In daily study and work, everyone has come into contact with papers. With the help of papers, the purpose of discussing problems and conducting academic research can be achieved. I believe many friends feel very distressed about writing papers. Below is a paper on power cable fault analysis and preventive measures compiled by the editor, for reference only, and everyone is welcome to read it.
Abstract: Power cable line faults not only threaten the safe operation of the power grid and interrupt the continuous power supply of local grids, but also the detection, elimination, and repair of faults consume a large amount of manpower, material resources, and financial resources. Reducing and avoiding the occurrence of cable faults is the ultimate goal of cable construction and operation. Starting from actual work, this paper briefly discusses the fault classification of power cable lines, analyzes the causes, and on this basis proposes preventive measures for power cable line faults.
During long-term operation of cables, due to overload or damage from external forces, the core wire and insulation suffer varying degrees of damage, causing cable accidents. The more common types of power cable faults mainly include the following:
When the voltage reaches a certain value, flashover breakdown occurs between phases or between phase and ground of the cable. When the voltage decreases, the breakdown stops. Sometimes even if the voltage is increased again, breakdown may not occur, but it may happen again after a period of time.
One phase or several phases of the cable have very low insulation resistance to ground or between phases, but the conductor has good continuity. When the insulation resistance value is below 100kΩ, it is low-resistance grounding; if it is much lower than the normal value but higher than 100kΩ, it is high-resistance grounding.
For cable lines with insulation requirements on the sheath, after accurately measuring the location of the sheath fault, a patch of the same material as the sheath can be used, hot-air welded with a plastic welding gun or tightly wrapped with self-adhesive rubber tape. For sheaths with more damage, a heat-shrinkable wrap-around sleeve can be applied and then heated to shrink. After repair, the sheath should undergo a DC withstand voltage test or insulation resistance measurement.
Under normal circumstances, the ground insulation of electrical equipment in the power system only withstands phase voltage, and the insulation of various motors only withstands a few volts to tens of volts, with a maximum not exceeding a hundred volts. Due to certain reasons, the voltage acting on the insulation of electrical equipment may far exceed the above values. The duration of such abnormal voltage is obviously extremely short, but its value is very high, which can cause insulation breakdown or flashover of electrical equipment. This is dangerous overvoltage for the insulation of electrical equipment. Even for transient overvoltage, even if it is very short, it can cause thyristors to break down or be falsely triggered. Therefore, measures must be taken to prevent thyristors from withstanding overvoltage. It is usually caused by the induced electromotive force generated by the sudden change in current in the circuit due to the presence of inductive elements when the device it is in or adjacent electrical equipment is switched off, or when the conducting tube commutates. Its characteristic is short action time and spike shape.
Corrosion causes moisture ingress, leading to insulation damage of cables. Moisture ingress caused by corrosion perforation of cables is a common phenomenon in old cables that have been in operation for many years or in areas with electrochemical corrosion and chemical corrosion. In addition, poor quality of the cable outer sheath can also accelerate corrosion perforation of cables. Corroded cable lead sheaths usually have light yellow or pink granular corrosion products, and the places with corrosion products are the channels for lead sheath perforation and moisture ingress.
The process of thermal-oxidative aging of cable oil is as follows: In the oxidation induction period (initial stage), oxygen reacts with unsaturated hydrocarbons in the oil that have lower dissociation energy of chemical magnesium, generating hydrogen peroxide. In the oxidation development period (middle stage), the oxidation products of the oil increase rapidly, including aldehydes, ketones, hydroxy groups, and keto acids; aromatic hydrocarbons generate phenols after thermal oxidation. At this stage, the electrical performance of the oil deteriorates, and it has a strong corrosive effect on solid insulating materials. When the acid value reaches a certain level, addition and condensation polymerization reactions occur, generating resinous and asphaltic substances, and precipitating water.
At the same time, the oil becomes turbid, precipitates appear, the water absorption of the oil increases, and if it adheres to solid insulation, it affects heat dissipation. Oil that has deteriorated to a certain extent can no longer be used.
