Electrostatic Fields and Field Stress Control
(b) Non uniform field
In high voltage most of the problems are related with electrical conduction fields and electrostatics. Permissible field strength in the materials are interlinked with electrostatic field distributions. Knowledge of electric field and controlling field stress's are important for following reasons.
- Researchers are trying to increase transmission line voltages, decreasing conductor size and its weight and make it competitive. It is only possible with careful studies of insulating materials and knowledge of field distribution and field stress.
- It is necessary to design insulating materials which can also sustain diverse conditions which requires to study electrostatic field profiles.
- For achieving reliability and economy optimum designing of insulating materials are required which is only possible through selecting materials carefully after studying their dielectric strength, field distribution and stresses in it.
- Breakdown voltage of materials are dependent on distribution of electric field in the gap and the maximum stress occurring into the material. Idea of breakdown voltage can be obtained by analyzing the field distribution in the gap.
- Thus one of the most determinant factors of the dielectric strength of the insulating materials is the field strength distribution inside the mass of the materials, when stressed by high voltages. The distribution of the field in the gap axis is strongly affected by the geometry of the electrodes and the arrangement of the gap and the values of the breakdown voltage are strongly related to the maximum values of field strength in the gap and the leakage current. Few field distribution for various gap arrangement are as shown in figures
(a) Uniform field
(b) Non uniform field
- The limit of electric strength of an insulating medium is reached when its discruptive field strength is exceeded at some point. In non-uniform it is seen that field stress is maximum near the radius of curvature of electrodes. Hence materials are more likely to puncture as compared to when placed in uniform field.