Electrostatic Finite Element Analysis (FEA) on High Voltage Bushings
High voltage bushings are the most critical insulation components used in power transformers & reactors. Dielectric performance and long-term operational reliability of bushings primarily depend on the controlled distribution of electric field & stress within the insulation structure. Non-uniform electric field distribution results in localized overstressing, partial discharge inception, insulation ageing, and eventually dielectric failure.
In order to achieve uniform electric field distribution, design engineers use Finite Element Analysis (FEA) to simulate & optimize radial and axial electric stresses & then finalise insulation design prior to manufacturing prototypes.
FEA is a design verification tool. Prior to manufacturing prototypes, FEA is used to verify dielectric clearances, insulation coordination, and stress levels at critical interfaces (conductor, flange, oil-paper, oil-air). This eliminates iterations during prototype manufacturing & thus shortens development cycles and ensures first time right & reliable performance under operating & routine test conditions.
During FEA, geometry of a bushing is divided into several thousands of elements (triangular, quadrilateral, or tetrahedral shapes). Each area comprising of several elements is assigned material properties, boundary conditions, and other electrical parameters. The software then solves governing equations.
There are several FEA software being used for electrostatic analysis of bushings. Some of the FEA software in use are, ANSYS Maxwell, COMSOL Multiphysics, Altair Flux, CST Studio Suite, FEMM 4.2. Most of these software support both 2D and 3D analysis. A bushing being an axis symmetric geometry, 2D analysis minimises time taken to carryout FEA.
Shared below is an example of electrostatic FEA which generates equipotential plots, stress distribution plots, and graphs that facilitates visualisation of voltage gradients and electric fields distribution across the bushing configuration.
Typical steps followed in FEA are:
Drawing preparation: Prepare the model in CAD (.dwg) or 3D format.
Import into FEA software: Load the CAD (.dwg) or 3D file into the solver environment
Property assignment: Define material properties, boundary conditions such as voltage and other electrical parameters.
Mesh Generation: Subdivide in auto mode the geometry into finite elements (triangles/quadrilaterals).
Solution process: Run the solver to compute electric field distribution, equipotential lines, and axial and radial electric stresses.
Result visualization: Analyse outputs using contour plots, vector fields, or numerical data.
Electric Field distribution along the insulation configuration of the bushing:
Axial Stress:
Radial stress:
FEA software are used for:
Mechanical & structural analysis: Evaluation of stress, deformation, stability and fatigue evaluation
Thermal analysis: Heat dissipation and hot spot estimation
Thermo-magnetic analysis: Combined effect of thermal and magnetic fields