A.  we were asked many times by our customers for this question. How to deal with cable after the cable is scraped by accident, and then the water or moisture comes into the cable? First, we have to profoundly recognize the harm to cable if there is water or moisture in it and to avoid the water coming into the cable. The phenomena of water-tree and aging will occur under the function of electric field after the water comes into the cable, which will result in the break-down of the cable. Water-tree congregates in the interstice with diameter of micron to 0.1m. The partial high electric field point caused by the inclusion and air hole in the insulation as well as the uneven integration between insulation and inner &outer semiconductive layer is the initial occurring point for water-tree. The progress for water-tree normally takes more than 8 years. The water-tree will develop more quickly if the humidity, temperature and voltage are higher and the amount of hydronium in the water is more. Next, there are generally following several reasons for water or moisture coming into the cable according to the experience: (1) during the store Two tips of the new cable are sealed with plastic packet. If the cable is cut one piece for use, the cutting point shall be sealed very well, or the water or moisture will come into the cable without good sealing. (2) during the laying of cable The tips sealed with plastic papers sometime may be immerged into water during the laying of cable, which will cause the water coming into the cable; the outer sheath may be scraped when the cable is pulled through a pipe, which will cause the water in the cable bridge coming into the cable. (3) after laying of cable If the cable tips are exposed in the air or even in the water for long time without sealing treatment on the tips after laying of cable, the water will come into the cable in a great amount. (4) during the making of cable connectors Owing to the carelessness of operator during the making of cable connectors (including the terminal and medium connectors), the cable tips may fall into the cable well accumulating with water. (5) during the cable running If the cable connector breaks down during the running, the accumulated water in the well may come into the cable along with the break-down gap. On the building site, water may come into the cable if cable is damaged or breaks down caused by outside force. Finally, the complete set of cable can not be changed although there is water or moisture in it, because the cable is with high value. In some condition, cable can be taken into use after the treatment of water or moisture removing. Thus, in order to reduce the loss, we have to do treatment on the cable with water and take it into use. High-voltage air pipe, bottled nitrogen, pyrocondensation sealing tip with air nozzle (normally used for communication cable, it also can be used for the sealing test for metal sheath of high voltage cable) and 2 to 3 bottles of drying reagent (a kind of reagent, which can turn into blue if meets with water) will be needed for the treatment. The time for filling of nitrogen shall be long enough. To use nitrogen as treatment medium not because it is cheap but also nitrogen without containing of oxygen is good for cable, in addition, bottled nitrogen is quite dry, and there is no necessary to dry the nitrogen any more. Process for the treatment: Seal with pyrocondensation sealing tip at one tip of the cable, fill the dry nitrogen into the cable with air nozzle. Seal the other cable tip after there is no water dropping. Open the air nozzle; connect the air pipe into the drying reagent through air nozzle until there is no blue color in the drying reagent. Stop for half hour after filling for 1-2 hours, then continue the filling, in this way, the drying efficiency will be better. Repeat filling the nitrogen like this way until the drying comes to the anticipated result. During the treatment process, we just can fill the nitrogen, not to deflate the air, the reason for this as follows: 1. If we deflate the air at on end of cable, the other end will be not easy to control; cable may sucks many moisture because some times the other end is exposed in the air by the operator. 2. The pressure of nitrogen is enough to be applied for hundred-meter cable, including the cable with 110kV. We can fill the nitrogen for the single core, which caused damage only. 3. We use the method of filling nitrogen into the cable mainly because of the electric performance: during the production, the XLPE cable passes through the CV-tube with high air pressure, after the cable comes out from the CV-tube with normal air pressure. If we deflate the air from the cable insulation, the tiny air hole in the insulation layer can be expanded, tiny crack will occur in the insulation layer, which will hide trouble for the following cable running: the cable will break down under the cable running test. So the only method can be used for treatment is filling the nitrogen.

A.  a drum operator have to mater the following initial knowledge of lifting and transportation: (1) A heavy thing shall be lift up and laid down separately by human at the same time, operators shall go together with each other to avoid hurt. To move a thing passing a slope, the height of back operator shall be higher than the frontal operator. To move a thing passing a declivity, the height of back operator shall be shorter than the frontal operator. (2) The direction for rolling a cable drum shall be commanded by a person who can use the control bar. (3) Mater the working principle and know-how of common lift tools. The cable drum shall be rolled according to the cable winding direction. In this way, the cable on the drum will be tightened during the rolling instead of getting loose, falling down causes hurt or being damaged.

A.  the conductor of cable normally is copper; this copper conductor with big density results in a heavy weight of a whole drum, so cable can be easily damaged. In addition, the insulation and outer sheath of cable is some kind of plastic, the performance of cable can be vitally damaged under fierce environment. The following requirements shall be applied during the transportation and maintenance of cable: (1) It is forbidden to throw the cable or drum with cable from higher place during the transportation. Throwing or falling cable may results in the split of the insulation and outer sheath layer especially under low temperature(up to 5 ¡æ). (2) To avoid storing cable exposed outside, do not put cable drum flatwise. (3) It is forbidden to lift several packaged cable drum together. Cable drum in vehicle or on board shall be fixed by suitable methods to prevent from collision or knocked down, which can avoid the mechanical damage to the cable. (4) Keep cable away from the contact with acid, alkali and mineral oil; cable shall be stored separately from corrosive material. Keep the storeroom used to store cable away from deleterious gas which can damage the insulation and erode the metal. (5) To roll the drum during the storage period of cable at intervals (once per 3 months in summer, the interval can be delayed timely in other seasons). To roll the downside to the upside to avoid erosion caused by moisture. During storage, be sure to check the sealing of the cable tip regularly. (6) The period of validity for storage shall base on the date cable leaving from the factory. Normally the period of storage shall not exceed one and half year, the max. period shall not exceed two years.

