How to skillfully use aluminum alloy cable in photovoltaic system?

The cost of control system is very important in the era of photovoltaic affordable Internet access. Over the past decade, the price of modules and inverters has decreased by 90%, which has made a great contribution to the overall cost reduction of photovoltaic system, but the cost of cables has not decreased. In large projects, the proportion of cables in the system reaches 10%, which is higher than that of inverters. In fact, as long as the design and installation are proper, on the premise of ensuring the normal operation and safety of the system, some AC cables adopt aluminum alloy cables, which can reduce some costs.
The cables of photovoltaic power station are divided into DC cables and AC cables. The DC cables between components and between components and inverter are generally required to use photovoltaic special DC cables, while the cables from inverter to AC distribution cabinet and from distribution cabinet to transformer are not required to use any ACSR Cables.

What is aluminum alloy cable: aluminum alloy cable is a new material power cable with aa8030 series aluminum alloy material as conductor. The resistivity of aluminum alloy is between aluminum and copper, higher than copper and slightly lower than aluminum. Under the premise of the same current carrying capacity, the weight of aluminum alloy conductor with the same length is only half of that of copper.
When the cross-sectional area of aluminum alloy conductor is 1.5 times that of copper, aluminum alloy ACSR Cable and copper cable achieve the same current carrying capacity, resistance and line loss.
Service life: different metal oxides are formed after the metal surface reacts with oxygen. Aluminum oxide can form a dense surface protective film with a certain hardness. Copper oxide, commonly known as copper green, is a toxic substance between the above two.
Economically, this is the most important aspect. The cost of aluminum alloy cable is about 25% ~ 50% of that of copper core cable. The cost advantage of aluminum alloy cable is relatively large. We can make a comparison. In a 400KW village level poverty alleviation power station, the distance from the AC distribution cabinet to the step-up transformer is 1500 meters, and the maximum output current of the 400KW power station is 580A. If copper cables are used, two 150 square meters are required for each phase and six for three phases, with a total length of 9000 meters and a price of 864000; If you use two 240 square meters of aluminum alloy, the total length is 9000 meters, and the price is 450000 yuan, 414000 yuan can be saved, and the loss of 240 square meters of aluminum wire is lower than that of 150 square meters of copper wire.

There is also a rare earth aluminum alloy cable, which is made of high elongation aluminum alloy material. By adding rare earth trace element materials such as boron to pure aluminum and treated by rolling technology and special annealing process, the cable has good flexibility. When its surface is in contact with air, it can form a thin and firm oxide layer, which can withstand all kinds of corrosion. Even when overloaded or overheated for a long time, it can ensure the stability of the connection, and the cost is about 10% higher than that of ordinary aluminum alloy cable.
Application scope of aluminum cable: aluminum cable can be considered for long-distance overhead line, underground cable trench with large space and places with reliable fixed bridge.
Precautions for use of aluminum cable:
The melting point of copper is 1080 ℃, while that of aluminum and aluminum alloy is 660 ℃, so copper conductor is a better choice for fire-resistant cable. At present, some aluminum alloy AAC Cable manufacturers claim that they can produce fire-resistant aluminum alloy cables and have passed the relevant national standard tests, but there is no difference between aluminum alloy cables and aluminum cables. If they are in the fire center, that is, when the temperature is higher than the melting point of aluminum alloy and aluminum cables, no matter what heat insulation measures are taken, the cables will melt in a very short time and lose their conductive function, Therefore, aluminum alloy should not be used as fire-resistant cable conductor, nor in densely populated urban distribution network, buildings, factories and mines.

Compared with aluminum core cable, the copper core is flexible, the allowable bending radius is small, and it is not easy to break after repeated bending. Therefore, aluminum cable should not be used when there are many bends, many pipes or complex lines.
As the terminals of electrical switchgear are made of copper, copper and aluminum are directly connected, and the chemical reaction of primary battery will occur after power on: aluminum with higher activity will accelerate oxidation, resulting in higher resistance and lower current carrying capacity at the joint. Therefore, some measures need to be taken when copper and aluminum are connected, such as using copper aluminum transition terminal or copper aluminum transition terminal block, Eliminate electrochemical reaction.

What are the advantages of overhead cables over underground cables?

