A method and system for commutation transformer transverse differential protection based on transverse differential current

Abstract

The present invention provides a method and system for commutator transformer transverse differential protection based on transverse differential current. The method comprises calculating the longitudinal differential current, longitudinal phase braking current, second harmonic effective value, and fundamental effective value of each of the Y / Y commutator transformer and the Y / Δ commutator transformer operating in parallel, as well as the transverse differential current, transverse phase braking current, second and third harmonic effective values, and fundamental effective value of the Y / Y commutator transformer and the Y / Δ commutator transformer. Furthermore, in addition to the protection initiation criteria based on the longitudinal differential current and phase braking current, the ratio differential action criteria, and the first harmonic blocking criteria, the transverse differential protection initiation criteria based on the transverse differential current and transverse phase braking current, the second harmonic blocking criteria, and the third harmonic blocking criteria are added to further determine the protection action. The method and system raise the threshold for the second harmonic of the magnetizing inrush current criterion and improve the sensitivity of the commutator transformer internal turn-to-turn fault differential protection, thereby effectively improving the safe operation of the power grid.

Description

Technical Field

[0001] The present invention relates to the field of power system relay protection, and more particularly to a commutator transformer transverse differential protection method and system based on transverse differential current. Background Art

[0002] Converter transformers are a critical component of DC transmission systems. Converter transformer protection is a crucial system component for ensuring safe and stable grid operation, crucial for the safety of the entire AC / DC transmission network. Improper converter transformer protection can damage power equipment, disrupt system stability, and even cause a power outage at the converter station. In severe cases, it can lead to the collapse of the entire power system. Currently, converter transformer protection generally uses conventional inrush current blocking principles to identify inrush currents and faults. This identification relies on accurate calculation of current signals. Sustained and sudden current fluctuations during a fault may increase the calculated current harmonics, leading to erroneous protection blocking. Therefore, converter transformer protection must be able to accurately calculate and identify fault waveforms and inrush current waveforms and initiate countermeasures.

[0003] The primary criterion for inrush current blocking in existing commutator transformer protection is that the second harmonic percentage exceeds the blocking value. When the longitudinal differential current of the commutator transformer exceeds the pickup set value, the corresponding phase protection of the commutator transformer is activated and the second harmonic percentage in the longitudinal differential current is calculated. If the second harmonic percentage exceeds the blocking value, it is identified as a magnetizing inrush current and the commutator transformer differential protection for that phase is blocked. If the second harmonic percentage in the differential current is less than the blocking value, the commutator transformer differential protection for that phase is tripped. However, the above-mentioned criterion based on the percentage content of the second harmonic cannot effectively distinguish between inrush current and developing inter-turn faults. When a developing inter-turn fault occurs in the commutator transformer, the longitudinal differential current exceeds the starting set value, and the waveform continues to change suddenly, causing the calculated second harmonic percentage content of the phase to increase at this time, which may be greater than the harmonic blocking value for a long time. The commutator transformer protection is mistakenly judged as inrush current blocking differential protection. The differential protection is not opened until the differential current waveform stabilizes and the calculated second harmonic percentage content is lower than the harmonic blocking value, resulting in delayed operation of the commutator transformer differential protection, which will lead to serious consequences and endanger system safety. Summary of the Invention

[0004] In order to solve the technical problem in the prior art that the commutator transformer differential protection is triggered solely based on the effective content of the second harmonic calculated based on the longitudinal differential current, but cannot identify the developing inter-turn faults occurring in the commutator transformer, thereby causing delayed action of the commutator transformer differential protection, the present invention provides a commutator transformer transverse differential protection method and device based on transverse differential current identification.

[0005] According to one aspect of the present invention, the present invention provides a commutation transformer transverse differential protection method based on transverse differential current, the method comprising:

[0006] Collecting high-voltage side three-phase currents of Y / Y commutation transformers and Y / Δ commutation transformers operating in parallel, as well as their respective low-voltage side three-phase currents, wherein the Y / Y commutation transformers and Y / Δ commutation transformers are connected to a protection device;

[0007] Calculating the longitudinal differential current, longitudinal phase braking current, second harmonic effective value and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer according to the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0008] When the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer meet the respective protection start criteria, starting the protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device;

[0009] When the Y / Y commutation transformer and / or the Y / Δ commutation transformer for which protection of the corresponding phase in the protection device has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phase meet the respective ratio differential action criteria, the second harmonic effective value and the fundamental effective value of the corresponding phase meet the respective first harmonic blocking criteria, and the transverse differential current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer meets the transverse differential protection activation criteria, calculating the ratio of the transverse differential current and the transverse phase braking current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0010] When the ratio is not less than a preset first threshold value, and the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are greater than a preset second threshold value, determining the protection action of the corresponding phase of the protection device according to the second harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the second harmonic blocking criterion;

[0011] When the ratio is less than the first threshold, the protection action of the corresponding phase of the protection device is determined directly according to the second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the third harmonic blocking criterion.

[0012] According to another aspect of the present invention, the present invention provides a commutation transformer transverse differential protection system based on transverse differential current, the system comprising:

[0013] A data acquisition module is used to collect the high-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, which are connected to a protection device, and the low-voltage side three-phase current of each of the Y / Y commutation transformer and the Y / Δ commutation transformer, which are connected to a protection device;

[0014] a first calculation module, configured to calculate the longitudinal differential current, longitudinal phase braking current, second harmonic effective value, and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value, and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer based on the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0015] a protection start module, configured to start protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device when the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer meet their respective protection start criteria;

[0016] a second calculation module, configured to calculate the ratio of the transverse differential current and the transverse phase braking current of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer, when the protection of the corresponding phases in the protection device has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phases satisfy the respective ratio differential action criteria, the second harmonic effective value and the fundamental effective value of the corresponding phases satisfy the respective first harmonic blocking criteria, and the transverse differential current of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer satisfy the transverse differential protection activation criteria;

[0017] a first judgment module, configured to, when the ratio is not less than a preset first threshold value and the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are greater than a preset second threshold value, determine, based on the second harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer and a second harmonic blocking criterion, a protection action for the corresponding phase of the protection device;

[0018] The second judgment module is used to determine the protection action of the corresponding phase of the protection device directly according to the second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the third harmonic blocking criterion when the ratio is less than the first threshold.

