Method and system for preventing differential protection from being rejected by inverter harmonics

Abstract

The present application relates to the technical field of power system relay protection, and provides a method and system for preventing differential protection from being refused by harmonics of inverters, which is applied to a power system including a transformer protection device, and the method comprises the following steps: collecting primary side voltage and current of the transformer and secondary side voltage and current of the transformer; calculating first phase angle difference and second phase angle difference of the transformer based on the primary side voltage and current of the transformer and the secondary side voltage and current of the transformer; judging whether the first phase angle difference and the second phase angle difference meet a first preset condition; if yes, entering a second harmonic locking mode; judging whether a second preset condition is met; if yes, exiting the second harmonic locking mode. The present application can solve the problem that when a new energy station such as wind power, photovoltaic and energy storage is connected to a grid, a large amount of harmonics generated by inverters causes differential protection to be mislocked and further causes protection to be refused.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system relay protection, and in particular to a method and system for preventing differential protection from being refused to act due to harmonics of inverters. BACKGROUND

[0002] New energy power generation methods such as photovoltaic and wind power have developed rapidly, and a large number of new energy power sources have been successfully integrated into power grids. Usually, these power sources will realize AC-DC conversion through inverters, and then be connected to grid-connected transformers, and then be connected to high-voltage power grids for power transmission. Therefore, the stable operation of the grid-connected transformer is crucial for the transmission of new energy power.

[0003] In order to quickly respond to transformer faults and protect the safety thereof, the transformer protection device is equipped with current differential protection as a fast main protection. However, when the transformer is in no-load operation, the core may be saturated, thereby generating a differential current, which may cause the differential protection to malfunction. In order to avoid this situation, a second harmonic blocking element is introduced to identify core saturation.

[0004] However, it is worth noting that in the application of new energy grid-connected transformers, the second harmonic blocking element may sometimes misjudge. When the transformer fails, the voltage may fluctuate. In particular, when the voltage drops below 0.9 times the rated voltage, the inverter will trigger a low voltage ride-through operation strategy, which will generate a second harmonic current. This current may cause the second harmonic blocking element in the differential protection to misjudge and incorrectly block the differential protection, thereby causing the differential protection to refuse to act, and further exacerbating the accident. Therefore, it is particularly important to study how to prevent the harmonics generated by the inverter during low voltage ride-through from causing the differential protection to be misblocked and refused to act. SUMMARY

[0005] The present application aims to solve at least one of the technical problems in the background art, and provides a method and system for preventing differential protection from being refused to act due to harmonics of inverters.

[0006] To achieve the above-mentioned purpose, the present application provides a method for preventing differential protection from being refused to act due to harmonics of inverters, which is applied to a power system comprising a transformer protection device, and the method comprises:

[0007] collecting transformer primary side voltage and current and transformer secondary side voltage and current;

[0008] based on the transformer primary side voltage and current and the transformer secondary side voltage and current, calculating a first phase angle difference and a second phase angle difference of the transformer; wherein the first phase angle difference is the phase difference between the transformer primary side positive sequence second harmonic voltage and the transformer primary side positive sequence second harmonic current, and the second phase angle difference is the phase difference between the transformer secondary side positive sequence second harmonic voltage and the transformer secondary side positive sequence second harmonic current;

[0009] determine whether the first phase angle difference and the second phase angle difference satisfy a first preset condition; if yes, enter a second harmonic locking mode;

[0010] determine whether a second preset condition is satisfied; if yes, exit the second harmonic locking mode.

[0011] Further, based on the transformer primary side voltage and current and the transformer secondary side voltage and current, a first phase angle difference and a second phase angle difference of the transformer are calculated, comprising:

[0012] Based on the transformer primary side voltage and current and the transformer secondary side voltage and current, the transformer primary side second harmonic voltage, the transformer primary side second harmonic current, the transformer secondary side second harmonic voltage, and the transformer secondary side second harmonic current are calculated.

