A composite sensor for detecting partial discharge of cables

Abstract

The present invention relates to a composite sensor based on a cable partial discharge detection, HFCT and capacitive sensor are designed in the same structure, both signals are output through the same port, it is ensured that this sensor has a wider detection frequency band, the detection signal of HFCT or capacitive sensor is screened by subsequent filtering network, and then more accurate detection and analysis of partial discharge is carried out. The present invention has two functions of HFCT and capacitive sensor, and HFCT detection result can be output in low frequency band (1MHz-30MHz), ensuring that it has a good signal-to-noise ratio; in frequency bands above 30MHz, the detection signal of capacitive sensor can be output, and there is an upper limit cut-off frequency of more than 100MHz. After applying the sensor structure of the present invention, the cable partial discharge signal detection in a wider frequency band can be carried out in conjunction with subsequent circuits.

Description

Technical Field

[0001] The present invention belongs to the technical field of power cable partial discharge operation and maintenance, and in particular is based on a composite sensor for detecting partial discharge of a cable. Background Art

[0002] With economic development and improved living standards, users are increasingly demanding higher reliability in power supply. In urban power grid systems, power cables of all voltage levels are becoming the most critical transmission network. However, because cables are typical capacitive power equipment, insulation damage anywhere can cause failure of the entire insulation system. Therefore, monitoring the condition of cable insulation is crucial to the stable operation of urban power systems.

[0003] Current power cable partial discharge sensors are primarily high-frequency current transformers (HFCTs). Due to their materials and inherent structure, they offer high detection sensitivity only within a certain frequency band. Compared to HFCTs, capacitive partial discharge sensors have a wider detection frequency band. However, their open structure makes complete shielding difficult, resulting in a low signal-to-noise ratio in the induced partial discharge signals. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and propose a composite sensor for cable partial discharge detection, which combines HFCT and capacitive sensors to achieve a wider monitoring frequency band and improve the sensitivity of partial discharge detection.

[0005] The present invention solves the technical problem by adopting the following technical solutions:

[0006] A composite sensor for detecting partial discharge of a cable includes a sensor body, a signal mixing circuit, and a signal output BNC connector. The sensor body includes a capacitance sensor, an HFCT sensor, and a plastic housing. The capacitance sensor, HFCT sensor, and plastic housing are arranged in sequence from the inside out. The signal mixing circuit is arranged on the surface of the housing. The signal input end of the signal mixing circuit is connected to the capacitance sensor and the HFCT sensor, and the input end of the signal output BNC connector is connected to the output end of the signal mixing circuit.

[0007] Furthermore, the capacitive sensor includes two aluminum electrodes and an XLPE layer, wherein the XLPE layer is disposed between the two aluminum electrodes.

[0008] Furthermore, the HFCT sensor includes a ferrite core and a HFCT, wherein the HFCT is wound around the ferrite core.

[0009] Moreover, the signal mixing circuit includes a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7 and an amplifier;

[0010] The output end of the capacitive sensor is connected to one end of capacitor C1, the other end of capacitor C1 is respectively connected to ground resistor R1 and one end of capacitor C2, the other end of capacitor C2 is respectively connected to ground resistor R2 and one end of resistor R3, and the other end of resistor R3 is connected to the negative input end of the amplifier; the output end of the HFCT sensor is connected to one end of resistor R6, the other end of resistor R6 is respectively connected to ground capacitor C3 and one end of resistor R7, the other end of resistor R7 is respectively connected to ground capacitor C4 and one end of resistor R5, and the other end of resistor R5 is respectively connected to the output end of the amplifier and the input end of the signal output BNC connector.

[0011] Furthermore, the amplifier uses AD8009.

[0012] Moreover, a rotating shaft hinge is provided on one side of the sensor body, and openings are respectively provided on one side of the rotating shaft hinge and on the opposite side of the rotating shaft hinge for clamping the sensor body on the cable to be tested.

[0013] The advantages and positive effects of the present invention are:

[0014] The present invention designs HFCT and capacitive sensor in the same structure, and outputs the signals of both through the same port, ensuring that the sensor has a wider detection frequency band, and uses the subsequent filtering network to screen the detection signal of HFCT or capacitive sensor, thereby more accurately detecting and analyzing partial discharge. The present invention has two functions of HFCT and capacitive sensor. It can output HFCT detection results in the low frequency band (1MHz-30MHz), ensuring that it has a good signal-to-noise ratio; in the frequency band above 30MHz, it can output the detection signal of the capacitive sensor, and has an upper cut-off frequency of more than 100MHz. After applying the sensor structure of the present invention, it can be used in conjunction with subsequent circuits to detect cable partial discharge signals in a wider frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the composite sensor structure of the present invention;

[0016] Figure 2 This is a signal mixing circuit diagram of the present invention;

[0017] Figure 3 This is a schematic diagram of the installation of the present invention. DETAILED DESCRIPTION

[0018] The present invention is further described below in conjunction with the accompanying drawings.

[0019] A composite sensor for detecting partial discharge of a cable, such as Figure 1 As shown, the structure and appearance are similar to traditional HFCT sensors, with a special capacitive sensor design added to the innermost layer. It includes a sensor body, its signal mixing circuit, and a signal output BNC connector. The sensor body comprises a capacitive sensor, an HFCT sensor, and a plastic housing. The capacitive sensor, HFCT sensor, and plastic housing are arranged in sequence from the inside out. The signal mixing circuit is located on the surface of the housing. The signal input of the signal mixing circuit is connected to the capacitive sensor and HFCT sensor, and the input of the signal output BNC connector is connected to the output of the signal mixing circuit. The output of the signal output BNC connector is connected to the subsequent partial discharge detection circuit.

