Device for detecting defects of outer sheath of 35kV single-core power cable

Abstract

The utility model relates to the technical field of power supply line fault detection, and particularly discloses a 35kV single-core power cable outer sheath defect detection device, which comprises a direct-current power supply transmitter, an intelligent receiver and a current coupling clamp, and is characterized in that the direct-current power supply transmitter is provided with a high-voltage output interface, a protection grounding interface and a working grounding interface; the protection grounding interface and the working grounding interface are connected with a transformer substation grounding copper bar, the high-voltage output interface is connected with one end of the cable metal shielding layer, and the other end of the cable metal shielding layer is a metal shielding layer throwing end. The intelligent receiver is provided with a signal input port and a display, the signal input port is linearly connected with a signal output port of the current coupling clamp, a fault detection waveform is displayed on the display, and the current coupling clamp is clamped outside a cable; according to the utility model, the position of a fault point can be judged by comparing the strength of signals, the test detection method is simple, the abnormal grounding condition of the metal shielding layer of the single-core cable can be found in time, and cable grounding and even short-circuit accidents are avoided.

Description

Technical Field

[0001] This utility model relates to the field of power line fault detection technology, specifically to a device for detecting defects in the outer sheath of a 35kV single-core power cable. Background Technology

[0002] 35kV single-core power cables are widely used due to their advantages such as high current carrying capacity, small bending radius, ability to withstand higher voltages, and flexible laying paths. However, the operation and maintenance management of power cables faces many new problems and challenges. For example, during the laying process of high-voltage single-core power cables, they are subjected to complex construction environments, especially at bends and shaft openings, where they are subjected to mechanical forces such as traction, lateral pressure, and clamping forces. Their outer sheaths may suffer damage such as impacts, cracks, deformation, and scratches. In addition, improper construction operations, poor quality of the cable's own insulation sheath, and aging can all cause damage to the cable's outer sheath insulation. This can lead to two or more grounding points in the cable's metal shielding layer, an increase in the circulating current generated by the cable's metal shielding, continuous heating of the metal shielding layer, accelerated aging of the main insulation, and even burning or igniting of the cable's outer sheath and main insulation, resulting in cable breakdown, grounding, and fire. Arc overvoltage can cause two-phase grounding, short circuit tripping, and power loss accidents. Some cables can also allow moisture to enter through the damaged outer sheath, causing water treeing aging in the main insulation, which can ultimately lead to cable failure. Existing technologies utilize cable partial discharge (PD) testers for preventative cable testing. However, PD testers are suitable for detecting cable defects with severe main insulation damage. They cannot effectively detect minor outer sheath defects in advance, even though these defects pose a high potential risk. If left unchecked, they can cause damage to the cable's main insulation, cable grounding, or even short-circuit faults. Therefore, there is an urgent need to design a 35kV single-core power cable outer sheath defect detection device to address the problem that existing cable testers cannot effectively detect outer sheath damage in advance, resulting in a high potential operational risk for the cable. Utility Model Content

[0003] In view of the problems existing in the prior art, the purpose of this utility model is to provide a defect detection device for the outer sheath of a 35kV single-core power cable, which can promptly detect abnormal grounding of the metal shielding layer of the single-core cable, and take timely measures to avoid damage to the main insulation of the cable, cable grounding, or even short circuit accidents.

[0004] The technical solution adopted by this utility model to solve its technical problem is: a 35kV single-core power cable outer sheath defect detection device, including a DC power transmitter, an intelligent receiver and a current coupling clamp. The DC power transmitter is provided with a high voltage output interface, a protective grounding interface and a working grounding interface. The protective grounding interface and the working grounding interface are connected to the substation grounding copper busbar. The high voltage output interface is connected to one end of the cable metal shielding layer. The other end of the cable metal shielding layer is set as the metal shielding layer unsupported end.

