Distribution transformer single-phase earth fault transfer overvoltage suppression method and system

Abstract

The invention relates to the technical field of distribution transformers, and provides a distribution transformer single-phase earth fault transfer overvoltage suppression method and system, and the method comprises the steps: calculating the product of the secondary current of a current transformer and the transformation ratio of the transformer, and enabling the product to serve as a primary current value flowing through a current-limiting resistor; the product of the primary current value and the equivalent grounding resistance of the distribution transformer is calculated to serve as a transfer overvoltage value, and if the transfer overvoltage value exceeds the maximum allowable value of the transfer overvoltage, shell-collision grounding transfer overvoltage occurs, a current-limiting resistor is acted to switch a contactor, and fault current is cut off; calculating the sum of the resistance value of the current-limiting resistor and the equivalent grounding resistance of the distribution transformer, calculating the multiple of the product of the sum of the resistance value of the current-limiting resistor and the equivalent grounding resistance of the distribution transformer and the secondary current of the current transformer, and taking the multiple as the shell voltage of the distribution transformer; and a high-voltage side boundary switch of the distribution transformer is tripped through delay. And on the premise of ensuring the safety grounding effectiveness, the transfer overvoltage value can be effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution transformers, and in particular relates to a method and system for suppressing overvoltage caused by a single-phase grounding fault transfer of a distribution transformer. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The working ground and safety ground of the distribution transformer usually adopt a common ground connection method, and the grounding resistance value is required to be no more than 4Ω. When a single-phase line touches the shell and grounding fault occurs on the high-voltage side, the fault current flows through the shell and the grounding resistance, which will significantly raise the neutral point voltage of the distribution transformer. The raised potential is transmitted to the shell of the electrical equipment through the neutral line on the low-voltage side to form a transfer overvoltage, causing personal injury, equipment damage, electrical fire, etc.

[0004] In response to the above problems, scholars in the field have conducted research on this issue. Some scholars have studied the impact of different grounding methods of the neutral point of the medium-voltage distribution network on the transfer overvoltage, and proposed to suppress the transfer overvoltage by separating the protection ground of the distribution transformer from the low-voltage working ground and increasing the number of repeated grounding on the low-voltage side; some scholars have taken street lamps as specific objects and studied the generation mechanism and suppression measures of the transfer overvoltage.

[0005] The methods proposed in the above studies have good effects in suppressing transfer overvoltage when the on-site conditions permit, but they are greatly restricted by the on-site environment. Summary of the invention

[0006] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a method and system for suppressing the transfer overvoltage of a single-phase grounding fault of a distribution transformer. By monitoring and limiting the transfer overvoltage value, the method and system act to disconnect the current-limiting resistor and switch the contactor to cut off the fault current. Under the premise of ensuring the effectiveness of safe grounding, the transfer overvoltage value can be effectively reduced, and only a suppression device needs to be added at the distribution transformer, without the need for an open area, and the distribution transformer can be safely separated from the working site.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A first aspect of the present invention provides a method for suppressing overvoltage caused by a single-phase ground fault transfer of a distribution transformer, comprising:

[0009] Obtain the resistance value of the current limiting resistor, the secondary current of the current transformer and the equivalent grounding resistance of the distribution transformer;

[0010] Calculate the product of the secondary current of the current transformer and the transformer ratio as the primary current value flowing through the current limiting resistor; calculate the product of the primary current value flowing through the current limiting resistor and the equivalent grounding resistance of the distribution transformer as the transfer overvoltage value. If the calculated transfer overvoltage value exceeds the maximum allowable value of the transfer overvoltage, a shell-touching grounding transfer overvoltage occurs, and the current limiting resistor is disconnected and the contactor is switched on to cut off the fault current.

[0011] Calculate the sum of the resistance of the current limiting resistor and the equivalent grounding resistance of the distribution transformer, and calculate the multiple of the product of the sum of the two and the secondary current of the current transformer as the distribution transformer casing voltage. When the calculated distribution transformer casing voltage is greater than the upper limit of the distribution transformer casing voltage, the boundary switch on the high-voltage side of the distribution transformer will trip after a delay.

