JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008

JNTU III B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008


(Electrical & Electronic Engineering)


1. What are the different dielectric materials according to their physical nature? Compare their merits and demerits.


2. The following observations were made in an experiment for determination of dielectric strength of transformer oil. Determine the power law equation.

Gap Spacing (mm) 4 6 8 10

Breakdown voltage (kV) 88 135 165 212


3. Discuss about various forms of plastic insulating materials used in high voltage engineering. Compare their relative merits and demerits with respect to their applications.


4. (a) How are the wave front and wave tail times controlled in impulse generator circuits.

(b) An impulse generator has eight stages with each condenser rated for 0.16 ?F and 125 kV. The load capacitor available is 100 pF. Find the series Resistance and damping Resistance needed to produce 1.2/50 ?s impulse wave. What is the maximum output voltage of the generator, if the charging voltage is 120 kV?


5. (a) Describe the generating voltmeter used for measuring high d.c voltages. How does it compare with a potential divider for measuring high dc currents.

(b) A generating voltmeter is to read 250kV with an indicating meter having a range of (0-20) ?A Calibrated accordingly . Calculate the capacitance of the generating voltmeter when the driving motor rotates at a constant speed of 1500 Rpm


6. Give the mathematical models for lightning discharges and explain them.


7. (a) What are partial discharges? Differentiate between internal and external discharges?

(b) Develop and draw equivalent circuit of insulating material during partial discharge?


8. Mention the different electrical tests done on isolators and circuits breakers.

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