XLPE cable

What are the common installation methods of cable tray?

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Bridge, also known as cable bridge, is composed of support, tray, cover plate and installation accessories. In a computer room project, compared with expensive and high-tech hardware and software, the bridge is very insignificant and rarely paid attention to, but it is also an indispensable part of the whole wiring project. Today, let’s talk about the process and common installation methods of bridge during construction.

1、 Common installation methods of bridge:
1. Horizontal hoisting (lifting frame)
It is applicable to the hoisting of trough and tray bridges with width < = 100mm
2. Horizontal hoisting (cross arm)
It is applicable to the hoisting of trough and tray bridges with width > 100mm
When the width is less than 600mm, the through wire suspender shall be used
Width > = 600mm, use angle steel suspender
3. Horizontal wall (supporting arm)
It is applicable to the horizontal installation of bridge against the wall
4. Vertical wall (horse stool / word stand)
It is ACSR Cables to the vertical installation of bridge along the wall
2、 Installation and construction process of cable tray:
Installation process flow of cable tray
1. Positioning and setting out → embedded iron parts or expansion bolts → support, hanger and bracket installation → bridge installation → protective grounding installation
2. Determine the position from the beginning to the end according to the construction drawing, mark the direction along the drawing, find the horizontal, vertical and curved connection, snap lines or draw lines along the bridge direction on the walls, ceilings, floors, beams, plates, columns, etc., and draw the positions of supports, hoists and brackets with uniform span.


3. Embedded iron parts or expansion bolts
(1) The self-made processing of embedded iron parts shall not be less than 120mm × 80mm × 6mm, and the diameter of anchor round steel shall not be less than 10mm.
(2) Closely cooperate with the construction of civil structure, keep the plane of embedded iron parts close to the formwork, and fix the anchor round steel on the reinforcement in the structure by binding or welding; After the concrete formwork is removed, the plane of embedded iron parts is exposed, and the support, hanger or bracket shall be welded on it for fixation.
(3) Select the corresponding expansion bolt and drill bit according to the load borne by the support; After the bolts are embedded, the supports or hangers can be directly fixed on the metal expansion bolts with nuts and corresponding washers.
Bridge installation
1. When the length of steel cable tray in straight section exceeds 30m, and the length of aluminum alloy or FRP cable tray exceeds 15m, expansion joints shall be set, compensation devices shall be set at the crossing of expansion joints, and bridges with expansion joints can be used.
2. The bolts between the bridge and the support and the bolts of the bridge connecting plate are fastened without omission, and the nuts are located outside the bridge. When the aluminum alloy bridge and the steel support are fixed, there are mutual insulation and anti electrochemical corrosion measures, and asbestos pad can be used generally.
3. The cable tray laid in the shaft and crossing different fire zones shall be provided with fire isolation measures according to the design requirements. The ABC Cable tray laid in the electrical shaft can be fixed with angle steel
When the cable tray passes through the firewall and fire floor, fire isolation measures shall be taken to prevent the fire from spreading along the line; For the fire separation wall and plate, the opening shall be reserved in cooperation with the civil construction, and the edge protection angle steel shall be embedded at the opening. During construction, L50 shall be used according to the number of layers and cables laid × fifty × 5. The angle steel shall be used as the fixed frame, and the fixed cabinet shall be welded on the edge protection angle steel at the same time; The frame can also be installed in the wall and slab during masonry or concrete pouring in civil construction.