[0012] Furthermore, if the boundary switch on the high-voltage side of the distribution transformer needs to cooperate with the current-limiting resistor switching contactor, the action time of the current-limiting resistor switching contactor should be longer than the protection action time of the boundary switch on the high-voltage side of the distribution transformer.

[0013] Furthermore, the distribution transformer housing, current transformer, current limiting resistor and current limiting resistor switching contactor are connected in series, and the switching contactor is connected to the neutral point of the low-voltage side of the distribution transformer.

[0014] Furthermore, the maximum permissible value of the transfer overvoltage and the upper limit of the voltage on the housing of the distribution transformer are both safe contact voltage limits for the human body;

[0015] Alternatively, the influencing factors of the shell-contact grounding transfer overvoltage include: the 10kV neutral point grounding method of the substation, the grounding resistance value of the 10kV distribution transformer and the 400V side grounding method.

[0016] A second aspect of the present invention provides a distribution transformer single-phase grounding fault transfer overvoltage suppression system, comprising:

[0017] A data acquisition module is configured to: acquire the resistance value of the current limiting resistor, the secondary current of the current transformer and the equivalent grounding resistance of the distribution transformer;

[0018] The first action module is configured to: calculate the product of the secondary current of the current transformer and the transformer ratio as the primary current value flowing through the current limiting resistor; calculate the product of the primary current value flowing through the current limiting resistor and the equivalent grounding resistance of the distribution transformer as the transfer overvoltage value. If the calculated transfer overvoltage value exceeds the maximum allowable value of the transfer overvoltage, a shell-touching grounding transfer overvoltage occurs, and the action is to disconnect the current limiting resistor and switch the contactor to cut off the fault current;

[0019] The second action module is configured to: calculate the sum of the resistance of the current limiting resistor and the equivalent grounding resistance of the distribution transformer, and calculate the multiple of the product of the sum of the two and the secondary current of the current transformer as the distribution transformer casing voltage. When the calculated distribution transformer casing voltage is greater than the upper limit value of the distribution transformer casing voltage, the high-voltage side boundary switch of the distribution transformer is tripped after a delay.

[0020] Furthermore, if the boundary switch on the high-voltage side of the distribution transformer needs to cooperate with the current-limiting resistor switching contactor, the action time of the current-limiting resistor switching contactor should be longer than the protection action time of the boundary switch on the high-voltage side of the distribution transformer.

[0021] Furthermore, the distribution transformer housing, current transformer, current limiting resistor and current limiting resistor switching contactor are connected in series, and the switching contactor is connected to the neutral point of the low-voltage side of the distribution transformer.

[0022] Furthermore, the maximum permissible value of the transfer overvoltage and the upper limit of the voltage on the housing of the distribution transformer are both safe contact voltage limits for the human body;

[0023] Alternatively, the influencing factors of the shell-contact grounding transfer overvoltage include: the 10kV neutral point grounding method of the substation, the grounding resistance value of the 10kV distribution transformer and the 400V side grounding method.

[0024] A third aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the method for suppressing overvoltage transfer due to a single-phase grounding fault of a distribution transformer as described above.

[0025] The fourth aspect of the present invention provides a computer device, including a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor, wherein when the processor executes the program, the steps in the method for suppressing overvoltage transfer of a single-phase grounding fault of a distribution transformer as described above are implemented.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention monitors and limits the transfer overvoltage value, operates to disconnect the current limiting resistor and switch the contactor to cut off the fault current. Under the premise of ensuring the effectiveness of safety grounding, the transfer overvoltage value can be effectively reduced to ensure the safety of people and electrical equipment and improve the power supply reliability.

[0028] The present invention only needs to add a suppression device at the distribution transformer, and does not require an open site, so that the distribution transformer can be safely separated from the work site. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0030] Figure 1 It is a topological structure diagram of a method for suppressing overvoltage of a single-phase grounding fault transfer of a distribution transformer according to a first embodiment of the present invention;

[0031] Figure 2 It is a circuit diagram of a medium and low voltage distribution network according to the first embodiment of the present invention;

[0032] Figure 3 A schematic diagram of a safety ground and a working ground being grounded separately in accordance with the first embodiment of the present invention;

[0033] Figure 4 This is a low voltage distribution network wiring diagram of the first embodiment of the present invention;

[0034] Figure 5 It is a structural diagram of a computer device according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0035] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0036] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0037] Embodiment 1

[0038] This embodiment provides a method for suppressing overvoltage caused by a single-phase grounding fault transfer of a distribution transformer.

