What are the common installation methods of cable tray?

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 and Countermeasures of wire joint heating

The phenomenon of wire joint heating is generally manifested in that there is peculiar smell around the wire joint, which can be smelled. This is because the heat of wire joint makes the outer insulation layer smell; Secondly, the ACSR Cables joint is smoking, red, the outer insulation layer is black, fire, or even broken. What are its hazards, causes and countermeasures?

1. Harm
Hot wire connection will not only cause a lot of power loss, but also seriously affect the normal operation of electrical equipment. At least, the working current in the line will increase and the service life of electrical equipment will be shortened. At worst, it will suddenly interrupt the ongoing production, scientific research, medical surgery and other activities, and lead to fire and electric shock accidents, resulting in incalculable losses.

2. Cause
(1) The connector is not tightened during equipment installation and repair. When the current passes through, it may generate heat, even redness, smoke, fire and disconnection. ABC Cables, switches and electrical appliances are connected through wire posts. Due to careless construction, no washer is added on the terminal post and the Gong cap is not tightened, which will also increase the contact resistance. For example, in a hotel, because of this reason, the conductor heated and melted, and the molten beads fell on the cardboard box below, causing a fire.
(2) The connector will also loosen after long-term operation. Some joints are of good quality during installation, but they will become loose due to thermal expansion and cold contraction or long-term vibration. For example, for copper aluminum joints in long-term operation, if there is no silver plating or tin hanging on the contact surface, the contact surface produces serious electrochemical corrosion and generates oxide film, which increases the resistance at the joint and is very easy to become a hot spot.

(3) For contacts with small current, the current increases suddenly due to the sudden change of the system, resulting in contact heating;
(4) In case of short circuit fault of the system, the over-current makes the contact with insufficient capacity or defective contact ignite instantly, etc.
Therefore, the contact heating is mainly caused by the increase of contact resistance.
3. Countermeasures
If the connector is well connected, the heating of the connector is prevented, and the heating problem of the AAAC Cable connector will not appear, so it does not need to be handled. Therefore, the wire joint shall be firm, tight and beautiful without overlap, bending, crack and concave convex; The mechanical strength of the joint shall not be less than 80% of the mechanical strength of the conductor; The insulation strength of the joint shall not be lower than that of the conductor. During installation and maintenance, the joints of wires shall be reduced as much as possible. Conductors with too many joints shall not be used. For joints of movable lines and outdoor lines, special attention shall be paid to the provision that only one joint is allowed between two adjacent wire stems.

What are the measures to speed up cable fault repair?

The speed of cable fault repair directly affects the economic benefits and social image of cable operation Department, and it is also an important symbol to measure the comprehensive management level of AAC Cable operation Department. The repair of cable fault, from receiving the cable fault repair order, checking data, measuring faults, finding fault points, troubleshooting, repairing faults to restoring power transmission, requires the cooperation of all departments. In case of problems or delay in a certain department or construction link, the speed of cable fault repair will be affected. In order to speed up cable fault repair, the following measures are taken:
(1) establish an efficient fault emergency repair command system, and be responsible for commanding emergency repair and coordination of various departments. According to the number of AAAC Cable faults, a fault emergency repair command center or a fault emergency repair dispatching center can be set up.

(2) provide reliable and effective communication equipment to enable the command center to obtain the repair information in time, maintain smooth communication with the emergency repair site, and the material and logistics departments can understand the information of the emergency repair site in time.
(3) formulate a standardized emergency repair software package, and clarify the standard process of emergency repair and the work standards of each department.
(4) provide a skilled emergency repair team and establish a 24-hour emergency repair duty system.

(5) advanced and fast means of transportation shall be equipped. All departments undertaking ABC Cable fault repair shall be equipped with engineering rescue vehicles approved by the government traffic management department.
(6) provide sufficient and orderly accident spare parts and effective and fast means of transportation.
(7) make public commitments to the society and accept social supervision.
Note: in addition, due to the sharp increase in the scale of cables and channels, perfect basic information (especially channel location information and joint location information), experienced skilled personnel and effective fault finding equipment are also the key elements to speed up cable fault repair.

Harm of harmonics in power system

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

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.