[0019] The present invention provides a method and system for commutator transformer transverse differential protection based on transverse differential current. The method comprises calculating the longitudinal differential current, longitudinal phase braking current, second harmonic RMS value, and fundamental RMS value of each of the Y / Y commutator transformer and the Y / Δ commutator transformer operating in parallel, as well as the transverse differential current, transverse phase braking current, second harmonic RMS value, third harmonic RMS value, and fundamental RMS value. Furthermore, in addition to determining protection action based on the longitudinal differential current and phase braking current protection initiation criteria, ratio differential action criteria, and first harmonic blocking criteria, the method and system further determine protection action based on the transverse differential current and transverse phase braking current transverse differential protection initiation criteria, second harmonic blocking criteria, and third harmonic blocking criteria. The method and system do not alter the differential current characteristics of internal faults in the commutator transformers, but effectively suppress the magnetizing inrush current of the commutator transformers operating in parallel, reduce the impact of the magnetizing inrush current on differential protection, raise the second harmonic criterion threshold for the magnetizing inrush current, and enhance the sensitivity of the commutator transformer internal turn-to-turn differential protection, thereby effectively improving the safe operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0021] Figure 1 Flow chart of a commutation transformer transverse differential protection method based on transverse differential current according to a preferred embodiment of the present invention;

[0022] FIG2( a ) is a schematic diagram showing the longitudinal differential current of a Y / Δ commutated transformer changing with time according to a preferred embodiment of the present invention;

[0023] FIG2( b ) is a schematic diagram showing the longitudinal differential current of a Y / Y commutated transformer changing with time according to a preferred embodiment of the present invention;

[0024] FIG2( c ) is a schematic diagram showing the time variation of the transverse differential current of the Y / Δ commutated transformer and the Y / Y commutated transformer operated in parallel according to a preferred embodiment of the present invention;

[0025] FIG3( a ) is a schematic diagram showing the change of the B-phase transverse current of the Y / Δ commutated transformer over time according to a preferred embodiment of the present invention;

[0026] FIG3( b ) is a schematic diagram showing the variation of the second harmonic content of the B-phase transverse differential current of the Y / Δ commutated transformer over time according to a preferred embodiment of the present invention;

[0027] Figure 4 Schematic diagram of the structure of a commutation transformer transverse differential protection system based on transverse differential current according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0028] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0029] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0030] Example Method

[0031] Figure 1 FIG. 1 is a flow chart of a commutation transformer transverse differential protection method based on transverse differential current according to a preferred embodiment of the present invention. Figure 1 As shown, the commutation transformer transverse differential protection method based on transverse differential current described in this preferred embodiment starts from step 101.

[0032] In step 101, the high-voltage side three-phase currents of the Y / Y commutation transformer and the Y / Δ commutation transformer operating in parallel, as well as the low-voltage side three-phase currents of each are collected, wherein the Y / Y commutation transformer and the Y / Δ commutation transformer are connected to a protection device.

[0033] In step 102, the longitudinal differential current, longitudinal phase braking current, second harmonic effective value and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are calculated based on the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer.

[0034] Preferably, the three-phase longitudinal differential current, longitudinal phase braking current, second harmonic effective value and fundamental effective value of the Y / Y commutation transformer and the Y / Δ commutation transformer are calculated based on the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, wherein:

[0035] I dYi =│I Yhi +I Yli │, IzdYi =│I Yhi +I Yli │ / 2

[0036] I dΔi =│I Δhi +I Δli │, I zdΔi =│I Δhi +I Δli │ / 2

[0037] I di =│I dYi -I dΔi │, I zdi =│I dYi +I dΔi │

[0038] Where, i is any one of the three phases A, B, and C of the Y / Y commutation transformer and the Y / Δ commutation transformer, I Yhi and I Yli are the high-voltage side and low-voltage side current phasors of the Y / Y commutation transformer i phase, I dYi and I zdYi are the longitudinal differential current and longitudinal phase braking current of the Y / Y commutation transformer i phase respectively; I Δhi and I Δli are the high-voltage side and low-voltage side current phasors of the Y / Δ commutation transformer i phase, I dΔi and I zdΔi are the longitudinal differential current and longitudinal phase braking current of the Y / Δ commutation transformer i phase respectively; I di and I zdi are the transverse differential current and transverse phase braking current of the i-phase of the Y / Y commutation transformer and the Y / Δ commutation transformer respectively;

[0039] Calculating the second harmonic effective value and the fundamental effective value of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer using a Fourier algorithm according to the longitudinal differential current of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0040] According to the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, a Fourier algorithm is used to calculate the second harmonic effective value, the third harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer.

[0041] In step 103, when the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer meet their respective protection start-up criteria, the protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is started.

[0042] Preferably, when the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer respectively meet their protection initiation criteria, the protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is initiated, wherein the calculation formula of the protection initiation criteria is:

[0043] I dYi >I cdqdY

[0044] I dΔi >I cdqdΔ

[0045] Where, I cdqdY and I cdqdΔ The protection start-up settings of the Y / Y commutation transformer and the Y / Δ commutation transformer are set according to the rated currents of the Y / Y commutation transformer and the Y / Δ commutation transformer respectively;

[0046] When the Y / Y commutation transformer and / or the Y / Δ commutation transformer each meet the protection start-up criterion for its i-phase, the protection of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is started; when the Y / Y commutation transformer and the Y / Δ commutation transformer each do not meet the protection start-up criterion for its i-phase, the protection of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is returned.