[0039] This embodiment provides a method for suppressing overvoltage caused by a single-phase grounding fault transfer of a distribution transformer, which is used for a 10kV distribution transformer.

[0040] Distribution transformers usually use a grounding method that safely shares the grounding electrode with the 400V side working ground. The problem caused by this is that when a phase line grounding fault occurs on the high-voltage side through the shell, the fault current flows through the grounding electrode and generates an overvoltage on the grounding electrode, which is then transmitted to the user's electrical equipment shell through the 400V side PE line or PEN line, causing a transfer overvoltage, endangering the safety of people and equipment. To solve this problem, the factors affecting the size of the transfer overvoltage were verified through an actual on-site shell-touching grounding fault test; on this basis, a method for suppressing the transfer overvoltage was proposed, and the specific implementation strategy of the method was studied based on its principle.

[0041] This embodiment provides a method for suppressing overvoltage caused by a single-phase ground fault transfer of a distribution transformer, comprising the following steps:

[0042] Step 1: Analysis of the mechanism of transfer overvoltage generation.

[0043] like Figure 2 As shown in the figure, it is a simple 10kV medium voltage distribution network, which supplies power to users through a 10 / 0.4kV distribution transformer. The neutral point of the 10kV system is connected to both the arc suppression coil L0 and the small resistor R0. By controlling the switching switch, the neutral point can be switched between ungrounded, grounded through the arc suppression coil, and grounded through a small resistor. The 10kV distribution transformer housing is connected to the neutral point on the low voltage side and then connected to the grounding electrode. The common grounding method is adopted, R T is the grounding resistance, U T is the neutral point voltage on the low voltage side. Here, we take the TN-S system on the 400V side as an example. R1, R2, ..., R n is the repeated grounding resistance of the PEN line.

[0044] like Figure 2 As shown in the figure, a phase line touches the shell and is short-circuited to ground at point f on the high-voltage side of the distribution transformer. The path of the short-circuit loop is: the neutral point grounding equipment in the substation (low resistance, arc suppression coil, grounding transformer, etc.), 10kV distribution line, distribution transformer grounding resistance, and PEN line repeated grounding resistance.

[0045] Ignoring the impedance of the grounding transformer, the line impedance, and the line-to-ground capacitance, the fault current I flowing through the 10kV line f The calculation can be simplified by using formula (1), where U N It is the phase voltage on the high voltage side of the distribution transformer.

[0046]

[0047] After the fault current flows through the grounding resistance of the distribution transformer and the repeated grounding resistance of the PEN line, a transfer overvoltage is generated as shown in formula (2).

[0048]

[0049] Step 2: Transfer overvoltage influencing factors.

[0050] Further analysis of formula (2) shows that the shell-to-ground transfer overvoltage U L The influencing factors include: 10kV neutral point grounding method of substation, 10kV distribution transformer grounding resistance value, and 400V side grounding method.

[0051] (1) Neutral point grounding method of 10kV system.

[0052] The magnitude of the 10kV grounding fault current is closely related to the neutral point grounding method. Traditionally, the commonly used grounding methods are: grounding through an arc suppression coil, no grounding, grounding through a small resistor, etc.

[0053] (101) The neutral point is grounded through an arc suppression coil. Relevant standards stipulate that when the arc suppression coil is used for grounding, the grounding current after compensation should not exceed 10A when a single-phase grounding occurs; it is also stipulated that the grounding resistance of the distribution transformer should be less than 4Ω. Therefore, it can be simplified to calculate that when a shell-touching grounding occurs, the maximum theoretical value of the transferred overvoltage is about 40V.

[0054] (102) Neutral point is not grounded. According to relevant standards, when the capacitive current of a single-phase grounding fault is 10A or less, the neutral point should be not grounded. In this case, when a shell-touching grounding fault occurs, the maximum theoretical value of the transfer overvoltage is related to the capacitive current, and the maximum theoretical value of the transfer overvoltage is also 40V.

