Grounding protection method and system for power supply of multiple paths of power supplies with different grounding modes

Abstract

The invention relates to the technical field of power utilization protection of a nuclear power plant, and provides a grounding protection method and system for supplying power by multiple paths of power supplies with different grounding modes. A resistance grounding mode is adopted for a main transformer of a power supply outside a plant and a low-voltage side neutral point of a self-contained generator in the plant, so that fault current flowing through a fault point not only comprises capacitance current, but also comprises capacitance current; the system further comprises a grounding resistance current, so that a grounding fault can be easily detected through the zero sequence current transformer, and a specific loop where the grounding fault is located can be more easily judged. After a grounding fault occurs, the grounding resistor is switched off through the neutral point grounding resistor switch, so that the magnitude of grounding fault current can be quickly reduced, and the impact of the current on system equipment is reduced. The grounding resistor provides a current limiting function at the initial stage of a fault, and after the grounding resistor is disconnected, channels for fault current to flow are further reduced, so that the fault influence is reduced to the minimum.

Description

Technical Field

[0001] The present disclosure relates to the technical field related to power protection for nuclear power plants or research reactors, and in particular to a grounding protection method and system for power supply of multiple power supplies with different grounding modes. Background Art

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

[0003] At present, in the power supply system of research reactors, in order to ensure the safety and reliability of nuclear facilities, multiple power supplies are usually used, including external public power grids and internal backup power supplies. The public power grid usually provides power supplies of multiple voltage levels, such as 35kV and 10kV, to meet the needs of different loads. At the same time, in order to cope with the situation of power outage outside the plant, the plant is equipped with a self-contained generator as an emergency power supply. The voltage level of the AC power distribution system in the plant is generally 10kV, which can be powered by an external 35kV power supply after voltage reduction through a transformer, or it can be directly powered by a 10kV power supply or a self-contained generator.

[0004] In the design and operation of power supply systems, ground faults are one of the common forms of electrical faults. Especially for nuclear facilities, the power supply system needs to adopt different grounding methods and protection strategies according to the importance of the load. In the prior art, the power supply reliability requirements for ordinary loads are relatively low. When a ground fault occurs in the circuit where they are located, the power supply can be cut off by tripping the protection device, thereby isolating the fault area. However, for important loads, such as core equipment of nuclear facilities and related systems, power outages may cause serious safety problems, so the circuits where these loads are located need to ensure the continuity of power supply as much as possible. In order to achieve this goal, the power supply system for important loads usually adopts ungrounded or high-resistance grounding methods, which can maintain the continuous operation of the load even if a single-phase grounding fault occurs.

[0005] When the AC power distribution system in the factory is powered by a 35 / 10kV transformer, the neutral point grounding method is determined by the grounding method on the low-voltage side of the 35 / 10kV transformer; when the AC power distribution system in the factory is powered by a 10kV power supply, the neutral point grounding method is determined by the public power grid; when the AC power distribution system in the factory is powered by a generator, the neutral point grounding method is determined by the neutral point grounding method of the generator. Since the single-phase grounding fault capacitance current of the 10kV AC power distribution system in the factory is small, the neutral point on the low-voltage side of the 35 / 10kV transformer and the neutral point of the generator are usually ungrounded. When a ground fault occurs in the system, the system's ground capacitance current will flow through the fault point and be detected by the zero-sequence current transformer, thereby determining the specific circuit where the ground fault occurs. However, the magnitude of the ground capacitance current varies with the scale of the power supply and distribution system. When the 35kV power supply and generator outside the factory supply power to the factory, the scale of the power supply and distribution system is limited to the power supply and distribution system inside the factory, and the capacitive current to the ground is usually only 0-7A; when the 10kV power supply outside the factory supplies power to the factory, the scale of the distribution system includes not only the power supply and distribution system inside the factory, but also the 10kV power supply and distribution system outside the factory, and the capacitive current to the ground can reach 20-30A. This leads to a large difference in the capacitive current that can be provided by the power systems inside and outside the factory when different power supplies are supplied. When the 35kV power supply and generator outside the factory supply power to the factory, when a grounding fault occurs, the capacitive current to the ground flowing through the fault point becomes smaller as the scale of the power supply and distribution system becomes smaller. If the specified standard specification design is used, the neutral point on the low-voltage side of the 35kV main transformer should be ungrounded, and the fault current is equal to the system capacitive current to the ground, and its amplitude is small, which is not easily detected by the zero-sequence current transformer.

[0006] The inventors discovered in their research that different grounding methods are used in different scales of power supply circuits in the prior art. For example, according to relevant standards, 35kV power supplies usually use a direct neutral point grounding method, while 10kV power supplies may use an ungrounded neutral point method. The difference in grounding method and system scale results in different fault current amplitudes generated by ground faults when different power supplies are supplied, which poses a challenge to the setting of the setting value of the protection device. When the ground fault current is small and the setting value of the protection device is set high, the protection device may not operate in time and the fault may not be cut off; on the contrary, when the ground fault current is large and the setting value of the protection device is set low, the protection device may malfunction due to the low setting value, affecting the stability of the power supply.

[0007] In summary, the existing technology faces many difficulties in the reasonable setting of the protection device setting value and its adaptability when multiple power supplies with different grounding methods are used. This problem is particularly prominent under ground fault conditions, and further research is needed to optimize the solution to improve the operational safety and reliability of the power supply system. Summary of the invention

[0008] In order to solve the above problems, the present disclosure proposes a grounding protection method and system for power supply of multiple power supplies with different grounding methods, improves the grounding method of the system and the hierarchical control method of important load branches, and can achieve effective protection of the system when grounding faults occur under different power supplies.