(1) The power transmission is not easily affected by the surrounding environment and has high reliability.
(2) The insulation distance between wires is small, the land occupation is small, and there is no interference with radio waves.
(3) When laying underground, it does not occupy the ground and space, which is not only safe and reliable, but also not easy to expose the target.
Therefore, in densely populated urban areas, large factories, power plants, traffic congestion areas and power grid intersection areas require small floor area, safety and reliability, reduce the impact of power grid on transportation and urban construction, and generally use AAC Cable power supply; In severely polluted areas, cables are often used to improve the reliability of power transmission; For the river crossing and river crossing lines with large span, it is not suitable to erect overhead lines, or cables are also used to avoid the interference of overhead lines to ship navigation or radio; Some national defense and military projects use cables to avoid exposing targets; Some also use cables due to the needs of architectural beauty.
Whenever encountering stormy weather, the high-voltage lines exposed in the air will be affected, resulting in power failure, and the power grid staff will nonstop start to repair and maintain the “injured” power grid. Therefore, some people will ask: since it is easy to be damaged when erected in the air, why not “hide” them underground?

Because if all the high-voltage lines are buried underground, once there is a fault, the power grid staff should first apply for the formalities of digging the ground channel, then work overtime to dig the channel, check the fault section by section, and finally find the fault point before repair. The whole process is time-consuming and labor-consuming. So, is it more appropriate to lay the high-voltage line underground or in the air?


Underground cables: AAAC Cables need to be wrapped in expensive and thick insulating shells.
Overhead wire: high enough to expose the conductor.


Underground cable: difficulty in manufacturing, construction and maintenance.
Overhead wire: it can quickly find and solve faults.


Underground cable: if electric leakage occurs, it will spread around and cause accidents. Therefore, the voltage level will be limited when laying.
Overhead wire: the exposed wire can be erected in the air according to a certain safe distance, because the air is a natural insulating medium. In this way, it can not only reduce the consumption in transportation, but also reduce the risk of electric shock.

To sum up, overhead high-voltage lines have obvious advantages! Therefore, the use of overhead lines in remote mountainous areas has the advantages of fast construction and low cost. However, there is no space for building overhead lines in many parts of the city, so we can only go underground, which saves space and gives consideration to the beauty of the city.

What are the maintenance items of bridge cable and special cable bridge?

Project Name: design and processing of high voltage ACSR Cable bridge
Innovative ideas: there are three 10kv High-voltage incoming lines for 112201 fully mechanized coal mining face, which are laid from 11 panel substation to equipment train of working face. The high-voltage cable enters the rubber conveying chute section and is suspended along the coal wall side. From the coal wall side to the cable storage vehicle, it needs to cross the belt.

Therefore, the design and processing of the bridge will cross the high-voltage cable belt into the cable storage vehicle.

Design principle: I-steel is used to process the bridge, the lower part is fixed with the equipment train pole, the high voltage cable is laid from the I-steel groove, and the protective skin is padded at the lower part of the cable.
Expected effect: after the processing, installation and use of the cable bridge, the three high-voltage cables inside the belt are smoothly led across the belt to the high-voltage cable car, and the cable bridge is integrated with the equipment train, each time the equipment is pulled and moved, there is no need to re hang the high-voltage cable, saving working hours.
(1) Check whether the cables on both sides of the bridge are under large tension.

(2) check whether there are cracks, oil leakage and corrosion on the cables on both sides of the bridge.
(3) whether the AAAC Cable, protective tube and groove are damaged by collision or external force.
(4) paint bracket and exposed protective pipe and groove.
(5) check the cable armour cover.

What operation data should be collected for cable fault?

To analyze the cause of the fault, first of all, we need to investigate the field situation of the fault and check the real fault, and collect the following installation and operation data.
(1) inspection and analysis of AAAC Cable or connector and terminal fault
1. Connector or terminal failure
(1) whether the joint sleeve or terminal box is complete and whether there is any trace of water invasion;

(2) whether the casing is cracked or flashover;
(3) whether the insulating glue is filled, whether there is a gap inside, and whether the ABC Cable oil is deteriorated;
(4) whether the conductor connection is in good condition, if necessary, the contact resistance of the crimping conductor should be measured;
(5) whether there is moisture in the conductor and insulation, and whether there is damage in the bending part;

(6) the path of insulation breakdown or flashover;

