Method and equipment for differential protection of protection section and relay protection device

Abstract

The invention relates to a differential protection method for a protection section of a power system. The two ends of the protection section are connected with a first current transformer and a second current transformer respectively. The differential protection method comprises the following steps: continuously obtaining a first secondary current value of a first current transformer and a second secondary current value of a second current transformer; calculating a differential current value and a braking current value based on the first secondary current value and the second secondary current value; the method comprises the following steps: starting a judgment window in response to a fault of a power system, and judging the fault as an internal fault under the condition that a differential current value and a brake current value meet an internal fault condition in the judgment window, the internal fault condition is that the absolute value of the differential current value is always greater than the absolute value of the brake current value, and the absolute value of the brake current value is not greater than the absolute value of the differential current value; and the absolute value of the differential current value is monotonically increased. The invention further relates to equipment for differential protection of the protection section of the power system, a relay protection device and a computer readable storage medium.

Description

Technical Field

[0001] The present disclosure relates to the field of relay protection, and in particular to a method and device for differential protection of a protection zone of an electric power system, a relay protection device, and a computer-readable storage medium. Background Art

[0002] The power system plays an important role in people's daily life. For example, when a power component (such as a generator, line, etc.) in the power system fails and endangers the safe operation of the power system, the relay protection is used to send a warning signal in time or directly send a trip command to the controlled circuit breaker to disconnect the faulty section from the power system. Differential protection is a commonly used relay protection method, which determines whether there is a fault in the protection section by detecting the imbalance of the current in the protection section, so as to take corresponding actions.

[0003] The monitoring and protection of power systems are often achieved with the help of current transformers, which use induced secondary current to reflect the primary current. However, in the case of a fault current caused by a fault, the core of the current transformer may reach saturation due to excessive magnetic flux density, resulting in a large transmission error in the current transformer, and the accuracy of the induced secondary current is greatly reduced. When the differential protection uses the current transformers at both ends of the protection zone to make fault judgments, the reliability of the judgment results is also greatly reduced. At present, with the continuous development of the power system, the short-circuit current level at the time of a fault is constantly increasing, and many protection misoperation accidents caused by current transformer saturation have occurred. Summary of the invention

[0004] In order to solve the above problems, the method and apparatus for differential protection of a protection zone of an electric power system, the relay protection device and the computer-readable storage medium according to the present disclosure can achieve differential protection with higher reliability when there is a possibility that the current transformer is saturated.

[0005] An embodiment of the present disclosure provides a differential protection method for a protection zone of an electric power system, wherein a first current transformer and a second current transformer are respectively connected to both ends of the protection zone, and the differential protection method comprises: continuously acquiring a first secondary current value of the first current transformer and a second secondary current value of the second current transformer; obtaining a differential current value and a braking current value based on the first secondary current value and the second secondary current value; and opening a judgment window in response to a fault in the electric power system, and if the differential current value and the braking current value meet an in-zone fault condition during the judgment window, judging the fault as an in-zone fault, otherwise judging the fault as a to-be-determined fault, wherein the in-zone fault condition is: the absolute value of the differential current value is always greater than the absolute value of the braking current value, and the absolute value of the differential current value is monotonically increasing.

[0006] According to an embodiment of the present disclosure, the determination window lasts from 3 ms to 5 ms.

[0007] According to an embodiment of the present disclosure, when a fault is determined to be an intra-zone fault, circuit breakers arranged at both ends of a protection zone are controlled to perform a protection action so that the protection zone is disconnected from the power system.

[0008] According to an embodiment of the present disclosure, when the fault is determined to be a pending fault, the protection action is blocked in a predetermined period of time, so that the protection section is not disconnected from the power system in the predetermined period of time.

[0009] According to an embodiment of the present disclosure, subsequent fault judgment is performed in a predetermined period, and when the predetermined period expires, it is judged whether to open the protection action, wherein the subsequent fault judgment includes judging the type of the fault by using harmonic braking.

