Analysis and development direction of semi-conductive shielding materials for medium and high voltage cables

The misapplication of carbon black

The nature of carbon black, is one hundred percent to determine the performance of semi-conductive shielding material, carbon black not only determines the conductive properties of semi-conductive shielding material, but also can affect the physical properties of the product, the excellent functionality of the product, and can even determine the market value of your product.

Semi-conductive shielding material is divided into two functions, one is the outer shielding, it is balanced XLPE electric field shielding, one is the inner shielding, it is balanced conductor electric field shielding, the function is not the same, the location in the cable structure is also not the same.

Now I clearly inform you that no matter what kind of power cable, whether it is AC, DC, semi-conductive inner and outer shielding material is not the same function, their conductivity, resistance to destruction is not the same, the conductivity of the outer screen may remain stable, while the conductivity of the inner screen is the opposite. A cable's life is mostly determined by the quality of the inner screen, the cable stops working, if restarted operation, there must be a re-heating problem, repeated heating of the inner screen resistance conductivity decline, the cable to be fatally damaged.

The carbon black used in the semi-conducting inner shield material is fundamentally different from the outer shield, it is selected carbon black must be high structure, its iodine absorption value should be greater than 75. DBP oil absorption rate must reach 170 or more, and those iodine absorption value less than 50 below, oil absorption rate less than 130 below the carbon black is not high structure. They are soft carbon blacks with low structure. Their electrical conductivity is very destructive, if the shear force is large, its conductive channel, electron tunneling interrupted, the conductivity of the grape bunches are broken into "peanut-shaped", the conductive channel is gone, the conductive tunnel is gone, only the electric field emission is still weakly present, the existence of such conductivity is pseudo-conductivity. The resistivity of the material factory detection is "pseudo-resistance", pseudo-resistance shielding material extruded into the cable, the loss of coherent conductive properties, this phenomenon in the power cable to do partial discharge, oscilloscope is similar to the hospital electrocardiogram dead wave shape, a straight line.Although the content of carbon black exists, but the function has become a coloring agent, not a conductive agent, is the sheath material only, because its functionality has been lost, changing the characteristics of the material.

Just mentioned that the soft carbon black is made after the detection of the inner screen resistance is "pseudo-resistance", is also the "right" resistance, is very delicate, can not withstand the cable factory second extrusion shear, carbon black with the processing in the polymer shows the resistance of two values are the same, that is, the left and right conductivity value, this left conductivity value. That is, the left and right conductivity value, this left and right value distribution in the resistance curve can be seen, is symmetrical.

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In the left side of the resistance of the secondary processing more excellent, conductivity in the promotion, that is, carbon black in the manufacturing process of good dispersion, conductive channel has been ideally established, and may even do full conductivity. The right side of the resistance is saturated dispersion, if then shear, processing, this re-shear also includes the cable factory application extrusion, then the carbon black structure is broken, the same 100Ωcm resistance, the conductivity of the right resistance will drop sharply, because the distance between the carbon and carbon structure is only a few Å,that is, carbon black conductive mechanism section said "microscopic electric field emission is ineffective, the distance is far, the conductive channel can not be established!

    This phenomenon, seen time and again, here very straightforwardly, semi-conductive shielding material inside and outside the two models, inside and outside the semi-conductive shielding material used in the structure of carbon black is completely different, inside the screen conductivity is often particularly destructive, and it is located in the working environment (with copper, aluminum different conductors, specific gravity is not the same, unable to volatilize low molecular substances), processing environment and outside the shield is completely different, outside the screen in the cable factory is constantly volatile, while the inner screen is in constant heating, insulation, especially the conductor of the aluminum core, very destructive.

Of course, I do not rule out innovation, innovation to have a scientific platform on the underlying theory!