Composite sensor device for detecting partial discharge and sheath circulation of cable

Abstract

The invention belongs to the technical field of electronic measurement and sensing, and particularly relates to a composite sensor device for detecting cable partial discharge and sheath ring current, which comprises a Rogowski coil, an electric small loop antenna, a shielding shell, a sampling resistor, an SMA joint and a BNC joint. By integrating the monitoring method, the number of required equipment is reduced, so that the workload and cost of overall production, installation, debugging and maintenance are reduced, effective fusion and analysis of signals to be detected are facilitated, and comprehensive diagnosis support for the insulation state of the power cable is provided.

Description

Technical Field

[0001] The invention belongs to the field of electronic measurement and sensor technology, and specifically relates to a composite sensor device for detecting cable partial discharge and sheath circulating current, and is specifically applied to the field of power cable monitoring in the power transmission and distribution link of a power system. Background Art

[0002] In the power transmission and distribution process of the power system, the operating status of the power cable is directly related to the safety and stability of the power system. The partial discharge (PD) phenomenon of cable insulation and the circulating current (Circulating Current) in the sheath are important precursors and manifestations of power cable failures. Partial discharge refers to the discharge phenomenon caused by the local electric field strength exceeding the breakdown strength of the material in the insulating material. The detection of partial discharge can effectively detect insulation defects and deterioration. When current flows through the conductor in the cable, a magnetic field will be formed around it. The magnetic field will pass through the metal sheath of the cable, and an induced voltage will appear on the metal sheath. When a loop is formed between the metal sheath and the earth, a grounding current will be generated on the metal sheath. Monitoring of the circulating current can identify problems such as abnormal cable grounding and shielding layer damage. Therefore, effective monitoring of partial discharge and circulating current is of great significance in the operation and maintenance of power systems.

[0003] At present, the main methods for partial discharge detection include high-frequency current method, electromagnetic wave method, capacitive coupling method and ultrasonic detection method, etc. Since the general partial discharge signal is a relatively weak pulse signal and the actual measurement environment is complex, the existing partial discharge detection methods have certain disadvantages when used alone, such as low sensitivity, poor anti-interference performance and narrow measurement frequency band. On the other hand, the monitoring of circulating current is usually achieved through traditional current transformers (CT). The monitoring of circulating current alone can only respond to sudden insulation failures between phases or to the ground, and has no obvious response to the deterioration of insulation.

[0004] In the prior art, single sensor technology is often used to measure partial discharge and circulating current respectively. This method increases the workload and cost of on-site construction, installation, commissioning and maintenance; or the single sensors are simply combined together without considering the size, cost and reliability of the sensors.

[0005] Therefore, the existing technology urgently needs a composite sensor that can detect partial discharge and circulating current at the same time to reduce equipment costs and improve monitoring accuracy and convenience. This sensor should be able to take into account the high anti-interference performance and high sensitivity detection requirements of partial discharge, and at the same time be able to stably and accurately monitor the changes in sheath circulating current, thereby realizing multi-faceted monitoring of the operating status of power cables. Summary of the invention

[0006] The purpose of the present invention is to provide a composite sensor device for detecting cable partial discharge and sheath circulating current and a measurement method thereof, which can simultaneously monitor the partial discharge and sheath circulating current of power cables to solve the limitations of the prior art.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: a composite sensor device for detecting partial discharge and sheath circulating current of a cable, comprising a Rogowski coil, an electric small loop antenna, a shielding shell, a sampling resistor, an SMA connector and a BNC connector; the Rogowski coil is located inside the shielding shell, the electric small loop antenna is located on the surface of the shielding shell, and the electric small loop antenna and the shielding shell are insulated from each other; the Rogowski coil is connected to sampling resistors of different resistance values ​​on the same magnetic core with different turns to form two current transformers with different measurement bandwidths and different measurement sensitivities, and the two transformers are connected to two BNC connectors through wires to realize the output to be measured; the electric small loop antenna realizes the output to be measured through the SMA connector on the shielding shell; the grounding ends of the output ends of the two transformers and the shielding shell are grounded together.

[0008] The Rogowski coil adopts a self-integration mode, which is composed of a certain number of turns of enameled wire wound on a magnetic core. The measurement bandwidth and sensitivity of the two current transformers can be obtained by adjusting the corresponding number of turns and the resistance value of the sampling resistor. The part with more turns corresponds to the part used to measure the circulating current, and the part with fewer turns corresponds to the part used to measure the partial discharge.

[0009] The electric small loop antenna consists of a signal line and a ground plane on the surface of a shielding shell. The signal line and the ground plane are located in the same plane, the signal line is located in the middle, and the ground plane is located on the left and right sides. Based on the electric small loop principle, the signal line of the magnetic field probe is wound into a ring structure to couple magnetic field energy. In addition, the end of the signal line wound into the ring structure is short-circuited with the ground plane, and the other end forms a coplanar waveguide transmission line structure with the ground plane, thereby forming a closed loop.

