How to identify the advantages and disadvantages when buying a wire
The state has explicitly stated that copper conductors should be used in new houses. However, copper conductors, as well as inferior copper conductors, have copper cores that use recycled copper and contain many impurities. Some poor-quality copper conductors are even less conductive than iron wires and can easily cause electrical accidents. At present, there are many kinds of wires on the market, many specifications, and prices are chaotic. It is very difficult for consumers to choose. In terms of the prices of 2.5 square millimetres and 4 square millimetres of two kinds of copper wires that are commonly used in home decoration, the price of one line of the same specification may vary by 20% to 30% because of different manufacturers. As for the quality, whether the length is up to standard, consumers are even more difficult to determine.
According to industry sources, the reason why the prices of wires are so different is that they are caused by different raw materials used in the production process. The main raw materials for producing wires are electrolytic copper, insulating materials and sheathing materials. At present, the raw material market has about 5 million yuan per ton of electrolytic copper, and only about 40,000 yuan per ton of recycled copper; the price of high-quality insulation materials and sheathing materials is between 8,000 yuan and 10,000 yuan per ton, and defective products. The price of only 4,000 yuan to 5,000 yuan per ton, the difference is even more disparity. In addition, the lack of length and inadequate insulation of the insulators are also important reasons for price differences. The length of each line, excellent products is 100 meters, while the defective product is only about 90 meters; the insulation content of excellent products accounted for 35% to 40%, while the defective products only 15%. By contrast, it is not difficult for consumers to see that the difference in the sales price of finished wire is due to the presence of tricky materials.
Breakdown test of cable
The breakdown test of the cable is to step up the voltage until the breakdown of the insulation, to obtain the breakdown voltage value of the cable. The purpose of this type of test is to assess the safety margin between the ability of the cable insulation to withstand voltage and the operating voltage. The AC breakdown field strength is one of the important parameters of cable design.
The AC breakdown strength has a great relationship with the boosting speed. Continuous boosting makes the breakdown of the cable within a few minutes as an instantaneous breakdown, which is basically no thermal factor and belongs to the type of electrical breakdown. Therefore, wire and cable are generally not tested in this way. The other is step-up step-up, starting from a lower voltage (for example, 0.5 to 2 times the operating voltage), and maintaining enough time for the cable to fully generate electricity and heat at this voltage level. Then rise to another voltage level again. Step up until breakdown. The level of voltage rise at each level increases step by step as a percentage of the initial pressure. This test reflects the factors of thermal breakdown. This test result has a good reference value. It is often used when studying product characteristics.
Common cable faults
Common faults in cable lines include mechanical damage, insulation damage, moisture insult, insulation degradation, overvoltage, and cable overheating. When the above fault occurs on the line, the power of the faulty cable should be cut off, the fault point should be found, the fault should be checked and analyzed, and then the repair and test should be carried out. The cut should be removed and the power supply can be restored after the fault is eliminated.
The most direct cause of a cable fault is the breakdown of insulation and breakdown.
There are:
a, overload operation. Long-term overload operation will increase the cable temperature, insulation aging, resulting in breakdown insulation, reduce construction quality.
b, electrical aspects are: cable head construction process is not up to the requirements, poor cable sealing, moisture intrusion into the cable, the cable insulation performance decreased; failed to take protective measures when laying the cable, the protective layer is damaged, the insulation is reduced.
c. Civil engineering aspects include: poor drainage of work wells, long-term cable immersion in water, damage to insulation strength, too small working hole, insufficient bending radius of cables, and long-term destruction by external forces of extrusion. This is mainly the construction of mechanical construction in municipal construction. Excavate and cut the cable.
d. Corrosion. The protective layer is subject to chemical corrosion or cable corrosion for a long time, resulting in failure of the protective layer and reduced insulation.
e. The quality of the cable itself or the cable head attachment is poor, the sealing of the cable head is poor, the insulation glue is dissolved, and the cracking occurs. The resonance phenomenon of the station causes the line disconnection fault to make the phase capacitance of the line and the capacitance of the ground resonate with the excitation inductance of the distribution transformer. Loops, thereby exciting ferromagnetic resonance.
Breakage failure causes resonance damage
Breaking resonance Under severe conditions, the high frequency is superimposed with the fundamental frequency resonance, which can make the overvoltage amplitude reach 2.5 times of the phase voltage [P], which may cause the neutral point of the system to move, and the windings and wires may overvoltage. Insulation flashover, lightning arrester explosion, electrical equipment damage. In some cases, the load transformer phase sequence may be reversed, and overvoltage may also be transmitted to the low voltage side of the transformer, causing harm.
Measures to prevent overvoltage and disconnection from resonance
The main measures to prevent overvoltage and disconnection overvoltage are:
(1) Do not use fuses to avoid non-full-phase operation.