[0047] In step 104, when the Y / Y commutation transformer and / or the Y / Δ commutation transformer whose protection of the corresponding phase in the protection device has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phase meet the respective ratio differential action criteria, the second harmonic effective value and the fundamental effective value of the corresponding phase meet the respective first harmonic blocking criteria, and the transverse differential current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer meets the transverse differential protection activation criteria, the ratio of the transverse differential current and the transverse phase braking current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer is calculated.

[0048] Preferably, when the Y / Y commutation transformer and / or the Y / Δ commutation transformer whose protection of the corresponding phase in the protection device has been activated, the longitudinal differential current and longitudinal phase braking current of the corresponding phase meet their respective ratio differential action criteria, the second harmonic effective value and fundamental effective value of the corresponding phase meet their respective first harmonic blocking criteria, and the transverse differential current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer meets the transverse differential protection activation criteria, the ratio of the transverse differential current and the transverse phase braking current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer is calculated, wherein:

[0049] The expression of the ratio differential action criterion is:

[0050] IdYi >I cdqdY +K r *(I zdYi –I e )

[0051] I dΔi >I cdqdΔ +K r *(I zdΔi –I e )

[0052] Where K r is the ratio action slope, generally set to 0.5, I e is the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0053] When the longitudinal differential current and longitudinal phase braking current of the Y / Y commutation transformer and / or the Y / Δ commutation transformer of which the protection of phase i in the protection device has been started do not meet the respective ratio differential action criteria, the protection of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is returned;

[0054] The expression of the first harmonic blocking criterion is:

[0055] H L2Yi / B LYi >K1

[0056] H L2Δi / B LΔi >K1

[0057] Where H L2Yi and B LYi are respectively the second harmonic effective value and the fundamental effective value determined by calculation based on the longitudinal differential current of the i-phase of the Y / Y commutation transformer; H L2Δi and B LΔi are respectively the second harmonic effective value and the fundamental effective value determined by calculation based on the longitudinal differential current of phase i of the Y / Δ commutation transformer; K1 is a constant, 0<K1<1, and is generally set to 15%;

[0058] When the Y / Y commutation transformer and / or the Y / Δ commutation transformer of which the protection of phase i in the protection device has been activated, and the longitudinal differential current and longitudinal phase braking current of its phase i meet the respective ratio differential action criteria, but the second harmonic effective value and fundamental effective value of its phase i do not meet the respective first harmonic blocking criteria, the protection output of the Y / Y commutation transformer and / or the Y / Δ commutation transformer of phase i in the protection device is activated;

[0059] The expression of the criterion for starting the transverse differential protection is:

[0060] I di >Idz1

[0061] Where, I dz1 It is the starting value of the transverse differential protection, which is set according to the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0062] When the Y / Y commutation transformer and / or the Y / Δ commutation transformer whose protection of phase i in the protection device has been started, the longitudinal differential current and longitudinal phase braking current of its i phase meet the respective ratio differential action criteria, and the second harmonic effective value and fundamental effective value of its i phase meet the respective first harmonic locking criteria, but the transverse differential current of phase i of the Y / Y commutation transformer and the Y / Δ commutation transformer does not meet the transverse differential protection starting criteria, the protection of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is locked.

[0063] In step 105, when the ratio is not less than a preset first threshold value and the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are greater than a preset second threshold value, the protection action of the corresponding phase of the protection device is determined based on the second harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the second harmonic blocking criterion.

[0064] Preferably, when the ratio is not less than a preset first threshold value, and the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are greater than a preset second threshold value, the protection action of the corresponding phase of the protection device is determined according to the second harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the second harmonic blocking criterion, wherein:

[0065] The first threshold K0 is a constant, 0<K0<1, and is generally set to 0.8;

[0066] The second threshold I dz2 The setting is performed according to the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer, and 0<I dz1 <I dz2 ;

[0067] The expression of the second harmonic blocking criterion is:

[0068] H T2i / B Ti >K2

[0069] Where H T2i and B Ti are the second harmonic effective value and the fundamental effective value calculated based on the transverse differential current of the i-phase of the Y / Y commutated transformer and the Y / Δ commutated transformer, respectively; K2 is a constant, 0<K2<1, and is generally set to 30%;

[0070] When the second harmonic effective value H of the Y / Y commutation transformer and the Y / Δ commutation transformer i phase T2i and the fundamental effective value B Ti If the second harmonic blocking criterion is met, the protection blocking of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined;

[0071] When the second harmonic effective value H of the Y / Y commutation transformer and the Y / Δ commutation transformer i phase T2i and fundamental effective value B Ti If the second harmonic blocking criterion is not met, a protection outlet of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined.

[0072] In step 106, when the ratio is less than the first threshold, the protection action of the corresponding phase of the protection device is determined directly based on the second harmonic effective value, the third harmonic effective value, and the fundamental effective value of the corresponding phase of the Y / Y commutated transformer and the Y / Δ commutated transformer, as well as the third harmonic blocking criterion.

[0073] Preferably, when the ratio is less than the first threshold, the protection action of the corresponding phase of the protection device is determined directly according to the second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutated transformer and the Y / Δ commutated transformer, and the third harmonic blocking criterion, wherein:

[0074] The expressions of the third harmonic blocking criteria are:

[0075]

[0076] Where H T3i is the effective value of the third harmonic determined based on the transverse differential current of the i-phase of the Y / Y commutated transformer and the Y / Δ commutated transformer; K3 and K4 are constants, 0<K3, K4<1, and K3<K4, K3 is generally 15%, and K4 is generally 30%;

[0077] When the second harmonic effective value H of the Y / Y commutation transformer and the Y / Δ commutation transformer i phase T2i , the effective value of the third harmonic H T3i and fundamental effective value B Ti If the third harmonic blocking criterion is met, the protection blocking of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined;

[0078] When the second harmonic effective value H of the Y / Y commutation transformer and the Y / Δ commutation transformer i phase T2i , the effective value of the third harmonic H T3i and fundamental effective value B TiIf the third harmonic blocking criterion is not met, a protection blocking exit of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined.

