A method and device for finding AC inrush fault in a DC power supply system

Abstract

The present invention provides a method and device for finding an AC intrusion fault in a DC power supply system, wherein the device includes a host and a clamp meter, the host is connected to the bus of the DC power supply system, and sends a fault finding signal to the bus; when an AC intrusion fault occurs in a feeder branch, the feeder switch of the branch is disconnected, cutting off the connection between the branch and the bus, and the host provides voltage to the feeder branch where the AC intrusion fault occurs alone. The clamp meter is used to detect the specific fault point on the faulty feeder branch. The present invention can force the feeder branch with the AC intrusion fault to be separated from the bus of the DC power supply system through manual or automatic mode, and then conduct a specific fault point investigation, thereby avoiding the AC intrusion fault from affecting other normal feeder branches, reducing the further spread of the fault range, and improving the safety of the DC system operation.

Description

Technical Field

[0001] The invention belongs to the technical field of power grid fault detection, and in particular relates to an AC inrush fault detection device for a DC power supply system. Background Art

[0002] The insulation condition of the DC system has a direct impact on the stability and reliability of the DC power supply system. Insulation failure will cause protection malfunction or refusal to operate. In the power system, AC intrusion fault is a kind of insulation fault that is easy to occur and very harmful to the power system. Whether the positive pole of the DC power supply system intrudes into AC or the negative pole intrudes into AC, it may cause protection malfunction or refusal to operate, endangering the normal operation of the primary system. At present, the phenomenon of AC intrusion into the DC system in substations occurs from time to time. The cause of the fault is complicated and it is very difficult to find and judge, which seriously affects the safe operation of the power grid.

[0003] The main reasons for AC inrush faults are: ① Operational errors by on-site personnel: Due to the staff's unfamiliarity with the on-site conditions, lack of professional skills, and relaxed thinking, the AC power may be connected to the DC circuit; ② Cable or equipment insulation damage: Since the on-site AC cables and DC cables are mostly in the same bridge, if the cable insulation is damaged or degraded, and the insulation of the electrical equipment is damaged, the conductors of the AC and DC cables will be interconnected; ③ The impact of the DC system's capacitance to ground: The DC system's capacitance to ground includes the distributed capacitance of long-distance cables to the ground and the anti-interference filter capacitor introduced by the system. Due to the existence of distributed capacitance, if the AC and DC cables are close, the AC power will discharge to the DC cable through the distributed capacitance; ④ Natural disasters: Due to natural reasons, the outdoor power supply operation box may be flooded or have a large amount of conductive dust, which will further cause electrical connection between the AC terminal and the DC terminal.

[0004] In the prior art, when detecting the AC intrusion fault point, all feeder branches need to be powered off for inspection, which affects the normal branch operation. In order to eliminate the impact of AC intrusion on the safe operation of DC and increase the safety factor of power system operation, it is necessary to improve the prior art. Summary of the invention

[0005] The purpose of the present invention is to provide a method and device for finding AC inrush faults in a DC power supply system, which can solve the problem in the prior art that power outages are required to detect AC inrush fault points, affecting the safe operation of the DC system.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for finding an AC inrush fault in a DC power supply system, comprising the following steps:

[0008] The host is connected to the busbar of the DC power supply system and sends fault finding signals to each feeder branch through the busbar;

[0009] When an AC inrush fault occurs in a feeder branch, the host provides voltage to the feeder branch where the AC inrush fault occurs.

[0010] The ground of the host is at the same potential as the ground of the AC inrush fault point. The AC inrush signal generates a loop between the fault point and the host, generating a short-circuit current in the feeder branch where the AC inrush fault occurs. The short-circuit current disconnects the feeder switch of the feeder branch where the AC inrush fault occurs.

[0011] The fault finding signal sent by the host flows back to the host through the loop;

[0012] The clamp meter is connected successively to different positions of the feeder branch where the AC inrush fault occurs. Each position is a detection point. Each detection point is detected to see if there is a fault finding signal. The AC inrush fault point is between the adjacent detection points with fault finding signals and the detection points without fault finding signals.

[0013] Furthermore, the AC inrush fault detection method for the DC power supply system also includes an alarm step: the host detects the bus voltage to ground and the inrush AC voltage, and when the bus voltage to ground and the inrush AC voltage exceed the alarm threshold value, the host emits an audible and visual alarm and displays an alarm message.

