Novel self-adaptive differential protection method and system for double-core controllable phase-shifting transformer

Abstract

The invention discloses a novel self-adaptive differential protection method and system for a double-core controllable phase-shifting transformer. The method comprises the following steps: calculating a transformation ratio error coefficient of the phase-shifting transformer; respectively determining the maximum unbalanced fault current during no-load voltage regulation and on-load voltage regulation of the phase-shifting transformer so as to determine an action current setting value; when the differential current of any phase is greater than the action current setting value, the electric balance differential protection acts; the output current of the excitation transformer self-coupling winding is corrected through the balance coefficient to serve as the magnetic balance differential current of the excitation transformer; according to the relation between the braking current and the initial braking current, different action threshold values of magnetic balance differential protection are determined; and when the differential current of any phase is greater than an action threshold value, the magnetic balance differential protection acts. According to the invention, the influence of the gear switching operation of the phase-shifting transformer on the setting of the protection setting value is calculated, and the influence of unbalanced current is reduced.

Description

Technical Field

[0001] This invention belongs to the field of transformer relay protection setting, specifically, it relates to a novel adaptive differential protection method and system for a dual-core controllable phase-shifting transformer. Background Technology

[0002] With the development of new power systems, the requirements for power transmission in distribution networks are constantly increasing. Currently, most 10kV distribution networks in my country adopt the principle of "closed-loop design, open-loop operation." This model increases the number of power outages and prolongs outage time during fault troubleshooting, system maintenance, and load transfer, thus reducing the reliability of the power supply. While closed-loop operation can achieve uninterrupted load transfer, in scenarios where the voltage difference or phase angle difference between the two sides of the closed-loop point in some distribution networks is large, direct closed-loop operation may generate excessive inrush current, leading to relay protection malfunctions and line overloads, significantly impacting the safe operation of the distribution network.

[0003] A phase-shifting transformer (PST) is a rectifier that alters the phase of current and voltage in a transmission line, thereby changing the power flow. It functions to regulate the three-phase balance of the system, enhance transmission capacity, and melt ice on transmission lines. During loop closing, the PST dynamically adjusts the voltage amplitude and phase angle on both sides of the closing switch, gradually bringing them into equilibrium, thus significantly reducing or even eliminating the current surge at the moment of closing. Current technologies for PST protection do not fully consider its inherent operating characteristics and generally neglect the potential impact of the PST's own tap-switching operation on protection setting values. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an adaptive differential protection method and system for a novel dual-core controllable phase-shifting transformer (NDCCPST). This method solves the problem of protecting the main body of the new dual-core controllable phase-shifting transformer. It improves the differential protection of the main body's electrical balance based on the turns ratio error coefficient of the series and parallel transformers in the phase-shifting transformer. Furthermore, by combining the voltage value corresponding to the real-time tap position of the regulating winding, it achieves adaptive dynamic adjustment of the magnetic balance protection, thereby improving the accuracy of the protection range.

[0005] The present invention adopts the following technical solution.

[0006] This invention proposes a novel adaptive differential protection method for a dual-core controllable phase-shifting transformer, wherein the phase-shifting transformer includes a series transformer and an excitation transformer; The methods include: Obtain the turns ratio of the series transformer, the turns ratio of the excitation transformer, and the ratio of the primary current of the series transformer to the primary current of the excitation transformer in order to calculate the turns ratio error coefficient of the phase-shifting transformer. When the phase-shifting transformer is under no-load voltage regulation, the maximum unbalanced fault current is determined based on the turns ratio error coefficient and the maximum through current during external faults. When the phase-shifting transformer is under on-load voltage regulation, the maximum unbalanced fault current is determined based on the error between the actual voltage and the rated voltage after the tap change and the maximum through current during external faults. The operating current setting value is determined based on the maximum unbalanced fault current. The current relationship between the primary side of the series transformer and the primary side of the excitation transformer is corrected using the maximum unbalanced fault current under no-load voltage regulation to obtain the differential current of each phase. When the differential current of any phase is greater than the operating current setting value, the electrical balance differential protection operates. Obtain the voltage at the maximum and actual voltage at each winding of the excitation transformer, as well as the turns ratio at the fixed voltage adjustment position, to determine the balance coefficient of the excitation transformer. Use the balance coefficient to correct the output current of the excitation transformer's autotransformer winding as the magnetic balance differential current of the excitation transformer. Use the absolute value of the magnetic balance differential current of the excitation transformer as the operating current setting value of the magnetic balance differential protection, and determine the minimum operating current setting value of the magnetic balance differential protection. Calculate the braking current of the magnetic balance differential protection and determine the initial braking current at the initial moment. Based on the relationship between the braking current and the initial braking current, determine the operating threshold values ​​for different magnetic balance differential protections. When the differential current of any phase exceeds the operating threshold value, the magnetic balance differential protection operates.

