A method for capacitor current compensation in T-connected line current differential protection

Abstract

This invention discloses a method for capacitor current compensation using differential current protection for T-connected lines, comprising the following steps: installing differential current protection devices on three sides of the T-connected line; real-time acquisition of three-phase AC current and three-phase AC voltage at the protection installation points, as well as line parameters; and calculating the three-phase current referred to the T-connection point on each side using long-line equations, based on the three-phase current, three-phase voltage, and line parameters, as the compensated current. This method enables real-time and accurate capacitor current compensation for faults outside the line zone and faults at the T-connection point within the line zone, even without knowing the specific location of the fault. For faults within the line zone that do not include the T-connection point, it improves the sensitivity of the differential current protection operation.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, and more specifically, relates to a method for capacitor current compensation in T-connection line current differential protection. Background Technology

[0002] For short-circuit lines, the effect of capacitive current can be ignored by differential current protection, and capacitive current compensation is not calculated. For longer cable lines and long overhead lines, the effect of capacitive current generally needs to be considered. Parallel reactors are installed on the lines, mainly for longer cable lines and long overhead lines, to compensate for most of the steady-state capacitive current, thereby reducing inrush current and suppressing overvoltage.

[0003] With the rapid development of new energy sources, T-connection lines have begun to be widely used.

[0004] Prior art document 1 (CN1858954) discloses a method for line differential protection based on long-line equations in high-voltage lines of power systems. This method uses vector calculation of long-line equations to convert the voltage and current measured at the protection installation location to the voltage and current at a reference point k within the protection range on the line, and the voltage at terminal m. Current Voltage converted to point k Current voltage at n-terminal Current Voltage converted to point k Current If there is a shunt reactor L at the midpoint of the line, the current on the shunt reactor must be subtracted first. have to Then, at reference point k, current is used or Differential calculations are performed using various differential formulas to determine whether an intra-zone fault has occurred. However, existing technical document 1 only applies to lines at both ends and does not consider applications in T-connected lines, making it unsuitable for T-connected lines. Furthermore, technical document 1 does not mention a specific method for calculating the current of the shunt reactor. If the current of the shunt reactor cannot be accurately calculated, the compensation effect of the capacitor current will be affected, and the operating performance of the line current differential protection will be reduced.

[0005] For capacitor current compensation technology in T-connection line current differential protection, existing technologies cannot meet the actual requirements of protection for long cable lines and long overhead lines. Existing capacitor current compensation schemes for T-connection line current differential protection and their existing problems include:

[0006] 1) Compensation is applied to each side at 1 / 3 of the total line capacitive reactance. This method obviously does not consider the actual length and line parameters of each branch line. For protection on the longer side of the branch, undercompensation of the capacitive current will occur, while for protection on the shorter side, overcompensation of the capacitive current will occur. This results in inaccurate capacitive current compensation for both in-zone and out-of-zone faults. The inability to accurately compensate for capacitive current during out-of-zone faults poses a risk. To prevent maloperation during out-of-zone faults, the operating threshold of the current differential protection needs to be raised, thus reducing the sensitivity of the current differential protection operation.

[0007] 2) The equivalent capacitance on each side is half the capacitive reactance of the corresponding line segment, while the capacitive reactance at the branch point T-junction is half of the total line capacitance. The capacitive reactance at the T-junction is then distributed to each side of the line inversely proportional to the branch line length. This method does not consider the case where the parameters of each branch line are different. Furthermore, because the voltage at the T-junction cannot be accurately calculated, the capacitive current at the T-junction cannot be accurately distributed to each side. These factors will lead to inaccurate capacitive current compensation during both in-zone and out-of-zone faults. Inaccurate capacitive current compensation during out-of-zone faults poses a risk. To prevent maloperation during out-of-zone faults, the operating threshold of the current differential protection needs to be raised, thus reducing the sensitivity of the current differential protection operation.

