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WorksheetsEL_6_PE-2(2160902)_2020
Total questions: 80
Worksheet time: 1hrs 20mins
A single phase full bridge inverter has a dc voltage source Vs = 230 V. Find the RMS value of the fundamental component of output voltage.
90 V
207 V
350 V
196 V
In single phase VSI, the harmonic which is not present is
2nd
3rd
5th
7th
Very large values of modulation index (greater than 3.24) lead to
Square AC output voltage
Sine AC output voltage
Triangular AC output voltage
Trapezoidal AC output voltage
Single phase VSI are mainly used in
Power supplies
Ups
Multilevel configuration
All of these
In the SPWM, the modulating signal is
Square
Sinusoidal
Triangular
Saw - tooth
In a full bridge VSI, in order to avoid the short circuit across the DC bus and the undefined AC output voltage condition, the modulating technique should ensure that
Top switch of each leg is on at any instant
Bottom switch of each leg is on at any instant
Either (a) or (b)
None of these
In a lossless inverter, the average power absorbed in one period by the load must be
Equal to the average power supplied by the dc source
Greater than the average power supplied by the dc source
Lesser than the average power supplied by the dc source
Equal to the average power supplied by the ac source
If energy is taken from the AC side of the inverter and sends it back into the DC side, then it is known as
Motoring mode operation
Braking mode operation
Regenerative mode operation
None of these
The ac output voltage waveform of VSI and AC output current waveform of CSI respectively is composed of
High dv / dt, low di / dt
Low dv / dt, low di / dt
Low dv / dt, high di / dt
High dv / dt, high di / dt
A capacitive load in voltage source inverters generates
Small current spikes and can be reduced by using an inductive filter
Large current spikes and can be increased by using an inductive filter
Small current spikes and can be increased by using an inductive filter
Large current spikes and can be reduced by using an inductive filter
The main objective of static power converters is to
Obtain an dc output waveform from a dc power supply
Obtain an ac output waveform from a dc power supply
Obtain an dc output waveform from a dc power supply
Obtain an ac output waveform from a ac power supply
A single phase full bridge inverter has load R = 2 Ω, and dc voltage source Vs = 230 V. Find the rms value of the fundamental load current.
96 A
0 A
103 A
none of the mentioned
A certain full bridge type inverter circuit has its rms value of fundamental load current component given by W. The fundamental frequency component of the load current would be given by
W sin ωt
(W/√2) sin ωt
√2 W sin ωt
sin ωt
In a half wave bridge inverter circuit, the power delivered to the load by each source is given by
Vs x Is
(Vs x Is)/2
2(Vs x Is)
None of the mentioned
In a half wave circuit, forced commutation is essential when the
load is inductive
load is restive
source voltage is below 150 V
none of the mentioned
A single phase full bridge inverter circuit, has load R = 2 Ω and dc source Vs = 230 V. Find the value of power delivered to the load in watts only due to the fundamental component of the load current.
5361.5 W
2142.5 W
21424.5 W
214.2 W
A single phase full bridge inverter has RLC load with R = 4 Ω, L = 35 mH and C = 155 μF. The dc input voltage is 230 V and the output frequency is 50 Hz. Find the rms value of the fundamental load current.
28.31 A
20.02 A
16.69 A
26.90 A
In a 3 phase CSI, if the required line output voltages are balanced and 120 degree out of phase, then the chopping angles are used to eliminate only the harmonics at frequencies
5
7
11
All of these
For similar carrier and modulating signals, the line current used in CSI is
Identical to line voltage in a VSI
Identical to line current in VSI
Identical to phase voltage in VSI
Identical to phase voltage in CSI
Under harmonic free load voltages, the 3 phase VSI
Does not contains second harmonic
Does not contains third harmonic
Does not contains fifth harmonic
Does not contains seventh harmonic
The square wave operation of 3 phase VSI lines contains the harmonics. The amplitudes are
Directly proportional to their harmonic order
Inversely proportional to their harmonic order
Not related to their harmonic order
None of these
In a square - wave operation of 3 phase CSIs, the power values are on for
60 degree
90 degree
120 degree
150 degree
A carrier based PWM technique in CSI is composed of
A switching pulse generator and a shorting pulse generator
A shorting pulse distributor
A switching and shorting pulse combination
All of these
In square wave operation mode of 3 phase VSI, the VSI
Can control the load voltage
Cannot control the load voltage
Cannot control the load voltage except by means of dc link voltage
Cannot control the load voltage except by means of dc link current
In a 3 phase VSI SPWM to use a single carrier signal and preserve the features of PWM technique, the normalized carrier frequency should be
Multiple of two
Odd multiple of three
Odd multiple of five
Odd multiple of seven
In a three phase voltage source inverters
Only amplitude of voltage is controllable
Only phase is controllable
Both amplitude and phase is controllable
Amplitude, phase and frequency of voltages should always be controllable
Identify the below given circuit.