[0014] In a second aspect, the present invention provides an AC intrusion fault finding device for a DC power supply system, comprising a host and a clamp meter, wherein the host comprises a main control unit, and respectively connected to the main control unit:

[0015] Disconnect bus control unit: It is electrically connected to the bus of the DC power supply system, receives control instructions from the main control unit, and controls the feeder branch with AC inrush fault to be disconnected from the bus;

[0016] Bus sampling unit: electrically connected to the bus, used to sample the voltage signal of the bus to the ground;

[0017] Test power supply unit: used to provide backup power to the feeder branch with AC inrush fault;

[0018] AC sampling unit: electrically connected to the busbar, used to sample the incoming AC voltage signal and convert it into a digital signal;

[0019] Signal sending unit: receives the signal sending instruction from the main control unit and is responsible for sending the fault finding signal to the DC power supply system;

[0020] Communication unit: communicate with the clamp meter to realize data transmission;

[0021] Alarm unit: When the bus-to-ground voltage or AC inrush voltage data of the DC power system is abnormal and exceeds the alarm threshold, an audible and visual alarm is issued;

[0022] Display unit: real-time display of busbar-to-ground voltage, incoming AC voltage data and alarm signals;

[0023] The clamp meter is used to detect fault points.

[0024] Further, the disconnected bus control unit includes a first normally open switch K1, a second normally open switch K2, a first intermediate relay KA1, a second intermediate relay KA2, a first contactor KM1, a second contactor KM2, a first diode D1, a second diode D2 and a current limiting resistor R;

[0025] One end of the first normally open switch K1, one end of the second normally open switch K2, one end of the normally open switch of the first intermediate relay KA1, one end of the normally open switch of the second intermediate relay KA2 and one end of the normally open switch of the first contactor KM1 are connected to the positive bus +KM;

[0026] One end of the coil of the first intermediate relay KA1, one end of the coil of the second intermediate relay KA2, one end of the coil of the first contactor KM1, one end of the coil of the second contactor KM2, and one end of the normally open switch of the second contactor KM2 are connected to the negative bus -KM;

[0027] The other end of the first normally open switch K1 is connected to the other end of the coil of the first intermediate relay KA1; the other end of the second normally open switch K2 is connected to the other end of the coil of the second intermediate relay KA2; the other end of the normally open switch of the first intermediate relay KA1 is connected to one end of the normally closed switch of the second contactor KM2, and the other end of the normally closed switch of the second contactor KM2 is connected to the other end of the coil of the first contactor KM1; the other end of the normally open switch of the second intermediate relay KA2 is connected to one end of the normally closed switch of the first contactor KM1, and the other end of the normally closed switch of the first contactor KM1 is connected to the other end of the coil of the second contactor KM2; the other end of the normally open switch of the first contactor KM1 is connected to the cathode of the first diode D1, and the other end of the normally open switch of the second contactor KM2 is connected to the anode of the second diode D2; the anode of the first diode D1 and the cathode of the second diode D2 are connected to one end of a current limiting resistor R, and the other end of the current limiting resistor R is connected to the ground of the host.

[0028] Furthermore, the test power supply unit includes a test power supply, a third diode D3, a fourth diode D4 and a DC output switch QF; the test power supply converts the AC voltage into a DC voltage, and the DC voltage passes through the third diode D3 and the fourth diode D4, and is output through the DC output switch QF to provide voltage for the feeder branch that sends the AC intrusion fault.

[0029] Further, the bus sampling unit includes a plurality of sampling resistors connected in series, one end of the plurality of sampling resistors connected in series is connected to the positive bus, and the other end is connected to the negative bus; there is a series node between two adjacent sampling resistors; the series node of the two middle sampling resistors is led out as a first sampling point, and a filter capacitor is connected in series between the remaining series nodes and the first sampling point; the two end points of the sampling resistors connected in series serve as a second sampling point and a third sampling point, and the voltage signal between the first sampling point and the second sampling point, or the voltage signal between the first sampling point and the third sampling point is a bus voltage sampling signal.

[0030] Furthermore, the sampling resistor is a resistor of megohm level.

[0031] Furthermore, the AC sampling unit includes a capacitor C1, an RC filter circuit, an optocoupler conversion circuit, an operational amplifier circuit and an output filter circuit which are sequentially connected in series.

