Method and device for positioning fault when single-phase grounding occurs on low-voltage side of main transformer

Abstract

The invention provides a method for positioning a fault when single-phase grounding occurs at a low-voltage side of a main transformer, which comprises the following steps of: detecting whether a zero-sequence current component exists in a low-voltage switch or not when a single-phase grounding fault occurs in a 10kV system; if the zero-sequence current component of the transformer low-voltage switch is detected, determining that the fault point is located at the side, far away from the 10kV low-voltage bus, of the transformer low-voltage switch; otherwise, if it is detected that no zero-sequence current component exists in the main transformer switch, it is judged that the fault point is located on the 10kV low-voltage bus side. According to the invention, not only can the fault point be accurately positioned, but also the fault point can be correctly isolated, and the purposes of saving time and labor and improving the safety of a power grid are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method and a device for locating a fault when a single-phase grounding occurs on a low-voltage side of a main transformer. Background Art

[0002] The low winding of the main transformer is usually connected in a delta connection, so the 10kV system needs to install a neutral point grounding device because there is no neutral point. However, for the 10kV ungrounded system, a grounding transformer is generally installed on each bus section, and the zero-sequence current path is formed between the fault point when a single-phase grounding fault occurs in the system, and the zero-sequence overcurrent protection is enabled to quickly cut off the short-circuit fault point.

[0003] like Figure 1 Shown is the wiring diagram of a 10kV system. Figure 1 In the process, no matter the transformer is far away from the fault point k1 on the 10kV low-voltage bus side or the fault point k2 on the 10kV low-voltage bus side has a single-phase grounding fault, both will use the grounding-to-zero-sequence protection action to trip the 10kV section switch and transformer. This creates a hidden danger that the fault point cannot be located because the grounding-to-zero-sequence protection actions of the two are consistent, causing the operation and maintenance personnel to spend time and effort to find the fault point, which is not conducive to on-site power restoration. In addition, the transformer is far away from the fault point k1 on the 10kV low-voltage bus side, and the grounding-to-zero-sequence protection action trips the 10kV section switch and transformer, but the fault point is not truly isolated. Due to the increase in phase voltage, the main transformer may be further damaged.

[0004] Therefore, there is an urgent need for a method for locating the fault when single-phase grounding occurs on the low-voltage side of the main transformer, which can not only accurately locate the fault point on the 10kV low-voltage bus side or the 10kV low-voltage bus side, but also correctly isolate the fault point. Summary of the invention

[0005] The technical problem to be solved by the embodiments of the present invention is to provide a method and device for locating a fault when a single-phase grounding occurs on the low-voltage side of a main transformer, which can not only accurately locate the fault point, but also correctly isolate the fault point, thereby achieving the purpose of saving time and effort and improving the safety of the power grid.

[0006] In order to solve the above technical problems, an embodiment of the present invention provides a method for locating a fault when a single-phase grounding occurs on the low-voltage side of a main transformer, which is used in a 10kV system including a high-voltage transformer switch, a low-voltage transformer switch and a 10kV section switch. The method comprises the following steps:

[0007] When a single-phase grounding fault occurs in the 10kV system, detecting whether there is a zero-sequence current component in the transformer lowering switch;

[0008] If it is detected that the transformer substation has a zero-sequence current component, the fault point is determined to be located on the side of the transformer substation away from the 10kV low-voltage bus; conversely, if it is detected that the main transformer substation has no zero-sequence current component, the fault point is determined to be located on the side of the 10kV low-voltage bus.

[0009] Wherein, the method further comprises:

[0010] When it is determined that the fault point is located at the low-voltage switch far away from the 10kV low-voltage bus side, after detecting that the fault phase difference current meets the predetermined conditions, the grounding transformer zero-sequence protection action is used to trip the high-voltage switch and the low-voltage switch, and the 10kV section switch is closed through the preset 10kV backup power supply automatic switching device.

[0011] Wherein, the method further comprises:

[0012] When it is determined that the fault point is located on the 10kV low-voltage bus side, the grounding transformer zero-sequence protection action is directly used to trip the 10kV section switch and the low-voltage switch.

[0013] The embodiment of the present invention further provides a device for locating a fault when a single-phase grounding occurs on the low-voltage side of a main transformer, which is used in a 10kV system including a high-voltage transformer switch, a low-voltage transformer switch and a 10kV section switch, and includes:

[0014] A zero-sequence current component detection unit, used to detect whether the transformer has a zero-sequence current component when a single-phase grounding fault occurs in the 10kV system;

[0015] The fault point accurate positioning unit is used to determine that the fault point is located on the side of the transformer lowering switch away from the 10kV low-voltage busbar if it is detected that the transformer lowering switch has a zero-sequence current component; conversely, if it is detected that the main transformer lowering switch has no zero-sequence current component, it is determined that the fault point is located on the side of the 10kV low-voltage busbar.

