EE1004 Power System Transients B.E Question Bank : drnnce.ac.in

Name of the College : Dr. Navalar Nedunchezhiyan College of engineering
University : Anna University Chennai
Subject Code/Name : EE1004-Power System Transients
Dept : Electrical And Electronics Engineering
Degree : B.E
SEM: : VIII
Website : drnnce.ac.in
Document Type : Question Bank

Download Model Question Paper : https://www.pdfquestion.in/uploads/drnnce.ac.in/3210-pst%20qb%20(2)(1).pdf

Power System Transients Question Paper

UNIT-I

SWITCHING TRANSIENTS
PART-B : (2MARKS)
21. What is meant by resistance switching?(AU-APR08)
A deliberate connection of a resistance in parallel with the contact space (arc) is made to overcome the effect of transient recovery voltage. This is known as resistance switching.
22. Define switching transients.
The switching transients is initiated whenever there is sudden change of circuit conditions. This transient is most frequently developed due to switching operations such as The closing of a switch (or) circuit breaker to energies a load. The opening of a circuit breaker to clear a fault.
23. Give the relation between time constant of parallel and series circuit.
Time constant of parallel circuit Tp=RC
Time constant of series circuit Ts=L/R
24. The product of there time constants is the square of the angular period of the undamped circuit which is given by TpTs=LC =T2
25. What is the need of resistance switching.(AU-MAY10)
The shunt resistors connected across circuit breaker have two functions. To distribute the transient recovery voltage more uniformly across the several breaks. To reduce the severity of transient recovery voltage at the time of interruption by introducing damping into oscillations.
26.Define power system transients.( AU-MAY11)
The power system transient is the outward manifestation of a sudden change in circuit conditions as when a switch opens are closes are fault occurs on a system the transient period is very short.

27.Mention the sources of power system transient.( AU-MAY08)
Internal sources :
Switching surges, insulation failure, arching ground, ferro resonance.
External sources :
Lightning.

28.What are the causes of switching surges?( AU-NOV09)
The making and breaking of electric circuits with switch gear may result in abnormal transients over voltages in a power system having large inductance and capacitance.
29.What is meant by arcing ground?( AU-MAY08)
The phenomena of intermittent arc taking place in line to ground fault of a three phase system with consequent production of transients is known as arcing ground.It can be prevented by earthing the neutral.
30.What is meant by lightning?
An electric discharge between cloud and earth, between clouds or between charges centres of the same cloud is known as lightning.
31.What are the types of lightning?
** Direct stroke
** Indirect stroke.

UNIT-II

LOAD SWITCHING
PART-A (1 MARK)
45.As compared to air the relative dielectric strength of sulphur hexafluoride is nearly
a. 1.5 times
b. 2.5 times
c. 4.0 times
d. 5.0 times
46.The electrical breakdown strength of insulating materials depends on
a. nature of applied voltage
b. imperfections in dielectric material
c. pressure, temperature and humidity
d. all of the above.
47.Which of the following gas has been used as insulating medium in electrical appliances ?
a. Nitrogen
b. Carbon dioxide
c. Sulphur hexafluoride
d. Freon.
48.Vacuum insulation is used in all of the following EXCEPT
a. Particle accelerators
b. EHT of color TV
c. Field emission tubes
d. X-rays.
49.Liquids are generally used as insulating materials up to voltage stresses of about
a. 100 MV/cm
b. 50 MV/cm
c. 50 kV/cm
d. 500 V/cm.
50.Electro-mechanical breakdown of solid insulating materials occurs due to
a. magnetic bum
b. vibrations
c. mechanical stresses produced by the electrical field

56.All of the following methods/techniques can be used for the measurement of high ac voltages EXCEPT
a. Potential dividers
b. Potential transformers
c. Electrostatic voltmeters
d. Half effect generators.

57.Surge diverters are
a. non-linear resistors in series with spark gaps which act as fast switches
b. arc quenching devices
c. shunt reactors to limit the voltage rise due to Ferranti effect
d. over-voltages of power frequency harmonics.

58.Impulse voltages are characterized by
a. polarity
b. peak value
c. time of half the peak value
d. all of the above.

DR.NNCE EEE/VIIISEM SY&QB
59.Paschen’s law is associated with
a. breakdown voltage
b. ionization
c. thermal radiations
d. none of the above.
60.The essential condition for the Paschen’s law to be valid is that
a. voltage must be dc
b. voltage must be ac
c. temperature must be constant
d. humidity must be low