Shielded vs unshielded cable, how to choose the answer here!

Shielded cable vs unshielded cable

Shielded cable? Or unshielded cable—— This is a problem. The choice of shielded or unshielded cables mainly depends on the specific application requirements. Today, Xiaobian sorted out the factors that should be considered when using shielded cables on AAC Cable treasure.
Shielded cable
Shielded cable is a transmission line that uses metal mesh braid to wrap the signal line. The braid is generally red copper or tinned copper; Shielded cables are mainly used to prevent interference signals from entering the inner conductor and are suitable for transformers and similar equipment.
The shielded cable complies with the national standard: gb12972.6-91. The long-term allowable working temperature of the conductor is 90 ℃. It is suitable for the connecting wires of control and monitoring circuits and protection lines with rated voltage of 450 / 750V and below. It is mainly used in places where electromagnetic wave interference is prevented and shielding is required.
In order to minimize the impact of electromagnetic and radio frequency interference, each component in the shielding system must be seamless and correctly installed and maintained. In addition, shielded cables and systems also need good grounding. Incorrect grounding can cause radiation and interference problems in the system.

Single layer shielding

double-layer screen
Shielded stray wire
Single layer shielding
double-layer screen
Shielded cable assembly
Unshielded cable
When wiring near EMI / RFI interference sources is not involved, unshielded ACSR Cables shall be selected in most cases. Unshielded cable has the advantages of light weight, high flexibility, wide use, reliability and low price. It is widely used in IT applications and office networks.

Unshielded dispersion
Unshielded cable assembly
However, it should be noted that when enterprise networks or SMB networks want to achieve high data rates such as 10Gbps or 40Gbps on copper wires, the use of shielded cables can significantly reduce or even eliminate external crosstalk (AXT) harmful to network performance. This problem is mainly aimed at high-speed networks using category 6 cables, and does not involve low-speed 10 / 100 / 1000 networks using category 5 and category 6 cables.
It can be seen that the type of cable selected depends on the physical location of the network and the technology adopted (such as 10Base-T). The best practice is to thoroughly evaluate the installation location and network technical requirements, and then select the appropriate cable according to the specific specification requirements.

Types of cable faults

(1) Mechanical damage accounts for a large proportion of AAC Cable accidents. There are three main causes of mechanical damage.
(1) it is directly damaged by external force. If the cable is damaged by accident in the process of urban construction, transportation, or excavation, piling, lifting and handling of underground pipeline engineering.
(2) damage during cable installation: for example, the cable is damaged due to excessive traction, or the insulation or shielding layer is damaged due to too small cable bending.
(3) damage caused by other factors, such as expansion of insulating glue in joint or terminal and cracking of shell or nearby cable sheath; Without proper cable expansion arc, the cable sheath installed on the pipe orifice or bracket is damaged due to thermal mechanical force; Excessive tension caused by land subsidence, breaking the joint or conductor; The breakage of terminal porcelain bushing; Due to the vibration of large mechanical parts or running vehicles nearby, the lead bag is damaged.
(2) damp insulation
(1) because of the joint box or terminal box structure is not sealed or poor installation, resulting in water.
(2) poor cable manufacturing: there are small holes or cracks in the metal sheath of the ACSR Cable.
(3) the metal sheath is pierced or corroded by foreign objects.
in the fault repair work, the damp insulation must be removed. At the same time, check whether there is moisture in the conductor and remove it.

