Abstract—This paper presents the experimental results on space charge distribution in cross-linked polyethylene (XLPE) insulating material for 22 kV power distribution system cable by using pulse electroacoustic measurement technique (PEA). Numbers of XLPE insulating material ribbon having thickness 60 μm taken from unused 22 kV high voltage cable were used as specimen in this study. DC electric field stress was applied to test specimen at room temperature (25°C). Four levels of electric field stress, 25 kV/mm, 50 kV/mm, 75 kV/mm and 100 kV/mm, were used. In order to investigate space charge distribution characteristic, space charge distribution characteristics were measured after applying electric field stress 15 min, 30 min and 60 min, respectively. The results show that applied time and magnitude of dc electric field stress play an important role to the formation of space charge. Keywords—Space charge distribution, pulsed electroacoustic (PEA) technique, cross-linked polyethylene (XLPE), DC electrical fields stress. I. INTRODUCTION OWADAYS, XLPE is used an insulating material in high voltage power cable. The advantages of XLPE are high dielectric strength and electrical resistivity combined with good physical properties such as resistance to cracking and moisture penetration[1-2]. However, under certain operating conditions, their good electrical insulation properties may become degraded. For example, trapped or low mobility electrically charged species within the bulk can give rise to space charge, resulting in localized electric stress enhancement. This can cause further concentration of charge and lead to premature failure of the material [3-4]. In a solid dielectric medium, space charge and electric displacement are related by the Maxwell-Gauss equation. In situations where quantities depending on only one spatial coordinate, z, this equation is expressed as[5]: ) ( ) ( ) ( ) ( z z z z z D p c ρ ρ ρ + = = ∂ ∂ (1) where: D(z) is the electric displacement, N. Ruangkajommathee and R. Thiamsri aremaster degree students with Suranaree University of Technology, Nakhonratchasima, 30000, Thailand. B. Marungsri is with Suranaree University of Technology, NakhonRatchasima, 30000, Thailand (corresponding author, phone: +66 44224366; fax: +66 4422 4601; e-mail: bmshvee@ sut.ac.th). ρ(z) is the total charge density, ρ c (z) is the volume density of space charges, defined as real charges, being positive or negative, including surface and bulk charge, ρ p (z) is the volume density of bound charges, defined in respect to material polarization P as: z z P z p ∂ ∂ − = ) ( ) ( ρ (2) If the polarization is uniform along the z direction, the total charge is the space charge. Space charge effects have been widely recognized as one of the major components of the electrical aging processes in polymeric insulation, because it may raise the electric field locally and hence initiate a degradation mechanism in insulator [3, 6-7]. Therefore, it is very important to understand space charge effects to polymer insulation. PEA technique is a nondestructive method, which has been developed to measure dynamically net charge density as a function of distance through solid insulating materials under an applied voltage. The principle of space charge measurement using the PEA technique is well known and reported elsewhere [5-6,8-9]. Kwang et al. [10] studied effects of constituents of XLPE on the formation of space charge by PEA technique, cross-linked part of low density polyethylene (LDPE) encourages antioxidant and residual byproducts on the formation of space charge in XLPE have been investigated. Montanari et al. [11] reported results the effect of humidity on space charge accumulation in XLPE at room temperature and humidity concentration from 5 to 95%. Space charge measurements were performed by using the PEA technique. Different levels of DC constant poling field were considered, ranging from 5 kV/mm to 185 kV/mm. Chen et al. [12] report the effect of mechanical deformation on space charge dynamics in XLPE. Thin films were peeled from a66 kV commercial XLPE cable. Space charge measurements under DC electric fields have been monitored using the PEA technique. Chong et al. [13] reports on space charge evolution in XLPE planar specimens approximately 1.20 mm thick subjected to electric stress level of 30 kV dc /mm at four temperatures 25, 50, 70 and 90 O C for 24 h. Space charge distributions are dominated by positive charge when tested at high temperatures regardless of specimens treatment and Space Charge Distribution in 22 kV XLPE Insulated Cable by using Pulse Electroacoustic Measurement Technique N. Ruangkajonmathee, R. Thiamsri, and B. Marungsri N World Academy of Science, Engineering and Technology International Journal of Electrical and Computer Engineering Vol:6, No:12, 2012 1494 International Scholarly and Scientific Research & Innovation 6(12) 2012 scholar.waset.org/1307-6892/15837 International Science Index, Electrical and Computer Engineering Vol:6, No:12, 2012 waset.org/Publication/15837