EE1402 HIGH VOLTAGE ENGINEERING question papers Anna university question papers NOVEMBER/DECEMBER 2007 Download

B.E/B.Tech DEGREE EXAMINATION, NOVEMBER/DECEMBER 2007

Seventh Semester
                                  
Electrical and Electronice Engineering

EE 1402 -- HIGH VOLTAGE ENGINEERING

(Regulation 2004)
Time: Three hours                                                    Maximum marks: 100
Answer ALL questions

PART A (10 x 2 =20 marks)

1. Draw and define impulse voltage wave shape and mention its specification as per standards.

2. Mention the different kinds of over voltages.

3. Define uniform and non-uniform fields and give example for each.

4. Define the following as applied to high voltage break down :

(a) Internal and external insulation

(b) Flash over.

5. Explain the superiority of cascaded transformers over two winding transformers used for generation of high A.C voltages.

6. An impulse generator has 10 stages with capacitors rated 0.15 μ F and 150 kV per stage. The load capacitor is 1000 pF. Find the front and tail resistances to produce an impulse if 1.2 /50 μs. (Use approximate formulae).

7. What is the need for generating high impulse currents?

8. Compare the measurement of very high voltages using potential dividers and standard sphere gaps.

9. What are atmospheric correction factors and mention their influence in high voltage testing?

10. Explain the role of Bureau of Indian Standards in high voltage testing.

PART B (5 x 16 = 80)

11 (a) What is meant by 'Co-efficient of Earthing' of a power system? Explain its implication on the design of insulation of system and connected equipment. (16)
(or)
(b) (i) State the different methods of protection against over voltages. (4)

(ii) Draw the cross-sectional view of a non linear resister lightning arrestor and explain its operation in detail including its V-I characteristics. (12)

12.  (a) State the criteria fir sparking potential and hence obtain the relation between sparking potential and (pd) values (Paschens Law). Discuss on the nature of variation of sparking potential with (pd) values. (16)
(or)
(b) (i) State why the vary high intrinsic strength of solid dielectrics is not fully realized in practice. Discuss in detail any one mechanism of break down in solid dielectrics. (12)

(ii) Name some of the important practical solid dielectrics and mention their dielectric properties. (4)

13 (a) (i) Explain the need for generating high DC voltages. (4)

(ii) Draw the circuit of an n-stage Cockroft-Walton circuit for generating very high DC voltages and explain its operation. Also derive an expression for the ripple content in the output wave form. (12)
(or)
(b) (i) Starting from the basic 'MARX' circuit, develop the circuit of a modern multi-stage impulse generator and explain its operation. Discuss on the significance of various parameters. (10)

(ii) Explain trippling of impulse generators. (6)

14. (a) (i) Explain why we resort to statistical approach for impulse studies. (4)

(ii) Define 50% impulse disruptive discharge voltage and discuss in detail any one method of obtaining the same. (12)
(or)
(b) Explain the measurement of very high voltages using sphere gaps. Mention the merits and demerites of using sphere gaps. (16)

15. (a) (i) What are the needs for high voltage testing of electrical apparatus? (4)

(ii) Discuss in detail the power frequency voltage test withstand on a 66 kV porcelain insulator. (12)
(or)
(b) (i) Explain the need for recording supplementary during impulse testing of transformers. (4)

(ii) Give the detailed procedure for impulse voltage withstand test on a 500 kVA, 11 KV/415 V, delta/star distribution transformer. (12)

FEEL USEFUL PLEASE GIVE +1