[0013] The first phase angle difference is calculated based on the transformer primary side positive sequence second harmonic voltage and the transformer primary side positive sequence second harmonic current, and the second phase angle difference is calculated based on the transformer secondary side positive sequence second harmonic voltage and the transformer secondary side positive sequence second harmonic current.

[0014] Further, the first preset condition includes that the first phase angle difference and the second phase angle difference are both within 0°-90°.

[0015] Further, the second preset condition includes that the first phase angle difference is greater than 0° or the second phase angle difference is greater than 0°.

[0016] To achieve the above-mentioned purpose, the application further provides a system for preventing differential protection from being refused to act due to harmonics of an inverter, applied to a power system including a transformer protection device, comprising:

[0017] A collection module is configured to collect transformer primary side voltage and current and transformer secondary side voltage and current.

[0018] A calculation module is configured to calculate a first phase angle difference and a second phase angle difference of the transformer based on the transformer primary side voltage and current and the transformer secondary side voltage and current; wherein the first phase angle difference is a phase difference between a transformer primary side positive sequence second harmonic voltage and a transformer primary side positive sequence second harmonic current, and the second phase angle difference is a phase difference between a transformer secondary side positive sequence second harmonic voltage and a transformer secondary side positive sequence second harmonic current.

[0019] A determination module is configured to determine whether the first phase angle difference and the second phase angle difference satisfy a first preset condition; if yes, enter a second harmonic locking mode.

[0020] The determination module is further configured to determine whether a second preset condition is satisfied; if yes, exit the second harmonic locking mode.

[0021] Further, the acquisition module comprises: a current transformer and a voltage transformer;

[0022] The two current transformers are connected in series at two ends of the transformer respectively, and are used for acquiring the primary side current of the transformer and the secondary side current of the transformer.

[0023] The two voltage transformers are connected in parallel at two ends of the transformer respectively, and are connected with the transformer protection device; the two voltage transformers are used for acquiring the primary side voltage of the transformer and the secondary side voltage of the transformer.

[0024] Further, the calculation module is further used for:

[0025] Based on the primary side voltage and current of the transformer and the secondary side voltage and current of the transformer, the primary side second harmonic voltage of the transformer, the primary side second harmonic current of the transformer, the secondary side second harmonic voltage of the transformer and the secondary side second harmonic current of the transformer are calculated.

[0026] The first phase angle difference is calculated based on the primary side positive sequence second harmonic voltage of the transformer and the primary side positive sequence second harmonic current of the transformer, and the second phase angle difference is calculated based on the secondary side positive sequence second harmonic voltage of the transformer and the secondary side positive sequence second harmonic current of the transformer.

[0027] Further, the first preset condition comprises that the first phase angle difference and the second phase angle difference are both in 0°-90°.

[0028] Further, the second preset condition comprises that the first phase angle difference is greater than 0° or the second phase angle difference is greater than 0°.

[0029] To achieve the above-mentioned purpose, the application further provides a transformer protection device applied to any one of the systems for preventing the differential protection from being refused to act due to the harmonics of the inverter as described above, and the transformer protection device comprises:

[0030] An AC unit is used for receiving analog input;

[0031] An SV unit is used for receiving digital input;

[0032] A main control unit is used for data acquisition and IO expansion;

[0033] A monitoring and communication unit is used for GPS time synchronization and sending alarm information, and is further used for communication with a background monitoring and external devices;

[0034] A GOOSE open-in and open-out unit is used for outputting corresponding GOOSE open-out and signals;

[0035] An MMI unit is used for connection with a host computer.

