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Mineral insulated fireproof cable model reference table
The continuous working temperature of the mineral cable is 250℃, and it can supply power continuously for 3 hours at 950℃-1000℃. It can work close to the melting point of copper at 1083℃ in a short or extraordinary period of time. Due to the excellent performance of mineral insulated cables, it is suitable for lines with rated voltages below 1000V.
   (1) Cable conductor: The conductor is made of metal copper with high conductivity.
  (2) Insulation layer: Use high temperature resistant, non-combustible inorganic minerals as insulation material.
  (3) Isolation layer: Use inorganic mineral material.
  (4) Outer sheath: low-smoke non-toxic plastic material with good anti-corrosion properties.
  Product display methodedit
  (1) Fireproof cloth wire, rated voltage 450/750V, single core, 2.5mm,
   is expressed as: BTTEB-450/750V 1×2.5
  (2) Fireproof power cable, rated voltage 0.6/1KV. 3-core, 120 mm,
   is expressed as: BTTE-0.6/1KV 3×120
  (3) Fireproof control cable, rated power 450/750V, 6 cores, 2.5 mm
   is expressed as: BTTEK-450/750V 6×2.5
  Using environmentedit
  The continuous working temperature of the mineral cable is 250℃, and it can supply power continuously for 3 hours at 950-1000℃. It can work close to the melting point of copper at 1083℃ in a short time or in an extraordinary period. Due to the excellent performance of mineral insulated cables, it is suitable for lines with rated voltages below 1000V.
  Main performance
  (1) Fire performance
  As all mineral cables are made of inorganic materials, they will not cause fire, cannot burn or support combustion, and will not produce toxic gas. Even if there is external flame burning, the cable can still work normally. After the fire is cleared, the cable does not need to be replaced. It is a true fire-resistant cable, which provides a foolproof guarantee for the fire-fighting line and has passed the test of the International Electrotechnical Commission IEC331.
  (2) Large current carrying capacity
   Because the normal use temperature of mineral insulated cables can reach 250℃. IEC60702 stipulates that the continuous working temperature of mineral insulated cables is 105℃. This is to consider the terminal sealing material and safety requirements. Even so, its interception capacity is far more than other cables, because magnesium oxide powder has a better conductor coefficient than plastic, so the same operating temperature, the interception capacity is greater, for the line above 16mm, you can reduce a cross section, right Where people are not allowed to touch, two cross-sections can be lowered.
  (3) Waterproof, explosion-proof, corrosion-resistant
  Because the cable adopts low-smoke, halogen-free and high-flame retardant materials as the sheath, it has high corrosion resistance (plastic outer sheath is only needed in the occasion of certain chemical corrosion), and the conductor, insulation and sheath are densely compressed. As a result, it not only protects against water, moisture, oil and some chemical substances, it is practically used in places where there is a risk of explosion and the wiring of various explosion-proof equipment and equipment.
  (4) Overload protection
   When the line is overloaded, the plastic cable will cause insulation heating or breakdown due to overcurrent or overvoltage. For mineral insulated cables, as long as the heat does not reach the melting point of copper, the cable will not be damaged. Even if the breakdown is instantaneous, the high temperature of the magnesium oxide at the breakdown point will not form carbides. After the overload is cleared, the performance of the cable will not change, and it can still be used normally.
  (5) High working temperature
   Because the melting point of the insulating layer of magnesium oxide is much higher than that of copper, the maximum normal working temperature of the cable can reach 250°C, and it can continue to operate at a temperature close to the melting point of copper, 1083°C in the short term.
  (6) Strong shielding performance
  The copper sheath of the cable is the best shielding and protective layer, which can prevent the cable itself from interfering with other cables, and it can also prevent the external magnetic field from interfering with itself.
  (7) Long life
  Because the cable is composed of inorganic materials, it will not get old, and its service life shall be more than one hundred years at least. And the cable can be re-disassembled and reused with equipment shifting or line modification.
  (8) Small outer diameter and light weight
   Compared with plastic cables with the same rules, the outer diameter of mineral insulated cables is reduced by 50%, and the weight is reduced by 30%, which can reduce the occupied space and facilitate installation.
  (9) High radiation resistance
  Since the cables are composed of inorganic materials, they have an effective neutron capture cross-section and maintain a high insulation resistance. Therefore, the electric
Testing method of power cable fault point
Testing method of power cable fault point
  There are two types of cables commonly used in power systems, power cables and control cables. Power cables are used to transmit and distribute high-power electrical energy. According to the different insulation materials, it can be divided into oil-impregnated paper-insulated power cables, rubber-insulated power cables and PVC insulated cables. The most widely used in engineering is oil-impregnated paper-insulated power cables. Because the cables are being manufactured and laid The country has express regulations for wiring, ambient temperature, construction principles, etc., so I won't repeat them here. This article mainly introduces the possible points of power cables that are prone to failure and how to test several methods.