(7) sealing condition of metal sheath;
(8) the condition of lead (aluminum) sheath at and near the stripped part of armor;
(9) equipotential bonding between armor and inner sheath;
(10) shielding connection of metal sheath of three core cable.
2. Cable body fault
(1) whether the conductor has barbs, sharp corners, broken and uneven strands;
(2) whether there is moisture in the conductor and insulation, whether there are wrinkles and creases on the paper tape, and whether the covering of each layer is uniform; Whether the gap overlaps repeatedly, whether the wrapping is too loose, whether the impregnation is sufficient, whether the insulating oil is deteriorated or waxy, whether the paper tape is brittle, and whether there are traces of carbonized branches on the surface, etc;
(3) whether the cross-linked insulation has impurities, pores, dendritic discharge traces, whether the insulation thickness and eccentricity meet the requirements of relevant standards, and whether the shielding layer is broken;
(4) whether there are impurities, oxides or pores in the metal sheath, whether the pressing lead (aluminum) is uniform, whether there are obvious seams or pinholes, and whether the sheath has mechanical damage, vibration deformation, cracking, tension cracking, etc;
(5) whether the outer protective layer of the metal sheath is damaged or has traces of mechanical damage;
(6) whether the overlapping distance of armor layer meets the standard, whether there is corrosion or damage by external force, and whether the outer sheath is in good condition.
(2) data collection of line operation and installation
(1) learn about cable line fault trip and relay protection action from dispatching department;
(2) the name of the line and the starting and ending terminals;
(3) the time and place of the failure;
(4) cable specification: such as voltage grade, type, conductor section, insulation type, manufacturer name, purchase date;
(5) device record: such as installation date and climate, connector or terminal design type. Type of insulating agent and heating temperature;
(6) field installation: such as cable bending radius size, terminal device height. The arrangement and grounding of three-phase single core cable, cable embedding mode, elevation, cover plate position, etc;
(7) surrounding environment: such as the ground conditions near the fault point, whether there are new excavation, piling or pipe laying projects, whether there are acid or alkali components in the soil, whether there are small stones, whether there are chemical factories in the nearby area, etc;
(8) operation conditions: such as cable line load and temperature, etc;
(9) calibration record: including test voltage, time, leakage current and insulation resistance value and historical record.
through the analysis of the real fault, combined with the above investigation materials and data, we can get more correct analysis results.

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.

Testing of sheath and corrosion protection

The intact cable sheath can effectively protect the insulation: it can prevent liquid water from immersing in the insulation, and the enclosed metal sheath can also prevent moisture from diffusing into the insulation, so it can obviously prevent the formation of water branches in PE / XLPE insulated cables. The sheath and anti-corrosion layer test which can provide scientific criteria can ensure that the cable will not fail in long-term operation; In addition, for oil filled AAAC Cable, it also makes an important contribution to environmental protection.

In general, the test is carried out with appropriate high DC voltage between the metal sheath or shield and the ground
Welded steel bushing for compressed air cable, 1kV
PVC sheath, 3KV (higher voltage may cause intact sheath breakdown due to moisture absorption of sheath)
Polyethylene sheath, 5 ~ 10KV
The duration of the test was about 1 min. Such a long time is enough to complete the charging process. The existing fault can be identified immediately by breakdown, and then the method described in Chapter 37 can be used for detection. Because this kind of test usually refers to fault detection, rather than insulation resistance test according to international electrical standard iec60229, longer test time is not recommended. For example, for PVC sheath, if the load is applied for a long time, it may cause breakdown of the innermost sheath.

Of course, the premise of reliable damage identification is to have a “corresponding electrode” with good conductivity to make the possible fault current return to the source point. For this purpose, the ABC Cable should be completely buried in the soil, and the water in the soil should be sufficient. Laboratory tests show that although the insulating layer in the sheath is still intact, it has no negative effect on the performance of the test. It has nothing to do with the structure of the isolation layer. The isolation layer either absorbs enough moisture (such as rubber inner cover and wrinkled paper), or forms a low resistance waterway at the overlapping position of the plastic film. That is to say, the expressiveness of the test mainly depends on the degree of moisture.
The graphite coating on the cable sheath can also improve the return circuit. However, this method is expensive and sensitive, so it can only be used in special cases according to the requirements. Before conducting DC voltage test on anti-corrosion protection, all grounding of metal sheath or shield and its connected accessories must be disconnected.