[0007] Preferably, the turns ratio error coefficient of the phase-shifting transformer As shown in the following formula:

[0008] In the formula, This refers to the turns ratio of a series transformer. This refers to the turns ratio of the excitation transformer. It is the ratio of the primary current of the series transformer to the primary current of the excitation transformer.

[0009] Preferably, during no-load voltage regulation, the maximum unbalanced fault current generated by an external fault in the transformer is shown in the following formula:

[0010] In the formula, For the maximum unbalanced fault current, This represents the maximum through-current during an external fault. Operating current setting value of electrical balance differential protection under no-load voltage regulation for: , This is the reliability coefficient.

[0011] Preferably, during on-load tap changing, the maximum unbalanced fault current generated by an external fault in the transformer is as follows:

[0012] In the formula, This refers to the error between the actual voltage and the rated voltage after the phase shifter tap is changed. This represents the maximum unbalanced fault current. The operating current setting value of the on-load tap changer differential protection is: .

[0013] Preferably, the maximum unbalanced fault current is utilized. The current relationship between the primary side of the series transformer and the primary side of the excitation transformer is corrected to obtain the differential current of each phase, as shown in the following formula:

[0014]

[0015]

[0016] In the formula, , , These are the corrected differential currents for each phase. , , These are the input currents of phases A, B, and C on the primary side of the series transformer, respectively. , , These are the input currents for phases A, B, and C on the primary side of the excitation transformer, respectively. , , These are the output currents of phases A, B, and C of the phase-shifting transformer, respectively.

[0017] Preferably, the balance factor of the excitation transformer is set to be... As shown in the following formula:

[0018] In the formula, This refers to the turns ratio of the excitation transformer when the voltage tap is fixed. This is the voltage at the maximum adjustable level of the autotransformer winding of the excitation transformer. This refers to the voltage at the actual tap position of the autotransformer winding of the excitation transformer. This is the voltage at the maximum adjustable level of the secondary winding of the excitation transformer. This refers to the voltage at the actual voltage adjustment level of the secondary winding of the excitation transformer.

[0019] Preferably, the magnetic balance differential currents of phases A, B, and C of the excitation transformer are as follows:

[0020]

[0021]

[0022] In the formula, , , These are the magnetic balance differential currents for phases A, B, and C of the excitation transformer, respectively. This is the balance factor of the excitation transformer.

[0023] Preferably, the absolute values ​​of the magnetic balance differential currents of phases A, B, and C of the excitation transformer are used as the operating current setting values ​​for the magnetic balance differential protection, as shown in the following formula: , ,

[0024] In the formula, , , These are the three-phase operating current setting values ​​for the magnetic balance differential protection; The magnetic balance differential current is a value that changes over time; the minimum operating current setting value is obtained. , , .

[0025] Preferably, the braking current of the magnetic balance differential protection is calculated using the following formula, as shown below:

[0026]

[0027]

[0028] In the formula, , , These are the three-phase braking currents for magnetic balance differential protection; The braking current is a value that changes over time; the initial braking current at the initial moment is obtained. , , .

[0029] Preferably, when the braking current of each phase... Less than the starting braking current At that time, the minimum operating current setting value of the magnetic balance differential protection is used. Action threshold value When the braking current of each phase Not less than the starting braking current of each phase At that time, the action threshold value is calculated using the following formula: , = , ,

[0030] In the formula, This is the slope coefficient of the braking current.

[0031] This invention also proposes a novel adaptive differential protection system for a dual-core controllable phase-shifting transformer, comprising: The electrical balance differential protection module is used to obtain the turns ratio of the series transformer, the turns ratio of the excitation transformer, and the ratio of the primary current of the series transformer to the primary current of the excitation transformer to calculate the turns ratio error coefficient of the phase-shifting transformer. When the phase-shifting transformer is under no-load tap changing, the maximum unbalanced fault current is determined based on the turns ratio error coefficient and the maximum through-current during an external fault. When the phase-shifting transformer is under on-load tap changing, the maximum unbalanced fault current is determined based on the error between the actual voltage and the rated voltage after tap change and the maximum through-current during an external fault. The operating current setting value of the electrical balance differential protection is determined based on the maximum unbalanced fault current. The current relationship between the primary sides of the series transformer and the excitation transformer is corrected using the maximum unbalanced fault current under no-load tap changing to obtain the differential current of each phase. When the differential current of any phase exceeds the operating current setting value, the electrical balance differential protection operates. The magnetic balance differential protection module is used to acquire the voltage of the maximum and actual voltage of each winding of the excitation transformer, as well as the turns ratio of the fixed voltage regulation position of the excitation transformer, to determine the balance coefficient of the excitation transformer; it uses the balance coefficient to correct the output current of the excitation transformer autotransformer winding as the magnetic balance differential current of the excitation transformer; it uses the absolute value of the magnetic balance differential current of the excitation transformer as the operating current setting value of the magnetic balance differential protection, and determines the minimum operating current setting value of the magnetic balance differential protection; it calculates the braking current of the magnetic balance differential protection and determines the initial braking current at the initial moment; based on the relationship between the braking current and the initial braking current, it determines the operating threshold value of different magnetic balance differential protections; when the differential current of any phase exceeds the operating threshold value, the magnetic balance differential protection operates.

