Calculating Dielectric Breakdown Voltage & Effects of Electrode Material

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Discussion Overview

The discussion revolves around calculating the dielectric breakdown voltage in a system with dielectric oil and electrodes, as well as the effects of different electrode materials on this voltage. The scope includes theoretical considerations and practical applications, particularly in the context of micro Electro Discharge Machining (EDM).

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the calculation of breakdown voltage for dielectric oil and requests relevant formulas.
  • Another participant suggests that dielectric breakdown voltage typically does not depend on the resistivity of the electrodes, as they are considered perfect conductors compared to the insulator.
  • It is noted that the geometry of the electrodes affects the electric field, with rough or sharply curved surfaces leading to lower breakdown voltages.
  • A participant challenges the assertion that electrode resistivity does not influence breakdown voltage, citing experiences from micro EDM where more conductive electrodes reduce breakdown voltage.
  • Another participant expresses skepticism about the dependence of dielectric breakdown on electrode resistivity and requests references to support the claim of it being a well-documented phenomenon.
  • One participant clarifies that while breakdown voltage is primarily a function of the electric field and dielectric strength, the efficiency of material erosion in EDM may be affected by the peak current, which can be influenced by electrode resistance.

Areas of Agreement / Disagreement

Participants express differing views on whether the resistivity of electrodes affects dielectric breakdown voltage. While some argue it does not, others present evidence suggesting it may have an impact, particularly in specific applications like micro EDM. The discussion remains unresolved regarding the influence of electrode material on breakdown voltage.

Contextual Notes

Participants reference the complexity of the relationship between electrode material properties and dielectric breakdown, indicating that further exploration of governing equations and empirical data may be necessary to clarify these interactions.

Tanveer Saleh
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I have another question. Let us assume we have some dielectric oil and two electrodes (submerged into dielectric oil) connected to positive and negative of a voltage source.

The system shall have some breakdown voltage , how can I calculate that? Any link available to get the formula?

Second question is more critical if I change the electrode material ie I use more conductive material as the electrodes how the breakdown voltage shall be affected? How is the breakdown voltage related to electrode resistivity?


Kindly help. Thanks a ton in advance.
 
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You might try this link for starters:
http://en.wikipedia.org/wiki/Dielectric_strength
The dielectric breaks down at a certain value of electric field. It typically won't depend on the resistivity of the conductors, since they are so much more conductive than the insulator that they are effectively perfect conductors. However, it will depend on the geometry of the conductors. The electric field depends inversely on the radius of curvature of the surface, so rough or sharply curved surfaces will increase the field and have a lower breakdown voltage. For a high breakdown voltage, you want the conductors to be as flat and smooth as possible.
 
hello phyzguy,
thanks for the reply. However I have some doubt. You said typically dielectric break down does not depend on the electrode resistivity. Typically term is bit confusing. Let me describe my prb more clearly. In micro EDM (Electro Discharge Machining) ease of machining increases if we use more conductive tool and workpiece. This is because the dielectric breakdown voltage reduces if conductivity of the electrodes increases. This is a well documented phenopena however I couldn't find governing equation for this phenomena. Kindly help in this regard.
 
I don't see why dielectric breakdown should depend on the resistivity of the conductors, assuming that they are conductors and not insulators, but maybe I am missing something. You say it is a well documented phenomenon. Do you have a reference?
 
As Physguy indicated, dielectric breakdown is primarily a function of the applied electrical field versus the dielectric strength of the oil, and is virtually independent of electrode resistivity for good electrical conductors (such as metals, alloys, and carbon/graphite). However, once electrical breakdown occurs, the "efficiency" of metal erosion will be a function of the peak current that flows through the resulting discharge. Higher resistance electrode materials (particularly for wire EDM) may create higher voltage drops in the discharge loop. If the higher electrode resistance significantly reduces peak current, it will also reduce the rate of material erosion, and thus EDM efficiency.
 
Hello BertHickman,
Thanks for the reply. It makes sense.
 

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