Why are mineral insulated cables so hot?

In recent years, the city has developed rapidly
Subway, station, hospital, school, high-rise housing
Expansion of public facilities construction
The number of high-rise buildings has soared
The demand for urban electricity is rising
Such a densely populated focus area
Serious consequences of fire
In recent years, the fire spread trend of such sites presents similar pattern

Analysis of experts in building and safety fire protection
There are still many AAC Cables for public facilities
No fire protection
It is difficult to play an appropriate role in the fire
The law expressly stipulates that the fire protection system needs mineral insulated cable in the code of fire protection design of building engineering to pass the fire inspection and acceptance.
Because mineral insulated ABC Cable can not only ensure the fire power supply within the fire duration (more than 180 minutes), but also will not delay the fire, no smoke and secondary disasters, thus winning valuable time for fire rescue.
It can be said that mineral insulated cable is a special cable used in the fire protection of important national facilities, large public areas, high-rise buildings and other places. Its fire resistance, durability, safety, reliability and economy are irreplaceable by traditional power cables.
1、 Structure form of mineral insulated cable
Chengtiantai mineral insulation cable is a kind of cable which is wrapped with copper sheath and separated from the conductor and sheath with magnesium oxide powder as inorganic insulation material (optional for outer sheath), and forms a close whole with metal core and sheath.
Magnesium oxide is also a kind of non combustible material, and it will not produce toxic smoke or other harmful substances when encountering high temperature. Therefore, the cable with magnesium oxide as the insulator of copper core and copper sheath has better performance and many advantages.
2、 The properties and advantages of mineral insulated cables
Chengtiantai mineral insulation cable mainly includes bbtrz (flexible mineral insulated fire-proof cable) and yttw (flexible inorganic mineral insulation cable), which has good fire resistance, high temperature resistance, high carrying capacity, waterproof, corrosion resistance, mechanical damage, radiation resistance, electromagnetic compatibility, beautiful and generous appearance. At the same time, the cable will not emit any smoke under fire conditions Halogen and toxic and harmful gases.
1. Fire protection performance
Because mineral cables are all made of inorganic materials, they will not cause fire, combustion or combustion supporting, and toxic gas will not be produced. Even if there is fire outside, the cable can still work normally. Mineral insulated cable is made of magnesium oxide as insulator, and the melting point of magnesium oxide is as high as 2800 ℃, which is difficult to burn easily, so the fire resistance of mineral insulated cable is excellent.
The test shows that the mineral insulated cable can be operated normally for 2 hours in a flame with temperature of 800 ℃ -900 ℃; The cable is still intact and continues to operate normally after 30 minutes of combustion under the flame of 1000 ℃.
2. High temperature resistant operation, high load flow
The normal operating temperature of mineral insulated cable can reach 250 ℃, and in special cases, the cable can be maintained in a short time at the temperature close to the melting point of copper sheath. It is very suitable for laying in high temperature places, such as metallurgy, boiler, glass furnace, blast furnace and other environments.
The cut-off flow of MgO powder is far higher than that of other cables. Because magnesia powder has better conductivity coefficient than plastic, the same working temperature and flow rate are larger. For lines with more than 16mm, one section can be reduced, and two sections can be reduced for places where people are not allowed to contact.

3. Waterproof, explosion-proof, high mechanical strength
The insulation layer of mineral insulated cable is processed by high density compaction process, and then protected by seamless copper sheath. In the product standard, it must be subject to three requirements of fire resistance, spray resistance and mechanical impact resistance, which can withstand severe impact and mechanical damage. Therefore, it not only prevents the water, moisture, oil and some chemical substances from being infringed, but also suitable for connecting the explosion-proof equipment and equipment in places with explosion risk.
4. Overload protection
When the line is overloaded, the plastic cable will cause insulation heating or breakdown due to over-current or overvoltage. For mineral insulated cables, as long as the heating temperature of copper is not reached, the cable will not be damaged. Even if the breakdown occurs in a short time, the high temperature of magnesium oxide at the breakdown point will not form carbides. After overload removal, the cable performance will not change and can still be used normally.
5. Long service life, more safe and reliable
Because the structure of mineral insulated cable is composed of copper core and insulating sheath, it is a closed whole, so it is difficult for the material to aging due to the oxygen action in the outside air. This makes the overall service life of the cable longer (2-3 times the life of the ordinary cable), and the copper sheath’s own characteristics make the cable better grounded, Therefore, the lightning protection and grounding measures are effectively implemented, so as to ensure the safety and reliability of the electrical line operation.
Due to the many excellent characteristics of mineral insulated cables, many electrical design codes or standards have been adopted in recent years, and also used in many engineering projects in different industries. It can be expected that the use of mineral insulated cables in China will increase greatly in the next ten years.