Insulation aging
cable insulation has been operating under the action of electricity and heat for a long time, and its physical properties change, which leads to the decrease of insulation strength or the increase of dielectric loss, and finally causes insulation breakdown, which is called insulation aging. If the operation time exceeds the designed service life of the cable, the aging of the insulation is called normal aging, which belongs to improper operation. If the similar situation occurs in a short period of time, it is regarded as premature aging of the insulation.
Overvoltage (IV)
it is rare to damage cable equipment due to lightning stroke or other impulse overvoltage. Generally, 3 ~ 4 times of instantaneous overvoltage will not affect the cable with good insulation. However, there are still some cases that the cable line is broken down when it is struck by lightning, such as the insulation of the vertical part of the terminal is dry, which may be broken down when it is struck by lightning.
there are many factors for cable overheating. Cable overload operation (over cable ampacity or under abnormal operation mode) will cause cable overheating; In areas with dense cables, poor ventilation of cable trench and tunnel, cables passing through dry ducts, etc., insulation damage may be accelerated due to overheating of cables. The vertical part of oil paper cable will lose insulating oil quickly due to overheating, resulting in dry insulation and even coking of insulating paper. Overload can also accelerate the recrystallization of lead clad grains, resulting in lead clad fatigue damage. In the oil paper cable line, when the shell of the joint filled with a large amount of asphalt insulating glue is welded with copper sheet, due to the large thermal expansion coefficient of the asphalt insulating glue itself, it is difficult to avoid the overload. The expansion of asphalt insulating glue will cause the copper shell to crack, or lead sheath of a section of cable at the lead sealing joint to crack.
Due to the fire or the influence of other adjacent cable faults and other external overheating damage, most of them can be determined from the burning phenomenon of the protective layer outside the cable, which is easier to identify.
(VI) material defects
this is a congenital defect of the cable. There are mainly mechanical damage of lead sheath, impurities in lead sheath, and joints in pressing lead. These are not easy to see outside the armor, and are often found in the process of accident repair. The end of the plastic cable is not sealed. After a large amount of moisture enters into the conductor, the insulation will gradually form “water branch” under the action of voltage, leading to insulation breakdown.

it belongs to congenital defects of cable accessories, such as sand holes in cast iron, insufficient mechanical strength of porcelain parts, rough and loose processing of assembly parts, non-conforming specification of waterproof rubber ring, rubber aging, etc. If the installation unit has a sound acceptance system, it can basically find these disadvantages and plug the loopholes.
(7) poor design
such as the joint and terminal waterproof design is not careful, the selection of materials is improper, the process requirements are not strict, the mechanical strength is poor and so on. For new equipment, new materials and new technology, trial operation should be arranged first, and then gradually popularized according to the maturity of operation experience, so that it is easy to correct even if problems occur.

Differences in use of brass, phosphor copper and red copper

Pure copper is a purplish red metal, commonly known as “red copper”, “red copper” or “red copper”. Pure copper is ductile. Pure copper, the size of a drop of ACSR Cable, can be drawn into two kilometers of filaments or rolled into almost transparent foil larger than a bed. The most valuable property of pure copper is its excellent conductivity, second only to silver in all metals, so it has become the “leading role” of the electrical industry.

Pure copper is more widely used than pure iron. Every year, 50% of copper is electrolyzed and purified into pure copper for electrical industry. The pure copper mentioned here is really very pure, with a copper content of more than 99.95%. A very small amount of impurities, especially phosphorus, arsenic, aluminum, will greatly reduce the conductivity of copper. The oxygen content in copper (easily mixed with a small amount of oxygen in copper smelting) has a great influence on the conductivity, so the copper used in electrical industry must be oxygen free copper. In addition, lead, antimony, bismuth and other impurities will make copper crystal can not be combined, resulting in hot brittleness, also affect the processing of pure copper.
This kind of pure copper with high purity is usually refined by electrolysis: the Impure Copper (crude copper) is used as anode, the pure copper as cathode, and the copper sulfate solution as electrolyte. When the current passes through, the Impure Copper on the anode gradually melts, and the pure copper gradually precipitates on the cathode. Copper thus refined; The purity can reach 99.99%.
Red copper is a relatively pure copper, generally can be considered as pure copper, conductivity, plasticity are better, but the strength, hardness is poor.
Properties and uses of brass
Brass is a kind of copper containing other alloy components. Its price is cheaper than that of red copper. Its conductivity and plasticity are worse than that of red copper, but its strength and hardness are higher.
Brass is an alloy of copper and zinc. The simplest brass is copper zinc binary alloy, which is called simple brass or ordinary brass. The higher the content of zinc in brass, the higher the strength and the lower the plasticity. The zinc content of brass used in industry is not more than 45%. No matter how high the zinc content is, brittleness will occur and the alloy properties will deteriorate.
Adding 1% tin to brass can significantly improve the corrosion resistance of brass in seawater and marine atmosphere, so it is called “Navy brass”. Tin can improve the machinability of brass. Lead yellow copper is what we usually call easy to cut national standard copper. The main purpose of adding lead is to improve the machinability and wear resistance, but lead has little effect on the strength of brass. Carved copper is also a kind of lead brass. Most brasses have good color, processability and ductility, and are easy to be electroplated or coated.
In industry and civil use, different materials are selected according to different use characteristics. If make electric wire, requirement is softer, red copper is better. If the connection piece is made, brass is often used for the screw.
Properties and uses of bronze