Three-phase bridge regulator
Three-phase bridge type semi-converter circuit
Three-phase bridge thyristor inverter
Three-phase bridge IGBT inverter
A three-phase bridge inverter requires minimum of _____________ switching devices.
3
4
6
8
In the three-phase bridge inverter, each step consists of
30°
60°
90°
will depend on the value of the firing angle
In inverters, to make the supply voltage constant
an inductor is placed in series with the load
capacitor is connected in parallel to the load side
capacitor is connected in parallel to the supply side
none of the mentioned
In the 180° mode VSI, ___________ devices conduct at a time.
5
2
3
4
In the figure given below, for 180° mode of operation if T1 is fired at 0°. Then SCRs T3 and T5 should be fired at _________ and _________ respectively.
180°, 360°
90°, 180°
120°, 240°
none of the mentioned
For a three phase bridge inverter in the 180° mode, ___________ devices are conducting from 120° to 180°.
T1, T6, T5
T2, T6, T5
T1, T6, T5
T1, T2, T3
_________ SCRs conduct from 300° to 360°.
T1, T6, T5
T2, T6, T5
T1, T6, T3
T4, T5, T6
The 120° mode of operation of a three phase bridge inverter requires ___________ number of steps.
2
4
6
8
In case of the 120° mode of operation, __________ devices conduct at a time.
2
4
6
8
Safe commutation can be achieved in case of the ____________ operating mode.
180°
120°
360°
none of the mentioned
What is the R phase voltage when only T1 and T2 are conducting from 60° to 120°. Consider star connected R load.
Vs
Vs/2
-Vs/2
0
If T1 is gated at 0 °, T3 and T5 will start conducting at _______ and _________ respectively.
180°, 270°
120°, 240°
180°, 300°
240°, 360°
The peak value of the line voltage in case of 120° mode of operation of a three-phase bridge inverter is
Vs/2
3Vs/2
Vs/√2
Vs
In pulse width modulated inverters, the output voltage is controlled by controlling the
input frequency
modulating index
amplification factor
none of the mentioned
In case of sinusoidal pulse width modulation with MI < 1, if the number of pulses per half cycle (N) = 5, then
harmonics of order 5 and 7 become significant
harmonics of order 5 and 7 are eliminated
harmonics of order 9 and 11 become significant
harmonics of order 9 and 11 are eliminated
In case of sinusoidal pulse width modulation with MI < 1, the order of the dominate harmonic can be raised by
increasing the number of pulses
reducing the number of pulses
lowering the input voltage frequency
raising the input voltage frequency
In case of sinusoidal pulse width modulation with MI < 1, if the number of pulses per half cycle (N) = 6, then
harmonics of order 7 and 9 become significant
harmonics of order 7 and 9 are eliminated
harmonics of order 11 and 13 become significant
harmonics of order 11 and 13 are eliminated
Increasing the number of pulses (N), ____________
reduces the output voltage amplitude
reduces the inverter efficiency
improves the inverter efficiency
none of the mentioned
In single-phase modulation of PWM inverters, the pulse width is 120°. For an input voltage of 220 V dc, the rms value of output voltage is
185 V
254 V
127 V
179 V
In MPM the amplitudes of square wave and triangular wave are respectively 1 V and 2 V. For generating 5 pulses per half cycle, the pulse width should be ___________
36°
24°
12°
18°
In an inverter, if the fundamental output frequency is 50 Hz, then the frequency of the lowest order harmonic will be
50 Hz
150 Hz
250 Hz
350 Hz
Calculate the pulse width in case of MPM, if the amplitudes of square wave and triangular wave are respectively 2 V and 3 V respectively. 16 pulses per cycle are generated.