[0036] The software and hardware of the application can be developed based on conventional relay protection devices, without additional external circuits such as mutual inductors; and the application has a small amount of calculation, and the relay protection equipment currently has mature harmonic calculation and sequence component calculation units, which can be realized through simple program development. Meanwhile, the application can reliably lock differential protection when the transformer core is saturated, prevent protection misoperation, reliably open differential protection when the transformer area fault inverter generates harmonics, prevent protection refusal, and can make up for the problem of insufficient adaptability of the transformer secondary harmonic locking element in the grid-connected transformer protection of the new type of power system inverter connection. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 a wiring diagram schematically representing a power system including a transformer protection device;

[0038] Figure 2 a flowchart schematically representing a method of preventing differential protection refusal caused by inverter harmonics according to an embodiment of the application;

[0039] Figure 3 a flowchart schematically representing a method of preventing differential protection refusal caused by inverter harmonics according to another embodiment of the application;

[0040] Figure 4 a decision logic diagram schematically representing a method of preventing differential protection refusal caused by inverter harmonics according to an embodiment of the application;

[0041] Figure 5 a hardware structure schematic diagram of a transformer protection device according to an embodiment of the application;

[0042] Figure 6 a structure diagram of a system of preventing differential protection refusal caused by inverter harmonics according to an embodiment of the application. DETAILED DESCRIPTION

[0043] The present application will now be discussed with reference to example embodiments. It should be appreciated that the discussed embodiments are merely for the purpose of enabling those of ordinary skill in the art to better understand and therefore implement the present application, and are not intended to imply any limitation on the scope of the present application.

[0044] As used herein, the term "includes" and its variants are to be read as open-ended terms that mean "includes, but is not limited to." The term "based on" is to be construed as "based at least in part on." The terms "one embodiment" and "an embodiment" are to be read as "at least one embodiment."

[0045] Embodiment One

[0046] Figure 1A schematic representation of a wiring diagram of a power system comprising a transformer protection device; Figure 2 A flow chart of a method for preventing the inverter harmonics from causing the differential protection to fail according to an embodiment of the present application. As shown in Figure 1 And Figure 2 As shown in the method for preventing the inverter harmonics from causing the differential protection to fail according to an embodiment of the present application, applied to a power system comprising a transformer protection device, the method comprises:

[0047] Step S102: Collecting the primary side voltage and current of the transformer and the secondary side voltage and current of the transformer;

[0048] The analog quantities collected by the transformer relay protection device are as follows:

[0049] The primary side voltage UHa, UHb, UHc of the transformer;

[0050] The primary side current IHa, IHb, IHc of the transformer;

[0051] The secondary side voltage ULa, ULb, ULc of the transformer;

[0052] The secondary side current ILa, ILb, ILc of the transformer.

[0053] Step S104: Calculating the first phase angle difference and the second phase angle difference of the transformer based on the primary side voltage and current of the transformer and the secondary side voltage and current of the transformer;

[0054] Wherein, the first phase angle difference is the phase difference between the primary side positive sequence second harmonic voltage of the transformer and the primary side positive sequence second harmonic current of the transformer, and the second phase angle difference is the phase difference between the secondary side positive sequence second harmonic voltage of the transformer and the secondary side positive sequence second harmonic current of the transformer;

[0055] Step S106: Judging whether the first phase angle difference and the second phase angle difference satisfy the first preset condition; if yes, entering the second harmonic locking mode;

[0056] Step S108: Judging whether the second preset condition is satisfied; if yes, exiting the second harmonic locking mode.

[0057] The method for preventing the inverter harmonics from causing the differential protection to fail in the embodiment adopts the existing transformer relay protection device software and hardware platform for development, and the protection measures the primary side and secondary side voltage and current of the new energy grid-connected transformer through the conventional AC mutual inductor or digital sampling, so as to calculate the phase angle difference between the primary side and secondary side voltage and current of the transformer, and when the phase angle difference satisfies the set condition, the second harmonic locking element is exited, the differential protection is opened, and the differential protection is prevented from being mislocked to cause the failure.

[0058] According to an embodiment of the present application, step S104 comprises:

[0059] Based on the transformer primary side voltage and current and the transformer secondary side voltage and current, the transformer primary side second harmonic voltage, the transformer primary side second harmonic current, the transformer secondary side second harmonic voltage, and the transformer secondary side second harmonic current are calculated.