Grounding of bridge
When the design allows the use of bridge system to form grounding trunk circuit, the following requirements shall be met:
1. The metal cable conduit led in or out of the metal cable tray and its support must be reliably grounded (PE) or connected to neutral (pen), and must comply with the following specifications:
(1) The total length of metal cable tray and its support shall be connected with grounding (PE) or neutral (pen) trunk line at least 2 places, so that the whole tray is an electrical path.
(2) The two ends connected between non galvanized AAAC Cable trays shall be connected with copper core grounding wire, and the minimum allowable cross-sectional area of grounding wire shall not be less than 4mm2.
(3) The two ends of the connecting plate between galvanized cable trays may not cross the grounding wire, but the two ends of the connecting plate shall not be less than 2 connecting and fixing bolts with anti loose nuts or anti loose washers.
2. The connection resistance between the end of tray and ladder shall not be greater than 0.00033 Ω, and shall be tested with equipotential bonding tester (continuity meter) or micro Ω meter. The test shall be carried out on both sides of the connection point. The connection resistance at both ends of the whole bridge length shall not be greater than 0.5 Ω or determined by the design, otherwise the grounding point shall be added to meet the requirements. The coating shall be removed from the grounding hole, and the flat pad on one side of the bolt in contact with the coating shall use a special grounding washer with claw.
3. The expansion joint or soft connection shall be connected with braided copper wire. When another grounding main line is laid along the whole length of the bridge, the tray and ladder of each section (including non-linear section) shall be reliably connected with the grounding main line at least at a small point; Spring washers shall be installed at the connection of grounding parts to avoid loosening.

Harm of harmonics in power system

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1. Hazards to distribution transformer:
For the distribution transformer with the wiring group of yyno, during the three-phase four wire system wiring, the third harmonic current generates harmonic voltage in the original and auxiliary windings of the distribution transformer and causes the neutral point voltage to rise. In addition, because the odd harmonics have the same phase, their phasors on the neutral line are superimposed, so that the phasors of the zero sequence current on the neutral line are superimposed. Therefore, the medium linearity is heated due to the harmonic current.
During three-phase three wire connection, the ACSR Cable sequence harmonic forms the neutral point voltage due to the same phase, which changes the phase voltage.
For the distribution transformer with dyno wiring group, the zero sequence harmonic current forms a circulating current in the winding to heat the distribution transformer winding and reduce the service life of the distribution transformer.
2. Hazards to power cables:
Due to the high frequency rise of harmonic number and the larger cross-sectional area of cable conductor, the skin effect is more obvious, resulting in the increase of AC resistance of conductor and the reduction of allowable current of cable. In addition, the resistance of the cable and the inductive reactance of the line are connected in series with the system, and the capacitor for improving the power factor and the capacitive reactance of the line are connected in parallel with the system. A certain value shows that the inductance and capacitance may vibrate.
3. Hazards to power capacitors:
When there are harmonics in the power grid, when the capacitor is input, the terminal voltage increases, the current passing through the capacitor increases, and the loss power of the capacitor increases. The capacitive reactance of the capacitor is inversely proportional to the frequency. The higher the frequency, the smaller the impedance. Therefore, the harmonic voltage can greatly increase the current of the capacitor. If the allowable conditions of the capacitor are exceeded, the capacitor will be overcurrent and overload, resulting in abnormal heating. Especially when the capacitor is put into the power grid with distorted voltage, it may also aggravate the harmonic of the power grid, that is, harmonic expansion. Partial discharge is induced in the medium. Due to the large voltage change rate and high partial discharge intensity, it can accelerate the aging of the insulating medium, so as to shorten the service life of the capacitor（ http://www.diangon.com/ Copyright) generally speaking, for every 10% increase in voltage, the service life of the capacitor will be shortened by about 1 / 2. When the harmonic is matched with the parameters of the capacitor, it will produce resonance and make the harmonic square. When the harmonic is serious, it will cause bulging, breakdown, group explosion and greater loss of the capacitor.
4. Damage to incandescent lamps:
Incandescent bulb is a widely used lighting fixture. Its life is closely related to the thermal effect of harmonics. The AAC Cable of distortion coefficient shortens the life of bulb, and changing the fundamental voltage has a greater impact than changing the distortion coefficient.