[0009] In order to achieve the above objectives, the present disclosure adopts the following technical solutions:

[0010] One or more embodiments provide a grounding protection system for power supply of multiple power supplies with different grounding modes, including multiple off-site power supplies and in-site self-provided generators, each power supply incoming branch and load branch is provided with a protection device and a current transformer respectively; a protection device and a bus voltage transformer are provided on the power supply bus;

[0011] The neutral point of the low-voltage side of the main transformer connected to the off-site power supply is grounded through a grounding resistor, and a neutral point grounding resistance switch is installed on the grounding line;

[0012] The protection device on the load branch is electrically connected to the neutral point grounding resistance switch and is used to control the action of the neutral point grounding resistance switch.

[0013] One or more embodiments provide a grounding protection method for a grounding protection system based on the above-mentioned multiple power supplies with different grounding modes, including a common load branch protection method and an important load branch protection method. The important load branch protection method performs hierarchical control on the switching of important load branches, including the following steps:

[0014] Setting thresholds for hierarchical control, including a first threshold Y1 and a second threshold Y2;

[0015] The difference C between the zero-sequence current on the important load branch and the ground fault current detected on the incoming branch of the power supply during normal operation;

[0016] When the difference C is not greater than the set first threshold value Y1, the protection device on the important load branch will not operate, and only an alarm signal may be issued;

[0017] When the difference C is between the first threshold value Y1 and the second threshold value Y2, the circuit breaker trips after a set delay time, cutting off the current important load branch;

[0018] When the difference C is greater than the second threshold value Y2, the circuit breaker is tripped immediately to cut off the current important load branch.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention adopts a resistance grounding method for the neutral point on the low-voltage side of the main transformer of the off-site power supply, so that the fault current flowing through the fault point includes not only the capacitive current but also the grounding resistance current, so that the grounding fault can be easily detected by the zero-sequence current transformer, making it easier to determine the specific circuit where the grounding fault is located; after the grounding fault occurs, the grounding resistance is disconnected by the neutral point grounding resistance switch, which can quickly reduce the magnitude of the grounding fault current and reduce the impact of the current on the system equipment. The grounding resistance provides the function of limiting the current at the initial stage of the fault, and after being disconnected, it further reduces the channel for the fault current to flow, thereby minimizing the impact of the fault. It solves the problem that the grounding protection cannot operate normally due to different neutral point grounding methods and the set value is difficult to select, and the equipment used to solve the fault is less and the protection sensitivity is high.

[0021] The advantages of the present disclosure and the advantages of additional aspects will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings constituting a part of the present disclosure are used to provide a further understanding of the present disclosure. The exemplary embodiments of the present disclosure and the description thereof are used to explain the present disclosure but do not constitute a limitation of the present disclosure.

[0023] Figure 1 is a circuit diagram of a grounding protection system powered by multiple power supplies with different grounding modes according to Embodiment 1 of the present disclosure;

[0024] Figure 2 is a flow chart of a grounding protection method according to Embodiment 2 of the present disclosure;

[0025] Among them: 100, one incoming branch, 101, one power incoming circuit breaker, 102, main transformer, 103, neutral point current transformer, 104, one neutral point grounding resistor, 106, one busbar incoming circuit breaker, 107, one busbar incoming circuit integrated protection device, 108, neutral point grounding resistor switch;

[0026] 200, incoming branch circuit 2, 201, power incoming circuit breaker 2, 205, bus incoming circuit zero-sequence current transformer 2, 206, bus incoming circuit breaker 2, 207, bus incoming circuit integrated protection device 2;

[0027] 300, generator, 301, power supply incoming line circuit breaker three, 304, neutral point grounding resistor two, 305, bus incoming line circuit zero sequence current transformer three, 306, bus incoming line circuit breaker three, 307, bus incoming line circuit integrated protection device three;

[0028] 500, power supply bus, 501, bus voltage transformer circuit fuse, 502, bus voltage transformer, 503, bus integrated protection device;

[0029] 601. One circuit breaker for common feeder circuit; 604. One common load branch circuit; 605. One zero-sequence current transformer for common feeder circuit; 607. One integrated protection device for common feeder circuit;

[0030] 611. Ordinary feeder circuit breaker 2, 614. Ordinary load branch 2, 615. Ordinary feeder circuit zero-sequence current transformer 2, 617. Ordinary feeder circuit integrated protection device 2;

[0031] 701. One circuit breaker for an important feeder circuit; 704. One important load branch circuit; 705. One zero-sequence current transformer for an important feeder circuit; 707. One integrated protection device for an important feeder circuit;

[0032] 711. Two important feeder circuit breakers, 714. Two important load branches, 715. Two important feeder circuit zero-sequence current transformers, 717. Two important feeder circuit integrated protection devices. DETAILED DESCRIPTION

[0033] The present disclosure is further described below in conjunction with the accompanying drawings and embodiments.

[0034] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present disclosure. 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 disclosure belongs.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof. It should be noted that, in the absence of conflict, the various embodiments in the present disclosure and the features in the embodiments can be combined with each other. The embodiments will be described in detail below in conjunction with the accompanying drawings.

[0036] Example 1

[0037] In the technical solutions disclosed in one or more embodiments, Figure 1 As shown, a grounding protection system for power supply of multiple power supplies with different grounding modes includes multiple off-site power supplies and in-plant self-provided generators. A protection device and a current transformer are respectively arranged on each power supply incoming branch and load branch; a protection device and a bus voltage transformer 502 are arranged on the power supply bus 500;

[0038] The neutral point of the low-voltage side of the main transformer 102 connected to the power supply outside the factory is grounded through a grounding resistor, and a neutral point grounding resistor switch 108 is set on the grounding line; the protection device on the important load branch is electrically connected to the neutral point grounding resistor switch 108 to control the operation of the neutral point grounding resistor switch 108.