[0008] 3) Before the current differential protection is activated, the differential current calculated by each side of the protection is used as the capacitance current value. When the current differential protection operates, the greater of the differential setting value and four times this capacitance current value is used as the operating threshold. This method cannot compensate for the capacitance current in real time, and it is necessary to increase the differential protection operating threshold to prevent false tripping due to faults outside the protection zone, thus reducing the sensitivity of the current differential protection operation.

[0009] To address the problems of the existing solutions, this invention proposes a method for capacitor current compensation in T-connection line current differential protection. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a method for capacitor current compensation in T-connection line current differential protection, which can achieve accurate capacitor current compensation and improve the sensitivity of current differential protection operation.

[0011] The present invention adopts the following technical solution.

[0012] A method for capacitor current compensation in a T-connected line current differential protection system includes the following steps:

[0013] Step 1: Collect the current and voltage of the differential protection of the T-connected line on the three sides, as well as the line parameters;

[0014] Step 2: Using the long-line equation, the three-phase currents and three-phase voltages on the three sides and the line parameters are used to calculate the three-phase currents referred to the T-junction on the three sides, which are then used as the compensated currents.

[0015] Preferably, in step 1, line current differential protection devices are installed on the three sides of the T-connection line, and the three-phase AC current and three-phase AC voltage at the installation location are collected through the line current differential protection devices.

[0016] Preferably, in step 1, the collected line parameters include the line length on each side, the line positive sequence propagation coefficient, and the line positive sequence wave impedance.

[0017] Preferably, in step 2, the compensated current on each side of the T-connected line satisfies the following relationship:

[0018]

[0019]

[0020]

[0021] In the formula, The three-phase currents after compensation are respectively connected to the first side of the line via T-connection. These are the three-phase voltages on the first side of the T-connected line. These are the three-phase currents on the first side of the T-connected line. These are the three-phase currents of the parallel reactor on the first side of the T-connected line, respectively.

[0022]

[0023]

[0024]

[0025] In the formula, The compensated three-phase currents on the second side of the T-connected line are respectively... These are the three-phase voltages on the second side of the T-connected line. These are the three-phase currents on the second side of the T-connected line. These are the three-phase currents of the parallel reactor on the second side of the T-connected line, respectively.

[0026]

[0027]

[0028]

[0029] In the formula, The compensated three-phase currents on the third side of the T-connected line are respectively... These are the three-phase voltages on the third side of the T-connected line. These are the three-phase currents on the third side of the T-connected line. These are the three-phase currents of the parallel reactor on the second side of the T-connected line; γ M γ N γ P These are the positive sequence propagation coefficients on each side of the T-connection, L M L N L P These represent the line lengths on each side of the T-connection, and Z... Mc Z Nc Z Pc These are the positive sequence impedances of the T-connected line on each side.

[0030] Preferably, the three-phase current of the first-side parallel reactor The three-phase current of the second-side parallel reactor The three-phase current of the third-side parallel reactor Calculate using the following formulas respectively:

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040] In the formula, X M1k X N1k X P1k These are the reactor impedance settings for each side of the T-connected line, X M0k X N0k X P0k These are the impedance settings of the small reactors on each side of the T-connected line. These are the three-phase voltages on the first side of the T-connected line. These are the three-phase voltages on the second side of the T-connected line. These are the three-phase voltages on the third side of the T-connected line. These are the zero-sequence voltages on each side of the T-connected line.

[0041] Preferably, obtaining the impedance setting of the reactor and the impedance setting of the small reactor further includes:

[0042] Determine whether parallel reactors are installed on each side, and based on whether parallel reactors are installed on each side, determine the reactor impedance setting X for the first, second, and third sides. M1k X N1k X P1k The value and the impedance setting of the small reactor X M0 k, X N0k X P0k The value;

[0043] If a parallel reactor is installed on this side, the impedance setting of the corresponding reactor and the impedance setting of the small reactor shall be set according to the actual parameters.

[0044] If no parallel reactor is installed on this side, the impedance setting of the corresponding reactor and the impedance setting of the small reactor shall be set to the maximum value of the setting range.

