A medium and low voltage DC distribution network busbar protection system and method

Abstract

The present invention discloses a busbar protection system and method for medium and low voltage DC distribution networks. In the system, a first DC current transformer is arranged on the DC bus incoming line DC switch side; a second DC current transformer is arranged near the DC bus, through which the incoming line passes in the forward direction and through which one or more outgoing lines pass in the reverse direction; the incoming line tripping output signal of the DC busbar protection device is connected to the incoming line switch opening input terminal, and the outgoing line tripping output signal is connected to the opening input terminal of each outgoing line switch. This technical solution can realize rapid detection, positioning and isolation of busbar faults in a DC power distribution system, and can locate and isolate busbar faults when they just occur and have not yet reached a steady state, and does not require communication between adjacent areas, nor does it require the current of each line on the DC busbar to be collected, thereby reducing the configuration cost and requiring relatively low processing and computing capabilities of the system, thereby improving the overall reliability and rapidity of the DC power distribution system.

Description

Technical Field

[0001] The present invention belongs to the technical field of direct current distribution of electric power systems, and in particular relates to a busbar protection system and a protection method for a medium- and low-voltage direct current distribution network system of 20 kV or below. Background Art

[0002] With the increase in domestic urban electricity demand and the increasing proportion of distributed power sources and DC loads, traditional AC distribution networks are increasingly unable to meet the needs of economical access to distributed power sources and DC loads, further increasing the power supply radius, and increasing power supply capacity. At the same time, DC distribution networks have become a hot topic in academic research in recent years due to their advantages such as good controllability, convenient access to renewable energy, high power transmission quality, large power supply radius and transmission power.

[0003] The DC power distribution system is very different from the AC system, and the fault has its own characteristics. When the DC system, especially the busbar, is grounded or short-circuited, the fault current rises rapidly, which can cause serious damage to the system equipment in a very short time. This requires that the DC protection should be able to detect the fault in microseconds and quickly locate and isolate the fault. At present, the scheme of DC distribution network busbar protection is still in the theoretical research stage. Common protection methods are:

[0004] (1) Following the AC protection scheme, the DC bus voltage and the current of each line on the bus are collected, and conventional overcurrent, over / undervoltage, differential and other protection schemes are used.

[0005] (2) Following the subway DC protection scheme, current change rate protection is adopted. For example, patent CN201210357913.X discloses a current change rate method suitable for urban rail transit.

[0006] (3) Patent CN201710070114.7 discloses using DC circuit breakers and busbars to divide the DC distribution network into regions, determine the direction of the fault current in each region, and then exchange information to ultimately determine the fault type and eliminate the fault.

[0007] (4) Patent CN200810234059.1 discloses combining DC bus voltage detection to determine whether the DC bus voltage decreases while the DC current increases, so as to distinguish between faults and interference or noise.

[0008] The above method has certain limitations:

[0009] Method (1) requires the protection device to collect bus voltage and current of multiple lines. Due to the characteristics of DC fault current rising rapidly and requiring fault detection in microseconds and fault removal in milliseconds or even microseconds, the protection device is required to complete the processing and analysis of multiple voltage and current signals in a shorter time, which places very high demands on the device processing capacity. However, the current conventional AC protection action time is generally more than 10ms, and the fault current generally reaches a stable value when the fault is removed. However, DC faults are expected to be cut off when the fault just occurs and before reaching a steady state. Therefore, conventional AC protection schemes are not suitable for fast DC protection. In addition, since the protection device can generally only collect the current and voltage on the secondary side, the collection of current of multiple lines will inevitably require the configuration of multiple current transformers. Since the DC fault current rises rapidly and is large, each transformer is required to have an extremely fast response time and a wide measurement range. The configuration of multiple transformers increases the operation and maintenance cost on the one hand, and on the other hand, there is a risk of misoperation or refusal of protection caused by inconsistent response time and dynamic range of each transformer.