It originally refers to copper tin alloy. Later, except brass and Cupronickel, all copper alloys are called bronze, and are often preceded by the name of the first major additive element. Tin bronze has good castability, antifriction and mechanical properties, and is suitable for manufacturing bearings, worm gears and gears. Lead bronze is widely used in modern engines and grinding machines. Aluminum bronze has high strength, good wear resistance and corrosion resistance. It is used for casting high load gears, shaft sleeves, marine propellers, etc. Beryllium bronze and phosphor bronze have high elastic limit and good conductivity. They are suitable for manufacturing precision springs and electrical contact elements. Beryllium bronze is also used to manufacture non sparking tools used in coal mines and oil depots.
Properties and uses of white copper
Copper alloy with nickel as the main additive. Copper nickel binary alloy is called ordinary white copper; Copper alloy with manganese, iron, zinc, aluminum and other elements is called complex copper. Industrial white copper can be divided into structural white copper and electrical white copper. The structural white copper is characterized by good mechanical properties, corrosion resistance and beautiful color. This kind of white copper is widely used in manufacturing precision machinery, chemical machinery and ship components. Electrical white copper generally has good thermoelectric properties. Manganin, constantan and Kaotong are white manganin copper with different manganese contents. They are used to manufacture precision electrical instruments, varistors, precision resistors, strain gauges and thermocouples.

How to distinguish red copper, brass, bronze and white copper
White copper, brass, red copper (also known as “red copper”) and bronze (cyan gray or grayish yellow) are distinguished from each other in color, among which white copper and brass are very easy to distinguish; It is difficult to distinguish red copper from pure copper (impurity < 1%) and bronze (about 5% of other alloy components). Before oxidation, the color of red copper is brighter than that of bronze, and the bronze is slightly cyan or yellow and dark; After oxidation, red copper turns black, while bronze turns Turquoise or chocolate.

How to prevent and control pests on cable lines?

For direct buried ACSR Cable laying, in addition to preventing external mechanical damage, there is another kind of external damage from insects, such as termites. South China is located in the subtropical zone with humid climate, which is suitable for termite breeding. Termites will damage the lead sheath of the cable, causing the insulation damp after the lead sheath is perforated. In the areas where termite activities are more frequent, the special sheathed cable with termite resistance should be selected for the cable line design. If termite breeding is found near the cable line that has been put into operation, it should immediately report to the local termite control department for termite control, and adopt centralized trapping and prevention measures.

[1] Shi Chuanqing, chief editor. Question and answer of power cable installation and operation technology

What is the valve performance of the sheath protector?

In order to ensure that the sheath insulation will not be damaged under the action of lightning overvoltage and switching overvoltage, the sheath protector should be used. The ball gap protector was used in the early stage, but its disadvantage was that its surface was burnt by power frequency afterflow after each action. This type is not only heavy maintenance, but also unreliable. At present, zinc oxide, a non-linear resistor, is widely used in sheath protectors.
under normal operation, the current flowing through the sheath protector is microampere, so as to ensure the reliable operation of the AAC Cable.

Function of cable sheath Protector:
1. Limit the power frequency induced voltage in the metal sheath of ACSR Cable line.
In the normal working state of the cable line, the high-voltage cable sheath protector presents a high resistance state, which cuts off the power frequency induced current circuit in the cable metal sheath.
2. The power frequency and impulse overvoltage in the metal sheath of cable line can be reduced rapidly.
When grounding fault, lightning over-voltage or internal over-voltage occurs in the cable line, which leads to high over-voltage in the metal sheath, the sheath protector presents a low resistance conduction state, which makes the fault current quickly pour into the earth through the protector.

