Tiankang high voltage cable wiring
The copper shield and steel truss of Tiankang high-voltage cable generally need to be grounded. What is the difference between grounding at both ends and grounding at one end? Can the steel truss and copper shield be welded together when making the cable termination? Can the steel sill and copper shield be welded together when making the middle of the cable?
The 35KV high-voltage cable is mostly a single-core cable. When the single-core cable is energized, an induced voltage is formed in the shielding layer. If the shielding at both ends is grounded at the same time, a loop is formed between the shielding layer and the ground, and an induced current is generated. The layer will generate heat and consume a large amount of electric energy, which will affect the normal operation of the line. In order to avoid this phenomenon, one end is grounded. When the line is long, the midpoint grounding and cross interconnection can also be used.
When making the cable head, the steel shovel and the copper shielding layer are separately grounded and grounded, in order to facilitate the detection of the inner layer of the cable. When detecting the cable sheath, the voltage between the steel sill and the copper shield is applied. The voltage is proof that the inner sheath is intact. If there is no such requirement, it is not necessary to detect the inner sheath of the cable. It is also possible to connect the steel shovel and the copper shield to the ground (we advocate separate grounding after extraction).
Why is a high-voltage single-core XLPE insulated power cable with a special grounding method?
The power safety regulations stipulate that cables of 35kV and below are grounded at both ends. This is because most of these cables are three-core cables. In normal operation, the total current flowing through the three cores is zero. There is basically no flux linkage outside the package or metal shield layer, so that there is substantially no induced voltage at both ends of the aluminum package or the metal shield layer, so that no induced current flows through the aluminum package or the metal shield layer after the two ends are grounded. However, when the voltage exceeds 35kV, most of them use a single-core cable. The relationship between the core of a single-core cable and the metal shield can be regarded as the primary winding of a transformer. When the single-core cable core passes current, there will be a magnetic wire cross-linked aluminum package or a metal shield layer, so that the induced voltage appears at both ends.
The magnitude of the induced voltage is proportional to the length of the cable line and the current flowing through the conductor. When the cable is long, the induced voltage on the sheath is superimposed to the extent that it can endanger personal safety, short circuit faults in the line, operation overvoltage or When lightning strikes, a high induced voltage is formed on the shield, and even the sheath insulation may be broken.
At this time, if the three-phase interconnection of the aluminum or metal shielding layer is still grounded, the aluminum package or the metal shielding layer will have a large circulation, and the value can reach 50%--95% of the core current, forming Loss causes the aluminum or metal shield to heat up, which not only wastes a lot of power, but also reduces the current carrying capacity of the cable and accelerates the insulation degradation of the cable. Therefore, the single-core cable should not be grounded at both ends. [In some cases (such as short cable or light load operation), the three-phase interconnection of the aluminum or metal shield can be grounded.
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Low content monomer plant extract, main content 1%-50%. Including but not limited to Pu-erh tea extract 40%, rhodiola rosea extract 1%, 3%, pueraria root extract 30%, 40%, celery extract 5%, salvia miltiorrhiza extract 5%, 10%, burdock seed extract, salicin 5%, aloe vera extract, gynost' pentaphyllum extract 20%, green tea extract, ginseng extract, chlorogenic acid extract.
Plant extraction process
1. Select plants/herbs. No more than ancient prescriptions, prescriptions, folk herbs to find. At present, common and uncommon herbs have been studied. At present, it is mostly to increase the amount of medicinal materials to extract and separate components with low content, or to find medicinal plants that have never been studied from miao medicine, Tibetan medicine, Mongolian medicine, Africa, Latin America and other places.
2. The extraction. Solvent petroleum ether, n-hexane, cyclohexane, benzene, chloroform, ethyl acetate, n-butanol, acetone, ethanol, methanol, water (low polarity → high polarity). Daily medicine decoction effective, water and ethanol and other solvents with large polarity, such as artemisinin boiling ineffective extraction with petroleum ether and other solvents with small polarity. Common medicinal materials water/alcohol/ether to go through, separation and identification of more compounds.
3. The separation. This is the most important work. In the solution extracted from the second step, there are dozens of compounds, usually by column chromatography, which is often referred to as the column flushing. It's a lot of work, it's boring, it's low tech. A master's student might do this every day for two years. The column for separating compounds, as shown below, is as large as 2 meters high and as small as 10 centimeters. Change the solvent condition of mobile phase, change the material of column, different conditions and different separation principles of column repeatedly punching, can be separated from the monomer compound.
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