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Electrical Engineering
Rectifiers And Converters
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Q.1
In a mercury arc rectifier, the anode is usually made of
copper
aluminium
silver
graphite
tungsten
Q.2
Selenium rectifier can be operated at temperatures as high as
25°C
40°C
60°C
75°C
Q.3
Which of the following is reversible in action?
Motor generator set
Motor converter
Rotary converter
Any of the above
None of the above
Q.4
A rotary converter operates at a
low power factor
high power factor
zero power factor
none of the above
Q.5
The voltage drop between the anode and cathode, of a mercury arc rectifier comprises of the following
anode drop and cathode drop
anode drop and arc drop
cathode drop and arc drop
anode drop, cathode drop and arc drop
Q.6
In which of the following appUcations, direct current is absolutely essential ?
Illumination
Electrolysis
Variable speed operation
Traction
Q.7
In phase-shift control method the control is carried out by varying the of grid voltage.
magnitude
polarity
phase
any of the above
none of the above
Q.8
A mercury arc rectifier possesses ________ regulation characteristics
straight line
curved line
exponential
none of the above
Q.9
The advantage of mercury arc rectifier is that
it is light in weight and occupies small floor space
it has high efficiency
it has high overload capacity
it is comparatively noiseless
all of the above
Q.10
The potential drop in the arc, in a mercury arc rectifier, varies
0.05 V to 0.2 V per cm length of the arc
0.5 V to 1.5 V per cm length of the arc
2 V to 3.5 V per cm length of the arc
none of the above
Q.11
The ionization potential of mercury is approximately
5.4 V
8.4 V
10.4 V
16.4 V
Q.12
Copper oxide rectifier is usually designed not to operate above
10°C
20°C
30°C
45°C
Q.13
In mercury arc rectifiers having grid, the arc can be struck between anode and cathode only when the grid attains a certain potential, this potential being known as
maximum grid voltage
critical grid voltage
any of the above
none of the above
Q.14
In selenium rectifiers efficiencies ranging from ______ to ______ percent are attainable
25, 35
40, 50
60, 70
75, 85
Q.15
The metal rectifiers, as compared to mercury arc rectifiers
operate on low temperatures
can operate on high voltages
can operate on heavy loads
give poor regulation
none of the above
Q.16
In a mercury arc rectifier positive ions are attracted towards
anode
cathode
shell bottom
mercury pool
Q.17
The internal efficiency of a mercury arc rectifier depends on
voltage only
current only
voltage and current
r.m.s. value of current
none of the above
Q.18
The ignited or auxiliary anode in mercury arc rectifier is made of
Graphite
Boron carbide
Aluminium
Copper
Q.19
In a glass bulb mercury arc rectifier the maximum current rating is restricted to
2000 A
1500 A
1000 A
500 A
Q.20
A rotary converter in general construction and design, is more or less like
a transformer
an induction motor
an alternator
any 'C. machine
Q.21
Which of the following are the applications of D.C. system?
Battery charging work
Arc welding
Electrolytic and electro-chemical processes
Arc lamps for search lights
All of the above
Q.22
Glass rectifiers are usually made into units capable of D.C. output (maximum continuous rating) of
100 A at 100 V
200 A at 200 V
300 A at 300 V
400 A at 400 V
500 A at 500 V
Q.23
Which of the following AC. motors is usually used in large motor-generator sets?
Synchronous motor
Squirrel cage induction motor
Slip ring induction motor
Any of the above
Q.24
Ageing of a selenium rectifier may change the output voltage by
5 to 10 per cent
15 to 20 per cent
25 to 30 per cent
none of the above
Q.25
In a rotary converter I2R losses as compared to a D.C. generator of the same size will be
same
less
double
three times
Q.26
The cathdde voltage drop, in a mercury arc rectifier, is due to
expenditure of energy in ionization
surface resistance
expenditure of energy in overcoming the electrostatic field
expenditure of energy in liberating electrons from the mercury
Q.27
In a rotary converter armature currents are
d.c. only
a.c. only
partly a.c. and partly d.c.
none of the above
Q.28
The applications of selenium rectifiers are usually limited to potential of
10 V
30 V
60 V
100 V
200 V
Q.29
The metal rectifiers are preferred to valve rectifiers due to which of the following advantages ?
They are mechanically strong
They do not require any voltage for filament heating
Both (A) and (B)
None of the above
Q.30
Which of the following methods may be used to convert A.C. system to D.C.?
Rectifiers
Motor converters
Motor-generator sets
Rotary converters
All of the above
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