[0032] The present invention is also a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to perform operations according to the instructions to execute the steps of the method.

[0033] The present invention is also a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0034] The beneficial effects of this invention, compared with the prior art, include at least the following: This invention fully considers the inherent operating characteristics of the phase-shifting transformer, calculates the impact of its own tap-switching operation on the protection setting value, focuses on the adaptive protection of the novel dual-core controllable phase-shifting transformer, and achieves a reduction in the impact of its unbalanced current. Based on the transformer's intrinsic protection, an improved adaptive differential calculation-based intrinsic protection scheme is proposed. First, the intrinsic electrical balance differential protection is improved based on the turns ratio coefficient of the phase-shifting transformer connected in series and parallel. Second, by combining the voltage value corresponding to the real-time tap position of the regulating winding, adaptive dynamic adjustment of the magnetic balance protection is achieved. Compared with existing protection schemes, the accuracy of the protection range is improved, achieving reliable protection for NDCCPST. Attached Figure Description

[0035] Figure 1 This is a flowchart of an adaptive differential protection method for a novel dual-core controllable phase-shifting transformer proposed in this invention.

[0036] Figure 2 This is a structural diagram of a new type of dual-core controllable phase-shifting transformer.

[0037] Figure 3 This is the wiring diagram for a new type of dual-core controllable phase-shifting transformer. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0039] This invention proposes a novel adaptive differential protection method for a dual-core controllable phase-shifting transformer, wherein the phase-shifting transformer includes a series transformer and an excitation transformer; such as Figure 1 As shown, the method includes: Step 1: Obtain the turns ratio of the series transformer, the turns ratio of the excitation transformer, and the ratio of the primary current of the series transformer to the primary current of the excitation transformer, in order to calculate the turns ratio error coefficient of the phase-shifting transformer.

[0040] Figure 2The complete structure diagram of the NDCCPST is shown below. The complete NDCCPST includes: an excitation transformer (ET), a series transformer (ST), a thyristor polarity control circuit, and a thyristor voltage regulation circuit. The excitation transformer is used to extract voltage from the line. By changing the tap position of the secondary winding of the parallel transformer, the extracted voltage can be changed. Then, the series transformer re-injects the changed voltage into the line, superimposing it on the original line voltage to generate a new voltage with the same amplitude but a changed phase angle. Therefore, by adjusting the tap position of the parallel transformer, the phase angle of the symmetrical two-core phase-shifting transformer can be changed.

[0041] Figure 2 In the diagram, the input currents of phases A, B, and C of the phase-shifting transformer are... , , The voltages flow into thyristor polarity control circuits A3, B3, and C3 respectively after passing through series transformers, and simultaneously into thyristor voltage regulating circuits A2, B2, and C2 respectively after passing through excitation transformers. One end of thyristor polarity control circuit A3 is connected to one end of thyristor voltage regulating circuit A1 and the other end of thyristor voltage regulating circuit B1. The other end of thyristor voltage regulating circuit A1 is connected to one end of thyristor voltage regulating circuit C2 and the other end of thyristor polarity control circuit B3. One end of thyristor polarity control circuit B3 is connected to one end of thyristor voltage regulating circuit B1, and the other end of thyristor voltage regulating circuit B1 is connected to one end of thyristor voltage regulating circuit A1. One end of the thyristor polarity control circuit C3 is connected to one end of the thyristor voltage regulating circuit C1, the other end of the thyristor voltage regulating circuit C1 is connected to one end of the thyristor voltage regulating circuit B2, and one end of the thyristor voltage regulating circuit B2 is connected to the other end of the thyristor polarity control circuit A3; the other end of the thyristor polarity control circuit C3 is connected to one end of the thyristor voltage regulating circuit A2, the other end of the thyristor polarity control circuit A3 is connected to one end of the thyristor voltage regulating circuit B2, and the other end of the thyristor voltage regulating circuit B3 is connected to one end of the thyristor voltage regulating circuit C2; the other ends of the thyristor voltage regulating circuits A2, B2, and C2 are all grounded. , , These are the input voltages for phases A, B, and C of the phase-shifting transformer, respectively. , , These are the output voltages of phase A, phase B, and phase C of the phase-shifting transformer, respectively.

