Grounding system switching method based on operation mode and grounding system

Abstract

The invention discloses a switching method of a grounding system based on an operation mode and the grounding system, the switching method is applied to the grounding system, the grounding system comprises a main transformer and at least one generator which can be electrically connected, and the main transformer and the at least one generator are respectively grounded through low resistance. The operation modes of the grounding system comprise a micro-grid mode and a grid-connected mode. The method comprises the following steps: acquiring the on-off state of the grounding system; and determining an operation mode of the grounding system based on the switching state. No matter in a grid-connected mode or a plurality of micro-grid modes, only one grounding point can be ensured to be grounded during operation of each electrical system, potential safety hazards such as grounding circulation and the like possibly caused by simultaneous grounding of a plurality of grounding points are effectively avoided, the grounding safety of the system is greatly improved, and the service life of the system is prolonged. And the system can be ensured to operate stably in different operation states.

Description

Technical Field

[0001] The present application relates to the technical field of the electric power industry, and in particular to a grounding system and a control method. Background Art

[0002] When the power system was relatively weak, the factory's external power grid supplied insufficient power and the transmission lines were imperfect. The factory faced the problem of frequent power outages during the production process. The factory adopted the method of microgrid operation of power station units in the event of a power outage to solve the problem of power supply reliability.

[0003] In the process of operation from grid-connected to microgrid, multi-machine microgrid to single-machine microgrid, the grounding method and the number of grounding points of the electrical system are changing, which brings difficulties to the consistency of the setting of the electrical system and the selection of equipment insulation.

[0004] In addition, the voltage level of some countries is 3-37.5kV, which is a direct grounding system. According to domestic specifications, 3-37.5kV generator sets cannot be directly grounded. In order to meet the application of domestic units in foreign projects and ensure that the high-current grounding method of the electrical system does not change, the protection setting does not change under any operating conditions, and does not affect the insulation of equipment and materials, the selection and switching of grounding methods in grid-connected and various microgrid modes need to be solved urgently. Summary of the invention

[0005] The purpose of the embodiment of the present application is to provide a switching method of a grounding system based on an operation mode, which is applied to a grounding system, wherein the grounding system includes an electrically connectable main transformer and at least one generator, wherein the main transformer and at least one generator are grounded through a low resistance, respectively, and the operation mode of the grounding system includes a microgrid mode and a grid-connected mode, including:

[0006] Obtaining a switch status of the grounding system;

[0007] determining an operating mode of the grounding system based on the switch state;

[0008] When the operation mode is switched between the microgrid mode and the grid-connected mode, the grounding point of the grounding system is adjusted based on the priority of the preset grounding points.

[0009] As an optional embodiment, the priority of the preset grounding point is that the grounding resistance of the main transformer takes precedence over the grounding resistance of at least one of the generators.

[0010] As an optional embodiment, when the operation mode is switched between the microgrid mode and the grid-connected mode, adjusting the grounding point of the grounding system based on the preset priority of the grounding resistance includes:

[0011] Determine the grounding point states respectively corresponding to the grounding system before and after the operation mode changes, wherein the grounding point states include the grounding point positions, the number of grounding points and the grounding states of the grounding points;

[0012] When the operation mode changes, the grounding point is switched based on the grounding point state and the switching strategy.

[0013] As an optional embodiment, the switching strategy is that there is only one effective grounding point in the same electrical system, which specifically includes the following:

[0014] When the grounding system is started, the grid-connected mode is set as the default, and the grounding point with the highest priority is switched on. When the operation mode changes, the grounding point is switched on and off according to the priority of the preset grounding point;

[0015] When the operation mode changes, and the grounding point is switched and it is determined during the switching process that there is a valid grounding point in the same electrical system, the switching of the grounding point is terminated;

[0016] When the operation mode changes, and the grounding point is switched and it is determined during the switching process that there are multiple valid grounding points in the same electrical system, a grounding point with the highest priority is retained, and the other grounding points are exited.

[0017] As an optional embodiment, the same electrical system includes:

[0018] The main transformer is operated alone and grounded at low resistance;

[0019] One of the generators is operated alone and is grounded at low resistance;

[0020] said main transformer and at least one said generator electrically connected and operating together;

[0021] The two generators are electrically connected and operate together.

[0022] As an optional embodiment, when the operation mode changes, switching the grounding point based on the grounding point state and the switching strategy includes:

[0023] Before the operation mode changes, it is in the microgrid mode, one of the generators operates independently, and one of the generators is grounded with a low resistance to form the effective grounding point;

[0024] After the operation mode is changed to the grid-connected mode, the main transformer is electrically connected to one of the generators and operates together to form the same electrical system;

[0025] Determine that there is an effective grounding point in the same electrical system, and terminate the switching of the grounding point.

[0026] As an optional embodiment, when the operation mode changes, switching the grounding point based on the grounding point state and the switching strategy includes:

[0027] Before the operation mode changes, it is in the microgrid mode, one of the generators operates independently, and one of the generators is grounded with a low resistance to form the effective grounding point;

[0028] Before the operation mode changes, it is in the microgrid mode, the main transformer operates alone, and the low resistance of the main transformer is grounded to form the effective grounding point;

[0029] After the operation mode is changed to the grid-connected mode, the main transformer is electrically connected to one of the generators and operates together to form the same electrical system;

[0030] It is determined that there are multiple effective grounding points in the same electrical system, the grounding point of the main transformer is retained, and a grounding point of the generator is withdrawn.

[0031] As an optional embodiment, the method further includes:

[0032] When the main transformer is electrically disconnected from one of the generators and they are operated separately, the grounding resistor of the main transformer and the grounding resistor of one of the generators are grounded respectively.

[0033] The purpose of the embodiment of the present application is to provide a grounding system, which is used to perform the aforementioned switching method, including:

[0034] A main transformer, the low voltage side of which is grounded through a low resistance and the side is connected to the busbar through a first circuit breaker;

[0035] At least one generator has one side connected to ground via a low resistance and the side connected to the busbar via a third circuit breaker.