[0032] The AC inrush fault finding device for a DC power supply system of the present invention can, in manual or automatic mode, force a feeder branch with an AC inrush fault to detach from the DC power supply system bus, and then conduct a specific fault point inspection, thereby avoiding the AC inrush fault from affecting other normal feeder branches, reducing the further spread of the fault range, and improving the safety of DC system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the application and installation of the AC intrusion fault finding device of the present invention;

[0034] Figure 2 It is a circuit principle block diagram of the host of the present invention;

[0035] Figure 3 It is a circuit principle block diagram of the clamp meter of the present invention;

[0036] Figure 4 The schematic diagram of the circuit of the busbar disconnecting control unit of the present invention;

[0037] Figure 5 A circuit diagram of a test power supply unit of the present invention;

[0038] Figure 6 It is a circuit principle diagram of the bus sampling unit of the present invention;

[0039] Figure 7 It is a circuit schematic diagram of the AC sampling unit of the present invention;

[0040] Figure 8 The present invention is a flowchart of the use of the AC intrusion fault finding device of the present invention. DETAILED DESCRIPTION

[0041] The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings.

[0042] The following describes the embodiments of the present disclosure through specific examples, and those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all of the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present disclosure.

[0043] The AC intrusion fault detection method of the DC power supply system of the present invention is implemented by a host and a clamp meter, and mainly includes the following steps:

[0044] The host is connected to the busbar of the DC power supply system, and a fault finding signal is sent to each feeder branch through the busbar; each feeder branch is connected to the busbar through a feeder switch;

[0045] When an AC inrush fault occurs in a feeder branch, the host provides voltage to the feeder branch where the AC inrush fault occurs.

[0046] The ground of the host is at the same potential as the ground of the AC inrush fault point. The AC inrush signal generates a loop between the fault point and the host, and the feeder branch generates a short-circuit current. The short-circuit current disconnects the feeder switch of the feeder branch, thereby disconnecting the faulty feeder branch from the busbar.

[0047] After a loop is generated between the feeder branch and the host, the fault finding signal sent by the host flows back to the host through the loop. The clamp meter is successively connected to different positions of the feeder branch where the AC intrusion fault occurs. Each position is a detection point. Each detection point is detected to see if there is a fault finding signal. The detection point with a fault finding signal and the detection point without a fault finding signal is the AC intrusion fault point.

[0048] Since the fault finding signal will flow in the loop generated between the fault point of the feeder branch and the host, the fault finding signal cannot be detected on the feeder branches other than the fault point. Under normal circumstances, the feeder switches on each feeder branch are closed. Only when an AC inrush fault occurs in a branch and a fault current is generated in the branch, the feeder switch of the feeder branch is disconnected.

[0049] Furthermore, the AC inrush fault detection method for a DC power supply system of the present invention also includes an alarm step: the host detects the bus voltage to ground and the inrush AC voltage. When the bus voltage to ground and the inrush AC voltage exceed the alarm threshold value, the host will emit an audible and visual alarm and display an alarm message.

[0050] The AC intrusion fault finding device of the DC power supply system of the present invention comprises a host and a clamp meter, wherein the host is connected to the busbar of the DC power supply system, and the clamp meter is used to find the fault line and the fault point. It mainly realizes three functions: AC measurement alarm function, AC intrusion fault finding function and AC intrusion fault branch disconnection busbar function;

[0051] AC measurement alarm function: responsible for detecting the bus-to-ground voltage and AC inrush voltage of the DC power supply, judging whether there is an AC inrush fault in the DC power supply system and its amplitude and polarity. When the bus-to-ground voltage and AC inrush voltage data of the DC power supply system are abnormal and exceed the alarm threshold, the host will issue an audible and visual alarm and display the alarm information.

[0052] AC intrusion fault finding function: responsible for sending fault finding signals to the DC power supply system, and tracking the fault finding signals of the faulty feeder branch with the use of the clamp meter. Since there is an AC intrusion fault in the feeder branch, the fault grounding point and the host grounding point are at the same potential to form a loop, so there will be a fault finding signal in the faulty branch. In this way, the feeder branch with AC intrusion fault is initially checked. Furthermore, after the AC intrusion fault branch is completely separated from the DC system, the final fault point is found.

[0053] AC inrush fault branch disconnect busbar function: responsible for disconnecting the AC inrush fault feeder branch from the DC power system busbar without power outage, and removing the impact of the fault on the DC system. The user can choose between manual and automatic modes, and by controlling the input of high-power diodes, the AC inrush fault branch generates a short-circuit current, causing the feeder switch to trip, and the host's test power supply is used to supply power to the branch load.