5. Damage to motor:
The damage of harmonic to motor is mainly caused by additional loss, mechanical vibration, noise and harmonic overvoltage.
The distorted wave can increase the magnetic saturation of the motor core, especially the magnetic saturation of the core clamp winding, and reduce the fundamental short-circuit impedance. It is generally believed that the magnitude of the Nth harmonic current of the three-phase asynchronous motor can be calculated by the following formula:
6. Impact on electric energy meter:
(1) mechanical watt hour meter is an inductive mechanism. When measuring electric energy, it can be divided into the following three situations:
① The distorted wave power supply provides linear load. At this time, the electric energy meter measures the fundamental wave electric energy and some harmonic electric energy, which will deteriorate the performance of user equipment. In this way, users not only suffer from harmonic pollution, but also pay more electricity charges.
② The sine wave power supply supplies the nonlinear load. At this time, the electric energy meter measures the fundamental wave electric energy minus part of the harmonic electric energy. This shows that users pollute the power grid and pay less electricity bills.
③ The distorted wave power supply supplies nonlinear loads, which is more complicated. The fundamental current flows to the load, while the harmonic current is not necessarily. It may flow to the load or to the power supply, depending on the specific situation. The most direct method is to measure with an instrument.
⑵ the electronic watt hour meter uses an integral circuit, whether the power grid provides harmonic current to the load or negative current
The harmonic current provided by the load to the power grid will be integrated and measured together, which will cause measurement error.
7. Hazards to low voltage switchgear:
For the circuit breaker for power distribution, the full electromagnetic circuit breaker is easy to be affected by the harmonic current, which increases the iron consumption and generates heat. At the same time, it is difficult to trip due to the influence on the electromagnet and eddy current, and the higher the harmonic number, the greater the influence; The thermal magnetic circuit breaker generates heat due to the skin effect of conductor and the increase of iron consumption, resulting in the reduction of rated current and tripping current; For electronic circuit breakers, harmonics should also reduce their rated current, especially for electronic circuit breakers that detect peak values. AAAC Cable can be seen that the above three distribution circuit breakers may misoperate due to harmonics.
For the leakage circuit breaker, because the harmonic will affect the leakage current, the circuit breaker may be abnormally heated and misoperate or refuse to operate. For electromagnetic contactors, the harmonic current increases the temperature rise of magnet components, and the increase of coil temperature reduces the rated current. For the relay, the current should also be reduced due to the influence of harmonic current. They may cause misoperation during operation.
8. Interference to weak current system equipment:
For weak current equipment such as computer network, communication, cable TV, alarm and building automation, harmonics in power system are coupled to these systems through electromagnetic induction, electrostatic induction and conduction to produce interference. The coupling strength of electromagnetic induction and electrostatic induction is directly proportional to the interference frequency, and the conduction is coupled through the common grounding. A large amount of unbalanced current flows into the grounding electrode to interfere with the weak current system.
9. Impact on communication lines:
Generally, the working frequency of audio channel is about 200-400hz, and many harmonics of power supply system are within this frequency range. Because the power levels of power lines and communication lines are very different, the harmonics in the power supply system will cause perceptible, sometimes even unacceptable interference noise.
10. Impact on rectifier, inverter and logic control circuit:
Rectifier devices and thyristor circuits are widely used in various electrical equipment, ranging from rectifier and inverter devices for DC transmission, DC power supply for urban trams, to frequency conversion equipment, television, microcomputer, AC regulated power supply, battery charger and uninterruptible power supply (UPS), https://www.diangon.com/m234091.html On the one hand, these devices open and close different circuits according to a certain law, resulting in harmonic current injected into the power grid and become a harmonic source. On the other hand, the distorted waveform affects the normal operation of them and their loads. The distortion wave will cause the error of the control circuit, cause the ignition angular displacement, and the excessive current change rate and voltage change rate or overheating of the rectifier will cause equipment failure and damage to the rectifier components. These will bring harm to the converter. At the same time, the logic control circuit of some rectifier devices often leads to operation error due to distorted voltage.
11. Influence on fuse melt:
Overheating of the harmonic current in the melt will cause the displacement of its ampere second characteristic curve. Therefore, for the fault with low current, special attention should be paid to the selection of fuse to prevent accidental fusing and power failure, affecting the power supply.
12. Influence of harmonic skin effect:
The alternating current generates alternating magnetic flux through the conductor, and the alternating magnetic flux generates induced electromotive force with the conductor, so that the current density inside the conductor increases from the center to the outside along the conductor section, and the central current density is the smallest, which is commonly known as skin effect. Skin effect not only reduces the current carrying capacity of the conductor, but also increases the loss of the conductor, and this skin effect becomes more serious with the increase of current frequency. In general, the loss caused by skin effect is small at power frequency (50 Hz), while when the harmonic frequency is high, the loss and impact caused by skin effect such as harmonic with fifth harmonic frequency above 250 Hz are very significant. Therefore, the skin effect of harmonics should be considered when selecting conductors, and the conductor section should be increased appropriately.
13. Harmonics are also harmful to human body:
From the perspective of human physiology, when human cells are stimulated and excited, they will fluctuate rapidly or flip reversibly on the basis of cell membrane resting potential. If its frequency is close to the harmonic frequency, the electromagnetic radiation of power grid harmonic will directly affect human brain and heart.
Harm of harmonics to cables
As we all know, harmonic refers to the electric quantity whose frequency is an integral multiple of the fundamental wave contained in the current.
Generally, harmonic generation comes from three aspects: harmonic generation due to low quality of power generation, harmonic generation due to transmission and distribution system and harmonic generation due to electrical equipment. The third point is the main cause of harmonics, such as nonlinear loads, such as rectifier, switching power supply, UPS, frequency converter, inverter, etc. As shown in Figure 1, the harmonic generated by the equipment.