[0045] Preferably, the setting range of the impedance setting of the reactor and the impedance setting of the small reactor are both 1Ω to 9000Ω.

[0046] Preferably, if the determination result is that a parallel reactor is installed on this side, the impedance setting of the reactor on this side is calculated based on the rated voltage U and capacity S of the parallel reactor installed on this side of the line, and is determined by the current inductance ratio N. CT and voltage transformer ratio N PT The reactor impedance setting is converted to a secondary value, and the converted secondary value is the set reactor impedance setting.

[0047] Preferably, if a parallel reactor is installed on this side, the grounding method of the neutral point on this side is determined, and the impedance setting of the small reactor on this side is adjusted according to the neutral point grounding method:

[0048] When the neutral point on this side is directly grounded, the secondary setting value is taken as the minimum value of the impedance setting range of the small reactor; when the neutral point on this side is grounded through a resistor, the impedance value of the neutral point reactor is converted into the secondary setting value; when the neutral point on this side is not grounded, the secondary setting value is taken as the maximum value of the impedance setting range of the small reactor.

[0049] Preferably, if no parallel reactor is installed on this side, the impedance setting of the corresponding reactor and the impedance setting of the small reactor are set to 9000Ω.

[0050] The beneficial effect of this invention is that, compared with the prior art, it solves the defect that T-connection line current differential protection cannot accurately compensate for capacitive current or cannot compensate for capacitive current in real time when there is a fault outside the protection zone, which necessitates raising the operating threshold and thus reducing the operating sensitivity. The method for achieving capacitive current compensation in T-connection line current differential protection proposed in this invention uses long-line equations to convert the current and voltage at the installation points of the three protection sides to the T-connection, calculates the compensated current, and then determines the operating conditions of the current differential protection based on the differential current and braking current at the T-connection. This invention can achieve real-time and accurate compensation of capacitive current when there is a fault outside the line zone or a fault at the T-connection within the line zone; when the fault is within the line zone but does not include a fault at the T-connection, it can improve the operating sensitivity of the current differential protection. It has achieved good results in practical field applications. Attached Figure Description

[0051] Figure 1 This is a flowchart illustrating the steps of a method for achieving capacitor current compensation using differential protection for T-connected line current according to the present invention.

[0052] Figure 2 This is a schematic diagram of a method for capacitor current compensation using differential protection of a T-connected line according to the present invention.

[0053] Figure 3 This is a schematic diagram of an external fault in the line zone for a method of capacitor current compensation by differential protection of T-connected line current according to the present invention.

[0054] Figure 4 This is a schematic diagram of a fault at the T-junction in the line area of ​​the method for achieving capacitor current compensation by differential protection of T-junction line current according to the present invention.

[0055] Figure 5 This is a schematic diagram of a fault at point B in the line zone of the present invention, which describes a method for achieving capacitor current compensation using differential protection of T-connected line current according to the present invention. Detailed Implementation

[0056] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0057] like Figure 1 As shown, this invention provides a method for capacitor current compensation in T-connected line current differential protection, comprising the following steps:

[0058] Step 1: Collect the current and voltage of the differential protection on the three sides of the T-connected line, as well as the line parameters.

[0059] Specifically, for T-connected lines, line current differential protection devices are installed on three sides of the T-connected line to collect the three-phase AC current and three-phase AC voltage at the installation location.

[0060] like Figure 2 As shown, Figure 2 This is a schematic diagram of a method for capacitor current compensation using T-connected line current differential protection according to the present invention. The T-connected line in this invention includes three sides: M, N, and P. T is the contact point, which divides the line into three segments: MT, NT, and PT. A line protection device is installed on each of the M, N, and P sides. These three line protection devices constitute a complete T-connected line current differential protection system.

