Visvesvaraya Technological University (VTU) 2007 B.E Electrical and Electronics Engineering 7th SEM .06/.07 HIGH VOLTAGE ENGINEERING - Question Paper
Seventh Semester B.E. Degree Examination, Dec. 06 / Jan. 07 Electrical and Electronics Engineering
High Voltage Engineering Time: 3 hrs.] [Max. Marks: 100
Note : L Answer any FIVE full questions.
2. Assume suitably any missing data.
1 a. Explain the process of ionization by collision and hence derive the Townsends
Current Growth Equation. (07 Marks)
b. Explain briefly formative time lag and statistical time lag. (05 Marks)
c. In an experiment in a certain gas it was found that the steady state current is 5.5xl0'8 A at 8 kV at a distance of 0.4 cm between the plane electrodes. Keeping the field constant and reducing the distance to 0,1 cm results in a current of 5.5*10'9 A. Calculate Townsends prinary ionization coefficient a. (OS Marks)
2 a. Briefly explain Cavitation and Bubble Theory" in the context of liquid dielectric
breakdown. (08 Marks)
b. The following observations were made in an experiment for determination of
|
j Gap spacing (mm) |
4 |
6 | 8 |
10 |
|
| Breakdown voltage (kV) |
SS |
t 135 165 |
(12 Marks)
a. Explain how high dircct voltages can be generated using a Cockroft Walton circuit.
(OS Marks)
b. A Cockroft Walton type voltage multiplier has eight stages with capacitances, all equal to 0.05 jiF. The supply transformer secondary' voltage is 125 kV at a frequency of 150 Hz. If the load current to be supplied is 5 mA, find
i) The percentage ripple
ii) The regulation
iii) The optimum number of stages for minimum voltage drop. (U.Marks)
a. Explain how high alternating voltages can be generated by Cascading of Transformers*. (07 Marks)
b. State the chief advantages of resonant transformers. (05 Marks)
c. A 100 kVA, 400 V/250 kV testing transformer has 8% leakage reactance and 2% resistance on 100 kVA base. A cable has to be tested at 500 kV using the above transformer as a resonant transformer at 50 Hz. If the charging current of the cable at 500 kV is 0.4 A, find the series inductance required. Assume 2% resistance for the inductor to be used and the connccting leads. Neglcct the dielectric loss of the cable. What will be the input voltage to the transformer? (OS Marks)
Contd.... 2
Page M>... 2 EE74
a. Explain ihe working principle of series capacitor peak voltmeter based on the Chubb-Frotscue method. (07 Marks)
b. Briefly explain the four factors influencing the Sparkover voltage of sphere gaps.
(08 Marks)
c. A generating voltmeter has to be designed so that it can have a range from 20 to 200 kV d.c. If the indicating meter reads a minimum current of 2 jaA and a maximum current of 25 jjA, what should the capacitance of the generating voltmeter be?
(05 Marks)
a. Give the general equation of a standard impulse wave and explain the wave shape giving the percentage tolerances allowed for front, tail and the peak. (07 Marks)
b. Which are the four main sources of errors in the measurement of impulse voltages with potential dividers. (08 Marks)
c. A resistance divider of 1400 kV (impulse) has a high voltage arm of 16 kQ and a low voltage arm consisting of 16 members of 250 D, 2 W resistors in parallel. The divider is connected to a CRO through a cable of surge impedance 75 Cl and is terminated at the other end through a 75 Q resistor. Calculate the exact divider ratio. (05 Marks)
a. Explain the method of measuring dielectric loss at power frequency using high \ oltage Sobering Bridge. ' (08 Marks)
b. Explain partial discharge detection using stiaight detectors. (07 Marks)
c. A Schering bridge was used to measure the capacitance and loss angle of a high voltage bushing. At balance, the observations were : the value of the standard condenser = 100 pF, R3 = 3180 Q, C3 = 0.00125 jiF and R4 = 636 Q. What are the values of the capacitance and loss angle of the bushing? (05 Marks)
Write short notes on any four of the following :
a. Trigatron gap
b. Mixed R-C potential dividers
c. Rogowski coil
d. Treeing and tracking
e. Van De Graff generator
f. Penning effect. (20 Marks)
*****
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Attachment: |
| Earning: Approval pending. |
