Fault alarm sensor with adjustable fault current threshold and panel type fault indicator

Abstract

The invention relates to a fault alarm sensor with an adjustable fault current threshold and a panel type fault indicator. The fault alarm sensor adopts a triode as an alarm switch element, the output of a current transformer is connected to an alarm signal circuit and is simultaneously used as a working power supply and a detection signal, and the base electrode of the triode is provided with a pull-down resistor branch capable of passing through the resistance value of a dial switch, so that the dial switch can be adjusted to set and adjust a fault current threshold. Light emitted by a light emitting diode in the alarm signal circuit is an alarm signal. The panel type fault indicator is provided with a panel host and the sensors, and the panel host can be used for setting and adjusting the short-circuit fault minimum discrimination time, the grounding fault minimum discrimination time and the fault reset time. The panel type fault indicator realizes electrical isolation of the sensor and the host, is simple in structure and convenient to use, and can be mainly used for current fault monitoring of power cables and related equipment.

Description

Technical Field

[0001] The invention relates to a fault alarm sensor with adjustable fault current threshold and a panel-type fault indicator, which can be mainly used for power system upgrade and intelligent transformation, and belongs to the field of electronic information and intelligent technology. Background Art

[0002] With the continuous upgrading and intelligent transformation of power systems, fault indicators, as a basic "two-remote" terminal, play an important role in the construction of distribution automation because of their low cost, easy and simple installation, and no need to transform primary equipment. Especially in power supply areas with low load density, such as Class D and Class E power supply areas, fault indicators are widely used. Among them, the panel-type fault indicator is a device installed on the power cable distribution line or in the box transformer, ring network cabinet, and branch box to indicate the flow of fault current. Once a short circuit occurs in the line, the line patrol personnel can use the red alarm display on the indicator to quickly determine the fault section, branch and fault point, which completely changes the backward practice of blindly patrolling the line, closing the switch in sections to test the power supply to find the fault, and can transmit the fault information to the remote monitoring system through remote communication, which greatly improves work efficiency, shortens power outage time, and effectively improves power supply reliability and economic benefits.

[0003] Existing current fault sensors mostly use current transformers, which are put on cables, and the cable current is used as the primary current to induce the secondary current, which is used as the analog induction signal output and sent to the data processing device (for example, the panel host of the panel type fault indicator) through the data acquisition circuit. The host performs corresponding analysis and processing, and generates an alarm signal when the primary current exceeds a certain limit. Although this type of current fault sensor can better meet the needs of fault monitoring, it still has certain shortcomings. First, there is no electrical isolation between the sensor and the host, and the anti-interference ability is relatively weak. Second, the current fault standard depends on the host software setting, and the induction signal is continuously connected, which increases the host load and increases the performance requirements of the host. Third, the transformer is not convenient to install and disassemble. Summary of the invention

[0004] The purpose of the present invention is to achieve electrical isolation between the mutual inductor and the panel host, and to facilitate the setting and adjustment of the current alarm threshold.

[0005] The technical solution of the present invention is: a fault alarm sensor with an adjustable fault current threshold is provided with a current transformer for current monitoring, and is also provided with an alarm signal circuit, the alarm signal circuit is provided with a transistor, the transistor is used as an alarm switch element, the output end of the current transformer is connected to the rectifier circuit (the first output end and the second output end of the current transformer are respectively connected to the two input ends of the rectifier circuit), the positive output and the negative output of the rectifier circuit are respectively connected to the high potential end (the collector of the NPN transistor, or the emitter of the PNP transistor) and the low potential end (the collector of the NPN transistor, or the emitter of the PNP transistor) of the load branch (the branch passing through the collector, the emitter and the load) of the transistor. The positive output of the rectifier circuit is also connected to the base of the transistor through a base current limiting resistor. A load current limiting resistor and a light-emitting diode for issuing an alarm signal are connected in series on the load branch. The base of the transistor is connected to the low potential end of the load branch through a pull-down resistor branch. The pull-down resistor branch is composed of a plurality of pull-down resistors connected in parallel. Each pull-down resistor is provided with (connected in series with) its own pull-down resistor switch. The resistance of the pull-down resistor branch can be controlled or adjusted by setting the state of each pull-down resistor switch to achieve the setting and adjustment of the fault current threshold.