[0060] Based on the transformer primary side positive sequence second harmonic voltage and the transformer primary side positive sequence second harmonic current, the first phase angle difference is calculated, and based on the transformer secondary side positive sequence second harmonic voltage and the transformer secondary side positive sequence second harmonic current, the second phase angle difference is calculated.

[0061] In this embodiment, the process of calculating the first phase angle difference and the second phase angle difference is as follows:

[0062] First step: calculate the second harmonic current and voltage vectors of the transformer primary side and secondary side current and voltage, the transformer primary side second harmonic voltage UHa2, UHb2, UHc2, the transformer primary side second harmonic current IHa2, IHb2, IHc2, the transformer secondary side second harmonic voltage ULa2, ULb2, ULc2, and the transformer secondary side second harmonic current ILa2, ILb2, ILc2.

[0063] Second step: using the transformer primary side and secondary side current and voltage second harmonic vectors, the transformer primary side positive sequence second harmonic voltage UHp2, the transformer primary side positive sequence second harmonic current IHp2, the transformer secondary side positive sequence second harmonic voltage ULp2, and the transformer secondary side positive sequence second harmonic current ILp2 are calculated.

[0064] Third step: using the transformer primary side and secondary side positive sequence second harmonic current and voltage vectors, the phase angle difference ФHp2 of the transformer primary side positive sequence second harmonic voltage UHp2 and current IHp2 and the phase angle difference ФLp2 of the transformer secondary side positive sequence second harmonic voltage ULp2 and current ILp2 are calculated.

[0065] In this embodiment, the primary side and secondary side voltage and current of the new energy grid-connected transformer are used to calculate the second harmonic components of the voltage and current, and the second harmonic components are in the form of vectors, i.e., the second harmonic voltage and current include amplitude and phase angle. The amplitude and phase angle of the new energy grid-connected transformer primary side and secondary side second harmonic voltage and current obtained by calculation are used to calculate the positive sequence components of the second harmonic voltage and current vector, i.e., the amplitude and phase angle of the positive sequence second harmonic voltage and current. The phase angle difference of the voltage and current is calculated by the phase angle of the new energy grid-connected transformer primary side and secondary side positive sequence second harmonic voltage and current obtained by calculation. The positive sequence components can avoid the influence of the transformer angle connection on the zero sequence components, and the second harmonic blocking element is exited and the differential protection is opened when the phase angle difference meets the second preset condition.

[0066] Figure 4A schematic representation of the discrimination logic of the method for preventing the inverter harmonic from causing the differential protection to fail to act according to an embodiment of the present application is shown in Figure 1, which shows that according to an embodiment of the present application, the first preset condition comprises that the first phase angle difference and the second phase angle difference are both within 0° ~ -90°. Figure 4

[0067] The second preset condition comprises that the first phase angle difference is greater than 0° or the second phase angle difference is greater than 0°

[0068] In this embodiment, in order to quickly remove the fault protection transformer when the transformer fails, the transformer protection device is configured with a fast main protection current differential protection, but when the transformer is in no-load operation, the core will be saturated, which will cause the differential protection to have a differential current and may cause the differential protection to malfunction. In order to avoid the malfunction of the differential protection, a second harmonic locking element is configured to identify core saturation. The inverter low-voltage ride-through operation strategy will generate a second harmonic current, which will cause the second harmonic locking element in the differential protection to misjudge.

[0069] However, the direction characteristics of the second harmonic current generated when the transformer core is saturated are different from those of the second harmonic current generated by the inverter. When the transformer core is saturated, the transformer becomes a second harmonic source, and the generated second harmonic current flows outside the transformer. When the transformer area fails, the voltage decreases, causing the second harmonic current generated by the inverter to flow into the transformer near the inverter side, and to flow out of the transformer away from the inverter side. The direction of the second harmonic current is different from that when the transformer core is saturated. Based on the above characteristics, the present application proposes a method for preventing the inverter harmonic from causing the differential protection to fail to act, which is briefly described below:

[0070] Taking the flow into the transformer as the positive direction, when the phase angle difference ФHp2 between the primary side positive sequence second harmonic voltage UHp2 and the current IHp2 of the transformer and the phase angle difference ФLp2 between the secondary side positive sequence second harmonic voltage ULp2 and the current ILp2 are both within 0° ~ -90°, the second harmonic locking element in the differential protection is put into operation.