[0016] Among them, it also includes:

[0017] The first protection action switch unit is used to, when it is determined that the fault point is located at the low-voltage switch far away from the 10kV low-voltage bus, and after detecting that the fault phase difference current meets the predetermined conditions, use the grounding zero-sequence protection action to trip the high-voltage switch and the low-voltage switch, and close the 10kV section switch through the preset 10kV backup power supply automatic switching device.

[0018] Among them, it also includes:

[0019] The second protection action switch unit is used to directly use the grounding zero-sequence protection action to trip the 10kV section switch and the low-voltage switch when it is determined that the fault point is located on the 10kV low-voltage bus side.

[0020] Implementing the embodiments of the present invention has the following beneficial effects:

[0021] 1. When a single-phase grounding fault occurs in a 10kV system, the present invention determines whether the fault point is located at the side of the low-voltage switch far away from the 10kV low-voltage bus or at the side of the 10kV low-voltage bus according to the detection condition of whether there is a zero-sequence current component in the low-voltage switch, thereby accurately locating the fault point and achieving the purpose of saving time and effort;

[0022] 2. The present invention isolates the fault point by tripping the high switch and the low switch and closing the 10kV section switch when the fault point is located on the side of the 10kV low-voltage busbar and the low-voltage switch is far away from the 10kV low-voltage busbar. The fault point is also located on the side of the 10kV low-voltage busbar and the 10kV section switch and the low switch are tripped to isolate the fault point. Therefore, based on the different positions of the fault point, the corresponding protection action switch can be used to correctly isolate the fault point, thereby achieving the purpose of improving the safety of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative labor, other drawings obtained based on these drawings still belong to the scope of the present invention.

[0024] Figure 1 It is the wiring diagram of 10kV system in the prior art;

[0025] Figure 2 for Figure 1 The equivalent composite sequence network diagram when a single-phase grounding fault occurs in the 10kV system;

[0026] Figure 3 A flow chart of a method for locating a fault when a single-phase grounding occurs on the low-voltage side of a main transformer provided by an embodiment of the present invention;

[0027] Figure 4 A schematic diagram of the structure of a device for locating a fault when a single-phase grounding occurs on the low-voltage side of a main transformer provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] The inventors have found that when a single-phase grounding fault occurs in a 10kV system, a composite sequence network of the grounding system (such as Figure 2 As shown), the composite sequence network and equipment parameters are used for data calculation.

[0030] At this time, the positive sequence current I1, negative sequence current I2 and zero sequence current I0 at the bus are calculated by the following formula:

[0031]

[0032] Among them, E S is the per unit value of the power supply electromotive force; Z S1 , Z S2 are the system equivalent positive and negative sequence impedances respectively; Z T1 , Z T2 They are respectively the equal positive and negative sequence impedances of the main transformer; Z JD0 is the grounding transformer equivalent zero-sequence impedance.

[0033] If the transformer switch is far away from the fault point k1 on the 10kV low-voltage bus side and a phase A ground fault occurs, the current of each phase on the high-voltage side of the main transformer is converted to the low-voltage side standard value I A =2I1、I B =-I1, I C = -I1 and there is no zero-sequence current; and, the unit current of each phase on the low-voltage side of the main transformer is calculated to be I a =-I1, I b =-I1, I c = -I1 and 3 I0= 3 I1. Therefore, the flow difference of each phase is I dA =I A -I a = 3 I1、I dB =I B -I b =0 and I dC =I C -I c =0, and the fault phase difference current is I d0 = 3 I0= 3 I1.

[0034] If a phase A ground fault occurs at the fault point k2 on the 10kV low-voltage bus side, the current of each phase on the high-voltage side of the main transformer is converted to the low-voltage side standard value I A = 2 I1、I B =I1,I C =I1 and 3 I0=0; and calculate the per unit current of each phase on the low voltage side of the main transformer to be I a = 2 I1、I b =I1,I c =I1 and 3 I0=0. Therefore, the phase flow difference is IdA =I A -I a =0,I dB =I B -I b =0 and I dC =I C -I c =0, and the fault phase difference current is I d0 =0.

[0035] In summary, when the transformer is far away from the fault point k1 on the 10kV low-voltage bus side and a phase A grounding fault occurs, the fault phase difference current is 3 I1 and the fault phase difference current is 3 I1, when a phase A grounding fault occurs at the fault point k2 on the 10kV low-voltage bus side, the fault phase difference current is 0 and the fault phase difference current is 0.