[0010] An embodiment of the present disclosure provides a relay protection device capable of providing differential protection for a protection zone of an electric power system, wherein a first current transformer and a second current transformer are respectively connected to both ends of the protection zone, and the relay protection device comprises: a current acquisition module, used to continuously acquire a first secondary current value of the first current transformer and a second secondary current value of the second current transformer; an obtaining module, used to obtain a differential current value and a braking current value based on the first secondary current value and the second secondary current value; and a judgment module, used to open a judgment window in response to a fault in the electric power system, and judge the fault as an intra-zone fault if the differential current value and the braking current value meet an intra-zone fault condition during the judgment window, otherwise judge the fault as a to-be-determined fault, wherein the intra-zone fault condition is that the absolute value of the differential current value is always greater than the absolute value of the braking current value, and the absolute value of the differential current value increases monotonically.

[0011] According to an embodiment of the present disclosure, the relay protection device further includes a control module. When the fault is judged as an in-zone fault, the control module is used to control the circuit breakers arranged at both ends of the protection section to perform a protection action so that the protection section is disconnected from the power system; when the fault is judged as a pending fault, the control module is used to lock the protection action in a predetermined period so that the protection section is not disconnected from the power system in the predetermined period.

[0012] According to an embodiment of the present disclosure, when the fault is judged as a pending fault, the judgment module performs subsequent fault judgment in a predetermined period, and judges whether to open the protection action when the predetermined period expires. The subsequent fault judgment includes using harmonic braking to judge the type of the fault.

[0013] An embodiment of the present disclosure provides a device for differential protection of a protection zone of an electric power system, comprising: a processor; and a memory, wherein an executable program is stored, and when the executable program is executed by the processor, the method according to one of the embodiments of the present disclosure is executed.

[0014] An embodiment of the present disclosure provides a computer-readable storage medium on which computer-readable instructions are stored. When the instructions are executed by a processor, the instructions are used to implement the method according to one of the embodiments of the present disclosure.

[0015] The embodiments of the present disclosure provide a computer program product or a computer program, which includes a computer instruction stored in a computer-readable storage medium. A processor of a computer device reads the computer instruction from the computer-readable storage medium, and the processor executes the computer instruction, so that the computer device executes a method according to one of the embodiments of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some exemplary embodiments of the present disclosure, and a person of ordinary skill in the art can obtain other drawings based on these drawings without creative work.

[0017] Figure 1 A schematic diagram of a power system according to an embodiment of the present disclosure is shown;

[0018] Figure 2 schematically shows a current curve of a current transformer over time;

[0019] Figure 3A The example shows Figure 1 Schematic current conditions of the power system in normal operation;

[0020] Figure 3B The example shows Figure 1 Schematic current situation of the power system when an out-of-region fault occurs;

[0021] Figure 3C The example shows Figure 1 Schematic current situation of the power system when an in-region fault occurs;

[0022] Figure 4 A flow chart schematically shows a differential protection method for a protection zone of a power system according to an embodiment of the present disclosure;

[0023] Figure 5A schematic diagram of a relay protection device according to an embodiment of the present disclosure is shown;

[0024] Figure 6 A schematic diagram showing a device for differential protection of a protection zone of a power system according to an embodiment of the present disclosure; and

[0025] Figure 7 A schematic diagram of a computer-readable storage medium according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present disclosure more obvious, the exemplary embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments of the present disclosure, and it should be understood that the present disclosure is not limited to the exemplary embodiments described here.

[0027] In this specification and the drawings, substantially the same or similar steps and elements are represented by the same or similar reference numerals, and repeated descriptions of these steps and elements will be omitted. At the same time, in the description of the present disclosure, the terms "first", "second", etc. are only used for determination and description, and cannot be understood as indicating or implying relative importance or ranking.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present disclosure belongs. The terms used herein are only for the purpose of describing the embodiments of the present disclosure and are not intended to limit the present disclosure.

[0029] To facilitate description of the present disclosure, concepts related to the present disclosure are introduced below.

[0030] Saturation of current transformer: The current transformer is based on the principle of electromagnetic induction. When a changing current flows through the primary side, a changing magnetic flux is induced on the core of the current transformer, and the changing magnetic flux induces a secondary current on the secondary side. In normal operation, the core in the current transformer is usually in an unsaturated state. When a fault such as a short circuit occurs, the fault current flowing through the primary side is too large, causing the magnetic flux density of the core to increase and reach saturation. The change in magnetic field strength is no longer obvious, the secondary current is distorted and cannot correctly reflect the primary current, and the current transformer has a large transmission error.