Instruments and accessories for cable path detection

Figure 6 t5000-3 transmitter and receiver
Instrument: t5000-3 color screen intelligent pipeline instrument
Signal output part: transmitter, direct connection, coupling clamp, LCC module
Direct connection: direct connection signal output line, used when finding the route of power cut cable
Coupling clamp: clamp method signal output line, used when finding live cable path
LCC module: it can isolate the AC voltage of 480v and below, and cooperate with transmitter to connect the AAC Cable with direct connection method, and find the live low voltage cable path and transmission cable path.
Figure 7 transmitter accessories
Receiving signal part: receiver, stethoscope, A-frame

Figure 8 receiver accessories
Stethoscope: it can be used in cooperation with receiver to identify the ABC Cable live and find the target cable from multiple cables;
A-Frame: it can be used in combination with receiver to accurately locate the fault point of buried cable, and the use method is step voltage method.

3、 Transmitter wiring method
1. direct connection method
It is suitable for finding the route of power cut cable, with high current and strong signal. The transmitting signal is injected into the primary core through the direct connection, and the test phase core at the end of the cable is grounded manually. The primary core and the earth constitute the test circuit, as shown in Figure 9 below.

Figure 9 schematic diagram of direct connection
1. the signal can not be transmitted between phases (short circuit at the end) and the test circuit can not be formed by phase. Because the current signal is in the opposite direction, the magnetic field signal is offset. The receiver is essentially the received loop magnetic field signal, and the signal will not be received;
2. the armored ground on both sides of the cable shall be removed, otherwise the current signal transmitted will be transmitted back from the armor, which will also offset the magnetic field signal;
3. in a word, the test circuit shall be one-way and only circuit.
If the cable circuit is connected incorrectly, such as poor grounding, phase sequence error, etc., the transmitter has no output current or low output current, and the “indicating square” is blank, as shown in Figure 10 below. If the circuit is connected correctly, the output current of transmitter can reach 25mA, and the “indicating square” turns black, as shown in Figure 11 below.

Figure 10 display of transmitter with wrong circuit connection
2. clamp method
It is suitable for finding the route of stop and live cable, with small current and weak signal. The transmission voltage signal is induced to the high voltage cable armour or low voltage cable zero line through coupling clamp. As shown in Figure 12, since both ends of the cable are armored or zero wire are grounded, there will be stable current signal naturally.
1. the same point between direct connection method and clamp method is that the magnetic field signal is generated by unidirectional stable current circuit. The difference is that direct connection method transmits signal in cable core through direct connection, and clamp method is used to couple transmission signal in cable armour or zero line through clamp coupling;
2. clamp method is relatively weak in signal application, and direct connection method is preferred for power cut cable;
3. for high voltage single core live cable, direct connection method can be used to find the path in aluminum sheath. The use of clamp method and direct connection method should be reasonably selected in combination with the grounding mode of aluminum sheath.
3.1 380V cable test method
380V power off cable:
① The direct connection method of conductor is shown in Figure 9, and the one-phase core is selected as the test phase, and the end of the line core is grounded with corresponding phase core, and the zero line grounding at both ends is removed. The fire line and terrain are single-phase and unique circuit;
② Zero line direct connection method: remove zero line grounding at one end of cable, and keep zero line grounding at the other end. The direct output line is connected to the suspended zero line, and the zero line and terrain are single-phase and unique circuit, as shown in Figure 13 below;