[0079] FIG2(a) is a schematic diagram showing the longitudinal differential current of a Y / Δ commutation transformer according to a preferred embodiment of the present invention, and FIG2(b) is a schematic diagram showing the longitudinal differential current of a Y / Y commutation transformer according to a preferred embodiment of the present invention, showing the longitudinal differential current of a Y / Y commutation transformer according to a preferred embodiment of the present invention. In the simulation test, as shown in FIG2(a) and FIG2(b), when the A-phase voltage closing angle is 0° and the residual magnetism of the two parallel commutation transformers reaches 0.2, the A-phase longitudinal differential current of each of the two commutation transformers (marked as differential current in the figure) is approximately 1 to 1.4Ie, where Ie is the rated current of the two commutation transformers. At this time, the amplitude of the A-phase transverse differential current is less than the starting constant value I dz1 =0.2Ie, does not meet the lateral start protection criterion, then after the duration of the lateral differential current of phase A reaches a certain delay, the protection of phase A of the commutator transformer is immediately locked to prevent the commutator transformer protection from malfunctioning. Figure 2(c) is a schematic diagram of the lateral differential current of the Y / Δ commutator transformer and the Y / Y commutator transformer running in parallel with time according to the preferred embodiment of the present invention. Comparing Figures 2(a), 2(b) and 2(c), it can be clearly seen that at about 0.8 seconds, phase A has an obvious sudden drop in lateral differential current and lasts for a period of time, which indirectly confirms the correctness of the present invention in identifying the inrush current characteristics of the commutator transformer.

[0080] Figure 3(a) is a schematic diagram showing the change of the horizontal current of the B phase of the Y / Δ commutation transformer over time according to a preferred embodiment of the present invention. As shown in Figure 3(a), when a developing inter-turn short circuit fault occurs in the B phase of the high-voltage side winding of the Y / Δ commutation transformer, the horizontal phase differential current I dB The amplitude is larger than the set value I soon after the fault occurs. dz2 =0.2Ie, and after 22.6ms, the ratio of the transverse phase differential current to the transverse braking current is greater than the set first threshold k0=0.8, and after 22.8ms, the transverse phase differential current I dB The amplitude is also greater than the fixed value I dz2 =1.5Ie. Figure 3(b) is a schematic diagram showing the change of the second harmonic content of the B-phase transverse differential current of the Y / Δ commutated transformer over time according to a preferred embodiment of the present invention. Corresponding to Figure 3(a), in Figure 3(b), the transverse differential current I dBThe ratio of the second harmonic RMS value to the fundamental RMS value, that is, the second harmonic percentage, is less than 30% after 23.6ms, the second harmonic blocking criterion. Therefore, the second harmonic blocking criterion is not met, and the protection output of phase B of the Y / Δ commutation transformer is determined. The simulation test fully demonstrates that the method of the present invention can complete data extraction and analysis within 30ms and automatically determine whether to activate or disable the commutation transformer protection, greatly improving equipment reliability.

[0081] In this preferred embodiment, the commutation transformer transverse differential protection method based on transverse differential current first calculates the longitudinal differential current, longitudinal phase braking current, second harmonic effective value, third harmonic effective value and fundamental effective value of each of the Y / Y commutation transformer and the Y / Δ commutation transformer operating in parallel, as well as the transverse differential current and transverse phase braking current. In addition to the protection start criterion based on the longitudinal differential current and the phase braking current, the ratio differential action criterion and the first harmonic blocking criterion for judging the protection action, the transverse differential protection start criterion based on the transverse differential current and the transverse phase braking current, the second harmonic blocking criterion and the third harmonic blocking criterion are added to further judge the protection action, which has the following beneficial effects:

[0082] 1. The method of the present invention uses the current data of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer operating in parallel to calculate the electrical characteristic value, innovatively processing the inrush current and inter-turn fault characteristics of the commutation transformer, improving the judgment efficiency and enhancing the inter-turn fault identification capability of the commutation transformer protection.

[0083] 2. Simulation tests show that the method of the present invention can complete data extraction and analysis within 30ms and automatically make a judgment on the converter transformer protection output or lockout of the converter transformer protection. This greatly improves equipment reliability, increases the sensitivity of converter transformer inter-turn fault identification, and reduces the risk of converter transformer inrush current characteristic identification, thereby effectively improving the safe operation level of the power grid.

[0084] 3. The method of the present invention is generally applicable to equipment such as transformers operating in parallel and can solve similar existing problems.

[0085] Example System

[0086] Figure 4 A schematic diagram of the structure of a converter transformer transverse differential protection system based on transverse differential current according to a preferred embodiment of the present invention. Figure 4 As shown, the commutation transformer transverse differential protection system 400 based on transverse differential current according to this preferred embodiment includes:

[0087] A data acquisition module 401 is configured to collect the high-voltage side three-phase currents of a Y / Y commutation transformer and a Y / Δ commutation transformer operating in parallel, as well as the low-voltage side three-phase currents of each of the Y / Y commutation transformer and the Y / Δ commutation transformer, wherein the Y / Y commutation transformer and the Y / Δ commutation transformer are connected to a protection device;

[0088] a first calculation module 402, configured to calculate the longitudinal differential current, longitudinal phase braking current, second harmonic effective value, and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value, and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer based on the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0089] a protection initiation module 403, configured to initiate protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device when the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer meet their respective protection initiation criteria;

[0090] a second calculation module 404 configured to calculate, when the Y / Y commutation transformer and / or the Y / Δ commutation transformer for which protection of the corresponding phase in the protection device has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phase meet respective ratio differential action criteria, the second harmonic RMS value and the fundamental RMS value of the corresponding phase meet respective first harmonic blocking criteria, and the transverse differential current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer meets the transverse differential protection activation criteria, the ratio of the transverse differential current and the transverse phase braking current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer to the transverse differential protection;

[0091] a first judgment module 405 configured to, when the ratio is not less than a preset first threshold and the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are greater than a preset second threshold, determine, based on the second harmonic RMS value and the fundamental RMS value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer and a second harmonic blocking criterion, a protection action for the corresponding phase of the protection device;

[0092] The second judgment module 406 is configured to determine, when the ratio is less than the first threshold, the protection action of the corresponding phase of the protection device directly based on the second harmonic effective value, the third harmonic effective value, and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as a third harmonic blocking criterion.