Figure 1 harmonics generated by equipment
The harmonics generated by the above three points have a serious impact on our electrical equipment. For the Xi’an Metro cable mentioned at the beginning of this article. Let’s focus on the harm of harmonics to cables.
Harmonic pollution will increase the dielectric loss, transmission loss, leakage current, temperature rise and partial discharge of dry-type cable, and increase the possibility of single-phase grounding fault.
Because the distributed capacitance of power cable can amplify the harmonic current, when the system load is low, the system voltage increases and the harmonic voltage increases accordingly. The higher the rated voltage level of the cable, the greater the risk of cable medium instability caused by harmonics, and the more prone to failure. As shown in Figure 2, it is cable combustion caused by harmonics.

Figure 2 cable combustion caused by harmonics
For the problem cables of Xi’an metro, the impact of harmonics will be more prominent. Unqualified cables and heating caused by harmonics are prone to accidents. This will be more serious in a relatively closed and crowded subway station. Of course, the problem with cable is not just about harmonics.
Therefore, for the safety of our transportation and other aspects, we should not only require from the transmission medium, but also check from the source of power quality. At this time, a device is needed to accurately capture and measure all parameters of power quality, and then analyze them to timely investigate possible potential safety hazards.

Take you to quickly understand the types of flame retardant cables

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Flame retardant wires and cables have unique flame retardant, low smoke emission and harmful smoke suppression properties. What flame retardant properties should AAC Cable materials have?


Type and performance of flame retardant wire and cable
1. General flame retardant wires and cables
Generally, the insulating layer and protective sleeve of flame-retardant wires and cables are generally made of polymer materials containing halogen bulbs (or modified materials added with halogen bulb flame retardant), and polyethylene (PVC) materials are common. The general PVC epoxy resin has higher electrolytic strength, acid resistance, wear resistance and anti-aging properties. The quality and cheap price of the epoxy resin become the raw material of AAAC Cable material which is in great demand in China. However, when PVC burns, hydrogen chloride, carbon monoxide, carbon dioxide, all kinds of fatty hydrocarbons, effective chlorine chemicals and other harmful substances will be released.


2. Low smoke halogen-free flame retardant wire and cable
Low smoke halogen-free cable flame retardant wire and cable can add inorganic nickel hydroxide flame retardant such as aluminum chloride and aluminum hydroxide to the insulating layer and protective wire sleeve materials. The basic principle of flame retardant is the basic principle of condensation phase flame retardant: the water released by the decomposition reaction of aluminum chloride and aluminum hydroxide, at the same time, digest and absorb the heat, reduce the specific temperature of insulating layer and protective wire sleeve materials, and inhibit the dissolution and release of combustible gases. The converted hydroxide is also a fireproof material, which is covered on the surface of the material to improve the working ability of the insulating layer and protective wire sleeve to resist fire, and has the purpose of blocking gas and blocking combustion. Aluminum chloride and aluminum hydroxide are the advantages of flame retardant: no poison, no evaporation, high quality and low price, flame retardant and destructed opium. However, the compatibility with the epoxy resin of the base material is poor. When it is used as a flame retardant, it must be added a lot to achieve a certain flame retardant grade. In addition, it is easy to reduce the forming process performance and structural mechanical properties of the material.


