Abstract
The field utilization factor Ξ· (the mean electric field/the maximum electric field) of the standard sphere gaps was calculated by the charge simulation method, taking into account the ground plane and shanks. A simple equation: Ξ· = 1 β (g/3__r__), where g is the gap length and r is the radius of a sphere, can be used generally as a representative value of Ξ·, although it changes by the length and the diameter of shanks in the range permitted by the IEC standard. The maximum electric field at sparkover of a standard sphere gap describes a Uβshaped curve against (g/r), up to the diameter of 1 m. Peek's equation characterizes that the rightβhand side of the curve is almost constant. However, the effect of the ground and the shanks makes Ξ· smaller and the part of the curve is rather expressed as monotonously increasing. The curves of the maximum electric field of diameters 1.5 and 2 m are different from Uβform. The curve for a 1.5βm sphere has its maximum point at g = 60 cm, and for a 2βm sphere, at 50 cm. Β© 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(4): 26β32, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.1165