[0093] Preferably, the first calculation module 402 calculates the longitudinal differential current, longitudinal phase braking current, second harmonic effective value and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer based on the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, wherein:

[0094] I dYi =│I Yhi +I Yli │, I zdYi =│I Yhi +I Yli │ / 2

[0095] I dΔi =│I Δhi +I Δli │, I zdΔi =│I Δhi +I Δli │ / 2

[0096] I di =│I dYi -I dΔi │, I zdi =│I dYi +I dΔi │

[0097] Where, i is any one of the three phases A, B, and C of the Y / Y commutation transformer and the Y / Δ commutation transformer, I Yhi and I Yli are the high-voltage side and low-voltage side current phasors of the Y / Y commutation transformer i phase, I dYi and I zdYi are the longitudinal differential current and longitudinal phase braking current of the Y / Y commutation transformer i phase respectively; I Δhi and I Δli are the high-voltage side and low-voltage side current phasors of the Y / Δ commutation transformer i phase, I dΔi and I zdΔi are the longitudinal differential current and longitudinal phase braking current of the Y / Δ commutation transformer i phase respectively; I di and I zdi are the transverse differential current and transverse phase braking current of the i-phase of the Y / Y commutation transformer and the Y / Δ commutation transformer respectively;

[0098] Calculating the second harmonic effective value and the fundamental effective value of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer using a Fourier algorithm according to the longitudinal differential current of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0099] According to the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, a Fourier algorithm is used to calculate the second harmonic effective value, the third harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer.

[0100] Preferably, the protection start module 403 starts the protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device when the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer respectively meet their protection start criterion, wherein the calculation formula of the protection start criterion is:

[0101] I dYi >I cdqdY

[0102] I dΔi >I cdqdΔ

[0103] Where, I cdqdY and I cdqdΔ The protection start-up settings of the Y / Y commutation transformer and the Y / Δ commutation transformer are set according to the rated currents of the Y / Y commutation transformer and the Y / Δ commutation transformer respectively;

[0104] When the Y / Y commutation transformer and / or the Y / Δ commutation transformer each meet the protection start-up criterion for its i-phase, the protection of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is started; when the Y / Y commutation transformer and the Y / Δ commutation transformer each do not meet the protection start-up criterion for its i-phase, the protection of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is returned.

[0105] Preferably, the second calculation module 404 calculates the ratio of the transverse differential current to the transverse phase braking current of the Y / Y commutation transformer and / or the Y / Δ commutation transformer corresponding to the phase of the protection device, when the protection of the corresponding phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phase meet the respective ratio differential action criteria, the second harmonic effective value and the fundamental effective value of the corresponding phase meet the respective first harmonic blocking criteria, and the transverse differential current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer meets the transverse differential protection activation criteria, wherein:

[0106] The expression of the ratio differential action criterion is:

[0107] I dYi >I cdqdY +K r *(I zdYi –I e )

[0108] I dΔi >I cdqdΔ +K r *(I zdΔi –I e )

[0109] Where K r is the ratio action slope, I e is the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0110] When the longitudinal differential current and longitudinal phase braking current of the Y / Y commutation transformer and / or the Y / Δ commutation transformer of which the protection of phase i in the protection device has been started do not meet the respective ratio differential action criteria, the protection of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is returned;

[0111] The expression of the first harmonic blocking criterion is:

[0112] H L2Yi / B LYi >K1

[0113] H L2Δi / B LΔi >K1

[0114] Where H L2Yi and B LYi are respectively the second harmonic effective value and the fundamental effective value determined by calculation based on the longitudinal differential current of the Y / Y commutation transformer i phase; H L2Δi and B LΔi are respectively the second harmonic effective value and the fundamental effective value determined by calculation based on the longitudinal differential current of the i-phase of the Y / Δ commutation transformer; K1 is a constant, 0<K1<1;

[0115] When the Y / Y commutation transformer and / or the Y / Δ commutation transformer of which the protection of phase i in the protection device has been activated, and the longitudinal differential current and longitudinal phase braking current of its phase i meet the respective ratio differential action criteria, but the second harmonic effective value and fundamental effective value of its phase i do not meet the respective first harmonic blocking criteria, the protection output of the Y / Y commutation transformer and / or the Y / Δ commutation transformer of phase i in the protection device is activated;

[0116] The expression of the criterion for starting the transverse differential protection is:

[0117] I di >I dz1

[0118] Where, I dz1 It is the starting value of the transverse differential protection, which is set according to the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer;

[0119] When the Y / Y commutation transformer and / or the Y / Δ commutation transformer whose protection of phase i in the protection device has been started, the longitudinal differential current and longitudinal phase braking current of its i phase meet the respective ratio differential action criteria, and the second harmonic effective value and fundamental effective value of its i phase meet the respective first harmonic locking criteria, but the transverse differential current of phase i of the Y / Y commutation transformer and the Y / Δ commutation transformer does not meet the transverse differential protection starting criteria, the protection of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is locked.

