The reason of high voltage cable faults

The reason of high voltage cable faults：

According to causes of fault:manufacturing reasons, quality of construction, design reasons, external damage.

1.manufacturing reasons

1.) Cable ontology：

Generally，problems happening in the cable manufacturing process are insulation eccentricity, uneven thickness of the insulating shield, insulating impurities, both inside and outside the shield protuberance, the degree of crosslinking is uneven, cable damp,and poor sealing cable metal sheath.

2.) Cable connector：

High voltage cable connector used wrapping, molded and Molding type etc, needing big workload of field fabrication, and because of restrictions of site conditions and the production process, inevitably there will be an air gap and impurities between the insulation tape layer, so prone to problems. The reason due to manufacturing faults cause the cable connector body have stress cone manufacturing defects, insulation fillers problem, seals oil spills and other reasons.

3.) Cable grounding system:

Ground systems include cable grounding cable boxes, cable grounding protection box (with a protective layer of protection), cable crossover interconnection boxes, protective layer of protection, and other parts. Generally prone to problems mainly because of poor box sealed lead to multi-point ground water, causing the metal sheath induced current is too large. Another parameter selection sheath protector unreasonable or poor quality zinc oxide crystals can easily lead to instability protective sheath damage.

2.Construction quality reason

First, the relatively poor field conditions, cables and connectors in the factory manufacturing environment and process requirements are high, and the construction site of temperature, humidity, dust is not well controlled.

Second, the construction process in the cable insulating surface will inevitably leave a small slip marks, abrasive grains and semi-conductive particles may also be embedded on the insulation, the additional joint construction process due to exposure to air insulation, the insulation will also suction water, which gave the long-term safe operation of the stay hidden.

Third, when the installation is not in strict accordance with the provisions of the construction process or process does not take into account the problems that may arise.

Fourth, the completion and acceptance of the use of DC voltage test result leads to the formation of the joint anti-electric insulation damage. Fifth, due to mismanagement led to seal the deal.

3.Design reason:

Cable because the cable thermal expansion caused by crushing cause breakdown. XLPE cable load is high, core temperature, thermal expansion of the cable, the cable bend in the tunnel at the top of the bracket facade, long-term high-load operation cable squirm with great force, causing the stent facade crush the cable sheath metal sheath, squeeze the cable insulation cause cable breakdown.

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Erection hanging overhead cable

When laying hanging wire, you should first have a good choice of strand wire rack with a tray placed on the turntable device,
Then rotate the turntable to put line the shelves began to put the line:

Generally use the following three methods.

1. The hanging wire hanging wire resting on pole groove plywood inside and outside of the nut to tighten slightly, so as not to emerge hanging wire trunking for the degree, then you can use manual traction.

2 hanging wire on the poles and plywood between the nut, but in a straight line from the pole with all the tension every corner bar and turn on the 6 pole line (ie, outer corner pole), still the hanging wire on the inside groove plywood

3 wire cloth hanging on the ground first, then moved manually put on piecewise hanging wire nut between the poles and plywood (generally stick a fork). However, using this method must not make the hanging cord is damaged, do not hinder traffic, does not make the pole hanging wire can not be cited as the principle.

4 In the course of laying hanging wire should be possible to use the whole strand to reduce intermediate connector and ask in a bar file can not have more than one connector.

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What is XLPE cable?

Since about 1970, the cross-linked Polyethylene (XLPE) -insulated power cables have been used in Germany. This insulation possesses very good electrical, mechanical and thermal characteristics in medium voltage networks. This type of insulation has excellent chemical resistance and is also resistant to cold temperatures. Due to various advantages, the XLPE-insulated type has vastly displaced the traditional classic paper-insulated types in many sectors.

In order to prevent the penetration of moisture and also to extend the duration of life, the XLPE insulated medium voltage cables are designed with longitudinally waterproof shielding including an additional swell tape and PE outer jacket.

The manufacture of this jacket is based on high density polyethylene (HDPE), in which an additive organic peroxide is mixed. Due to the heating and pressure the molecule chains are joined together, assuring the transition from thermo plastic to elastic condition.