Figure 13 zero wire direct connection
③ Clamp method, as shown in Figure 12, the output clamp is directly stuck in the cable body or cable zero line, and the signal circuit is formed between the zero line and the ground. Note: at this time, the zero line at both ends of the cable should be grounded.
380V live cable:
① Clamp method, the wiring is the same as above;
② LCC, live direct connection, transmitter on the user side directly outputs the signal on the live fire line through LCC module. For 380 power supply low voltage power supply system, neutral point of transformer in the station area is directly grounded. At this time, the live fire line and the ground form a loop. Note: this method can only be used in the user side wiring, and find the cable path from the power side, The site case is referred to the above official account.
3.2 10kV cable test method
10kV power off cable:
① The direct connection method of conductor is shown in Figure 9, and the one-phase core is selected as the test phase, and the end of the corresponding phase wire core is grounded, and the armored grounding at both ends is removed. The conductor and terrain are single-phase and unique circuit;
② Armor direct connection method: remove the armored grounding at one end of the cable, and keep the armored grounding at the other end. The direct output line is connected to the suspended armored lead wire, and the armor and terrain are single-phase and unique circuit, as shown in Figure 14 below;
③ Clamp method, as shown in Figure 12, shows that the output clamp is directly stuck on the cable body or cable armored ground wire, and the signal circuit is formed between the armor and the ground. The clamp connection demonstration is shown in Figure 15 below.
10kV live cable:
Clamp method, same as above.
3.3 test method of 110kV cable
110kV power off cable:
① Direct connection of conductors, as above;
② For the direct connection method of aluminum sheath, the grounding mode of aluminum sheath shall be referred to. For the single end grounded cable section of aluminum sheath, the direct connection signal of aluminum sheath coaxial cable conductor shall be directly connected at the protective grounding box; For the cross connected cable section with aluminum sheath, the conductor or shielding direct connection signal of aluminum sheath coaxial cable shall be conducted at any cross interconnection box.
110kV live cable:
① For the cable section with single end grounding of aluminum sheath, open the protective grounding box or cross connected box with no grounding end. First, use multimeter to measure the induced voltage of the aluminum sheath. If the induction voltage is less than 25V (t5000-3 fuse fuse fuse fuse fuse fuse voltage), direct connection method can be directly used for aluminum sheath, as shown in Figure 16 below;
② If the induction voltage of aluminum sheath without grounding terminal exceeds 25V, LCC module incoming voltage shield shall be used and the live direct connection method shall be used for test;
③ Clamp method: because the aluminum sheath of cross connected large section is directly grounded at both ends, although the cable is transposed, the overall aluminum sheath still forms a circuit with the ground. Therefore, clamp method is only applicable to the path finding of 110kV cable section cross connected by aluminum sheath, and clamp the clamp directly on the coaxial cable at the cable body or any grounding box, as shown in Figure 18 below.
1. when finding the path of 110kV cable live, it is better to search by sections according to aluminum sheath, and apply signal from the ground end to find the cable path to the grounding end;
2. for the cable section with no grounding at the direct grounding end of one end of aluminum sheath, the clamp method signal is weak. At this time, the output power of transmitter shall be increased and the output frequency shall be adjusted to test. It is recommended to use direct connection method or live direct connection method for finding out the ungrounded end;
3. because 110kV single core cable will generate induction voltage on aluminum sheath, if clamp is directly stuck on cable body, inductive voltage will also be generated in clamp. At this time, if clamp jaws are completely closed, circulation will be formed on clamp coil, and clamp will be burned by heating, that is, paper sheet shall be pad for closing jaw, as shown in Figure 19 below.

Figure 19 jaw treatment of clamp method when using the body

The causes and solutions of overheating of wires and cables

When the power cable passes through a certain load current, it will be heated. With the increase of load current, the higher the cable surface temperature is. If it is not managed in time, the consequences can be imagined. For example, PVC cable is considered with core temperature of 70 ℃ as the upper limit, and the surface temperature will be 5-10 degrees lower. Therefore, the ACSR Cable surface temperature is basically safe below 60 degrees. Considering the power supply maintenance, the lower the temperature is, the better.