[0071] When either the phase angle difference ФHp2 between the primary side positive sequence second harmonic voltage UHp2 and the current IHp2 of the transformer or the phase angle difference ФLp2 between the secondary side positive sequence second harmonic voltage ULp2 and the current ILp2 is greater than 0°, the second harmonic locking element in the differential protection is withdrawn.

[0072] In this way, the method for preventing the inverter harmonic from causing the differential protection to fail to act can reliably lock the differential protection when the transformer core is saturated, preventing the protection from malfunctioning, and can reliably open the differential protection when the inverter generates harmonics due to a transformer area fault, preventing the protection from failing to act.

[0073] ​The positive sequence second harmonic current when the transformer is saturated is flowed to the outside of the transformer, and the second harmonic generated by the inverter when the transformer is faulty is flowed to the inside of the transformer, and the directions of the two are different. With the flow into the transformer as the positive direction, whether the second harmonic is generated by the transformer saturation or the inverter can be identified by judging whether the phase angle difference of the positive sequence second harmonic voltage and current of the primary side and the secondary side of the transformer is within 0°~90°, when the phase angle difference of the positive sequence second harmonic voltage and current of the primary side and the phase angle difference of the positive sequence second harmonic voltage and current of the secondary side are both within 0°~90°, the second harmonic locking element in the differential protection is put into, and when any one of the phase angle difference of the positive sequence second harmonic voltage and current of the primary side and the phase angle difference of the positive sequence second harmonic voltage and current of the secondary side is greater than 0°, the second harmonic locking element in the differential protection is exited.

[0074] The application provides a method for preventing the transformer differential protection from being refused to act due to the harmonic generated by the inverter, which is suitable for a power system comprising a transformer protection device; the phase angle difference of the positive sequence second harmonic voltage and current of the primary side and the secondary side of the transformer is calculated by collecting the voltage and current signals of the primary side and the secondary side of the transformer; whether the preset condition is met is further judged based on the phase angle difference to determine whether to enter or exit the second harmonic locking mode; the false protection caused by the inverter harmonic is effectively avoided, and the reliability and stability of the power system are improved.

[0075] Embodiment two

[0076] Figure 3 A flow chart schematically showing a method for preventing the inverter harmonic from causing the differential protection to be refused to act according to another embodiment of the application; Figure 5 A hardware structure schematic diagram of a transformer protection device according to an embodiment of the application is shown in FIG. 2. Figure 3 and Figure 5 As shown in FIG. 2, according to an embodiment of the application, a method for preventing the inverter harmonic from causing the differential protection to be refused to act is applied to a power system comprising a transformer protection device; when using an electronic transformer to access, the SV unit pre-processes the digital sampling data, which is then transmitted to two independent main control units by an internal protocol, and the corresponding GOOSE opening and signal is output after the logical operation of the CPU; when using a conventional sampling to access, the AC unit converts the secondary voltage and current analog quantity into a small voltage signal and sends it to the two independent main control units, and the main control unit performs AD conversion on the small voltage signal, and then performs logical operation and outlet tripping on the digital quantity, and the outlet tripping mode can be GOOSE opening or conventional IO unit output.

[0077] The protection collects the primary side voltage UHa, UHb, UHc of the transformer; the primary side current IHa, IHb, IHc of the transformer; the secondary side voltage ULa, ULb, ULc of the transformer; and the secondary side current ILa, ILb, ILc of the transformer.

[0078] The secondary harmonic current voltage vector is calculated by the collected transformer primary side and secondary side current voltage, the transformer primary side secondary harmonic voltage UHa2, UHb2, UHc2, the transformer primary side secondary harmonic current IHa2, IHb2, IHc2, the transformer secondary side secondary harmonic voltage ULa2, ULb2, ULc2, the transformer primary side secondary harmonic current ILa2, ILb2, ILc2.