[0036] As an optional embodiment, when the grounding system includes a plurality of the generators, the plurality of generators are grounded respectively through low resistance, and there is a priority between the plurality of generators.

[0037] The beneficial effects of the embodiments of the present application are:

[0038] Whether in grid-connected mode or multiple microgrid modes, this application can ensure that each electrical system is grounded at only one grounding point during operation, effectively avoiding safety hazards such as ground loops that may be caused by multiple grounding points being grounded at the same time, greatly improving the grounding safety of the system and ensuring that the system can maintain stable operation under different operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A flowchart of a switching method according to an embodiment of the present application;

[0040] Figure 2 This is a flow chart of step S30 of the switching method according to an embodiment of the present application;

[0041] Figure 3 A schematic diagram of the structure of the grounding system of an embodiment of the present application;

[0042] Figure 4 It is a structural schematic diagram of the grounding system of the prior art;

[0043] Figure 5 This is a rendering of the grid-connected mode of the switching method according to an embodiment of the present application. DETAILED DESCRIPTION

[0044] Various aspects and features of the present application are described herein with reference to the accompanying drawings.

[0045] It should be understood that various modifications may be made to the embodiments of the present application. Therefore, the above description should not be considered as limiting, but only as an example of an embodiment. Other modifications within the scope and spirit of the present application will occur to those skilled in the art.

[0046] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present application and, together with the general description of the present application given above and the detailed description of the embodiments given below, serve to explain the principles of the present application.

[0047] These and other characteristics of the present application will become apparent from the following description of a preferred form of embodiment given as a non-limiting example with reference to the accompanying drawings.

[0048] It should also be understood that although the present application has been described with reference to some specific examples, those skilled in the art will be able to readily implement many other equivalent forms of the present application.

[0049] The above and other aspects, features and advantages of the present application will become more apparent in view of the following detailed description when taken in conjunction with the accompanying drawings.

[0050] Specific embodiments of the present application are described hereinafter with reference to the accompanying drawings; however, it should be understood that the embodiments applied for are merely examples of the present application, which may be implemented in a variety of ways. Well-known and / or repeated functions and structures are not described in detail to avoid unnecessary or redundant details that obscure the present application. Therefore, the specific structural and functional details applied for herein are not intended to be limiting, but merely serve as a basis and representative basis for the claims to teach those skilled in the art to use the present application in a variety of ways with substantially any suitable detailed structure.

[0051] This specification may use the phrases "in one embodiment," "in another embodiment," "in yet another embodiment," or "in other embodiments," all of which may refer to one or more of the same or different embodiments according to the present application.

[0052] A method for switching a grounding system based on an operation mode in an embodiment of the present application is as follows: Figure 3 As shown, it is applied to a grounding system, the grounding system includes a main transformer and at least one generator that can be electrically connected, the main transformer and at least one generator are grounded through low resistance respectively, and the operating modes of the grounding system include a microgrid mode and a grid-connected mode.

[0053] In this embodiment, the grounding system is an integrated device that provides grounding protection for the power system, including various equipment and lines connected to the earth, such as grounding resistors, grounding wires, etc. Its function is to introduce current into the earth when an electrical equipment fails, so as to ensure the safety of equipment and personnel.

[0054] The operating mode refers to the working state of the grounding system, which mainly includes microgrid mode (a small power system composed of distributed power sources, loads, energy storage systems, etc. operates independently or has a certain connection with the main grid) and grid-connected mode (a distributed power generation system is connected to the public power grid, and electric energy can flow in both directions).

[0055] The main transformer is a device used to transform voltage levels in the power system, converting electrical energy from one voltage level to another. It is usually used in power plants or substations. In the grounding system, its grounding condition has an important impact on the system grounding method. The generator is a device that generates electrical energy and is one of the power sources of the power system. In this grounding system, the grounding method of the generator needs to be adjusted according to the operating mode. The grounding resistor is a current limiting element used to limit the magnitude of the ground fault current, so that the grounding current is within a safe range, while ensuring that the grounding protection device can operate normally.

[0056] In the existing technology, when the power system is relatively weak, some original foreign systems use direct grounding. However, according to domestic specifications, 3-37.5kV generator sets cannot be directly grounded. In order to enable domestic units to be used in foreign projects, while ensuring that the high-current grounding method of the electrical system does not change, the protection setting remains unchanged under any operating conditions, and does not affect the insulation of equipment and materials, it is necessary to transform the original foreign direct grounding system into a low-resistance grounding system.

[0057] Specifically, we must first conduct a detailed analysis and evaluation of the original direct grounding system in foreign countries to determine the key parameters such as the size of the grounding resistance and the layout of the grounding system. Then, use appropriate methods and materials to carry out low-resistance grounding transformation, such as using high-quality grounding materials (such as copper, galvanized steel, etc.), designing a reasonable grounding grid shape and size (such as mesh or ring grounding grid), and taking measures to reduce soil resistivity (such as using resistance reducing agents, soil replacement methods, etc.) to ensure that the grounding resistance can meet the requirements.

[0058] At the same time, the generator also needs to use a low-resistance grounding method to match it. When choosing the neutral point grounding method of the generator, many factors need to be considered, such as the requirements of the generator voltage circuit for capacitive current, the overvoltage of the stator winding, and the realization of stator grounding protection. Generally speaking, the neutral point can be grounded through low impedance.

[0059] The switching method proposed in this application can only be applied when the grounding method successfully adopts low-resistance grounding. Through this switching method, it can be ensured that in different operating modes, each electrical system is grounded at only one grounding point, effectively avoiding safety hazards such as ground loops that may be caused by multiple grounding points being grounded at the same time, greatly improving the grounding safety of the system and ensuring that the system can operate stably under various operating conditions.

[0060] like Figure 1 As shown, the method includes:

[0061] S10, obtaining the switch status of the grounding system;

[0062] S20, determining an operation mode of the grounding system based on the switch state;

[0063] S30: When the operation mode is switched between the microgrid mode and the grid-connected mode, the grounding point of the grounding system is adjusted based on the priority of the preset grounding point.