[0039] In this embodiment, the neutral point of the low-voltage side of the main transformer 102 of the off-site power supply is grounded by a resistor, so that the fault current flowing through the fault point includes not only the capacitive current but also the grounding resistance current, so that the grounding fault can be easily detected by the zero-sequence current transformer, making it easier to determine the specific circuit where the grounding fault is located; after the grounding fault occurs, the grounding resistance is disconnected by the neutral point grounding resistance switch 108, which can quickly reduce the magnitude of the grounding fault current and reduce the impact of the current on the system equipment. The grounding resistance provides the function of limiting the current in the early stage of the fault, and after being disconnected, it further reduces the channel for the fault current to flow, thereby minimizing the impact of the fault.

[0040] Specifically, a bus voltage transformer 502 and a bus integrated protection device 503 are connected to the power supply bus 500 through a bus voltage transformer loop fuse 501 .

[0041] In this embodiment, the feeder line circuit (load branch) and the incoming line circuit (incoming line branch) of the medium voltage distribution system adopt zero-sequence current transformer as a method for detecting ground fault current, and the voltage to ground detected by the bus voltage transformer 502 is used as an auxiliary criterion. A current transformer is installed on the neutral point lead-out line on the low voltage side of the main transformer 102. The detection method is more reliable and has higher sensitivity, which is conducive to achieving the reliability, selectivity, sensitivity and speed of protection.

[0042] In a further technical solution, protection devices are respectively provided on the power supply incoming branch, the load branch and the power supply bus, and the setting method of the setting value is:

[0043] The load branch is used as the final feeder line circuit, and the zero-sequence protection action current setting value set in the protection device is between 5 and 30A;

[0044] On the incoming branch and the power supply busbar as the upper level line of the load branch, the zero-sequence protection action current setting value of the protection device is 2 to 5 times the zero-sequence protection action current setting value of the load branch;

[0045] After the load branch detects a fault, if the time difference exceeds the set time difference, it will not act, and the incoming branch of the upper level will act to remove the fault. The time difference can be set to 0.1 second to 0.3 second.

[0046] Specifically, the protection device of the incoming branch and the protection device of the load branch can establish a communication connection through high-speed Ethernet, and transmit data through the data bus. When the protection device of the load branch and the integrated protection device of the bus incoming line circuit of the incoming branch detect the ground fault current at the same time, the integrated protection device of the bus incoming line circuit will not operate within 0.3 seconds to 0.5 seconds. When the time exceeds 0.5 seconds, and the integrated protection device of the bus incoming line circuit can still detect the ground fault current, the protection device will operate. This ensures that when a ground fault occurs in the feeder circuit, only the circuit where the fault occurs is cut off. If the protection device fails and the fault cannot be cut off, the integrated protection device of the bus incoming line circuit will operate to cut off the fault and ensure the stability of the power supply system.

[0047] The circuit structure of the above ground protection system is described below with a specific embodiment.

[0048] In some embodiments, the power supply line branch is configured as follows:

[0049] When the power supply outside the factory is connected to the power supply bus in the factory through the main transformer, the power supply incoming line circuit breaker, the main transformer and the bus incoming line circuit breaker are connected in series in sequence on the incoming line branch. The neutral point of the main transformer is grounded with a grounding resistor. The neutral point grounding resistor switch, the neutral point current transformer and the neutral point grounding resistor are connected in series on the grounding line;

[0050] When the power supply outside the factory is directly connected to the power supply, there is no need to connect the main transformer. The power supply incoming line circuit breaker, zero-sequence current transformer and bus incoming line circuit breaker are connected in sequence on the incoming line branch;

[0051] In a specific implementation manner, the off-site power supply may include multiple types, such as 3kV, 6kV, 10kV, 20kV, 35kV, 66kV, 110kV or 220kV, etc. The access mode may be accessed through the main transformer 102, or may be directly accessed according to the voltage level; in this embodiment, two off-site power supplies are set up, namely 35kV and 10kV power supplies, for example;

[0052] The power supply outside the factory is a 35kV power supply, which is connected to the power supply bus 500 after the power conversion through the main transformer 102, and is the power supply incoming branch 100;

[0053] It is achievable that the incoming end of the incoming branch 100 is connected to the main transformer 102 through the power incoming circuit breaker 101;

[0054] Furthermore, when the power supply outside the factory is connected to the power supply bus 500 in the factory through the main transformer 102, the power supply incoming line circuit breaker 101, the main transformer 102 and the bus incoming line circuit breaker 106 are connected in series in sequence on the incoming line branch;

[0055] The neutral point of the main transformer 102 is grounded by a grounding resistor, and a neutral point grounding resistor switch 108, a neutral point current transformer 103 and a neutral point grounding resistor 104 are connected in series on the grounding line; the output end of the main transformer 102 is connected to the power supply bus 500 through a bus incoming line circuit breaker 106, and the load is supplied with power through the power supply bus 500; it also includes a bus incoming line circuit comprehensive protection device 107, which is respectively connected to the neutral point current transformer 103 and the bus incoming line circuit breaker 106, and the action of the bus incoming line circuit breaker 106 is controlled according to the current size on the neutral point grounding line of the main transformer 102;

[0056] In this embodiment, the feeder line circuit and the incoming line circuit of the medium voltage distribution system use zero-sequence current transformers as a method for detecting ground fault current, and current transformers are installed on the neutral point lead-out line on the low voltage side of the main transformer. The detection method is relatively reliable and has high sensitivity, which is conducive to achieving reliability, selectivity, sensitivity and speed of protection.