Pithy formula and interpretation of common cable selection

In our daily sales, we may encounter customers asking about ACSR Cable selection in the process of maintenance and repair. As a cable salesman, choosing the right cable for customers is the top priority of this work.
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First, the actual power of the load should be considered, at the same time, the maximum current to be borne by the cable should be calculated, and then the appropriate cable should be selected. The following is the relevant contents sorted out by the editor in AAAC Cable treasure. I hope I can provide some help for my colleagues.

[doggerel]: five out of ten, two out of one hundred, fifty-three out of four, and 75% off for buried casing.
[explanation]: according to the total current required by the insulated conductor, when the total current is less than 10a, the cross-sectional area of the conductor per square millimeter can pass 5A current, if it is more than 100A, it can only pass 2A current per square millimeter, 4A current per square millimeter between 10 ~ 50A and 3a current per square millimeter between 50 ~ 100A. After this calculation, In case of buried or casing laying, the current value that can be passed shall be multiplied by 0.75.
The calculation method given above obtains the allowable current per square millimeter. The selection of the actual specific conductor section should be: first determine the current required by the electrical equipment (including rated current and appropriate margin), then compare the current range in the doggerel according to the required current value, and then the conductor section that should be selected can be obtained by “allowable current per square millimeter” belonging to the range at the required current value.


For example, the rated current of an electrical equipment is 20A. Considering a certain margin, the required current is determined to be 22a. Then, find out that the current range of 22a current in the above doggerel belongs to 10 ~ 50a, and the available current per square millimeter is 4a. Finally, divide 22a by 4a to obtain the conductor section s that should be selected as:
S = 22 / 4 = 5.5 (mm2). According to this value, the conductor with corresponding section can be selected. If the calculated sectional area is not in the conductor section specification series, a slightly larger conductor section can be selected.

Maintenance contents of cable channel

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.

What are the cable maintenance items?

1. Manhole and drainage pipe
(1) water samples were taken for chemical analysis.
(2) remove the water in the well and remove the sludge.
(3) paint the iron parts such as cable bracket and hook.

(4) check the well cover and ventilation, and check the well body for settlement and cracks.
(5) dredge the spare pipe hole.

(6) check the condition of ACSR Cables and joints in the manhole to see if there is any oil leakage, whether the insulation gasket on the bracket is in good condition and whether the grounding is good.
(7) check the circuit name plate.
(8) check whether there is electric erosion, and measure the potential and current distribution of cables in the manhole.
2. Cable trench and tunnel
(1) check whether the door lock is normal and whether the access is smooth.
(2) check whether there is water seepage and ponding in the tunnel, remove the ponding and repair the leakage.

(3) check whether the ABC Cable bracket falls.
(4) check whether the insulation gasket between the metal sheath of the cable and connector and the bracket is intact, and whether there is any damage on the bracket; Whether the bracket has fallen off.
(5) check whether the fireproof tape, coating, blocking material and fireproof box are in good condition, whether the fireproof equipment and ventilation equipment are perfect and normal, and record the room temperature.

(6) check whether the grounding condition is good, and measure the grounding resistance if necessary.

(7) clean cable trench and tunnel.
(8) check the cable and cable joint for oil leakage.
(9) check cable tunnel lighting.

Learn cable knowledge, start here

1、 Basic introduction of wire and cable
Wire and cable: usually twisted by several wires or groups of wires [at least two in each group], similar to rope. Each group of wires is insulated from each other and twisted around the center of a wire. The whole wire is covered with a highly insulating covering layer. It is mainly used for transmission, distribution of electric energy or transmission of electric signals.
Wires and ACSR Cables are mainly composed of the following four parts
1. Conductive core: made of high conductivity material (copper or aluminum). According to the requirements of laying and using conditions for cable flexibility, each wire core may be made of a single wire or multiple wires.
2. Insulating layer: the insulating material used for cables shall have high insulation resistance. The common insulation materials used in cables are oil impregnated paper, PVC, PE, XLPE, rubber, etc.