[0061] The M-side line protection device collects the current at its installation location. Voltage is The N-side line protection device collects the current at its installation location. Voltage is The current collected by the P-side line protection device at its installation location is... Voltage is

[0062] Specifically, the current and voltage at the installation points of the line protection devices on each side are three-phase current and three-phase voltage. Therefore, the line protection device on side M can collect and calculate the three-phase current at its installation point. and three-phase voltage The N-side line protection device can collect and calculate the three-phase current at its installation location. and three-phase voltage The P-side line protection device can collect and calculate the three-phase current at its installation location. and three-phase voltage

[0063] The reference directions of the current on each side are shown in the figure. The reference directions of the current on each side are from the M, N, and P sides to the T junction, respectively.

[0064] The distance from the M-side line protection device installation point to the T-contact is L. M The distance from the N-side line protection device installation point to the T-contact is L. N The distance from the installation point of the P-side line protection device to the T-contact is L. P .

[0065] The collected line parameters include: the line lengths of the three line segments MT, NT, and PT, the line positive sequence propagation coefficient, and the line positive sequence wave impedance.

[0066] Step 2: Using the long-line equation, the three-phase currents, three-phase voltages and line parameters of the three sides are used to calculate the three-phase currents referred to the T-junction on the three sides, which are then used as the compensated currents.

[0067] Reference Figures 3-5 As illustrated, based on the location of the fault point, the fault can be divided into faults outside the T-connection area, faults at the T-connection point within the T-connection area, and faults at non-T-connection points within the T-connection area.

[0068] Select the T-junction of the line as the reference point for capacitor current compensation. The current on the M side... and voltage The current referred to at the T-junction is N-side current and voltage The current referred to at the T-junction is P-side current and voltage The current referred to at the T-junction is

[0069] Specifically, for faults outside the T-connection line zone, where the fault point is outside the T-connection line zone, the inflow and outflow currents are equal, except for the capacitor current and the shunt reactor current. According to the long-line equation, the current at the T-connection can be accurately calculated in real time using the voltage and current at the protection installation point. The difference between the current value at the protection installation point minus the shunt reactor current and the corresponding current value referred to the T-connection is the capacitor current value that needs to be compensated. For faults outside the T-connection line zone, the three-phase current referred to the T-connection is sufficient to compensate for the capacitor current, achieving accurate capacitor current compensation.

[0070] For a fault at the T-contact point within a T-connection line zone, according to the long-line equation, the current referred to the T-contact point can be accurately calculated using the voltage and current at the protection installation location. The difference between the current value at the protection installation location (minus the current of the shunt reactor) and the corresponding current value referred to the T-contact point is the capacitance current value that needs to be compensated. Therefore, for a fault within the line zone at the T-contact point, the current referred to the T-contact point already compensates for the capacitance current, achieving accurate capacitance current compensation.

[0071] For faults outside the T-connection area within the T-connection zone, the calculation method of this invention will result in undercompensation of the capacitor current. However, when real-time and accurate capacitor current compensation is achieved for faults outside the zone, undercompensation of the capacitor current within the zone will increase the differential current, which is beneficial to the current differential protection. Therefore, this invention does not need to know the specific location of the fault point, whether it is inside or outside the zone, to ensure that the sensitivity of the current differential protection operation is not reduced. Having the function of real-time and accurate capacitor current compensation for faults outside the zone, when setting the current differential protection settings, it is only necessary to ensure a certain sensitivity for faults within the zone under the minimum operating mode; there is no need to consider the influence of capacitor current and raise the operating threshold.

[0072] The compensated currents on each side of the T-connected line satisfy the following relationship:

[0073]

[0074]

[0075]

[0076] In the formula, The three-phase currents after compensation are respectively connected to the first side of the line via T-connection. These are the three-phase voltages on the first side of the T-connected line. These are the three-phase currents on the first side of the T-connected line. These are the three-phase currents of the parallel reactor on the first side of the T-connected line, respectively.

[0077]

[0078]

[0079]

[0080] In the formula, The compensated three-phase currents on the second side of the T-connected line are respectively... These are the three-phase voltages on the second side of the T-connected line. These are the three-phase currents on the second side of the T-connected line. These are the three-phase currents of the parallel reactor on the second side of the T-connected line, respectively.