[0031] In-zone fault: The fault point occurs within the protection zone.

[0032] Out-of-zone fault: The fault point occurs outside the protection zone.

[0033] Differential protection: A local protection for a protected section of a power system, based on the comparison of the currents at both ends of the protected section. Differential protection is based on Kirchhoff's current law, and in the event of a fault within the protected section, the currents at both ends of the protected section deviate significantly from the balance. Differential protection is performed with the help of current transformers at both ends of the protected section.

[0034] Differential current: One of the parameters used in differential protection, also known as unbalanced current, mathematically defined as the vector sum of the secondary currents induced by the current transformers at both ends of the protection zone.

[0035] Figure 1 A schematic diagram of a power system according to an embodiment of the present disclosure is shown.

[0036] like Figure 1 As shown, the power system PS is, for example, a dual-power power system. The dual-power power system includes an AC first power source PA and a second power source PB. The current flow direction is determined by the specific electromotive force conditions during the operation of the power system.

[0037] The protection zone GS requiring differential protection is connected between the first busbar W1 on the first power source PA side and the second busbar W2 on the second power source PB side. The protection objects of the protection zone of the power system include, for example, lines, transformers, busbars, generators, motors, and the like.

[0038] The first current transformer CT1 and the second current transformer CT2 are connected at both ends of the protection section GS, which are included in the protection section and are used to reflect the primary current between the first power supply PA and the second power supply PB. The first circuit breaker CB1 and the second circuit breaker CB2 are arranged at both ends of the protection section GS, which are used to perform protection actions when the differential protection method determines that the fault in the zone is detected, that is, disconnect the protection section GS from the power system PS, reduce the operating time under the fault current, and reduce the damage degree of the protection object.

[0039] As described above, the current transformer may be saturated due to the fault primary current, so that the induced secondary current can no longer correctly reflect the primary current situation, and the reliability of the fault judgment result is reduced.

[0040] Below with the help of Figure 2 The influence of the saturation of the current transformer on the induced secondary current is illustrated by way of example. Figure 2 The current curve of a current transformer over time is schematically shown.

[0041] like Figure 2 As shown, the horizontal axis represents time t, the vertical axis represents the induced secondary current I, the dotted line shows the current curve of the induced secondary current over time under ideal conditions, and the solid line shows the current curve of the induced secondary current over time when the current transformer is saturated.

[0042] Time points t0, t1, t2, and t3 represent the zero-crossing points of the alternating current. Ideally, the current transformer accurately transmits and the current curve of the induced secondary current shows the same waveform as the primary current. On the contrary, when the current transformer is gradually saturated due to the fault current, taking the half cycle from t0 to t1 as an example, in the time period from the zero-crossing point t0 to the saturation time point tk, the current transformer is not saturated and basically accurately transmits and transforms, but due to, for example, the measurement error of the current transformer itself, the induced secondary current curve cannot completely fit the ideal curve, but is closer to a linear curve. This stage is called the linear transmission stage. After the saturation time point tk, the induced secondary current is distorted, drops rapidly and decreases to 0 at the time point tn. In other words, after the current transformer is saturated, the fault primary current is large, and the secondary current used to reflect the primary current decreases rapidly or even becomes 0, and the current transformer cannot accurately transmit and transform.

[0043] Therefore, in the event of a fault, the current transformer may have been saturated, and the reliability of fault judgment based on the secondary current is reduced.

[0044] Figure 3A The example shows Figure 1 Schematic current conditions of the power system in normal operation.

[0045] like Figure 3A As shown, for example, the primary current IA flows through the protection zone GS from the first power source PA to the second power source PB. The first current transformer CT1 and the second current transformer CT2 of the protection zone GS respectively induce the first secondary current I1 and the second secondary current I2 in the same direction as the primary current IA.

[0046] According to Kirchhoff's current law, the sum of the currents entering the protection zone GS is equal to the sum of the currents leaving the protection zone GS. Entering the protection zone GS is the positive direction of the current. This results in that, ideally, the vector sum of the first secondary current I1 and the second secondary current I2, i.e., the differential current, is zero.