[0006] Specifically, by setting the state of each pull-down resistor switch, the pull-down resistor branch resistance (the total resistance value of the pull-down resistor branch) is controlled or adjusted, and the resistance ratio between the control-end current-limiting resistor and the pull-down resistor branch is controlled or adjusted, thereby controlling or adjusting the minimum voltage output of the current transformer that can turn on the transistor. When the current transformer voltage output reaches or exceeds the minimum voltage, the light-emitting diode on the transistor load branch is powered on to emit light, forming an alarm signal. When in use, the switch state of each pull-down resistor switch can be set or adjusted according to actual needs, and the resistance of the pull-down resistor branch is adjusted to the required resistance value (gear), thereby realizing the setting and adjustment of the fault current (alarm current) threshold (or set value).

[0007] The current transformer forms a DC output after passing through a rectifier circuit. The specific form of the rectifier circuit can be selected according to actual needs to determine the performance of the rectifier circuit.

[0008] Preferably, the rectifier circuit is formed by a rectifier diode and a rectifier capacitor (or filter capacitor) connected in series, and the positive electrode and the negative electrode of the rectifier capacitor constitute the positive output and the negative output of the rectifier circuit respectively.

[0009] The rectifier diode can be arranged on the positive electrode side of the rectifier capacitor.

[0010] Preferably, a filtering / voltage stabilizing branch is connected between the first output end and the second output end of the current transformer, and a filtering / voltage stabilizing capacitor is provided on the filtering / voltage stabilizing branch.

[0011] Furthermore, the rectifier capacitor may be connected in parallel with a filter capacitor to improve the DC output.

[0012] Preferably, a shunt resistance branch is connected or not connected between the two output ends (the first output end and the second output end) of the current transformer, and one or more shunt resistors (connected in series, in parallel, or in a combination of series and parallel) are provided on the shunt resistance branch to form a required shunt resistance value (resistance value of the shunt resistance branch).

[0013] Preferably, a dip switch is provided on the pull-down resistor branch, the dip switch is composed of a plurality of independent switches, and each pull-down resistor switch adopts a different independent switch in the dip switch.

[0014] Preferably, the sensor is provided with a transformer body and a U-shaped clamp for fixing the transformer body on the cable. The secondary winding (or secondary coil) of the current transformer and its iron core (the secondary coil is sleeved / wound on the iron core) are arranged in the shell of the transformer body. The U-shaped clamp is made of magnetic conductive material, and its two ends are respectively fastened to the two ends of the iron core by connecting bolts, and connected with the iron core to form a magnetic circuit (the connection with the iron core can be a direct contact connection or an indirect connection through connecting bolts). At the same time, the clamp is also mechanically connected to the transformer body, thereby realizing the installation and fixation of the transformer on the cable. The cable passes through the magnetic circuit formed by the U-shaped clamp and the iron core in the corresponding transformer, and the current therein constitutes the primary current of the current transformer.

[0015] Preferably, the alarm signal circuit of the current transformer is arranged in the shell of the transformer body, and the operating part (usually a manual part, such as a button, a lever, a sliding key, etc.) of the pull-down resistor switch (for example, a dip switch used as a pull-down resistor switch) is exposed from the shell surface (for example, the front, or the side) of the transformer body for easy operation.

[0016] A panel-type fault indicator with an adjustable fault current threshold comprises a panel host (referred to as the host) and a sensor, wherein the sensor is any fault alarm sensor with an adjustable fault current threshold disclosed in the present invention, a photodiode corresponding to the light-emitting diode on the sensor is provided on the signal acquisition circuit of the host, and an optical connection (or optical path connection, so that the light of the light-emitting diode can be transmitted to the corresponding photodiode through the optical fiber) between the corresponding light-emitting diodes and the photodiode is realized through an optical fiber, and the signal acquisition circuit converts the optical signal received by the photodiode into an electrical signal (usually a digital signal) for fault alarm and sends it to the panel host.

[0017] The panel host can implement the set alarm mode according to existing technology or other appropriate technology (for example, control the alarm light to turn on the power, or send corresponding fault and / or alarm information to the remote device and monitoring center).