[0042] Figure 3 This is a structural diagram of the series transformer and excitation transformer of the NDCCPST. From... Figure 3The voltage and current relationship in the excitation transformer and series transformer of the phase-shifting transformer can be seen. At the same time, it can visually reflect the voltage and current relationship between the primary and secondary sides of the excitation transformer and series transformer. This is the primary input current of the excitation transformer. The input current is for the voltage regulating winding of the excitation transformer. The output current of the excitation transformer autotransformer winding. Let x be the secondary voltage of the series transformer, where x = a, b, c. Based on the structure and principle of the NDCCPST phase-shifting transformer, neglecting the leakage impedance of the phase-shifting transformer, its positive-sequence equivalent model is determined. According to Kirchhoff's current law, the current relationship equation between the primary side of the NDCCPST series transformer and the primary side of the excitation transformer is as follows: , ,

[0043] In the formula, , , These are the input currents of phases A, B, and C on the primary side of the series transformer, respectively. , , These are the input currents for phases A, B, and C on the primary side of the excitation transformer, respectively. , , These are the output currents of phases A, B, and C of the phase-shifting transformer, respectively. The series-parallel regulating transformers configured in phase-shifting transformers have a wider regulation range, especially the NDCCPST, which changes the excitation voltage based on the traditional controllable phase shifter, and its tap changer can switch between all tap positions with positive and negative polarity. This wide-range voltage regulation characteristic means that if fixed rated voltage parameters are still used for calculation when operating at different tap positions, significant differences in differential current will occur. Conventional proportional braking characteristics are difficult to achieve reliable braking, posing a risk of protection malfunction. Traditional electrically balanced differential current protection cannot effectively self-adjust when faced with the above problems, and the original protection range may not be applicable. Therefore, a compensation amount is needed to ensure that the differential protection error caused by unbalanced current is reduced.

[0044] Based on the structural analysis of the NDCCPST, the relationship between the number of turns in the windings of the NDCCPST series transformer and the excitation transformer is as follows:

[0045]

[0046] In the formula, The turns ratio of a series transformer is the number of turns in the primary winding of the series transformer. Number of turns of the secondary winding coil The ratio, This refers to the turns ratio of the excitation transformer. , , These represent the number of turns in the primary winding, autotransformer winding, and secondary winding, respectively.

[0047] Using the turns ratio of a series transformer The turns ratio of the excitation transformer And the ratio of the primary current of the series transformer to the primary current of the excitation transformer. The turns ratio error coefficient of the phase-shifting transformer is calculated using the following formula. :

[0048] When calculating the differential current in the transformer electrical balance differential protection, the ratio of the current measurement values ​​of the current transformers on both sides of the phase-shifting transformer is first introduced to calculate the transformer ratio error coefficient, thereby effectively reflecting the difference between the current measurement values ​​on both sides of the phase-shifting transformer. By comparing the difference, the magnitude of the current error can be easily determined to determine whether there is a fault.

[0049] Step 2: When the phase-shifting transformer is under no-load voltage regulation, the maximum unbalanced fault current is determined based on the turns ratio error coefficient and the maximum through-current during an external fault. When the phase-shifting transformer is under on-load voltage regulation, the maximum unbalanced fault current is determined based on the error between the actual voltage and the rated voltage after the tap change and the maximum through-current during an external fault. The operating current setting value of the electrical balance differential protection is determined based on the maximum unbalanced fault current. The current relationship between the primary side of the series transformer and the primary side of the excitation transformer is corrected using the maximum unbalanced fault current under no-load voltage regulation to obtain the electrical balance differential current of each phase. When the differential current of any phase is greater than the operating current setting value, the electrical balance differential protection operates.

[0050] For the electrical balance differential protection of a phase-shifting transformer, the protection operating current is set according to the maximum unbalanced fault current generated during an external fault in the transformer, as shown in the following formula:

[0051] In the formula, This is the operating current setting value for the electrical balance differential protection; The reliability factor is set to 1.2 to 1.3 in the examples; This represents the maximum unbalanced fault current generated when an external fault occurs in the transformer.

[0052] When a phase-shifting transformer is under no-load tap changing conditions, the protection device needs to reconfigure its parameters by switching the setting zone to ensure that its rated ratio setting reflects the adjusted transformer tap status in real time. Therefore, this invention, based on Kirchhoff's current law and combined with NDCCPST's own structure, determines an adaptive electrical balance differential protection. Based on the ratio error coefficient, it adds a compensation amount to the rated ratio of the phase-shifting transformer after tap adjustment to reduce the differential protection error caused by unbalanced current. The maximum unbalanced fault current generated by an external fault in the transformer during no-load tap changing is shown in the following formula:

[0053] In the formula, For the maximum unbalanced fault current, This represents the maximum through-current during an external fault. The operating current setting value of the electrical balance differential protection under no-load voltage regulation is: .