[0079] The transformer primary side positive sequence secondary harmonic voltage UHp2, the transformer primary side positive sequence secondary harmonic current Ihp2, the transformer secondary side positive sequence secondary harmonic voltage ULp2, the transformer primary side positive sequence secondary harmonic current ILp2 are calculated by the transformer primary side and secondary side current voltage secondary harmonic vector.

[0080] The phase angle difference of the transformer primary side positive sequence secondary harmonic voltage UHp2 and current Ihp2 and the phase angle difference of the transformer secondary side positive sequence secondary harmonic voltage ULp2 and current ILp2 are calculated by the transformer primary side and secondary side positive sequence secondary harmonic current voltage vector.

[0081] When the phase angle difference of the transformer primary side positive sequence secondary harmonic voltage UHp2 and current Ihp2 and the phase angle difference of the transformer secondary side positive sequence secondary harmonic voltage ULp2 and current ILp2 are all in 0°~90°, the secondary harmonic locking element in the differential protection is put in.

[0082] When any one of the phase angle difference of the transformer primary side positive sequence secondary harmonic voltage UHp2 and current Ihp2 and the phase angle difference of the transformer secondary side positive sequence secondary harmonic voltage ULp2 and current ILp2 is greater than 0°, the secondary harmonic locking element in the differential protection is exited.

[0083] The software and hardware of the application can be developed based on the conventional relay protection device, without additional increase of external loop such as mutual inductor; and the application has small calculation amount, and the relay protection equipment currently has mature harmonic calculation and sequence component calculation unit, so that the application can be realized through simple program development. Meanwhile, the application can reliably lock the differential protection when the transformer core is saturated, prevent protection misoperation, reliably open the differential protection when the transformer area fault inverter generates harmonic, prevent protection refusal, and can make up the problem of insufficient adaptability of the transformer secondary harmonic locking element in the grid-connected transformer protection of the new type power system inverter connection.

[0084] Example three

[0085] Figure 6 The structure diagram of the system for preventing the differential protection refusal caused by inverter harmonic according to an embodiment of the application is schematically shown. As shown in the figure, Figure 6As shown, according to an embodiment of the present application, a system for preventing the inverter harmonic from causing the differential protection to refuse to act is applied to a power system comprising a transformer protection device, and the system for preventing the inverter harmonic from causing the differential protection to refuse to act comprises:

[0086] A collecting module is configured to collect the primary side voltage and current of the transformer and the secondary side voltage and current of the transformer.

[0087] A calculating module is configured to calculate the first phase angle difference and the second phase angle difference of the transformer based on the primary side voltage and current of the transformer and the secondary side voltage and current of the transformer.

[0088] The first phase angle difference is the phase difference between the primary side positive sequence second harmonic voltage of the transformer and the primary side positive sequence second harmonic current of the transformer, and the second phase angle difference is the phase difference between the secondary side positive sequence second harmonic voltage of the transformer and the secondary side positive sequence second harmonic current of the transformer.

[0089] A judging module is configured to judge whether the first phase angle difference and the second phase angle difference satisfy a first preset condition; if yes, the system enters a second harmonic locking mode.

[0090] The judging module is further configured to judge whether a second preset condition is satisfied; if yes, the system exits the second harmonic locking mode.

[0091] According to an embodiment of the present application, the collecting module comprises a current transformer and a voltage transformer.

[0092] The two current transformers are respectively connected in series to the two ends of the transformer, and are configured to collect the primary side current of the transformer and the secondary side current of the transformer.

[0093] The two voltage transformers are respectively connected in parallel to the two ends of the transformer and are connected with the transformer protection device; the two voltage transformers are configured to collect the primary side voltage of the transformer and the secondary side voltage of the transformer.

[0094] According to an embodiment of the present application, the calculating module is further configured to:

[0095] Calculate the primary side second harmonic voltage of the transformer, the primary side second harmonic current of the transformer, the secondary side second harmonic voltage of the transformer and the secondary side second harmonic current of the transformer based on the primary side voltage and current of the transformer and the secondary side voltage and current of the transformer.