[0010] Method (2) can quickly detect fault current and find faults when the fault current has not reached a stable value. It is suitable for operation modes with simple line structures and obvious step differences. However, since this method is not selective, it is difficult to accurately locate the fault point inside or outside the area for complex multi-input and multi-output medium and low voltage DC distribution buses.

[0011] Method (3) requires collecting fault currents in each area, determining the direction and exchanging information. In theory, the fault can be located and isolated. However, the article also points out that the current direction changes at the millisecond level and needs to be based on communication, which can only be done in adjacent areas.

[0012] Method (4) can effectively eliminate noise and interference signals, but it does not further discuss the DC current protection principle and how to distinguish between busbar faults inside and outside the zone. Summary of the invention

[0013] The purpose of the present invention is to provide a busbar protection system and method for a medium and low voltage DC distribution network, which can realize rapid detection, positioning and isolation of busbar faults in a DC distribution system, and can locate and isolate the busbar fault just after it occurs and before it reaches a steady state, and does not require communication between adjacent areas, nor does it require the current of each line on the DC busbar to be collected, thereby reducing the configuration cost, and the requirements for the system's processing and computing capabilities are relatively low, which can improve the overall reliability and rapidity of the DC distribution system.

[0014] In order to achieve the above object, the solution of the present invention is:

[0015] A busbar protection system for a medium- and low-voltage DC distribution network comprises a first DC current transformer, a second DC current transformer, a DC busbar protection device, an incoming switch and an outgoing switch, wherein the first DC current transformer is arranged at the DC switch side of the incoming line of the DC busbar, the output signal of the DC current transformer is connected to the DC busbar protection device, and the protection device measures the incoming line current; the second DC current transformer is a through-type transformer, which is arranged near the DC busbar, the incoming line passes through the second DC current transformer in the forward direction, and one or more outgoing lines pass through the second DC current transformer in the reverse direction, the output signal of the second DC current transformer is connected to the DC busbar protection device, and the DC busbar protection device measures the differential current; the incoming line tripping output signal of the DC busbar protection device is connected to the incoming line switch opening input terminal, and the outgoing line tripping output signal is connected to the opening input terminals of each outgoing line switch.

[0016] The first DC current transformer adopts a current sensor with a wide measurement range, and the second DC current transformer adopts a current sensor with a high response speed.

[0017] A plurality of wire holes arranged in a regular equilateral shape are provided at the center of the second DC current transformer, and the direction of the wire holes is perpendicular to the plane of the second DC current transformer. The incoming and outgoing wires pass through the wire holes of the second DC current transformer, and a small section of the cable remains perpendicular to the plane of the second DC current transformer before and after passing through the second DC current transformer.

[0018] The above-mentioned DC bus protection device includes an acquisition module, a data processing module, a human-machine input module, a display module and an output module, wherein the acquisition module includes a first transformer data acquisition module and a second transformer data acquisition module, the acquisition module receives the output signals of the first and second DC current transformers, and then outputs the data to the data processing module; the data processing module includes a protection processing module and a human-machine interface processing module, the data processing module also receives data from the human-machine input module, and after the data is processed by the human-machine interface processing module and the protection processing module, the data to be displayed is transmitted to the display module, and the signal to be output is transmitted to the output module.

[0019] A method for protecting a busbar of a medium- and low-voltage DC distribution network comprises the following steps:

[0020] Step 1: Install a first DC current transformer on the DC switch side of the DC bus incoming line, connect the output signal of the first DC current transformer to the DC bus protection device, and the DC bus protection device measures the incoming line current;

[0021] Step 2: install a through-type second DC current transformer near the DC bus, so that the incoming line passes through the second DC current transformer in the forward direction, and one or more outgoing lines pass through the second DC current transformer in the reverse direction, and the output signal of the second DC current transformer is connected to the DC bus protection device, and the DC bus protection device measures the differential current;

[0022] Step 3, the DC bus protection device detects the transformer output signal in real time according to the output signals of the first and second DC current transformers connected. When it is detected that the second DC current transformer signal changes to exceed the threshold value, the main protection is activated to trip all incoming and outgoing line switches connected to the bus; when it is detected that the first DC current transformer signal exceeds the threshold value, the backup protection is activated to trip the incoming line switch.