[0005] The intelligent receiver is equipped with a signal input port and a display. The signal input port is linearly connected to the signal output port of the current coupling clamp. The display shows the fault detection waveform. The current coupling clamp is clamped on the outside of the cable.

[0006] Specifically, the high-voltage output interface, protective grounding interface, and working grounding interface are all located on the transmitter panel of the DC power transmitter. The transmitter panel is also equipped with a main power switch, a display screen, a working mode switch, a start / stop switch, and a step-up / step-down switch.

[0007] Specifically, the main power switch turns the DC power transmitter on or off; the operating mode switch can select DC mode, withstand voltage mode, and pulse mode; the start / stop switch controls the on / off of the high voltage output interface; and the boost / buck switch controls the adjustment of boost or buck voltage by tossing it left or right.

[0008] Specifically, the smart receiver is also equipped with a power switch, a gain increase adjustment button, a gain decrease adjustment button, and a battery charging dock.

[0009] Specifically, the switch turns the power supply of the smart receiver on or off.

[0010] Specifically, the cable includes, but is not limited to, an internal cable core and an external cable sheath. A cable metal shielding layer is provided between the cable core and the cable sheath. One end of the cable is a substation-side cable terminal, which is connected to the substation feeder switchgear. The cable metal shielding layer of the substation-side cable terminal is connected to the high-voltage output interface of the DC power transmitter. The other end of the cable is a user-side cable terminal.

[0011] This utility model has the following beneficial effects:

[0012] This utility model designs a 35kV single-core power cable outer sheath defect detection device. It uses a DC power supply transmitter to transmit a pulse signal from one side of the metal shielding layer where voltage is applied to the other side. The signal is strong before the fault point, and the signal strength drops sharply after passing the fault point. The location of the fault point can be determined by comparing the signal strength on the cable fault intelligent receiver. The testing and detection method is simple and can detect abnormal grounding of the metal shielding layer of the single-core cable in a timely manner, avoiding cable grounding or even short circuit accidents. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the wiring structure of the metal shielding layer of a 35kV single-core power cable in the prior art.

[0014] Figure 2 This is a schematic diagram of the wiring structure of the 35kV single-core power cable outer sheath defect detection device of this utility model.

[0015] Figure 3 This is a schematic diagram of the panel layout of the DC power transmitter of this utility model.

[0016] Figure 4 This is a schematic diagram of the panel layout of the intelligent receiver of this utility model.

[0017] Figure 5 This is a schematic diagram of the current coupling clamp of this utility model.

[0018] Figure 6 This is a flowchart of the test method for the 35kV single-core power cable outer sheath defect detection device of this utility model.

[0019] In the diagram: 1-Cable core; 2-Cable outer sheath; 3-Cable metal shielding layer; 4-Substation side cable terminal; 5-User side cable terminal; 6-Metal shielding layer grounding; 7-Metal shielding layer overvoltage protector grounding;

[0020] 8-DC power transmitter, 8.1-Transmitter panel, 8.2-Main power switch, 8.3-Display screen, 8.4-High voltage output interface, 8.5-Protective grounding interface, 8.6-Working grounding interface, 8.7-Working mode switch, 8.8-Start / stop switch, 8.9-Boost / buck switch;

[0021] 9-Smart receiver, 9.1-Signal input port, 9.2-Switch, 9.3-Gain increase adjustment button, 9.4-Gain decrease adjustment button, 9.5-Battery charging dock, 9.6-Display;

[0022] 10 - Current coupling clamp; 10.1 - Signal output port;

[0023] 11-Metallic shielding layer unloaded terminal; 12-Substation grounding copper busbar. Detailed Implementation

[0024] The technical solutions of the present utility model will be described in further detail below with reference to the accompanying drawings of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present utility model without creative effort are within the scope of protection of the present utility model.