[0055] (103) The neutral point is grounded through a small resistor. The neutral point resistance recommended in the technical guidelines for distribution networks is 10Ω, and the distribution transformer grounding resistance takes the maximum value of 4Ω. When there is no repeated grounding on the low-voltage side of the distribution transformer, the transfer overvoltage value can be obtained from formula (2) to be 1731.4V. It can be seen that under this grounding method, the transfer overvoltage is significantly greater than other grounding methods.

[0056] (2) Grounding method of distribution transformer.

[0057] (201) Safely share the grounding electrode with the work site. The distribution transformer safely shares the grounding electrode with the work site, such as Figure 2 As shown in Figure 2, according to equation (2), the transferred overvoltage is directly transmitted from the grounding resistor to the low-voltage side of the distribution transformer.

[0058] (202) Safely separate from the work site. The distribution transformer is safely grounded separately from the work site, such as Figure 3 In this grounding mode, the overvoltage is transmitted to the neutral point on the low-voltage side through the earth. The magnitude of the overvoltage is determined by the distance between the working ground and the safety ground. The longer the distance, the lower the value. According to the step voltage theory, the magnitude of the transferred overvoltage is inversely proportional to the distance.

[0059] (3) 400V side grounding method.

[0060] There are three main grounding methods for 400V power distribution: IT, TT, and TN. The TN grounding method can be further divided into TN-S, TN-C, and TN-CS grounding methods. Their respective topological structures are as follows: Figure 4 shown.

[0061] (301) IT and TT grounding systems. In IT and TT systems, since the casing of the electrical equipment is grounded separately and there is no neutral line connection with the neutral point of the distribution transformer, the transferred overvoltage will not be transmitted to the casing of the electrical equipment.

[0062] (302) TN grounding system. In the TN system, the neutral line will transfer the overvoltage to the outer casing of the electrical equipment. The regulations stipulate that in the TN system, the PE line must be repeatedly grounded when entering the user. From the theoretical analysis of formula (2), it can be obtained that the overvoltage transferred to the outer casing of the electrical equipment decreases as the number of repeated grounding increases.

[0063] Step 3: Test and verify the factors affecting transfer overvoltage.

[0064] In order to verify the influence of various factors on the transfer overvoltage, actual grounding fault tests were carried out in the 10kV system according to different 10kV system neutral point grounding methods, different distribution transformer grounding methods, different 400V system grounding methods, etc. The test results are shown in Table 1.

[0065] Table 1. Grounding test results

[0066]

[0067] Step 4: Transfer overvoltage suppression method

[0068] In order to effectively suppress the transfer overvoltage, this embodiment proposes a transfer overvoltage suppression strategy and device. An automatically switched current limiting resistor is configured between the distribution transformer casing and the grounding point, and the current flowing through the resistor is monitored in real time, and the voltage value of the distribution transformer casing is calculated to determine whether a shell-touching grounding fault occurs. The specific implementation is as follows: Figure 1 The function of the current limiting resistor is, firstly, to suppress the fault current when a ground short circuit fault occurs, and secondly, to share the fault voltage so that the voltage borne by the grounding electrode is as small as possible to reduce the transfer overvoltage.

[0069] like Figure 1 As shown, this embodiment designs a transfer overvoltage suppression device, and the power system wiring is the service object of this device. The distribution transformer housing is first connected to the current transformer CT, and then the current transformer is connected to the current limiting resistor Rx, and the current limiting resistor is connected in series with the current limiting resistor switching contactor K x After that, it is connected to the neutral point of the low-voltage side of the distribution transformer; the secondary output current of the current transformer is connected to the control logic, and the tripping output of the controller is connected to the current-limiting resistor switching contactor control circuit; the controller is also connected to a local alarm light.

[0070] This embodiment adopts the method of connecting a current transformer in series with a current limiting resistor to measure the current value flowing through the current limiting resistor in real time, and calculate the voltage between the housing of the distribution transformer and the ground and the transfer overvoltage.