3. Low smoke halogen-free flame retardant wire and cable
Thermosetting polyurethane elastomer materials are often used for the insulation layer and protective sleeve of low smoke halogen-free flame retardant wires and cables. The materials do not contain halogen elements such as fluorine, chlorine, bromine and iodine. Mercury, chromium, cadmium, lead and other heavy metal elements that cause great environmental pollution to the natural environment are removed in the manufacturing process. Acrylic resin is often used. The flame retardant principle of this kind of ABC Cable is the flame retardant principle of final break interchange. Final flame retardant refers to taking away part of the calorific value caused by the combustion of flame retardant materials, resulting in that the materials can not maintain the decomposition reaction temperature, so it can not continuously cause flammable gases, so the combustion will extinguish itself. For example, when the flame-retardant material is subjected to strong heat or burning, it can melt, and when the molten material drops, it can take away most of the calorific value, resulting in slow combustion, which is likely to stop combustion.

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

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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.
01
PART
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
02
PART
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
picture
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.

Causes of blackening of copper wire of heavy rubber sheathed flexible cable

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2.1 catalytic aging of copper is an important reason for rubber hair adhesion
The experiment of the former Soviet Union Institute of AAAC Cable science proved that copper infiltrated into the insulating rubber from the contact with rubber during vulcanization, and the thickness of 1.0-2.0mm contained 0.009-0.0027% copper. As we all know, trace copper has a great damage to rubber, that is, heavy metal is the catalytic aging of rubber. During the process of insulation vulcanization, qiulanm precipitates some free sulfur to react with copper to form active copper containing groups: CH3 ■ ch2-ch-c-ch2- ■ ■ SS ■ ■ cucu, when aging, weak s-s-bond breaks, forming active copper containing base: cu-s-, which acts with rubber, and acts with oxygen, breaks down long bond molecules of rubber, making rubber soft and sticky, which is a combination of low molecular chain. The French Academy of rubber also pointed out that if there are harmful metals in rubber, such as copper, manganese and other heavy metal salts, the rubber viscosity will occur regardless of the type of promoter.

2.2 sulfur migration to the surface of insulating rubber and copper wire in rubber sheath cable
The possibility of sulfur diffusion in cable sheath rubber was confirmed by the use of radioisotope by former Soviet scientists. The diffusion coefficient of free sulfur is about 10-6cm2 / s at 130-150 ℃ in the vulcanized rubber based on natural rubber. In the continuous vulcanization factory, when vulcanizing sheath rubber, the temperature is between 185-200 ℃, and the diffusion coefficient is greater. Because of the diffusion of free sulfur in rubber sheath, the structure of the colum rubber is changed, and the polysulfide bond may be formed. These polysulfide compounds migrate through chemical decomposition and chemical combination, namely “chemical diffusion”. Due to the migration, not only the structure of the insulating rubber can be changed, the heat resistance of the rubber can be reduced, but the reaction between sulfur and copper surface will result in copper sulfide and cuprous sulfide, which leads to the blackening of copper wire. In turn, copper sulfide and cuprous sulfide accelerate the aging of rubber, and lead to the occurrence of adhesion.

3. Reasons for processing technology
3.1 reasons for processing rubber
In the insulation formula based on the combination of natural rubber and SBR, the plastic of rubber needs to be improved by plastic refining. In order to produce, some factories use internal mixer to improve plasticity by adding a small amount of chemical plasticizer, accelerator M. If the temperature of plastic refining and rubber filtration are not well controlled, high temperature above 140 ℃ appears. When the raw rubber is put on the opening mill, it passes through the drum slowly. Because the rubber is affected by hot oxygen and accelerator M, it will be found that the rubber surface seems to be coated with oil. In fact, rubber molecules are more serious in promoting the chain breaking under the promotion of chemical plasticizer, A relatively soft and sticky rubber with smaller molecular weight was produced.
Although the rubber was mixed with SBR and then mixed with insulating rubber, these small molecular weight natural rubber were evenly dispersed in the rubber. After the rubber was extruded on the copper wire for continuous vulcanization, there might be no problem at that time, but a hidden danger was buried for the rubber copper ABC Cables. That is, the local copper wire sticking phenomenon will appear in the first place for these small molecular weight natural rubber.

