Electrical characteristics of the heat shrinkable tube shield layer
typically shrink tube production process selected resistivity semiconductive shield factor is based on the theory and operating temperature, process, etc., and generally resistivity ρν = 4 Ω cm 10 of power this is because a large effect size ρν resistivity value of tanδ cable shield. In this regard, according to the equivalent circuit we can analyze the resistivity of tanδ ρν impact on the cable. U effect under external applied voltage, capacitance to ground of current cable L, it can be seen on the insulating layer and the shield voltage ratio.
Indeed, without considering the above-described equivalent circuit capacitance effect shielding layer. If the shield resistance is large, should be considered in parallel with the capacitance value of the capacitor, there will therefore affect the entire shield dielectric loss dielectric loss measurement, the measuring dielectric loss. While theoretically estimated as ρν the relationship between the cable shield and dielectric loss tanδ resistivity layer.
According to reports, theoretical calculations and experimental curve shape exactly the same, just to be on a slightly different magnitude. This difference comes mainly from ignoring equivalent circuit of the original cable structure. From the figure, with the increase of the resistivity of the shield, the cable dielectric loss tanδ increases, the maximum value appears at about ρν = 10 ^ 9, and when the shield resistivity ≤10³ Ω cm, cable loss tanδ hardly decreased dielectric loss tends X LPE, the shielding layer can be considered at this time there is no loss attached.
When the pressing operation, and the voltage distribution from the perspective of capacitive division in the semi-conductive shielding layer should withstand voltage, but the absolute [epsilon] <ε half, so U, n U2, the pressure drop is dispensed on the shield small, when the size of the cable constant, U1 / U2 ∞ ε2 / ε1 . While working through long cable having semi-conductive shielding frequency, short-term frequency and voltage surge failure characteristic, found semi-conductive shield layer has the role of long-term damage is significantly reduced in exchange, such that the long-term effect of AC corona prevented occur.