100 Transmission and Distribution MCQs

Correct Answer: B. To transmit electrical energy from one location to another. Transmission lines are used to transfer electrical energy over long distances from power plants to distribution networks.

Correct Answer: D. In-house. In-house lines are not considered transmission lines, which typically refer to overhead, underground, and submarine lines used for large-scale power transfer.

Correct Answer: C. Copper. Copper is widely used due to its excellent conductivity and mechanical strength.

Correct Answer: B. Aluminium Conductor Steel Reinforced. ACSR conductors combine aluminium and steel to enhance strength and conductivity.

Correct Answer: A. Resistance. Resistance in conductors causes power losses due to the conversion of electrical energy into heat.

Correct Answer: B. It causes voltage drop and reactive power flow. Inductance in transmission lines affects voltage regulation and reactive power management.

Correct Answer: C. Farad. Capacitance is measured in farads, representing the ability to store charge.

Correct Answer: D. Conductance. Conductance represents dielectric losses in the insulation material of the transmission line.

Correct Answer: A. Ohm. Impedance is measured in ohms and represents the combined effect of resistance and reactance in a transmission line.

Correct Answer: B. The difference between sending end voltage and receiving end voltage expressed as a percentage. Voltage regulation indicates how much the voltage drops along the transmission line.

Correct Answer: C. Both (a) and (b). Line losses depend on both the conductor material and line impedance.

Correct Answer: A. Nominal π model. The nominal π model includes series impedance and shunt admittance to represent a transmission line.

Correct Answer: D. Better representation of distributed parameters. The T model accurately represents the distributed nature of transmission line parameters.

Correct Answer: C. Power input to the transmission line. Sending end power is the power input at the beginning of the transmission line.

Correct Answer: B. Corona loss. Corona loss occurs due to ionization of the air around high-voltage conductors.

Correct Answer: C. Aesthetic appeal and reduced environmental impact. Underground lines are less visually intrusive and have lower environmental impact.

Correct Answer: B. (Power output / Power input) × 100%. Efficiency is calculated as the ratio of power output to power input, expressed as a percentage.

Correct Answer: A. A simplified representation of a complex electrical network. Equivalent circuits model the complex behavior of transmission lines using simpler components.

Correct Answer: C. Transformer efficiency. Transmission line losses typically consider resistance, corona discharge, and the skin effect, but not transformer efficiency.

Correct Answer: B. High conductivity and lower cost compared to copper. Aluminium provides good conductivity at a lower cost, making it a popular choice for conductors.

Correct Answer: C. To protect against lightning strikes. Ground wires protect the line from lightning by providing a path to ground.

Correct Answer: A. The ratio of real power to apparent power. Power factor measures how effectively the current is being converted into useful work output.

Correct Answer: D. Skin effect loss. Skin effect loss increases with the frequency of the current, causing more current to flow near the surface of the conductor.

Correct Answer: C. It influences the power transfer capability and reflection coefficients. Characteristic impedance is crucial for matching and minimizing reflections in transmission lines.

Correct Answer: B. Increasing the conductor diameter. Larger conductor diameters reduce resistance and, consequently, power losses.

Correct Answer: A. Radial. In a radial distribution system, power flows in a single path from the substation to the consumers.

Correct Answer: C. Improved reliability and flexibility. A ring main system can supply power from multiple directions, enhancing reliability and flexibility.

Correct Answer: C. Looped. A looped distribution system has multiple interconnections, providing alternate paths for power flow.

Correct Answer: B. To decrease voltage levels. Step-down substations reduce the high transmission voltage to lower levels suitable for distribution.

Correct Answer: B. Busbar. Busbars represent the main points where incoming and outgoing circuits are connected in a single line diagram.

Correct Answer: A. Below 1 kV. Low voltage (LV) systems typically operate at voltages below 1 kV.

Correct Answer: B. Between 1 kV and 33 kV. Medium voltage (MV) systems typically operate between 1 kV and 33 kV.

Correct Answer: C. Between 33 kV and 132 kV. High voltage (HV) systems typically operate between 33 kV and 132 kV.