[0023] In the above step 3, the main protection adopts the current change rate protection, and is provided with the main protection change rate start threshold value, the main protection overcurrent threshold value 1 and the main protection overcurrent threshold value 2; when any of the following main protection action conditions is met, the main protection is actuated:

[0024] First, after detecting that the current change rate of the output signal of the second DC current transformer is greater than the start threshold value of the current change rate of the main protection, the protection device enters the standby state, and after detecting that the current value of the output signal of the second DC current transformer is greater than the main protection overcurrent threshold value 1, the main protection is activated;

[0025] Article 2: After detecting that the current value of the output signal of the second DC current transformer is greater than k times the main protection overcurrent threshold value 2, the protection device enters the preparatory state. After detecting that the current value of the output signal of the second DC current transformer is greater than the main protection overcurrent threshold value 2, the main protection is activated, where k is a constant with a value range of 0.8 to 1.0.

[0026] In the above step 3, the backup protection of the DC bus protection device adopts overcurrent protection, and is provided with a backup protection change rate start threshold, a backup protection overcurrent threshold 1, a backup protection overcurrent threshold 2, a time threshold 1 and a time threshold 2; when any of the following backup protection action conditions is met, the backup protection is actuated:

[0027] First, after detecting that the current change rate of the output signal of the first DC current transformer is greater than the backup protection current change rate start threshold value, the protection device enters the standby state, and after detecting that the current value of the output signal of the first DC current transformer is greater than the backup protection overcurrent threshold value 1, the backup protection is actuated after the delay time threshold value 1;

[0028] Article 2: After detecting that the current value of the output signal of the first DC current transformer is greater than k times the backup protection overcurrent threshold value 2, the protection device enters the standby state. After detecting that the current value of the output signal of the first DC current transformer is greater than the overcurrent threshold value 2, the backup protection is activated after the delay time threshold value 2, where k is a constant with a value range of 0.8 to 1.0.

[0029] In the above step 3, the DC bus protection device processes data in multiple levels of interruption.

[0030] The above DC bus protection device uses a solid-state relay when it is activated.

[0031] After adopting the above scheme, since the second DC current transformer of the present invention obtains the differential current of the current flowing into and out of the bus, the differential current is very small when there is a fault outside the zone, and the differential current is very large when there is a fault inside the zone. Therefore, the protection device can realize fault location and isolation, and does not require communication between adjacent areas, nor does it need to collect the current of each line on the DC bus, which reduces the configuration cost and has relatively low requirements on the processing and computing power of the device, which can improve the overall reliability and rapidity of the bus protection of the DC distribution system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the wiring of busbars, input / output lines, DC transformers and switches according to an embodiment of the present invention;

[0033] Figure 2 is a schematic diagram of the arrangement of cables and a DC current transformer 2 according to an embodiment of the present invention;

[0034] Figure 3 1 is a schematic structural diagram of a DC bus protection device according to an embodiment of the present invention;

[0035] Figure 4 is a schematic diagram of a curve showing changes of current and current change rate over time during a fault in an embodiment of the present invention;

[0036] Figure 5 It is a logical diagram of the main protection and backup protection actions in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The technical solutions and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0038] like Figure 1 As shown, the present invention provides a medium and low voltage DC distribution network bus protection system, including a DC current transformer 1, a DC current transformer 2, a DC bus protection device, an incoming switch and an outgoing switch, which are respectively introduced below.