18°
7.5°
6.4°
9°
In a PWM inverter, if the frequency of the lowest harmonic is 180 Hz, then the frequency of the fundamental component would be ___________
50 Hz
60 Hz
540 Hz
90 Hz
AC voltage controllers convert
fixed ac to fixed dc
variable ac to variable dc
fixed ac to variable ac
variable ac to fixed ac
In AC voltage controllers the
variable ac with fixed frequency is obtained
variable ac with variable frequency is obtained
variable dc with fixed frequency is obtained
variable dc with variable frequency is obtained
Earlier then the semiconductor technology, ___________ devices were used for voltage control applications.
cycloconverters
vacuum tubes
tap changing transformer
induction machine
The AC voltage controllers are used in __________ applications.
power generation
electric heating
conveyor belt motion
power transmission
In the principle of phase control
the load is on for some cycles and off for some cycles
control is achieved by adjusting the firing angle of the devices
control is achieved by adjusting the number of on off cycles
control cannot be achieved
A single-phase half wave voltage controller consists of
one SCR is parallel with one diode
one SCR is anti parallel with one diode
two SCRs in parallel
two SCRs in anti parallel
In the below given voltage controller circuit
the positive half cycle at the load is same as the supply Vs
the negative half cycle at the load is same as the supply Vs
the positive and negative half cycles at the load are identical to the supply
none of the mentioned
The below shown controller circuit is a
half wave controller
full wave controller
none of the mentioned
will depend upon the firing angle
The below given controller circuit is a
half wave controller
full wave controller
none of the mentioned
will depend upon the firing angle
In the below given voltage controller circuit
only the negative cycle can be controlled
only the positive cycle can be controlled
both the cycles can be controlled
none of the mentioned
A cycloconverter is a :
Frequency changer from higher to lower frequency with one-state conversion
Frequency changer from higher to lower frequency with two-stage conversion
Frequency changer from lower to higher frequency with one-stage conversion
Either a or c
The cycloconverter require natural or forced commutation as under :
Natural commutation in both step-up and step down cycloconverter
Forced commutation in both step-up and step-down cycloconverter
Forced commutation in step-up cycloconverter
Forced commutation in step-down cycloconverter
The quality of output ac voltage of a cycloconverter is improved with :
Increase in output voltage at reduced frequency
Increase in output voltage at increased frequency
decrease in output voltage at reduced frequency
decrease in output voltage at increased frequency
How many switches are used to construct a three-phase to three-phase cycloconverter ?
3
6
12
18
A four quadrant chopper cannot be operated as :
One quadrant chopper
Cycloconverter
Inverter
Bidirectional rectifier
A cycloconverter is a _________
one stage power converter
one stage voltage converter
one stage frequency converter
none of the mentioned
Applications of cycloconverters include
speed control of ac drives
induction heating
static VAr compensation
all of the mentioned
The single phase mid-point type cycloconverter uses __________ number of SCRs.
4
8
6
none of the mentioned
The single phase bridge type cycloconverter uses __________ number of SCRs.
4
8
6
none of the mentioned
The principle of three phase cycloconverter is to
add and remove number of SCRs
vary progressively the firing angle of the devices
keep the firing angle as 0° for all the devices
none of the mentioned
In three phase cycloconverters, the reduction factor is given by
input frequency/output frequency
(input frequency/output frequency) -1
(input frequency/output frequency) -1/2
(input frequency/output frequency) 1/2
The consideration involved in the selection of the type of electric drive for a particular application depends upon
Speed control range and its nature
Starting Nature
Environmental condition
All of the above
Which of the following motor is preferred for automatic drives?
Ward Leonard controlled dc motors
Squirrel cage induction motor
Synchronous motors
Shunt Motor
The consideration involved in the selection of the type of electric drive for the Load Variation application depends upon
Constant Load
Continuous Variable Load
Pulsating Load
All of the above
__________ drive is also called as Line shaft drive
Individual drive
Multimotor drive
Group Drive
None of the above
In __________ drive each machine is driven by its own separate motor with the help of gears and pulley
Individual drive
Multimotor drive
Group Drive
None of the above
The drive which is used for metal-cutting machines tools, rolling mills etc. are
Individual drive
Multimotor drive
Group Drive
None of the above
Which of the following motors is used for elevators?
Induction motor
Synchronous motor
Capacitor start single phase motor
Any of the above
For blowers which of the following motor is preferred?
D.C. series motor
D.C. shunt motor
Squirrel cage induction motor
Wound rotor induction motor
Which of the following happens when star-delta starter is used?
Starting voltage is reduced
Starting current is reduced
Both (A) and (B)
None of the above