[0025] like Figure 1The diagram shows a schematic of the wiring structure of the metallic shielding layer of a 35kV single-core power cable in the prior art. Under normal circumstances, only one end of the cable's metallic shielding layer 3 is directly grounded, while the other end is grounded via an overvoltage protector or left ungrounded. The function of the cable's metallic shielding layer 3 is to maintain ground potential. During normal operation, a small capacitive current flows through the cable's metallic shielding layer 3. In the event of a short circuit or ground fault in the system, the cable's metallic shielding layer 3 can act as a path for the short-circuit current and also serves to shield the electric field. Figure 1 The cable metal shielding layer 3 shown is directly grounded 6 on the substation side and grounded 7 on the user side via the cable metal shielding layer overvoltage protector.

[0026] like Figures 2-5 As shown, a defect detection device for the outer sheath of a 35kV single-core power cable includes a DC power transmitter 8, an intelligent receiver 9, and a current coupling clamp 10. The DC power transmitter 8 is equipped with a transmitter panel 8.1, which includes a main power switch 8.2, a display screen 8.3, a high-voltage output interface 8.4, a protective grounding interface 8.5, a working grounding interface 8.6, a working mode switch 8.7, a start / stop switch 8.8, and a step-up / step-down switch 8.9. The protective grounding interface 8.5 and the working grounding interface 8.6 are connected to the substation grounding copper busbar 12. The high-voltage output interface 8.4 is connected to one end 6 of the cable's metal shielding layer 3, and the other end of the cable's metal shielding layer 3 is set as a metal shielding layer unsupported end 11.

[0027] The main power switch 8.2 is used to turn the DC power transmitter 8 on or off; the start / stop switch 8.8 controls the high-voltage output on / off switch. After the main power switch 8.2 is turned on, starting or stopping this switch controls the on / off state of the high-voltage output interface 8.4; the boost / buck switch 8.9 allows for voltage adjustment by tossing it left and right. The percentage display in the lower left corner of the display 8.3 shows the voltage boost level, with 100% indicating the maximum high-voltage output of the high-voltage output interface 8.4; the high-voltage output interface 8.4 provides a stable and reliable high voltage for fault measurement and withstand voltage testing. During operation, a dedicated high-voltage cable is used to reliably connect the high-voltage output interface 8.4 to one end 6 of the cable's metal shielding layer 3; Before operating the instrument for testing, the protective grounding interface 8.5 should be reliably grounded separately and connected to the substation grounding copper busbar 12 to ensure personal and equipment safety. Before operating the instrument for testing, the working grounding interface, being the current return terminal, should be reliably grounded to the substation grounding copper busbar 12 to ensure personal and equipment safety. The LCD display 8.3 displays the current operating status and parameters through a human-machine interface. The working mode switch 8.7 has three positions: DC, withstand voltage, and pulse. Before powering on, the working mode should be selected, and a specific working state should be entered according to the work requirements. After entering a specific working state, the start / stop switch 8.8 should be pressed, and the boost / buck switch 8.9 should be toggled to raise the voltage or current to the required value for corresponding work.

[0028] The DC power transmitter 8 has the following specifications: Operating AC power: AC220V±10%, 50Hz; Input power: 1000W; Display: 5.6-inch LCD screen; Output voltage: DC 0~15kV negative high voltage; continuously adjustable; Operating mode: DC, withstand voltage, pulse; Maximum output current: 1A. It can operate continuously with a short circuit; Withstand voltage range: 00~15kV negative high voltage; Maximum current: 1000μA. Dimensions: 450mm×330mm×350mm; Weight: 20kg.

[0029] Work style selection:

[0030] DC output: Outputs DC power, mainly used for initial fault testing. The continuous output power is generally adjusted to between 200W and 700W.

[0031] Pulse output: Outputs a pulsed DC pulse, with a 1-second pulse width DC pulse output every 3 seconds. It is mainly used for fault location. The output power is generally adjusted to between 200W and 400W.

