Extruded insulating materials are polymer insulating materials, and their physical and chemical properties are determined by their chemical structure, chemical natural force and size.
electrical properties of extruded insulating materials shall be graded according to their response under operating field strength. Under low operating field strength, the electrical properties of polymer materials used as cable insulation are related to their structure; At high field strength (actually borne or locally concentrated), other factors become significant and exceed the former (structural factors).

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cross linked polyethylene (XLPE), ethylene propylene rubber (EPR) or polyvinyl chloride (PVC) are used as insulating materials to protect conductors from the surrounding environment; Ensure that the current path remains stable.
They tend to age, but need to meet the above functions of the cable throughout the project life cycle. Whether the environment is dry or wet, they are expected to play the above role. Under the operating field strength, the key properties of good insulating materials include volume resistivity, dielectric constant and loss factor. Any material intended to be used as insulation must meet these three performance requirements specified in the standard. Polarization is another key performance.
for electrical insulating materials, volume resistivity is a well-defined parameter. It is the resistance between the inner and outer surfaces of the tubular insulating sample under the specified temperature and pressure.
The loss factor represents the energy loss value in the form of heat, not the transmitted electric energy; Therefore, it is a measurement of dielectric loss.

Dielectric constant is a quantity that reflects the ability of insulation to maintain charge. A good dielectric (insulating) material should have strong charge retention ability (low dielectric constant) and low loss (low loss factor).
Polyolefin materials (such as polyethylene, XLPE and most EPR) have excellent performance in the above indicators. These three indicators are intrinsically linked.
under high electric field strength, the ability of insulation to prevent electron movement is challenged. At this time, the main insulation performance is the dielectric strength. If the insulation corresponding to this value (very high at the initial stage of operation and usually decreases with aging) cannot prevent the movement of electrons, a fault occurs. There are several failure mechanisms, the common one is partial discharge.

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