[0036] Therefore, based on the existence of the zero-sequence current component of the transformer, the inventors proposed a new fault location method to determine the location of the fault point. If the transformer has no zero-sequence current component, it means that the fault point is the fault point k2 on the 10kV low-voltage bus side; if the transformer has a zero-sequence current component, it means that the fault point is the transformer far away from the fault point k1 on the 10kV low-voltage bus side.

[0037] like Figure 3 As shown in the figure, in an embodiment of the present invention, the inventor proposes a method for locating a fault when a single-phase grounding occurs on the low-voltage side of a main transformer, which is used in a 10kV system including a high-voltage switch, a low-voltage switch and a 10kV section switch (see Figure 1 ), the method comprising the following steps:

[0038] Step S1, when a single-phase grounding fault occurs in the 10kV system, detecting whether the transformer has a zero-sequence current component;

[0039] Step S2: If it is detected that the transformer substation has a zero-sequence current component, it is determined that the fault point is located on the side of the transformer substation away from the 10kV low-voltage bus; conversely, if it is detected that the main transformer substation has no zero-sequence current component, it is determined that the fault point is located on the side of the 10kV low-voltage bus.

[0040] The specific process is that in step S1, if a single-phase grounding fault occurs in the 10kV system, it is possible to detect whether the low-voltage switch has a zero-sequence current component. It should be noted that a single-phase grounding fault can be obtained by a person skilled in the art using common techniques in the art; and positive and negative sequence current components and zero sequence current components can also be obtained by a person skilled in the art using common techniques in the art. Therefore, the above-mentioned related technical contents will not be repeated here one by one.

[0041] In step S2, if it is detected that there is a zero-sequence current component in the transformer, it is determined that the fault point is located at the transformer away from the 10kV low-voltage bus side. Figure 1 On the contrary, if it is detected that there is no zero-sequence current component in the main transformer switch, it is determined that the fault point is located on the 10kV low-voltage bus side. Figure 1 The fault point k2 in .

[0042] In order to avoid the hidden dangers caused by using the same protective action switch at the fault point, it is necessary to deploy action strategies targeted according to the location of the fault point to improve the safety of the power grid.

[0043] Therefore, for the fault point k1 located at the low-voltage switch far away from the 10kV low-voltage bus side, the method further includes: when it is determined that the fault point is located at the low-voltage switch far away from the 10kV low-voltage bus side, after detecting that the fault phase difference current meets the predetermined conditions, the grounding zero-sequence protection action is used to trip the high-voltage switch and the low-voltage switch, and the 10kV section switch is closed through the preset 10kV backup power supply automatic switching device, so that the 10kV bus does not lose load, so as to reduce the scope of power outage.

[0044] However, for the fault point k2 located on the 10kV low-voltage bus side, the method further includes: when it is determined that the fault point is located on the 10kV low-voltage bus side, directly using the grounding transformer zero-sequence protection action to trip the 10kV section switch and the transformer.

[0045] It should be noted that the grounding zero-sequence protection action is a common technical means in this field; the fault phase difference flow is calculated based on the above content, and the fault phase difference flow is added as an auxiliary starting criterion (i.e., whether the fault phase difference flow meets the predetermined conditions) to enable the grounding zero-sequence protection action. At this time, the predetermined conditions can be flexibly designed according to the actual situation, and will not be repeated here.

[0046] like Figure 4 As shown in the figure, a device for locating a fault when a single-phase grounding occurs on the low-voltage side of a main transformer is provided in an embodiment of the present invention, and is used in a 10kV system including a high-voltage switch, a low-voltage switch and a 10kV section switch, comprising:

[0047] A zero-sequence current component detection unit 110 is used to detect whether a zero-sequence current component exists in the transformer lowering switch when a single-phase grounding fault occurs in the 10kV system;

[0048] The fault point accurate positioning unit 120 is used to determine that the fault point is located on the side of the transformer lower switch away from the 10kV low-voltage bus if it is detected that the transformer lower switch has a zero-sequence current component; conversely, if it is detected that the main transformer lower switch has no zero-sequence current component, it is determined that the fault point is located on the side of the 10kV low-voltage bus.

[0049] Among them, it also includes:

[0050] The first protection action switch unit is used to, when it is determined that the fault point is located at the low-voltage switch far away from the 10kV low-voltage bus, and after detecting that the fault phase difference current meets the predetermined conditions, use the grounding zero-sequence protection action to trip the high-voltage switch and the low-voltage switch, and close the 10kV section switch through the preset 10kV backup power supply automatic switching device.