[0039] The DC current transformer 1 is arranged on the DC switch side of the DC bus incoming line, and the output signal of the DC current transformer 1 is connected to the DC bus protection device (hereinafter referred to as the protection device), and the protection device measures the incoming line current;

[0040] The signal collected by the DC current transformer 1 is used as backup protection for the bus protection device. In case the fault inside or outside the zone is not removed in time, the protection device can also trip the incoming line according to the signal provided by the DC current transformer 1 to prevent the accident from expanding. When a DC line or bus fails, if the fault is not removed in time, the fault current is often very large, and the signal collected by the DC current transformer 1 is used as backup protection. When the backup protection is to be activated, the fault current is generally close to a larger steady-state value. In order to prevent the DC current transformer 1 from saturating at high current, the DC current transformer 1 uses a current sensor with a wide measurement range, such as a wide-range open-loop Hall current sensor.

[0041] The DC current transformer 2 is a through-type transformer, which is arranged near the DC busbar. The incoming line passes through the transformer in the forward direction, and one or more outgoing lines pass through the transformer in the reverse direction. The output signal of the DC current transformer 2 is connected to the protection device, and the protection device measures the differential current.

[0042] In order to facilitate installation, reduce the impact of unbalanced current, and improve the accuracy of differential current collection, the center of the DC current transformer 2 has multiple wire holes arranged in a regular equilateral shape. Figure 2 As shown, the direction of the wire hole is perpendicular to the plane of the transformer, and the incoming and outgoing wires pass through the wire hole of the transformer. A small section of the cable is perpendicular to the plane of the transformer before and after passing through the transformer. Since the cable passes through the wire hole in the center of the transformer, this solution can prevent the insulation distance and heat dissipation of the cables from being affected by contact with each other when passing through the transformer.

[0043] When the DC bus operates normally or a bus fault occurs outside the bus area, the current flowing into and out of the DC bus is theoretically the same, and the differential current is basically 0 at this time. Since the DC current transformer 2 obtains the differential current of the current flowing into and out of the bus, that is, when the DC bus operates normally or a fault occurs outside the area, the current detected by the DC current transformer 2 is almost 0. When a fault occurs within the DC bus area, there will be a significant difference between the current flowing into and out of the DC bus, and there will be a large differential current. The DC current transformer 2 will detect a significant current change. Since the current rises rapidly when a DC bus fault occurs and the fault is often serious, in order to ensure that the bus protection device can quickly detect the fault current and trip the switch, the DC current transformer 2 must respond quickly. In order to ensure that the DC current transformer 2 has a fast response time and high sensitivity, the DC current transformer 2 needs to use a current sensor with a high response speed, such as a high-sensitivity giant magnetoresistance current sensor or a high-bandwidth closed-loop Hall current sensor.

[0044] The incoming line tripping output signal of the DC bus protection device is connected to the incoming line switch opening input terminal, and the outgoing line tripping output signal is connected to the opening input terminals of each outgoing line switch.

[0045] like Figure 3 As shown, the DC bus protection device includes an acquisition module, a data processing module, a human-machine input module, a display module and an output module, wherein the acquisition module includes a data acquisition module for transformer 1 and a data acquisition module for transformer 2; the data processing module includes a protection processing module and a human-machine interface processing module; the output module includes a protection action output module and other signal output modules; when working, the acquisition module receives the output signal of the external transformer (including DC current transformer 1 and DC current transformer 2), and then outputs the data to the data processing module, and the data processing module also receives the data from the human-machine input module, and after the data is processed by the human-machine interface processing module and the protection processing module, the data to be displayed is transmitted to the display module, and the signal to be output is transmitted to the output module.

[0046] The present invention also provides a method for protecting a busbar of a medium- and low-voltage DC distribution network, comprising the following steps:

[0047] Step 1: a DC current transformer 1 is configured on the DC switch side of the DC bus incoming line, and the output signal of the DC current transformer 1 is connected to a protection device, which measures the incoming line current.

[0048] Cooperate Figure 1 As shown, a DC current transformer 1 is arranged on the upper side of the DC incoming line switch. During installation, the incoming line is installed at the center of the transformer 1 as much as possible, and the cable and the plane of the transformer 1 are in a vertical position. At the same time, the transformer 1 adopts a current sensor with a wide measurement range, such as a wide-range open-loop Hall current sensor, to collect the incoming line current.