The process of adding vulcanizing agent and accelerator to insulating rubber is also very important. Some small factories add vulcanizing agent on the mixer, that is, pour the pot containing vulcanizate into the middle of the drum, with many in the middle, and less on both sides. When the vulcanizate into rubber, the number of turning triangle was less, which would make the vulcanizate distributed unevenly in the rubber. In this way, copper wire blackening is easy to appear in many places with vulcanizing agent when extrusion is continuous vulcanization. In the blackening place for a long time, the phenomenon of rubber adhesive copper wire will appear.
3.2 reasons for vulcanization of insulating rubber
In order to pursue the production, some enterprises only have 60 meters long continuous vulcanization tubes, 1.3mpa steam pressure, and the vulcanization speed is 120 m / min. thus, the residence time of insulating rubber in the pipe is only 30 seconds. Rubber itself is a bad conductor of heat. The surface temperature of the insulating core is more than 190 ℃, and when the temperature is transferred to the inner rubber contacting with copper wire, it is also absorbed by copper wire. When the copper wire is heated to close to the inner rubber temperature, the vulcanized rubber wire core has been discharged from the vulcanizing tube. So the temperature of the inner rubber is relatively low, about 170 ℃, and the vulcanization tube will be left only a few seconds. When it enters the cooling and winding, the insulation rubber will not be vulcanized enough.
In order to achieve sufficient vulcanization, the amount of promoter TMTD (as vulcanizing agent) is up to 3.4%. The excess of vulcanizing agent also releases more free sulfur during the curing process. Besides the crosslinking rubber molecules, there are also excess free sulfur. This is the reason why the copper wire surface is blackened.
In short, it is still difficult to solve the problem of copper wire blackening. Every process from copper wire to rubber should be taken seriously to achieve better results. The key to the problem is the choice of rubber species and the adoption of vulcanization system. The solution to this problem needs to go through the test of time.

Maintenance contents of cable channel

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1. Replace the damaged well cover, cover plate and protection plate, and complete the missing well cover, cover plate and protection plate.
2. Maintain the working shaft stop.
3. Clean up the water and debris in the passage.
4 stairs (ladder) for tunnel maintenance personnel entering and leaving the shaft

5. Maintain the ventilation, lighting, drainage and low voltage power supply system in the tunnel.
6. Maintain fire prevention and isolation facilities and fire fighting facilities in cable trench and tunnel.
7 prune and cut branches and vines with insufficient safety distance around AAAC Cable terminal tower (pole) and T-joint platform.
8 repair the grounding down lead with loose connection, poor grounding, corrosion and other defects.
9 replace the missing, faded and damaged stakes, warning signs and signs, and timely correct the inclined stakes, warning signs and signs.
10. Carry out anti-corrosion treatment for corroded cable support, and replace or repair the missing, damaged and severely corroded support parts.
11. Bailey frame, I-beam and other facilities can be used to protect the cable trench in operation, and the suspension and support protection shall be well done. When the suspension protection is carried out, the cable trench body or row pipe shall be protected as a whole, and direct suspension of bare cables is prohibited.


12. If the cable passage in the green belt or sidewalk is changed to slow lane or fast lane, it should be relocated. Before the relocation, the relevant parties should be required to take reinforcement measures according to the load-bearing road standard to protect the working shaft, drainage pipe and cable trench.
10.2.13 when there are excavators, cranes and other large machinery passing through the non load bearing AAC Cable channel, the relevant parties shall be required to take protective measures such as setting steel plates above, and the protective measures shall prevent noise from disturbing the residents.
10.2.14 if the elevation of the working shaft or trench body is inconsistent with the surrounding due to the change of the environment of the cable passage, the elevation of the working shaft or trench body shall be adjusted by prefabricated shaft or cast-in-place method.

Types of cable faults

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（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.
Overheating
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.