Selection of cable sheath Protector:
1. The residual voltage under the action of the possible maximum impulse current shall not be greater than the value of [impulse withstand voltage of cable sheath] – (37.5kv for 110kV cable) divided by 1.4 (included in the insulation coordination coefficient).
2. The possible maximum power frequency overvoltage shall be able to withstand without breakdown or damage under the action of 5S.
3. The protector shall not be damaged after 20 times cumulative action of the maximum possible impulse current.
Regular inspection and maintenance of cable sheath Protector:
Regularly measure the DC reference voltage of cable sheath protector at 1mA and the leakage current at 0.75 times of the reference voltage, especially after the system failure.

What is the national standard cable

National standard ACSR Cable, literally, is the wire and cable produced in strict accordance with national standards. China has clear regulations on the appearance, mechanical strength, insulation of sheath, withstand voltage strength and line resistance of cables. There are different national standards for different types of cables, mainly as follows:
·Executive standard for irradiation crosslinked power cable (0.6 / 1KV): GB / t12706.1-2008
·Executive standard for medium voltage XLPE cable (6 / 6kv-26 / 35kV): GB / t12706.2-2008
·Executive standard for high voltage XLPE cable (64 / 110kV): GB / t11017 – [/ b] 2002
·Executive standard of control AAAC Cable (450 / 750V): gb9330-88
·Executive standard for aluminum strand and ACSR (0.6 / 1KV): GB / t1179-1999

How to distinguish national standard cable?
I want to see it. See if there is quality system certification; Check whether the certificate is standard or not; Check whether there is factory name, address, inspection seal and production date; See if the trademark, specification, voltage, etc. are printed on the wire. But also look at the cross-section of the wire copper core, superior copper color bright, soft color, otherwise it is inferior.
Try. Take a wire head and bend it repeatedly by hand. Those with soft handle, good fatigue resistance, high elasticity of plastic or rubber handle and no crack on the wire insulator are excellent products.
weighing. Good quality wires are generally within the specified weight range. For example, the commonly used plastic insulated single strand copper wire with a cross-sectional area of 1.5mm2 weighs 1.8-1.9kg per 100m; The weight of 2.5mm2 plastic insulated single strand copper wire is 3-3.1kg per 100m; The weight of the poor wire is not enough, or the length is not enough, or the copper core of the wire is too much impurity.
Look at the copper. Qualified copper wire copper core should be purplish red, glossy and soft. The copper core of the fake copper wire is purple black, yellow or white, with many impurities, poor mechanical strength and poor toughness. It will break with a little force, and the wire is often broken. When checking, you only need to strip one end of the wire for 2cm, and then rub it on the copper core with a piece of white paper. If there is black substance on the white paper, it means that there are more impurities in the copper core. In addition, the insulation layer of fake wires seems to be very thick. In fact, most of them are made of recycled plastics. Over time, the insulation layer will age and leak electricity.
Look at the price. Because of the low production cost of fake wires, vendors often sell them at low prices under the guise of low price and good quality.

“Non standard / enterprise standard / market national standard” and “national standard of resistance protection”?
When many sales companies are asked whether they are GB cables, they often hear such words as “GB for market” and “GB for resistance protection”. Many people have little understanding. What do these vague words mean?
Resistance national standard: cable is used for power, and conductor resistance directly affects the conductivity. If the conductor resistance is too large, the conductivity is poor, when there is a large current through, it will produce a lot of heat, which will cause a fire. At the same time, because of the high resistance, it will also produce heat and inaction consumption of electric energy.
Resistance cable is to ensure that the resistance value of the cable is in line with the national standard, but it does not guarantee that the component materials of the cable are completely produced in accordance with the national standard, such as conductor square, insulation, sheath, etc. To put it bluntly, it means that through various technological innovations (or means), the manufacturer can make the cable reach the safe use condition on the premise of reducing the material cost.
Note that two words are used here: innovation and means. Innovation refers to the cost reduction through technological innovation, such as the current aluminum alloy conductor, special-shaped conductor, etc., which reduces the price on the premise of ensuring safe use. Some manufacturers reduce the cost through some illegal means, such as using second-generation materials, reducing the purity of conductor, etc. even if the resistance value of such cable is within the standard range, its use is extremely unsafe. When purchasing this kind of cable, it must be screened again and again.
“Enterprise standard / non-standard / market national standard”: these words are easy to understand, “enterprise standard / non-standard” is non-national standard cable, the price is extremely low, and it is also extremely unsafe“ Market national standard “generally refers to 9 fold cable (or 95 fold), we must not regard it as national standard, we must ask clearly. In addition, we should pay attention to the fact that the enterprise standard is higher than the national standard in accordance with the principle, but the domestic standard does come in the opposite direction!
In recent years, there are more and more fire accidents caused by unqualified wires and cables, many of which are purchased unqualified products due to the lack of cable knowledge. It is our duty and responsibility to produce and purchase GB cables, so as to ensure the safety of power supply and the healthy development of cable market.