[0064] In this embodiment, the switch status refers to the opening and closing conditions of various circuit breakers, disconnectors and other devices in the grounding system. The status of these switches can reflect the electrical connection status of the system, thereby determining the operating mode of the system.

[0065] The switching method of the present application is applied in a specific grounding system, which includes a main transformer and at least one generator that can be electrically connected to each other, which are grounded through low resistance respectively, and the system has two operating states: microgrid mode and grid-connected mode.

[0066] When applied, first obtain the status of the switch in the grounding system, and then determine which operating mode the system is in based on the switch status. When the operating mode is switched between microgrid and grid-connected, adjust the docking location according to the pre-set grounding point priority.

[0067] Specifically, the status information of switches such as the low-voltage side circuit breaker of the main transformer and the generator side circuit breaker in the grounding system is obtained in real time through sensors or monitoring modules in the control system, such as whether they are closed or open.

[0068] According to the switch status obtained, the electrical connection relationship is analyzed. If the main transformer is connected to the grid and the relevant switches are closed, the generator is also normally connected to the grid, which is generally the grid-connected mode; if the main transformer is disconnected from the grid, some or all of the generators and local loads form an independent or relatively independent power supply system, which is the microgrid mode.

[0069] When it is detected that the operation mode is initially the grid-connected mode, the preset main transformer grounding resistance has a high priority, so the main transformer grounding conditions are checked first (such as whether the grounding resistance is normal, whether the grounding loop is intact, etc.), and if they are satisfied, the main transformer side grounding point is put into operation. When it is detected that the operation mode is switched from the grid-connected mode to the microgrid mode, the appropriate generator side grounding point is selected according to the priority, the load in the microgrid, and the generator operation status.

[0070] For example, a factory has a main transformer and two generators. During normal operation, the low-voltage side circuit breaker of the main transformer is closed and connected to the grid, the circuit breaker of generator 1 is closed, and the circuit breaker of generator 2 is disconnected. At this time, it is in grid-connected mode, and the main transformer is grounded with low resistance.

[0071] When the power grid fails and the main transformer low-voltage side circuit breaker is disconnected, generator 1 and some important loads form a microgrid. The automatic switching system detects the switch state change, determines the operation mode switch, and according to the priority (assuming that the main transformer> generator 1> generator 2), since generator 1 is running in the microgrid, generator 1 is grounded with low resistance and the grounding point on the main transformer side is cut off (the connection with the grid has been disconnected and no grounding is required).

[0072] This application avoids grounding anomalies when the operating mode changes by reasonably switching the grounding points, such as multi-point grounding generating circulating currents that cause equipment overheating and damage or grounding protection malfunction, to ensure the safety of equipment and personnel.

[0073] Moreover, the grounding system can adapt well to the needs of different operating modes, whether it is the coordinated work with the large power grid when connected to the grid, or the independent or partially independent operation in the microgrid mode, which can ensure the effectiveness of the grounding system and improve the overall adaptability of the system.

[0074] Determine the grounding point according to the operation mode and priority to achieve rational use of grounding resources, avoid unnecessary grounding resistance investment or wrong grounding point selection, and reduce the cost and complexity of the grounding system.

[0075] In one embodiment, the priority of the preset grounding point is that the grounding resistance of the main transformer takes precedence over the grounding resistance of at least one of the generators.

[0076] In this embodiment, in the process of determining the grounding point of the grounding system, the pre-set rule is to give priority to the grounding resistance of the main transformer as the grounding point. The grounding resistance of the generator is considered only when the main transformer side does not meet the grounding conditions or there are other special circumstances.

[0077] The main transformer is usually a key node for power transmission in the power system. Prioritizing its grounding stability helps maintain the stability of the grounding potential of the entire system and reduce the impact of grounding potential fluctuations on system equipment.

[0078] When the operating mode is switched or the grounding point needs to be determined, there is a clear priority order, which enables the control system to make decisions quickly and accurately, reduce unnecessary judgments and switching operations, and improve system response speed.

[0079] In the grid-connected mode, priority is given to ensuring that the grounding of the main transformer meets the requirements of the grid, which is conducive to the management and protection of the grounding system on the grid side; in the microgrid mode, if the main transformer is not grounded, the grounding can be reasonably selected according to the operating conditions of the generator to achieve safe grounding within the microgrid.

[0080] In one embodiment, if Figure 2 As shown, when the operation mode is switched between the microgrid mode and the grid-connected mode, adjusting the grounding point of the grounding system based on the preset priority of the grounding resistance includes:

[0081] S31, determining the grounding point states respectively corresponding to the grounding system before and after the operation mode changes, wherein the grounding point states include the grounding point positions, the number of grounding points and the grounding states of the grounding points;

[0082] S32: When the operation mode changes, switching the grounding point based on the grounding point state and the switching strategy.

[0083] In this embodiment, it is emphasized that in the dynamic process of the grounding system switching from the microgrid mode to the grid-connected mode or from the grid-connected mode to the microgrid mode, it is necessary to pay attention to the situations at two different time points before and after the switching.

[0084] The grounding point status corresponding to the grounding system refers to the specific situation of the grounding point of the grounding system under different operating modes, including the location of the grounding point (whether it is on the main transformer side, the generator side or other locations), the number of grounding points (how many grounding points there are) and the grounding status of the grounding point (such as whether the grounding is good, whether the grounding resistance value is normal, whether the grounding loop is conductive, etc.).

[0085] When the operating mode of the grounding system changes between the microgrid mode and the grid-connected mode, it is necessary to first clarify the status of the grounding points of the grounding system before (in the microgrid mode) and after (in the grid-connected mode). Then, based on these statuses and the pre-set grounding resistance priority, the docking points are put into operation (connected to the grounding system) or cut off (disconnected from the grounding system) to ensure that the grounding points of the grounding system are reasonably configured in the new operating mode to ensure safe and stable operation of the system.

[0086] Specifically, before the operating mode is about to change (such as switching from microgrid mode to grid-connected mode), the grounding point status of the grounding system in the current microgrid mode is detected through sensors (such as grounding resistance measurement sensors, current transformers, voltage transformers, etc.) and monitoring equipment installed at various key positions of the grounding system.