[0081]

[0082]

[0083]

[0084] In the formula, The compensated three-phase currents on the third side of the T-connected line are respectively... These are the three-phase voltages on the third side of the T-connected line. These are the three-phase currents on the third side of the T-connected line. These are the three-phase currents of the parallel reactor on the third side of the T-connected line; γ M γ N γ P These are the positive sequence propagation coefficients on each side of the T-connection, L M L N L P These represent the line lengths on each side of the T-connection, and Z... Mc Z Nc Z Pc These are the positive sequence impedances of the T-connected line on each side.

[0085] The three-phase current of the first-side parallel reactor The three-phase current of the second-side parallel reactor The three-phase current of the third-side parallel reactor Calculate using the following formulas respectively:

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095] In the formula, X M1k X N1k X P1k These are the reactor impedance settings for each side of the T-connected line, X M0k X N0k X P0k These are the impedance settings of the small reactors on each side of the T-connected line. These are the three-phase voltages on the first side of the T-connected line. These are the three-phase voltages on the second side of the T-connected line. These are the three-phase voltages on the third side of the T-connected line. These are the zero-sequence voltages on each side of the T-connected line.

[0096] Furthermore, The calculation formulas are as follows:

[0097]

[0098]

[0099]

[0100] Combination Figure 2 As illustrated, in this embodiment, the first side, the second side, and the third side respectively correspond to Figure 2 The M side, N side, and P side in the middle.

[0101] The impedance setting of the parallel reactors for line protection calculations includes the impedance setting of the main reactor and the impedance setting of the small reactor. Obtaining the impedance setting of the main reactor and the small reactor further involves determining whether parallel reactors are installed on the M, N, and P sides, and determining the reactor impedance setting X based on whether parallel reactors are installed on those sides. M1k X N1k X P1k The value and the impedance setting of the small reactor X M0k X N0k X P0k The value of .

[0102] For three-terminal T-connected lines, if a shunt reactor is installed, the shunt reactor is usually installed inside the station, that is, at the M-side, N-side, and P-side outlets.

[0103] Reference Figure 2 The indication, Figure 2 The diagram shows a case where a shunt reactor is installed on the M side. In practical applications, shunt reactors may or may not be installed on the M, N, or P sides. Therefore, it is necessary to first determine whether a shunt reactor is installed on each side, and then determine the reactor impedance setting X on the M, N, and P sides based on whether a shunt reactor is installed on each side. M1k X N1k X P1k The value and the impedance setting of the small reactor X M0k X N0k X P0k The value of .

[0104] For the M, N, and P sides, if a parallel reactor is installed on the side, the impedance setting of the corresponding reactor and the impedance setting of the small reactor shall be set according to the actual parameters; if no parallel reactor is installed on the side, the impedance setting of the corresponding reactor and the impedance setting of the small reactor shall be set to the maximum value of the setting range.

[0105] The setting range for the impedance setting of the reactor and the small reactor is 1Ω to 9000Ω.

[0106] If the determination result indicates that a shunt reactor is installed on this side, the impedance setting of the reactor on this side is calculated based on the rated voltage U (in V) and capacity S (in VA) of the shunt reactor installed on this side of the line, and then determined by the CT (current transformer) transformation ratio N. CT and PT (voltage transformer) turns ratio N PT The reactor impedance setting is converted to a secondary value, and the unit of the reactor impedance setting is Ω. The converted secondary value is the set reactor impedance setting.

[0107] The specific formula for calculating the reactor impedance setting is as follows:

[0108] Specifically, if a parallel reactor is installed on this side, the grounding method of the neutral point on this side is further determined, and the impedance setting of the small reactor on this side is adjusted according to the neutral point grounding method: when the neutral point on this side is directly grounded, the secondary setting is taken as the minimum value of the small reactor impedance setting range, 1Ω; when the neutral point on this side is grounded through a resistor, the impedance value of the neutral point reactor is adjusted through the CT ratio N. CT and PT ratio N PT The value is converted to a secondary setpoint, with the unit being Ω. When the neutral point on this side is not grounded, the secondary setpoint is taken as the maximum value of the small reactor impedance setting range, which is 9000Ω. The obtained secondary setpoint is the set impedance setting of the small reactor after adjustment.

