AdvancedTopic 99 of 106Electrical Engineering
Insulation and dielectric breakdown
Insulating materials fail when field exceeds dielectric strength.
In depth
Insulation fails when the electric field exceeds dielectric strength (air ≈3 kV/mm, transformer oil ≈ 15 kV/mm, polyethylene ≈ 20+). Mechanisms: ionisation, partial discharge, treeing, thermal runaway. Ageing is accelerated by heat, moisture, contamination.
Key points
- Creepage and clearance
- Withstand and impulse tests
- Insulation class temperature
ExamplePower cables use XLPE insulation rated 90 °C.
What is Insulation and dielectric breakdown?
Insulating materials fail when field exceeds dielectric strength.
Why is it important to understand insulation and dielectric breakdown?
Insulation fails when the field exceeds its dielectric strength, so knowing this limit is essential for safe high-voltage design.
What is dielectric strength?
The maximum electric field a material can withstand before breakdown, usually given in kilovolts per millimetre.
Why does insulation fail over time?
Partial discharge, heat, moisture and contamination gradually weaken insulation, so it can fail well below its rated strength.
How is Insulation and dielectric breakdown used in practice?
Typical applications include choosing the clearance between conductors in a high-voltage switchgear, selecting the thickness of cable insulation for a 11 kV line and designing a capacitor dielectric to avoid breakdown in service.
What should I learn before Insulation and dielectric breakdown?
Study "Electromagnetic compatibility" first (topic 98 of 106 in Electrical Engineering). It covers the groundwork this topic builds on.
What are the key points of Insulation and dielectric breakdown?
Creepage and clearance. Withstand and impulse tests. Insulation class temperature.
Can you give an example of Insulation and dielectric breakdown?
Power cables use XLPE insulation rated 90 °C.
What comes after Insulation and dielectric breakdown?
The next topic is "Electrical wiring and standards", which builds directly on this one.
How difficult is Insulation and dielectric breakdown?
It is classed as Advanced in Electrical Engineering (topic 99 of 106). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Electrical Engineering.