[0057] In a specific implementation mode, the 10 kV power supply outside the factory is connected to the power supply bus 500 through the second power supply incoming branch 200;

[0058] The second power supply incoming line branch 200 is sequentially connected with a second power supply incoming line circuit breaker 201, a second zero-sequence current transformer 205 and a second bus incoming line circuit breaker 206, and is also provided with a second bus incoming line circuit integrated protection device 207. The second bus incoming line circuit integrated protection device 207 is respectively connected to the second zero-sequence current transformer 205 and the second bus incoming line circuit breaker 206, and controls the action of the second bus incoming line circuit breaker 206 according to the detected current size;

[0059] In some embodiments, the voltage level of the self-provided generator in the factory is 10kV, and the generator 300 is grounded or not grounded through the neutral point grounding resistor 2 304, wherein high resistance grounding is adopted for grounding; the branch line of the generator 300 connected to the power supply bus is sequentially connected with the power supply incoming line circuit breaker 3 301, the bus incoming line circuit zero-sequence current transformer 3 and the bus incoming line circuit breaker 3 306, and is also provided with a bus incoming line circuit comprehensive protection device 3 307, which is respectively connected to the bus incoming line circuit zero-sequence current transformer 3 and the bus incoming line circuit breaker 3 306, and controls the action of the bus incoming line circuit breaker 3 306 according to the detected current size;

[0060] In some embodiments, the circuit configuration of the load branch is as follows:

[0061] Load branches include common load branches and important load branches;

[0062] The loads that may cause serious safety problems if the power supply is interrupted are important loads, such as the core equipment of nuclear facilities and their related systems. The circuits where important loads are located need to ensure the continuity of power supply as much as possible. Important load branches are branches where important loads are set.

[0063] In this embodiment, two important load branches are provided as examples, including an important load branch 1 704 and an important load branch 2 714; loads other than the important loads are common loads, and the corresponding branches are common load branches;

[0064] In this embodiment, two common load branches are provided as examples, including common load branch 1 604 and common load branch 2 614;

[0065] A further technical solution is that the protection device on the common load branch controls the removal and input of the common load branch according to the magnitude of the zero-sequence current on the load branch;

[0066] In some embodiments, each common load branch includes a common feeder circuit breaker, a common feeder circuit integrated protection device, and a common feeder circuit zero-sequence current transformer connected in sequence; the common feeder circuit integrated protection device is respectively communicated with the common feeder circuit breaker and the common feeder circuit zero-sequence current transformer on the common load branch, and controls the on and off of the current common feeder circuit breaker according to the detected current zero-sequence current, so as to realize the removal and input of the current common load branch;

[0067] In a specific implementation manner, the common load branch 1 604 is provided with: a common feeder circuit breaker 1 601, a common feeder circuit integrated protection device 1 607, and a common feeder circuit zero-sequence current transformer 1 605 in sequence; the common feeder circuit integrated protection device 1 607 is respectively connected to the common feeder circuit breaker 1 601 and the common feeder circuit zero-sequence current transformer 1 605 in communication;

[0068] Ordinary feeder circuit breaker 601: As a switching device in the circuit, ordinary feeder circuit breaker 601 is connected to the entrance of the power supply bus 500 and the ordinary load branch 604 to control the on and off of the circuit; it is connected to the ordinary feeder circuit comprehensive protection device 607.

[0069] Common feeder circuit integrated protection device 607: used to protect the operation of the circuit and comprehensively detect faults such as overload and short circuit; connected to common feeder circuit zero-sequence current transformer 605 and common feeder circuit breaker 601 respectively, and controls the switching action of common feeder circuit breaker 601 according to the current size of the detected common load branch 604;

[0070] Ordinary feeder circuit zero-sequence current transformer 605: used to detect the zero-sequence current in the ordinary load branch 604 to determine whether there is a ground fault.

[0071] The ordinary load branch 1 604 is connected to an ordinary load, which is specifically an electrical device or apparatus for receiving electrical energy supply from a feeder circuit.

[0072] Specifically, for a ground fault of a common load branch 604, when the ground fault current is greater than the above-set zero-sequence protection action current setting value (5 to 30A), the common feeder circuit breaker 601 is controlled to open and directly cut off;

[0073] In a specific implementation manner, the common load branch 2 614 is provided with:

[0074] Ordinary feeder circuit breaker 2 611: As a switching device in the circuit, ordinary feeder circuit breaker 2 611 is connected to the entrance of the power supply bus 500 and ordinary load branch 2 614 to control the on and off of the circuit; it is connected to ordinary feeder circuit integrated protection device 2 617.

[0075] Common feeder circuit integrated protection device 2 617: used to provide protection for circuit operation, including monitoring of overload, short circuit, etc.; connected to common feeder circuit zero-sequence current transformer 2 615 and common feeder circuit breaker 2 611 respectively, and controls the switching action of common feeder circuit breaker 2 611 according to the current size of common load branch 2 614 detected;

[0076] Ordinary feeder loop zero-sequence current transformer 2 615: Ordinary feeder loop zero-sequence current transformer 2 615 is used to detect the zero-sequence current in the circuit to determine whether there is a ground fault.

[0077] A further technical solution is that the protection device on the important load branch is connected to the protection device arranged on the power supply incoming branch. When the power is supplied by the external power supply, the switching of the important load branch is controlled in stages according to the difference between the zero-sequence current on the load branch and the ground fault current detected on the power supply incoming branch.

[0078] Furthermore, when a ground fault occurs in the important load branch, the protection device on the important load branch performs hierarchical control on the switching of the important load branch according to the difference between the zero-sequence current on the load branch and the ground fault current detected on the incoming line branch that supplies power normally, including the following steps:

[0079] Step A1, setting thresholds for hierarchical control, including a first threshold Y1 and a second threshold Y2;

[0080] Step A2: a difference C between the zero-sequence current on the important load branch and the ground fault current detected on the incoming branch of the power supply during normal operation;

[0081] Step A3: When the difference C is not greater than the set first threshold value Y1, the protection device on the important load branch does not operate, and only an alarm signal may be issued;

[0082] Step A4: When the difference C is between the first threshold value Y1 and the second threshold value Y2, the circuit breaker trips after a set delay time to cut off the current important load branch;

[0083] Step A5: When the difference C is greater than the second threshold value Y2, the circuit breaker is tripped immediately to cut off the current important load branch;

[0084] A further technical solution is that when the off-site power supply is connected to the power supply through the main transformer 102, a ground fault is detected in an important load branch, and the zero-sequence current on the important load branch is greater than the set first threshold value Y1, the neutral point grounding resistance switch is controlled to open the gate to reduce the fault current; at this time, the fault is not removed, only the fault current is reduced; and then the above-mentioned step A1-step A5 hierarchical control process is executed; in this embodiment, a tripping method is adopted when a ground fault occurs, which effectively meets the requirements of two different power supplies for grounding protection.