[0018] The panel host may be provided with a local memory, and the fault and alarm information may be stored in the local memory.

[0019] The panel host may be provided with a display screen for displaying relevant information.

[0020] Preferably, the sensors are grouped into four, including three short-circuit fault sensors and one ground fault sensor. The short-circuit fault sensors are respectively installed on each phase cable to collect the short-circuit signal of the corresponding cable. The ground fault sensor can be installed on the unshielded part at the bifurcation of the three-phase cable to collect the grounding signal of the cable.

[0021] Different fault reset times can be set or adjusted via the host (grading).

[0022] Preferably, the host is provided with a fault reset time setting switch circuit, and the fault reset time setting switch circuit is provided with a fault reset time setting switch, and the fault reset time setting switch is a two-position vertical plug-in dip switch, which adopts binary control of four reset times, uses a power supply as input, and outputs to the host (the host's main chip), and the host determines different fault reset times according to different states of the fault reset time setting switch (different signal inputs formed based on different states).

[0023] Different short-circuit fault minimum discrimination times can be set or adjusted through the host.

[0024] Different minimum ground fault detection times can be set or adjusted through the host.

[0025] Preferably, the host is provided with a minimum fault judgment time setting switch circuit, and the minimum fault judgment time setting switch circuit is provided with a minimum fault judgment time setting switch, and the minimum fault judgment time setting switch is a four-position vertical plug-in dip switch (equivalent to two groups of two-position vertical plug-in dip switches), wherein the 1st and 2nd position switches control the minimum short-circuit fault judgment time, and the 3rd and 4th position switches control the minimum grounding fault judgment time, and all four minimum judgment times are controlled in binary, and all are input by the power supply and output to the host (the host's main chip), and the host determines different short-circuit fault minimum judgment times according to different states of the 1st and 2nd position switches (based on different signal inputs formed in different states), and the host determines different grounding fault minimum judgment times according to different states of the 3rd and 4th position switches (based on different signal inputs formed in different states). The beneficial effects of the present invention are as follows: since the alarm signal of the sensor is an optical signal, it is transmitted to the host through a photoelectric coupling method, so that the electrical isolation between the sensor and the host is realized, which is conducive to improving the anti-interference ability during the transmission process, and helps to avoid the damage to the host circuit caused by the excessive output of the sensor; since the sensor only sends out an optical signal when the measured current exceeds the alarm threshold, when there is no fault alarm, the host does not need to perform relevant signal processing, and the processing method after obtaining the alarm signal is simple, which helps to reduce the performance requirements of the host, thereby allowing the use of simple and durable host products to reduce costs and energy consumption and improve the adaptability to harsh environmental conditions; since a U-shaped clamp made of magnetic conductive material is provided on the sensor (main body), when in use, the cable is placed between the U-shaped magnetic strip and the transformer main body, and the two ends of the U-shaped magnetic strip are connected to the two ends of the cylindrical iron core through threads, forming a closed magnetic circuit together with the iron core, and realizing mechanical connection and fixation, thereby facilitating the installation and removal of the sensor on the cable. Since the output of the current transformer is used as the working power supply and detection signal of the alarm signal circuit at the same time, it helps to simplify the circuit structure, and no power supply needs to be configured separately, ensuring long-term operation.

[0026] This panel-type fault indicator realizes electrical isolation between the sensor and the host, and has a simple structure and is easy to use. It can be mainly used for current fault monitoring of power cables and related equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a circuit schematic diagram of the short-circuit fault sensor of the present invention; Figure 2 is a schematic diagram of the mechanical structure of the short-circuit fault sensor of the present invention (front view); Figure 3 is a schematic diagram of the mechanical structure of the short-circuit fault sensor of the present invention (side view); Figure 4 is a circuit schematic diagram of a ground fault sensor of the present invention; Figure 5 is a schematic diagram of the mechanical structure of the ground fault sensor of the present invention (front view); Figure 6 is a schematic diagram of the mechanical structure of the ground fault sensor of the present invention (side view); Figure 7 It is a schematic diagram of the magnetic circuit connection of the sensor of the present application; Figure 8 Schematic diagram of the panel type fault indicator of the present invention.