[0054] In addition, during no-load tap changing, there may be a deviation between the receiving tap position and the actual tap changing in the parallel transformer tap changing process. To address this issue, measures such as adding a non-sensitive section longitudinal differential protection are adopted. When the system detects that the phase-shifting transformer is tap changing, the original protection switches to the non-sensitive section. By increasing the starting value and adjusting the slope of the braking characteristic curve, the protection sensitivity is reduced.

[0055] When a phase-shifting transformer is under on-load tap changing, it is difficult to introduce the transformer tap position status in real time. Therefore, the maximum unbalanced current is determined based on the error between the actual voltage and the rated voltage after tap change and the maximum through current during external faults. The maximum unbalanced fault current generated by an external fault during on-load tap changing is shown in the following formula:

[0056] In the formula, This refers to the error between the actual voltage and the rated voltage after the phase shifter tap is changed. This represents the maximum unbalanced fault current. The operating current setting value of the on-load tap changer differential protection is: .

[0057] Specifically, the influence of the current transformer models on the current must also be considered, utilizing the maximum unbalanced current. The current relationship between the primary side of the series transformer and the primary side of the excitation transformer is corrected to obtain the differential current of each phase, as shown in the following formula:

[0058]

[0059]

[0060] In the formula, , , These are the corrected differential currents for each phase. , , These are the input currents of phases A, B, and C on the primary side of the series transformer, respectively. , , These are the input currents for phases A, B, and C on the primary side of the excitation transformer, respectively. , , These are the output currents of phases A, B, and C of the phase-shifting transformer, respectively. When the differential current of any phase exceeds the operating current setting value, the electrical balance differential protection will operate.

[0061] The differential current calculation method proposed in this invention solves the contradiction between sensitivity and reliability caused by the unbalanced current introduced by the voltage regulation behavior itself when traditional differential protection is applied to PST. It clearly distinguishes between no-load voltage regulation and on-load voltage regulation and performs accurate unbalanced current calculations for each. In the no-load voltage regulation, a transformation ratio error coefficient is introduced to quantify the inherent manufacturing and measurement errors under fixed tap position. In the on-load voltage regulation, the error between the actual voltage and the rated voltage after the tap change is introduced, dynamically capturing the real-time changes in system parameters caused by tap operation. This makes the operating current setting value no longer a fixed value, but a variable that can adaptively adjust according to the PST voltage regulation stage and tap position. Through accurate modeling of different operating conditions, adaptive setting of the operating setting value and source correction of differential current are realized.

[0062] Step 3: Obtain the voltage at the maximum and actual voltage at each winding of the excitation transformer, as well as the turns ratio at the fixed voltage adjustment position of the excitation transformer, to determine the balance coefficient of the excitation transformer; use the balance coefficient to correct the output current of the excitation transformer autotransformer winding as the magnetic balance differential current of the excitation transformer; use the absolute value of the magnetic balance differential current of the excitation transformer as the operating current setting value of the magnetic balance differential protection, and determine the minimum operating current setting value of the magnetic balance differential protection; calculate the braking current of the magnetic balance differential protection, and determine the initial braking current at the initial moment; determine the operating threshold value of different magnetic balance differential protections based on the relationship between the braking current and the initial braking current; when the differential current of any phase is greater than the operating threshold value, the magnetic balance differential protection operates.

[0063] A magnetic balance current protection system is designed to protect both the excitation transformer and the series transformer based on the characteristics and magnetic flux principle of a two-core phase-shifting transformer. When an inter-turn short-circuit fault occurs inside the transformer windings, the fault current does not flow out of the windings, and the currents flowing into and out of the windings still follow Kirchhoff's current law. Therefore, traditional current differential protection and electrical balance differential protection cannot detect the abnormality. To address this, magnetic balance differential protection is developed, which determines the fault by monitoring the magnetomotive force balance between the primary and secondary windings of the transformer. Under normal operating conditions, the magnetomotive forces on both sides cancel each other out; however, an inter-turn fault disrupts this balance, generating a differential current that triggers the protection operation. To prevent inter-turn faults, magnetic balance differential protection is implemented, and an adaptive magnetic balance differential protection system is determined based on the NDCCPST's own structure. The protection parameters are adaptively adjusted according to the phase shifter tap position. Since the series transformer in the NDCCPST does not have a voltage regulating winding, no adjustment is needed, while the excitation transformer requires adaptive adjustment based on the tap position.

[0064] Based on the magnetic flux balance relationship of a series transformer, the magnetic balance differential current of phases A, B, and C of the series transformer can be obtained as shown in the following formula:

[0065]

[0066]

[0067] In the formula, , , These are the magnetic balance differential currents of phases A, B, and C of the series transformer, respectively. , , These are the output currents of phases A, B, and C of the excitation transformer autotransformer winding, respectively. When operating normally or when an external fault occurs, the magnetic balance differential current of each phase is 0; when an internal fault occurs, the magnetic balance differential current of the faulty phase is not 0; this differential current can reflect ground faults, inter-turn faults, and turn-to-ground faults.

