Master this deck with 20 terms through effective study methods.
Generated from uploaded pdf
The key heat transfer characteristics of insulating materials include thermal conductivity and viscosity, which determine how well the material can transfer heat and resist flow.
Chemical stability in liquid dielectrics is crucial as degradation can lead to corrosion, impaired heat transfer, deterioration of electrical properties, increased losses, and potential discharges and arcing.
Townsend's primary ionization coefficient, α, is a measure of the number of ion pairs produced per unit length of the path of an electron in a gas. It can be determined experimentally by measuring the steady-state current at different distances between electrodes under a constant electric field.
During electrical breakdown in gases, when the applied voltage exceeds a certain threshold, the gas becomes conductive, leading to a sharp increase in current and the formation of a conducting spark that effectively creates a short circuit between electrodes.
The breakdown voltage is the maximum voltage that can be applied to an insulating material before it becomes conductive and allows current to flow, resulting in electrical breakdown.
The two types of electrical discharges in gases are: 1) ionization by collision, where free electrons collide with gas molecules to produce more electrons and positive ions, and 2) photo-ionization, where photons release secondary electrons from gas molecules.
Paschen's curve illustrates the relationship between breakdown voltage (V) and the product of gas pressure (p) and electrode gap distance (d). It shows that this relationship is not linear and has a minimum value for any gas.
Gases are suitable as insulating media due to their high dielectric strength, thermal stability, chemical inactivity towards construction materials, non-flammability, environmentally non-hazardous nature, low temperature of condensation, and good heat transfer capabilities.
Ionization by collision occurs when a free electron collides with a neutral gas molecule, resulting in the production of a new electron and a positive ion, which contributes to the overall ionization process leading to gas breakdown.
The ionization potential (Vi) is the energy required to dislodge an electron from an atom's shell. If the energy gained by an electron during its travel exceeds this potential, ionization occurs, leading to the breakdown of the gas.
Reducing the distance between electrodes in a gas while keeping the electric field constant can lead to a decrease in current, as observed in experiments where current changes with varying electrode distances.
Sulphur hexafluoride (SF6) is used in high voltage applications due to its excellent insulating properties, high dielectric strength, and ability to prevent electrical breakdown, making it a preferred choice for insulating mediums.
Photo-ionization is the process where photons interact with gas molecules, releasing electrons and creating positive ions, which contributes to the ionization process in gases under high voltage conditions.
The breakdown voltage of a gas is influenced by factors such as gas pressure, electrode gap distance, the type of gas, and the material of the electrodes, as described by Paschen's law.
Thermal conductivity and viscosity are interrelated properties in insulating materials; high thermal conductivity allows for efficient heat transfer, while viscosity affects the flow and movement of the material, impacting its overall performance as an insulator.
Understanding the degradation of liquid dielectrics is important to prevent failures in electrical systems, as degradation can lead to reduced performance, increased losses, and potential safety hazards due to arcing and discharges.
Environmental factors such as temperature, pressure, and humidity can significantly affect the performance of gaseous dielectrics by altering their dielectric strength, ionization potential, and overall stability under electrical stress.
Secondary ionization processes are significant in gas breakdown as they amplify the initial ionization events, leading to a rapid increase in free charge carriers and facilitating the transition from an insulating to a conducting state.
Gases offer several advantages over solids as insulating materials, including lower weight, better thermal management, higher dielectric strength, and the ability to fill complex geometries without the risk of voids or defects.
Dielectric strength refers to the maximum electric field that a dielectric material can withstand without breakdown. In gaseous dielectrics, it is a critical parameter that determines the safe operating limits for electrical equipment.