[0032] Withstand voltage test: Set the operating mode selection switch to the DC position, follow the prompts on the LCD touchscreen to enter the DC mode interface, increase the voltage to the preset withstand voltage value, and the duration is the same as the withstand voltage test time. If there is no high voltage breakdown of the sheath, return to the withstand voltage mode interface to start the withstand voltage test. The withstand voltage test is mainly used for preventive testing of cables and can measure the leakage current of the cable; the current measurement accuracy is μA level. When the current is greater than 1000μA, the system current test automatically switches to the mA range.

[0033] The intelligent receiver 9 is equipped with a signal input port 9.1, a switch 9.2, a gain increase adjustment button 9.3, a gain decrease adjustment button 9.4, a battery charging dock 9.5, and a display 9.6. The signal transmission port 9.1 is linearly connected to the signal output port 10.1 of the current coupling clamp 10. The display 9.6 shows the fault detection waveform. The current coupling clamp 10 is clamped on the outside of the cable.

[0034] Switch 9.2 is used to turn the power on or off; signal input port 9.1 is the connection port between the intelligent receiver 9 and the current coupling clamp 10; LCD display 9.6, the intelligent receiver 9 uses a color LCD display to show signal waveform, intensity, gain, and battery level; gain increase adjustment button 9.3: pressing this button increases the gain by 1 division, up to a maximum of 10 divisions; gain decrease adjustment button 9.4: pressing this button decreases the gain by 1 division, down to a minimum of 0 divisions. The adjustable range of gain is 0 to 10 divisions. During testing, if the signal amplitude is too large, the user should reduce the gain; battery charging port 9.5 (spare), when the instrument is equipped with a rechargeable battery, it can be charged through this port; when the battery power is low, please replace the battery in time, or charge the rechargeable battery.

[0035] The current coupling clamp 10 is an open type, allowing the faulty phase cable to pass through by opening the opening. The current coupling clamp 10 has markings indicating the direction of the current arrow; the direction of the pulse current flowing into the single-core cable must be the same as the direction indicated by the current arrow.

[0036] The specifications of the Smart Receiver 9 are as follows: Display method: color LCD display; Display range: 50-0-50 (wider display range and higher resolution); Sensitivity: 0.10mV; Power supply: 6×1.5V; Dimensions: 120mm×120mm×230mm; Weight: 1kg.

[0037] During testing, the signal output port 10.1 of the current coupling clamp 10 is connected to the signal input port 9.1 of the smart receiver 9 via a control cable.

[0038] The cable includes an inner cable core 1 and an outer cable sheath 2. A cable metal shielding layer 3 is provided between the cable core 1 and the cable sheath 2. One end of the cable is a substation-side cable terminal 4, which is connected to the substation feeder switch cabinet. One end 6 of the cable metal shielding layer 3 of the substation-side cable terminal 4 is connected to the high-voltage output interface 8.4 of the DC power transmitter 8. The other end of the cable is a user-side cable terminal 5.

[0039] like Figure 6 As shown, a test method for a 35kV single-core power cable outer sheath defect detection device includes the following steps:

[0040] 1. Change the substation feeder switchgear cable line from operation to maintenance.

[0041] Disconnect the circuit breaker on the user side of the substation feeder switchgear line; open the isolating switches on both sides of the circuit breaker; close the grounding switch on the user's incoming power supply side; close the grounding switch on the outgoing side of the substation feeder switchgear.

[0042] 2. Disconnect one end of the metal shielding layer 3 of the three-phase power cable on the feeder switchgear side of the substation from the direct grounding 6, leaving it in an unsupported state. Disconnect the other end of the metal shielding layer of the three-phase power cable on the user side from the grounding 7 via the voltage protector, leaving it in an unsupported state, and maintain a sufficient safe distance from the grounding body.

[0043] 3. Install a DC power supply transmitter for testing cable outer sheath faults.