[0068] When a phase-shifting transformer operates at different taps, calculating the differential current using the rated tap ratio will introduce a certain degree of error. The larger the gap between the rated tap and the actual operating tap, the greater the unbalanced current. Therefore, adaptive adjustment based on the tap position of the phase shifter is necessary. Series transformers do not have a regulating winding and do not require adjustment, while excitation transformers must be adaptively adjusted according to the tap position.

[0069] Let the balance factor of the excitation transformer be... As shown in the following formula:

[0070] In the formula, This refers to the turns ratio of the excitation transformer when the voltage tap is fixed. This is the voltage at the maximum adjustable level of the autotransformer winding of the excitation transformer. This refers to the voltage at the actual tap position of the autotransformer winding of the excitation transformer. This is the voltage at the maximum adjustable level of the secondary winding of the excitation transformer. This refers to the voltage at the actual tap position of the secondary winding of the excitation transformer; The revised differential current equation for the magnetic balance of the excitation transformer is as follows:

[0071]

[0072]

[0073] In the formula, , , These are the magnetic balance differential currents for phases A, B, and C of the excitation transformer, respectively. This is the balance factor of the excitation transformer; NDCCPST's magnetic balance differential protection uses ratio braking differential protection. The core feature of this protection is the introduction of braking current. Its operating threshold increases proportionally with the increase of braking current. Its protection characteristics are similar to the structure of the operating current. When an external short-circuit current is introduced, the equivalent through current of the series transformer is used as the braking quantity. The absolute values ​​of the magnetic balance differential currents of phases A, B, and C of the excitation transformer are used as the operating current setting values ​​for the magnetic balance differential protection, as shown in the following formula: , ,

[0074] In the formula, , , These are the three-phase operating current setting values ​​for the magnetic balance differential protection; Since the magnetic balance differential current is a value that changes with time, there exists a minimum operating current setting value. , , ; The braking current of the magnetic balance differential protection is calculated using the following formula, as shown below:

[0075]

[0076]

[0077] In the formula, , , These are the three-phase braking currents for magnetic balance differential protection; Since the braking current is a value that changes with time, there exists an initial braking current at the initial moment. , , ; The operating characteristic equation of the magnetic balance differential protection is: When the braking current of each phase Less than the starting braking current At that time, the minimum operating current setting value of the magnetic balance differential protection is used. Action threshold value When the braking current of each phase Not less than the starting braking current of each phase At that time, the action threshold value is calculated using the following formula: , = , ,

[0078] In the formula, The slope coefficient of the braking current is determined based on practical engineering experience. =0.4~1.0; When the differential current of any phase exceeds the operating threshold, the magnetic balance differential protection will operate.

[0079] The excitation transformer module, also known as a parallel transformer, consists of three autotransformers and a thyristor voltage regulation control circuit. One end of the primary winding of each phase transformer is connected in parallel to the power grid, and the other end is star-grounded. Its function is to obtain voltage from the power grid.

[0080] The series transformer module consists of three single-phase, double-winding transformers connected in series to the circuit via their primary windings. Its function is to superimpose voltage onto the system. The autotransformer's autotransformer windings and secondary windings are sequentially connected to the series transformer's secondary windings.

[0081] The thyristor polarity control circuit module controls the phase lead and lag relationship of the input and output voltages of the device through the P and N pairs of thyristors, thereby realizing the forward and reverse voltage regulation function of the phase-shifting transformer. A tap changer allows switching between all polarity ranges. Its wide voltage regulation characteristic means that when operating at both positive and negative polarity ranges, a large unbalanced current will be generated if traditional protection methods are used for setting calculations.

[0082] The thyristor voltage regulation circuit module is used to control the connection between the equidistant taps of each stage of the excitation transformer's autotransformer winding and the external circuit, so as to quickly and accurately output the desired compensation voltage phasor. Each phase of the excitation transformer has two voltage regulation circuit modules, A1 and A2. The number of taps and the number of turns in the tap coil of the excitation transformer's autotransformer winding, as well as the number of series layers and turns in the secondary winding, determine the voltage amplitude range and accuracy of the phase-shifting transformer. Its tap adjustment amplitude is much larger than that of ordinary transformers; if the setting calculation is based on the original voltage magnitude, the transformer protection will produce errors. The protection action module is used to receive protection action commands, disconnect the corresponding lines, and adjust the tap position of the dual-core symmetrical phase-shifting transformer until the loop closing conditions are met.