[0085] In the event of a ground fault, if the neutral point grounding resistor is always connected, a large fault current may continue to flow, further causing equipment damage or instability in other circuits. By disconnecting the grounding resistor, the neutral point grounding resistor switch 108 effectively interrupts the flow path of the fault current and prevents the fault from spreading from a local part to other parts of the system. The disconnection action of the grounding resistor switch 108 greatly reduces the amplitude of the fault current, thereby reducing the thermal effect and electrodynamic damage of the fault current on transformers, generators and other equipment, effectively extending the service life of the equipment and improving the reliability of the system, while providing good technical support for fault detection and system maintenance.

[0086] In some embodiments, each important load branch includes an important feeder circuit breaker, an important feeder circuit integrated protection device, and an important feeder circuit zero-sequence current transformer connected in sequence; the important feeder circuit integrated protection device is respectively connected to the important feeder circuit breaker and the important feeder circuit zero-sequence current transformer in communication; and the important feeder circuit integrated protection device is connected to the protection device on the power supply incoming branch in communication;

[0087] In a specific implementation manner, an important load branch 704 is provided with: an important feeder circuit breaker 701, an important feeder circuit integrated protection device 707, and an important feeder circuit zero-sequence current transformer 705 in sequence; the important feeder circuit integrated protection device 707 is respectively connected to the important feeder circuit breaker 701 and the important feeder circuit zero-sequence current transformer 705 for communication; the important feeder circuit integrated protection device 707 is respectively connected to the protection device and the circuit breaker on the power supply incoming branch, and the connected power supply incoming branch is determined according to the circuit breaker breaking signal on the power supply incoming branch, and the current on the corresponding power supply incoming branch is obtained through the protection device on the power supply incoming branch to realize the control of the important load branch;

[0088] The specific description of the important load branch 704 is as follows:

[0089] Important feeder circuit breaker 701: As a switch device in the circuit, the important feeder circuit breaker 701 is connected to the entrance of the power supply bus 500 and the important load branch 704 to control the on and off of the circuit. The important feeder circuit breaker 701 is connected to the important feeder circuit integrated protection device 707, which controls the switch action to ensure the power supply safety of the important load branch 704;

[0090] Important feeder circuit integrated protection device 707: used to protect the operation of important load branch 704, and comprehensively detect faults such as overload and short circuit. Its input end is connected to the important feeder circuit zero-sequence current transformer 705, and is used to receive the zero-sequence current signal and determine whether there is a ground fault. At the same time, the important feeder circuit integrated protection device 707 controls the switching action of the important feeder circuit breaker 701, so as to protect the important load according to the detected current size or ground fault signal.

[0091] Further, in the important load branch 1 704, the important feeder circuit integrated protection device 1 707 is also connected to the protection devices and circuit breakers on the power supply incoming branch 1 100 and the incoming branch 2 200. In this embodiment, the important load branch 1 704 is respectively connected to the bus incoming circuit breaker 1 106, the bus incoming circuit breaker 2 206, and the bus incoming circuit integrated protection device 1 107 and the bus incoming circuit integrated protection device 2 207;

[0092] Important feeder circuit zero-sequence current transformer 705: used to detect the zero-sequence current in the important load branch 704 to determine whether there is a ground fault. Its output signal is transmitted to the important feeder circuit integrated protection device 707 for fault determination.

[0093] Important loads are connected to the important load branch 1 704. The important loads are specifically electrical equipment or devices that have high requirements for power supply stability and reliability. The important loads receive power supply from the feeder circuit to ensure stable operation under normal circumstances.

[0094] When the bus incoming line circuit breaker 106 is closed, power is supplied through the incoming line branch 100. Through the auxiliary contact signal of the bus incoming line circuit breaker 106, the bus incoming line circuit integrated protection device 107, the important feeder circuit integrated protection device 707, the important feeder circuit integrated protection device 2 717 and other protection devices obtain the auxiliary contact signal to determine whether power is supplied through the incoming line branch 100.

[0095] The busbar incoming line circuit integrated protection device 107 records the current flowing through the neutral point current transformer 103 under normal conditions, and transmits it to the important feeder circuit integrated protection device 1 707 and the important feeder circuit integrated protection device 2 717 through the data bus.

[0096] Specifically, the important feeder circuit integrated protection device 707 on the important load branch performs hierarchical control on the switching of the important load branch according to the difference between the zero-sequence current on the load branch and the ground fault current detected on the incoming branch of the power supply in normal time, and the specific process is as follows:

[0097] When power is supplied through the incoming branch 100, when a ground fault occurs in the important load branch 704, the first threshold value Y1 is set to 5A, and the second threshold value Y2 is set to any value between 10A and 15A, such as 10A. The fault protection control method of the important feeder circuit integrated protection device 707 using hierarchical control is as follows:

[0098] 11) If the current detected by the zero-sequence current transformer 705 of the important feeder circuit is greater than 5A, the important feeder circuit integrated protection device 707 directly controls the neutral point grounding resistance switch 108 to operate and open. At this time, the fault is not removed, only the fault current is reduced.