[0054] like Figure 2 As shown, the host includes a main control unit, a bus-disconnected control unit, a bus sampling unit, a test power supply unit, an AC sampling unit, a signal sending unit, a communication unit, an alarm unit and a display unit, wherein:

[0055] Main control unit: It is electrically connected to other units and is the system control center. It is responsible for data analysis, processing, fault judgment, and command sending and receiving, etc.

[0056] Disconnect bus control unit: electrically connected to the bus, receiving control instructions from the main control unit, and controlling the feeder branch with AC inrush fault to disconnect from the bus;

[0057] Bus sampling unit: electrically connected to the bus, used to sample the voltage signal of the DC power bus to the ground, divide the high voltage signal and then process the signal;

[0058] Test power supply unit: used to provide backup power to the feeder branch with AC inrush fault, to ensure that the load of the feeder branch does not lose power;

[0059] AC sampling unit: It is electrically connected to the busbar and is used to sample the incoming AC voltage signal. After a series of signal processing, it is converted into a digital signal that can be received by the AD converter.

[0060] Signal sending unit: receives the signal sending instruction from the main control unit and is responsible for sending the fault finding signal to the DC power supply system;

[0061] Communication unit: communicate with the clamp meter via GPRS to achieve data transmission;

[0062] Alarm unit: When the busbar-to-ground voltage and AC inrush voltage data of the DC power system are abnormal and exceed the alarm threshold, an audible and visual alarm is issued;

[0063] Display unit: Real-time display of busbar-to-ground voltage, incoming AC voltage data and alarm signals.

[0064] The host of the device is responsible for collecting signals such as the busbar voltage to ground and AC voltage, and after processing and analysis by the internal software and hardware of the device, it outputs the operating data such as the voltage to ground and AC voltage of the current DC power supply system, makes abnormal state judgments and issues alarms. Before the faulty feeder branch is disconnected from the busbar, a test power supply is added to the feeder load through an adapter on the terminal block, and its supply voltage is slightly lower than the DC system voltage.

[0065] The clamp meter of the present invention is as follows Figure 3 As shown, it includes a CPU, a signal sampling unit, a display unit and a communication unit. The CPU is responsible for executing operations, controlling time and processing data; the signal sampling unit is used to collect fault finding signals on the feeder branch; the display unit is used to display the waveform of the fault finding signal; the communication unit is responsible for transmitting the fault finding signal and the alarm signal to the host via GPRS.

[0066] Further, in a preferred embodiment of the present application, the busbar disconnection control unit includes a control circuit such as Figure 4As shown, the control circuit includes a first normally open switch K1, a second normally open switch K2, a first intermediate relay KA1, a second intermediate relay KA2, a first contactor KM1, a second contactor KM2, a first diode D1, a second diode D2 and a current limiting resistor R. The first intermediate relay KA1 includes a coil KA11 and a normally open switch KA12; the second intermediate relay KA2 includes a coil KA21 and a normally open switch KA22; the first contactor KM1 includes a coil KM11, a normally open switch KM12 and a normally closed switch KM13; the second contactor KM2 includes a coil KM21, a normally open switch KM22 and a normally closed switch KM23. +KM is the positive busbar, and -KM is the negative busbar. One end of the first normally open switch K1, one end of the second normally open switch K2, one end of the normally open switch of the first intermediate relay KA1, one end of the normally open switch of the second intermediate relay KA2 and one end of the normally open switch of the first contactor KM1 are connected to the positive bus +KM; one end of the coil of the first intermediate relay KA1, one end of the coil of the second intermediate relay KA2, one end of the coil of the first contactor KM1, one end of the coil of the second contactor KM2 and one end of the normally open switch of the second contactor KM2 are connected to the negative bus -KM. The other end of the first normally open switch K1 is connected to the other end of the coil of the first intermediate relay KA1; the other end of the second normally open switch K2 is connected to the other end of the coil of the second intermediate relay KA2; the other end of the normally open switch of the first intermediate relay KA1 is connected to one end of the normally closed switch of the second contactor KM2, and the other end of the normally closed switch of the second contactor KM2 is connected to the other end of the coil of the first contactor KM1; the other end of the normally open switch of the second intermediate relay KA2 is connected to one end of the normally closed switch of the first contactor KM1, and the other end of the normally closed switch of the first contactor KM1 is connected to the other end of the coil of the second contactor KM2; the other end of the normally open switch of the first contactor KM1 is connected to the cathode of the first diode D1, and the other end of the normally open switch of the second contactor KM2 is connected to the anode of the second diode D2; the anode of the first diode D1 and the cathode of the second diode D2 are connected to one end of a current limiting resistor R, and the other end of the current limiting resistor R is connected to the ground of the host.

