Explain the breakdown phenomena with respect to influence of nearby earthed objects, humidity and dust particles
Answers
Answer:
Explanation:
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Explanation:
Influence of humidity:
The a.c. breakdown voltage is slightly less than d.c. voltage. i.e. The breakdown voltage increases with the partial pressure of water vapour.
It has also been observed that the humidity effect increases with the size of spheres and is largest for uniform field electrodes, i.e. The voltage change for a given humidity change increase with gap length.
The increase in breakdown voltage with increase in partial pressure of water vapour and this increase in voltage with increase in gap length is due to the relative values of ionisation and attachment coefficients in air.
The water particles readily attach free electrons, forming negative ions. These ions therefore slow down and are unable to ionize neutral molecules under field conditions in which electrons will readily ionise.
Influence of Dust particles:
When a dust particle is floating between the gap this results into erratic breakdown slightly inhomogeneous or homogeneous electrode configurations. When the dust particle comes in contact with one electrode under the application of d.c voltage, it gets charged to the polarity of the electrode and gets attracted by the opposite electrode due to the field forces and the breakdown is triggered shortly before arrival is a major. Gaps subjected to ac voltages are also sensitive to dust particles but the probability of erratic breakdown is less.