[0087] The system operating parameters (such as grid voltage, frequency, generator operating status, circuit breaker opening and closing status, etc.) are monitored in real time. When the changes in these parameters meet the conditions for switching from microgrid mode to grid-connected mode or vice versa, it is determined that the operating mode has changed.

[0088] After the operation mode is switched (such as switching to the grid-connected mode), the grounding point status of the grounding system is immediately detected again to obtain new grounding point locations, quantity and grounding status information, and compare them with the status before the switch.

[0089] The grounding point switching operation is performed according to the preset grounding resistance priority (such as the main transformer grounding resistance takes precedence over the generator grounding resistance) and the grounding point status before and after the operation mode changes. For example, if the main transformer is grounded with low resistance in the grid-connected mode, when switching to the microgrid mode and the generator grounding is required, the main transformer grounding point is cut off and the appropriate generator grounding point is switched on.

[0090] This application can accurately judge the state of the grounding point before and after the operation mode changes, and reasonably adjust the grounding point according to the characteristics and requirements of different operation modes, so that the grounding system is perfectly matched with the operation mode. Whether it is independent or partially independent operation in microgrid mode, or coordinated operation with the large power grid in grid-connected mode, the grounding system can be guaranteed to work effectively and the adaptability and reliability of the system can be improved.

[0091] Adjustments are made based on the grounding point status and priority to avoid unreasonable use of grounding equipment such as grounding resistors during operation mode switching. For example, unnecessary generator grounding in grid-connected mode can be removed in time to reduce unnecessary losses and costs and improve the utilization efficiency of grounding resources.

[0092] Reasonable grounding point adjustment helps maintain the stability of the grounding system potential and reduce problems such as grounding current fluctuations and equipment overvoltage caused by changes in the grounding point, thereby enhancing the stability of the entire power system during the switching of operating modes, reducing the risk of equipment damage and ensuring power supply quality.

[0093] In one embodiment, the switching strategy is that there is only one effective grounding point in the same electrical system, which specifically includes the following:

[0094] When the grounding system is started, the grid-connected mode is set as the default, and the grounding point with the highest priority is switched on. When the operation mode changes, the grounding point is switched on and off according to the priority of the preset grounding point;

[0095] When the operation mode changes, and the grounding point is switched and it is determined during the switching process that there is a valid grounding point in the same electrical system, the switching of the grounding point is terminated;

[0096] When the operation mode changes, and the grounding point is switched and it is determined during the switching process that there are multiple valid grounding points in the same electrical system, a grounding point with the highest priority is retained, and the other grounding points are exited.

[0097] In this embodiment, the switching strategy refers to a series of rules and methods followed when performing switching-on and switching-off operations at the docking location. It is clearly stipulated here that under any circumstances, there must be only one effective grounding point in the same electrical system.

[0098] When the grounding system is started, it is assumed that the system is in grid-connected mode by default. At this time, according to the pre-set grounding resistance priority, the grounding point with the highest priority (such as the main transformer grounding resistance) is selected and put into the grounding system, so that the system has a suitable grounding point in the initial state, ensuring that the system starts safely and enters the grid-connected operation state.

[0099] When the operation mode changes (such as from grid-connected to microgrid or vice versa), the grounding point switching operation shall be performed according to the preset grounding point priority. At the same time, if it is found that there is already a valid grounding point in the same electrical system during the switching process, the current grounding point switching operation shall be stopped to avoid confusion of grounding points due to repeated operations or wrong operations; if multiple valid grounding points are found, the grounding point with the highest priority shall be retained, and other grounding points shall be withdrawn from the grounding system, so that the system is restored to a state with only one valid grounding point, ensuring the correctness and stability of the grounding system.

[0100] That is, the grounding point switching strategy of the grounding system is to ensure that under any operating conditions, there is always only one effective grounding point in the same electrical system. When the system starts, it enters the grid-connected mode by default and gives priority to the grounding point with the highest priority. When the operating mode changes, the grounding point switching operation is strictly carried out according to the priority, and the decision on whether to continue switching or adjust the grounding point is made based on the grounding point status detected during the switching process (one or more effective grounding points) to maintain the stable operation of the grounding system.

[0101] Specifically, the entire process of this application needs to meet the following switching strategies:

[0102] ① During the startup phase, the grounding system is in grid-connected mode, and the grounding resistance on the low-voltage side of the main transformer is put into operation. When an abnormality occurs in the grid, it is switched to microgrid operation, and the connection points are put into operation and withdrawn according to the priority above.

[0103] ② During the switching process, if it is found that there is already a grounding point in the same electrical system (if there is an electrical connection between the devices, it is the same electrical system; if there is no electrical connection, it is a different electrical system), the switching method will not be started.

[0104] When the program of the switching method of the grounding system is ready to carry out the operation of putting the grounding point in or out, it will first detect whether there is a valid grounding point in the current electrical system.

[0105] If there is already a grounding point, it means that the grounding system is currently in a normal grounding state and no additional grounding point adjustment operation is required. At this time, the program will not start a new grounding point insertion and withdrawal action to avoid unnecessary operations and possible interference or risks.

[0106] For example, in the grid-connected operation mode, the grounding resistor on the low-voltage side of the main transformer is normally grounded, which is the only grounding point at present. At this time, due to grid fluctuations and other reasons, it is detected that the operation mode has changed to microgrid mode, and the grounding point needs to be switched. However, in the detection before the switching method is started, it is found that the grounding point on the main transformer side already exists, then the program will not start, the grounding state on the main transformer side remains unchanged, and the grounding system continues to operate normally, and the current stable grounding configuration will not be changed due to program malfunction.

[0107] Alternatively, in the microgrid mode, the low-resistance grounding of the generator, when the generator is electrically connected to the main transformer to form an electrical system, since the current electrical system has an effective grounding point (i.e., the low-resistance grounding of the generator), the switching method of the present application is not started at this time.

[0108] ③ If there are multiple grounding points, retain the one with the highest priority and exit the other grounding points.