[0047] For example, the normal primary current IA is 100A, and the measured first secondary current I1 and second secondary current I2 are 5A. Considering the current directionality,

[0048] In normal operation, the current transformer is usually not saturated. However, due to the manufacturing accuracy of the current transformer itself, the measurement result of the current transformer has a certain error, and the error range is, for example, -2% to +2%. Therefore, in the above example, the first secondary current I1 and the second secondary current I2 are, for example, in the range of 4.9 to 5.1A and -4.9 to -5.1A, respectively, and the magnitude of their vector sum, that is, the absolute value of the differential current, is in the range of 0 to 0.2A.

[0049] Figure 3B The example shows Figure 1 Schematic current conditions of the power system when an out-of-region fault occurs.

[0050] like Figure 3B As shown, a fault point k1 appears in the section between the protection section GS and the second power supply PB, that is, an out-of-zone fault occurs. In the event of a fault, the electromotive force at the fault point is the lowest, and the current flows from the power supply to the fault point. Therefore, on the left side of the fault point k1, the fault primary current IA flows through the protection section GS in the direction from the first power supply PA to the second power supply PB. The first current transformer CT1 and the second current transformer CT2 of the protection section GS respectively induce the first secondary current I1 and the second secondary current I2 in the same direction as the primary current IA.

[0051] For example, when the primary fault current IA is 1000A and both the first current transformer CT1 and the second current transformer CT2 are not saturated and can be accurately transmitted,

[0052] When the measurement error of the current transformer itself is taken into account without considering the saturation of the current transformer, and assuming that the current transformer has an error range of, for example, -2% to +2%, the first secondary current I1 and the second secondary current I2 are respectively in the ranges of 49 to 51A and -49 to -51A, and the magnitude of their vector sum, that is, the absolute value of the differential current, is in the range of 0 to 2A.

[0053] When at least one current transformer is saturated, the first secondary current I1 and / or the second secondary current I2 is distorted, resulting in that the vector sum, ie, the differential current, may deviate seriously from zero.

[0054] Figure 3C The example shows Figure 1 Schematic current situation of the power system when an intra-regional fault occurs.

[0055] like Figure 3CAs shown, a fault point k2 appears in the protection zone GS, that is, an in-zone fault occurs. On the left side of the fault point k2, the fault primary current IA flows from the first power supply PA to the fault point k2, that is, into the protection zone GS, and on the right side of the fault point k2, the fault primary current IB flows from the second power supply PB to the fault point k2, that is, into the protection zone GS. The fault primary current IA and the fault primary current IB are not necessarily equal. The current directions of the first secondary current I1 and the second secondary current I2 induced by the first current transformer CT1 and the second current transformer CT2 are both positive.

[0056] For example, the fault primary current IA and the fault primary current IB are both 1000A. When the first current transformer CT1 and the second current transformer CT2 are not saturated and can be accurately transmitted,

[0057] When the measurement error of the current transformer itself is taken into account without considering the saturation of the current transformer, and assuming that the current transformer has an error range of, for example, -2% to +2%, the first secondary current I1 and the second secondary current I2 are respectively in the ranges of 49 to 51A and 49 to 51A, and the magnitude of their vector sum, that is, the absolute value of the differential current, is in the range of 98 to 102A.

[0058] In the case where at least one current transformer may be saturated, the first secondary current I1 and / or the second secondary current I2 are distorted, and the magnitude of their vector sum may seriously deviate from 100A.

[0059] Combined with Figure 3A , Figure 3B , Figure 3C For example, when a fault occurs within the protection zone GS, the first secondary current I1 and the second secondary current I2 deviate significantly from the balance, which is manifested as the differential current deviating significantly from zero.

[0060] A known differential protection method is that when the absolute value of the differential current is greater than a predetermined threshold, the fault is determined to be an intra-zone fault.

