# WBUT Exam Papers EE

## Advanced High Voltage Engineering B Tech 8^{th} Sem 2010

Time Allotted : 3 Hours

Full Marks : 70

The figures in the margin indicate Jull marks.

Candidates are required to give their answers in their own words

as far as practicable.

GROUP – A (Multiple Choice Type Questions )

- Choose the correct alternatives for any ten of the following :

10 x 1 = 10

1) Average electrical field is the magnitude of electrical field

a) at mid-point between conductors

b) ratio of potential difference to the distance between the conductors

c) at surface Of the lower potential electrode

d) ratio of potential difference to half the distance between the conductors.

11) An experimental method for computing the field distribution is

a) solution of Laplace equation ‘

b) eledrolytic tank method

c) digital simulation

d) field intensity method.

iii) Field enhancement factor is the ratio of

a) maximum field to average fielc

b) rms value to electric field to average value

c) potential difference to radius of the conductor

d) electric field at the surface of the h.v. conductor to electric field at ground conductor.

iv) A unique feature of the Boundary Element Method is that

a) it can be used for electric fields which are uniform only

b) it can be used only with bounded fields

c) electric field is proportional to the charge densities

on an enclosed electrode which is simulated by real charges

d) none of these.

v) Finite Element Method can be used onfy

a) with fields which are bounded

b) with fields which are unbounded

c) with fields which are both bounded and unbounded

d) when high accuracy is not required.

vi) A comparison of the accuracies of various computational methods shows a good agreement between the results of

• a) FEM and FDM

b) FDM and BEM

c) FEM and CSM

d) BEM and FEM. yii) Corona discharge is

a) an internal discharge

b) surface discharge ^{
}

c) a spark between conductors

d) partial discharge around a high voltage conductor.

viii) Partial discharge magnitude is

a) quantity of charge measured at the terminals of the specimen

‘ b) quantity of charge inside a specimen ‘•

c) voltage across the terminals of a specimen

d) average current through the terminals of the specimen.

ix) Partial discharge detector is a device that measures or detects

a) a partial discharge

b) corona discharge V c) leakage current

d) fault current.

x) A simple partial discharge detector circuit consists of a power unit and a

a) coupling capacitor and test capacitor

b) coupling capacitor, test capacitor, measuring impedance and detector

c) test capacitor, measuring impedance and a detector

d) test capacitor, calibratng unit and detector.

The discharge energy in a partial discharge in terms of

discharge magnitude q and inception voltage v is

a) q* b) 0.707 q*

C) 0.5 q* d) 1.414 q_{vi}

GROUP -B ( Short Answer Type gnestioas)

Answer any three of the following. 3 x 5 = 15

- Explain the difference between photo-ionization and photoelectric emission.

- Discuss the advantages and limitations of Charge Simulation

method.

- How would you measure dielectric constant and loss angle for a cable ?

- How would you measure resistivity of a dielectric ?
- What are formitive and statistical time lags ? Explain.

GROUP -C

( Long Answer Type Questions )

Answer any three of the following. 3 x 15 = 45 ‘ V . . ‘

- What Is PD ? Find out the relation between measured charge

and apparent charge in case of a PD. Draw the PD equivalent circuit for a cavity within a dielectric: Wfite down the different techniques of PD measurement.

- What are tile different types of voltage dividers used in HV laboratory ? Describe the method of impulse ypltage measurement with the help of such dividers with proper mathematical analysis. 12

- a) Draw the circuit diagram and explain the principle an#-

operation of Cockroft-Walton cascade rectifier circuit for generation of high d.p. voltage.

b) Derive an expression for the voltage drop in a loaded Cockcroft-Walton voltage multiplier circtiit. Also, derive the expression for the ripple voltage.

- Explain the mechanism involved in the breakdown of vacuum.

- Write short notes on any thee of the following :

a) Electron attachment and its role in the breakdown of electronegative gases. ‘

b) Voltage measurement by sphere gaps.

c) Determination of front and tail time of lightning impulse wave as per I.S.

d) Generation of high impulse current.

e) Discharge characteristics of a rod-plane gap in air.