[0028] Markings in the figure: 1. Main body; 2. U-shaped magnetic strip; 3. Selection switch; 4. Connecting bolts; 5. Top column; 6. Iron core; 7. Secondary coil; 8. Lead wire. DETAILED DESCRIPTION

[0029] See also Figures 1 to 8 This sensor usually has two main uses: one is for phase current detection, which can be called a short-circuit fault sensor (or short-circuit sensor); the other is for ground current detection, which can be called a ground fault sensor (or ground sensor).

[0030] like Figure 2 and Figure 3 Shown and referenced Figure 7 The short-circuit fault sensor includes a sensor body 1 housing, a U-shaped clamp 2, a top column (tightening bolt) 5, a fault current setting value dial switch (selection switch) 3, an iron core 6 and a secondary coil 7 wound (set) on the iron core. The lead 8 of the secondary coil can be connected to the rectifier circuit, and the positive and negative outputs of the rectifier circuit are used as the first output end and the second output end of the mutual inductor respectively. When appropriate, the lead of the secondary coil can also be directly used as the first output end and the second output end of the mutual inductor. The housing is provided with a bayonet at both ends, the iron core passes through the secondary coil, and the two ends are installed on the bayonet, and are fixed by a hexagonal stud used as a connecting bolt 4. The U-shaped clamp is provided with an oblique notch at both ends, and the U-shaped clamp is clamped with the hexagonal stud through the oblique notch. The top column passes through the top of the U-shaped clamp and is threadedly connected with the U-shaped clamp, so as to tighten the cable between the U-shaped clamp and the main body of the mutual inductor and firmly fix the mutual inductor on the cable. The fault current setting value dip switch adopts an eight-position dip switch, corresponding to eight pull-down resistors. In the simplest way (only one pull-down resistor is connected), the eight-position dip switch can control eight different current setting values, and the appropriate fault current setting value can be selected according to different needs.

[0031] like Figure 4 , Figure 5 and Figure 7 As shown, the ground fault sensor includes a housing of a transformer body 1, a U-shaped clamp 2, a fault current setting value dial switch (selection switch) 3, an iron core 6, and a secondary coil 7 wound (sleeved) on the iron core, and the secondary coil is provided with a lead 8. The two ends of the housing are provided with a bayonet, the iron core 6 passes through the secondary coil 7, and its two ends are installed on the bayonet, and the two ends of the U-shaped clamp are provided with a cross screw used as a connecting bolt 4, and the two ends of the U-shaped clamp are connected to the two ends of the iron core through the cross screw. The fault current setting value dial switch adopts an eight-position dial switch, and the eight-position dial controls eight different current setting values. The appropriate fault current setting value can be selected according to different needs.

[0032] The panel host fault minimum discrimination time setting switch uses a four-digit dial switch to set the setting value, and uses binary control to control eight different time setting values. The 1st and 2nd digits of the four-digit dial switch control the short circuit discrimination time, and the 3rd and 4th digits control the grounding discrimination time. The fault reset time switch and the minimum fault discrimination time setting switch are located at the lower left of the panel host, side by side. The front cover of the panel host opens corresponding holes to display them, and is protected by an acrylic plate. The instructions for use are marked with a mask above the dial.

[0033] The data transmission between the panel host (photodiode) and each sensor (light-emitting diode) adopts optical fiber communication, which has the following advantages: 1) High electrical performance, mechanical strength, good sealing and corrosion resistance, ensuring that the optical fiber index does not decrease in harsh environments and has a long service life; 2) Optical fiber has good anti-electromagnetic interference performance.

[0034] Among the sensors in a group of four, there are three short-circuit fault sensors, which are respectively connected to the A-phase, B-phase and C-phase cables of the three-phase power supply, and one grounding fault sensor, which is connected to the neutral line of the three-phase power supply. The short-circuit fault sensor and the grounding fault sensor are connected to the panel host optical fiber. The panel host is provided with an A-phase short-circuit fault indicator light, a B-phase short-circuit fault indicator light, a C-phase short-circuit fault indicator light and a grounding fault indicator light on the panel.

[0035] Short-circuit fault alarm prompt: The short-circuit fault sensor monitors the current of the line during operation. When a short-circuit fault occurs in the line and the short-circuit current reaches or exceeds the alarm current setting value, the short-circuit fault sensor sends a light signal to the host, and the host will also receive this signal and present a flashing light effect on the host, and transmit the fault signal remotely.

