Transmission and Distribution Systems MCQs (Part-10)
What is line impedance in a power transmission system?
A Resistance
B Power loss
C Voltage drop
D Opposition to current
Line impedance refers to the opposition that a transmission line offers to the flow of alternating current. It includes both the resistance and reactance of the line, which affects the current flow and causes voltage drops and power losses.
What type of power loss is primarily caused by line impedance?
A Resistive loss
B Inductive loss
C Reactive loss
D Capacitance loss
Resistive loss occurs due to the resistance component of line impedance, which causes energy to be dissipated as heat. The greater the resistance, the higher the power loss in the transmission lines, which reduces overall system efficiency.
How does line inductance affect the power transmission?
A Increases power
B Creates voltage lag
C Reduces current flow
D Improves efficiency
Line inductance causes the current to lag behind the voltage. This effect, known as inductive reactance, results in an imbalance between voltage and current, which can lead to poor power factor and decreased system efficiency.
What is the main effect of capacitance in transmission lines?
A Voltage drop
B Current flow reduction
C Voltage rise
D Power loss increase
Capacitance in transmission lines can cause a rise in voltage, particularly at lighter loads. This effect can lead to overvoltage conditions, which can damage equipment and reduce the stability of the system.
What is the typical cause of line impedance in transmission lines?
A Inductive reactance
B High voltage
C Grounding
D Conductor length
Line impedance is primarily determined by the length of the conductor. Longer transmission lines have higher impedance, which increases resistive losses and causes greater voltage drops, making the system less efficient.
What is the effect of increased line inductance on power systems?
A Increased voltage stability
B Increased current flow
C Reduced power factor
D Reduced current flow
Increased line inductance results in a reduced power factor, as the current lags behind the voltage. This means that a larger proportion of the power is reactive, reducing the efficiency of the system and increasing energy losses.
How can line capacitance affect voltage regulation?
A Increases current flow
B Causes voltage fluctuations
C Stabilizes voltage
D Reduces voltage fluctuations
Line capacitance can lead to voltage fluctuations, especially under light load conditions. The capacitive effect may cause voltage to rise above the desired levels, leading to instability and potential damage to equipment.
Which of the following parameters is part of the total line impedance?
A Resistance
B Voltage
C Power factor
D Frequency
Line impedance consists of both resistance and reactance. Resistance causes real power loss, while reactance (inductive and capacitive) affects the phase relationship between voltage and current. Both components influence the overall efficiency of power transmission.
What is the purpose of line impedance in a power system?
A Improve voltage stability
B Increase power loss
C Limit current flow
D Control reactive power
Line impedance helps limit the current flow in the system. By offering resistance and reactance to the current, it ensures that the system does not exceed safe operational limits, protecting equipment from damage due to excessive current.
How does inductance affect the power quality in a transmission line?
A Improves power factor
B Causes harmonic distortion
C Increases reactive power demand
D Reduces power losses
Inductance increases the demand for reactive power, which does not perform any useful work but is necessary to maintain voltage levels. This increase in reactive power reduces the efficiency of the system and can lead to poor power quality.
What does the term “capacitive reactance” refer to in transmission lines?
A The reduction in current flow
B The opposition to AC current due to capacitance
C The opposition to DC current
D The resistance of the transmission line
Capacitive reactance refers to the opposition to AC current caused by the capacitance of the transmission line. This reactance can cause voltage rise and impact the stability of the transmission system, especially during low‐load conditions.
What is one method used to reduce line impedance in power systems?
A Adding more transformers
B Increasing conductor resistance
C Shortening the line length
D Use of high‐voltage transmission
Shortening the length of transmission lines reduces line impedance, which minimizes resistive losses and voltage drops. Shorter lines are more efficient, leading to lower energy consumption and reduced system instability.
How does line capacitance impact power factor correction?
A Increases the power factor
B No effect on power factor
C Decreases the power factor
D Stabilizes the power factor
Line capacitance can help improve the power factor by supplying reactive power that offsets inductive loads, making the system more efficient. It balances the reactive power, reducing the need for additional reactive power sources.
What is the impact of high line inductance on power transmission?
A Increases power loss
B Reduces current flow
C Increases voltage
D Improves power quality
High line inductance causes increased power loss by introducing reactance into the system. This reduces the amount of usable power transferred over the transmission lines and requires more energy to maintain voltage and current stability.
What is one way to compensate for the effects of line capacitance in a power system?
A Adding reactors or inductors
B Using inductive loads
C Increasing voltage levels
D Using more conductors
To compensate for the effects of line capacitance, reactors or inductors are added to the system. These components introduce inductive reactance that offsets the capacitive effects, helping to maintain voltage stability and improving power factor.