[0010] The part of the Rogowski coil corresponding to measuring partial discharge of the present invention forms a sub-composite sensor together with the electric small loop antenna on the shell. The former has high measurement sensitivity and can realize the quantification of partial discharge, but has poor anti-interference performance and a narrow frequency band; the latter has a wide measurement frequency band and good anti-interference performance, but cannot realize the quantification of partial discharge; the two are combined together to achieve complementarity and realize effective monitoring of partial discharge in power cables.

[0011] Another object of the present invention is to provide a composite measurement method for detecting partial discharge and sheath circulating current of a cable, which comprises the following steps:

[0012] (1) The composite sensor is installed at the middle joint or terminal of the power cable, so that the Rogowski coil and the electric loop antenna can sense the current signal and electromagnetic field signal in the cable respectively;

[0013] (2) The sheath circulating current signal and the partial discharge signal are detected respectively by combining different turns of the Rogowski coil with different sampling resistors;

[0014] (3) Detect high-frequency electromagnetic signals caused by partial discharge through electric small loop antenna;

[0015] (4) Output the signals from the Rogowski coil and the electric small loop antenna through the BNC connector and the SMA connector;

[0016] (5) Combine the output signals of the two sensors to comprehensively analyze the insulation status of the cable. By analyzing and processing the measured partial discharge signal and sheath circulating current signal respectively, real-time monitoring of the operating status of the power cable can be achieved.

[0017] The present invention combines two measurements to be measured, local discharge and sheath circulating current, to form a composite device and a measurement method, and combines a high-frequency current method (HFCT) and a very high frequency method (VHF) to form a sub-composite measurement method. This method not only improves the measurement bandwidth and anti-interference capability of local discharge, but also reduces the number of required equipment by integrating monitoring methods, thereby reducing the workload and cost of overall production, installation, commissioning and maintenance, which is beneficial to the effective fusion and analysis of the signals to be measured, and provides comprehensive diagnostic support for the insulation status of power cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the overall structure of the device of the present invention;

[0019] Figure 2 It is a schematic diagram of the structure of the Rogowski coil inside the device of the present invention;

[0020] Figure 3 It is a schematic diagram of the process of the present invention;

[0021] In the figure, 1 is the signal line of the small loop antenna, 2 is the upper cover of the shielding shell of the sensor, 3 is the lower shell of the shielding shell of the sensor, 4 is the right half ground plane of the small loop antenna, 5 is a BNC interface connected to the output of the partial discharge measuring part in the Rogowski coil, 6 is a BNC interface connected to the sheath circulating current measuring part in the Rogowski coil, 7 is an SMA interface connected to the signal line and the ground plane of the small loop antenna, 8 is the left half ground plane of the small loop antenna, 9 is the sampling resistor corresponding to the partial discharge measuring part in the Rogowski coil, 10 is the sampling resistor corresponding to the sheath circulating current measuring part in the Rogowski coil, 11 is the enameled wire wound on the Rogowski coil, and 12 is the magnetic core of the Rogowski coil. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0023] Example 1

[0024] like Figure 1-2 As shown, a composite sensor device for detecting partial discharge and sheath circulating current of a cable comprises a Rogowski coil, an electric small loop antenna, a shielding shell, a sampling resistor, an SMA connector and a BNC connector;

[0025] In this example, the Rogowski coil adopts a self-integral mode, which is composed of an enameled wire with a certain number of turns wound around a magnetic core.

[0026] In this example, the Rogowski coil of the device is connected to sampling resistors of different resistance values ​​on the same magnetic core with different turns to form current transformers with different measurement bandwidths and different measurement sensitivities. The measurement bandwidths and sensitivities of the two current transformers can be obtained by adjusting the corresponding turns and sampling resistor values. The part with more turns corresponds to the part for measuring the circulating current, and the part with fewer turns corresponds to the part for measuring the partial discharge. The middle joint of the power cable and the grounding wire at the terminal are passed through the center hole of the sensor, and the corresponding output is obtained through electromagnetic coupling. The relationship between the turns and the sampling resistor and the object to be measured and the output is as follows:

[0027]

[0028] In this example, two mutual inductors formed by connecting different sampling resistors with different numbers of turns in the Rogowski coil are connected to two BNC connectors through wires to realize the output of the measurement to be measured.

[0029] In this example, the Rogowski coil is located inside the shielding shell, the electric small loop antenna is located on the surface of the shielding shell, and the electric small loop antenna and the shielding shell are insulated from each other.