[0061] However, as can be seen from the above description, judging the fault in the zone based on the absolute value of the differential current being greater than the predetermined threshold value has the following defects:

[0062] The current transformer itself has errors. When the normal primary current in the power system is large or a faulty primary current occurs, the induced secondary current and its error also become larger. For example, when the predetermined threshold is 1A, according to Figure 3BTaking the case where the magnitude of the vector sum of the first secondary current I1 and the second secondary current I2 may be in the range of 0 to 2A, this judgment condition misjudges the out-of-zone fault as an in-zone fault and causes malfunction. On the contrary, when the predetermined threshold is set too high, the in-zone fault may be missed and cause refusal to operate.

[0063] Therefore, another known differential protection method introduces a new intra-zone fault condition based on restraining current.

[0064] The braking current is set as the proportional braking coefficient K and the vector difference between the first secondary current I1 and the second secondary current I2. The product of The proportional braking coefficient K is selected as needed, for example, between 0.5 and 0.8. The new intra-zone fault condition of the differential protection method is that the absolute value of the differential current is greater than the absolute value of the braking current. In the case of an intra-zone fault in the power system, the currents of the first secondary current and the second secondary current are the same in sign, the absolute value of the braking current is small, and the braking effect is small, so that the intra-zone fault condition can be met and the protection action can be triggered. On the contrary, in the case of normal operation or an out-of-zone fault, the currents of the first secondary current and the second secondary current are opposite in sign, the absolute value of the braking current is large, and the braking effect is large, so that even if the differential current is higher than a certain threshold but still within the braking range of the braking current, it cannot meet the intra-zone fault condition and will not trigger the protection action. The new intra-zone fault condition is no longer based on a fixed predetermined threshold, but is based on a dynamic braking current that also changes with the first secondary current and the second secondary current, thereby improving the reliability of intra-zone fault judgment.

[0065] However, this differential protection method based on proportional braking can only ensure the reliability of the current transformer within a certain error range, such as + / -10%. When, for example, the fault current is too large, causing the current transformer to be saturated or even severely saturated, exceeding or even severely exceeding the error interval, it cannot be guaranteed to be reliable without false operation.

[0066] Figure 4 The flowchart of the differential protection method for the protection zone of the power system according to the embodiment of the present disclosure is schematically shown.

[0067] In a first step S1, a first secondary current value I1 of a first current transformer and a second secondary current value I2 of a second current transformer are continuously acquired. The first step S1 is performed, for example, by means of a current detection unit of the current transformer.

[0068] In the second step S2, a differential current value is obtained based on the first secondary current value I1 and the second secondary current value I2. and braking current value As mentioned above, the differential current value reflects the current balance at both ends of the protection zone. In the normal operation of the power system, the differential current value is basically zero.

[0069] In the third step S3, a judgment window is opened in response to a fault in the power system. The fault in the power system is manifested, for example, in that the induced secondary current deviates from the normal range, or the absolute value of the differential current value is greater than a certain predetermined threshold. In this judgment window, it is determined whether the fault is an intra-zone fault.

[0070] In the fourth step S4, it is determined whether the differential current value and the braking current value meet the zone fault condition during the determination window. The zone fault condition includes a first condition and a second condition. The first condition is: the absolute value of the differential current value Always greater than the absolute value of the braking current The second condition is: the absolute value of the differential current Monotonically increasing.

[0071] The first condition is based on proportional braking. When the current transformer transmits the current accurately, the first condition can be satisfied to determine that the fault is an internal fault.

[0072] The second condition is based on Figure 2 The current curve of the secondary current under the saturation condition of the current transformer is shown. In the linear transmission stage before the current transformer is not saturated, the current transformer basically transmits accurately, and the reliability of the induced secondary current and the differential current and braking current obtained based on the secondary current is high. In the case of an in-zone fault, in the linear transmission stage, the absolute value of the vector sum of the first secondary current and the second secondary current with the same current direction increases monotonically, that is, the absolute value of the differential current value increases monotonically.

[0073] Based on this, it can be determined whether the judgment window completely falls into the linear transmission stage. If the judgment window completely falls into the linear transmission stage, the absolute value of the differential current value increases monotonically, that is, the second condition is met, then the differential current value and braking current value used in the first condition are regarded as accurate, and the fault judgment result is regarded as reliable; if the judgment window does not completely fall into the linear transmission stage, but the saturation of the current transformer has appeared in the judgment window, the absolute value of the differential current value is not monotonically increasing but fluctuates, that is, the second condition is not met, then the differential current value and braking current value used in the first condition are regarded as inaccurate, and the fault judgment result is regarded as unreliable.