[0099] 12) If the current detected by the zero-sequence current transformer 705 of the important feeder circuit minus the current flowing through the neutral point current transformer 103 in normal state is less than or equal to 5A, the protection device will not operate and only send out an alarm signal;

[0100] 13) If the current detected by the zero-sequence current transformer 705 of the important feeder circuit minus the current flowing through the neutral point current transformer 103 in normal state is greater than 5A and less than or equal to 10A, the circuit breaker will trip after the set delay time; the set delay time can be set to 0.5 to 2.0s;

[0101] 14) If the current detected by the zero-sequence current transformer 1 705 of the important feeder circuit minus the current flowing through the zero-sequence current transformer 2 205 of the busbar incoming line circuit under normal conditions is greater than 10A, the important feeder circuit breaker 1 701 will immediately operate to open the circuit.

[0102] When power is supplied through the incoming branch 200 and the bus incoming circuit breaker 206 is closed, it is determined that power is supplied through the incoming branch 200. The auxiliary contacts of the bus incoming circuit breaker 206 transmit the circuit breaker closing signal to the important feeder circuit integrated protection device 1 707, the important feeder circuit integrated protection device 2 717 and other protection devices through cables.

[0103] On the incoming branch line 200, the bus incoming line circuit integrated protection device 207 records the current flowing through the bus incoming line circuit zero sequence current transformer 205 when normal, and transmits it to the important feeder circuit integrated protection device 1 707 and the important feeder circuit integrated protection device 2 717 through the data bus;

[0104] When power is supplied through the incoming branch 200, when a ground fault occurs in the important load branch 1 704, the first threshold value Y1 is set to 5A, and the second threshold value Y2 is set to any value between 10A and 15A, such as 10A. The fault protection control method of the important feeder circuit integrated protection device 1 707 using hierarchical control is as follows:

[0105] B1) If the current detected by the zero-sequence current transformer 1 705 of the important feeder circuit minus the current flowing through the zero-sequence current transformer 2 205 of the busbar incoming circuit in normal state is less than or equal to 5A, the important feeder circuit integrated protection device 1 707 will not operate, and only send out an alarm signal;

[0106] B2) If the current detected by the zero-sequence current transformer 1 705 of the important feeder circuit minus the current flowing through the zero-sequence current transformer 2 205 of the busbar incoming circuit under normal conditions is greater than 5A and less than or equal to 10A, the circuit breaker will trip after a delay of 0.5 to 2.0 seconds;

[0107] B3) If the current detected by the zero-sequence current transformer 1 705 of the important feeder circuit minus the current flowing through the zero-sequence current transformer 2 205 of the busbar incoming circuit under normal conditions is greater than 10A, the important feeder circuit breaker 1 701 will immediately operate to open the circuit.

[0108] A specific implementation method, the important load branch 2 714 is provided with: an important feeder circuit breaker 2 711, an important feeder circuit integrated protection device 2 717 and an important feeder circuit zero-sequence current transformer 2 715 in sequence; the important feeder circuit integrated protection device 2 717 is respectively communicated with the important feeder circuit breaker 2 711 and the important feeder circuit zero-sequence current transformer 2 715; the important feeder circuit integrated protection device 1 707 is respectively connected to the protection device and the circuit breaker on the power supply incoming branch, and the connected power supply incoming branch is determined according to the circuit breaker opening signal on the power supply incoming branch, and the current on the corresponding power supply incoming branch is obtained through the protection device on the power supply incoming branch to realize the control of the important load branch.

[0109] The detailed description of the important load branch 2 714 is as follows:

[0110] Important feeder circuit breaker 2 711: It is a switch device in the circuit, connected to the entrance of the power supply bus 500 and the important load branch 2 714, and is used to control the on and off of the circuit. Important feeder circuit breaker 2 711 is connected to the important feeder circuit integrated protection device 2 717 in communication, which controls the switch action according to the operating status to ensure the power supply of the important load branch 2 714.

[0111] Important feeder circuit integrated protection device 2 717: used to protect the operation of important load branch 2 714, and can comprehensively detect faults such as overload and short circuit. Its input end receives the zero-sequence current signal from the important feeder circuit zero-sequence current transformer 2 715 to determine whether there is a ground fault, and at the same time controls the switching action of the important feeder circuit breaker 2 711 through communication to protect the normal operation of the important load branch 2 714.

[0112] Further, in the important load branch 2 714, the important feeder circuit integrated protection device 2 717 is also connected to the protection devices and circuit breakers on the power supply incoming branch 1 100 and the incoming branch 2 200. In this embodiment, the important load branch 2 714 is respectively connected to the bus incoming circuit breaker 1 106, the bus incoming circuit breaker 2 206, and the bus incoming circuit integrated protection device 1 107 and the bus incoming circuit integrated protection device 2 207;

[0113] Important feeder circuit zero-sequence current transformer 2 715: used to detect the zero-sequence current signal in the important load branch 2 714 to identify whether there is a ground fault. Its output signal is transmitted to the important feeder circuit integrated protection device 2 717 for fault determination and protection action triggering.

[0114] When a ground fault occurs in the important load branch 2 714, the first threshold value Y1 is set to 5A, the second threshold value Y2 is set to 10A-15A, and the important feeder circuit integrated protection device 2 717 adopts the same fault protection control method of hierarchical control as the important feeder circuit integrated protection device 1 707, which will not be described in detail here;

[0115] Through the above configuration, the important load branch 2 714 can realize safe and reliable power supply from the power supply bus 500 to the important loads, and has comprehensive protection functions. When a ground fault or other abnormality occurs, the important feeder circuit integrated protection device 2 717 can cut off the important feeder circuit breaker 2 711 in time, thereby protecting the safe operation of the power supply system and important loads.

