1. What is the primary advantage of using thyristors in series operation?
a) Increased voltage handling capability
b) Enhanced current regulation
c) Improved efficiency
d) Greater power dissipation
Answer: a) Increased voltage handling capability
Explanation: When thyristors are connected in series, their voltage handling capability adds up, allowing the circuit to handle higher voltages.
2. In parallel operation of thyristors, what is the main challenge to be addressed?
a) Voltage imbalance
b) Current sharing
c) Thermal runaway
d) Gate triggering synchronization
Answer: b) Current sharing
Explanation: Ensuring proper current sharing among parallel-connected thyristors is essential to prevent overloading of individual devices.
3. Which method is commonly used for turning off thyristors in commutation circuits?
a) Forward biasing
b) Reverse biasing
c) Gate signal withdrawal
d) Trigger pulse application
Answer: b) Reverse biasing
Explanation: Reverse biasing the thyristor helps in turning it off by reducing the forward current below the holding current.
4. What is the purpose of line frequency phase controlled rectifiers using SCR?
a) Voltage regulation
b) Current rectification
c) Power factor correction
d) Harmonic suppression
Answer: a) Voltage regulation
Explanation: Line frequency phase-controlled rectifiers using SCRs regulate the output voltage by controlling the firing angle of the thyristors.
5. In a single-phase half-wave rectifier with RL load, what effect does increasing source inductance have?
a) Decreases output voltage
b) Increases output voltage
c) Improves output current regulation
d) Reduces output current
Answer: a) Decreases output voltage
Explanation: Increasing source inductance causes voltage drop across the inductor, leading to a decrease in the output voltage.
6. What is a characteristic of a three-phase half-wave rectifier with RL loads?
a) High ripple voltage
b) Low output current
c) Improved power factor
d) Reduced harmonic distortion
Answer: c) Improved power factor
Explanation: Three-phase rectifiers typically have improved power factor compared to single-phase rectifiers due to better utilization of the input power.
7. What is the advantage of using fully controlled converters with constant current output?
a) Reduced harmonics
b) Improved efficiency
c) Better voltage regulation
d) Enhanced power factor
Answer: a) Reduced harmonics
Explanation: Fully controlled converters with constant current output tend to produce fewer harmonics, resulting in a cleaner output waveform.
8. How does input side harmonics affect the performance of rectifiers?
a) Increases efficiency
b) Reduces voltage ripple
c) Degrades power quality
d) Improves power factor
Answer: c) Degrades power quality
Explanation: Input side harmonics can degrade power quality by causing distortion in voltage and current waveforms.
9. What is the main disadvantage of half-wave rectifiers compared to full-wave rectifiers?
a) Higher ripple voltage
b) Lower efficiency
c) Greater size
d) Limited voltage handling capability
Answer: a) Higher ripple voltage
Explanation: Half-wave rectifiers have higher ripple voltage compared to full-wave rectifiers, resulting in poorer voltage regulation.
10. What is the primary function of commutation circuits in thyristor applications?
a) Turn on the thyristor
b) Turn off the thyristor
c) Control the firing angle
d) Limit the current flow
Answer: b) Turn off the thyristor
Explanation: Commutation circuits are used to turn off thyristors by reducing the forward current below the holding current.
11. Which parameter is crucial for the parallel operation of thyristors?
a) Forward voltage
b) Reverse voltage
c) Forward current
d) Gate trigger voltage
Answer: c) Forward current
Explanation: Ensuring proper current sharing among parallel thyristors is essential for reliable operation.
12. What is the advantage of using fully controlled converters over half-controlled converters?
a) Improved efficiency
b) Reduced complexity
c) Lower cost
d) Higher voltage handling capability
Answer: a) Improved efficiency
Explanation: Fully controlled converters offer better control over the output waveform, leading to improved efficiency compared to half-controlled converters.
13. How does the addition of source inductance affect the performance of rectifiers?
a) Increases voltage ripple
b) Reduces voltage ripple
c) Improves power factor
d) Enhances voltage regulation
Answer: a) Increases voltage ripple
Explanation: Source inductance causes voltage drop across it, leading to increased voltage ripple in the rectified output.
14. What is the primary function of a rectifier in a power supply system?
a) Convert AC to DC
b) Convert DC to AC
c) Voltage regulation
d) Current amplification
Answer: a) Convert AC to DC
Explanation: Rectifiers convert alternating current (AC) to direct current (DC) in power supply systems.
15. What is the significance of continuous current output in rectifiers?
a) Smoother output waveform
b) Lower output voltage
c) Higher efficiency
d) Reduced harmonic distortion
Answer: a) Smoother output waveform
Explanation: Continuous current output results in a smoother output waveform with less ripple.
16. What role does the firing angle play in phase-controlled rectifiers?
a) Controls output voltage
b) Determines output current
c) Regulates input power
d) Limits peak current
Answer: a) Controls output voltage
Explanation: The firing angle determines when during the AC cycle the thyristor starts conducting, thus controlling the output voltage.
17. How does the inclusion of RL loads affect the performance of rectifiers?
a) Increases output voltage
b) Decreases output current
c) Improves power factor
d) Introduces phase shift
Answer: d) Introduces phase shift
Explanation: RL loads introduce a phase shift between voltage and current waveforms, affecting the performance of rectifiers.
18. Which rectifier configuration provides better voltage regulation: half-wave or full-wave?
a) Half-wave
b) Full-wave
c) Both provide equal voltage regulation
d) None, voltage regulation depends on load type
Answer: b) Full-wave
Explanation: Full-wave rectifiers provide better voltage regulation due to reduced ripple compared to half-wave rectifiers.
19. What is the primary purpose of constant current output in rectifiers?
a) Ensure load stability
b) Minimize voltage ripple
c) Maximize power factor
d) Reduce harmonic distortion
Answer: a) Ensure load stability
Explanation: Constant current output ensures stable operation of loads, especially those sensitive to current variations.
20. What is the key advantage of using thyristors in rectifier circuits?
a) High switching speed
b) Low conduction losses
c) Enhanced voltage regulation
d) Improved transient response
Answer: b) Low conduction losses
Explanation: Thyristors have low conduction losses, making them efficient for high-power rectifier applications.