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Frequently Asked Questions from TANO CABLE

What is the Differences between Overhead transmission line and Power cable transmission line?
There are two kinds of electric transmission lines are used currently, one is the most common overhead transmission line, which generally uses non-insulated bare conductor through the ground towers stand as a support, it will lead to the suspension tower with insulators; another is power cable transmission line, which producing by a special process, laying underground or laid in cable tunnel.
Transmission capacity and transmission distance of transmission line are all related to voltage. The higher voltage the farther can deliver. Voltage of lines and the system needs to be determined by distance and capacity of its delivery.

1. Overhead transmission line
Overhead transmission line are made up of route line towers, conductors, insulators etc., set up above the ground.

Conductor is made of metal with good conductivity, enough wide cross section (to maintain proper through-flow density) and a larger radius of curvature (to reduce corona discharge). EHV transmission line usually use bundled conductors. Overhead ground wire (also called lightning-protection line) disposed above the transmission line for protecting line against lightning. Important transmission lines use two overhead ground wires commonly. Insulator chain concatenating by single suspension (or rod) insulator,  which need to meet the dielectric strength and mechanical strength requirements. The number of insulator is determined by the transmission voltage levels. Towers are made of steel or reinforced concrete, is the main support structure of overhead transmission line. Overhead line construction and maintenance is more convenient and lower cost. Overhead transmission lines should take into consideration of natural conditions when design, such as temperature changes, strong storms, lightning, rain, ice, floods, wet fog etc. The path of overhead transmission lines need sufficient width and ground clearance corridor.

The decided maximum transmission power of transmission line, after considering all the factors of technical, economic and other factors, called the transmission capacity of the overhead transmission line. Transmission capacity substantially proportional to the square of the transmission voltage. Therefore, improving the transmission voltage is the main technical means to achieve high capacity or long-distance transmission, also is the main indicator of transmission technological development level. At home and abroad (including American and European countries) commonly use overhead transmission lines as the most important way to supply electric power.

2. Power cable transmission line

Power cables are generally composed of conductor, insulation and protection layers, there are single core power cable, 2 cores power cable and 3 cores power cable.

Power cable transmission line generally used in areas where overhead transmission lines erection difficulties, such as city or special cross section. Currently used power cable transmission line, mainly considering the urban landscape and line security. But the cable line troubleshooting and repair time is very long, effect the power grid reliability and normal use of electricity users seriously. Therefore, in power grid construction, the power cable transmission line total replace of overhead transmission lines can not be achieved.

Power Cable Transmission Line Features:
(1) Reliable power supply.
(2) Save space and ground.
(3) Don’t use poles, saving wood, steel and cement.
(4) Easy operation and maintenance, save line maintenance cost.
(5) Power cable is expensive, difficult branch lines, cable connectors construction process more complicated, more difficult to find the point of malfunction, inconvenience promptly deal with the accident.
How to calculate the carrying capacity of HV power cable?
HV power cable is a kind of power cable which is used for transmitting more than 10KV electricity, more used in the main transmitting line.

For HV power cable below 35kV, carrying capacity calculation is same as general power cable. For 35kV HV Power Cable and above, carrying capacity should be calculated according to the economic current density. For HV power cable below 35kV, you can cousult common cable carrying capacity table.

HV power cable carrying capacity calculation formula

For 35KV HV Power Cable and above, the carrying capacity calculation formula is:
The maximum carrying capacity (J) = cable cross-sectional area (A: mm2) × economic current density (J: A / mm2)

Power Cable economic current density table:
Conductor Material Annual maximum load utilization duration
Below 3000H 3000H-5000H Above 5000H
Copper Conductor 2.5 2.25 2.00
Aluminum Conductor 1.92 1.73 1.54
Economic current density unit is A/mm2

Effect conditions of HV power cable carrying capacity
Under the above formula for the ideal conditions to calculate HV Power Cable carrying capacity, for practical use, the cable system operating environment and operating parameters of the conductor cross-section choose to have a very big impact, with the same cable conductor cross-section in different environments and operating conditions, its carrying capacity vary greatly. The following article will individually on various factors ampacity Analysis.