[0020] The capacitive sensor includes two aluminum electrodes and an XLPE layer, wherein the XLPE layer is arranged between the two aluminum electrodes.

[0021] The HFCT sensor includes a ferrite core and an HFCT, wherein the HFCT is wound on the ferrite core.

[0022] like Figure 2 As shown, the signal mixing circuit includes capacitor C1, capacitor C2, capacitor C3, capacitor C4, resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7 and amplifier AD8009;

[0023] The output end of the capacitive sensor is connected to one end of capacitor C1, the other end of capacitor C1 is connected to the ground resistor R1 and one end of capacitor C2 respectively, the other end of capacitor C2 is connected to the ground resistor R2 and one end of resistor R3 respectively, and the other end of resistor R3 is connected to the negative input end of amplifier AD8009; the output end of the HFCT sensor is connected to one end of resistor R6, the other end of resistor R6 is connected to one end of ground capacitor C3 and one end of resistor R7 respectively, the other end of resistor R7 is connected to one end of ground capacitor C4 and one end of resistor R5 respectively, and the other end of resistor R5 is connected to the output end of amplifier AD8009 and the input end of the signal output BNC connector respectively.

[0024] The output signal of the capacitance sensor enters a high-pass filter circuit composed of a resistor and a capacitor. The cutoff frequency of the filter circuit is 30 MHz, which allows partial discharge signals with a frequency above 30 MHz to reach resistor R3 through this circuit.

[0025] The output signal of the HFCT sensor enters a low-pass filter circuit composed of a resistor and a capacitor, whose upper cutoff frequency is 30MHz. This allows partial discharge signals with a frequency below 30MHz to reach resistor R5 through this circuit.

[0026] AD8009, resistors R3, R4 and R5 together form an adder. After u1 and u2 enter the adder, the output signal u o , the relationship satisfies u o =u1+u2. After passing through this circuit, the composite signal of the two sensors can be obtained.

[0027] In order to facilitate installation, a rotating shaft hinge is provided on one side of the sensor body, and openings are respectively provided on one side of the rotating shaft hinge and on the opposite side of the rotating shaft hinge for the sensor body to be clamped on the cable to be tested.

[0028] like Figure 3 As shown, the present invention is installed in a cable grounding box. The figure takes the online monitoring of partial discharge of phase A as an example. During installation, the composite sensor of the present invention is connected to the grounding wire, and then connected to the ±5V power line and the signal line for use.

[0029] It should be emphasized that the embodiments described in the present invention are illustrative rather than restrictive. Therefore, the present invention includes but is not limited to the embodiments described in the specific embodiments. Any other embodiments derived by those skilled in the art based on the technical solutions of the present invention also fall within the scope of protection of the present invention.

Claims

1. A composite sensor for detecting partial discharge of a cable, characterized by: The sensor body includes a sensor body, a signal mixing circuit, and a signal output BNC connector. The sensor body includes: a capacitive sensor, an HFCT sensor, and a plastic shell. The capacitive sensor, HFCT sensor, and plastic shell are arranged in sequence from the inside to the outside. The signal mixing circuit is arranged on the surface of the shell. The signal input end of the signal mixing circuit is connected to the capacitive sensor and the HFCT sensor, and the input end of the signal output BNC connector is connected to the output end of the signal mixing circuit.

2. A composite sensor for detecting partial discharge of a cable according to claim 1, characterized in that: The capacitive sensor includes two aluminum electrodes and an XLPE layer, wherein the XLPE layer is arranged between the two aluminum electrodes.

3. A composite sensor for detecting partial discharge of a cable according to claim 1, characterized in that: The HFCT sensor includes a ferrite core and a HFCT, wherein the HFCT is wound on the ferrite core.

4. A composite sensor for detecting partial discharge of a cable according to claim 1, characterized in that: The signal mixing circuit includes a capacitor C1, a capacitor C2, a capacitor C3, a capacitor C4, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7 and an amplifier; The output end of the capacitive sensor is connected to one end of capacitor C1, the other end of capacitor C1 is respectively connected to ground resistor R1 and one end of capacitor C2, the other end of capacitor C2 is respectively connected to ground resistor R2 and one end of resistor R3, and the other end of resistor R3 is connected to the negative input end of the amplifier; the output end of the HFCT sensor is connected to one end of resistor R6, the other end of resistor R6 is respectively connected to ground capacitor C3 and one end of resistor R7, the other end of resistor R7 is respectively connected to ground capacitor C4 and one end of resistor R5, and the other end of resistor R5 is respectively connected to the output end of the amplifier and the input end of the signal output BNC connector.

5. A composite sensor for detecting partial discharge of a cable according to claim 4, characterized in that: The amplifier is AD8009.

6. A composite sensor for detecting partial discharge of a cable according to claim 1, characterized in that: A rotating shaft hinge is provided on one side of the sensor body, and openings are respectively provided on one side of the rotating shaft hinge and on the opposite side of the rotating shaft hinge for clamping the sensor body on the cable to be tested.

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