[0067] Combination Figure 1 and Figure 4 The working principle of the control circuit is described as follows:

[0068] Switch K1 and switch K2 are normally open hard contacts, KA1 and KA2 are intermediate relays, KM1 and KM2 are contactors, R is a current limiting resistor, and D1 and D2 are high-power diodes. Figure 1As shown, suppose an AC inrush fault occurs in the nth feeder branch, and the fault point is at the negative pole of the nth feeder branch. The inrush AC will be transmitted along the negative pole of the nth feeder branch to the negative bus. At this time, the AC sampling unit of the host will collect the AC signal of the negative bus. The main control unit sends a high-level square wave pulse to K2, the K2 hard contact is closed, the KA2 intermediate relay coil is energized, and the normally open switch KA22 of KA2 is closed. As a result, the KM2 contactor coil KM21 is energized, the normally open switch KM22 of KM2 is closed, and the AC signal of the negative bus that is inrushed flows into the ground of the host through the normally open switch KM22 of KM2, the diode D2, and the current limiting resistor R. Due to the ground potential of the host and the fault point, a short circuit loop is formed between the fault point and the host. A short-circuit current is generated in the short-circuit loop, and the short-circuit current disconnects the feeder switch QFn on the nth feeder branch, thereby disconnecting the branch from the busbar and cutting off the AC source from the DC system. The AC fault branch is powered by the test power supply, realizing the function of disconnecting the AC fault branch from the busbar without power outage.

[0069] In addition, an interlocking circuit is designed between the KM1 and KM2 contactors. Only one contactor is allowed to close at the same time, that is, when KM1 is closed, KM2 is disconnected, and vice versa, when KM2 is closed, KM1 is disconnected. Continuing with the above example: KM2's normally open switch KM22 is closed, and KM2's normally closed switch KM23 is disconnected. At this time, even if KA1's normally open switch KA12 is closed, no current will flow through KM1's coil KM11. Therefore, when KM2 is closed, KM1 must be disconnected, and vice versa.

[0070] Further, in a preferred embodiment of the present application, the circuit schematic diagram of the test power supply unit is as follows: Figure 5 As shown, it includes a test power supply, a diode D3, a diode D4 and a DC output switch QF. Its principle is to convert AC / DC power from a single-phase AC voltage of 220V. When receiving an instruction to disconnect the bus function from the AC entering the fault branch, the DC output switch QF is controlled by the main control unit to close and output DC power to supply power to the fault branch load.

[0071] Further, in a preferred embodiment of the present application, the circuit schematic diagram of the bus sampling unit is as follows: Figure 6As shown, it includes several sampling resistors (R101 to R106) connected in series, one end of the several sampling resistors connected in series is connected to the positive bus, and the other end is connected to the negative bus. There is a series node between two adjacent sampling resistors. The series node of the two middle sampling resistors is led out as the first sampling point, and the filter capacitor (C101 to C104) is connected in series between the remaining series nodes and the first sampling point. The two end points of the sampling resistors connected in series serve as the second sampling point and the third sampling point, and the voltage signals between the first sampling point and the second sampling point, and between the first sampling point and the third sampling point are sampled, so that it can be determined whether the AC signal entering is on the positive bus or the negative bus.

[0072] The sampling resistor is a megohm-level resistor. The positive and negative voltage signals to the ground are divided and filtered through the corresponding positive and negative sampling resistors to output a voltage signal in the range of 0-3.3V. When an AC signal is injected, the voltage signal will fluctuate. When the fluctuation exceeds the alarm threshold, the alarm unit of the host will sound an alarm.

[0073] Further, in a preferred embodiment of the present application, the circuit schematic diagram of the AC sampling unit is as follows: Figure 7 As shown, it includes a capacitor C1, an RC filter circuit, an optocoupler conversion circuit, an operational amplifier circuit and an output filter circuit which are connected in series in sequence.