   Power cable fault point test method
   1. Types of cable faults and test methods
After the cable fails, generally use a 1500V or higher shake meter or a high resistance meter to determine the type of fault, and then use different instruments and methods to first measure the fault, and finally use the fixed-point method to accurately determine the fault point. The precise measurement methods for the fault point include induction method and acoustic measurement. Two methods.
The principle of the induction method is that when the audio current passes through the cable core, there are electromagnetic waves around the cable. Because some carry electromagnetic induction receivers, when walking along the line, you can hear the sound of the electromagnetic waves. When the audio current flows to the fault point , Sudden changes in current, sudden changes in the audio frequency of electromagnetic waves, this method is very convenient to find low-resistance short-circuit faults between disconnected phases, but it is not suitable for finding high-resistance short-circuits and single-phase grounding faults.
The principle of   acoustic measurement is to use high-voltage pulses to prompt the discharge of the fault point to produce a discharge sound. The sensor is used to receive the discharge sound on the ground to measure the precise location of the fault point.
  The specific fault types are tested according to the following methods.
  1.1 Low resistance ground fault
   1.1.1 Single-phase low resistance ground fault
  (1) Test of failure point.
   The single-phase low-resistance earth fault of the cable means that the insulation resistance of one core wire of the cable to the ground is less than 100kΩ, and the core wire has good continuity. This kind of fault is highly concealed, and we can use the principle of loop fixed-point method to test. The wiring diagram is shown in Figure 1a. The faulty core wire and another intact core wire form a measurement loop, measure with a bridge, one end is connected with a jumper, the other end is connected with a power supply, a bridge or a galvanometer, and the bridge resistance is adjusted. To balance the bridge, when the material and cross-section of the cable core wire are the same, it can be calculated according to the following formula
If the damaged core and the good core are interchanged on the bridge, then there is the formula: Z——distance from the measuring end to the fault point in m; L——total cable length, m; R1, R2——electricity The resistance arm of the bridge.
  Under normal circumstances, the measurement results of these two wirings should be the same, and the error is generally 0.1% to 0.2%. If it exceeds this range or X>L/2, the measuring instrument can be moved to the other end of the line for measurement.
   In addition, we can also use continuous scanning pulse oscilloscope method (MST-1A or LGS-1 digital tester) for testing. The reflected wave at the short-circuit or ground fault point will be negative reflection, as shown in Figure 1b on the oscilloscope screen. At this time, the distance to the fault point can be calculated according to the following formula: X-reflection time μs; V-wave speed, m/μs.
   (2) Matters needing attention during measurement.
  A. The cross-section of the jumper should be close to the cross-section of the cable core, and the jumper should be as short as possible and kept well.
  B. The measurement loop should bypass the branch box or substation or power distribution station as much as possible, the shorter the better.
  C. The DC power supply voltage should not be less than 1500V.
  D. The negative pole of the DC power supply should be connected to the cable conductor via an electric bridge, and the positive pole should be connected to the inner sheath of the cable and grounded.
  E. The operator should stand on the insulating pad and place the bridge arm resistance, galvanometer, shunt, etc. on the insulating pad.
   1.1.2 Two-phase short circuit fault point test
   When a two-phase short-circuit fault occurs, the measurement wiring method is shown in Figure 2. When measuring, any faulty core wire can be used as a grounding wire, and the other faulty core wire ca
Analysis of Several Reasons for the Aging of Wires and Cables
List of main types of wires and cables
List of main types of wires and cables
  The characteristics of commonly used cables are as follows
  CEF——Ethylene-propylene rubber insulated neoprene sheath, flame-retardant power cable for ships
  CVV——PVC insulated, PVC sheathed flame-retardant power cable for ships
  Oxygen cabin wires often use BV, BX, RV, RVV series wires, of which:
   BV-copper core PVC insulated wire, long-term allowable temperature 65℃, minimum temperature -15℃, working voltage AC 500V, DC 1000V, fixedly laid indoors and outdoors, and can be laid in the open or in the dark.
  BX——Copper core rubber insulated wire, the highest operating temperature is 65℃, for indoor use.
  RV——PVC insulated single-core flexible cord, maximum operating temperature 65℃, minimum operating temperature -15℃, working voltage AC 250V, DC 500V, used as internal wiring of instruments and equipment.