[0036] Ground fault alarm indication: The ground fault sensor monitors the line zero-sequence current during operation. When a ground fault occurs in the line and the ground current reaches or exceeds the alarm current setting value, the ground fault sensor sends out a light signal, the host also receives this signal, and a flashing light effect appears on the host, and the fault signal is remotely transmitted.

[0037] The panel host is provided with a fault alarm circuit, a fault reset circuit and a low-battery alarm circuit, and these circuits can be connected to the main board via pin headers.

[0038] The fault alarm circuit is composed of four LEDs and four resistors, with a power supply as input and output to the mainboard chip. Its function is to flash lights as a fault warning.

[0039] The fault reset circuit consists of a button and a resistor. The button adopts a pull-up resistor, connected to the ground as input, and output to the mainboard chip. The function is fault reset and self-test. The button adopts a waterproof key switch with a size of 6*6*14mm.

[0040] The low battery alarm circuit is composed of an LED, four resistors, a monitoring and reset chip and a PNP transistor, with power as input and ground as output. The monitoring and reset chip controls the transistor to form an LED switch circuit to start the low battery warning function.

[0041] The model of the monitoring and resetting chip is XC61CC2702MR and the model of the PNP transistor is 9012.

[0042] The main board is provided with a fault reset time switch circuit, a fault minimum discrimination time setting switch circuit, a main chip related circuit and a relay related circuit.

[0043] The main chip related circuit includes the main chip and the auxiliary circuit, which is the core of the entire fault indicator. The model of the main chip is PIC16F723A.

[0044] The relay-related circuit is a circuit formed by the main chip as input, the ground as output, and the relay as a switch for signal triggering and resetting. The model of the relay is RELAY_HFD2.

[0045] The fault reset time switch circuit is provided with a fault reset time switch, which is a two-position vertical plug-in DIP switch, adopts binary control for four reset times, takes power as input and outputs to the main chip, and the DIP is the core of reset time control.

[0046] The minimum fault judgment time setting switch circuit is provided with a minimum fault judgment time setting switch, which is a four-position vertical plug-in DIP switch. 1 and 2 control the minimum short-circuit fault judgment time, and 3 and 4 control the minimum ground fault judgment time. All four minimum judgment times are controlled by binary. The power supply is used as input and output to the main chip. The DIP is the core of the minimum fault judgment time control.

[0047] The fault reset time switch and the minimum fault discrimination time setting switch are located at the lower left of the panel host, side by side, and the corresponding holes are opened in the front cover of the panel host to display them and are protected by an acrylic plate. The instructions for use are marked with a mask above the dial.

[0048] The sensor is installed on the cable and is used to collect the current signal passing through the detected cable, determine whether a fault occurs in the circuit to be tested, and generate an optical alarm signal; the optical fiber transmits the optical alarm signal generated by the sensor to the panel host; the panel host will obtain the optical alarm signal transmitted by the optical fiber and make a fault indication.

[0049] The sensors are grouped into four, including three short-circuit fault sensors and one ground fault sensor; the short-circuit fault sensor is installed on a single-phase cable to collect the short-circuit signal of the cable, and the ground fault sensor is installed on the non-shielded part at the bifurcation of the three-phase cable to collect the ground signal of the cable. The ground fault sensor and the short-circuit fault sensor are both connected to the panel host via optical fiber to transmit the collected signals to the panel host.

[0050] The secondary coil of the short-circuit fault sensor uses 0.14 mm enameled wire.

[0051] The secondary coil is connected to the short-circuit circuit board, and the circuit board is powered by induction current. The short-circuit circuit board has the functions of drawing power and induction current. The circuit board is provided with an alarm current setting value setting switch and an LED circuit controlled by an NPN transistor.

[0052] The alarm current setting value setting switch is an eight-position direct plug-in dial switch, which is connected to the base of the transistor at the top and eight resistors with different resistance values ​​at the bottom to control eight alarm current setting values; the model of the NPN transistor is 9014.

[0053] The short-circuit circuit board is installed on the inner side of the shell, and the alarm current setting value setting switch is displayed through a hole in the side of the shell and is fixed by casting the shell with resin.