[0071] Through the above analysis, the 10kV system adopts the neutral point through a small resistor grounding method. When a shell-touching grounding fault occurs on the high-voltage side of the distribution transformer, the value of the transfer overvoltage generated is much greater than that of other grounding methods. In this paper, the 10kV system adopts the neutral point through a small resistor grounding method, and the selection of the current limiting resistor value is studied as shown in formula (3).

[0072]

[0073] In the formula, R x is the resistance of the current limiting resistor, U N is the rated phase voltage on the high-voltage side of the distribution transformer, R Tequ is the equivalent grounding resistance of the distribution transformer, U max is the transfer overvoltage allowable value, R0 is the small resistor value, Z T0 is the grounding impedance, Z l It is the line impedance between the starting point of the high-voltage outgoing line of the distribution transformer and the distribution transformer.

[0074] Control logic loop for acquisition Figure 1 The secondary current of the current transformer is then calculated, and the transfer overvoltage value is calculated using the formula (4).

[0075] UL=If2×Rtequ×nCT (4)

[0076] In the formula, I f2 is the secondary current of the current transformer collected by the control loop, n CT is the current transformer ratio. The product of the current transformer secondary current and the transformer ratio is the primary current value flowing through the current limiting resistor.

[0077] The calculated value is compared with the maximum allowable value of the transfer overvoltage. If it exceeds the set value, a shell-to-ground transfer overvoltage occurs, and a shell-to-ground fault alarm signal is sent. At the same time, the current limiting resistor is disconnected and the contactor K is switched on. x , cut off the fault current, if it does not exceed, it is judged to be in normal operation. If it needs to cooperate with the boundary switch protection of the distribution transformer, the current limiting resistor switching contactor K x The action time should be longer than the boundary switch protection action time Δt (recommended 0.2s). If it is not necessary to cooperate with the boundary switch protection, the contactor will trip instantly without delay. After the current limiting resistor is connected, the fault current is limited to a short-circuit current value far less than the metallic grounding. Contactor K can be used. x Cut off the fault current.

[0078] It should be noted that whether to coordinate with the boundary switch protection of the distribution transformer does not require any conditions, and it is only related to the operation and maintenance concept of the equipment operation and maintenance unit. If the operation and maintenance unit hopes to ensure power supply and improve power supply reliability, the two do not need to coordinate. After the current-limiting resistor switching contactor quickly trips, the fault current disappears without affecting the power supply, but the fault still exists. The operation and maintenance personnel can carry out maintenance as soon as possible according to the alarm of this device; if the operation and maintenance unit hopes to quickly and completely isolate the faulty transformer to protect the equipment, the two can coordinate, and the current-limiting resistor switching contactor will be tripped after the boundary switch is tripped.

[0079] The function of the distribution transformer safety ground is to make the transformer housing consistent with the earth potential to avoid personal electric shock accidents. In order not to affect the function of the safety ground, the control logic circuit has the distribution transformer housing voltage U C The real-time detection function, as shown in formula (5), when the voltage is greater than the reasonable setting value of the upper limit of the distribution transformer shell voltage, the high-voltage side boundary switch of the distribution transformer is tripped after a delay. Among them, the high-voltage side boundary switch of the distribution transformer is between the distribution transformer and the 10 kV line, and each distribution transformer is equipped with a boundary circuit breaker.

[0080] UC=If2×(Rtequ+Rx)×nCT (5)

[0081] According to the IEC 60479 standard "Effects of Electric Current Passing Through the Human Body", in a dry environment, the safe contact voltage limit for the human body is 50V, and in a humid environment, the safe contact voltage limit for the human body is 25V. Therefore, the reasonable setting values ​​of the transfer overvoltage upper limit (maximum allowable transfer overvoltage value) and the distribution transformer housing voltage upper limit mentioned above are both 25V.

[0082] This example analyzes the generation mechanism and influencing factors of the transfer overvoltage of the distribution transformer, and verifies the accuracy of the above analysis through an actual 10kV grounding fault. Based on the above research, a transfer overvoltage suppression method is proposed, which can effectively reduce the transfer overvoltage value while ensuring the effectiveness of safety grounding, ensure the safety of people and electrical equipment, and improve power supply reliability.