[0120] Preferably, when the ratio is not less than a preset first threshold and the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are greater than a preset second threshold, the first judgment module 405 determines the protection action of the corresponding phase of the protection device according to the second harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the second harmonic blocking criterion, wherein:

[0121] The first threshold K0 is a constant, 0<K0<1;

[0122] The second threshold I dz2 The setting is performed according to the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer, and 0<I dz1 <I dz2 ;

[0123] The expression of the second harmonic blocking criterion is:

[0124] H T2i / B Ti >K2

[0125] Where H T2i and B Ti are respectively the second harmonic effective value and the fundamental effective value calculated based on the transverse differential current of the i-phase of the Y / Y commutated transformer and the Y / Δ commutated transformer; K2 is a constant, 0<K2<1;

[0126] When the second harmonic effective value H of the Y / Y commutation transformer and the Y / Δ commutation transformer i phase T2i and fundamental effective value B Ti If the second harmonic blocking criterion is met, the protection blocking of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined;

[0127] When the second harmonic effective value H of the Y / Y commutation transformer and the Y / Δ commutation transformer i phase T2i and fundamental effective value B Ti If the second harmonic blocking criterion is not met, a protection outlet of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined.

[0128] Preferably, when the ratio is less than the first threshold, the second judgment module 406 directly determines the protection action of the corresponding phase of the protection device according to the second harmonic effective value, the third harmonic effective value, and the fundamental effective value of the corresponding phases of the Y / Y commutated transformer and the Y / Δ commutated transformer, and the third harmonic blocking criterion, wherein:

[0129] The expressions of the third harmonic blocking criteria are:

[0130]

[0131] Where H T3i is the effective value of the third harmonic determined based on the transverse differential current of the i-phase of the Y / Y commutated transformer and the Y / Δ commutated transformer; K3 and K4 are constants, 0<K2K3, K4<1, and K3<K4;

[0132] When the second harmonic effective value H of the i-phase of the Y / Y commutation transformer and the Y / Δ commutation transformer is T2i , the effective value of the third harmonic H T3i and fundamental effective value B Ti If the third harmonic blocking criterion is met, the protection blocking of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined;

[0133] When the second harmonic effective value H of the i-phase of the Y / Y commutation transformer and the Y / Δ commutation transformer is T2i , the effective value of the third harmonic H T3i and the fundamental effective value B Ti If the third harmonic blocking criterion is not met, a protection blocking exit of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined.

[0134] The steps of the converter transformer transverse differential protection system based on transverse differential current in this preferred embodiment for judging the inrush current characteristics and inter-turn fault characteristics of two converter transformers operating in parallel, thereby determining to lock the converter transformer protection or the converter transformer protection outlet are the same as the steps in the converter transformer transverse differential protection method based on transverse differential current, and the technical effects achieved are also the same, which will not be repeated here.

[0135] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0136] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / the [means, component, etc.]" are to be interpreted openly as referring to at least one instance of the means, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily need to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0137] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0138] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0139] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0140] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0141] 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, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for commutation transformer transverse differential protection based on transverse differential current, characterized in that: The method comprises: Collecting high-voltage side three-phase currents of Y / Y commutation transformers and Y / Δ commutation transformers operating in parallel, as well as their respective low-voltage side three-phase currents, wherein the Y / Y commutation transformers and Y / Δ commutation transformers are connected to a protection device; Calculating the longitudinal differential current, longitudinal phase braking current, second harmonic effective value and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer according to the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer; When the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer meet the respective protection start criteria, starting the protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device; When the Y / Y commutation transformer and / or the Y / Δ commutation transformer for which protection of the corresponding phase in the protection device has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phase meet the respective ratio differential action criteria, the second harmonic effective value and the fundamental effective value of the corresponding phase meet the respective first harmonic blocking criteria, and the transverse differential current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer meets the transverse differential protection activation criteria, calculating the ratio of the transverse differential current and the transverse phase braking current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer; When the ratio is not less than a preset first threshold value, and the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are greater than a preset second threshold value, determining the protection action of the corresponding phase of the protection device according to the second harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the second harmonic blocking criterion; When the ratio is less than the first threshold, the protection action of the corresponding phase of the protection device is determined directly according to the second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the third harmonic blocking criterion.

2. The method according to claim 1, characterized in that The longitudinal differential current, longitudinal phase braking current, second harmonic effective value and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are calculated based on the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, wherein: I dYi =│I Yhi +I Yli │,I zdYi =│I Yhi +I Yli │ / 2 I dΔi =│I Δhi +I Δli │,I zdΔi =│I Δhi +I Δli │ / 2 I di =│I dYi -I dΔi │,I zdi =│I dYi +I dΔi │ Where, i is any one of the three phases A, B, and C of the Y / Y commutation transformer and the Y / Δ commutation transformer, I Yhi and I Yli are the high-voltage side and low-voltage side current phasors of the Y / Y commutation transformer i phase, I dYi and I zdYi are the longitudinal differential current and longitudinal phase braking current of the Y / Y commutation transformer i phase respectively; I Δhi and I Δli are the high-voltage side and low-voltage side current phasors of the Y / Δ commutation transformer i phase, I dΔi and I zdΔi are the longitudinal differential current and longitudinal phase braking current of the Y / Δ commutation transformer i phase respectively; I di and I zdi are the transverse differential current and transverse phase braking current of the i-phase of the Y / Y commutation transformer and the Y / Δ commutation transformer respectively; Calculating the second harmonic effective value and the fundamental effective value of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer using a Fourier algorithm according to the longitudinal differential current of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer; According to the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, a Fourier algorithm is used to calculate the second harmonic effective value, the third harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer.

3. The method according to claim 2, characterized in that When the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer each meet their respective protection initiation criteria, the protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is initiated, wherein the calculation formula of the protection initiation criteria is: I dYi >I cdqdY I dΔi >I cdqdΔ Where, I cdqdY and I cdqdΔ The protection start-up settings of the Y / Y commutation transformer and the Y / Δ commutation transformer are set according to the rated currents of the Y / Y commutation transformer and the Y / Δ commutation transformer respectively; When the Y / Y commutation transformer and / or the Y / Δ commutation transformer each meet the protection start-up criterion for its i-phase, the protection of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is started; when the Y / Y commutation transformer and the Y / Δ commutation transformer each do not meet the protection start-up criterion for its i-phase, the protection of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is returned.