[0109] If multiple grounding points are found in the same electrical system during the inspection process, these grounding points need to be adjusted to ensure the normal operation and safety of the system.

[0110] According to the pre-set grounding point priority (such as the grounding resistance of the main transformer takes precedence over the grounding resistance of the generator), the grounding point with the highest priority is identified and retained, and then other grounding points with lower priorities are removed from the grounding state, so that the system is restored to a normal state with only one grounding point, avoiding problems such as grounding loops and protection malfunctions that may be caused by multiple grounding points.

[0111] For example, during the operation of a microgrid in a factory, due to some abnormal conditions, the grounding resistances of generator 1 and generator 2 are both in a grounded state (there should be only one grounding point). Assuming that the preset priority is main transformer > generator 1 > generator 2, multiple grounding points are detected at this time.

[0112] The program will retain the grounding status of generator 1 (because its priority is higher than that of generator 2), and issue a command to disconnect the grounding connection of the grounding resistor of generator 2, so that generator 2 exits the grounding state. In this way, the grounding system is restored to a state with only one grounding point (generator 1), ensuring the correctness and stability of the grounding system during the operation of the microgrid, and preventing the circulating current generated by multiple grounding points from damaging the equipment or affecting the normal operation of the grounding protection.

[0113] Therefore, during the operation mode switching process, the present application ensures that the grounding system is always in an effective grounding state by reasonably adjusting the grounding point, avoiding the loss of grounding protection of the equipment due to grounding interruption caused by mode switching, and improving the reliability of system operation.

[0114] For systems operating in different countries or regions (which may face different grid standards and microgrid operation requirements), this switching method can make the grounding system better adapt to various situations and improve the compatibility and versatility of the system in different environments.

[0115] In one embodiment, the same electrical system comprises:

[0116] The main transformer is operated alone and grounded at low resistance;

[0117] One of the generators is operated alone and is grounded at low resistance;

[0118] said main transformer and at least one said generator electrically connected and operating together;

[0119] The two generators are electrically connected and operate together.

[0120] In this embodiment, the main transformer that operates independently and is grounded with low resistance means that the main transformer is in operation independently without being electrically connected to the generator, and its low-voltage side is connected to the earth through a grounding resistor to form an independent electrical system. At this time, the grounding resistance of the main transformer provides grounding protection for this independent electrical system, preventing the main transformer and its related equipment from becoming electrified due to leakage and other reasons, thereby ensuring the safety of equipment and personnel.

[0121] A generator running alone and grounded with low resistance: refers to a single generator that is in operation when it is not electrically connected to the main transformer and other generators, and one side of the generator is grounded with low resistance to form an independent electrical system. The grounding resistance of the generator provides grounding protection for its own operation, ensuring that the generator can safely conduct current to the ground even if a grounding fault occurs during independent operation, such as when supplying power to a specific independent load, to avoid equipment damage and electric shock to personnel.

[0122] Main transformer and at least one generator that are electrically connected and operate together: When the main transformer and one or more generators are connected by electrical lines and they participate in the operation of the power system together, they constitute a unified electrical system. In this system, there is transmission and distribution of electric energy between the main transformer and the generator. Their grounding methods are interrelated and jointly affect the grounding performance of the entire system. It is necessary to coordinate the setting of grounding points according to the operation mode and grounding system design to ensure the safe and stable operation of the system in different operation modes such as grid-connected or microgrid.

[0123] Two generators that are electrically connected and run together: This means that the two generators are connected together through an electrical connection line and are in operation at the same time, and together they constitute an electrical system. In this system, there may be a mutual influence between the two generators in terms of load distribution, voltage regulation, etc. The setting of their grounding resistance and grounding method need to be considered uniformly to ensure the effectiveness of the grounding system under different operating conditions (such as two generators jointly supplying power to the load in microgrid mode) and to prevent equipment failures and system instability caused by grounding problems.

[0124] In short, when there are electrical connections to form an electrical system, a unified grounding system can maintain the stability of the grounding potential of the entire system. If there are multiple grounding systems and they are independent of each other, ground loops may occur due to the potential differences at different grounding points, increasing equipment losses and the risk of failure.

[0125] When the electrical connection is disconnected to form two electrical systems, the respective grounding systems are the basic requirement to ensure the safety of the equipment. For example, when the generator is running alone, if there is no independent grounding, once a grounding fault occurs, the live shell of the equipment will not be able to be connected to the ground in time, which will pose a serious safety threat to the operator.

[0126] Specifically, when the main transformer and the generator are electrically connected, they form an electrical system. In this case, in order to ensure the safe and stable operation of the system, a unified grounding system is usually adopted. The purpose of this is to ensure that when a ground fault occurs at any point in the system, the grounding current can flow into the earth along a predetermined path to protect the safety of equipment and personnel, and also facilitate the coordination of grounding protection devices.

[0127] When the main transformer and generator are electrically disconnected, they become two relatively independent electrical systems. At this point, each system needs to have its own independent grounding system to prevent leakage, overvoltage and other problems from causing equipment damage or electric shock to personnel during their respective operations. For example, the main transformer side may still be connected to the power grid or have its own operating needs that require grounding protection, and the generator must also have reliable grounding to ensure safety when operating alone or in a microgrid with other equipment.

[0128] In one embodiment, when the operation mode changes, switching the grounding point based on the grounding point state and the switching strategy includes:

[0129] Before the operation mode changes, it is in the microgrid mode, one of the generators operates independently, and one of the generators is grounded with a low resistance to form the effective grounding point;

[0130] After the operation mode is changed to the grid-connected mode, the main transformer is electrically connected to one of the generators and operates together to form the same electrical system;

[0131] Determine that there is an effective grounding point in the same electrical system, and terminate the switching of the grounding point.

[0132] In this embodiment, before the operation mode of the grounding system is switched, it is in the microgrid mode. At this time, there are generators that are not electrically connected to the main transformer, but supply power to their respective loads separately, and the generators that operate separately (such as Figure 5 The grounding resistance of the generator on the far right in the figure is in a grounded state. This grounded generator forms an effective grounding point in the microgrid mode, providing grounding protection for its corresponding load.

