In this paper, the results of investigation carried out to understand the influence of barrier in a short air gap with the Rod-Rod configuration under oscillatory impulse voltages (UOIV, SBOIV, CBOIV) of different frequencies and dampings are presented. For the purpose of comparison, results obtained under AC, DC, LI and SI voltages are also provided. IntroductionElectric or dielectric strength is an important concept for an insulation design engineer. With the advancement of power transmission capacity, it has become necessary to design a reliable, compact and cost effective insulation system. The major cause of failure of electrical insulation and subsequent damages and outages in electrical power systems are due to transient over voltages caused by lightning, switching operations, line faults, etc., cause a wide variety of non-standard wave-shapes which are oscillatory in nature. The generated Oscillatory Impulse Voltages (OIVs) are complex in nature, identified by their freYpency, decay rate etc. These oscillatory transient voltages are either unidirectional, cos-bidirectional or sine-bidirectional in nature. The frequency of oscillations produced by lightning is in the range of several hundred Hertz and that of produced by line faults or switching over voltages is in the order of 1 to 100 kHz [l].