Power systems Important questions helpful for TsGenco ,Transco ,NPDCL, SPDCL

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1. The percentage of occurrence of the following fault is more
a)SLG  b) LL  c) LLG  d) LLL

ans: a

Hint:
In power systems chances of occurrence of faults..
LG - 70%
LL -  15%
LLG - 10%
LLLG - 5%

2.  for the fault at the terminals of synchronous generator , the fault current is maximum for a
a) 3-phase fault
b) 3-phase to ground fault
c) line to ground fault
d) line to line fault

ans: c

Hint:
The decreasing order of fault currents is given below

fault current (LG) > fault current (LLG) > fault current (3-phase) > fault current (LL)
The fault current is maximum for line to ground

3.Equal area criterion gives the information regarding
a) Stability region
b) absolute stability
c) relative stability
d) swing curves

ans: b

4. A negative sequence relay is commonly used to protect
a) an alternator
b) an transformer
c) a transmission lines
d) feeders

ans: a

Hint: Negative sequence relays are used for protection of alternators against unbalanced loading that may a raise due to phase to phase faults

5. for a fully transposed line
a) positive , negative , & zero sequence impedances are equal
b) negative and zero sequence impedances are equal
c) zero & positive sequence impedances are equal
d) positive & negative sequence impedances are equal

ans:  d

6) Bundled conductors are mainly used in high voltage overhead transmission lines to

a) reduce corona
b) reduce sag
c) reduce transmission line losses
d) to balance voltage drops

ans: a

7) In thermal power plants , the pressure in the working fluid cycle is developed by
a) condenser
b) feed water pump
c) super heater
d) turbine

ans:c

8) for long transmission lines which relay is used
a) Mho  relay
b)impedance relay
c)reactance relay
d)none of these

ans: a

Hint:  we use
for short transmission lines - reactance relay
for medium transmission lines- impedance relay
for long transmission lines - MHO relays

9) The rated voltage of a 3-phase power system is given by
a) RMS phase voltage
b)peak phase voltage
c) Rms line to line voltage
d)peak line to line voltage

ans:c

10) for capacitor bank switching which circuit breaker is used
a) vaccum
b) airblast
c)air break
d) oil circuit beaker

ans : a