Search

The electrical insulation system of high-temperature superconducting (HTS) cable consists of liquid nitrogen (N2(l)) and polypropylene laminated paper (PPLP). Partial discharge (PD) may occur in butt gaps of the insulation layers and its characteristics imply the insulation performance of HTS cables. N2(l) cooling system is installed in the power system and N2(l) will flow through the cables during the system operation. Filling the HTS cable with N2(l) in order to perform pre-shipment inspection is timeconsuming and costly for cable manufacturers. Therefore, the authors are trying to find a cost effective method for pre-shipment inspections. One alternative is to use high pressure gaseous nitrogen (N2(g)) instead of N2(l). This article investigates PD characteristics such as PD inception electric field (PDIE) and PD extinction electric field (PDEE) in butt gaps of HTS cables in 0.1-MPa to 0.3-MPa N2(l) and 0.1-MPa to 1.0-MPa N2(g) environments. For assessing the surface/volume effects, PD characteristics are measured with changing the size of butt gaps. It turns out that PDIE and PDEE in N2(g) are linearly correlated with those in N2(l) at any gas pressure in our testing, and PDIE in 1.0-MPa N2(g) is almost 30% of that in 0.2-MPa N2(l). It suggests that PD characteristics in N2(l) can be extrapolated from those in N2(g). [ABSTRACT FROM AUTHOR]

When a DC voltage is applied to an insulating spacer, the electric field distribution around it is determined by the resistivity of the material. Consequently, charges are accumulated on the surface of the insulator, and its breakdown voltage may become low. In this paper, the charge density distribution of the insulator is measured. The measured data indicate that the surface conductance is the main factor in charge accumulation. Therefore, the conductivity of the insulator is also measured, and the influence of the surface conductivity on charge accumulation is examined both experimentally and by numerical computation. It is confirmed that nonuniformity of surface conductivity is responsible for charge accumulation and the conductivity of the insulator in atmospheric-pressure SF6 is estimated to be $\sigma = 1 \times 10^{-18} \Omega^{-1}$. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(2): 29-36, 2012; Published online in Wiley Online Library (). DOI 10.1002/eej.22272 [ABSTRACT FROM AUTHOR]

A square pulse voltage is useful for studying electrical discharge physics or very fast transient overvoltage issues. This paper describes sparkover voltages and time lag (V– t) characteristics of CF3I gas, which has very low environmental effects and high dielectric strength, and its mixtures with nitrogen gas or air in a very short time range below a microsecond. They are measured by using a steep-front square voltage with a rise time of 16 ns and a peak value of 200 kV. Pure CF3I gas has 20% higher dielectric strength than SF6 gas. The V– t characteristics of CF3I–N2 or CF3I– air gas mixtures, which contain 60% CF3I gas, are equivalent to those of pure SF6 gas at the same total pressure. A quantitative evaluation of V– t characteristics by the equal-area criterion is also performed. The equal-area parameter which is obtained by applying a voltage high enough to make the formative time lag dominant should be chosen. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 1–7, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20325 [ABSTRACT FROM AUTHOR]

Presents a study that investigated the electrical discharge characteristics of relatively long-gap configurations in air and nitrogen at a cryogenic temperature. Analysis of the discharge characteristics in uniform electric field and non-uniform field; Effect of electronegative gas and transit time on discharge characteristics; Evaluation of the direct current breakdown voltage and the lightning impulse breakdown voltage.

The breakdown voltages of the longer-gap configurations in gaseous nitrogen and air that are necessary in designing superconducting electrical power apparatuses are measured at temperatures of 293 and 93 K. The quasi-uniform electric field made by a sphere-to-sphere electrode with a diameter of 150 mm and a gap length of about 10 to 100 mm is used in the measurement of the breakdown voltages. When 50-Hz ac and dc voltages are applied to the sphere-to-sphere gap, the breakdown voltages in nitrogen and air obey Paschen's law even at cryogenic temperatures (93 K). When a 1.4/50-μs lightning impulse voltage is applied to the gap, the 50% breakdown voltage of nitrogen also obeys Paschen's law under UV irradiation of the cathode electrode. However, the breakdown voltage in air at 93 K is higher in the case of lightning impulse voltage applications, and the delay from impulse voltage application to breakdown occurrence is apparently longer at 93 K than at 293 K. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 28–33, 2000 [ABSTRACT FROM AUTHOR]