[0051] Among them, it also includes:

[0052] The second protection action switch unit is used to directly use the grounding zero-sequence protection action to trip the 10kV section switch and the low-voltage switch when it is determined that the fault point is located on the 10kV low-voltage bus side.

[0053] Implementing the embodiments of the present invention has the following beneficial effects:

[0054] 1. When a single-phase grounding fault occurs in a 10kV system, the present invention determines whether the fault point is located at the side of the low-voltage switch far away from the 10kV low-voltage bus or at the side of the 10kV low-voltage bus according to the detection condition of whether there is a zero-sequence current component in the low-voltage switch, thereby accurately locating the fault point and achieving the purpose of saving time and effort;

[0055] 2. The present invention isolates the fault point by tripping the high switch and the low switch and closing the 10kV section switch when the fault point is located on the side of the 10kV low-voltage busbar and the low-voltage switch is far away from the 10kV low-voltage busbar. The fault point is also located on the side of the 10kV low-voltage busbar and the 10kV section switch and the low switch are tripped to isolate the fault point. Therefore, based on the different positions of the fault point, the corresponding protection action switch can be used to correctly isolate the fault point, thereby achieving the purpose of improving the safety of the power grid.

[0056] It is worth noting that in the above-mentioned device embodiment, the various device modules included are only divided according to functional logic, but are not limited to the above-mentioned division, as long as the corresponding functions can be realized; in addition, the specific names of the various functional modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of the present invention.

[0057] A person skilled in the art can understand that all or part of the steps in the above-mentioned embodiment method can be completed by instructing related hardware through a program, and the program can be stored in a computer-readable storage medium, such as ROM / RAM, disk, CD-ROM, etc.

[0058] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for locating a fault when a single-phase ground fault occurs on the low-voltage side of a main transformer, which is used in a 10kV system including a high-voltage transformer switch, a low-voltage transformer switch and a 10kV section switch, and is characterized in that: The method comprises the following steps: When a single-phase grounding fault occurs in the 10kV system, detecting whether there is a zero-sequence current component in the transformer lowering switch; If it is detected that the transformer substation has a zero-sequence current component, the fault point is determined to be located on the side of the transformer substation away from the 10kV low-voltage bus; conversely, if it is detected that the main transformer substation has no zero-sequence current component, the fault point is determined to be located on the side of the 10kV low-voltage bus.

2. The method for locating a fault when a single-phase ground fault occurs on the low-voltage side of a main transformer according to claim 1, characterized in that: The method further comprises: When it is determined that the fault point is located at the low-voltage switch far away from the 10kV low-voltage bus side, after detecting that the fault phase difference current meets the predetermined conditions, the grounding transformer zero-sequence protection action is used to trip the high-voltage switch and the low-voltage switch, and the 10kV section switch is closed through the preset 10kV backup power supply automatic switching device.

3. The method for locating a fault when a single-phase ground fault occurs on the low-voltage side of a main transformer according to claim 1, characterized in that: The method further comprises: When it is determined that the fault point is located on the 10kV low-voltage bus side, the grounding transformer zero-sequence protection action is directly used to trip the 10kV section switch and the low-voltage switch.

4. A device for locating a fault when a single-phase ground fault occurs on the low-voltage side of a main transformer, used in a 10kV system including a high-voltage transformer switch, a low-voltage transformer switch and a 10kV section switch, characterized in that: include: A zero-sequence current component detection unit, used to detect whether the transformer has a zero-sequence current component when a single-phase grounding fault occurs in the 10kV system; The fault point accurate positioning unit is used to determine that the fault point is located on the side of the transformer lowering switch away from the 10kV low-voltage busbar if it is detected that the transformer lowering switch has a zero-sequence current component; conversely, if it is detected that the main transformer lowering switch has no zero-sequence current component, it is determined that the fault point is located on the side of the 10kV low-voltage busbar.

5. The device for locating fault when single-phase grounding occurs on the low-voltage side of the main transformer as claimed in claim 4, characterized in that: Also includes: The first protection action switch unit is used to, when it is determined that the fault point is located at the low-voltage switch far away from the 10kV low-voltage bus, and after detecting that the fault phase difference current meets the predetermined conditions, use the grounding zero-sequence protection action to trip the high-voltage switch and the low-voltage switch, and close the 10kV section switch through the preset 10kV backup power supply automatic switching device.

6. The device for locating fault when single-phase grounding occurs on the low-voltage side of the main transformer as claimed in claim 4, characterized in that: Also includes: The second protection action switch unit is used to directly use the grounding zero-sequence protection action to trip the 10kV section switch and the low-voltage switch when it is determined that the fault point is located on the 10kV low-voltage bus side.

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