Correct Answer: B. Single power path with no loops. A radial feeder has a single path for power to flow, without any loops.

Correct Answer: B. Because of impedance in the conductors. Voltage drops occur due to the impedance of the conductors in the feeder.

Correct Answer: B. To protect the circuit from overcurrent. Fuses protect electrical circuits by breaking the connection when excessive current flows through them.

Correct Answer: C. Recloser. Reclosers automatically restore power after temporary faults by resetting themselves.

Correct Answer: C. To protect the system by interrupting fault currents. Circuit breakers interrupt fault currents to protect the electrical system from damage.

Correct Answer: C. Feeder substation. Feeder substations distribute power directly to consumers through feeders.

Correct Answer: B. Impedance of the conductors. Voltage drops in a radial feeder are primarily due to the impedance of the conductors.

Correct Answer: C. Increased reliability and fault tolerance. Looped feeders provide alternative paths for power flow, improving reliability and fault tolerance.

Correct Answer: B. Low Voltage. LV stands for Low Voltage, typically referring to voltages below 1 kV.

Correct Answer: D. Surge arrester. Surge arresters protect distribution systems from lightning strikes and high voltage surges.

Correct Answer: B. Ring main. In a ring main system, consumers can be fed from two different directions, enhancing reliability.

Correct Answer: B. To distribute power from substations to consumers. Feeders distribute electrical power from substations to the end consumers.

Correct Answer: B. Circuit breaker. Circuit breakers isolate faulty sections to prevent system damage and outages.

Correct Answer: C. Step-down substation. Step-down substations lower high transmission voltages to levels suitable for distribution.

Correct Answer: B. They automatically restore power after temporary faults. Reclosers are useful in rural systems to automatically restore power after temporary faults, reducing downtime.

Correct Answer: C. Reduced power losses. Medium voltage reduces power losses compared to low voltage distribution.

Correct Answer: B. Simplified representation of major electrical components. Single line diagrams provide a simplified view of the main electrical components and their connections.

Correct Answer: B. To prevent electrical faults and equipment damage. Protection systems are crucial for preventing faults and minimizing damage to electrical equipment.

Correct Answer: C. L-L-L fault. A three-phase fault (L-L-L) involves short-circuiting all three phases together.

Correct Answer: C. L-G fault. An L-G (line-to-ground) fault is an example of an unsymmetrical fault.

Correct Answer: C. Overcurrent relay. Overcurrent relays detect and respond to excessive current flow in the power system.

Correct Answer: D. Overload relay. Overload relays protect equipment from damage due to prolonged overcurrent conditions.

Correct Answer: B. Differential relay. Differential relays compare the current at two points to detect faults within a protected zone.

Correct Answer: B. To detect faults based on impedance. Distance relays protect lines by measuring impedance to identify the location of faults.

Correct Answer: A. By using high-pressure air to extinguish the arc. Air blast circuit breakers use high-pressure air to blow out the arc during a fault.

Correct Answer: D. SF6 circuit breaker. SF6 circuit breakers use sulfur hexafluoride gas for insulation and arc suppression.

Correct Answer: C. They can interrupt high fault currents without being destroyed. HRC fuses are designed to handle high fault currents and remain intact.

Correct Answer: B. L-L fault. A line-to-line (L-L) fault involves a short circuit between two phases.

Correct Answer: C. Fuse. Fuses are commonly used in low voltage applications to protect against short circuits and overloads.

Correct Answer: B. Time-delayed response to overcurrent conditions. Overload relays have a time delay to respond to overcurrent conditions, allowing for temporary overloads.

Correct Answer: C. Vacuum circuit breaker. Vacuum circuit breakers use a vacuum to extinguish the arc.

Correct Answer: B. Differential relay. Differential relays protect transformers by detecting differences in current between the input and output.

Correct Answer: A. HRC fuse. High Rupturing Capacity (HRC) fuses are used to protect electric motors from high fault currents.

Correct Answer: A. To detect and respond to low voltage conditions. Under-voltage relays detect low voltage situations and initiate corrective actions.