[0083] Embodiment 2

[0084] The present embodiment provides a distribution transformer single-phase grounding fault transfer overvoltage suppression system, which specifically includes a controller, a current transformer, a current limiting resistor, and a current limiting resistor switching contactor.

[0085] The controller includes:

[0086] A data acquisition module is configured to: acquire the resistance value of the current limiting resistor, the secondary current of the current transformer and the equivalent grounding resistance of the distribution transformer;

[0087] The first action module is configured to: calculate the product of the secondary current of the current transformer and the transformer ratio as the primary current value flowing through the current limiting resistor; calculate the product of the primary current value flowing through the current limiting resistor and the equivalent grounding resistance of the distribution transformer as the transfer overvoltage value. If the calculated transfer overvoltage value exceeds the maximum allowable value of the transfer overvoltage, a shell-touching grounding transfer overvoltage occurs, and the action is to disconnect the current limiting resistor and switch the contactor to cut off the fault current;

[0088] The second action module is configured to: calculate the sum of the resistance of the current limiting resistor and the equivalent grounding resistance of the distribution transformer, and calculate the multiple of the product of the sum of the two and the secondary current of the current transformer as the distribution transformer casing voltage. When the calculated distribution transformer casing voltage is greater than the upper limit value of the distribution transformer casing voltage, the high-voltage side boundary switch of the distribution transformer is tripped after a delay.

[0089] Furthermore, if the boundary switch on the high-voltage side of the distribution transformer needs to cooperate with the current-limiting resistor switching contactor, the action time of the current-limiting resistor switching contactor should be longer than the protection action time of the boundary switch on the high-voltage side of the distribution transformer.

[0090] Furthermore, the distribution transformer housing, current transformer, current limiting resistor and current limiting resistor switching contactor are connected in series, and the switching contactor is connected to the neutral point of the low-voltage side of the distribution transformer.

[0091] Furthermore, the maximum permissible value of the transfer overvoltage and the upper limit of the voltage on the housing of the distribution transformer are both safe contact voltage limits for the human body;

[0092] Furthermore, the influencing factors of the shell-contact grounding transfer overvoltage include: the 10kV neutral point grounding method of the substation, the grounding resistance value of the 10kV distribution transformer and the 400V side grounding method.

[0093] It should be noted here that each module in this embodiment corresponds to each step in Example 1 one by one, and the specific implementation process is the same, which will not be repeated here.

[0094] Embodiment 3

[0095] This embodiment provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the steps in the method for suppressing overvoltage transfer caused by a single-phase grounding fault of a distribution transformer as described in the first embodiment above are implemented.

[0096] Embodiment 4

[0097] This embodiment provides a computer device, such as Figure 5As shown, it includes a display device, an input device, a computer-readable storage medium (volatile memory and non-volatile storage medium), a processor, a communication interface (i.e., a network interface), and a computer program stored on the computer-readable storage medium and executable on the processor, wherein the processor, the communication interface, and the computer-readable storage medium can be connected via a bus or other means. The communication interface is used to receive and send data, and when the processor executes the program, the steps in the method for suppressing overvoltage transfer of a single-phase grounding fault of a distribution transformer as described in the first embodiment above are implemented.

[0098] Among them, any reference to memory, storage, database or other media provided by the present application and used in the embodiments may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual-speed data rate SDRAM (SSRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0099] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0100] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0101] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for suppressing overvoltage caused by a single-phase ground fault transfer of a distribution transformer, characterized in that: include: Obtain the resistance value of the current limiting resistor, the secondary current of the current transformer and the equivalent grounding resistance of the distribution transformer; Calculate the product of the current transformer secondary current and the transformer ratio as the primary current value flowing through the current limiting resistor; The product of the primary current flowing through the current limiting resistor and the equivalent grounding resistance of the distribution transformer is calculated as the transfer overvoltage value. If the calculated transfer overvoltage value exceeds the maximum allowable value of the transfer overvoltage, a shell-touching grounding transfer overvoltage occurs, which acts on the current limiting resistor switching contactor to cut off the fault current. Calculate the sum of the resistance of the current limiting resistor and the equivalent grounding resistance of the distribution transformer, and calculate the multiple of the product of the sum of the two and the secondary current of the current transformer as the distribution transformer casing voltage. When the calculated distribution transformer casing voltage is greater than the upper limit of the distribution transformer casing voltage, the boundary switch on the high-voltage side of the distribution transformer will trip after a delay.