A.  in addition to the bare wire only with conductor, wire with conductor and insulation as well as aerial cable with insulation, the structure of other cable mainly can be divided into three parts, which are conductor, insulation and protection layer, and these can be divided into the following several parts in detail, the brief introduction of individual parts as follows: (1)conductor Conductor is the part acting to conduct current. Normally, it is made of pure copper or aluminum with good conductivity and heat-conducting property. The conductor types for low voltage power cable are: single round, stranded round, stranded sector. The conductor of single cored and multi-cored cable with voltage 3.6/6kV and above adopts stranded round compacting core, which can reduce the cable outer diameter. Conductor can be also made into required core with longitudinal water proof function. (2) conductor shield Power cable with voltage 3.6/6kV and above has conductor shield layer. The conductor working intensity of medium and high voltage cable is quite high. Although the structure of conductor is compacting round, the surface of the stranded conductor exists protrusion and fall-in partially, these will cause the gas break-down partially (dissociating discharge), which can damage the insulation partially. The conductor extruded with semiconductive material is located in an equipotential circle. The semiconductive material can contact with insulation layer closely, which eliminates the gas discharge, improves the internal electric field and radial distributing to increase the working field intensity. (3)insulation Insulation is used to isolate electriferous conductor from other non- electriferous part or to isolate conductors with different electric potential to guarantee the current flows according to a certain direction without leakage. Insulation layer is made of extruded PVC, PE and XLPE material with fine electric insulated performance. The performance for cable with different voltages varies from each other. Cable with rated voltage up 35kV uses super-clean XLPE material. Insulation is extruded around the conductor shield. The standard thickness of insulation accords with related standard. (4insulation shield The gap may exist between the insulation and metal sheath, which is the factor to cause partial discharge. Thus a semiconductive insulation shield is added around the insulation. It contacts perfectly with the insulation, has the equal electric potential with metal sheath, which can avoid the partial discharge between the insulation and metal sheath. Normally, the insulation shield is made of semiconductive material and extruded around each insulation layer, which can improve the electric field distribution and to increase the electric performance of cable. (5) metal shield Metal shield is made of copper tape or copper wire. It plays a role as ground shield, guide the capacitor current and short-circuit current. The metal sheaths around the multi-core of the cable has credible contacts, each core under the metal sheath is marked with different colors. Cable up to 35kV with sing core or multi-core adopts winding copper tape as metal sheath. Special required cable up to 35kV with sing core also can adopt copper wire as metal sheath. (6) filling Multi-core cable adopts suitable fillings to be cabled with cores, which forms the cable to be round and can be convenient to the following process. The cabled cores is binded with suitable taping. The filling material includes filling rope and filling tape according to the actual production requirement. (7) The metal sheath of cable with 35kV and above contains lead, aluminum, copper and stainless steel, which can be used not only as ground shielding layer, but also as water proof sealing layer. (8) The compositive water-proof layer combining longitudinal-covered aluminum-formed composite taping with extrued outer sheath takes a role as water proof function, forming composite water-proof sheath takes the place of metal sheath. (9) Metal armoring: the armoring of multi-core cable is made of double steel tape or galvanized round steel wire. If there is armoring requirement for sing-core cable used in AC system, this cable shall adopt nonmagnetic material or steel after magnetism-removing treatment for armoring. Some kind of magnetism proof armoring structure (certain amount of copper wire is evenly mixed between armoring steel wire) do not have the function of magnetism proof and can not be used as armoring structure for AC system sing-core cable, which are tested by authorized department. If there is armoring requirement for metal shielded or metal sheathed cable, PVC or PE extruded isolated sheath shall be taken as resilient coating under the armoring. (10)The outer sheath of cable is made of PVC or PE. It is normally black except special requirement. Conductive coating layer is coated on the surface of cable with 35kV and above to be an electrode for the voltage test of outer sheath. (11) The mark on the finished cable: the finished cable is marked with cable type, rated voltage, manufacturer etc., which is convenient for the user to recognize and maintenance.

A.  ampacity current means the current which can chronically passes through a cable or a wire during the electricity transportation. Under the thermal stability condition, the ampacity current is called cable long-term admissible ampacity current when the cable conductor comes to the long-term working temperature. In actual project, cable with different type can be chosen, the amount of cable and cable laying type can be defined according to requirement referring to the long-term admissible ampacity current under different environment and conditions. Thus, it has great significance to calculate the long-term admissible ampacity current. The main factors which can influence the cable long-term admissible ampacity current are: (1) Cable conductor long-term admissible working temperature: the higher temperature is, the greater amount cable long-term admissible ampacity current will be for the cable. (2) The environment where cable will be used: the admissible ampacity current varies according to the ambient temperature, the humidity of air and earth. (3) The cross section of cable: the bigger the cross section is, the greater amount cable long-term admissible ampacity current will be for the cable. (4) The resistivity of cable conductor: the bigger the resistivity is, the smaller amount cable long-term admissible ampacity current will be for the cable. (5) Thermal resistance in the environment around the cable: the bigger the thermal resistance is, the slower for the cooling down, the smaller amount cable long-term admissible ampacity current will be for the cable.

A.  choosing power cable shall comply with the following regulations: (1)The rated voltage of cable shall equal to or more than the rated voltage of power supply system at the installation place. (2)The continuous admissible current of cable (ampacity current) shall equal to or more than the max. continuous current of power supply load. (3)The cross section shall meet the requirement of stability during short circuit of the power supply system. (4)To calculate the voltage drop and check according to the cable length whether it accords with the requirement or not. (5) The Min. short circuit current at the end of the cable shall guarantee the protection device to function reliably.