The causes of heating during operation of cables are as follows:
1. The resistance of ABC Cable conductor does not meet the requirements, which causes the cable to generate heat during operation.
2. Improper cable selection causes the conductor cross-section of the cable used is too small, and overload occurs during operation. After a long time of use, the heating and heat dissipation imbalance of the cable cause heating phenomenon.
3. The cable is arranged too densely, the ventilation and heat dissipation effect is not good, or the cable is too close to other heat sources, which affects the normal heat dissipation of the cable, and may also cause the heating phenomenon of the cable in operation.
4. The joint manufacturing technology is not good, and the crimping is not tight, which causes the contact resistance at the joint is too large, and the cable will generate heat.
5. The insulation performance of the cable is not good, which causes the insulation resistance is small, and the heating phenomenon will also occur in the operation.
6. The partial sheath of armored cable is damaged, which causes slow damage to the insulation performance after water inflow, which results in the gradual decrease of insulation resistance and also the heating phenomenon in the operation of the cable.
After the cable has a heating phenomenon, if the cause is not found, the cable will continue to be powered on continuously and will cause insulation thermal breakdown. The short circuit between phases of the cable trip phenomenon, serious fire may be caused.
After the cable has a heating phenomenon, if the cause is not found, the cable will continue to be powered on continuously and will cause insulation thermal breakdown. The short circuit between phases of the cable trip phenomenon, serious fire may be caused.

The reason and solution of plug power cord heating are everywhere in family life. The electric appliances can not be separated from the power cord. This small power cord may despise him.
The heat of the power cord of water heater is usually caused by the poor coordination with the socket. Meanwhile, the normal heating phenomenon should be considered. If the surface temperature of the plug is less than the ambient temperature plus 50 ℃, it is normal. If abnormal heat is abnormal, it is necessary to consider replacing the socket or checking the cooperation between the plug and the socket.
1. the connection between plug and socket is poor, and the load power is high, which causes the plug to heat up. Such as electric kettle, electric iron, etc.
2. the thread head in the new plug is loose, which is caused by rough production process and other reasons.
3. the old plug is used for a long time, and the insulation performance is reduced (or the plug is loose).
How to use plug wire safely
The main reason for the heating of plug wire is that the load of the wire is increased due to the long-term power consumption of electrical equipment. Special multi-function socket, if connected with several high-power electrical equipment at the same time, the power line of the socket must be overloaded, and in that case, it is very easy to cause the wire to burn.
Therefore, we should pay attention to the reasonable distribution of electricity in our life, and regularly check the plug wires and sockets to see if the wires are old and whether the contact between the plug and socket is bad. Sometimes because the production department process is not fine, the plug wire head will not be firm, so the plug in the plug power supply will cause poor contact and lead to plug heating. At the same time, every household should pay attention to that the plug will be old for a long time, and the insulation property will be reduced. It should be replaced in time. For plug wires of high-power appliances, we suggest that the wire core is used to increase the type, and it is better to use the pin with grounding. If it is found that the power socket or wire plug is hot, which causes the electric appliances to burn, do not act recklessly, and take care of the management.

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What are the three rules for selecting wires and cables

The application of wire and cable in life is essential. What people pay more attention to is the quality of wires and cables, but the types of cables are also various. The more kinds, the more difficult it is to choose. Many people don’t know how to choose the right wires and cables to use, which leads to problems. To teach you how to choose the right wires and cables
Nowadays, more and more ACSR Cable lines are used in distribution lines, but it is very important to choose the cable type. Combined with the actual work, the paper simply discusses the application scope and selection of 10kV cable lines. First, it is necessary to determine where the cable is applied, where the cable passes, the load nature, capacity, etc. to select the cable.

1、 Application scope of wire and cable line: the place where the power equipment is clustered, prosperous area, important section, major roads, urban planning and urban environment with special requirements. In the area of serious pollution and corrosion which is difficult to solve, the reliability of power supply is high or the users with important load are required, key scenic spots, high load density urban center areas, new residential areas and high-rise buildings with large building area are built.
2、 Selection of wires and cables: determine the section according to the long-term allowable current carrying capacity, select the cable section according to short circuit thermal stability, select the cable section according to the voltage drop of the connecting circuit, check the section according to the mechanical strength, and select the section of neutral wire (n), protective ground wire (PE), protective grounding neutral line (pen).

3、 Correction of the current carrying capacity of electric wires and cables: long-term allowable current carrying temperature correction of cables, soil correction of long-term allowable current carrying capacity of cables, long-term allowable current carrying capacity correction for directly buried and parallel laying power cables, and correction of carrying capacity of 10kV and below cables laying through pipes.ç

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