[0074] According to the embodiment of the present disclosure, the intra-area fault condition verifies the reliability of the first condition through the second condition. Only when the two conditions are met at the same time, the intra-area fault condition is met, which greatly improves the reliability of judging the intra-area fault.

[0075] Advantageously, the duration of the judgment window is greater than or equal to 3ms, preferably selected to be between 3ms and 5ms, preferably 3ms, 4ms, 5ms. In the industry standard of current transformers in power systems, it is usually required that the linear transition time is greater than 5ms, and at least can be greater than 3ms.

[0076] The short duration of the judgment window can ensure the accuracy of the judgment, and is conducive to the differential protection method according to the embodiment of the present disclosure to achieve rapid fault judgment and subsequent action execution. Even if the current transformer saturation occurs after the judgment window, the judgment of the fault condition during the judgment window is still accurate.

[0077] In the case that the differential current value and the braking current value meet the in-zone fault condition during the judgment window, the fault is judged as an in-zone fault in step S5, and in the optional step S5' represented by the dotted line, the circuit breakers at both ends of the protection zone are controlled to perform a protection action so that the protection zone is disconnected from the power system. The control of the circuit breakers at both ends of the protection zone to perform a protection action includes, for example, transmitting a protection action execution signal to the circuit breaker so that the circuit breaker is disconnected.

[0078] In the case that the differential current value and the braking current value do not meet the zone fault condition during the judgment window, the fault is judged as a pending fault in step S5', and the protection action is blocked within a predetermined period of time in the optional dotted line step S6', so that the protection zone is not disconnected from the power system within the predetermined period of time. The predetermined period of time is, for example, 60ms. In the case that the zone fault condition is not met, for example, the second condition is not met, the fault may be a zone fault, an external zone fault, or both a zone fault and an external zone fault exist.

[0079] Optionally, when the fault is judged as a pending fault, when the differential current value and the braking current value meet the out-of-zone fault condition during the judgment window, the pending fault can be judged as an out-of-zone fault. The out-of-zone fault condition can be: the absolute value of the differential current value is always less than the absolute value of the braking current value. In the case of judging it as an out-of-zone fault, the protection action for the protection section should not be triggered. However, out-of-zone faults, such as short-circuit currents, may also cause in-zone faults.

[0080] Optionally, when the fault is determined as a pending fault, a subsequent fault judgment may be performed according to a conventional fault judgment method to accurately identify whether a fault exists in the protection zone. The subsequent fault judgment may include, for example, further analyzing the fault condition using harmonic braking.

[0081] By blocking the protection action within a predetermined period and further judging the fault condition, it is advantageous to avoid misprotection and protection rejection, and improve the accuracy of differential protection. It is judged whether to open the protection action when the predetermined period expires. For example, in the case of an out-of-zone fault, when the out-of-zone fault has been removed by the corresponding out-of-zone protection device within the predetermined period, the protection action can be opened when the predetermined period expires, so that differential protection can continue to be performed on the power system.

[0082] According to the intra-zone fault condition of the differential protection method according to the embodiment of the present disclosure, in particular, the saturation condition of the current transformer is verified through the second condition, which solves the problem of using inaccurate secondary current values ​​for fault judgment in the prior art, improves the accuracy and reliability of intra-zone fault judgment, and effectively avoids false operation of the differential protection.

[0083] For example, the differential protection method for the protection zone of the power system according to the embodiment of the present disclosure may be implemented for each phase of the power system respectively.

[0084] Figure 5 A schematic diagram of a relay protection device according to an embodiment of the present disclosure is shown. The relay protection device 100 can provide differential protection for a protection zone of a power system, and a first current transformer and a second current transformer are connected to both ends of the protection zone, respectively.

[0085] like Figure 5 As shown, the relay protection device 100 comprises a current acquisition module 101 , a determination module 102 , a determination module 103 and a control module 104 .