2. A method for suppressing overvoltage caused by a single-phase ground fault transfer of a distribution transformer as claimed in claim 1, characterized in that: If the boundary switch on the high-voltage side of the distribution transformer needs to work in coordination with the current-limiting resistor switching contactor, the action time of the current-limiting resistor switching contactor should be longer than the protection action time of the boundary switch on the high-voltage side of the distribution transformer.

3. A method for suppressing overvoltage caused by a single-phase ground fault transfer of a distribution transformer as claimed in claim 1, characterized in that: The distribution transformer housing, current transformer, current limiting resistor and current limiting resistor switching contactor are connected in series, and the switching contactor is connected to the neutral point of the low-voltage side of the distribution transformer.

4. A method for suppressing overvoltage caused by a single-phase grounding fault transfer of a distribution transformer as claimed in claim 1, characterized in that: The maximum permissible value of the transfer overvoltage and the upper limit of the voltage on the shell of the distribution transformer are both safe contact voltage limits for the human body; Alternatively, the influencing factors of the shell-contact grounding transfer overvoltage include: the 10kV neutral point grounding method of the substation, the grounding resistance value of the 10kV distribution transformer and the 400V side grounding method.

5. A distribution transformer single-phase grounding fault transfer overvoltage suppression system, characterized in that: include: A data acquisition module is configured to: acquire the resistance value of the current limiting resistor, the secondary current of the current transformer and the equivalent grounding resistance of the distribution transformer; A first action module is configured to: calculate the product of the secondary current of the current transformer and the transformer ratio as the primary current value flowing through the current limiting resistor; The product of the primary current flowing through the current limiting resistor and the equivalent grounding resistance of the distribution transformer is calculated as the transfer overvoltage value. If the calculated transfer overvoltage value exceeds the maximum allowable value of the transfer overvoltage, a shell-touching grounding transfer overvoltage occurs, which acts on the current limiting resistor switching contactor to cut off the fault current. The second action module is configured to: calculate the sum of the resistance of the current limiting resistor and the equivalent grounding resistance of the distribution transformer, and calculate the multiple of the product of the sum of the two and the secondary current of the current transformer as the distribution transformer casing voltage. When the calculated distribution transformer casing voltage is greater than the upper limit value of the distribution transformer casing voltage, the high-voltage side boundary switch of the distribution transformer is tripped after a delay.

6. A distribution transformer single-phase grounding fault transfer overvoltage suppression system as claimed in claim 5, characterized in that: If the boundary switch on the high-voltage side of the distribution transformer needs to work in coordination with the current-limiting resistor switching contactor, the action time of the current-limiting resistor switching contactor should be longer than the protection action time of the boundary switch on the high-voltage side of the distribution transformer.

7. A distribution transformer single-phase grounding fault transfer overvoltage suppression system as claimed in claim 5, characterized in that: The distribution transformer housing, current transformer, current limiting resistor and current limiting resistor switching contactor are connected in series, and the switching contactor is connected to the neutral point of the low-voltage side of the distribution transformer.

8. A distribution transformer single-phase grounding fault transfer overvoltage suppression system as claimed in claim 5, characterized in that: The maximum permissible value of the transfer overvoltage and the upper limit of the voltage on the shell of the distribution transformer are both safe contact voltage limits for the human body; Alternatively, the influencing factors of the shell-contact grounding transfer overvoltage include: the 10kV neutral point grounding method of the substation, the grounding resistance value of the 10kV distribution transformer and the 400V side grounding method.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps in a method for suppressing overvoltage of a distribution transformer single-phase grounding fault transfer are implemented as described in any one of claims 1 to 4.

10. A computer device comprising a computer-readable storage medium, a processor, and a computer program stored in the computer-readable storage medium and executable on the processor, characterized in that: When the processor executes the program, the steps of a method for suppressing overvoltage transfer of a single-phase grounding fault of a distribution transformer as described in any one of claims 1-4 are implemented.

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