Power cable with insulating layer of oil-impregnated paper. The insulating layer is made of a certain width of cable paper spirally wrapped around the conductive wire core, and is impregnated with an impregnant after vacuum drying treatment.
Viscose impregnated paper insulated power cable 电缆 The viscosity of the impregnating agent is relatively high, and it is not easy to flow in the working temperature range of the cable, but it has a lower viscosity at the impregnation temperature, which can ensure good impregnation. The viscous impregnant is generally made of a mixture of bright oil and rosin (bright oil accounts for about 65-70%, and rosin accounts for about 30-35%). In many countries, synthetic resins (such as polyisobutylene) are used instead of rosin and mixed with bright oil to form low-voltage cable impregnants. Viscose-impregnated paper-insulated power cables can be divided into belt-insulated (all-in-one) and split-phase shielded (lead-in) types according to their structure. With insulated cable, a layer of paper insulation (phase insulation) is wrapped around a certain thickness of each conductive core, and then the three insulated cores are twisted together to form a layer of insulation (with insulation). A metal is shared outside Sheath; split-phase shielded cable is wrapped around the insulation of each insulated core and squeezed into a lead sheath. With insulation type, but the direction of the electric field strength in the insulation layer is not perpendicular to the paper surface, and there is a component along the paper surface, so it is generally only used for cables below 10 kV. The direction of the electric field strength in the split-phase shielded insulation is perpendicular to the paper surface, and it is mostly used for cables above 10 kV. Although the impregnating agent of the viscous impregnated paper-insulated power cable has a large viscosity, it still has a certain fluidity. When the laying drop is large, the upper end of the cable forms a gap due to the downward flow of the impregnating agent, the breakdown strength decreases, and the lower end impregnating agent is deposited, and the pressure increases, which can swell the cable sheath. Therefore, its laying drop is limited, and generally should not be greater than 30 meters.
1. Drip-drying paper-insulated power cables is a type of viscous impregnated paper-insulated power cables, that is, a drip-drying process is added after the viscous-impregnated cables are impregnated to reduce the impregnating agent between the viscous impregnated paper by 70% and the impregnating agent in the paper by 30. % To eliminate the disadvantages caused by the impregnating agent flow when the viscous impregnated paper insulated cable is laid at high drop. However, because the content of the impregnant is reduced, the dielectric strength of the insulation is reduced. For example, when the insulation thickness is the same, the withstand voltage strength of drip-dried paper-insulated power cables is 6 kV, and the withstand voltage strength of viscous impregnated paper cables is 10 kV. But the former can greatly improve the allowable laying gap.
2. Non-dripping paper-insulated power cable The difference between 粘性 and viscous impregnated paper-insulated cables is that its impregnating agent does not flow within the operating temperature range and is a plastic solid. The viscosity reduction at the impregnation temperature can ensure full impregnation. This cable laying drop is not limited by the insulation itself. It will gradually replace adhesive-impregnated paper-insulated cables.
3. Viscosity impregnation, drip-drying, and no dripping are all viscous impregnation type insulations. Because the thermal expansion coefficient of the solid material paper and the impregnant is very different, gas will inevitably be produced due to temperature changes during manufacturing and operation. Gap. Air gap is one of the main causes of cable damage. Therefore, sticky impregnated paper-insulated cables can only be used below 35 kV.
4. Oil-filled cables: Use the method of supplementary impregnation to eliminate air gaps in the cables. Its working principle is shown in Figure 3. When the temperature of the cable rises, the impregnating agent expands, the internal pressure of the cable increases, and the impregnating agent flows into the fuel supply tank; when the cable cools, the impregnating agent contracts, the internal pressure of the cable decreases, and the impregnating agent in the fuel supply tank flows into the cable again, preventing the generation of air gaps. It can be used for 110 kV and above. Its structure is divided into two categories. One is self-contained oil-filled cable. The impregnating agent is a low-viscosity mineral oil or dodecylbenzene. There is a hollow oil channel in the core of the conductive wire. The impregnating agent can be replenished into the insulation or inflow in time through it. Oil tank; another type is steel pipe oil-filled cable, impregnating agent is polybutene oil with a slightly higher viscosity, the core of the conductive wire is solid, and 3 insulated wires are placed in the seamless steel pipe together, and the pipe is filled with high pressure (generally (Approximately 1.5 MPa, 15 atmospheres) impregnating agent, the space between the steel pipe and the cable is the oil supply channel, and is connected to the oil supply system. It has excellent electrical performance and mechanical protection, but it has large fuel consumption and complicated joints, which is not suitable for high drop installation. Inflatable cable Insulated with drip-dry paper and filled with a certain pressure of gas to increase the breakdown field strength of the air gap and eliminate partial discharge. The cable structure is mostly three-core, and the space between the three cores is used as a gas transmission pipe. The gas is generally nitrogen or sulfur hexafluoride, etc., which is suitable for vertical 10kV to 110kV lines.
5. Pipe inflatable cable Also called compressed gas insulated cable. Its conductive core is placed in a pipe filled with a certain pressure gas (SF6). According to the number of cores, it can be divided into three-core and single-core cables. Single-core cables are divided into rigid and flexible types. The conductive wire core is usually an aluminum pipe or a copper pipe, and is supported in the pipe by a solid insulation gasket at a certain distance. The outer pipe is a cable jacket that doubles as a gas medium pressure vessel. Single-core cables are usually sheathed with aluminum or stainless steel pipes, and three-core cables can also be sheathed with steel pipes. Because the gas medium (SF6) is used, it has a small capacitance, low dielectric loss, and good thermal conductivity, so it has a large transmission capacity of 50,000 MVA. It is often used as a high-voltage outgoing line for large-capacity power plants, and the connection between closed power stations and overhead lines.