PT small current grounding fault monitoring device

Abstract

The utility model discloses a PT small-current grounding fault monitoring device, and relates to the technical field of power system detection and protection. The device comprises an insulating shell, wherein a high-voltage capacitor, a low-resistance sampling resistor, an intelligent on-off switch and an LED indicating lamp are integrated in the insulating shell; one end of the high-voltage capacitor is connected with an input wiring terminal used for being connected to a neutral point of a voltage transformer through a wire, the other end of the high-voltage capacitor is connected to the low-resistance sampling resistor, and the low-resistance sampling resistor is connected with a grounding wiring terminal through an internal wire; two switch ends of the intelligent on-off switch are respectively connected to electrodes at two ends of the high-voltage capacitor; the positive electrode of the LED indicating lamp is connected to one end of the low-resistance sampling resistor through the current limiting element, and the negative electrode is connected to the other end of the low-resistance sampling resistor. According to the utility model, a high-impedance detection loop is formed by the high-voltage capacitor and the low-resistance sampling resistor, so that the abnormal state of the neutral point can be sensitively sensed on the premise of guaranteeing the stability of the system.

Description

Technical Field

[0001] This utility model belongs to the field of power system detection and protection technology, and in particular relates to a PT low current grounding fault monitoring device. Background Technology

[0002] In medium-voltage distribution network systems, voltage transformers (PTs) are critical measurement and protection devices widely used in voltage sampling, energy metering, and relay protection. To prevent damage from ferroresonant overvoltages, the primary winding of a PT is typically connected in a star configuration with the neutral point grounded via a high-impedance or harmonic suppression device. However, in the event of a single-phase ground fault, especially in low-current grounding systems, a significant displacement voltage may appear at the PT neutral point. If this is not monitored and addressed promptly, it can lead to serious consequences such as persistent arcing, resonant overvoltages, or even insulation breakdown. Traditional monitoring methods rely heavily on secondary-side zero-sequence voltage detection or manual inspection, which have limitations such as delayed response, inability to directly reflect the true state of the primary neutral point, lack of local visualization indicators, and lack of proactive intervention capabilities.

[0003] To address this issue, we provide a PT low-current grounding fault monitoring device. Utility Model Content

[0004] The purpose of this invention is to provide a PT low-current grounding fault monitoring device. By connecting a high-impedance detection circuit consisting of a high-voltage capacitor and a low-resistance sampling resistor to the neutral point of the voltage transformer, and combining it with a local LED indicator, the invention solves the problems of lack of local visual indication and lack of active protection capability in the prior art.

[0005] To solve the above-mentioned technical problems, this utility model is achieved through the following technical solution:

[0006] This utility model relates to a PT low-current grounding fault monitoring device, comprising an insulating shell, inside which are integrated a high-voltage capacitor, a low-resistance sampling resistor, an intelligent on / off switch, and an LED indicator. One end of the high-voltage capacitor is connected via a wire to an input terminal for connecting to the neutral point of a voltage transformer, and the other end is connected to the low-resistance sampling resistor. The low-resistance sampling resistor is connected via an internal wire to a grounding terminal. The two terminals of the intelligent on / off switch are respectively connected to the two electrodes of the high-voltage capacitor. The positive terminal of the LED indicator is connected to one end of the low-resistance sampling resistor via a current-limiting element, and the negative terminal is connected to the other end of the low-resistance sampling resistor.

[0007] The present invention is further configured such that a control circuit board is provided inside the insulating shell, on which a signal acquisition circuit, a microcontroller and a drive circuit are provided. The two input terminals of the signal acquisition circuit are respectively connected to the two ends of the low resistance sampling resistor, and the output terminal of the microcontroller is connected to the control terminal of the drive circuit.

[0008] The output of the drive circuit is electrically connected to the control terminal of the intelligent on / off switch, which is a relay; the output of the drive circuit is connected to the control circuit of the LED indicator; the output of the signal acquisition circuit is connected to the analog signal input pin of the microcontroller.

[0009] The present invention is further configured such that the control circuit board also includes an isolated power supply module, the input end of which is connected to an external auxiliary power supply, and the output end of which supplies power to the signal acquisition circuit, the microcontroller and the drive circuit through the control circuit board wiring.

