HVE Introduction

High Voltage Engineering -----Importance

Insulation Engineering• Any Electrical Apparatus• Conductor/s• Dielectric Material (Insulation)• Magnetic material• Others

• Conductor - Material with a Very Large Number of Free Electrons

- Conduct electric current readily.

• Dielectric - Ideal Dielectric - Has no Free Electrons - So, No current on application of Voltage

(Non – conductor) - Real Dielectric

Has an extremely small number of free electrons (or charges).

Electrical breakdown at much much lower levels (orders lower) than ‘Intrinsic Strength’.

• Dielectrics used to support/segregate conductors at different Potentials (Voltages) without affecting Current Flowing Paths – Electrical Insulation.

• Conductors at different potentials coming into contact at undesired locations -> Short Circuit

(Fault/Short).

Dielectric Supports/Barriers are to prevent short circuit

• Electrical Insulations – Essential in Electrical Apparatus.

• Failure of Electrical Apparatus – almost always due to failure of Electrical Insulation.

• Failure of Electrical Insulation - Dielectric Material transforming into a Conducting Material –may be in Portions.

• Thus - Study of Dielectrics is very crucial to enable proper choice of materials as well as design of Electrical Apparatus (Insulation Engineering).

Classification of Dielectric Materials

1. Classification based on Physical State (at room temperature) :• Gases• Liquids• Solids• Vacuum• Combination of 2 or more of above.All of the above known as Insulation System.

2. Classification based on maximum permissible working temperature (to realise desired long life)

3. Classification based on Post-breakdown behavior:

• Self-restoring insulation : A medium which recovers insulation properties after breakdown and de energisation

• Non self-restoring insulation –A medium which gets permanently damaged on occurrence of breakdown.

4. Another related classification

• Exposed Insulation : Insulation whose surface is exposed to atmosphere (and hence its vagaries such as presence of dust moisture, rain, sun varying temperatures, solar, UV and other radiations.

• Enclosed Insulation : Insulation which is sealed/enclosed in a Container and thus is not exposed to atmosphere ( and its various parameters listed above).

Parameters that influence Life of Electrical insulation :

1.Electrical Stress (E) : working Stress

Excessive stresses due to OVER VOLTAGES.Factor of safety.

2. Thermal Stress (T) : variations in Ambient temperatureoverloading –higher temperatures.‘Hot-spot Temperatures’

3. Ambient Conditions :(other than temperature)Presence of Humidity;Corrosive vapours, other pollutants-dustRadiation ( solar, cosmic etc;)

4. Mechanical Stresses (M) :During: initial handling of raw materials,Manufacturing processes, transportation,Commissioning ‘in-service’ mechanical stresses- faults, vibrations