[0133] When the system operation mode switches from microgrid mode to grid-connected mode, the main transformer is connected to a generator that was previously operating separately through an electrical line. Electric energy can be transmitted and distributed between them to form a unified electrical system. At this time, the operating status and grounding requirements of the entire system have changed, and the docking location needs to be adjusted according to the new situation.

[0134] like Figure 5 As shown in the figure, after the operation mode is switched from microgrid to grid-connected, the state of the grounding point is detected, and it is found that although the system structure has changed, there is already an effective grounding point in the newly formed same electrical system (that is, the grounding resistance of the generator running alone in the previous microgrid mode is still grounded and working normally). According to the switching strategy (there is only one effective grounding point in the same electrical system), there is no need to perform additional grounding point switching or cutting operations at this time. The switching process of the grounding point is terminated, and the existing grounding point is maintained to ensure the stable operation of the system in the grid-connected mode.

[0135] After the operating mode is switched, the present application can quickly determine whether the grounding point needs to be adjusted by detecting the grounding point status, thereby avoiding unnecessary switching operations when there is an effective grounding point, reducing equipment wear and operating risks, while also saving system resources and improving system operating efficiency.

[0136] During the switching process from microgrid mode to grid-connected mode, if the original effective grounding point can be directly used without interrupting the grounding, the continuity of the grounding system can be ensured, and safety problems such as equipment leakage and overvoltage that may be caused by instantaneous grounding interruption caused by grounding point switching can be prevented, thereby ensuring the safety of system equipment and personnel.

[0137] Maintaining the existing effective grounding point helps to maintain the stability of the system grounding potential, avoid grounding current fluctuations and grounding potential shifts caused by changes in the grounding point, enable the system to transition to the grid-connected mode more smoothly, reduce interference with the operation of other equipment in the system, and improve the overall stability and reliability of the system.

[0138] In one embodiment, when the operation mode changes, switching the grounding point based on the grounding point state and the switching strategy includes:

[0139] Before the operation mode changes, it is in the microgrid mode, one of the generators operates independently, and one of the generators is grounded with a low resistance to form the effective grounding point;

[0140] Before the operation mode changes, it is in the microgrid mode, the main transformer operates alone, and the low resistance of the main transformer is grounded to form the effective grounding point;

[0141] After the operation mode is changed to the grid-connected mode, the main transformer is electrically connected to one of the generators and operates together to form the same electrical system;

[0142] It is determined that there are multiple effective grounding points in the same electrical system, the grounding point of the main transformer is retained, and a grounding point of the generator is withdrawn.

[0143] In this embodiment, the operation mode is in microgrid mode before it changes. In the microgrid mode, a generator operates independently and is grounded with low resistance, thereby forming an effective grounding point in the microgrid mode, providing grounding protection for the load carried by the generator; and when the main transformer operates alone, the low-resistance grounding on its low-voltage side also forms an effective grounding point, ensuring the safety of the main transformer and its related equipment when operating alone.

[0144] When the system operation mode switches from microgrid mode to grid-connected mode, the main transformer and a generator that were originally operating separately are connected through electrical lines, and electric energy begins to be transmitted and interacted between them, forming a unified electrical system. At this time, the operating status and grounding requirements of the entire system have changed, and the docking location needs to be reasonably adjusted according to the new situation.

[0145] After the operation mode is switched from microgrid to grid-connected, the grounding point status is detected, and it is found that there are multiple valid grounding points in the newly formed same electrical system (that is, the main transformer grounding resistance and the generator grounding resistance that were previously operating separately in the microgrid mode are both grounded and working normally). According to the pre-set switching strategy (there is only one valid grounding point in the same electrical system and there are priorities), in this case, the grounding point of the main transformer with a higher priority is retained, and the grounding point of the generator is withdrawn from the grounding system, so that the system is restored to a state with only one valid grounding point, so as to ensure the correctness and stability of the grounding system in the grid-connected mode.

[0146] This application determines the priority of the grounding resistance of the main transformer and the generator, and processes them according to the priority when multiple valid grounding points are found, which can ensure the stability of the grounding system in the grid-connected mode. The main transformer usually plays an important role in the power system. Preserving its grounding point first helps maintain the stability of the overall grounding potential of the system, reduce the grounding current fluctuations and equipment overvoltage caused by improper grounding point switching, and improve the reliability of system operation.

[0147] In the grid-connected mode, appropriate grounding points are selected according to priority, avoiding problems such as ground loops and ground resistance heating that may be caused by the existence of multiple grounding points at the same time. The configuration of the grounding system is optimized, the loss of the grounding system is reduced, and the service life of the grounding equipment is extended. At the same time, the adaptability of the grounding system to the power grid is improved, ensuring that the system coordinates with the power grid grounding system when connected to the grid.

[0148] The grounding point handling method under such operating mode changes is clarified, and a unified switching strategy is followed to facilitate the operation of system design, operation and maintenance personnel. Whether in normal operation or in the process of operating mode switching, there are clear rules to follow, which reduces human errors and uncertainties, improves the standardization and predictability of grounding system management, and is conducive to ensuring the safe and stable operation of the power system.

[0149] In one embodiment, the method further comprises:

[0150] When the main transformer is electrically disconnected from one of the generators and they are operated separately, the grounding resistor of the main transformer and the grounding resistor of one of the generators are grounded respectively.

[0151] In this embodiment, during the operation of the power system, due to some reason (such as equipment maintenance, failure, etc.), the electrical connection between the main transformer and a generator is cut off, and there is no more transmission of electric energy between them.

[0152] At this time, if the main transformer and one of the generators operate separately, two independent electrical systems are formed. There can only be one effective grounding point in the same electrical system. Therefore, the grounding resistance of the main transformer and the grounding resistance of the generator are grounded separately.

[0153] That is, when the main transformer and the generator are electrically disconnected, the grounding resistance of the main transformer and the grounding resistance of each generator must be connected to the earth to form an independent grounding loop, ensuring that the main transformer and the generator are still grounded in this special state, preventing equipment from experiencing safety problems such as leakage and insulation damage due to loss of grounding.