4. The method according to claim 2, characterized in that When the Y / Y commutation transformer and / or the Y / Δ commutation transformer whose protection of the corresponding phase in the protection device has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phase meet the respective ratio differential action criteria, the second harmonic effective value and the fundamental effective value of the corresponding phase meet the respective first harmonic blocking criteria, and the transverse differential current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer meets the transverse differential protection activation criteria, the ratio of the transverse differential current and the transverse phase braking current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer is calculated, wherein: The expression of the ratio differential action criterion is: I dYi >I cdqdY +K r *(I zdYi –I e ) I dΔi >I cdqdΔ +K r *(I zdΔi –I e ) Where K r is the ratio action slope, I e is the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer; When the longitudinal differential current and longitudinal phase braking current of the Y / Y commutation transformer and / or the Y / Δ commutation transformer of which the protection of phase i in the protection device has been started do not meet the respective ratio differential action criteria, the protection of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is returned; The expression of the first harmonic blocking criterion is: H L2Yi / B LYi >K1 H L2Δi / B LΔi >K1 Where H L2Yi and B LYi are respectively the second harmonic effective value and the fundamental effective value determined by calculation based on the longitudinal differential current of the Y / Y commutation transformer i phase; H L2Δi and B LΔi are respectively the second harmonic effective value and the fundamental effective value determined by calculation based on the longitudinal differential current of the i-phase of the Y / Δ commutation transformer; K1 is a constant, 0<K1<1; When the Y / Y commutation transformer and / or the Y / Δ commutation transformer of which the protection of phase i in the protection device has been activated, and the longitudinal differential current and longitudinal phase braking current of its phase i meet the respective ratio differential action criteria, but the second harmonic effective value and fundamental effective value of its phase i do not meet the respective first harmonic blocking criteria, the protection output of the Y / Y commutation transformer and / or the Y / Δ commutation transformer of phase i in the protection device is activated; The expression of the criterion for starting the transverse differential protection is: I di >I dz1 Where, I dz1 It is the starting value of the transverse differential protection, which is set according to the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer; When the Y / Y commutation transformer and / or the Y / Δ commutation transformer whose protection of phase i in the protection device has been started, the longitudinal differential current and longitudinal phase braking current of its i phase meet the respective ratio differential action criteria, and the second harmonic effective value and fundamental effective value of its i phase meet the respective first harmonic locking criteria, but the transverse differential current of phase i of the Y / Y commutation transformer and the Y / Δ commutation transformer does not meet the transverse differential protection starting criteria, the protection of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is locked.

5. The method according to claim 4, characterized in that When the ratio is not less than a preset first threshold value, and the transverse differential current of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer is greater than a preset second threshold value, the protection action of the corresponding phase of the protection device is determined according to the second harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the second harmonic blocking criterion, wherein: The first threshold K0 is a constant, 0<K0<1; The second threshold I dz2 The setting is performed according to the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer, and 0<I dz1 <I dz2 ; The expression of the second harmonic blocking criterion is: H T2i / B Ti >K2 Where H T2i and B Ti are respectively the second harmonic effective value and the fundamental effective value calculated based on the transverse differential current of the i-phase of the Y / Y commutated transformer and the Y / Δ commutated transformer; K2 is a constant, 0<K2<1; When the second harmonic effective value H of the i-phase of the Y / Y commutation transformer and the Y / Δ commutation transformer is T2i and the fundamental effective value B Ti If the second harmonic blocking criterion is met, the protection blocking of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined; When the second harmonic effective value H of the Y / Y commutation transformer and the Y / Δ commutation transformer i phase T2i and fundamental effective value B Ti If the second harmonic blocking criterion is not met, a protection outlet of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined.

6. The method according to claim 5, characterized in that When the ratio is less than the first threshold, the protection action of the corresponding phase of the protection device is determined directly according to the second harmonic effective value, the third harmonic effective value and the fundamental effective value of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the third harmonic blocking criterion, wherein: The expressions of the third harmonic blocking criteria are: Where H T3i is the effective value of the third harmonic determined based on the transverse differential current of the i-phase of the Y / Y commutated transformer and the Y / Δ commutated transformer; K3 and K4 are constants, 0<K3, K4<1, and K3<K4; When the second harmonic effective value H of the i-phase of the Y / Y commutation transformer and the Y / Δ commutation transformer is T2i , the effective value of the third harmonic H T3i and the fundamental effective value B Ti If the third harmonic blocking criterion is met, the protection blocking of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined; When the second harmonic effective value H of the Y / Y commutation transformer and the Y / Δ commutation transformer i phase T2i , the effective value of the third harmonic H T3i and fundamental effective value B Ti If the respective third harmonic blocking criteria are not met, a protection blocking exit of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer is determined.

7. A commutation transformer transverse differential protection system based on transverse differential current, characterized in that: The system comprises: A data acquisition module is used to collect the high-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, which are connected to a protection device, and the low-voltage side three-phase current of each of the Y / Y commutation transformer and the Y / Δ commutation transformer, which are connected to a protection device; a first calculation module, configured to calculate the longitudinal differential current, longitudinal phase braking current, second harmonic effective value, and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value, and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer based on the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer; a protection start module, configured to start protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device when the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer meet their respective protection start criteria; a second calculation module, configured to calculate the ratio of the transverse differential current and the transverse phase braking current of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer, when the protection of the corresponding phases in the protection device has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phases satisfy the respective ratio differential action criteria, the second harmonic effective value and the fundamental effective value of the corresponding phases satisfy the respective first harmonic blocking criteria, and the transverse differential current of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer satisfy the transverse differential protection activation criteria; a first judgment module, configured to, when the ratio is not less than a preset first threshold value and the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer are greater than a preset second threshold value, determine, based on the second harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer and a second harmonic blocking criterion, a protection action for the corresponding phase of the protection device; The second judgment module is used to determine the protection action of the corresponding phase of the protection device directly according to the second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, and the third harmonic blocking criterion when the ratio is less than the first threshold.