[0116] A further technical solution is to cut off the common load branch when the power is supplied through the power supply in the factory, and supply power to the important load branch separately; at the same time, when a ground fault occurs in the important load branch, the protection device of the important load branch does not operate, and only sends out an alarm signal;

[0117] Specifically, when the busbar incoming line circuit breaker 306 is closed, the ordinary feeder circuit breaker 1 601 and the ordinary feeder circuit breaker 2 611 are opened through the circuit breaker auxiliary contacts; the important load branch protection devices such as the important feeder circuit comprehensive protection device 1 and the important feeder circuit comprehensive protection device 2 717 obtain the closing of the busbar incoming line circuit breaker 306, and execute the control strategy of using the factory power supply:

[0118] When a ground fault occurs in the important load branch 704, the important feeder circuit integrated protection device 707 does not operate but only sends out an alarm signal.

[0119] In the above scheme, when all power sources outside the factory are lost, the generator 300 supplies power to the AC power distribution system inside the factory, and the AC power distribution system inside the factory should cut off the common feeder loop and only supply power to the important feeder loop. In order to ensure the continuity of power supply as much as possible, at this time, when a single-phase grounding fault occurs, the generator 300 adopts a high-resistance grounding method, which can reduce the fault current and keep the system running under the fault condition as much as possible.

[0120] The system of this embodiment adopts the protection mode of circuit breaker tripping, which can quickly cut off the fault. Although the fault current is increased, the fault time is shortened, thereby ensuring the safety of equipment and personnel. In this way, when different power sources are used, the ground fault protection of the AC power distribution system in the factory can be ensured to operate smoothly and reliably, and at the same time, the adverse effects of the fault on the factory power supply are minimized to protect personal safety.

[0121] Example 2

[0122] Based on Example 1, this embodiment provides a grounding protection method for a grounding protection system for power supply of multiple power supplies with different grounding modes based on Example 1, including a common load branch protection method and an important load branch protection method. The important load branch protection method performs hierarchical control on the switching of important load branches, which can be executed in a protection device configured in the important load branch, such as Figure 2 As shown, the following steps are included:

[0123] Step A1, setting thresholds for hierarchical control, including a first threshold Y1 and a second threshold Y2;

[0124] Step A2: a difference C between the zero-sequence current on the important load branch and the ground fault current detected on the incoming branch of the power supply during normal operation;

[0125] Step A3: When the difference C is not greater than the set first threshold value Y1, the protection device on the important load branch does not operate, and only an alarm signal may be issued;

[0126] Step A4: When the difference C is between the first threshold value Y1 and the second threshold value Y2, the circuit breaker trips after a set delay time to cut off the current important load branch;

[0127] Step A5: When the difference C is greater than the second threshold value Y2, the circuit breaker is tripped immediately to cut off the current important load branch;

[0128] Furthermore, when the off-site power supply is connected to the main transformer for power supply, a ground fault is detected in an important load branch, and the zero-sequence current on the important load branch is greater than the set first threshold value Y1, before performing hierarchical control, the neutral point grounding resistance switch is controlled to open;

[0129] Furthermore, the ordinary load branch protection method can be executed in a protection device configured in an important load branch, and the removal and input of the ordinary load branch can be controlled according to the magnitude of the zero-sequence current on the ordinary load branch. When the ground fault current is greater than the set zero-sequence protection action current setting, the ordinary feeder loop circuit breaker is controlled to operate and open, and directly remove the current.

[0130] Furthermore, protection devices are respectively provided on the power supply incoming branch, the load branch and the power supply bus, and the setting method of the setting value is:

[0131] The load branch is used as the final feeder line circuit, and the zero-sequence protection action current setting value set in the protection device is between 5 and 30A;

[0132] On the incoming branch and the power supply busbar as the upper level line of the load branch, the zero-sequence protection action current setting value of the protection device is 2 to 5 times the zero-sequence protection action current setting value of the load branch;

[0133] After the load branch detects a fault, if the time difference exceeds the set time difference, it will not act, and the incoming branch of the upper level will act to remove the fault. The time difference can be set to 0.1 second to 0.3 second.

[0134] Specifically, the protection device of the incoming branch and the protection device of the load branch can establish a communication connection through high-speed Ethernet, and transmit data through the data bus. When the protection device of the load branch and the integrated protection device of the bus incoming line circuit of the incoming branch detect the ground fault current at the same time, the integrated protection device of the bus incoming line circuit will not operate within 0.3 seconds to 0.5 seconds. When the time exceeds 0.5 seconds, and the integrated protection device of the bus incoming line circuit can still detect the ground fault current, the protection device will operate. This ensures that when a ground fault occurs in the feeder circuit, only the circuit where the fault occurs is cut off. If the protection device fails and the fault cannot be cut off, the integrated protection device of the bus incoming line circuit will operate to cut off the fault and ensure the stability of the power supply system.

[0135] The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. For those skilled in the art, the present disclosure may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

[0136] Although the above describes the specific implementation methods of the present disclosure in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present disclosure. Technical personnel in the relevant field should understand that on the basis of the technical solution of the present disclosure, various modifications or variations that can be made by those skilled in the art without creative work are still within the scope of protection of the present disclosure.

Claims

1. A grounding protection system powered by multiple power supplies with different grounding modes, including multiple off-site power supplies and in-plant generators, characterized by: Each power supply incoming branch and load branch is provided with a protective device and a current transformer respectively; A protection device and a bus voltage transformer are provided on the power supply bus; The neutral point of the low-voltage side of the main transformer connected to the off-site power supply is grounded through a grounding resistor, and a neutral point grounding resistance switch is installed on the grounding line; The protection device on the load branch is electrically connected to the neutral point grounding resistance switch and is used to control the action of the neutral point grounding resistance switch.