[0044] At the feeder switchgear of the substation, the high-voltage output interface 8.4 of the DC power transmitter 8 is connected to one end 6 of the metal shielding layer 3 of phase A of the power cable via a dedicated cable. The working grounding interface 8.6 of the DC power transmitter 8 is connected to the grounding copper busbar via a dedicated cable. The protective grounding interface 8.5 of the DC power transmitter 8 is connected to the grounding copper busbar via a dedicated cable.

[0045] 4. Perform insulation resistance testing on the metal shielding layer of phase A cable.

[0046] Use a 1kV or 500V megohmmeter to test the insulation resistance of the metal shield layer 3 of phase A of the power cable. A reading of 15MΩ indicates normal insulation resistance. The standard value should be greater than 0.5MΩ / km.

[0047] 5. Conduct a DC withstand voltage leakage test on the metal shielding layer 3 of phase A cable. Gradually increase the DC power supply voltage to 5000V and continue for 1 minute. Check if the leakage current value is normal. If the leakage current value is very small, it indicates that the cable outer sheath 2 is normal. If it is higher than the leakage current setting value, it indicates that the cable outer sheath 2 has a damage defect.

[0048] First, turn on the main power switch 8.2 of the DC power transmitter 8, rotate the working mode switch 8.7 to the withstand voltage position, and start rotating the boost / buck switch 8.9 to the boost position. The DC power supply will gradually increase to 30% of the rated voltage, i.e., the set value (5000V), and continue for a certain period of time (1 minute). Observe the leakage current value on the LCD screen 8.3 of the tester to see if it is normal. When normal, the leakage current value is very small, such as 2.5mA. If the discharge leakage current is large, reaching tens of milliamps, such as 50mA or even 300mA, it indicates that there is a defect in the cable outer sheath 2, and the metal shielding layer discharges to ground during DC withstand voltage testing. The larger the leakage current value, the more serious the defect in the outer sheath.

[0049] If it is determined that the discharge leakage current of the metal shielding layer 3 of the phase cable is higher than the set current value (e.g., it can be set to 20mA), it indicates that there is an abnormal discharge of the metal shielding layer 3 of the phase cable to the ground or cable tray, indicating that the outer sheath 2 of the cable is damaged.

[0050] 6. After the A-phase test is completed, first slowly reduce the DC voltage to 0V, disconnect the main power switch 8.2 of the DC power transmitter 8, and fully discharge the metal shielding layer 3 of the A-phase cable to ground.

[0051] 7. Using the test method described above for phase A, test the metal shielding layer 3 of the cable for phases B and C respectively.

[0052] 8. Cable outer sheath 2 defect point search: Send DC pulse voltage to the cable metal shielding layer 3 of the defective phase of the outer sheath, hold the intelligent cable fault receiver 9 and current coupling clamp 10, and test along the cable power supply path from the substation side to the user side.

[0053] Rotate the operating mode switch 8.7 to the pulse position, and activate the rotary boost / buck switch 8.9 to the boost position to send a DC pulse voltage. At this time, there will be a relatively high leakage current. Then, use the handheld cable fault intelligent receiver 9 and current coupling clamp 10 to perform tests along the cable power supply path from the substation side to the user side.

[0054] 9. If the intelligent receiver for cable faults shows a normal pulse waveform, the defect point of the outer sheath is somewhere between this point and the user-side cable. If the waveform attenuation is severe or there is no waveform display at the test point, it indicates that the defect point of the outer sheath is somewhere between this point and the substation-side cable. Continue testing and troubleshooting in this way until the defect point of the cable outer sheath is found.