[0083] This invention also proposes a novel adaptive differential protection system for a dual-core controllable phase-shifting transformer, comprising: The electrical balance differential protection module is used to obtain the turns ratio of the series transformer, the turns ratio of the excitation transformer, and the ratio of the primary current of the series transformer to the primary current of the excitation transformer to calculate the turns ratio error coefficient of the phase-shifting transformer. When the phase-shifting transformer is under no-load tap change, the maximum unbalanced fault current is determined based on the turns ratio error coefficient and the maximum through-current during an external fault. When the phase-shifting transformer is under on-load tap change, the maximum unbalanced fault current is determined based on the error between the actual voltage and the rated voltage after tap change and the maximum through-current during an external fault. The operating current setting value is determined based on the maximum unbalanced fault current. The current relationship between the primary sides of the series transformer and the excitation transformer is corrected using the maximum unbalanced fault current under no-load tap change to obtain the differential current for each phase. When the differential current of any phase exceeds the operating current setting value, the electrical balance differential protection operates. The magnetic balance differential protection module is used to acquire the voltage of the maximum and actual voltage of each winding of the excitation transformer, as well as the turns ratio of the fixed voltage regulation position of the excitation transformer, to determine the balance coefficient of the excitation transformer; it uses the balance coefficient to correct the output current of the excitation transformer autotransformer winding as the magnetic balance differential current of the excitation transformer; it uses the absolute value of the magnetic balance differential current of the excitation transformer as the operating current setting value of the magnetic balance differential protection, and determines the minimum operating current setting value of the magnetic balance differential protection; it calculates the braking current of the magnetic balance differential protection and determines the initial braking current at the initial moment; based on the relationship between the braking current and the initial braking current, it determines the operating threshold value of different magnetic balance differential protections; when the differential current of any phase exceeds the operating threshold value, the magnetic balance differential protection operates.

[0084] Finally, a distribution network and phase-shifting transformer model was built on the Matlab / Simulink platform. By simulating various typical faults inside the phase-shifting transformer, the proposed protection scheme was verified on the simulation platform to determine the correctness and reliability of the protection scheme.

[0085] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0086] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0087] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0088] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A novel adaptive differential protection method for a dual-core controllable phase-shifting transformer, characterized in that, include: When tap changing is not under load, the maximum unbalanced fault current is determined based on the transformer ratio error coefficient and the maximum through current during an external fault. When tap changing is on load, the maximum unbalanced fault current is determined based on the error between the actual voltage and the rated voltage after the tap change and the maximum through current during an external fault. The operating current setting value of the electrical balance differential protection is determined based on the maximum unbalanced fault current; the differential current of each phase is determined using the maximum unbalanced fault current under no-load voltage regulation; the electrical balance differential protection operates when the differential current of any phase is greater than the operating current setting value. The output current of the excitation transformer autotransformer is corrected using the balance coefficient as the magnetic balance differential current of the excitation transformer; the absolute value of the magnetic balance differential current of the excitation transformer is used as the operating current setting value of the magnetic balance differential protection; the braking current and initial braking current of each magnetic balance differential protection are used to determine the operating threshold value of the magnetic balance differential protection; when the differential current of any phase is greater than the operating threshold value, the magnetic balance differential protection operates.

2. The adaptive differential protection method for a novel dual-core controllable phase-shifting transformer according to claim 1, characterized in that, A phase-shifting transformer includes a series transformer and an excitation transformer. The turns ratio of the series transformer, the turns ratio of the excitation transformer, and the ratio of the primary current of the series transformer to the primary current of the excitation transformer are obtained to calculate the turns ratio error coefficient of the phase-shifting transformer. As shown in the following formula: In the formula, This refers to the turns ratio of a series transformer. This refers to the turns ratio of the excitation transformer. It is the ratio of the primary current of the series transformer to the primary current of the excitation transformer.

3. The adaptive differential protection method for a novel dual-core controllable phase-shifting transformer according to claim 2, characterized in that, The maximum unbalanced fault current generated by an external fault in the transformer during no-load voltage regulation is shown in the following formula: In the formula, For the maximum unbalanced fault current, This represents the maximum through-current during an external fault. Operating current setting value of electrical balance differential protection under no-load voltage regulation for: , This is the reliability coefficient.

4. The adaptive differential protection method for the novel dual-core controllable phase-shifting transformer according to claim 3, characterized in that, When the transformer is under on-load tap changing, the maximum unbalanced fault current generated by an external fault is shown in the following formula: In the formula, This refers to the error between the actual voltage and the rated voltage after the phase shifter tap is changed. This represents the maximum unbalanced fault current. The operating current setting value of the on-load tap changer differential protection is: .

