Physics
Textbooks
Boundless Physics
Electric Potential and Electric Field
Capacitors and Dielectrics
Physics Textbooks Boundless Physics Electric Potential and Electric Field Capacitors and Dielectrics
Physics Textbooks Boundless Physics Electric Potential and Electric Field
Physics Textbooks Boundless Physics
Physics Textbooks
Physics
Concept Version 9
Created by Boundless

Dieletrics and their Breakdown

Dielectric breakdown is the phenomenon in which a dielectric loses its ability to insulate, and instead becomes a conductor.

Learning Objective

  • Identify conditions that can lead to a dielectric breakdown and its effect on materials


Key Points

    • All insulators can, when exposed to enough voltage, experience dielectric breakdown and become conductors.
    • Because dielectric breakdown is a failure that depends on a probability, an exact breakdown voltage is in most cases impossible to calculate with a high degree of certainty.
    • Lightning is a common instance of dielectric breakdown, as air loses its ability to separate the potential difference between clouds and the point of a lightning bolt's impact.

Terms

  • dielectric

    An electrically insulating or nonconducting material considered for its electric susceptibility (i.e., its property of polarization when exposed to an external electric field).

  • conductor

    A material which contains movable electric charges.

  • breakdown

    A failure, particularly mechanical; something that has failed.


Full Text

Dielectric breakdown (illustrated in ) is the phenomenon in which a dielectric loses its ability to insulate, and instead becomes a conductor. Dielectrics are commonly used either to isolate conductors from a variable external environment (e.g., as coating for electrical wires) or to isolate conductors from one another (e.g., between plates of a parallel-plate capacitor). In all applications, they are selected for their ability to act as insulators. By definition, an insulator is unable to conduct electricity. Under certain conditions, however, a material that is an insulator can become a conductor.

Eventually, exposing any insulator to increasing voltage will result in the insulator becoming conductive. This point (the minimum voltage for the insulator to become a conductor) is known as the breakdown voltage. Breakdown is more of a rough concept than an exact science. A material's breakdown voltage cannot be precisely defined. As a failure, there is a probabilistic element and thus a dielectric may experience a breakdown at any of a range of voltages. Additionally, the nature of the voltage used to induce breakdown must be considered. Short pulses can be used in stress testing to resemble lightning strikes, as could a continuous applied voltage.

However, for the case of a gas being used as a dielectric, the following equation has been proven to be rather reliable in predicting breakdown voltage (Vb):

$V_b=\frac {Bpd}{\ln {Apd} - \ln {(\ln {(1+\frac {1}{\gamma_{se}})})}}$

where A and B are constants that depend on the surrounding gas, p is the pressure of the surrounding gas, d is distance between the electrodes (in cm) and γse is the secondary electron emission coefficient. Gaseous dielectrics commonly experience breakdown in nature (the phenomenon of lightning is the most common example).

Dielectric breakdown of plexiglas

The treelike pattern in the plexiglas stems from the root of the breakdown. Current is dispersed in many different directions, creating different stems.

[ edit ]
Edit this content
Prev Concept
Combinations of Capacitors: Series and Parallel
Cathode Ray Tube, TV and Computer Monitors, and the Oscilloscope
Next Concept
Subjects
  • Accounting
  • Algebra
  • Art History
  • Biology
  • Business
  • Calculus
  • Chemistry
  • Communications
  • Economics
  • Finance
  • Management
  • Marketing
  • Microbiology
  • Physics
  • Physiology
  • Political Science
  • Psychology
  • Sociology
  • Statistics
  • U.S. History
  • World History
  • Writing

Except where noted, content and user contributions on this site are licensed under CC BY-SA 4.0 with attribution required.