  RVV——Copper core PVC insulated and sheathed flexible wire, allowing long-term working temperature of 105℃, working voltage of AC 500V, DC 1000V, used in damp, high mechanical protection requirements, frequent movement and bending occasions.
   Common cable models
  VV means: PVC insulation (the first V), PVC sheath (the second V)
   YJV22 means: cross-linked polyvinyl chloride insulation (YJ), polyvinyl chloride sheath (V), steel tape Kaizhuang (22)
   type plus "ZR" or "FR" are flame-retardant cables (wires). Add "L" for aluminum wire
  Wire and cable model naming rules
The model of    wire is relatively simple:
  BVV--PVC insulated and sheathed copper core wire,
  BV--PVC insulated copper core wire,
  BVR--PVC insulated copper core cord,
  BX--rubber insulated copper core wire,
   RHF--chloroprene rubber sheathed copper core cord.
Safety measures for fireproof cable wiring
Safety measures for fireproof cable wiring
  【一】Fire prevention measures for indoor and outdoor wiring
  1. Reasonable design
  When wiring indoors and outdoors, it is necessary to choose the correct route, try to take short cuts, go straight, avoid twists and turns, and reduce crossovers. At the same time, when selecting the line conductor, the type of conductor should be selected correctly according to the specific environmental characteristics. Generally, factors such as moisture resistance, moisture resistance, heat resistance, and corrosion resistance should be considered to prevent fire accidents.
  2, strict construction
When installing indoor and outdoor circuits, the burying of fixings and the connection and laying of wires must be strictly constructed in accordance with regulations to ensure quality and prevent problems before they occur. In particular, when the wires pass through walls, they must pass through wall bushings. Otherwise, It is prone to wear and tear, resulting in leakage, short circuit and fire.
  3, the wiring must meet the requirements
In actual production and life, electrical equipment is in different environments, and the types of wires and cables required to be used are also different, and the installation and laying methods should also be adapted to them. Only in this way can the safe operation of the wires in various environments and prevent fires happened. In order to ensure the safe operation of indoor and outdoor circuits, when wiring, attention should be paid to keeping a certain distance between the wires, between the fixed points of the wires, and between the wires and the pipes and the ground to prevent short circuits from causing fires.
  4, the wire connection should be firm
   The connection between wires or the connection of wires and electrical equipment is the main part that causes excessive contact resistance and local overheating and fire. Therefore, the wire connection must be firm to prevent loosening, oxidation, etc. of the contact surface. The insulation strength of the insulating material wrapped around the joint should be the same as that of the original wire.
   5. Regular inspection
   In order to ensure the normal operation of indoor and outdoor circuits, frequent inspections are required. In the work of checking the lines, it is necessary to arrange the use time of electrical equipment correctly and reasonably according to whether the line can withstand the current total power consumption. Check whether the joints of the line are loose and sparking, and re-reinforce or replace the old and aging wires. At the same time, the temporarily connected line must be removed in time to avoid fire accidents.
  【二】Fire protection measures for cable wiring
  1, standard construction
   When laying cables, the construction personnel must ensure the construction quality and standardize the construction. During construction, it is necessary to prevent mechanical damage caused by excessive traction, excessive bending, improper filling, and insufficient embedding depth. The middle joint and terminal head of the cable are collectively called the cable head. The cable head is a key part that affects the insulation performance of the cable and is the easiest source of ignition. Therefore, the withstand voltage and insulation resistance of the cable head should be measured before it is put into operation to ensure the construction quality and ensure the good connection of the joints.
  2, plugging cable holes
Cables must pass through the holes in floors, walls, cable trenches, roads and cable shafts, and seal them with non-combustible materials to isolate them to prevent the spread of cable fires; at the bifurcations of cable trenches and roads and the cable leading to the building For the exiting population, fire partition walls or fire doors should be installed. Non-combustible materials should also be used to seal the pores through which cables pass through fire partition walls; if the cables pass through floors, walls and other places, if metal pipes are used, the gaps between the metal pipe openings should be tightly filled with asbestos or asbestos mud.
   3. Use cable fireproof materials
  Common cable fireproof materials are fireproof coatings. Non-combustible trough boxes, fire-resistant partitions, fire-resistant blocking materials, fire-resistant nets, etc. Through the use of fireproof materials, it has a better effect on preventing heat transfer, preventing direct flame damage, reducing the scope of the fire, and preventing the spread of fire.
  4. Strengthen testing and maintenance
   It is necessary to conduct frequent inspection and maintenance of cables, strengthen line inspections, withstand voltage and load measurement, and eliminate faults and temperature rise in time to ensure the safe operation of cables and prevent accidents during operation.
   [3] Fire protection requirements for temporary power lines
  Temporary power lines are mainly used for surp
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