[0154] In the special case where the main transformer and the generator are electrically disconnected, the present application enables their respective low-resistance grounding, providing independent grounding protection for the equipment, preventing the equipment casing from becoming electrified due to loss of grounding, avoiding the risk of electric shock to personnel and damage to equipment, and ensuring the safety of the equipment during maintenance or failure.

[0155] A grounding system according to an embodiment of the present application is used to perform the switching method as described above, such as Figure 3 As shown, including:

[0156] The low voltage side of the main transformer is grounded through a low resistance, and this side is connected to the busbar through the first circuit breaker. The main transformer converts the input high voltage into a suitable voltage and connects it to the busbar through the first circuit breaker. The main transformer converts the high voltage electricity input from the power grid into the voltage required by the factory. The first circuit breaker can cut off the connection between the main transformer and the busbar in case of a fault, protecting the entire system.

[0157] One side of at least one generator is grounded through a low resistance, and the side is connected to the busbar through a third circuit breaker.

[0158] In one embodiment, when the grounding system includes a plurality of the generators, the plurality of generators are grounded respectively through low resistance, and there is a priority between the plurality of generators. For example, the plurality of generators include a biomass generator, two waste heat generators, or other types of generators.

[0159] Among them, the grounding resistance of the low-voltage side of the main transformer is greater than the grounding resistance of the waste heat generator 1 (first-phase waste heat generator set) and the grounding resistance of the waste heat generator 2 (second-phase waste heat generator set) and the grounding resistance of the biomass generator 3 (biomass generator set).

[0160] Specifically, the busbar is connected to the biomass generator and the plant power load respectively through the second circuit breaker. The busbar is connected to the biomass generator and the plant power load respectively through the second circuit breaker. The second circuit breaker can control the connection state of the biomass generator and the plant power load with the busbar.

[0161] For example, when a biomass generator fails, it can be disconnected from the busbar by operating the second circuit breaker without affecting the normal operation of other equipment.

[0162] The third circuit breaker is connected to the busbar through the kiln head medium voltage outlet cabinet, the kiln head medium voltage outlet cabinet is connected to the kiln head load circuit and the fourth circuit breaker respectively, and the fourth circuit breaker is connected to the waste heat generator and the plant power load respectively.

[0163] The third circuit breaker connects the busbar and the kiln head medium voltage outlet cabinet, which in turn connects the kiln head load circuit and the fourth circuit breaker, which connects the waste heat generator and the plant power load. For example, in the cement production process, the kiln head load circuit is powered by the coordinated work of these devices, and the waste heat generator is used to provide part of the power.

[0164] The busbar is also connected to the medium-voltage outlet cabinet of the raw material mill, the medium-voltage outlet cabinet of the cement mill, and the electric load balancing device. These devices are used to supply power to the raw material mill and the cement mill and to balance the electric load. For example, in a cement plant, the raw material mill and the cement mill require a stable power supply, which is achieved through the medium-voltage outlet cabinet connected to the busbar. The electric load balancing device can adjust the load distribution of the entire system and improve the power supply efficiency.

[0165] The main transformer is connected to a controller, the biomass generator and the waste heat generator are respectively connected to collectors, and the collector is connected to the controller for sending collected information to the controller.

[0166] In this embodiment, the main transformer is connected to the controller, the biomass generator and the waste heat generator are connected to the collector, and the collector is connected to the controller to send the collected information to the controller. The controller can monitor and control the entire grounding system based on this information.

[0167] In one embodiment, the grid-connected mode of the grounding system includes that the first circuit breaker to the fourth circuit breaker are all closed and all power sources are in operation.

[0168] The microgrid mode includes at least one of the following:

[0169] The waste heat generator 1 is disconnected from the corresponding third circuit breaker and then operates in the microgrid to provide the load of the corresponding kiln head load circuit;

[0170] The waste heat generator 2 is disconnected from the corresponding third circuit breaker and then operates in the microgrid to provide the load of the corresponding kiln head load circuit;

[0171] The biomass generator, the waste heat generator 1 and the waste heat generator 2 are disconnected from the first circuit breaker to form a microgrid to provide loads for two kiln head load circuits, wherein the two waste heat generators are powered by heat and the biomass generator is used for peak load regulation;

[0172] After the two waste heat generator sets are disconnected from the corresponding third circuit breakers and the city power is disconnected from the first circuit breaker, the biomass generator microgrid operates to provide loads for the two kiln head load circuits;

[0173] After the biomass generator is disconnected from the second circuit breaker and the city power is disconnected from the first circuit breaker, the two groups of waste heat generators operate in parallel.

[0174] In the factory's power system, different microgrid modes can be selected according to different operating requirements. For example, when the mains fails, one of the microgrid modes can be activated to allow the waste heat generator or biomass generator to provide power to the kiln head load circuit to ensure continued production.

[0175] In the prior art, Figure 4 As shown, the 6.6kV side grounding system of the original main transformer adopts a direct grounding system. When there are no three generator sets, the main transformer is used as the power supply for the cement plant. Then the insulation of the cement plant's 6.3kV lines, electrical equipment, transformers and other electrical equipment to the ground does not adopt the line voltage value according to domestic requirements. When a grounding fault occurs, it cannot continue to operate and should trip in time. Therefore, both the ungrounded and arc-extinguishing grounding systems cannot be used.

[0176] In addition, according to the requirements of relevant regulations, the generator cannot be directly grounded. The generator is grounded with high resistance, the contact current is too small, and the protection is easy to fail to operate. Most cement plants are connected by cables, and the capacitive current is very large. In China, it is also not allowed to continue to operate after grounding to avoid damage to the equipment. The original factory grounding values ​​are all set according to the direct grounding system.

[0177] In the actual application of this application, after analysis, the low-resistance grounding system can meet the grounding requirements of domestic generator sets and can also be applied to foreign electrical systems. We have transformed the grounding system of the entire plant.