[0074] The AC voltage signal that enters is passed through the DC blocking capacitor C1 to obtain an AC voltage signal, and then is low-pass filtered through the RC filter circuit, and then enters the optocoupler conversion circuit composed of the AMC1200 optocoupler to perform electrical-optical-electrical conversion, and also plays a role in electrical isolation. The converted voltage signal is then amplified by the operational amplifier circuit, and finally a secondary RC filter is performed to obtain a digital signal that can be received by the final AD converter. The circuit sampling of the RC filter circuit, the optocoupler conversion circuit, the operational amplifier circuit, and the output filter circuit is implemented by the existing technology, which is not the focus of the present invention. The present invention does not limit the components and specific connection relationships of these circuits.

[0075] The AC intrusion fault finding device of the DC power supply system of the present invention is based on the following Figure 1 The busbar disconnection function of the present invention can be manually or automatically connected. After disconnection, the test power supply will immediately supply power to the load of the faulty feeder branch, so that the load can be safely transferred without power outage. Then, the host computer will track the fault search signal on the branch to find the final fault point and handle it in time. Figure 8 The specific usage process is as follows:

[0076] 1. Wiring method

[0077] (1) Use the test wire to connect the busbar terminal of the AC fault finding device to the positive and negative busbars and ground of the DC power supply system.

[0078] (2) After determining the feeder branch with AC inrush voltage, use the test lead to connect the branch terminal of the AC inrush fault finding device to the positive and negative terminals of the corresponding feeder branch through the grounding terminal block adapter.

[0079] (3) After the feeder branch with the AC inrush fault is successfully disconnected from the busbar, the busbar terminal of the AC inrush fault finding device is connected to the branch terminal of the AC inrush fault finding device.

[0080] 2. Steps to find AC inrush fault

[0081] (1) After completing the above wiring method (1), set the parameters and start with one button.

[0082] (2) Determine the feeder branch with AC inrush voltage: The device issues an alarm to the DC system and displays it, and preliminarily determines the feeder branch with AC inrush voltage.

[0083] (3) After completing the above wiring method (2), start the test power supply and set the supply voltage to be slightly lower than the DC bus voltage.

[0084] (4) Manual / automatic mode branch disconnection bus function: The device determines whether to use the automatic mode. If so, it automatically determines its polarity based on the AC inrush voltage, closes the corresponding normally open switch (K1 or K2), and puts the high-power diode (D1 or D2) into the DC system. Otherwise, it is necessary to manually put the corresponding high-power diode into operation to disconnect the feeder branch with AC inrush voltage from the DC system bus.

[0085] (5) After completing the above wiring method (3), use a clamp meter to track the signal sent by the host until the specific AC intrusion fault point is found.

[0086] 3. Restoration of the scene

[0087] Remove all test lines and restore the site.

[0088] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0089] The above is only for explaining the implementation mode of the present invention and is not intended to limit the present invention. For those skilled in the art, any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention without creative work should be included in the protection scope of the present invention.

Claims

1. A method for finding an AC inrush fault in a DC power supply system, characterized in that: The following steps are involved: The host is connected to the busbar of the DC power supply system and sends fault finding signals to each feeder branch through the busbar; When an AC inrush fault occurs in a feeder branch, the host provides voltage to the feeder branch where the AC inrush fault occurs. The ground of the host is at the same potential as the ground of the AC inrush fault point. The AC inrush signal generates a loop between the fault point and the host, generating a short-circuit current in the feeder branch where the AC inrush fault occurs. The short-circuit current disconnects the feeder switch of the feeder branch where the AC inrush fault occurs. The fault finding signal sent by the host flows back to the host through the loop; The clamp meter is connected successively to different positions of the feeder branch where the AC inrush fault occurs. Each position is a detection point. Each detection point is detected to see if there is a fault finding signal. The AC inrush fault point is between the adjacent detection points with fault finding signals and the detection points without fault finding signals.

2. The method for finding AC inrush fault in a DC power supply system according to claim 1, characterized in that: It also includes an alarm step: the host detects the bus voltage to ground and the incoming AC voltage. When the bus voltage to ground and the incoming AC voltage exceed the alarm threshold, the host sends out an audible and visual alarm and displays an alarm message.