[0086] The current acquisition module 101 is, for example, a current detection device of a current transformer, and is used to continuously acquire a first secondary current value of a first current transformer and a second secondary current value of a second current transformer.

[0087] The obtaining module 102 is used to obtain the differential current value and the braking current value based on the first secondary current value and the second secondary current value. The differential current value is the vector sum of the first secondary current value and the second secondary current value. The braking current value is the product of the proportional braking coefficient and the vector difference between the first secondary current value and the second secondary current value.

[0088] The judgment module 103 is used to open a judgment window in response to a fault in the power system. If the differential current value and the braking current value meet the fault condition within the judgment window, the fault is judged as an internal fault. Otherwise, the fault is judged as a pending fault. The internal fault condition is: the absolute value of the differential current value Always greater than the absolute value of the braking current And the absolute value of the differential current Monotonically increasing. Meeting the zone fault condition, that is, simultaneously meeting the first condition and the second condition, ensures that the fault judgment is performed in the linear transmission stage of the current transformer, thereby improving the reliability of the judgment result. When the zone fault condition is met, the fault can be judged as a zone fault and the protection action can be controlled. When the zone fault condition is not met, further fault judgment is still required.

[0089] The control module 104 is used to control whether to perform a protection action according to the fault judgment result. In the case where the fault is judged as an in-zone fault, the control module 104, for example, issues an instruction to make the circuit breakers arranged at both ends of the protection section perform a protection action, thereby disconnecting the protection section from the power system. In the case where the fault is judged as a pending fault, the control module 104 locks the protection action within a predetermined period of time, so that the protection section is not disconnected from the power system within the predetermined period of time to avoid malfunction.

[0090] In the case where the fault is determined as a pending fault, the judgment module 103 can additionally perform subsequent fault judgment in a predetermined period, and judge whether to open the protection action when the predetermined period expires. The subsequent fault judgment, for example, includes judging the type of the fault by using harmonic braking.

[0091] The implementation manner and advantages of the differential protection method for a protection zone of an electric power system according to an embodiment of the present disclosure are also applicable to the relay protection device according to an embodiment of the present disclosure.

[0092] Figure 6 A schematic diagram of a device 200 for differential protection of a protection zone of a power system according to an embodiment of the present disclosure is shown.

[0093] like Figure 6 As shown, the device 200 for differential protection of a protection zone of a power system includes one or more processors 201 and one or more memories 202. The memory 202 stores an executable program, and when the processor 201 executes the executable program, the method described above is executed.

[0094] The processor in the embodiments of the present disclosure may be an integrated circuit chip having signal processing capabilities. The processor may be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), an off-the-shelf programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components. The methods, steps and logic block diagrams disclosed in the embodiments of the present application may be implemented or executed. The general-purpose processor may be a microprocessor or the processor may be any conventional processor, etc., and may be an X86 architecture or an ARM architecture.

[0095] Figure 7A schematic diagram of a computer-readable storage medium 300 according to an embodiment of the present disclosure is shown.

[0096] like Figure 7 As shown, the computer-readable storage medium 300 stores computer-readable instructions 301. When the computer-readable instructions 301 are executed by the processor, the method according to the embodiment of the present disclosure described with reference to the above figures can be executed. The computer-readable storage medium in the embodiment of the present disclosure can be a volatile memory or a non-volatile memory, or can include both volatile and non-volatile memories. The non-volatile memory can be a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM) or a flash memory. The volatile memory can be a random access memory (RAM), which is used as an external cache. By way of example but not limitation, many forms of RAM are available, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDRSDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous connection dynamic random access memory (SLDRAM) and direct memory bus random access memory (DR RAM). It should be noted that memory of the methods described herein is intended to include, but is not limited to, these and any other suitable types of memory. It should be noted that memory of the methods described herein is intended to include, but is not limited to, these and any other suitable types of memory.