How to prevent and control pests on cable lines?

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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.

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

Methods to prevent cable corrosion

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(1) The cable manufacturer is required to use the protective layer outside the metal sheath of the AAC Cable when manufacturing the cable, and the aluminum sheathed cable must have polyethylene or PVC outer sheath.
2) When selecting the cable route, it is necessary to make full investigation, collect the soil data near the area where the line passes, and carry out chemical analysis, so as to judge the degree of soil and groundwater erosion. If necessary, measures should be taken, such as changing the route of the line, partially replacing the bad soil, or adding special protective measures, such as putting the cable through the corrosion-resistant pipe.


Prevent external damage and theft of facilities
Design and infrastructure stage
The setting of cable route, auxiliary equipment and facilities (ground grounding box, entrance and exit, ventilation Pavilion, etc.) shall be approved by the planning department. It should be avoided that the cable passage is adjacent to the thermal pipeline, flammable and explosive pipeline (oil and gas) and corrosive medium pipeline.
Note: it is a new clause. It is proposed that the route, auxiliary equipment and facilities should be approved by the planning department, and the requirements of avoiding the cable passage adjacent to thermal pipelines, flammable and explosive pipelines (oil and gas) and pipelines with corrosive media should be avoided.
It is difficult to understand the corrosion degree of the cable on the running cable line. In the area where the corrosion of the cable has been found or the leakage of some chemicals piled on the ACSR Cable line, the soil should be dug to check the cable, and the nearby soil should be chemically analyzed to determine the damage degree
2. Methods to prevent electrolytic corrosion
(1) strengthen the insulation between the metal sheath of the cable and the huge metal objects nearby.
(2) installation of drainage or forced drainage, polarity drainage equipment, cathode station, etc.
(3) for areas with serious electrolytic corrosion, shielding pipes should be installed.
stray current is related to the distribution of electrical track, the maintenance of joints and the layout of other underground metal pipelines. In order to protect the underground pipelines and communication cables, the departments of underground oil and gas pipelines and local communication cables sometimes adopt cathodic protection. Therefore, the cable operation Department must systematically measure the potential difference between the lead sheath and the earth and other pipelines, the stray current density of the lead sheath and the current density flowing into the earth, so as to accumulate data. When we know which area is in danger of corrosion, we should take preventive measures in time, and work together with relevant units to try to eliminate the source of stray current and do a good job of corrosion prevention.


the operation experience shows that when the current density from the cable metal sheath reaches the average value of one day and night, the metal sheath will be corroded. This paper introduces a method of measuring stray current density auxiliary electrode method,
the auxiliary electrode is made of a section of cable similar to the tested cable, and its length should be such that the contact surface between the electrode and the earth is not less than 500. Peel off the outer protective layer of the electrode surface, wipe off the armored surface, weld the connecting wire, and pour asphalt or other insulating materials on the solder joint insulation and both ends of the electrode.
In addition to cable corrosion, there are also corrosion phenomena such as metal bracket, metal hoop and grounding wire in cable channel.

Is the thicker the cable insulation, the better?

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Many friends may think that the thicker the AAC Cable, the better the insulation performance, the more durable the cable, and the better the quality. In fact, this idea is taken for granted, and there are some misunderstandings.
This is because the insulation performance of cables depends on the technical indicators. The state has strict technical standards for cables. Compared with the cable thickness specified in the national standards, it is unnecessary to say that if the cable thickness is thinner, even if it is thicker, it is also unqualified as long as it exceeds the specified value.

When the thickness exceeds the standard, the performance of the cable will be affected, such as the service life will be greatly shortened. Because when the cable is laid and put into use, it will be in the state of continuous power supply, and the heat will be generated in the process of power supply. If the thickness exceeds the standard, although the insulation looks better, the result is that the heat is difficult to dissipate（ Learn more cable technology, please click here, a large number of dry goods waiting for you) with the accumulation of time, more and more heat accumulation, of course, will affect the normal service life of the cable.


When the situation is serious, it will even lead to short circuit, power failure, causing greater damage.
The so-called “too much is not as good as it can be”. Those who meet the national standards are the best.

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