[0010] The present invention is further configured such that the input terminal and the grounding terminal are respectively disposed at both ends of the insulating shell.

[0011] The present invention is further configured such that the control circuit board is also equipped with a communication interface circuit, the communication interface circuit is connected to the microcontroller, and the communication interface circuit is connected to an external monitoring system.

[0012] The present invention is further configured such that the capacitance value of the high-voltage capacitor is set to 1.5 to 2.5 times the distributed capacitance to ground of the bus section of the connected power system, and the on-resistance of the intelligent on / off switch in the closed state is less than 0.1 ohms.

[0013] The present invention is further configured such that the microcontroller is equipped with a self-test module, the self-test module periodically sends test pulse signals to the drive circuit, and monitors the feedback voltage across the low-resistance sampling resistor through the signal acquisition circuit.

[0014] This utility model has the following beneficial effects:

[0015] 1. This utility model uses a high-voltage capacitor and a low-resistance sampling resistor to form a high-impedance detection circuit. Under normal operating conditions, it has minimal impact on the original grounding method of the system, effectively avoiding the risks of increased system capacitive current, protection malfunction, or resonance that may be caused by traditional direct grounding or high-resistance grounding methods. Thus, it achieves sensitive detection of abnormal states of the neutral point while ensuring system stability.

[0016] 2. This utility model provides intuitive local alarms through LED indicator lights, and at the same time drives the relay to short-circuit the capacitor to achieve forced neutral point grounding, effectively suppressing overvoltage caused by intermittent arc grounding, and improving the insulation safety of equipment and the reliability of system operation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this utility model, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0018] Figure 1 This is a schematic diagram of one side of a PT low-current grounding fault monitoring device.

[0019] Figure 2 This is a schematic diagram of the other side of a PT low-current grounding fault monitoring device.

[0020] Figure 3 This is a schematic diagram of a PT low-current grounding fault monitoring device.

[0021] The attached diagram lists the components represented by each number as follows:

[0022] 1. Insulating shell; 11. High voltage capacitor; 11a. Input terminal; 11b. Grounding terminal; 12. Low resistance sampling resistor; 13. Intelligent on / off switch; 14. LED indicator; 15. Control circuit board; 15a. Signal acquisition circuit; 15b. Microcontroller; 15c. Drive circuit; 15d. Isolated power supply module; 15e. Communication interface circuit. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Example

[0024] Please see Figure 1-3 This utility model relates to a PT low-current grounding fault monitoring device, comprising an insulating shell 1. The insulating shell 1 integrates a high-voltage capacitor 11, a low-resistance sampling resistor 12, an intelligent on / off switch 13, and an LED indicator 14. One end of the high-voltage capacitor 11 is connected via a wire to an input terminal 11a for connecting to the neutral point of a voltage transformer, and the other end is connected to the low-resistance sampling resistor 12. The low-resistance sampling resistor 12 is connected via an internal wire to a grounding terminal 11b. The input terminal 11a and the grounding terminal 11b are respectively located at both ends of the insulating shell 1. The two terminals of the intelligent on / off switch 13 are respectively connected to the two electrodes of the high-voltage capacitor 11. The positive terminal of the LED indicator 14 is connected to one end of the low-resistance sampling resistor 12 via a current-limiting element, and the negative terminal is connected to the other end of the low-resistance sampling resistor 12.

[0025] This embodiment provides a PT low-current grounding fault monitoring device that uses a voltage divider sampling path composed of a high-impedance capacitor and a low-resistance sampling resistor 12 to achieve sensitive detection of abnormal current at the neutral point without significantly changing the original grounding characteristics of the system. Specifically, the high-voltage capacitor 11, as a front-end coupling element, has high capacitive reactance characteristics, which can effectively isolate the power frequency high voltage to ensure the safety of the downstream circuit. On the other hand, when a single-phase grounding fault occurs, it works together with the system's ground distribution parameters to generate a measurable displacement voltage at the neutral point, thereby forming a weak current signal reflecting the fault state on the low-resistance sampling resistor 12. This signal is conditioned and amplified by the signal acquisition circuit 15a and then sent to the microcontroller 15b for real-time analysis and judgment. Once an abnormal current characteristic is detected, the microcontroller 15b immediately triggers the drive circuit 15c to light up the LED indicator 14, realizing local visual alarm.

