Abstract
The electric field distributions in high voltage direct current cable termination are investigated with silicone rubber nanocomposite being the electric stress control insulator. The nanocomposite is composed of silicone rubber, nanoscale carbon black and graphitic carbon. The experimental results show that the physical parameters of the nanocomposite, such as thermal activation energy and nonlinearity-relevant coefficient, can be manipulated by varying the proportion of the nanoscale fillers. The numerical simulation shows that safe electric field distribution calls for certain parametric region of the thermal activation energy and nonlinearity-relevant coefficient. Outside the safe parametric region, local maximum of electric field strength around the stress cone appears in the termination insulator, enhancing the breakdown of the cable termination. In the presence of the temperature gradient, thermal activation energy and nonlinearity-relevant coefficient work as complementary factors to produce a reasonable electric field distribution. The field maximum in the termination insulator show complicate variation in the transient processes. The stationary field distribution favors the increase of the nonlinearity-relevant coefficient; for the transient field distribution in the process of negative lighting impulse, however, an optimized value of the nonlinearity-relevant coefficient is necessary to equalize the electric field in the termination.
Highlights
Nowadays, there is a worldwide increasing demand for electrical energy
The experimental results show that the physical parameters of nonlinear silicone rubber (NLSR), such as thermal activation energy (TAE) and nonlinearityrelevant coefficient (NRC), can be manipulated by varying the proportion of the nanoscale fillers
To ensure the effective electric stress control, TAE and NRC of the cable termination insulator should be picked from the region below the boundary lines at temperatures T c=30°C, 60°C, 90°C
Summary
There is a worldwide increasing demand for electrical energy. Usually, powergenerating stations are significantly distant from electricity-consumption cities, such as wind farms and Sahara solar energy stations. Graphite nanosheet can be added into silicone rubber, resulting conducting nanocomposite with a low percolation threshold and it was reported a prototype field-grading element for a dry and compact high voltage termination had been developed.[23,24,25] In addition, functionally graded materials has been utilized to obtain effective stress control in insulators.[26] the characteristics of the electric field distribution inside the termination still lack research and deserve further exploration to evaluate the effectiveness of the electric field grading materials. The carbon black (CB) and graphitic carbon (GC) filled silicone rubber nanocomposites are prepared experimentally, which show good conductivity nonlinearity and can be used as the electric stress control insulator in the cable termination. The stationary and transient electric field characteristics are explored and the present nanocomposite with high breakdown strength lie within the safe parameter region and is readily used as HVDC cable termination insulator
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