Correct Answer: C. By using sulfur hexafluoride gas. SF6 circuit breakers use sulfur hexafluoride gas to extinguish arcs.

Correct Answer: C. L-L-L fault. A three-phase fault (L-L-L) is the most severe type of fault in a power system.

Correct Answer: C. Recloser. Reclosers can automatically reset themselves after clearing a temporary fault.

Correct Answer: C. Limited breaking capacity. Low-voltage (L) fuses have a limited breaking capacity and are used in low voltage applications.

Correct Answer: C. Distance relay. Distance relays operate based on the impedance, which involves comparing the phase angle between voltage and current.

Correct Answer: B. To automatically restore power after a temporary fault. Reclosers restore power automatically after clearing temporary faults.

Correct Answer: B. By comparing input and output currents to detect internal faults. Differential relays protect equipment by detecting differences in input and output currents.

Correct Answer: B. Oil circuit breaker. Oil circuit breakers use oil to extinguish arcs during fault conditions.

Correct Answer: C. Air insulated and gas insulated. Substations are primarily classified into air insulated and gas insulated types based on their insulation.

Correct Answer: C. Busbar. Busbars are used in substations to connect multiple incoming and outgoing circuits.

Correct Answer: C. To step up or step down voltage levels. Transformers in substations are used to change the voltage levels as required.

Correct Answer: B. Circuit breaker. Circuit breakers are used to interrupt current flow during faults in substations.

Correct Answer: C. To safely isolate sections of the circuit for maintenance. Isolators are used to disconnect parts of the circuit for safe maintenance operations.

Correct Answer: C. Distribution substation. Distribution substations transfer electricity from high-voltage transmission lines to lower-voltage distribution lines.

Correct Answer: C. To connect different parts of the transmission network. Transmission substations connect different parts of the transmission network.

Correct Answer: C. To ensure safety by dissipating fault currents. Grounding dissipates fault currents to the earth, ensuring safety in substations.

Correct Answer: B. Non-isolated grounding. Non-isolated grounding involves a direct connection to the earth without any intentional isolation.

Correct Answer: B. Smaller footprint and higher reliability. Gas insulated substations (GIS) have a smaller footprint and offer higher reliability compared to air insulated substations (AIS).

Correct Answer: D. Substation general layout. A substation general layout includes components like transformers, circuit breakers, and busbars.

Correct Answer: C. Transmission substation. Transmission substations adjust voltage levels between long-distance transmission lines and local distribution networks.

Correct Answer: C. Intentional isolation from other grounding systems. Isolated grounding involves intentional isolation from other grounding systems to prevent interference.

Correct Answer: C. To interrupt current flow during faults. Circuit breakers in substations interrupt current flow during faults to protect the system.

Correct Answer: C. HVDC converter substation. HVDC converter substations handle the conversion of high-voltage AC power to high-voltage DC power for long-distance transmission.

Correct Answer: B. To maintain constant voltage levels. Automatic Voltage Regulation (AVR) ensures that the voltage levels in the power system remain constant.

Correct Answer: D. Automatic Generation Control (AGC). Automatic Generation Control (AGC) maintains the balance between power generation and load demand.

Correct Answer: C. Frequency and load balance. Load Frequency Control (LFC) regulates the frequency and load balance in a power system.

Correct Answer: C. Supervisory Control and Data Acquisition (SCADA). SCADA systems use real-time data to monitor and control power systems.

Correct Answer: C. By maintaining steady voltage levels. AVR improves power system stability by ensuring voltage levels remain steady.

Correct Answer: C. Generators. Generators are essential in AGC for regulating frequency by adjusting their output.

Correct Answer: C. Synchronized frequency across areas. LFC helps maintain synchronized frequency across interconnected power systems.

Correct Answer: C. Supervisory Control and Data Acquisition (SCADA). SCADA systems provide operators with remote control and monitoring capabilities.

Correct Answer: B. To provide real-time monitoring and control. SCADA systems play a crucial role in providing real-time monitoring and control of power systems.

Correct Answer: D. Automatic Generation Control (AGC). AGC ensures that the total power generation matches the total load demand plus losses.