(2) Strengthen the line inspection and maintenance to prevent the occurrence of broken lines.
(3) Do not hang the transformer on the line for a long time.
(4) Use ring or dual power supply.
(5) Adding interphase capacitance on the transformer side,
The principle is: the use of capacitors as energy-absorbing elements to absorb the energy of the transient process, thereby reducing the impact of disturbance intensity to suppress the occurrence of resonance .s a (o + 3C,,) 1C., with additional phase capacitance on the transformer side â–³ C To increase the value of 8-[Co+3(C U+ A0)/Ca, the capacitance required to increase the equivalent capacitance C and the equivalent electromotive force Eo can be calculated according to the method in [6]. (6) Excitation characteristics are used. A better transformer helps reduce the chance of breakage and overvoltage.
Graphite Electrode
Graphite electrode, mainly in petroleum coke, needle coke as raw material, coal tar pitch as a binder, calcined, ingredients, mixed kneading, pressure, roasting, graphitization, machining and made in the arc furnace in the form of arc The energy can be divided into Ordinary Power Graphite Electrode, High Power Graphite Electrode and Ultra High Power Graphite Electrode according to its quality index.
Graphite electrode transport
1, graphite electrode in the long-distance transport to be covered with anti-rain Pengbu.
2, with lifting machinery unloading wooden box packaging electrodes, you must use the wire rope, not directly hook the electrode steel packing belt for lifting.
3, in order to protect the electrode end and thread, not directly with hook hook electrode hole hanging electrode.
4, loading and unloading joints box, you should gently take to prevent damage to the thread.
Second, the graphite electrode storage
1, the electrode should be stored in a clean, dry place; temporarily do not use the electrode and connector, do not remove the packaging, to prevent dust, debris fall into the thread or electrode hole, affecting product docking accuracy.
2, open field stacking electrodes, must be covered with rain pants. In the case of
3, the electrode in the Treasury storage to be placed neatly, the electrode stack on both sides to pad well, to prevent the cartoons.
4, bulk electrode stacking height is usually not more than 2.8 meters, the height of the box electrode should not be more than 4 layers.
5, the temperature of the place where the joints should be stored should not be too high to prevent the asphaltene joint bolt melting.
Third, the graphite electrode connection operation
1, by the wet electrode, before use to dry.
2, remove the spare electrode hole on the foam protective cap, check the electrode hole thread is complete.
3, with no oil and water compressed air cleaning spare electrode surface and hole thread; to avoid the use of wire or metal brush cloth cleaning.
4. Do not touch the threads in the electrode holes where the joint is carefully screwed into one end of the backup electrode (it is not recommended to insert the connector directly into the electrode that is replaced on the furnace).
5, the electrode spreader (recommended the use of graphite material spreader) screw into the other side of the electrode electrode electrode hole.
6, lifting the electrode, the mat soft objects to the bottom of the alternate electrode assembly to prevent the ground to break the joints; with a hook into the spreader after the lifting ring, lifting the electrode to be smooth, to prevent the electrode from the B-loose Off or collide with other fixtures.
7, the spare electrode hanging to the top of the electrode to be connected to the electrode hole slowly after the fall; rotating the backup electrode, so that the screw hook and the electrode with the rotation down; in the two electrode end distance 10-20mm, again with compressed air Clean the two ends of the electrode and the exposed parts of the joint; in the final complete discharge of the electrode, not too much, or because of violent collision, will lead to electrode holes and joints of the thread damage.
8. Tighten the backup electrode with a torque wrench until the ends of the two electrodes are in close contact (the correct connection of the electrode and the connector is less than 0.05 mm).
Fourth, the graphite electrode in the use of the precautions
1, the electrode holder should be caught in the top of the cord outside the cordon, otherwise easily lead to electrode break. The contact surface of the gripper and the electrode should always be cleaned to maintain good contact with the electrode, and the gripper cooling water jacket should be kept leaking. In the case of
2, the electrode connection found cracks exist to identify the cause, to eliminate the gap before use.
3, connecting the electrode, found that the phenomenon of joint peeling off, to fill the joints and then connect the bolt.
4, the electrode should be used vertically, to avoid tilting operation, in particular, can not be connected to a group of electrodes placed horizontally, so as not to break.
5, to the furnace into the charge, the bulk material should be installed near the bottom of the furnace to reduce the collapse of the large pieces of charge impact electrode.
6, smelting, should avoid a large number of insulation material stacked in the electrode just below, so as not to affect the use of electrodes, or even electrode break.
7, the electrode in the rise or fall, should avoid touching the lid, resulting in electrode damage.
· 8, in the smelting site, to avoid slag splashing to the site of the electrode or connector threaded buckle, damage the thread accuracy.