3. Sealed sheath: protect insulated wire core from mechanical, moisture, moisture, chemicals, light and other damage. For the insulation susceptible to moisture, lead or aluminum extrusion sealing sheath is generally used.
4. Protective coating: used to protect the sealing sheath from mechanical damage. Generally, galvanized steel strip, steel wire or copper strip, copper wire, etc. are used as armor to wrap around the sheath (called armored cable), and the armor layer plays the role of electric field shielding and preventing external electromagnetic interference at the same time. In order to avoid the corrosion of steel strip and steel wire by the surrounding medium, they are usually coated with asphalt or wrapped with impregnated jute layer or extruded with polyethylene or PVC sleeve.
2、 Wire and cable specifications
Wire and cable specification is the meaning of the expression of the number of cores and section size of wire and cable. The complete naming of wires and AAC Cables is usually more complex, so people sometimes use a simple name (usually the name of a category) combined with model specifications to replace the complete name. For example, “low voltage cable” represents all plastic insulated power cables of 0.6/1kv class. It can be said that as long as the standard models and specifications of wires and cables are written, specific products can be identified.
3、 Wire and cable application classification
(1) Classified by insulating materials, such as oil impregnated paper insulated cable, PVC cable, XLPE cable, etc.
(2) According to the use classification, it is divided into power cable, communication cable and control cable. They are used in power system, information transmission system, mechanical equipment and instrument system.
1. Power system
The wire and cable products used in power system mainly include overhead bare wire, bus bar (bus bar), power cable (plastic cable, oil paper power cable (basically replaced by plastic power cable), rubber sheathed cable, overhead insulated cable), branch cable (replacing part of bus bar), electromagnetic wire and electric equipment wire and cable for power equipment.


2. Information transmission system
The wires and cables used in information transmission system mainly include local telephone cable, television cable, electronic cable, radio frequency cable, optical fiber cable, data cable, electromagnetic wire, power communication or other composite cables.
3. Mechanical equipment and instrument system
Except for overhead bare wires, almost all other products have applications, but mainly power cables, electromagnetic wires, data cables, instrument cables, etc.
(3) According to product classification, it can be divided into five categories
1. Bare wire and bare conductor products
The main features of this kind of products are: pure conductor metal, no insulation and sheath layer, such as ACSR, Cu al bus bar, electric locomotive line, etc; The processing technology is mainly pressure processing, such as melting, calendering, drawing, stranding / tight stranding, etc; Products are mainly used in suburbs, rural areas, user main line, switch cabinet, etc.
2. Power cable
The main features of this kind of products are: extruding (winding) the insulating layer outside the conductor, such as overhead insulated cable, or twisting several cores (corresponding to the phase line, zero line and ground wire of power system), such as overhead insulated cable with more than two cores, or adding sheath layer, such as plastic / rubber sheathed wire and cable. The main process technologies include drawing, stranding, insulation extrusion (wrapping), cabling, armor, sheath extrusion, etc. different process combinations of various products have certain differences.
The products are mainly used in the transmission of strong electric energy in power generation, distribution, transmission, transformation and power supply lines, with large current (tens to thousands of a) and high voltage (220 V to 500 kV and above).
3. Wires and cables for electrical equipment
The main features of these products are: a wide range of varieties and specifications, a wide range of applications, the use of voltage in 1kV and below more, in the face of special occasions continue to derive new products, such as fire-resistant cable, flame retardant cable, low smoke halogen-free / low smoke halogen-free cable, termite proof, mouse proof cable, oil / cold / temperature / wear-resistant cable, medical / agricultural / mining cable, thin-walled wire, etc.
4. Communication cable and optical fiber
From simple telephone and telegraph cables in the past to thousands of pairs of telephone cables, coaxial cables, optical cables, data cables, and even combined communication cables. This kind of product structure size is usually small and uniform, high manufacturing accuracy requirements.
5. Electromagnetic wire (winding wire)
It is mainly used for various motors, instruments, etc.
4、 What’s the difference between wire and cable?
In fact, there is no strict boundary between “wire” and “cable”. Generally, the products with few cores, small diameter and simple structure are called wires, the ones without insulation are called bare wires, and the others are called cables; The conductor with larger cross-sectional area (more than 6 square mm) is called large wire, the smaller one (less than or equal to 6 square mm) is called small wire, and the insulated wire is also called cloth wire. But with the expansion of the scope of use, many varieties of “cable in the cable”, “cable in the cable”. So there is no need to make a strict distinction. In daily habits, people call household cloth wires wires and power cables for short.
The wire is composed of one or several soft wires with light and soft protective layer; The cable is composed of one or several insulated wires, which are wrapped with a tough outer layer made of metal or rubber. Cables and wires are generally composed of core wire, insulation sheath and protective sheath.

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.
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.