2. The grounding protection system for power supply of multiple power supplies with different grounding modes as claimed in claim 1, characterized in that: When the power supply outside the factory is connected to the power supply bus in the factory through the main transformer, the power supply incoming line circuit breaker 1, the main transformer and the bus incoming line circuit breaker 1 are connected in series in sequence on the incoming line branch, the neutral point of the main transformer is grounded by a grounding resistor, and the grounding line is connected in series with a neutral point grounding resistor switch, a neutral point current transformer and a neutral point grounding resistor 1; it also includes a bus incoming line circuit integrated protection device 1, which is respectively connected to the neutral point current transformer and the bus incoming line circuit breaker 1; Alternatively, when the power supply outside the factory is directly connected to the power supply, the incoming branch is connected with a second power incoming circuit breaker, a second zero-sequence current transformer and a second bus incoming circuit breaker in sequence; a second bus incoming circuit integrated protection device is also provided, which is respectively connected with the second zero-sequence current transformer and the second bus incoming circuit breaker; Alternatively, the factory is powered by a self-provided generator, which is grounded through a neutral point grounding resistor 2; the branch line connecting the generator to the power supply bus is connected in sequence with a power supply incoming line circuit breaker 3, a zero-sequence current transformer 3 and a bus incoming line circuit breaker 3, and a bus incoming line circuit integrated protection device 3 is also provided, and the bus incoming line circuit integrated protection device 3 is respectively connected to the zero-sequence current transformer 3 and the bus incoming line circuit breaker 3.

3. The grounding protection system for power supply of multiple power supplies with different grounding modes as claimed in claim 1, characterized in that: Load branches include common load branches and important load branches; The protection device on the common load branch controls the removal and input of the common load branch according to the magnitude of the zero-sequence current on the load branch; The protection device on the important load branch is communicated with the protection device installed on the incoming branch. When the power is supplied by the external power supply, the switching of the important load branches is controlled in stages according to the difference between the zero-sequence current on the load branch and the ground fault current detected on the incoming branch of the power supply.

4. The grounding protection system for power supply of multiple power supplies with different grounding modes as claimed in claim 3, characterized in that: The switching of important load branches is controlled in stages, including the following steps: Setting thresholds for hierarchical control, including a first threshold Y1 and a second threshold Y2; The difference C between the zero-sequence current on the important load branch and the ground fault current detected on the incoming branch of the power supply during normal operation; When the difference C is not greater than the set first threshold value Y1, the protection device on the important load branch will not operate and an alarm signal will be issued; When the difference C is between the first threshold value Y1 and the second threshold value Y2, the circuit breaker trips after a set delay time, cutting off the current important load branch; When the difference C is greater than the second threshold value Y2, the circuit breaker is tripped immediately to cut off the current important load branch.

5. The grounding protection system for power supply of multiple power supplies with different grounding modes as claimed in claim 4, characterized in that: When the off-site power supply is connected to the main transformer for power supply, when a grounding fault is detected in an important load branch and the zero-sequence current on the important load branch is greater than the set first threshold value Y1, the neutral point grounding resistance switch is controlled to open.

6. The grounding protection system for power supply of multiple power supplies with different grounding modes as claimed in claim 3, characterized in that: Each important load branch includes an important feeder circuit breaker, an important feeder circuit integrated protection device, and an important feeder circuit zero-sequence current transformer connected in sequence; the important feeder circuit integrated protection device is respectively connected to the important feeder circuit breaker and the important feeder circuit zero-sequence current transformer in communication; and the important feeder circuit integrated protection device is connected to the protection device on the power supply incoming branch in communication; Alternatively, each ordinary load branch includes an ordinary feeder circuit breaker, an ordinary feeder circuit integrated protection device and an ordinary feeder circuit zero-sequence current transformer connected in sequence; the ordinary feeder circuit integrated protection device is respectively communicated with the ordinary feeder circuit breaker and the ordinary feeder circuit zero-sequence current transformer on the ordinary load branch.

7. A grounding protection method for a grounding protection system for power supply of multiple power supplies with different grounding modes according to any one of claims 1 to 6, comprising a common load branch protection method and an important load branch protection method, characterized in that: The important load branch protection method performs hierarchical control on the switching of important load branches, including the following steps: Setting thresholds for hierarchical control, including a first threshold Y1 and a second threshold Y2; The difference C between the zero-sequence current on the important load branch and the ground fault current detected on the incoming branch of the power supply during normal operation; When the difference C is not greater than the set first threshold value Y1, the protection device on the important load branch will not operate and an alarm signal will be issued; When the difference C is between the first threshold value Y1 and the second threshold value Y2, the circuit breaker trips after a set delay time, cutting off the current important load branch; When the difference C is greater than the second threshold value Y2, the circuit breaker is tripped immediately to cut off the current important load branch.

8. The grounding protection method according to any one of claims 7, characterized in that: When the off-site power supply is connected to the main transformer, a ground fault is detected in an important load branch, and the zero-sequence current on the important load branch is greater than the set first threshold Y1. Before performing hierarchical control, the neutral point grounding resistance switch is controlled to open.

9. The grounding protection method according to any one of claims 7, characterized in that: The ordinary load branch protection method controls the removal and input of the ordinary load branch according to the size of the zero-sequence current on the ordinary load branch. When the ground fault current is greater than the set zero-sequence protection action current setting, the ordinary feeder circuit breaker is controlled to operate and open, and the load is directly removed.

10. The grounding protection method according to any one of claims 7, characterized in that: Protection devices are respectively installed on the power supply incoming branch, load branch and power supply busbar, and the setting value is set as follows: The load branch is used as the final feeder line circuit, and the zero-sequence protection action current setting value set in the protection device is between 5 and 30A; On the incoming branch and the power supply busbar as the upper level line of the load branch, the zero-sequence protection action current setting value of the protection device is 2 to 5 times the zero-sequence protection action current setting value of the load branch; After the load branch detects a fault and does not operate for a set time difference, the incoming branch at the upper level will operate to eliminate the fault.

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