1993 Fiscal Year Final Research Report Summary
Positive Breakdown Mechanism in Transformer Oil subjected to a Non-Uniform DC Field
| Project/Area Number |
03650241
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
電力工学
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| Research Institution | Kanazawa Institute of Technology |
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Principal Investigator |
ISHIBASHI Ryozo Kanazawa Inst.of Tech., Depart.of Tech., Professor, 工学部, 教授 (50019692)
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| Project Period (FY) |
1991 – 1993
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| Keywords | Transformer Oil / Liquid Nitrogen / Dust Figure / EHD Motion / Pre-breakdown Current / Composite Insulation / Breakdown Mechanism in Liquid |
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| Research Abstract |
Many experiments were performed with electrode geometries, neelde to plane and blade to plane, in transformer oil and in liquid nitrogen, and several important results were obtained as follows.
1.Positive Breakdown Mechanism in Transformer Oil
Above the critical voltage V_c, the positive charge injection from the sharp electrode increases rapidly, and at the same time a violent liquid motion occurs. It was found in this research that at the voltage close to the positive breakdown, the field strength E_p in front of the plane electrode grows up rapidly, and a new emission of negative charge occurs. This was proved by the method of dust figure. Moreover it was found that the negative charges move along with liquid flow up to the tip of sharp electrode, and at that time the breakdown occurs.
2.Relationships of Current I and Voltage V in transformer Oil accompanied with EHD motion under Negative DC stresses.
These relations are shown generally by linear plots of V vs I^<1/>(n=2 for the needle and n=3 for the blade).
When voltage V and current I exceed their critical values, it was found in this experiment that the power 1/ of I changes suddenly into a lower constant, and this fact was found by us to be caused by the occurence of minute turbulance of liquid flow which has been analyzed by Kolmogoroff.
3.Prebreakdown Current in Liquid Nitrogen under DC Nonuniform Field New Facts are calrified as fallows.
1)In the negative point to plane geometry, a current recess of about 3mus exist prior to the actual breakdown.
2)When the pressure is high, bubbles are liquified due to the effect of supercooling. Then the streamer velocity increases.
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