[0109] When the setting is set to the maximum value of 9000Ω, the influence of the shunt reactor impedance setting can be ignored, which is equivalent to not installing a shunt reactor. Therefore, if no shunt reactor is installed on this side, the impedance settings of both the reactor and the small reactor should be selected as the maximum value of the setting range, i.e., 9000Ω.

[0110] Based on the calculated currents after compensation on each side of the T-connected line, the phase differential current and phase braking current, as well as the zero-sequence differential current and zero-sequence braking current, can be calculated.

[0111] The typical calculation formulas for phase-separated differential current and phase-separated braking current are as follows:

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[0118] Among them, I Da I Db I Dc For the compensated phase differential current, I Ba I Bb I Bc This is the compensated phase braking current.

[0119] The typical calculation formulas for zero-sequence differential current and zero-sequence braking current are as follows:

[0120]

[0121]

[0122] Among them, I D0 For the compensated zero-sequence differential current, I B0 This is the zero-sequence braking current after compensation.

[0123] Specifically, according to the usual requirements of current differential protection, the three currents used to calculate the differential current and braking current should be the current values ​​at the same time.

[0124] Based on the compensated phase differential current, phase braking current, zero-sequence differential current, and zero-sequence braking current, determine whether the current differential protection meets the operating conditions.

[0125] The operating condition of current differential protection is to determine whether the phase differential current, phase restraint current, zero-sequence differential current and zero-sequence restraint current meet the typical operating equation. If they meet, the current differential protection will operate; otherwise, no operation is required.

[0126] The typical operating equations for phase A, phase B, phase C, and zero-sequence current differential protection are as follows:

[0127] I Da >I Z And I Da >KI Ba

[0128] I Db >I Z And I Db >KI Bb

[0129] I Dc >I Z And I Dc >KI Bc

[0130] I D0 >I z And I D0 >KI B0

[0131] Among them, I Da I Db I Dc For the compensated phase differential current, I D0 For the compensated zero-sequence differential current, I Ba I Bb I Bc For the compensated phase braking current, I B0 For the compensated zero-sequence braking current, I z K is the differential current setting, and K is the braking coefficient.

[0132] The current differential protection can only operate when the differential current is greater than a set value and within the operating characteristic range.

[0133] For faults outside the T-connection zone, due to the real-time and accurate compensation of the capacitor current, the above-mentioned typical operating equations can be accurately calculated, ensuring reliable operation of the current differential protection. For faults within the zone where the fault point is at the T-connection, the above-mentioned typical operating equations can be accurately calculated, ensuring reliable operation of the current differential protection of the faulty phase. For faults within the zone where the fault point is not at the T-connection, the faulty phase has undercompensated capacitor current, and the above-mentioned typical operating equations cannot be accurately calculated, resulting in a different phase differential current I. Da I Db I Dc Or I D0 The calculated value is larger than the actual value, making it easier to satisfy the condition that the differential current is greater than the differential setting value in the above typical action equation, thus improving the action sensitivity of the current differential protection.

[0134] The beneficial effects of this invention are that, compared with the prior art, the method for capacitor current compensation in the T-connection line current differential protection of this invention sets the reference point for calculating the differential current and braking current at the T-connection, eliminating the need for protection ranging results. This allows for accurate capacitor current compensation for faults outside the protection zone and faults at the T-connection within the protection zone. Furthermore, it improves the sensitivity of the current differential protection when a line fault occurs within the protection zone that does not include the T-connection. This facilitates the correct operation of the current differential protection under various fault conditions.