3. A device for finding faults caused by AC intrusion in a DC power supply system, characterized in that: It includes a host and a clamp meter, wherein the host includes a main control unit, and the main control unit is used for data analysis, processing, fault judgment, and command sending and receiving; And respectively connected to the main control unit: Disconnect bus control unit: It is electrically connected to the bus of the DC power supply system, receives control instructions from the main control unit, and controls the feeder branch with AC inrush fault to be disconnected from the bus; Bus sampling unit: electrically connected to the bus, used to sample the voltage signal of the bus to the ground; Test power supply unit: used to provide backup power to the feeder branch with AC inrush fault; AC sampling unit: electrically connected to the busbar, used to sample the incoming AC voltage signal and convert it into a digital signal; Signal sending unit: receives the signal sending instruction from the main control unit and is responsible for sending the fault finding signal to the DC power supply system; Communication unit: communicate with the clamp meter to realize data transmission; Alarm unit: When the bus-to-ground voltage or AC inrush voltage data of the DC power system is abnormal and exceeds the alarm threshold, an audible and visual alarm is issued; Display unit: real-time display of busbar-to-ground voltage, incoming AC voltage data and alarm signals; The clamp meter is used to be connected to different positions of the feeder branch where an AC inrush fault occurs. Each position is a detection point. Each detection point is detected to see if there is a fault search signal. The AC inrush fault point is located between adjacent detection points with fault search signals and detection points without fault search signals.

4. The AC intrusion fault detection device for a DC power supply system according to claim 3, characterized in that: The disconnected bus control unit includes a first normally open switch K1, a second normally open switch K2, a first intermediate relay KA1, a second intermediate relay KA2, a first contactor KM1, a second contactor KM2, a first diode D1, a second diode D2 and a current limiting resistor R; One end of the first normally open switch K1, one end of the second normally open switch K2, one end of the normally open switch of the first intermediate relay KA1, one end of the normally open switch of the second intermediate relay KA2 and one end of the normally open switch of the first contactor KM1 are connected to the positive bus +KM; One end of the coil of the first intermediate relay KA1, one end of the coil of the second intermediate relay KA2, one end of the coil of the first contactor KM1, one end of the coil of the second contactor KM2, and one end of the normally open switch of the second contactor KM2 are connected to the negative bus -KM; The other end of the first normally open switch K1 is connected to the other end of the coil of the first intermediate relay KA1; the other end of the second normally open switch K2 is connected to the other end of the coil of the second intermediate relay KA2; the other end of the normally open switch of the first intermediate relay KA1 is connected to one end of the normally closed switch of the second contactor KM2, and the other end of the normally closed switch of the second contactor KM2 is connected to the other end of the coil of the first contactor KM1; the other end of the normally open switch of the second intermediate relay KA2 is connected to one end of the normally closed switch of the first contactor KM1, and the other end of the normally closed switch of the first contactor KM1 is connected to the other end of the coil of the second contactor KM2; the other end of the normally open switch of the first contactor KM1 is connected to the cathode of the first diode D1, and the other end of the normally open switch of the second contactor KM2 is connected to the anode of the second diode D2; the anode of the first diode D1 and the cathode of the second diode D2 are connected to one end of a current limiting resistor R, and the other end of the current limiting resistor R is connected to the ground of the host.

5. The AC intrusion fault detection device for a DC power supply system according to claim 3, characterized in that: The test power supply unit includes a test power supply, a third diode D3, a fourth diode D4 and a DC output switch QF; the test power supply converts the AC voltage into a DC voltage, and the DC voltage passes through the third diode D3 and the fourth diode D4, and is output through the DC output switch QF to provide voltage for the feeder branch that sends the AC intrusion fault.

6. The AC intrusion fault detection device for a DC power supply system according to claim 3, characterized in that: The bus sampling unit includes a plurality of sampling resistors connected in series, one end of the plurality of sampling resistors connected in series is connected to the positive bus, and the other end is connected to the negative bus; there is a series node between two adjacent sampling resistors; the series nodes of the two middle sampling resistors are led out as the first sampling point, and a filter capacitor is connected in series between the remaining series nodes and the first sampling point; the two end points of the sampling resistors connected in series serve as the second sampling point and the third sampling point, and the voltage signal between the first sampling point and the second sampling point, or the voltage signal between the first sampling point and the third sampling point is the bus voltage sampling signal.

7. The AC intrusion fault detection device for a DC power supply system according to claim 6, characterized in that: The sampling resistor is a resistor of megohm level.

8. The AC inrush fault detection device for a DC power supply system according to claim 3, characterized in that: The AC sampling unit comprises a capacitor C1, an RC filter circuit, an optocoupler conversion circuit, an operational amplifier circuit and an output filter circuit which are connected in series in sequence.

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