[0096] Calculate the first phase angle difference based on the primary side positive sequence second harmonic voltage of the transformer and the primary side positive sequence second harmonic current of the transformer, and calculate the second phase angle difference based on the secondary side positive sequence second harmonic voltage of the transformer and the secondary side positive sequence second harmonic current of the transformer.

[0097] According to an embodiment of the present application, the first preset condition comprises whether the first phase angle difference and the second phase angle difference are both within 0° ~ -90°.

[0098] According to an embodiment of the present application, the second preset condition comprises that the first phase angle difference is greater than 0° or the second phase angle difference is greater than 0°.

[0099] The present application provides a power system suitable for comprising a transformer protection device; by collecting voltage and current signals of a primary side and a secondary side of a transformer, phase angle differences of positive sequence second harmonic voltages and currents of the primary side and the secondary side of the transformer are calculated; based on the phase angle differences, it is further determined whether a preset condition is met to determine whether to enter or exit a second harmonic lockout mode; false protection caused by inverter harmonics is effectively avoided, and the reliability and stability of the power system are improved.

[0100] Embodiment four

[0101] As shown in Figure 5 According to an embodiment of the present application, a transformer protection device is applied to any system for preventing inverter harmonics from causing differential protection failure as described above, and the transformer protection device comprises:

[0102] An AC unit is configured to receive analog input;

[0103] An SV unit is configured to receive digital input;

[0104] A master control unit is configured to perform data collection and IO extension;

[0105] A monitoring and communication unit is configured to perform GPS time synchronization and send alarm information, and is further configured to communicate with a background monitoring and external devices;

[0106] A GOOSE input and output unit is configured to output corresponding GOOSE output and signals;

[0107] An MMI unit is configured to be connected with a host computer.

[0108] According to an embodiment of the present application, an electronic device comprises a processor, a memory, and a computer program stored on the memory and executable on the processor, and the computer program is executed by the processor to implement any method for preventing inverter harmonics from causing differential protection failure as described above.

[0109] According to an embodiment of the present application, a computer readable storage medium stores a computer program, and the computer program is executed by a processor to implement any method for preventing inverter harmonics from causing differential protection failure as described above.

[0110] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the above-described device and medium can refer to the corresponding process in the foregoing method embodiments, which will not be described herein.

[0111] The software and hardware of the application can be developed based on conventional relay protection devices, without additional increase of external circuits such as mutual inductors; and the application has a small amount of calculation, and the current relay protection equipment is provided with mature harmonic calculation and sequence component calculation units, so that the application can be realized through simple program development. The application can reliably lock differential protection when the transformer core is saturated, prevent protection misoperation, reliably open differential protection when the transformer area fault inverter generates harmonics, prevent protection refusal, and can make up for the problem that the transformer secondary harmonic locking element is not adaptive in the grid-connected transformer protection of the new power system inverter connection.

[0112] The above description is merely the preferred embodiment and the explanation of the applied technical principles of the application. Those skilled in the art should understand that the application scope involved in the application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or equivalent features without departing from the inventive concept. For example, the above features are replaced with the technical features disclosed in the application (but not limited to) having similar functions to form a technical solution.

[0113] It should be understood that the size of the serial number of the steps in the summary and the embodiments of the application does not absolutely mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the application.

Claims

1. A method for preventing inverter harmonics from causing differential protection failure, applied to a power system including a transformer protection device, characterized in that: The method comprises: Collect the transformer primary voltage and current and the transformer secondary voltage and current; Calculating a first phase angle difference and a second phase angle difference of the transformer based on the transformer primary voltage and current and the transformer secondary voltage and current; wherein the first phase angle difference is a phase difference between the transformer primary positive-sequence second harmonic voltage and the transformer primary positive-sequence second harmonic current, and the second phase angle difference is a phase difference between the transformer secondary positive-sequence second harmonic voltage and the transformer secondary positive-sequence second harmonic current; determining whether the first phase angle difference and the second phase angle difference satisfy a first preset condition; if so, entering a second harmonic blocking mode; Determine whether a second preset condition is met; if so, exit the second harmonic blocking mode; The first preset condition includes: the first phase angle difference and the second phase angle difference are both between 0° and -90°; The second preset condition includes: the first phase angle difference is greater than 0° or the second phase angle difference is greater than 0°.