In comparison to PVC and paper-insulated cables, the advantage of XLPE-insulated medium voltage power cables is that they possess a low dielectric factor, such as it is 100 times smaller than of PVC-insulated cables.
Moreover, a better dielectric constant value has has an effect on the low mutual
capacitance, the short circuit to ground and the charging current of XLPE-insulated cables.
The good properties of these cables remain constant at a wide temperature range.

Cable Installation(Visit http://www.qscable.com to get more information)

In order to avoid any damage, the XLPE insulated medium voltage power cables should be carefully laid and installed. It must be ensured that the cables should not be pulled over hard or sharp edges. The cable ends must be sealed water-tight. After cutting the length both ends must be sealed immediately.

An installation depth of 60 to 80 cm is recommended. Single conductor cables are normally arranged in a trefoil touching or triangular shape.

For installation in conduits, especially the influence of thermal insulation of air space between the cable and the inner wall of the conduit should be considered. The inner diameter of the conduit should be at least 1.5 times that of the diameter of the cable.

Aluminum alloy cable -YJHLV22 0.6~35KV steel tape armoured power cable

Aluminum alloy power cable is AA-8000 series aluminum alloy material for conductor, using special pressing process and annealing treatment and other advanced technology inventions of new materials power cable. Alloy power cable for the previous pure aluminum cable, improves cable conductive properties, flexural properties, creep resistance and corrosion resistance, to ensure cable in long time overload and overheat maintaining continuous stable performance, using AA-8000 series aluminum alloy conductor, can greatly improve the conductivity, aluminum alloy cable high temperature resistant, while addressing the pure aluminum conductor electrochemical corrosion, creep problem.

Aluminum alloy electrical conductivity is the most commonly used reference materials copper IACS 61.5%, carrying capacity is 79% better than that of pure copper, aluminum standard. But in the same volume, aluminum alloy actual weight is around 1/3 copper. According to the calculation, meet the same conductive performance of the premise, the same weight of aluminum alloy cable length is two times of the copper cable. Therefore, the same carrying capacity of aluminum alloy and the weight of the cable is approximately half the copper. Using aluminum alloy cables instead of copper, can reduce the weight of the cable, reduce the installation cost, reduce equipment and cable wear, making installation easier.

YJHLV22 0.6~35KV steel tape armoured power cable characteristics analysis:

Crosslinked polyethylene is the use of silane crosslinking or peroxide crosslinking method, so that the polyethylene into thermosetting cross-linked polyethylene, thus greatly improving the cable heat resistance, aging resistance and service life.

My company independent research and development of aluminum alloy conductor creep, high flexible, stable connection, high ductility, low rebound, and the pure aluminum conductor is compared, not only economic performance and has excellent mechanical performance, security performance, connecting performance and many other characteristics. Cable sheath environment-friendly PVC, in wet places to install, can also be buried or laid in cement and use; according to the requirements of different use occasions, can also be based on user needs the production of low smoke halogen-free, flame retardant cable, can achieve the flame retardant A-level, refractory level, in line with the GA306.1 and GA306.2 standard.

YJHLV22 0.6~35KV steel tape armoured power cable requirements:

Applicable to 600V~35kV voltage grade; applied to 90℃dry or moist places; can be indoor, outdoor installation, can be installed vertically, but also along the wall bracket or laying, can also be buried installation bending radius is 7 times; the smallest diameter, but also 360°bend; applies to civil, commercial, industrial, school, large venues.

ABC cable standard NFC33-209

NFC33-209 standard specifies the rated voltage 0.6/1kV.

Low voltage overhead power systems use the XLPE insulated wire bundles.

Structural characteristics and performance requirements must be met.

Wire bundle can contain public lighting lines and testing lines.

This standard specifies performance characteristics of this insulated wire bundles and the test items that must be met.

Insulation shall be black extruded XLPE which is easily stripped.

For slings neutral, Conductor should be around the package tape isolation layer.For other wire (line, public lighting line and test line),it will be both ok whether to adopt an optional isolation barrier . However, if using insolation layer, It should be overall colored, and the wiring harness of the same nominal cross section of the conductors are all the same.