[0097] It should be noted that the flowcharts and block diagrams in the accompanying drawings illustrate the possible architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each box in the flowchart or block diagram can represent a module, a program segment, or a part of a code, and the module, program segment, or a part of the code contains at least one executable instruction for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flowchart, and the combination of boxes in the block diagram and / or flowchart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0098] In general, various example embodiments of the present disclosure may be implemented in hardware or dedicated circuits, software, firmware, logic, or any combination thereof. Certain aspects may be implemented in hardware, while other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor, or other computing device. When various aspects of the embodiments of the present disclosure are illustrated or described as block diagrams, flow charts, or using some other graphical representation, it will be understood that the blocks, devices, systems, techniques, or methods described herein may be implemented in hardware, software, firmware, dedicated circuits or logic, general purpose hardware or controllers or other computing devices, or some combination thereof as non-limiting examples.

[0099] The exemplary embodiments of the present disclosure described in detail above are merely illustrative and not restrictive. It should be understood by those skilled in the art that various modifications and combinations may be made to these embodiments or their features without departing from the principles and spirit of the present disclosure, and such modifications should fall within the scope of the present disclosure.

Claims

1. A differential protection method for a protection zone of an electric power system, wherein two ends of the protection zone are respectively connected to a first current transformer and a second current transformer, and the differential protection method comprises: continuously acquiring a first secondary current value of the first current transformer and a second secondary current value of the second current transformer; obtaining a differential current value and a braking current value based on the first secondary current value and the second secondary current value; as well as In response to a fault in the power system, a judgment window is opened, and if the differential current value and the braking current value meet an in-zone fault condition during the judgment window, the fault is judged as an in-zone fault, otherwise the fault is judged as a to-be-determined fault, The intra-zone fault condition is that the absolute value of the differential current value is always greater than the absolute value of the braking current value, and the absolute value of the differential current value increases monotonically.

2. The differential protection method according to claim 1, wherein: The determination window lasts from 3 ms to 5 ms.

3. The differential protection method according to claim 1, wherein: In the case where the fault is determined to be an intra-zone fault, circuit breakers arranged at both ends of the protection zone are controlled to perform protection actions so as to disconnect the protection zone from the power system.

4. The differential protection method according to claim 1, wherein: In the case where the fault is determined to be a pending fault, a protection action is blocked in a predetermined period of time, so that the protection section is not disconnected from the power system in the predetermined period of time.

5. The differential protection method according to claim 4, wherein: Perform subsequent fault judgment in the predetermined time period, and judge whether to open the protection action when the predetermined time period expires, Wherein, the subsequent fault judgment includes using harmonic braking to judge the type of the fault.

6. A relay protection device capable of providing differential protection for a protection zone of a power system, wherein two ends of the protection zone are respectively connected to a first current transformer and a second current transformer, and the relay protection device comprises: - a current acquisition module, used to continuously acquire a first secondary current value of the first current transformer and a second secondary current value of the second current transformer; - an obtaining module, configured to obtain a differential current value and a braking current value based on the first secondary current value and the second secondary current value; as well as - a judgment module, configured to open a judgment window in response to a fault in the power system, and judge the fault as an intra-zone fault if the differential current value and the braking current value meet an intra-zone fault condition during the judgment window, otherwise judge the fault as a pending fault; The intra-zone fault condition is that the absolute value of the differential current value is always greater than the absolute value of the braking current value, and the absolute value of the differential current value increases monotonically.

7. The relay protection device according to claim 6, wherein: The relay protection device also includes: - Control module, In the case where the fault is determined to be an in-zone fault, the control module is used to control the circuit breakers arranged at both ends of the protection zone to perform a protection action so as to disconnect the protection zone from the power system. In the case where the fault is determined to be a pending fault, the control module is used to lock the protection action in a predetermined period of time, so that the protection section is not disconnected from the power system in the predetermined period of time.

8. The relay protection device according to claim 7, wherein: In the case where the fault is determined to be a pending fault, the judgment module performs subsequent fault judgment in the predetermined period, and judges whether to open a protection action when the predetermined period expires. Wherein, the subsequent fault judgment includes using harmonic braking to judge the type of the fault.

9. A device for differential protection of a protection zone of an electric power system, comprising: processor; as well as A memory having an executable program stored therein, wherein when the executable program is executed by the processor, the method according to any one of claims 1 to 5 is executed.

10. A computer-readable storage medium having computer-readable instructions stored thereon, wherein the instructions are used to implement the method according to any one of claims 1 to 5 when executed by a processor.

Images