When selecting the cable type, attention should be paid to the rated voltage of the cable being greater than or equal to the rated voltage of the network it is in, and the maximum working voltage of the cable should not exceed 15% of its rated voltage. The continuous allowable current of the wire should be greater than or equal to the maximum continuous current of the power supply load. The cable conductor should use aluminum core as much as possible; only when movement is required or in places with severe vibration should steel core cables be used. Cables laid in cable structures should preferably use bare lead cables, and cables directly buried underground should use armored cables with a protective layer. Mobile machinery should use heavy-duty rubber-sheathed cables. Different cable sheaths should be selected according to the medium conditions. For corrosive soils, direct burial cables are generally not used; otherwise, cables with special anti-corrosion layers should be selected.
The quality of the cable is crucial for preventing water tree deterioration. Cable quality problems are mainly caused by poor production equipment, improper material selection, backward technology, and quality management and production management issues. Therefore, when selecting cables, one should have a certain understanding of the production process and management of the cable to be able to purchase high-quality cables and lay the foundation for reducing faults. Even if the cable quality is high, if the construction quality is not high, it can also cause hidden dangers. For this reason, the construction quality must be strictly controlled. The basic approaches are as follows: The quality of heat-shrink joint construction depends on sealing. To ensure good sealing, the following points should be strictly done: The heating temperature should be appropriate. Control the temperature of the blowtorch or propane spray gun to prevent overheating or underheating. During heat shrinking, the torch should be kept moving forward to preheat the tube and drive out the gas inside. The torch should be moved continuously to avoid burning the tube. Before moving the torch along the cable direction, it must be ensured that the tube has been fully and evenly shrunk in the circumferential direction. The two ends of the tube should be reheated. After the entire tube has been heat-shrunk, the two ends should be reheated again to ensure that the internal adhesive or hot-melt adhesive is fully melted and sealed. If the sealing parts of the joint are moved, they should be heated again to prevent opening. Judgment of good heat shrinking: After the tube is heat-shrunk, the surface should be smooth, without wrinkles or bubbles, and the outline of the internal structure should be clearly visible. After the adhesive or hot-melt adhesive at both ends of the tube is fully melted, there should be a slight overflow phenomenon.
Using capacitance to absorb overvoltage means storing the energy of overvoltage as electric field energy in the capacitor, and then dissipating it through the resistor. Common methods include connecting appropriate resistors across the thyristor. Capacitance absorption devices use the characteristic that the voltage across a capacitor cannot change abruptly to prevent thyristors from withstanding overvoltage. At the input or output end of the rectifier circuit, an RC absorption device is connected to protect against overvoltage caused by other reasons. Selenium stack protection is a nonlinear resistance element. It has a steep reverse characteristic and allows large currents to flow; after overvoltage, the selenium stack quickly breaks down, causing its resistance to decrease immediately, thereby suppressing the impact of overvoltage. The connection method of the selenium stack is to connect two groups of selenium stacks in reverse series and then connect them in parallel at the input end of the AC circuit.
The safe operation level of 10kV power cables directly affects the economic benefits of power enterprises and is closely related to power customers. Power enterprises should take corresponding preventive measures to avoid the occurrence of faults, eliminate defects in a timely manner, and ensure the safe operation of the 10kV distribution network.
[1] Zhang Gaoqing, Yang Jizhou, Liu Jianguo, Dong Anhua, Analysis of High-Voltage Power Cable Faults and Application of Detection Technology [J]. Zhongzhou Coal, 2008, (02).
[2] Yang Zhong, Zhou Xin, Niu Haiqing, Overview of Power Cable Fault Location Technology [J]. Electrical Applications, 2008, (21).
[3] Lu Honggang, Qin Jian, Chen Xiangxun. 35kV Power Cable Online] Fu Wenguang, Liu Zhilin, Liu Shixin. Fault Analysis and Preventive Measures for Heat-Shrinkable Termination Heads of 35kV Cross-linked Polyethylene Power Cables [J]. Inner Mongolia Electric Power Technology, 2008, (04).
[5] Wang Ming, Ye Qingshan. Analysis of Common Faults and Causes of Power Cables [J]. Rural Electrician, 2008, (02).
[6] Liu Jiyong, Several Practical Measurement Methods for Fault Points of Railway Power Cables [J] Industry and Technology Forum, 2009, (01).
