Faculty Of Engineering
High Voltage 1
rd
Year 3
Dr Ahmed M Ewais
EwaisA@aswu.edu.org
9 October 2019
1
List of Contents

Breakdown (BD) in Liquids
– Ionisation of Gases
• Ionisation Processes in gas discharge
• Relevant Gas Ionisation Processes
 Breakdown Characteristic in Gas
Electron Avalanche Mechanism (Townsend BD Process)
Paschen’s Law
Streamer Mechanism
2
Breakdown of commercial liquids
The passage of a spark through a liquid involves the following:
Tests on highly purified transformer oil show that:
The categories of the impurities which lead to the bd of the commercial liquids:
3
1. Breakdown due to gaseous inclusions
Where
The field in the liquid in absence of the bubble
4
2. Breakdown due to liquid globules
Where
The field in the liquid in absence of the globule
The critical field at which the globule becomes unstable:
5
3. Breakdown due to solid particles
6
Purification of a liquid for testing
7
3- Breakdown of solid
3.1- Electro-mechanical breakdown
8
3.2 Breakdown due to internal discharge
9
3.3 Surface Breakdown
3.3.1 Surface Flashover
3.3.2 Tracking
3.3.3 Erosion
10
3.3.4 Thermal Breakdown
11
The End
12
Directed reading
High Voltage Engineering
1st EditionRohan Lucas
9 June 2023
13