5. The adaptive differential protection method for a novel dual-core controllable phase-shifting transformer according to claim 4, characterized in that, Utilizing the maximum unbalanced fault current The current relationship between the primary side of the series transformer and the primary side of the excitation transformer is corrected to obtain the differential current of each phase, as shown in the following formula: In the formula, , , These are the corrected differential currents for each phase. , , These are the input currents of phases A, B, and C on the primary side of the series transformer, respectively. , , These are the input currents for phases A, B, and C on the primary side of the excitation transformer, respectively. , , These are the output currents of phases A, B, and C of the phase-shifting transformer, respectively.

6. The adaptive differential protection method for a novel dual-core controllable phase-shifting transformer according to claim 1, characterized in that, To determine the balance coefficient of the excitation transformer, obtain the voltage at the maximum and actual voltage at each regulating tap of each winding, as well as the turns ratio at the fixed regulating tap. As shown in the following formula: In the formula, This refers to the turns ratio of the excitation transformer when the voltage tap is fixed. This is the voltage at the maximum adjustable level of the autotransformer winding of the excitation transformer. This refers to the voltage at the actual tap position of the autotransformer winding of the excitation transformer. This is the voltage at the maximum adjustable level of the secondary winding of the excitation transformer. This refers to the voltage at the actual voltage adjustment level of the secondary winding of the excitation transformer.

7. The adaptive differential protection method for a novel dual-core controllable phase-shifting transformer according to claim 6, characterized in that, The magnetic balance differential currents of phases A, B, and C of the excitation transformer are shown in the following formula: In the formula, , , These are the magnetic balance differential currents for phases A, B, and C of the excitation transformer, respectively. This is the balance factor of the excitation transformer.

8. The adaptive differential protection method for a novel dual-core controllable phase-shifting transformer according to claim 7, characterized in that, The absolute values ​​of the magnetic balance differential currents of phases A, B, and C of the excitation transformer are used as the operating current setting values ​​for the magnetic balance differential protection, as shown in the following formula: ， ， In the formula, , , These are the three-phase operating current setting values ​​for the magnetic balance differential protection; The magnetic balance differential current is a value that changes over time; the minimum operating current setting value is obtained. , , .

9. The adaptive differential protection method for a novel dual-core controllable phase-shifting transformer according to claim 8, characterized in that, The braking current of the magnetic balance differential protection is calculated using the following formula, as shown below: In the formula, , , These are the three-phase braking currents for magnetic balance differential protection; The braking current is a value that changes over time; the initial braking current at the initial moment is obtained. , , .

10. The adaptive differential protection method for a novel dual-core controllable phase-shifting transformer according to claim 8, characterized in that, When the braking current of each phase Less than the starting braking current At that time, the minimum operating current setting value of the magnetic balance differential protection is used. Action threshold value When the braking current of each phase Not less than the starting braking current of each phase At that time, the action threshold value is calculated using the following formula: ， = 、 、 In the formula, This is the slope coefficient of the braking current.

11. A novel adaptive differential protection system for a dual-core controllable phase-shifting transformer, used to implement the method described in any one of claims 1 to 10, characterized in that, include: The electrical balance differential protection module is used to obtain the turns ratio of the series transformer, the turns ratio of the excitation transformer, and the ratio of the primary current of the series transformer to the primary current of the excitation transformer, in order to calculate the turns ratio error coefficient of the phase-shifting transformer. When the phase-shifting transformer is tap-changing under no-load conditions, the maximum unbalanced fault current is determined based on the turns ratio error coefficient and the maximum through-current during external faults. When the phase-shifting transformer is tap-changing under load conditions, the maximum unbalanced fault current is determined based on the error between the actual voltage and the rated voltage after the tap change and the maximum through-current during external faults. The operating current setting value of the electrical balance differential protection is determined based on the maximum unbalanced fault current; the current relationship between the primary side of the series transformer and the primary side of the excitation transformer is corrected using the maximum unbalanced fault current under no-load voltage regulation to obtain the differential current of each phase; when the differential current of any phase is greater than the operating current setting value, the electrical balance differential protection operates. The magnetic balance differential protection module is used to obtain the voltage of the maximum and actual voltage of each winding of the excitation transformer, as well as the turns ratio of the fixed voltage regulation position of the excitation transformer, in order to determine the balance coefficient of the excitation transformer; the output current of the excitation transformer autotransformer winding is corrected using the balance coefficient as the magnetic balance differential current of the excitation transformer; the absolute value of the magnetic balance differential current of the excitation transformer is used as the operating current setting value of the magnetic balance differential protection, and the minimum operating current setting value of the magnetic balance differential protection is determined. Calculate the braking current of the magnetic balance differential protection and determine the initial braking current at the initial moment; determine the operating threshold value of different magnetic balance differential protections based on the relationship between the braking current and the initial braking current; the magnetic balance differential protection operates when the differential current of any phase is greater than the operating threshold value.

12. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-10.

13. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-10.

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