[0030] In this example, the electric small loop antenna mainly plays the role of near-field detection. Generally speaking, the maximum geometric size of the antenna is much smaller than the working wavelength of the antenna, that is, the antenna that satisfies the following formula can be called an electric small antenna:

[0031]

[0032] In this example, the cable joints and terminals have a high failure rate of up to 70%, which is a high-risk point for failures. Therefore, the sensor is usually installed near the middle joint and terminal of the power cable. In addition to ensuring that the grounding wire at the middle joint and terminal of the power cable passes through the center hole of the sensor, it is also necessary to ensure that the electric loop antenna is facing the middle joint or terminal of the power cable to ensure that the electromagnetic waves transmitted from there can be received. The expression of the magnetic field strength generated by the pulse current is:

[0033]

[0034] The time-varying electric field generated by the time-varying magnetic field is:

[0035]

[0036] In this example, the total length of the wound electric small loop antenna wire is much smaller than its operating wavelength, so it can be assumed that the magnetic field through the loop area is uniformly distributed, and the magnitude of the induced electromotive force can be further obtained:

[0037]

[0038] In this example, the electric loop antenna is mainly composed of a signal line and a ground plane on the surface of the shielding shell. The signal line and the ground plane are located in the same plane, the signal line is located in the middle, and the ground plane is located on the left and right sides. Based on the electric loop principle, the signal line of the magnetic field probe is wound into a ring structure to couple the magnetic field energy. In addition, the end of the signal line wound into a ring structure is short-circuited with the ground plane, and the other end forms a coplanar waveguide transmission line structure with the ground plane, thereby forming a closed loop. The designed probe upper cutoff frequency is mainly affected by the stray capacitance of the probe, that is, the equivalent size of the electric loop. That is, for a single-turn electric loop probe, the frequency of the highest measurable signal and its loop radius have the following relationship:

[0039]

[0040] In addition, S 12 To represent the frequency response characteristics of the probe, where b 1 represents the normalized output wave voltage of port 1, a 1 、a 2 Represent the normalized incident wave voltage at ports 1 and 2 respectively:

[0041]

[0042] In this example, the electric loop antenna achieves the output to be measured through the SMA connector on the shielded housing.

[0043] In this example, the part of the Rogowski coil corresponding to measuring partial discharge forms a sub-composite sensor together with the electric small loop antenna on the outer casing. The former has high measurement sensitivity and can realize the quantification of partial discharge, but has poor anti-interference performance and a narrow frequency band; the latter has a wide measurement frequency band and good anti-interference performance, but cannot realize the quantification of partial discharge; the two are combined together to achieve complementarity and realize effective monitoring of partial discharge in power cables.

[0044] In this example, the ground terminals of the two transformer output terminals formed by connecting different sampling resistors with different numbers of turns in the Rogowski coil and the shielding shell are connected to a common ground.

[0045] The composite measurement method for detecting partial discharge and sheath circulating current in cables is carried out through the following steps:

[0046] (1) The sub-composite sensor formed by the first current transformer in the Rogowski coil and the electric small loop antenna is used to monitor partial discharge; and the output is output through the first BNC connector and the SMA connector on the shielding shell;

[0047] The second current transformer in the Rogowski coil is used to monitor the sheath circulating current; the output is carried out through the second BNC connector on the shielding shell;

[0048] (2) The measured partial discharge signal and sheath circulating current signal are analyzed respectively to realize real-time monitoring of the operating status of the power cable.

[0049] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A composite sensor device for detecting partial discharge and sheath circulating current of a cable, characterized in that: The invention comprises a Rogowski coil, an electric small loop antenna, a shielding shell, a sampling resistor, an SMA connector and a BNC connector; the Rogowski coil is located inside the shielding shell, the electric small loop antenna is located on the surface of the shielding shell, and the electric small loop antenna and the shielding shell are insulated from each other; the Rogowski coil is connected to sampling resistors with different resistance values ​​on the same magnetic core with different turns to form two current transformers with different measurement bandwidths and different measurement sensitivities, and the two transformers are connected to two BNC connectors through wires to realize the output to be measured; the electric small loop antenna realizes the output to be measured through the SMA connector on the shielding shell; the grounding ends of the output ends of the two transformers and the shielding shell are grounded in common.

2. The composite sensor device for detecting cable partial discharge and sheath circulating current according to claim 1 is characterized in that: The Rogowski coil adopts a self-integrating mode and is composed of an enameled wire with a certain number of turns wound around a magnetic core.

3. The composite sensor device for detecting cable partial discharge and sheath circulating current according to claim 1, characterized in that: The electric small loop antenna consists of two parts: a signal line and a ground plane on the surface of a shielding shell.

4. A composite measurement method for detecting partial discharge and sheath circulating current of a cable, using the composite sensor device according to any one of claims 1 to 3, characterized in that Go through the following steps: (1) The composite sensor is installed at the middle joint or terminal of the power cable, so that the Rogowski coil and the electric loop antenna can sense the current signal and electromagnetic field signal in the cable respectively; (2) The sheath circulating current signal and the partial discharge signal are detected respectively by combining different turns of the Rogowski coil with different sampling resistors; (3) Detect high-frequency electromagnetic signals caused by partial discharge through electric small loop antenna; (4) Output the signals from the Rogowski coil and the electric small loop antenna through the BNC connector and the SMA connector; (5) Combine the output signals of the two sensors to conduct a comprehensive analysis of the insulation status of the cable.

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