For a High voltage pulse power supply of 140KV amplitude, rise time 1usec , fall time 1usec, pulse width 6 usec and PRF is 10 Hz to 200Hz . For this what is the minimum value of breakdown voltage for transfomer oil for safe operation?
Depending on the type of oil used the breakdown voltage can be up to 60kV/mm (dried oil) or 40kV/mm (non dried-oil). However, it really depends on the application and again, the type of oil. I always like to stay below 15kV/mm (pulsed). For your application you might get away with 20-30 kV/mm.
In our country minimum breakdown voltage for oil transformers when it is tested according IEC is 30 kV/mm
Breakdown phenomenon depends on the energy supplied to the insulation material. I have never dealt with application of pulse voltages directly on transformer oil instead dealt with impulse voltage application in transformers. The logic of breakdown remains the same. From my experience, untreated, raw transformer oil has to withstand 40 kV per 2.5 mm for 1 minute (rate of rise of the voltage : 2 kV/s). The area under this trapezium is 1400 kV S. The area under your pulse should be less than this value. Your requirement clearly shows this. The breakdown voltage should be nearly 16 kV/mm.
According to the Standards IEC 60422 you have to distinguish between following categories of transformers: type A rated voltage over 170kV, type B over 72,5kV and type C under 72,5kV. Then there were following areas for evaluation of the result: good (A >60kV, B>50kV, C>40kV), fair (A 50-60kV, B 40-50kV, C 30-40kV), poor (A
Since I was talking about our distribution transformers under 35 kV voltage level, IEC, the value C < 30 kV from C. Sumereder, corresponding to what I had written above.
I recommend, as a supplement, to read the properties of the transformer oil under the pulse mode in the corresponding publications. The values mentioned above are usually valid for voltages with power frequency.
can we have the draft of this standard, or the number of this standard?
best regards,
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