[0026] Specifically, the insulating outer casing 1 also houses a control circuit board 15, which includes a signal acquisition circuit 15a, a microcontroller 15b, and a drive circuit 15c. The two input terminals of the signal acquisition circuit 15a are respectively connected to the two ends of the low-resistance sampling resistor 12. The output terminal of the microcontroller 15b is connected to the control terminal of the drive circuit 15c. The output terminal of the drive circuit 15c is electrically connected to the control terminal of the intelligent on / off switch 13. The intelligent on / off switch 13 is a relay, which can actively short-circuit the two ends of the high-voltage capacitor 11 when necessary, forcibly grounding the neutral point reliably and preventing secondary risks such as equipment insulation breakdown or resonant overvoltage caused by continuous high voltage. The output terminal of the drive circuit 15c is connected to the control circuit of the LED indicator 14. The output terminal of the signal acquisition circuit 15a is connected to the analog signal input pin of the microcontroller 15b.

[0027] Furthermore, the control circuit board 15 also includes an isolated power supply module 15d. The input terminal of the isolated power supply module 15d is connected to an external auxiliary power supply, and the output terminal of the isolated power supply module 15d supplies power to the signal acquisition circuit 15a, the microcontroller 15b, and the drive circuit 15c through the wiring of the control circuit board 15, ensuring electrical isolation between the internal low-voltage system and the external high-voltage environment and improving operational safety. The control circuit board 15 is also equipped with a communication interface circuit 15e, which is connected to the microcontroller 15b and to an external monitoring system, supporting remote status uploading and centralized management, thereby constructing a comprehensive monitoring mechanism that integrates local perception, intelligent judgment, active intervention, and remote communication.

[0028] Furthermore, the capacitance value of the high-voltage capacitor 11 is set to 1.5 to 2.5 times the system's distributed capacitance to ground, and the on-resistance of the intelligent on / off switch 13 in the closed state is less than 0.1 ohms. By controlling the capacitance value of the high-voltage capacitor 11 within the range of 1.5 to 2.5 times the distributed capacitance to ground of the bus section of the connected power system, the capacitive current in the grounding circuit can be increased by more than 50% without triggering resonance, significantly improving the detectability of weak grounding faults while maintaining the dynamic stability of the connected power system. The on-resistance of the intelligent on / off switch 13 in the closed state is strictly limited to less than 0.1 ohms to ensure that the discharge / injection circuit formed at the moment of switch closure has extremely low impedance, avoiding weakening of the injection current amplitude or unnecessary heat loss due to excessive internal resistance of the switch.

[0029] In addition, the microcontroller 15b is equipped with a self-test module, which periodically sends test pulse signals to the drive circuit 15c and monitors the feedback voltage across the low-resistance sampling resistor 12 through the signal acquisition circuit 15a. This enables automatic detection and diagnosis of the working status of the drive circuit 15c, the LED indicator 14 loop, the low-resistance sampling resistor 12, and the signal acquisition circuit 15a, ensuring accurate response and reliable operation when a PT low-current ground fault occurs. This avoids missed or false alarms due to malfunctions in the PT low-current ground fault monitoring device itself, thereby enhancing the safety and stability of the power system operation.

[0030] The operation process of this embodiment is as follows: First, the input terminal 11a at one end of the insulating shell 1 is reliably connected to the neutral point lead of the PT, and the grounding terminal 11b at the other end is firmly connected to the system grounding network to ensure that the electrical connection is stable and meets safety specifications; then, in order to connect the control circuit board 15 to the external auxiliary power supply, the isolation power supply module 15d is immediately started to provide a stable and isolated low-voltage working power supply for the signal acquisition circuit 15a, the microcontroller 15b and the drive circuit 15c; the high-voltage capacitor 11 and the low-resistance sampling resistor 12 are connected in series to form a high-impedance path. During normal operation, only a very small capacitive current flows through it, and the voltage drop across the low-resistance sampling resistor is weak. The microcontroller 15b continuously monitors the voltage signal through the signal acquisition circuit 15a and determines that the system is in a fault-free state, and the LED indicator 14 remains off; when a single-phase ground fault occurs in the system, the PT neutral point potential shifts, causing the current flowing through the high-voltage capacitor 11 and the low-resistance sampling resistor to increase. The signal acquisition circuit 15a converts this change into an analog voltage signal and sends it to the microcontroller 15b;