[0054] The secondary coil of the ground fault sensor uses 0.08 mm enameled wire.

[0055] The secondary coil of the ground fault sensor is connected to the ground circuit board, which is powered by induction current. The ground circuit board has the functions of drawing power and induction current. The circuit board is provided with an alarm current setting value setting switch and an LED circuit controlled by an NPN transistor.

[0056] The alarm current setting value setting switch is an eight-position direct plug-in dial switch, which is connected to the base of the transistor at the top and eight resistors with different resistance values ​​at the bottom to control eight alarm current setting values. The model of the NPN transistor is 9014.

[0057] The grounding circuit board is installed on the inner side of the shell, and the alarm current setting value setting switch is displayed through a hole in the side of the shell and is fixed by casting the shell with resin.

[0058] See also Figure 1 and Figure 4The alarm signal circuit of the sensor converts the AC output of the current transformer into DC through a simple rectifier circuit (composed of a rectifier diode D1 and a rectifier capacitor C2, or a rectifier diode D2 and a rectifier capacitor C3). The first output terminal L1 and the second output terminal L2 of the current transformer are respectively connected to the two input points (or input terminals) of the rectifier circuit. Since a phase line short circuit will generate a large current, Figure 1 In the illustrated embodiment, a shunt resistor branch (composed of resistors R1 and R4 connected in series) is further provided between L1 and L2 for protection. Figure 1 The rectifier capacitor C2 shown is also connected in parallel with the filter capacitor C1 to improve the DC output.

[0059] The eight-position dip switches SW1 and SW2 are used to set the fault current setting value. They are composed of eight independent switches. Each independent switch is connected to a pull-down resistor R5 or R8. When the corresponding independent switch is closed, the pull-down resistor to which it is connected is connected. When only one pull-down resistor is connected, eight setting values ​​can be formed by connecting eight different pull-down resistors respectively.

[0060] The parameters of each component (resistance, capacitance, transistor, etc.) and their proportional relationship can be reasonably set according to actual needs.

[0061] The present invention has the following characteristics: 1) High accuracy and strong anti-interference ability: The panel-type fault indicator adopts electromagnetic induction, photoelectric conversion, signal optical fiber transmission and single-chip microcomputer control technologies to ensure the accuracy and reliability of fault alarm, and has strong anti-interference ability.

[0062] 2) Real-time monitoring and alarm: The indicator can monitor the current changes of the line in real time. When a short circuit or ground fault occurs, it can immediately send out an alarm signal and transmit it to the host through optical fiber to generate a corresponding alarm indication signal.

[0063] 3) Remote transmission and automation: The panel-type fault indicator is equipped with a remote transmission output port, which is suitable for distribution network automation. It can output the alarm signal for remote transmission and can also receive the reset signal from a distance to realize remote reset operation.

[0064] 4) Automatic and manual reset function: After the indicator sends out an alarm signal, it can be reset automatically or manually, which is convenient and quick.

[0065] 5) Self-check function: The indicator can perform self-check to ensure the normal operation of the equipment and detect problems in time.

[0066] 6) Low power consumption design: Powered by high-capacity lithium battery, the battery has a long working life and is suitable for long-term operation.

[0067] 7) Simple and convenient structure: The external structure adopts a lock-and-clip design, making the whole machine easy to load and unload, suitable for installation and use in various environments.

[0068] 8) The fault current setting value can be set: the setting value is set by a dip switch, and the appropriate gear can be selected according to the on-site conditions.

[0069] 9) The minimum fault discrimination time can be set: the setting value is set by using the DIP switch, and the appropriate gear can be selected according to the on-site conditions.

[0070] 10) Reset time can be set: Use the DIP switch to set the set value and select the appropriate gear according to the site conditions.

[0071] Unless otherwise specified or when one preferred or optional technical means is a further limitation of another technical means, the preferred and optional technical means disclosed in the present invention can be arbitrarily combined to form several different specific implementation methods.

