Elect_thermal - Computation of Thermal Electrical and Mechanical Fields at a Defect in Polyethylene Jinbo Kuang Department of Electrical Computer

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Computation of Thermal, Electrical, and Mechanical Fields at a Defect in Polyethylene Jinbo Kuang Department of Electrical & Computer Engineering University of Toronto 10 King’s College Road Toronto, ON, Canada M5S 3G4 Abstract: Power frequency voltage and lightning surges cause space charge formation and power dissipation at defects in high voltage systems. In the case of lightning impulses, the power dissipation can cause substantial tem- perature rise in the dielectric which results in mechanical stresses from space charge and non-uniform thermal ex- pansion induced forces. Two-dimensional transient non- linear finite element analysis has been applied to compute the space charge, power dissipation, temperature rise, and mechanical stress at a defect in XLPE. INTRODUCTION The electric field near a conducting defect in a dielec- tric is limited by space charge formation resulting from field-dependent conductivity in the dielectric. Under impulse conditions, the current densities necessary to form such space charge can cause substantial power dissipation in the microscopic region around such a defect. Space charge and thermal expansion induced forces cause mechanical stresses in the dielectric which are relevant to electrical tree initiation and growth. The finite element method (FEM) with time stepping for time domain discretization has been applied to com- pute simultaneously the electric, thermal, and mechani- cal field distributions in the region around a defect in polyethylene. The problem is transient, nonlinear, and coupled because the electrical conductivity is field and temperature dependent, and the thermal properties of dielectric are also temperature dependent. The thermal field is caused by power dissipation induced by the electric field, and mechanical stress is caused by non- uniform thermal expansion as well as space charge in- duced forces (the action of the large electric field at the defect on the space charge in that region). The results of the simulation provide an indication of the roles of space charge and thermal expansion induced forces on electrical treeing. NUMERICAL MODELING The electrical field in the presence of space charge is governed by a diffusion equation [ 11 (1) a V.(o,Vv) + -/V.(EeVv)} = 0 at Steven A. Bogs Electrical Insulation Research Center University of Connecticut Storrs, CT 06269-3136 and Department of Electrical & Computer Engineering University of Toronto where oe is the electric conductivity, E, the dielectric constant and V the electric potential. The second term on the left hand side of eq (1) represents the rate of space charge generation. The thermal field is governed by another diffusion equation (2) where k is the thermal conductivity, Q is the volume power dissipation, pm is the mass density and c is the heat capacity.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 06/08/2011 for the course ELECTRICAL 124 taught by Professor Ghjk during the Spring '11 term at Institute of Technology.

Page1 / 4

Elect_thermal - Computation of Thermal Electrical and Mechanical Fields at a Defect in Polyethylene Jinbo Kuang Department of Electrical Computer

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online