[0031] The microcontroller 15b intelligently judges based on preset thresholds or waveform characteristics. Once a valid grounding fault is confirmed, it immediately outputs a control signal: on the one hand, it drives the drive circuit 15c to light up the LED indicator 14, realizing a local audible and visual alarm; on the other hand, it sends a closing command to the intelligent on / off switch 13, causing its contacts to short-circuit the two ends of the high-voltage capacitor 11, forcing the neutral point to be directly grounded, suppressing resonant overvoltage and ensuring the insulation safety of the equipment. At the same time, the microcontroller 15b uploads data such as fault information, action time, and the status of the PT low-current grounding fault monitoring device to an external monitoring system through the communication interface circuit 15e, allowing maintenance personnel to view and analyze remotely. After the fault is cleared and normal operation is restored, the microcontroller 15b automatically resets the intelligent on / off switch 13 to the open state through the drive circuit 15c, restoring the high-impedance monitoring mode.

[0032] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

Claims

1. A PT low-current grounding fault monitoring device, comprising an insulating shell (1), wherein the insulating shell (1) integrates a high-voltage capacitor (11), a low-resistance sampling resistor (12), an intelligent on / off switch (13), and an LED indicator (14); characterized in that: One end of the high-voltage capacitor (11) is connected to an input terminal (11a) for accessing the neutral point of a voltage transformer via a wire, and the other end is connected to a low-resistance sampling resistor (12). The low-resistance sampling resistor (12) is connected to a grounding terminal (11b) via an internal wire. The two terminals of the intelligent on / off switch (13) are respectively connected to the two electrodes of the high-voltage capacitor (11). The positive terminal of the LED indicator (14) is connected to one end of the low-resistance sampling resistor (12) via a current-limiting element, and the negative terminal is connected to the other end of the low-resistance sampling resistor (12).

2. The PT low-current grounding fault monitoring device according to claim 1, characterized in that, The insulating shell (1) is also provided with a control circuit board (15), which is provided with a signal acquisition circuit (15a), a microcontroller (15b) and a drive circuit (15c). The two input terminals of the signal acquisition circuit (15a) are respectively connected to the two ends of the low resistance sampling resistor (12), and the output terminal of the microcontroller (15b) is connected to the control terminal of the drive circuit (15c). The output of the drive circuit (15c) is electrically connected to the control terminal of the intelligent on / off switch (13), which is a relay; the output of the drive circuit (15c) is connected to the control circuit of the LED indicator (14); the output of the signal acquisition circuit (15a) is connected to the analog signal input pin of the microcontroller (15b).

3. The PT low-current grounding fault monitoring device according to claim 2, characterized in that, The control circuit board (15) also includes an isolated power supply module (15d). The input terminal of the isolated power supply module (15d) is connected to an external auxiliary power supply, and the output terminal of the isolated power supply module (15d) supplies power to the signal acquisition circuit (15a), the microcontroller (15b) and the drive circuit (15c) through the wiring of the control circuit board (15).

4. The PT low-current grounding fault monitoring device according to claim 1, characterized in that, The input terminal (11a) and the grounding terminal (11b) are respectively disposed at both ends of the insulating shell (1).

5. The PT low-current grounding fault monitoring device according to claim 2, characterized in that, The control circuit board (15) is also equipped with a communication interface circuit (15e), which is connected to the microcontroller (15b) and to an external monitoring system.

6. The PT low-current grounding fault monitoring device according to claim 1, characterized in that, The capacitance value of the high-voltage capacitor (11) is set to 1.5 to 2.5 times the distributed capacitance to ground of the bus section of the connected power system, and the on-resistance of the intelligent on / off switch (13) in the closed state is less than 0.1 ohms.

7. The PT low-current grounding fault monitoring device according to claim 2, characterized in that, The microcontroller (15b) is equipped with a self-test module, which periodically sends test pulse signals to the drive circuit (15c) and monitors the feedback voltage across the low-resistance sampling resistor (12) through the signal acquisition circuit (15a).

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