PowerPoint Presentation

Energy Processes When the voltage is provided to gas and passed through vacuum chamber ionized and called as plasma. OR

On heating ionization (loss or gain of electrons) of molecules or atom of the gas results turns into plasma.

Gas high temperature ionized gas (plasma)

PLASMA:

Fourth state of matter:The existence of the plasma is in the form of ions.Electron makes the plasma electronically conductive.Different gases have different plasma color.e.g oxygen gas purple colorHydrogen gas orange colorIf it is the equal positive and negative charges so it is neutral plasma.If it is composed of a single species called as non-neutral plasma, in such plasma electric fields play a dominant role.

For plasma to exist ionization is necessaryPlasma density referring to electron density, i.e the number of free electron per unit volume.The degree of the ionization of plasma is controlled by the temperature.Even a partially ionized gas in which as little as 1% of the atom are ionized possess the characteristics of plasma (i.e response to magnetic field and have electrical conductivity).

When the dielectric strength of the air/medium is weak so the flow path is complete and the spark is caused. ORA spark is caused when the electric field strength exceed a certain critical value to overcome the dielectric strength of the medium between high voltage electrodes so a very rapid increase in the number of free electrons and ions in the air Process is called dielectric breakdown.

SPARKThe particles of the air are ionized and we see it is the form of spark/light.The spark is also the form of plasma.Due to which high temperature is cause.The high voltage spark caused explosion.The spark is used for the welding, spark plug, nickel plating etc.

Puncture Voltage:It is the voltage across the insulator cause a breakdown and conduction through the interior of insulator.

Tracking:It is the slowly and gradually carbonization of insulator surface.Due to the carbonization leakage of current cause the surface flash over.It is caused due to high humidity and temperature rise.It provides low resistive path.The process of tracking continues until the insulator is short circuited.

For each type of insulator the threshold voltage and current values are defined.When the voltage is increased from the threshold voltage so that it breaks.Due to breakdown the dielectric strength of the insulator is weak and provides a low resistive path.The breakdown can occur in the solid, liquid, gas and vacuum.

The characteristics are classified as solid, liquid, gaseous and vacuum insulators.The following are the general characteristics features of an insulators used in practice.It should be high resistive.It should have high dielectric strength.It should be mechanically tough.It should have high viscosity (for liquid).It should not be hygroscopic (Hygroscopyis the ability of a substance to attract and holdwatermoleculesfrom the surroundingenvironment.).It should be capable of withstanding high temperature.

Characteristics of an InsulatorIt should be non-flammable.It should be chemically inert and stable.It should be resistive to acidic compounds.It should be capable of withstanding high service voltages.It should be non-corrosive.It should be non-toxic and environmentally friendly.

There are five general factors that causes insulation degradation.Thermal stresses.Electrical stresses.Mechanical stresses.Chemical stresses.Environmental contamination.

Each shell has its own energy level.The energy of the outer shell is more as compare to the inner shell.The half-filled/ incomplete shell means the outermost shell, because there is also some shell present after the last shell and es moves through them by getting energy.For the conduction the es should be on the conduction band.The energy gap between the C.B and V.B is the forbidden energy gap.In case of conductor, the C.B and V.B are slightly overlap each other. Because the forbidden energy gap is small/less.But in case of insulator, the forbidden energy gap is high between C.B and V.B

Energy Band Theory:Band gap energy

Now the energy required to moves the es from the V.B to the C.B is called as band gap energy.The breakdown of insulator due to the energy band theory as when the external energy is more than the band gap energy so the breakdown of insulator occur due to which the motion of es from V.B to C.B caused.eV> E2-E1 (1ev=1.610-19j)The voltage V is applied across the insulator with n number of the es in the ground state as; neV= E2-E1 (to move n es from E2 to E1where E2-E1 (the band gap energy) is the difference of the energy of the ground state and valence band

The motion of the es from ground state to the excited state is due to;1) Heat/ temp2) Voltage /electric field provided 3) Due to hitting / bombardment with particle4) Light of shore wave length 5) Sound 6) Radiations7) Pressure Ionization potential:

The energy required to eject removing the electron from the outermost shell of gaseous atom is called the ionization potential.For the ionization fast moving electron is necessary.eV> I.PMeans the K.E of the electron must be greater than the ionization potential External energy >ionization potential

Collision ionization:The production of electron from an atom due to energetic incident electrons, under the electric field, so the energy of incident electron is transported to the atom. Resulting in positively charge ion

e- +A A+ +2e- e- shows fast moving incident electron A0 shows stationary target atomThis process is also called e- pair productionThe ionization is due to collision of es-The moving or incident electron possess the K.Ei.e ev =1/2mv2so v=(2ev/m)The velocity of the incident e- depend upon the applied voltage so the dependence of K.E of the incident e -is also based on the applied voltage When the kinetic energy or electron volts (ev) is less than the ionization potential then excitation will take place.i.e K.E/ev