[0049] Step 2, all the input and output lines connected to the busbar are arranged in the order of input line inflow and output line outflow, and a through-type DC current transformer 2 is installed near the DC busbar;

[0050] Specifically, with Figure 2As shown, a through-type DC current transformer 2 is installed near the DC bus. For DC lines, generally each incoming line or outgoing line includes two wires, a positive pole and a negative pole. When detecting current, this embodiment only detects the current of the positive line. According to the mark on the transformer, the positive line cable of the incoming line passes through the transformer in the forward direction, and the positive line cable of one or more outgoing lines passes through the transformer in the reverse direction. The output signal of the DC current transformer 2 is connected to the protection device, and the protection device measures the differential current. The DC current transformer 2 uses a current sensor with a high response speed, such as a high-sensitivity giant magnetoresistance current sensor or a high-bandwidth closed-loop Hall current sensor. During installation, it is necessary to pay attention to the insulation distance and heat dissipation between the incoming and outgoing lines, and the incoming and outgoing lines should be installed at the center of the transformer as much as possible, and all cables should be perpendicular to the plane of the transformer when passing through the transformer.

[0051] Step 3, connecting the output signals of the DC current transformer 1 and the DC current transformer 2 to a DC bus protection device;

[0052] Specifically, the primary DC current in the incoming and outgoing lines is converted into receivable secondary side signals through the output devices of DC current transformer 1 and DC current transformer 2. These output signals are smaller DC voltages or DC currents or digital signals. The output signals of DC current transformer 1 and DC current transformer 2 are connected to the DC bus protection device. The DC bus protection device has a corresponding acquisition module to receive the signal. The data is then processed inside the protection device. At the same time, the tripping output signal of the DC bus protection device is connected to the tripping input terminals of the incoming switch and the outgoing switch, so that the corresponding switch can be tripped when the protection device is activated. Figure 3 As shown, the DC bus protection device consists of an acquisition module, a data processing module, a human-machine input module, a display module and an output module. The output signal of the transformer is a DC voltage or a DC current signal. After the DC signal is converted by the A / D inside the protection device, it enters the data processing module. The data processing module also receives instructions input by the human-machine input module, such as fixed value setting, screen switching, printing, etc. After processing the data, the data processing module transmits the results to the output module and the display module.

[0053] Step 4, the DC bus protection device detects the output signal of the transformer in real time according to the output signals of the connected DC current transformers 1 and 2. When it is detected that the signal change of transformer 2 exceeds the threshold value, the protection device is activated and all incoming and outgoing line switches connected to the bus are tripped; when it is detected that the signal of transformer 1 exceeds the threshold value, the bus protection device is activated and the incoming line switch is tripped.

[0054] The DC bus protection device has main protection and backup protection. The signal collected by DC current transformer 2 is used for the main protection of the bus protection device. When the main protection is activated, the incoming switch and the outgoing switch are tripped; the signal collected by DC current transformer 1 is used for the backup protection of the bus protection device. When the backup protection is activated, the incoming switch is tripped.

[0055] Specifically, the main protection means that when the DC bus protection device detects that the signal change of the DC current transformer 2 meets the pre-set action conditions, the DC bus protection device will be activated (main protection action) and all incoming and outgoing line switches connected to the bus will be tripped; the backup protection means that when the DC bus protection device detects that the signal change of the DC current transformer 1 meets the pre-set action conditions, the DC bus protection device will be activated (backup protection action) and the incoming line switch will be tripped. The backup protection prevents the fault inside or outside the zone from being removed in time. The protection device can also trip the incoming line according to the signal provided by the transformer 1 to prevent the accident from expanding.