When multiple cables run in parallel, the load distribution will be uneven?

When multiple cables are running in parallel, load measurement shall be conducted regularly to understand the load distribution and correctly grasp the operation status of ACSR Cables.

The load distribution of multiple cables is uneven when running in parallel, and even one phase load of one cable will be close to zero. The main reason for the serious uneven load distribution is the large difference of contact resistance of terminal connection (especially outdoor copper aluminum transition contact).
Because, the corrosion battery with two different metal contacts will cause poor contact; Due to the change of load current, temperature and natural environment, contact resistance of contact will increase to different extent. In this way, the current distribution is not uniform. For example, three cables a, B and C are running in parallel. If the contact resistance of cable a contact is large, the current is small and the normal load is mostly transferred to ABC Cables B and C. This may cause overload of cable B and C. if the contact of cable B terminal is heated due to the increase of load, the contact will be burnt and the load will be transferred to cable C, resulting in overload, thus forming a vicious cycle, and even heating will be caused by serious uneven distribution of three-phase current on the cable armour. This phenomenon will certainly endanger the safe operation of cable lines, and should be paid full attention.

Note: in design, the cable model and path length used in parallel are the same in general. Even if the models are different, the current distribution problem will be considered to meet the actual operation requirements. The provisions of this article are designed to consider that different types of cables are used for laying parallel cables due to tight construction period and incomplete cable goods, which may cause overload of one cable and insufficient load of another cable to affect operation safety. Because of the different insulation types of cables, the maximum allowable operating temperature of the core is different, and the allowable carrying capacity of the cables with the same material and specification and different insulation types is also different. Therefore, if different types of cables are used in construction, the length of cables shall be the same as possible during laying, so as to avoid the impact of operation safety due to the disproportionate distribution of load.

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High voltage cable intelligent anti breaking system

Project background

If the city grid is given life, the AAAC Cable is his blood vessel, which injects the energy of the power grid.
However, with the development, the construction frequency is high, which leads to the explosion of the risk of cable external force damage. Please see, this is the scene after the cable has been destroyed. Then, once the underground cable is damaged by the external force of construction machinery, it may cause chain reaction and lead to large-scale power failure.
If the power outage occurs in hospitals, transportation hub, government agencies and other important places, how much loss will be suffered to the people’s lives and property, and the indirect economic losses caused by the power failure are immeasurable; On the other hand, cable damage may also lead to the construction of personnel casualties. In view of this, it is urgent to prevent external damage!

Traditional cable inspection mainly relies on manual field inspection, which makes it difficult to find out the cable external breakage due to various mechanical construction on the ACSR Cable path in time and accurately. There are few operation and maintenance personnel, and the inspection mode mainly depends on the drawing and oral communication to confirm the cable location. Inspection efficiency is low and maintenance cost is high.

Function and characteristics of the scheme

With the national policy support for the digital transformation of state-owned enterprises and the promotion and application of 5g technology, our team seized the opportunity to break through the bottleneck, combined smart IOT technology with cable anti-external breaking work organically, and independently developed “intelligent brain – high voltage cable intelligent external breaking system based on artificial intelligence”.

Function 1
The full time visual monitoring device is applied to improve the real-time visibility of the equipment channel. The visual monitoring device is installed on the smart light pole in key cable channels and construction intensive areas, which can automatically identify the hidden dangers outside the cable channels such as large construction machinery.
The real-time data collected by camera is compared with the hidden danger image database of cable channel, and all kinds of external damage hazards on cable channel are automatically studied and identified.
At the same time, the system has the ability of autonomous learning, and with the deep use of the system, the recognition efficiency is improved.
Function 2
The fiber vibration technology is applied to improve the state perception of the equipment. The abnormal vibration caused by external force is automatically captured, and the warning is given before the external force endangers the power cable. According to the external vibration of optical fiber, the external force failure signal is automatically identified and the location of the hidden danger of external failure is accurately located.