This product is suitable for AC rated voltage of 450/750V or less,like subway, high-rise buildings, shopping malls, theaters, power plants, chemical plants, city squares and other public utilities which have higt requirements of flame-retardant properties of the cable. The cables characteristics of LSZH and low smoke low halogen have many benefits,like when the fire broke out, the fire spread slowly, low smoke density, high visibility, small emission of harmful gases, to facilitate evacuation. Less corrosive combustion gases, also to avoid damage to the equipment, low halogen, halogen-free, which makes the cable materials greatly enhance the anti-aging and resistance to ultraviolet light and other radiation performance, thereby extending the life of the cable.

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How to install underground cable

It is not particularly hard to run underground cable to a detached garage or other outbuilding, especially if you have some basic wiring experience. If you just need to add some lighting and a few outlets, you can tap into an existing circuit in the house. For bigger electrical needs, though, plan to run a circuit or two from the service entrance panel to a subpanel mounted in the garage. If you are not sure what your future electrical needs might be in the garage, install the subpanel.

You may want to hire an electrician to handle wiring connections in the house and garage. But you can still save a lot of money on the project by digging the trench yourself and installing underground conduit.

Use the Right Type of Cable

When running underground cable, the only kind of cable to use is type UF (underground feeder) electrical cable. 

Types of Conduit

When running electrical wiring underground, type UF cable should be routed through rigid conduit. There are two types of conduit that can be used for underground cable. Schedule 40 PVC conduit is the most common and affordable choice. This type of conduit is gray, and it is joined with PVC cement. You can also use rigid metal conduit, although it will cost significantly more. Do not use thinwall (EMT) conduit underground. Use conduit that is at least 3/4-inch wide. 

PVC conduit needs to be buried at least 18 inches deep unless it will be covered by concrete, in which case it can be buried 12 inches deep. Rigid metal conduit can be buried as little as 6 inches deep, with or without a concrete cap. Be sure to check with your local code before you start installing underground cable.

Dig a Trench

Use a trenching shovel to dig a narrow channel from the house to the garage. If you have to dig a long trench, you may want to consider renting a trenching machine for this job. 

Install the Conduit

PVC conduit can be cut with a hacksaw or PVC saw. Dry fit all of the pieces along the entire run. Join the pieces of conduit with PVC cement. Run type UF cable through the conduit, and then make the necessary connections in the house and garage. Always check your local building code before you begin running underground cable.

With underground cables the individual conductors, being insulated, can be closer together, leading to greater cancellation and lower fields. However, unless they are buried very deeply, they can also be approached more closely, leading to higher fields. Overall, ground-level magnetic fields from underground cables fall much more rapidly with distance than those from a corresponding overhead line, but can actually be higher at small distances from the cable.

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Helpful XLPE insulated cables specifications and advantages

XLPE insulated cable has advantages which pvc insulated cable can not match. Simple structure, light weight, good heat resistance, high load capacity, without melting, chemical resistance and high mechanical

strength.

The details of advantage as follow:

1, Heat resistance: XLPE dimensional mesh structure has very excellent heat resistance. Cant decompose and carbonation below 300 ℃, long-term working temperature is up to 90 ℃, and the thermal life is up to 40 years.

2, Insulation: XLPE maintain the original good insulation properties of PE , and insulation resistance is further increased. Its dielectric loss tangent is small, and not affected by temperature.

3, Mechanical properties: Since the establishment of a new chemical bond in macromolecule, the hardness, stiffness, wear resistance and impact resistance are increased to compensate for the shortcoming of

PE vulnerable to environmental stress cracking.

Learn more information about XLPE insulated cable and PVC insulated cable, Please visit www.qscable.com

Armored cable type and specification

Armored cable is the processed flexible solid combination which is made of different materials mounted in a insulated metal casing,Including armored cable sheathed thermocouple, sheathed thermoresistor, armored heater and Sheathed lead wire , mainly used in temperature measurement, signal transmission and special heating of chemical, metallurgy, machinery manufacturing, power generation and scientific experiments etc., the largest amount is sheathed thermocouple.

Armored cable is generally fixed Fixed installation of power cable, Popularly speaking it is fixed in one place without moving, power line transmission power. Also it can enhance the tensile strength, compressive strength and other mechanical protection and prolong life. Armored has some resistance to external performance, also beware of rat bite, will not cause a power transmission problem through out armor, armored bend radius should be large, armored ground layer can protect the cable.

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