[0135] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A method for capacitor current compensation in T-connected line current differential protection, characterized in that, Includes the following steps: Step 1: Collect the current and voltage of the differential protection on the three sides of the T-connection line, and obtain the line parameters through the current differential protection settings; Step 2: Using the long-line equation, the three-phase currents and three-phase voltages on the three sides and the line parameters are used to calculate the three-phase currents referred to the T-junction on the three sides, which are then used as the compensated currents. The compensated currents on each side of the T-connected line satisfy the following relationship: in, After compensation for the X side of the T-connection line Phase current, For the X side of the T-connection line Phase voltage, For the X side of the T-connection line Phase current, For the parallel reactor on the X side of the T-connected line Phase current, γ X L is the positive sequence propagation coefficient on the X side of the T-connection line. X Z is the length of the line on the X side of the T-connection. Xc The positive sequence impedance of the line on the X side of the T-connection line; The three-phase current of the first-side parallel reactor The three-phase current of the second-side parallel reactor The three-phase current of the third-side parallel reactor Calculate using the following formulas respectively: In the formula, X M1k X N1k X P1k These are the reactor impedance settings for each side of the T-connected line, X M0k X Nok X P0k These are the impedance settings of the small reactors on each side of the T-connected line. These are the three-phase voltages on the first side of the T-connected line. These are the three-phase voltages on the second side of the T-connected line. These are the three-phase voltages on the third side of the T-connected line. These are the zero-sequence voltages on each side of the T-connected line, where j represents the imaginary unit; X takes M, N, and P, which represent the M, N, and P sides of the T-connected line, respectively; Let a, b, and c represent the three phases a, b, and c, respectively.

2. The method for capacitor current compensation using differential protection of T-connected line current according to claim 1, characterized in that, In step 1, current differential protection devices are installed on the three sides of the T-connection line respectively, and the three-phase AC current and three-phase AC voltage at the installation location are collected through the current differential protection devices.

3. The method for capacitor current compensation using differential protection for T-connected lines according to claim 1, characterized in that, In step 1, the line parameters obtained through the current differential protection settings include the line length on each side, the line positive sequence propagation coefficient, and the line positive sequence wave impedance.

4. The method for capacitor current compensation using differential protection for T-connected lines according to claim 3, characterized in that, Obtaining the impedance setting of the reactor and the impedance setting of the small reactor also includes: Determine whether parallel reactors are installed on each side, and based on whether parallel reactors are installed on each side, determine the reactor impedance setting X for the first, second, and third sides. M1k X N1k X P1k The value and the impedance setting of the small reactor X M0k X N0k X P0k The value; If a parallel reactor is installed on this side, the impedance setting of the corresponding reactor and the impedance setting of the small reactor shall be set according to the actual parameters. If no parallel reactor is installed on this side, the impedance setting of the corresponding reactor and the impedance setting of the small reactor shall be set to the maximum value of the setting range.

5. The method for capacitor current compensation using differential protection for T-connected lines according to claim 4, characterized in that, The setting range for both the impedance setting of the reactor and the impedance setting of the small reactor is 1Ω to 9000Ω.

6. The method for capacitor current compensation using differential protection for T-connected lines according to claim 4, characterized in that, If the determination result indicates that a shunt reactor is installed on this side, the impedance setting of the reactor on this side is calculated based on the rated voltage U and capacity S of the shunt reactor installed on this side of the line, and determined by the current inductance ratio N. CT and voltage transformer ratio N PT The reactor impedance setting is converted to a secondary value, and the converted secondary value is the set reactor impedance setting.

7. The method for capacitor current compensation using differential protection of T-connected line current according to claim 4, characterized in that, If a parallel reactor is installed on this side, determine the grounding method of the neutral point on this side, and adjust the impedance setting of the small reactor on this side according to the neutral point grounding method: When the neutral point on this side is directly grounded, the secondary setting value is taken as the minimum value of the impedance setting range of the small reactor; when the neutral point on this side is grounded through a resistor, the impedance value of the neutral point reactor is converted into the secondary setting value; when the neutral point on this side is not grounded, the secondary setting value is taken as the maximum value of the impedance setting range of the small reactor.

8. The method for capacitor current compensation by differential protection of T-connected line current according to claim 4, characterized in that, If no parallel reactor is installed on this side, the impedance setting of the corresponding reactor and the impedance setting of the small reactor are set to 9000Ω.

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