Claims

1. A fault alarm sensor with adjustable fault current threshold, provided with a current transformer for current monitoring, characterized in that An alarm signal circuit is also provided, the alarm signal circuit is provided with a triode, the output end of the current transformer is provided with a rectifier circuit, the positive output and the negative output of the rectifier circuit are respectively connected to the high potential end and the low potential end of the load branch of the triode, the positive output of the rectifier circuit is also connected to the base of the triode through a base current limiting resistor, a load current limiting resistor and a light-emitting diode for sending an alarm signal are connected in series on the load branch, the base of the triode is connected to the low potential end of the load branch through a pull-down resistor branch, the pull-down resistor branch is composed of a plurality of pull-down resistors connected in parallel, each pull-down resistor is provided with its own pull-down resistor switch, and the setting and adjustment of the fault current threshold are realized by setting the state of each pull-down resistor switch to control or adjust the pull-down resistor branch resistance.

2. The fault alarm sensor according to claim 1, characterized in that A dip switch is arranged on the pull-down resistor branch, and the dip switch is composed of a plurality of independent switches, and each pull-down resistor switch adopts a different independent switch in the dip switch.

3. The fault alarm sensor according to claim 1, characterized in that The rectifier circuit is formed by a rectifier diode and a rectifier capacitor connected in series, and the positive electrode and the negative electrode of the rectifier capacitor constitute the positive output and the negative output of the rectifier circuit respectively.

4. The fault alarm sensor according to claim 1, characterized in that A shunt resistor branch is connected or not connected between the two output ends of the current transformer, and one or more shunt resistors are arranged on the shunt resistor branch.

5. The fault alarm sensor according to any one of claims 1 to 4, characterized in that A transformer body and a U-shaped clamp for fixing the transformer body on the cable are provided. The secondary winding of the current transformer and its iron core are arranged in the shell of the transformer body. The U-shaped clamp is made of magnetic conductive material, and its two ends are fastened to the two ends of the iron core by connecting bolts respectively, and connected with the iron core to form a magnetic circuit. The cable passes through the magnetic circuit formed by the U-shaped clamp and the iron core in the corresponding transformer, and the current therein constitutes the primary current of the current transformer.

6. The fault alarm sensor according to claim 5, characterized in that The alarm signal circuit of the current transformer is arranged in the shell of the transformer body, and the operating member of the pull-down resistor switch is exposed from the shell surface of the transformer body.

7. A panel-type fault indicator with adjustable fault current threshold, comprising a panel host and a sensor, characterized in that The sensor is a fault alarm sensor with an adjustable fault current threshold as described in any one of claims 1 to 6. A photodiode corresponding to the light-emitting diode on the sensor is provided on the signal acquisition circuit of the panel host. An optical connection between the corresponding light-emitting diodes and the photodiode is achieved through optical fibers. The signal acquisition circuit converts the optical signal received by the photodiode into an electrical signal for fault alarm and sends it to the panel host.

8. The panel type fault indicator according to claim 7, characterized in that The sensors are grouped into four, including three short-circuit fault sensors and one ground fault sensor. The short-circuit fault sensors are respectively installed on each phase cable to collect the short-circuit signal of the corresponding cable. The ground fault sensor can be installed on the unshielded part at the bifurcation of the three-phase cable to collect the ground signal of the cable.

9. The panel type fault indicator according to claim 7, characterized in that The panel host is provided with a fault reset time setting switch circuit, and the fault reset time setting switch circuit is provided with a fault reset time setting switch. The fault reset time setting switch is a two-position vertical plug-in dip switch, which uses binary control for four reset times. The power supply is used as input and output to the panel host. The panel host determines different fault reset times according to different states of the fault reset time setting switch.

10. The panel type fault indicator according to claim 7, characterized in that The panel host is provided with a minimum fault judgment time setting switch circuit, and the minimum fault judgment time setting switch circuit is provided with a minimum fault judgment time setting switch. The minimum fault judgment time setting switch is a four-position vertical plug-in dial switch, wherein the 1st and 2nd position switches control the minimum short-circuit fault judgment time, and the 3rd and 4th position switches control the minimum grounding fault judgment time. All four minimum judgment times are controlled in binary, and all are input by the power supply and output to the panel host. The panel host determines different short-circuit fault minimum judgment times according to different states of the 1st and 2nd position switches, and the panel host determines different grounding fault minimum judgment times according to different states of the 3rd and 4th position switches.

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