Function 3
The application of “four-dimensional” visualization technology can enhance the visual operation and maintenance capability of underground cables. Realize the operation and maintenance personnel to stereoscopic view the cable lines and auxiliary facilities in VR form on site through PDA terminal, and guide the accurate operation.

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Common sense of high temperature wire and cable

High temperature wire and cable are everywhere in our life, and widely used, it brings a lot of convenience to our life, and high temperature wire and cable has many advantages compared with ordinary ACSR Cable. Today, Shanghai Qiyue high temperature cable editor will talk about some common sense problems of high temperature wire and cable.

1、 What should be paid attention to during transportation and loading of high temperature wires and cables?
In the process of transportation and loading and unloading, the cable and cable reel shall not be damaged. It is strictly forbidden to push down the cable reel directly from the vehicle. Cables shall not be transported and stored horizontally. Before transporting or moving the cable reel, it is necessary to ensure that the cable reel is firm, the cable is tightly wound, the oil pipe between the oil filled cable and the pressure oil tank shall be fixed without damage, the pressure oil tank shall be firm, and the pressure indication shall meet the requirements.
2、 What are the fire prevention measures for high temperature wires and cables?
Flame retardant cable is used. Fire proof cable tray is adopted. Fire retardant coating is used. Fire partition wall and fire damper shall be set at cable tunnel and interlayer exit.

The strike cable should avoid oil pipeline and explosion-proof door, otherwise it should take local pipe or heat insulation and fire prevention measures.
3、 Which aspects should be considered when selecting the section of high temperature wire and cable?
The following aspects should be considered: the working current that the cable is allowed to pass for a long time. The voltage drop on the line should not exceed the allowable working range.

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Choose the wire and cable, quickly identify the type!

The main function of wire and cable is to transmit electric energy, signal and realize electromagnetic conversion. The transmission of electric power, such as power cable, overhead line, etc., is the same as shaft ABC Cable, and the wire with electromagnetic conversion is like paint wrapped wire. If you choose a wire or cable, you need to quickly identify the type and type to select the right cable to use.

According to the number of transmission lines of each other with each other which are fixed together, the insulated wires can be divided into single core wires and multi-core wires. Multi core wires can also fix multiple single core wires in one insulating sheath. The multi-core wires in the same sheath can be as many as 24 cores. The parallel multi-core line is indicated by “B”, and the twisted multi-core wire is indicated by “s”.
Insulated wires can be divided into single wire and multi-core wire according to the stock number of each transmission line. Generally, the insulated wires above 6 square mm are all multi-core wires. The insulated wires with 6 square mm and below can be single wires and can also be multi-core wires. We call the single wire of 6 square mm and the following as hard wire, and multi-core wire is called copper wire.
Hard wire is indicated by “B” and copper wire is indicated by “R”. The common insulating materials of ACSR Cable are polyethylene and high pressure polyethylene. The “V” of PE indicates that “Y” is used for high-pressure polyethylene.

Bv copper core polyethylene insulated wire; BLV aluminum core polyethylene insulated wire; BVV copper core polyethylene insulation layer polyethylene protective cable; Blvv aluminum core polyethylene insulation layer polyethylene protective cable; BVR copper core polyethylene insulation copper wire;
RV copper core polyethylene insulation layer is installed with copper wire; RVB copper core polyethylene insulation layer flat electrode connecting wire copper wire; BVS copper core polyethylene insulation layer twisted copper wire; RVV copper core polyethylene insulation layer polyethylene wire sheath copper wire;
BYR high voltage polyethylene insulated soft cable; Byvr high voltage polyethylene insulation layer polyethylene wire sheath copper wire; Ry high voltage polyethylene insulated copper wire; RYV high voltage polyethylene insulation layer polyethylene wire sheath copper wire;
BVVB copper core polyethylene insulation layer polyethylene protective wire sleeve flat cable; BLVVB aluminum core polyethylene insulation layer polyethylene protective wire sleeve flat cable; Bv-105 copper core high temperature resistant 105 ℃ polyethylene insulated wire.

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