[0056] After the protection device enters the preparatory state, the device starts to start the fault recording. Since the DC bus protection device detects the output signal of the transformer in real time and needs to complete the processing and analysis of each signal in a very short time, in order to ensure the overall reliability and rapidity of the bus protection of the DC power distribution system, each calculation interrupt processing time of the DC bus protection device needs to be very short. However, considering the wide application of medium and low voltage DC distribution networks in the future and the sensitivity to cost, in order to reduce calculation processing and resource consumption, the DC bus protection device processes data in multiple levels of interruption, wherein the sampling interrupt time of the protection processing module is typically 0.01ms, 0.02ms, 0.05ms or 0.1ms, and the processing calculations of the main protection and backup protection are completed within the protection sampling interruption to ensure fast and reliable. The interrupt processing time of the human-machine interface processing module is typically 5ms, 10ms or 20ms. Figure 3 In the data processing module, two interrupt times are set. One interrupt time is 0.02ms, which is used for processing the data required for the main protection and backup protection and the protection logic, and the other interrupt time is 10ms, which is used for human-machine interface processing such as display and message.

[0057] If a DC line or bus fails to be cleared in time when a fault occurs, the fault current will often be very large. The signal collected by the DC current transformer 1 is used as backup protection. When the backup protection is to be activated, the fault current is generally close to a larger steady-state value. In order to prevent the DC current transformer 1 from saturating at high currents, the DC current transformer 1 adopts a current sensor with a wide measurement range, such as a wide-range open-loop Hall current sensor.

[0058] In order to quickly and reliably detect faults inside and outside the zone, the main protection of the DC bus protection device adopts current change rate protection, including main protection change rate start threshold value, main protection overcurrent threshold value 1, and main protection overcurrent threshold value 2. There are two main protection action conditions. When any one of them is met, the main protection will act:

[0059] (1) After detecting that the current change rate of the output signal of the DC current transformer 2 is greater than the main protection current change rate start threshold value, the protection device enters the standby state. After detecting that the current value of the output signal of the DC current transformer 2 is greater than the main protection overcurrent threshold value 1, the main protection is activated;

[0060] (2) It is detected that the output signal current value of DC current transformer 2 is greater than k (k is a constant with a value range of 0.8 to 1.0, Figure 4 When k is 0.95) times the main protection overcurrent threshold value 2, the protection device enters the standby state. After detecting that the output signal current value of DC current transformer 2 is greater than the main protection overcurrent threshold value 2, the main protection is activated and the incoming and outgoing line switches are tripped.

[0061] The backup protection of the DC bus protection device adopts overcurrent protection, including the backup protection change rate start threshold, backup protection overcurrent threshold 1, backup protection overcurrent threshold 2, time threshold 1, time threshold 2. There are also two backup protection action conditions. The backup protection will be activated when any one of them is met:

[0062] (1) After detecting that the current change rate of the output signal of the DC current transformer 1 is greater than the backup protection current change rate start threshold value, the protection device enters the standby state. After detecting that the current value of the output signal of the DC current transformer 1 is greater than the backup protection overcurrent threshold value 1, after a delay ( Figure 4 As the time threshold value 1 fixed value) backup protection action, the incoming line switch is tripped;

[0063] (2) It is detected that the output signal current value of DC current transformer 1 is greater than k (k is a constant with a value range of 0.8 to 1.0, Figure 5 k is 0.95) times the backup protection overcurrent threshold value 2, the protection device enters the standby state, and after detecting that the output signal current value of the DC current transformer 1 is greater than the overcurrent threshold value 2, after a delay ( Figure 5 As the time threshold value 2 fixed value) backup protection action, the incoming line switch is tripped.

[0064] Figure 4A schematic diagram of the curve of the current and current change rate of the output signal of the DC current transformer 1 or the DC current transformer 2 changing with time during a fault is listed. In the figure, t1 is the moment when the fault just occurs, t2 is the moment when the current change rate of the DC current transformer output signal is greater than the corresponding main protection or backup protection change rate start threshold value, t3 is the moment when the current of the DC current transformer output signal is greater than the corresponding main protection or backup protection overcurrent threshold value 1, t4 is the moment when the current of the DC current transformer output signal is greater than the corresponding main protection or backup protection overcurrent threshold value 2, and t5 is the moment when the current of the DC current transformer output signal reaches a steady state when the fault is not cleared.