2. The method for preventing inverter harmonics from causing differential protection failure according to claim 1, characterized in that: Calculating a first phase angle difference and a second phase angle difference of the transformer based on the primary voltage and current of the transformer and the secondary voltage and current of the transformer, including: Calculating the transformer primary side second harmonic voltage, the transformer primary side second harmonic current, the transformer secondary side second harmonic voltage, and the transformer secondary side second harmonic current based on the transformer primary side voltage and current and the transformer secondary side voltage and current; The first phase angle difference is calculated based on the transformer primary positive-sequence second harmonic voltage and the transformer primary positive-sequence second harmonic current, and the second phase angle difference is calculated based on the transformer secondary positive-sequence second harmonic voltage and the transformer secondary positive-sequence second harmonic current.

3. A system for preventing inverter harmonics from causing differential protection failure, applied to a power system including a transformer protection device, characterized in that: include: An acquisition module is used to acquire the voltage and current of the primary side of the transformer and the voltage and current of the secondary side of the transformer; a calculation module, configured to calculate a first phase angle difference and a second phase angle difference of the transformer based on the transformer primary voltage and current and the transformer secondary voltage and current; wherein the first phase angle difference is a phase difference between the transformer primary positive-sequence second harmonic voltage and the transformer primary positive-sequence second harmonic current, and the second phase angle difference is a phase difference between the transformer secondary positive-sequence second harmonic voltage and the transformer secondary positive-sequence second harmonic current; a judging module, configured to judge whether the first phase angle difference and the second phase angle difference satisfy a first preset condition; if so, enter a second harmonic blocking mode; The judgment module is further configured to judge whether a second preset condition is satisfied; if satisfied, exit the second harmonic blocking mode; The first preset condition includes: the first phase angle difference and the second phase angle difference are both between 0° and -90°; The second preset condition includes: the first phase angle difference is greater than 0° or the second phase angle difference is greater than 0°.

4. The system for preventing inverter harmonics from causing differential protection failure according to claim 3, characterized in that: The acquisition module includes: a current transformer and a voltage transformer; The two current transformers are respectively connected in series at both ends of the transformer, and are used to collect the primary current and the secondary current of the transformer; The two voltage transformers are respectively connected in parallel to the two ends of the transformer and are connected to the transformer protection device; the two voltage transformers are used to collect the primary voltage and the secondary voltage of the transformer.

5. The system for preventing inverter harmonics from causing differential protection failure according to claim 3, characterized in that: The calculation module is also used for: Calculating the transformer primary side second harmonic voltage, the transformer primary side second harmonic current, the transformer secondary side second harmonic voltage, and the transformer secondary side second harmonic current based on the transformer primary side voltage and current and the transformer secondary side voltage and current; The first phase angle difference is calculated based on the transformer primary positive-sequence second harmonic voltage and the transformer primary positive-sequence second harmonic current, and the second phase angle difference is calculated based on the transformer secondary positive-sequence second harmonic voltage and the transformer secondary positive-sequence second harmonic current.

6. A transformer protection device, applied to the system for preventing inverter harmonics from causing differential protection failure as described in any one of claims 3 to 5, characterized in that: The transformer protection device comprises: AC unit, used to receive analog input; SV unit, used to receive digital input; Main control unit, used for data acquisition and IO expansion; Monitoring and communication unit, used for GPS timing and sending alarm information, and also for communicating with background monitoring and external equipment; GOOSE input and output unit is used to output the corresponding GOOSE output; MMI unit, used to connect to the host.

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