open contacts of the bus tie breaker are positively energized);

[0224] b) Select any two branches on busbar I with the same transformation ratio and add currents in opposite directions to phase A;

[0225] c) Select a branch on busbar II with the same transformation ratio, inject current into phase A, and adjust the current to achieve differential operation on busbar II. If the transformation ratios are different, use the largest transformation ratio as a reference for unified conversion. For example: main transformer ratio: 600 / 5; line ratio: 1600 / 5; the coefficient ratio on each side is: 600 / 1600 = 0.375:1.

[0226] d) Record the applied current and verify the high value coefficient of the differential ratio.

[0227] 3) Verify the low value of the differential ratio coefficient:

[0228] a) The bus tie breaker is disconnected (only the normally closed contacts of the bus tie breaker are positively energized);

[0229] b) Select any two branches on busbar I with the same transformation ratio and add currents in opposite directions to phase A;

[0230] c) Select a branch with the same transformation ratio on bus II, add current to phase A, and adjust the current to make bus II differential operation;

[0231] d) Record the applied current and verify the low value coefficient of the differential ratio.

[0232] 4) Verify the small difference ratio coefficient;

[0233] a) Select two branches with the same transformation ratio on the same busbar and add currents with opposite directions and different magnitudes to phase A;

[0234] b) Fix the current in one branch and adjust the current in the other branch to make the busbar differential operate;

[0235] c) Record the applied current and verify the small difference ratio coefficient.

[0236] 3. Simulate the fault conditions in the busbar area during the double busbar switching operation: do not apply voltage to make the "lock open" light turn on.

[0237] 1) Select any branch on a busbar and close the I and II switches of the branch;

[0238] 2) Load the C-phase current in this branch, and the current value is greater than the differential threshold value;

[0239] 3) The busbar differential protection should operate instantaneously to cut off all branches on the busbar and the busbar;

[0240] 4) The I and II mother differential action signal lights are on.

[0241] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A multiple ratio differential calibration method for multiple distributed renewable energy feeders, characterized in that: It includes the speed check of ratio differential protection, the reliability and stability check of ratio differential protection and the sensitivity check of ratio differential protection; specifically: Step 1: Calculate the theoretical compound ratio Kr; collect the actual compound ratio setting value Kr'; Step 2: The speed check of the ratio differential protection is as follows: compare Kr with the actual compound ratio setting value Kr'. If Kr is equal to the actual compound ratio setting value Kr', it is judged that the speed check has passed; if Kr is greater than or less than the actual compound ratio setting value Kr', it is judged that the speed check has failed; Step 3: The reliability and stability check of the ratio differential protection is as follows: obtain the transmission error δ caused by the CT saturation of the fault branch, and then perform a reliability and stability check. If δ / (2-2δ)≤Kr, the check passes, otherwise, the check fails. Step 4: The sensitivity check of the ratio differential protection is as follows: obtain the ratio of the current flowing out of the busbar to the total fault current Ext, and then perform a sensitivity check. If 1 / (Ext)≤Kr, the sensitivity check passes, otherwise, the check fails. Step 5: If any step fails the verification in the second, third and fourth steps, it is necessary to return to the first step and recalculate the compound ratio Kr. When the second, third and fourth steps all pass the verification, it is considered that the ratio differential verification has passed.

2. The multiple ratio differential calibration method for multiple distributed renewable energy access feeders according to claim 1 is characterized in that: When checking the reliability and stability of the ratio differential protection, it is necessary to simulate the fault conditions outside the busbar area. The specific method is as follows: 1) Select two branches with the same transformation ratio on the same busbar, and add a phase current to these two branches at the same time. The currents are equal in magnitude but opposite in direction; 2) The busbar differential protection should not operate; 3) The large differential current and the small differential current should be equal to zero.

3. The multiple ratio differential calibration method for multiple distributed renewable energy access feeders according to claim 1 is characterized in that: When checking the sensitivity of the ratio differential protection, it is necessary to simulate the fault conditions in the busbar area. The specific method includes the following steps: Step (1), verify the differential threshold setting: a) Select any branch on the busbar and add a certain current to a phase in this branch, and the current value is greater than the differential threshold value; b) The bus differential protection should act instantaneously to cut off the bus tie and all branches on the bus where the branch is located. The line differential action signal light should be on; Step (2), verify the high value of the differential ratio coefficient: a) The busbar tie breaker is closed; b) Select any two branches with the same transformation ratio on bus I and add currents with opposite directions to one phase; c) Select a branch with the same transformation ratio on bus II, add current to a phase, and adjust the current to make bus II differential action; d) Record the applied current and verify the high value coefficient of the differential ratio; Step (3), verify the low value of the differential ratio coefficient: a) The busbar breaker is disconnected; b) Select any two branches with the same transformation ratio on bus I and add currents with opposite directions to one phase; c) Select a branch with the same transformation ratio on bus II, add current to a phase, and adjust the current to make bus II differential action; d) Record the applied current and verify the low value coefficient of the differential ratio; Step (4), verify the small difference ratio coefficient: a) Select two branches with the same transformation ratio on the same busbar and add currents with opposite directions and different magnitudes to a certain phase; b) Fix the current in one branch and adjust the current in the other branch to make the busbar differentially operated; c) Record the applied current and verify the small difference ratio coefficient.