[0065] Figure 5 In the figure, I1 represents the current of the output signal of DC current transformer 1, and I2 represents the current of the output signal of DC current transformer 2. After the protection device enters the preparatory state, the device starts to start the fault recording. In this embodiment, k in the main and backup protection is set to 0.95.

[0066] like Figure 5 As shown, a logical schematic diagram of the current change rate protection curve is listed, wherein the main protection at transformer 1 is that when it is detected that the current change rate of transformer 1 is greater than the starting threshold value of the current rise rate of transformer 1, the protection device enters the preparatory state, and when it is detected that the current value of transformer 1 is greater than the current action threshold value of the change rate of transformer 1, the protection is activated after a delay of transformer 1 time threshold value 1, and the incoming line switch is tripped; the backup protection at transformer 1 is that when it is detected that the current of transformer 1 is greater than 0.95 times the overcurrent threshold value of transformer 1, the protection device enters the preparatory state, and when the current value is greater than the overcurrent of transformer 1, the protection is activated after a delay of transformer 1 time threshold value 2, and the incoming line switch is tripped.

[0067] The main protection at transformer 2 is that when it is detected that the current change rate of transformer 2 is greater than the starting threshold value of the current rise rate of transformer 2, the protection device enters the preparatory state. When it is detected that the current value of transformer 2 is greater than the current action threshold value of the change rate of transformer 2, since the time threshold value of transformer 2 is 0, the protection is immediately activated and the incoming and outgoing switches are tripped; the backup protection at transformer 2 is that when it is detected that the current of transformer 2 is greater than 0.95 times the overcurrent threshold value of transformer 2, the protection device enters the preparatory state. When the current value is greater than the overcurrent of collector 2, since the time threshold value of transformer 2 is 0, the protection is immediately activated and the incoming and outgoing switches are tripped.

[0068] At the same time, in order to ensure that the DC bus protection device can quickly protect the output when a fault occurs while taking into account economy, the protection action output module in the output module of the DC bus protection device uses solid-state relays, typically IGBT relays, for fast jumping in and outgoing line switches; relays for non-tripping outputs such as alarm, lockout and other signal outputs use conventional electromagnetic relays. If other relays also have extremely high requirements for speed, solid-state relays can also be used. Figure 2 In the DC bus protection device, when the protection action is in progress, the IGBT output is used to trip the in-line and out-line switches. When the alarm, lockout and other signals are output, conventional relays are used to output other signals.

[0069] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A protection method for a busbar protection system of a medium and low voltage DC distribution network, characterized in that The steps include: Step 1: Install a first DC current transformer on the DC switch side of the DC bus incoming line, connect the output signal of the first DC current transformer to the DC bus protection device, and the DC bus protection device measures the incoming line current; Step 2: install a through-type second DC current transformer near the DC bus, so that the incoming line passes through the second DC current transformer in the forward direction, and one or more outgoing lines pass through the second DC current transformer in the reverse direction, and the output signal of the second DC current transformer is connected to the DC bus protection device, and the DC bus protection device measures the differential current; Step 3, the DC bus protection device detects the transformer output signal in real time according to the output signals of the first and second DC current transformers connected thereto. When it is detected that the second DC current transformer signal changes to exceed the threshold value, the main protection is activated to trip all incoming and outgoing line switches connected to the bus; when it is detected that the first DC current transformer signal exceeds the threshold value, the backup protection is activated to trip the incoming line switch; In step 3, the main protection adopts current change rate protection, and is provided with a main protection change rate start threshold value, a main protection overcurrent threshold value 1, and a main protection overcurrent threshold value 2; when any of the following main protection action conditions is met, the main protection is actuated: First, after detecting that the current change rate of the output signal of the second DC current transformer is greater than the start threshold value of the current change rate of the main protection, the protection device enters the standby state, and after detecting that the current value of the output signal of the second DC current transformer is greater than the main protection overcurrent threshold value 1, the main protection is activated; Article 2: After detecting that the current value of the output signal of the second DC current transformer is greater than k times the main protection overcurrent threshold value 2, the protection device enters the standby state, and after detecting that the current value of the output signal of the second DC current transformer is greater than the main protection overcurrent threshold value 2, the main protection is actuated, where k is a constant with a value range of 0.8 to 1.0; The medium and low voltage DC distribution network bus protection system comprises a first DC current transformer, a second DC current transformer, a DC bus protection device, an incoming switch and an outgoing switch, wherein the first DC current transformer is arranged at the DC switch side of the incoming line of the DC bus, the output signal of the DC current transformer is connected to the DC bus protection device, and the protection device measures the incoming current; the second DC current transformer is a through-type transformer, which is arranged near the DC bus, the incoming line passes through the second DC current transformer in the forward direction, and one or more outgoing lines pass through the second DC current transformer in the reverse direction, the output signal of the second DC current transformer is connected to the DC bus protection device, and the DC bus protection device measures the differential current; the incoming line tripping output signal of the DC bus protection device is connected to the incoming line switch opening input terminal, and the outgoing line tripping output signal is connected to the opening input terminals of each outgoing line switch.

