Temperature Cable conductors

Multicore cables having thermoplastic (PVC) or thermosetting insulation, non-armoured COPPER CONDUCTORS Table 4D2A of lET Regulations and Table F5(i) of the On Site Guide Ambient temperature SOX. Conductor operating temperature 70°C Current-carrying capacity (amperes) BS 6004, BS 7629... 

Cable conductors to the anodes are made fi om copper or aluminum. These conductors must, therefore, be insulated. High-density polyethylene has good properties with respect to abrasion and high-temperature while maintaining excellent dielectric properties. Technical information about cables is provided by the manufacturers. 

Thermostats—bimetallic strip, snap-action disk, and thermostatic cable Continuous discrete conductors Thermistor sensors Rate of temperature rise Copper tubing heat-actuated devices (HADs) Thermoelectric Combined rate of rise/fixed temperature Rate compensation Oil mist ... 

Cooling of Extruded PE Wire5 Consider a copper conductor, 0.16 in in diameter, coated by extrusion to a 0.62-in insulated wire (first transatlantic cable core wire). The conductor is preheated to the extrusion temperature 412°F, and... 

Superconductivity The ability of a material to act as a conductor for electricity without the gradual loss of electricity over distance (due to resistance) that is normally associated with electric transmission. There are two types of superconductivity. Low-temperature superconductivity (LTS) requires that transmission cable be cooled to -418 degrees Fahrenheit. Even newer technologies are creating a so-called high-temperature superconductivity... 

In a similar way, the maximum temperature of cables in rated service is limited to values of +70°C for the entry point and of +80°C for the branching point of the conductors in cable entries (this is a general requirement for all types of protection, given in EN 50014 and IEC 60079-0). 

For currents exceeding approx. 500 mA it shall be taken into account that inadmissible high temperatures may occur for inadequate small conductor cross-sections (cable near to breakoff ) or for poor contact making (terminal tightened insufficiently). This effect is well known as ignition by incandescence. 

The one-meter-long conductor, based on a bismuth-strontium-calcium-copper oxide superconductor, carries over 2300 amps of direct current at liquid nitrogen temperatures (77 K). This is more than twice the current-carrying capability of conventional copper cables. 

These cables are designed to carry the specified current load and to provide adequate electrical insulation with a wide margin of safety. Present requirements for XLPE 9) specify a 90°C maximum operating and a 130°C maximum emergency temperature at the conductor and a minimum of 0.016 mil/V insulation thickness. 

Extrusion-Applied Insulations. The polymers used in extrusion applications can be divided into two classes low-temperature applications and high-temperature applications. Polymers in the first category are poly(vinyl chloride), polyethylene, polypropylene, and their copolymers along with other elastomers. Polymers in the second category are mainly halocarbons such as Teflon polytetrafluoroethylene (which requires special extrusion or application conditions), fluoroethylene-propylene copolymer (FEP), perf luoroalkoxy-modified polytetrafluoroethylene (PFA), poly(ethylene-tetrafluoroethylene) (ETFE), poly(vinylidene fluoride) (PVF2) (borderline temperature of 135 °C), and poly(ethylene-chlorotrifluoroethylene). Extrusion conditions for wire and cable insulations have to be tailored to resin composition, conductor size, and need for cross-linking of the insulating layer. 

Fig. 90. Diagram for remote control measurement of temperature of air injected into oil-bearing bed. 1-weld of thermocouple 2-thermometer 3-conductor cables M-direct current bridge P-potentiometer.

The maximum time that a 4000 A fault current can be applied to this lOmm cable without dangerously raising the conductor temperature is 82.66 ms. Therefore, the protective device must disconnect the supply to the cable in less than 82.66 ms under short-circuit conditions. Manufacturers information and Appendix 3 of the IFF Regulations give the operating times of protective devices at various short-circuit currents in the form of graphs. Let us come back to this problem in a few moments. 

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