QWhy would a high voltage electric cable water?AHigh voltage electric cable water, generally because of three reasons:
1. In the cable production process, the inner liner pull extrusion unglued or loopholes, watering when the water cooled sink, production workers did not pay attention, or found it but not timely handled it. (If the water in the production process, the finished cable partial discharge test is greater than the index inevitable 10pC, cable is impossible qualified)
2. After high voltage electric cable produced, cable end sealing cap is not ready, place in the open air and rain water into the internal cables.
3. When high voltage electric cable laying, cable has been truncated, but neither made cable terminal head in time, nor bandage sealed. With watered in cable trench, resulting in an unsealed cable water.
For XLPE high voltage electric cable, the cable inside watered, especially the water inside the inner liner, it is very dangerous, because XLPE insulation afraid of water, under the influence of high voltage electric field, the water will make XLPE insulation water trees again produce electrical trees, resulting in cable insulation breakdown.
If the water is caused by the cable manufacturer, you can contact the manufacturer to replace the cable to ensure proper use of the cable.
If the result of improper storage or water due to construction negligence, vacuum methods can be used to drain the water in the cable, that is, to do with the cable inlet section of the valve core cable sealing cap, the inner core removed, sealing cap with the cable jacket seal with a vacuum pump and valve core connection, pumping out the water inside the cable; the other end of the cable to do the same sealing cap (with the valve core) and add a valve, internal cable to be evacuated to a certain degree of vacuum, dry air into the valve opening. Vacuum - the intake valve open - close the vacuum valve - open the intake valves - vacuum ........ this is repeated several times until the internal cables damp parts dry. Too much trouble, but there is no other good way. Practice has proved that this approach is indeed feasible.
QHow to select good quality building wire?A1. Appearance of building wire
Smooth and round, uniform color, rubber insulation and copper conductor closely difficult to peel, bad quality rubber insulation looks thick, but after squeezing, the squeeze point will turn into white, it is easy for cable aging and fall off lead to electric leakage loss in the future.
2.Eccentricity ratio of building wire
Thickness of every rubber insulation circle is consistent, that is, whether the copper core in the middle of building wire, the eccentricity ratio is low.
3.Retardant of building wire
Burned rubber insulation with a lighter, the fire should be extinguished when lighter left the wire, and release of a small amount of white smoke, if the flames spread, release large amounts of white smoke indicates the rubber insulation is poor quality.
4. Copper core of building wire
High purity copper core is with features of anti-aging, high conductivity, and inferior copper core is with color yellow or white, with impurities. You can use a piece of paper rubbing on the copper core, if there is a black substance on the white paper, indicates impurities in the copper core .
5. Mark of building wire
You should notice whether the wire is with Certification of Quality, "CCC" sign, complete information on the rated voltage, length, date, manufacturer name and address etc.
6. Thickness of building wire
The size of poor quality copper core is smaller than regular factory, Good quality copper core insulation is thick, and wire section diameter deviation should not be exceed 0.02%.
7. Length of building wire
Length of building wire should meet the national standard 100 ± 0.5m (That is take 100m as standard, permissible error 0.5 meters).
8. Weight of building wire
The whole plate building wire (100m), 1.5mm2 is not less than 1871 g, 2.5 square is not less than 2915 g, 4 square is not less than 4312 g, 6 mm2 is not less than 6107g.
QHow to select Marine Cable?ASelection steps and principles of Marine Cable
1. According to the application, laying location, and working conditions of marine cable to select the appropriate marine cable.
2. According to the duty, power type, cable core and load current of electrical equipment to select the appropriate cable cross-section.
3. According to system short-circuit current calculations, determine whether the cable short-circuit capacity to meet the requirements.
4. According to ambient temperature to amend the rated ampacity, and then determine whether the cable allowable current is greater than the load current.
5. According to bunched laying correction factor to amend the rated ampacity, and then determine whether the cable allowable current is greater than the load current.
6. Check line voltage drop, and determine whether the line voltage drop is less than the predetermined value.
7. According to the setting value of the protection device to determine whether the cable is coordinate with protection device; if uncoordinated, determine whether you can change the appropriate protective devices or setting value, or you should re-select the appropriate cable cross-section.
Marine cable type selection should consider the following factors:
1. Application of the marine cable-- for power, lighting or radio communications.
2. Cabling position of marine cable --- dry, wet, cold, or whether requiring shielding.
3. Working conditions of marine cable --- fixed laying, pipe wear or portable
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QHow to choose suited cross-linked polyethylene(XLPE) insulating power cable?ABasic requirements of choosing cross-linked polyethylene (XLPE) insulating power cable
1. Cable core temperature maximum operating current is applied, shall not exceed the allowable value of the continuous operating current loop cable core temperature must not exceed the permissible values listed in section 2.4 of Schedule that cross-linked polyethylene (XLPE) insulating power cable core maximum rated temperature is 90 ℃.
2. The maximum short-circuit current thermal effects produced by the role of time, should not undermine the continued use of the cable characteristics. For non-fuse protection circuit, according to the short-circuit current core temperature does not exceed a Linear Section 2.4 of the Schedule are allowable values, namely cross-linked polyethylene (XLPE) insulating power cable cores maximum temperature of 250 ℃.
3. Circuit connection is very long, the limits for voltage drop should not exceed the allowable value.
4. For longer distances large current loop or more than 35kV high-voltage cable, to meet the three requirements under the premise of economic current density law should press the selection line core cross section, namely the cable core cross section can be determined as follows
Wherein Y • max-- normal working hours maximum continuous operating current, A; J-- economic current density, A / mm2.
QWhat is the difference between THHN and THWN electric wire?ATHHN and THWN are all nylon sheath electric wire, one type of American Standard electric wires, they are according to UL62 and UL83 Standard.
THHN is short for thermoplastic high-heat resistant nylon-coated wire; it is with better electrical properties and physical properties than common PVC insulation electric wires, which are with better features of heat resistance, rotproofness, self-lubrication and oil resistance. THHN nylon electric wire is used to connect branch circuit and various kinds of electronics.
THWN is short for thermoplastic heat- and waterproofness nylon-coated wire, it is with features of thermoplasticity and water-resistant. The application of THWN is same as THHN, it is known as THWN is evolution of THHN.
In conclusion, the basic difference between THHN and THWN is the waterproofness.
QWhy there are so many layers in power cable?APower cables outermost layer is generally rubber or synthetic rubber sleeve, this layer is not only insulation layer, but also play a role to protect cable from harm.
High voltage power cables with a layer of resin-like filler which mainly play the role of insulation, low voltage power cables without this stuff. Power cables are with some similar ribbons wrapped around, which are to secure the each cable core, filled the middle of the gap.
Shield layer, there are two cases, the power cable shield has two effects: first, because the current through the power cable is relatively large, the current creates a magnetic field around, in order not to affect other elements, so add that to shield electromagnetic fields shield in the cable; the second is to play a role ground protection, if damaged, leaked current can occur within the cable core role shield along the outflow, played security protection.
Power cable is made of a conductive core, an insulating layer, a protective layer. Detailed: conductive core, an inner semiconducting layer, an insulating layer and an outer semiconductive layer, copper shield, filler, inner liner, double steel protective layer, the outer sheath. Above the main structure is for 10kV power cable.