2. The protection method of a medium and low voltage DC distribution network busbar protection system according to claim 1, characterized in that: The first DC current transformer adopts a current sensor with a wide measurement range, and the second DC current transformer adopts a current sensor with a high response speed.

3. The protection method of a medium and low voltage DC distribution network busbar protection system according to claim 1, characterized in that: The center of the second DC current transformer is provided with a plurality of wire holes arranged in a regular equilateral shape, the direction of the wire holes is perpendicular to the plane of the second DC current transformer, the incoming and outgoing lines pass through the wire holes of the second DC current transformer, and a small section of the cable is kept perpendicular to the plane of the second DC current transformer before and after passing through the second DC current transformer.

4. The protection method of a medium and low voltage DC distribution network busbar protection system according to claim 1, characterized in that: The DC bus protection device includes an acquisition module, a data processing module, a human-machine input module, a display module and an output module, wherein the acquisition module includes a first transformer data acquisition module and a second transformer data acquisition module, the acquisition module receives the output signals of the first and second DC current transformers, and then outputs the data to the data processing module; the data processing module includes a protection processing module and a human-machine interface processing module, the data processing module also receives data from the human-machine input module, and after the data is processed by the human-machine interface processing module and the protection processing module, the data to be displayed is transmitted to the display module, and the signal to be output is transmitted to the output module.

5. The protection method of a medium and low voltage DC distribution network busbar protection system according to claim 1, characterized in that: In step 3, the backup protection of the DC bus protection device adopts overcurrent protection, and is provided with a backup protection change rate start threshold, a backup protection overcurrent threshold 1, a backup protection overcurrent threshold 2, a time threshold 1 and a time threshold 2; when any of the following backup protection action conditions is met, the backup protection is actuated: First, after detecting that the current change rate of the output signal of the first DC current transformer is greater than the backup protection current change rate start threshold value, the protection device enters the standby state, and after detecting that the current value of the output signal of the first DC current transformer is greater than the backup protection overcurrent threshold value 1, the backup protection is actuated after the delay time threshold value 1; Article 2: After detecting that the current value of the output signal of the first DC current transformer is greater than k times the backup protection overcurrent threshold value 2, the protection device enters the standby state. After detecting that the current value of the output signal of the first DC current transformer is greater than the overcurrent threshold value 2, the backup protection is activated after the delay time threshold value 2, where k is a constant with a value range of 0.8 to 1.

0.

6. The protection method of a medium and low voltage DC distribution network busbar protection system according to claim 1, characterized in that: In step 3, the DC bus protection device processes data in multiple levels of interruption.

7. The protection method of a medium and low voltage DC distribution network busbar protection system according to claim 1, characterized in that: The DC bus protection device uses a solid-state relay when it is activated.

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