It's very kind to spend your time for this completed answer.
My intention is just to estimate the influence of water in breakdown strength in some materials.
I've done some experiences after immersing my material in deionized water (conductivity=1.36 microSiemen/cm)and i've found that the breakdown strength of my material dramatically decreases (the breakdown voltage before and after about 100kV/mm and 15kV/mm). I think that it is due to the presence of water, and the breakdown took place in water (existing in microcavities of interfaces in the material)at first and then it developed in all material.
But i've found your value of 1,5kV/mm is very useful for the estimation.
Thanks you very much
: --Previous Message--
: I'm looking for the value of breakdown voltage of pure water(deionised)
: under uniforme field (50Hz AC). Could you telle me about this or at least
: show me the source where i can find?
: Best regard
: Hello Tim,
: Although water is useful as a switching and energy storage medium for
: pulsed power applications, it only behaves as a "great"
: dielectric for a short pulses (nanoseconds to microseconds). Under low
: frequency AC excitation or DC, it behaves as a "leaky" ionic
: conductor, with the degree of conductivity being a function of the water's
: Deionized, degassed pure water still contains residual and autoionized
: ionic conductors, causing it to have an effective resistivity of between 1
: and 100 megohm-cm. Under lower frequency voltage stress over time, gas
: bubbles begin to form at the electrode-water interface as a result of the
: ionic conduction. Under sufficient E-field stress, these bubbles may
: become elongated parallel to the applied field. In still water, the
: E-field tends to align groups of bubbles, forming chains that partially
: bridge the water gap. Since gases typically have a lower breakdown voltage
: and because of the dramatic difference in dielectric constant between
: water (k=80) and common gases (k~1), AC breakdown of the gap will tend to
: be initiated as partial discharges within these bubbles. If the voltage
: stress is sufficient, breakdown will then propagate into the remaining
: water in the gap, breaking down the entire gap.
: However, if the DI water is continually circulated between the electrodes,
: then reprocessed to remove ions and degassed, it can withstand significant
: voltage stress even though being somewhat conductive. This insulating
: property is used in high voltage water cooling applications such as high
: power transmitting tubes, and cascaded high voltage thyristor chains used
: in HVDC-to-AC power conversion, or in aqueous resistors for high energy
: pulsed power loads and capacitor bank energy dumping. Note that DI water
: can be extremely corrosive, particularly when combined with
: conductivity-induced electrolysis - this will require careful selection of
: electrode materials.
: A related application (i.e., using doped aqueous resistors for pulsed
: power work) uses stresses of no more than 15 kV/cm. However, since your
: application requires continued operation at 50 Hz, you will need to
: operate at MUCH lower levels. You may be able to find some information
: from the power industry folks who make HVDC conversion equipment (such as
: ABB), or high power broadcasting tubes (where they use high voltage DC on
: water cooled anodes). Per Whitaker (Power Vacuum Tubes Handbook, ISBN
: 0442308949) DI water is commonly used for anode cooling at a DC stress of
: ~10 kV/foot. Here is also an on-line reference you may find useful:
: "Application Notes for Aqueous-Electrolyte Resistors", R. E.
: Beverly III and R. N. Campbell, http://www.reb3.com/pdf/r_appl.pdf
: It's difficult to provide any more quantitative information without
: knowing a bit more about your intended application.
: Good luck and best regards,
: -- Bert --