---
title: "Types of dielectric breakdown"
subject: "Electrical Engineering Material"
chapter: 3
key: "semester_3/electrical_engineering_material:dielectric-breakdown-types"
source: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/dielectric-breakdown-types
site: BCT Engineering
---

# Types of dielectric breakdown

Electrical Engineering Material · Chapter 3: Dielectric Materials

- Asked in: 2070 Chaitra, 4 marks; 2069 Asar, 4 marks (asked 2 times)
- Video: [Dielectric Breakdown](https://www.youtube.com/watch?v=2s6vY4aG3MI) — Kavitha Sureshkumar
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electrical_engineering_material/dielectric-breakdown-types
- Whole chapter: https://www.bctengineer.com/md/semester_3/electrical_engineering_material/chapter-3

## Question

What are the different types of dielectric breakdown? Explain any two of them.

## Short answer

Breakdown types: intrinsic (electronic), thermal, electromechanical, partial discharge, and electrochemical. Intrinsic: in pure material, ~10^-8 s, electron avalanche from impact ionization when field exceeds ~10^8–10^9 V/m, independent of temperature. Thermal: heating from leakage and dielectric loss raises conductivity exponentially; if heat exceeds dissipation, thermal runaway causes melting/charring over seconds to minutes, worsened by higher frequency.

## Answer

**Dielectric breakdown** is the sudden loss of insulating property of a dielectric when the applied field exceeds a critical value called the **dielectric strength** $E_{br}$; a large current flows and solids are usually damaged permanently.

#### Types of breakdown in solids

1. **Intrinsic (electronic) breakdown**
2. **Thermal breakdown**
3. **Electromechanical breakdown**
4. **Discharge (partial-discharge) breakdown** in internal voids
5. **Electrochemical breakdown** (slow chemical ageing of the insulation)

#### Intrinsic breakdown

- Depends only on the material itself, under pure, defect-free conditions; it occurs in about $10^{-8}$ s.
- The few free electrons in the conduction band gain energy from the field. When the field is high enough, they gain more energy than they lose to the lattice and can **ionize** atoms by impact, freeing more electrons. This chain reaction is an **electron avalanche**, and the current rises sharply.
- It sets the highest possible strength of a material (e.g. about $10^{8}$–$10^{9}$ V/m for good insulators). It is almost independent of temperature and thickness.

```text
 e- -> * -> 2e- -> * -> 4e- -> 8e- ...
       ionising collisions (avalanche)
```

#### Thermal breakdown

- Leakage current and dielectric loss ($\propto \omega E^2\tan\delta$) heat the dielectric.
- Conductivity of insulators rises exponentially with temperature, so the current and heat increase further.
- If heat generated exceeds heat conducted away, temperature runs away until the material melts or chars.
- Slow (seconds to minutes); breakdown voltage falls with higher frequency, ambient temperature and longer stress. Common in power cables and capacitors.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What drives intrinsic breakdown?
   A. Heat accumulation over minutes
   B. Electrons gaining energy and causing an avalanche by impact ionization
   C. Electrostatic compression of the sample
   D. Chemical ageing
   Answer: B. Conduction electrons gain more energy than they lose to the lattice and ionize atoms, causing an avalanche in about 10^-8 s. (Key point: Intrinsic breakdown)

2. Intrinsic breakdown strength is:
   A. Strongly dependent on temperature and thickness
   B. Dependent mainly on the frequency of the applied voltage
   C. Zero for pure materials
   D. Almost independent of temperature and thickness, and sets the maximum strength
   Answer: D. It reflects the material's ideal limit, about 10^8 to 10^9 V/m for good insulators. (Key point: Intrinsic dependence)

3. Thermal breakdown voltage falls with:
   A. Higher frequency, higher ambient temperature and longer stress
   B. Lower frequency and lower temperature
   C. Shorter stress time
   D. Better cooling
   Answer: A. These increase heating or reduce cooling, so runaway occurs at lower voltage. (Key point: Thermal breakdown conditions)

4. How do intrinsic and thermal breakdown compare in time?
   A. Both take minutes
   B. Intrinsic about 10^-8 s, thermal seconds to minutes
   C. Thermal is faster than intrinsic
   D. Both take microseconds
   Answer: B. Avalanche is nearly instantaneous while heating takes time. (Key point: Speed comparison)

## Related in Electrical Engineering Material

- [Thermal and electromechanical dielectric breakdown](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Athermal-electromechanical-breakdown) — Electrical Engineering Material, chapter 3, asked 4×
- [Capacitor plate spacing and dielectric breakdown](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Aplate-spacing-breakdown) — Electrical Engineering Material, chapter 3, asked 2×
- [Dielectric strength and types of breakdown](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Adielectric-strength-breakdown) — Electrical Engineering Material, chapter 3
- [Breakdown mechanisms; electronic vs orientational polarization](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_engineering_material%3Abreakdown-and-polarization-types) — Electrical Engineering Material, chapter 3

## Related in other subjects

- [Breakdown mechanisms in solids, explain two](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Asolid-breakdown-explain-two) — High Voltage Engineering, chapter 6, asked 4×
- [Breakdown by treeing and tracking](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Atreeing-tracking-breakdown) — High Voltage Engineering, chapter 6
- [Capacitance of dielectric-filled spherical shells](https://www.bctengineer.com/question.md?key=semester_1%2Fengineering_physics%3Aspherical-shells-dielectric-capacitance) — Engineering Physics, chapter 7
- [Conduction and breakdown theories in commercial liquids](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Aliquid-conduction-breakdown-theories) — High Voltage Engineering, chapter 6, asked 2×