4. The multiple ratio differential verification method for multiple distributed renewable energy access feeders according to claim 3 is characterized in that: In step (2), the specific method for verifying the high value coefficient of the differential ratio is: The high value coefficient of the differential ratio is Id is the action current of the differential protection. At this time, the calculation method of Id is: after the busbar is connected, the sum of the current vectors of all branches except the busbar; I r is the braking current, which is the sum of the absolute values ​​of all branches; Among them, S n Indicates L n Current transformer ratio of the branch; I L2 ,I L3 ,I L4 ...I Ln is the secondary current of each corresponding branch; I Lx The current added to the Lx branch during differential action; S represents the base transformation ratio; If the equation holds, the verification is successful.

5. The multiple ratio differential calibration method for multiple distributed renewable energy access feeders according to claim 3 is characterized in that: In step (3), the specific method for verifying the low value coefficient of the differential ratio is: The low value coefficient of the differential ratio is Id is the action current of the differential protection. At this time, the calculation method of Id is: after the bus tie is disconnected, the sum of the current vectors of all branches on the bus; I r is the braking current, which is the sum of the absolute values ​​of all branches; If the equation holds, the verification is successful.

6. The multiple ratio differential calibration method for multiple distributed renewable energy access feeders according to claim 3 is characterized in that: In step (4), the specific method for verifying the small difference ratio coefficient is: k x represents the small difference ratio coefficient, and Id is the action current of the differential protection; at this time, the calculation method of Id is: the sum of the current vectors of all branches on I bus or II bus, I r is the braking current, which is the sum of the absolute values ​​of all branches of I mother or II mother; If the equation holds, the verification is successful.

7. The multiple ratio differential calibration method for multiple distributed renewable energy feeder access according to claim 1 is characterized in that: When checking the sensitivity of the ratio differential protection, it is also necessary to simulate the fault conditions in the busbar area during the double busbar switching operation. The specific method is as follows: 1) Select any branch on a busbar and close the I and II switches of the branch; 2) A single-phase current is loaded in this branch, and the current value is greater than the differential threshold value; 3) The busbar differential protection should act instantaneously to cut off all branches on the busbar and busbar; 4) The I and II mother differential action signal lights are on.

8. The multiple ratio differential calibration method for multiple distributed renewable energy feeder access according to claim 1 is characterized in that: In the fourth step, the value range of δ is greater than or equal to 1.5 and less than or equal to 3.

9. The multiple ratio differential verification method for multiple distributed renewable energy access feeders according to claim 8 is characterized in that: The value of δ is 2.

10. A multiple-distributed new energy access feeder duplex ratio differential calibration device, using the multiple-distributed new energy access feeder duplex ratio differential calibration method as claimed in any one of claims 1 to 9, characterized in that: include: The acquisition module is used to collect the actual compound ratio setting value Kr', the transmission error δ caused by the CT saturation of the fault branch, and the proportion of the current flowing out of the bus to the total fault current Ext; The first processing module is connected to the acquisition module and is used to calculate the theoretical compound ratio Kr, and then perform the ratio differential protection speed check, comparing Kr with the actual compound ratio setting value Kr'. If Kr is equal to the actual compound ratio setting value Kr', it is judged that the speed check has passed; if Kr is greater than or less than the actual compound ratio setting value Kr', it is judged that the speed check has passed. If the formula ratio setting value Kr' is not met, it is judged that the speed check fails; The second processing module is connected to the acquisition module and is used to perform a reliability stability check. If δ / (2-2δ)≤Kr, the check passes, otherwise, the check fails; The third processing module is connected to the acquisition module and is used to perform sensitivity verification. If 1 / (Ext)≤Kr, the sensitivity verification passes, otherwise, the verification fails; The display processing module is respectively connected to the acquisition module, the first processing module, the second processing module, and the third processing module, and is used to display the verification results; if any of the verifications fails, it is necessary to return to the acquisition module for collection and re-perform subsequent verifications; if all the verifications pass, it is considered that the ratio differential verification has passed.

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