8. The system according to claim 7, characterized in that The first calculation module calculates the longitudinal differential current, longitudinal phase braking current, second harmonic effective value and fundamental effective value of the three phases of the Y / Y commutation transformer and the Y / Δ commutation transformer according to the high-voltage side three-phase current and the low-voltage side three-phase current of the Y / Y commutation transformer and the Y / Δ commutation transformer, as well as the transverse differential current, transverse phase braking current, second harmonic effective value, third harmonic effective value and fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, wherein: I dYi =│I Yhi +I Yli │,I zdYi =│I Yhi +I Yli │ / 2 I dΔi =│I Δhi +I Δli │,I zdΔi =│I Δhi +I Δli │ / 2 I di =│I dYi -I dΔi │,I zdi =│I dYi +I dΔi │ Where, i is any one of the three phases A, B, and C of the Y / Y commutation transformer and the Y / Δ commutation transformer, I Yhi and I Yli are the high-voltage side and low-voltage side current phasors of the Y / Y commutation transformer i phase, I dYi and I zdYi are the longitudinal differential current and longitudinal phase braking current of the Y / Y commutation transformer i phase respectively; I Δhi and I Δli are the high-voltage side and low-voltage side current phasors of the Y / Δ commutation transformer i phase, I dΔi and I zdΔi are the longitudinal differential current and longitudinal phase braking current of the Y / Δ commutation transformer i phase respectively; I di and I zdi are the transverse differential current and transverse phase braking current of the i-phase of the Y / Y commutation transformer and the Y / Δ commutation transformer respectively; Calculating the second harmonic effective value and the fundamental effective value of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer using a Fourier algorithm according to the longitudinal differential current of each phase of the Y / Y commutation transformer and the Y / Δ commutation transformer; According to the transverse differential currents of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer, a Fourier algorithm is used to calculate the second harmonic effective value, the third harmonic effective value and the fundamental effective value of the corresponding phases of the Y / Y commutation transformer and the Y / Δ commutation transformer.

9. The system according to claim 8, characterized in that The protection start module starts the protection of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device when the longitudinal differential currents of the corresponding phases of the Y / Y commutation transformer and / or the Y / Δ commutation transformer respectively meet their protection start criteria, wherein the calculation formula of the protection start criteria is: I dYi >I cdqdY I dΔi >I cdqdΔ Where, I cdqdY and I cdqdΔ The protection start-up settings of the Y / Y commutation transformer and the Y / Δ commutation transformer are set according to the rated currents of the Y / Y commutation transformer and the Y / Δ commutation transformer respectively; When the Y / Y commutation transformer and / or the Y / Δ commutation transformer each meet the protection start-up criterion for its i-phase, the protection of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is started; when the Y / Y commutation transformer and the Y / Δ commutation transformer each do not meet the protection start-up criterion for its i-phase, the protection of the i-phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is returned.

10. The system according to claim 8, wherein: The second calculation module calculates the ratio of the transverse differential current and the transverse phase braking current of the Y / Y commutation transformer and the Y / Δ commutation transformer corresponding to the phase of the Y / Y commutation transformer and / or the Y / Δ commutation transformer, when the protection of the corresponding phase in the protection device has been activated, the longitudinal differential current and the longitudinal phase braking current of the corresponding phase meet the respective ratio differential action criteria, the second harmonic effective value and the fundamental effective value of the corresponding phase meet the respective first harmonic blocking criteria, and the transverse differential current of the corresponding phase of the Y / Y commutation transformer and the Y / Δ commutation transformer meets the transverse differential protection activation criteria, wherein: The expression of the ratio differential action criterion is: I dYi >I cdqdY +K r *(I zdYi –I e ) I dΔi >I cdqdΔ +K r *(I zdΔi –I e ) Where K r is the ratio action slope, I e is the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer; When the longitudinal differential current and longitudinal phase braking current of the Y / Y commutation transformer and / or the Y / Δ commutation transformer of which the protection of phase i in the protection device has been started do not meet the respective ratio differential action criteria, the protection of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is returned; The expression of the first harmonic blocking criterion is: H L2Yi / B LYi >K1 H L2Δi / B LΔi >K1 Where H L2Yi and B LYi are respectively the second harmonic effective value and the fundamental effective value determined by calculation based on the longitudinal differential current of the i-phase of the Y / Y commutation transformer; H L2Δi and B LΔi are respectively the second harmonic effective value and the fundamental effective value determined by calculation based on the longitudinal differential current of the i-phase of the Y / Δ commutation transformer; K1 is a constant, 0<K1<1; When the Y / Y commutation transformer and / or the Y / Δ commutation transformer of which the protection of phase i in the protection device has been activated, and the longitudinal differential current and longitudinal phase braking current of its phase i meet the respective ratio differential action criteria, but the second harmonic effective value and fundamental effective value of its phase i do not meet the respective first harmonic blocking criteria, the protection output of the Y / Y commutation transformer and / or the Y / Δ commutation transformer of phase i in the protection device is activated; The expression of the criterion for starting the transverse differential protection is: I di >I dz1 Where, I dz1 It is the starting value of the transverse differential protection, which is set according to the rated current of the Y / Y commutation transformer and the Y / Δ commutation transformer; When the Y / Y commutation transformer and / or the Y / Δ commutation transformer whose protection of phase i in the protection device has been started, the longitudinal differential current and longitudinal phase braking current of its i phase meet the respective ratio differential action criteria, and the second harmonic effective value and fundamental effective value of its i phase meet the respective first harmonic locking criteria, but the transverse differential current of phase i of the Y / Y commutation transformer and the Y / Δ commutation transformer does not meet the transverse differential protection starting criteria, the protection of phase i of the Y / Y commutation transformer and / or the Y / Δ commutation transformer in the protection device is locked.

Images