1. The cable burial depth
In order to protect cables buried in the ground, to avoid or reduce its external impact, cable lines are generally to guarantee a certain depth. But as the depth increases, the cable also will be cooling conditions deteriorate, under the same conditions as maximum allowable operating temperature, cable ampacity also becomes smaller with increasing depth.
2. Mutual thermal effects of multi-loop cable
When the multi-loop cable laying in compact form, since the mutual thermal effect of the cooling conditions will deteriorate between the multi-loop cable, so the carrying capacity correspondingly reduced.
3. Press the cable with spaced impact
Similar interaction between thermal effects and multi-circuit cable, with cable and white back there mutual thermal effects.
4. The soil temperature around the cable system
Select the cable cross-section that is allowing current to determine the cable, while allowing current to allow the core wire is temperature-dependent. Core temperature is not only related to the current, but also on the surrounding medium temperature and thermal resistance. Therefore, buried soil temperature around the cable has a greater impact on the carrying capacity.
5. The soil thermal resistivity
In a preliminary assessment of the cable ampacity, the soil such as abnormally dry or no heat resistance.
Usually for larger cable systems, required before the route survey design when, for a more detailed measurements confirm that the soil thermal resistivity along the line. There is also taking into account the soil thermal resistivity changes with the seasons.

6. Other relevant data
If the cable is not directly buried installation but laid in the conduit and then buried in the ground, in addition to the operational and environmental data to be collected more, the thermal resistivity of the conduit is also necessary, which is also an important influence data to cable carrying capacity.
Quality FAQ and improved methods of ACSR Conductor
ACSR Conductor is stranded together by aluminum wire and steel wire, which is widely used in overhead transmission lines, its quality directly affects the safety of electricity delivery. This paper will discuss the main reasons and improved methods that affecting the quality of ACSR conductor.

Firstly, the ACSR Conductor strands technology.

1. Single Line break:

Main reason:
1) Single line was pulled around the spool too loose or too tight on the line position;
2) Conduit friction due to the trench line inlay dead; single line knot or reel brake too tight.

1) Check whether single line is uneven or pressure line, so they should pay attention to receive reel in cable tidy drawing process;
2) Replace badly worn conduit timely.
3) Check whether the top reel rotation is flexible, to ensure good bearing lubrication;
4) Check whether the reel set is uniform tension, tension should be adjusted according to the size of the actual situation.

2. single line arch camber, loose, serpentine bend

Main reason:
1) The pitch diameter ratio selected is unreasonable;
2) reaming each single line splitter board positions staggered and uneven distribution;
3) The die aperture is too large;
4) Individual single line tension is too large.

1) First, select the appropriate pre-production section diameter ratio haul rate, stranding pitch length and twist to the other parameters. Their product quality, stability, strength, resistance and material consumption compared with a straight impact;
2) According to rationalize the work experience in a single line splitter plate position distribution;
3) The appropriate choice of the pressure the cells, generally require small die aperture between the outer diameter of 0.3-0.5mm than the line;
4) To properly regulate the tension reel, single line to ensure that all tension is moderate and consistent;
5) Adjust the back-twisting device, the angle to be consistent, to remove the guide as an internal stress generated in the process;
6) Twisted manufacturing process to minimize the number of stops, as far as possible uniform production.

Secondly, ACSR Conductor production management
In the production process to strictly control the quality of raw materials into the plant; Note To avoid mechanical damage reels during transport due to the bump caused; attention aluminum storage location should avoid corrosive media humid air and erosion damage.
How to prevent high voltage power cable watering?
High voltage power cable is a kind of cable used in special occasion, we should obey operation rules strictly when using, once accidents happened, the consequences are very serious. High voltage power cable once watered, under the influence of electric field, aging will occur, leading to cable breakdown.

In the practical application of high voltage power cable, the solution to high voltage power cable watering is as following:

1. If the cable end has water, the front end can amputate a few meters of the cable.

2. If the entire cable has water, can only be scrapped.

So how to prevent high voltage power cable water is crucial, usually take the following measures:

1, The high-voltage power cable should be sealed up, if it is amputated the end of the cable, either stacked or laid up, the cable all should be sealed with plastic so as to prevent moisture penetration.

2, High voltage power cable must make cable joints and terminations timely after cable laying, which can effectively prevent cable watering from the cable end.

3, When purchase high voltage power cable, you must select a good quality cable (such as Tano Cable), can effectively prevent cable insulation aging and other conditions.

4, The Insulation impurities and porosity of high voltage power cable is the starting point for the movement of water molecules, so the cable must be regular maintenance when using. 
Why would a high voltage electric cable water?
High 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.
How to select good quality building wire?
1. 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.  
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