Question

The oil in good condition in circuit breaker should withstand
strength
(A) 10 kV for one minute
(B) 20 kV for one minute
(C) 30 kV for one minute
(D) 40KV for one minutee​

Answer 1

Answer:

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 <50kV, B<40kV, C <30kV). The breakdown test is done with an equipment according to IEC 60156.

The IEEE Standard C57.106 is a little bit different: methods according to ASTM D877 or ASTMD1816 (service aged). recommended limits for rated voltage <=69kV: 40kV for 2mm test gap.

Answer 2

Concept Introduction: The breakdown phenomenon happens in Transformers.

Explanation:

We have been Given: The oil in good condition in circuit breaker should withstand

strength

(A) 10 kV for one minute

(B) 20 kV for one minute

(C) 30 kV for one minute

(D) 40KV for one minutee

We have to Find: The Correct answer.

The correct option is Option No. C,

$30kV$

for one minute. Avalanche breakdown (or avalanche effect) is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of electron avalanche. The avalanche process occurs when carriers in the transition region are accelerated by the electric field to energies sufficient to create mobile or free electron-hole pairs via collisions with bound electrons.

Final Answer:

$30kV$

for one minute.

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