[0178] like Figure 3 As shown in the figure, according to the cable length of the 6.6kV system of the whole plant, the total cable length of the whole plant is 14629 meters, and the grounding capacitance current I of the whole plant can be estimated. C =(0.1x6.6x14629x10 -3 )x(1+18%)=11.4 amperes. The low resistance grounding system ensures that the resistive current is greater than the capacitive current. A resistance value between 100 and 1000A is selected to meet the sensitivity requirements of the protection device, and the resistance value is as large as possible. Finally, a 100A resistance grounding current is selected. According to the formula, the resistance value R=6.6x10 3 / (√3x100)=38.1 ohms.

[0179] After the grounding system is transformed, the grounding protection setting of the original factory area needs to be modified. The grounding setting of the original factory area is changed from the direct grounding system setting to the low-resistance grounding system setting, and the setting of the new power station system is set according to the low-resistance system.

[0180] In order to ensure that the 6.3kV side of the entire plant electrical system has only one grounding point during normal operation and avoid ground loops and damage to equipment, it is necessary to switch the low-resistance grounding system according to the system's operating mode.

[0181] Figure 3 There are four low-resistance grounding points, but the distance between them is between 500 and 1000 meters. When the system operation mode changes, such as switching between grid-connected, three-unit microgrid, two-unit microgrid, and single-machine microgrid, due to the long distance, changes in operation mode losses, and the complex logic of switching the grounding system, the system is equipped with a low-resistance grounding resistance automatic switching system.

[0182] According to the characteristics of the system's operating mode, when the power generation system is started, it is in grid-connected mode (the main transformer is put into operation). Later, when an abnormality occurs in the power grid, it switches to three-unit microgrid operation. It may also be that only one or two generator sets are operating in microgrid mode due to the shutdown of the generator set. In this case, a controller for the automatic switching device of the grounding system is set on the low-voltage side of the main transformer, and a collector for the automatic switching device is set on the three-unit side to collect status information of each unit, main transformer, and plant electrical lines and transmit it to the controller for logical operation, thereby controlling the low-resistance grounding system to be automatically switched according to the operating mode of the entire plant.

[0183] The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and protection scope of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present application.

Claims

1. A method for switching a grounding system based on an operation mode, characterized in that: Applied to a grounding system, the grounding system includes an electrically connectable main transformer and at least one generator, the main transformer and at least one generator are grounded through low resistance respectively, and the operation modes of the grounding system include a microgrid mode and a grid-connected mode, including: Obtaining a switch status of the grounding system; determining an operating mode of the grounding system based on the switch state; When the operation mode is switched between the microgrid mode and the grid-connected mode, the grounding point of the grounding system is adjusted based on the priority of the preset grounding points.

2. The switching method according to claim 1, characterized in that: The priority of the preset grounding point is that the grounding resistance of the main transformer takes precedence over the grounding resistance of at least one of the generators.

3. The switching method according to claim 2, characterized in that: When the operation mode is switched between the microgrid mode and the grid-connected mode, adjusting the grounding point of the grounding system based on the preset priority of the grounding resistance includes: Determine the grounding point states respectively corresponding to the grounding system before and after the operation mode changes, wherein the grounding point states include the grounding point positions, the number of grounding points and the grounding states of the grounding points; When the operation mode changes, the grounding point is switched based on the grounding point state and the switching strategy.

4. The switching method according to claim 3, characterized in that: The switching strategy is that there is only one effective grounding point in the same electrical system, which specifically includes the following: When the grounding system is started, the grid-connected mode is set as the default, and the grounding point with the highest priority is switched on. When the operation mode changes, the grounding point is switched on and off according to the priority of the preset grounding point; When the operation mode changes, and the grounding point is switched and it is determined during the switching process that there is a valid grounding point in the same electrical system, the switching of the grounding point is terminated; When the operation mode changes, and the grounding point is switched and it is determined during the switching process that there are multiple valid grounding points in the same electrical system, a grounding point with the highest priority is retained, and the other grounding points are exited.

5. The switching method according to claim 4, characterized in that: Said same electrical system comprises: The main transformer is operated alone and grounded at low resistance; One of the generators is operated alone and is grounded at low resistance; said main transformer and at least one said generator electrically connected and operating together; The two generators are electrically connected and operate together.

6. The switching method according to claim 5, characterized in that: When the operation mode changes, switching the grounding point based on the grounding point state and the switching strategy includes: Before the operation mode changes, it is in the microgrid mode, one of the generators operates independently, and one of the generators is grounded with a low resistance to form the effective grounding point; After the operation mode is changed to the grid-connected mode, the main transformer is electrically connected to one of the generators and operates together to form the same electrical system; Determine that there is an effective grounding point in the same electrical system, and terminate the switching of the grounding point.

7. The switching method according to claim 5, characterized in that: When the operation mode changes, switching the grounding point based on the grounding point state and the switching strategy includes: Before the operation mode changes, it is in the microgrid mode, one of the generators operates independently, and one of the generators is grounded with a low resistance to form the effective grounding point; Before the operation mode changes, it is in the microgrid mode, the main transformer operates alone, and the low resistance of the main transformer is grounded to form the effective grounding point; After the operation mode is changed to the grid-connected mode, the main transformer is electrically connected to one of the generators and operates together to form the same electrical system; It is determined that there are multiple effective grounding points in the same electrical system, the grounding point of the main transformer is retained, and a grounding point of the generator is withdrawn.

8. The switching method according to claim 1, characterized in that: The method further comprises: When the main transformer is electrically disconnected from one of the generators and they are operated separately, the grounding resistor of the main transformer and the grounding resistor of one of the generators are grounded respectively.

9. A grounding system, used to perform the switching method according to any one of claims 1 to 8, characterized in that: include: A main transformer, the low voltage side of which is grounded through a low resistance and the side is connected to the busbar through a first circuit breaker; At least one generator has one side connected to ground via a low resistance and the side connected to the busbar via a third circuit breaker.

10. The grounding system according to claim 9, characterized in that When the grounding system includes a plurality of the generators, the plurality of generators are grounded respectively through low resistance, and there is a priority between the plurality of generators.

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