[0055] Turn on the main power switch 8.2 of the DC power transmitter 8, rotate the working mode switch 8.7 to the pulse position, and start the boost switch 8.9 to the boost position. The DC power supply starts to boost and outputs pulsed DC. It outputs a 1-second pulse width DC every 3 seconds. This pulse signal is transmitted along the metal shielding layer 3 of the cable to the terminal. The signal is stronger before the fault point and the signal strength drops sharply after passing the fault point. The location of the fault point can be determined by comparing the strength of the signal. If the voltage is boosted to 1700V, sometimes it fails to rise. In this case, the leakage current is observed to be 690mA. Simultaneously, use the handheld cable fault intelligent receiver 9 and current coupling clamp 10 to test along the cable power supply path from the substation side to the user side. To improve the efficiency of the search, observe the waveform on the cable fault intelligent receiver 9 at the middle of the faulty phase cable. If there is a normal pulse waveform, the defect point of the cable outer sheath 2 is somewhere between that point and the user cable. If the test waveform is severely attenuated or there is no waveform display, it indicates that the defect point of the cable outer sheath 2 is somewhere between that point and the substation cable. Continue this testing and troubleshooting until the defective part of the cable outer sheath is found.

[0056] The test method for defects in the outer sheath of 35kV single-core power cables is simple and can detect abnormal grounding of the metal shielding layer of single-core cables in a timely manner, thus avoiding cable grounding or even short-circuit accidents.

[0057] Typical Case 1: During a DC withstand voltage test on the outer sheath of a 35kV converter line I cable at a certain company, a leakage current of 260mA was detected. After transmitting a DC pulse voltage, a handheld cable fault intelligent receiver and current coupling clamp were used on-site to test segment by segment. The waveform amplitude was relatively small, indicating a large leakage current in the cable, which also indicated that the cable outer sheath was severely damaged.

[0058] This utility model is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this utility model, and any technical solutions that are the same as or similar to this utility model, fall within the protection scope of this utility model.

[0059] The technologies, shapes, and structures not described in detail in this utility model are all known technologies.

Claims

1. A defect detection device for the outer sheath of a 35kV single-core power cable, characterized in that, The system includes a DC power transmitter, a smart receiver, and a current coupling clamp. The DC power transmitter is equipped with a high-voltage output interface, a protective grounding interface, and a working grounding interface. The protective grounding interface and the working grounding interface are connected to the substation grounding copper busbar. The high-voltage output interface is connected to one end of the cable's metal shielding layer, and the other end of the cable's metal shielding layer is set as the metal shielding layer's unsupported end. The intelligent receiver is equipped with a signal input port and a display. The signal input port is linearly connected to the signal output port of the current coupling clamp. The display shows the fault detection waveform. The current coupling clamp is clamped on the outside of the cable.

2. The 35kV single-core power cable outer sheath defect detection device according to claim 1, characterized in that, The high-voltage output interface, protective grounding interface, and working grounding interface are all located on the transmitter panel of the DC power transmitter. The transmitter panel is also equipped with a main power switch, a display screen, a working mode switch, a start / stop switch, and a step-up / step-down switch.

3. The 35kV single-core power cable outer sheath defect detection device according to claim 2, characterized in that, The main power switch turns the DC power transmitter on or off; the working mode switch can select DC mode, withstand voltage mode, and pulse mode; the start / stop switch controls the on / off of the high voltage output interface; the boost / buck switch controls the adjustment of boost or buck voltage by tossing it left or right.

4. The 35kV single-core power cable outer sheath defect detection device according to claim 1, characterized in that, The smart receiver is also equipped with a power switch, a gain increase adjustment button, a gain decrease adjustment button, and a battery charging dock.

5. The 35kV single-core power cable outer sheath defect detection device according to claim 4, characterized in that, The switch turns the power supply of the smart receiver on or off.

6. The 35kV single-core power cable outer sheath defect detection device according to claim 1, characterized in that, The cable includes, but is not limited to, an internal cable core and an external cable sheath. A cable metal shielding layer is provided between the cable core and the cable sheath. One end of the cable is a substation-side cable terminal, which is connected to the substation feeder switchgear. The cable metal shielding layer of the substation-side cable terminal is connected to the high-voltage output interface of the DC power transmitter. The other end of the cable is a user-side cable terminal.

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