Explanation: Electric power transmission is the bulk movement of electrical energy from generation sites to substations using high voltages, whereas distribution delivers electricity at lower voltages to end consumers.

Explanation: A transmission network comprises high-voltage lines for bulk energy transfer, distinct from the low-voltage lines used for local power distribution.

Explanation: The primary function of electric power transmission is the bulk transfer of electrical energy from generation facilities to the network of substations that feed into distribution systems.

Explanation: Transmission involves the bulk movement of electricity at high voltages over long distances from generation sites to substations. Distribution then takes over, stepping down the voltage for local delivery to end consumers.

Explanation: High voltages are employed in transmission lines to *decrease* the current for a given power level (P=VI). This reduction in current minimizes resistive energy losses (I²R) over long distances.

Explanation: High voltages are used to reduce current, thereby minimizing resistive losses (I²R). This allows for the use of *smaller* conductors for a given power transmission capacity, not larger ones.

Explanation: Kelvin's law seeks an optimal balance between the cost of energy losses and the capital cost of the conductor, suggesting a size that minimizes the sum of these annual costs, not necessarily the smallest possible size.

Explanation: Reactive power in AC circuits does not transmit useful energy to the load; rather, it is associated with the oscillating energy storage in inductive and capacitive components. While it does not contribute to net power transfer, it does cause additional current flow, leading to increased resistive heating (I²R losses) and reduced system efficiency.

Explanation: Transmitting at high voltages reduces the current required for a given power level (P=VI). Since energy loss is proportional to the square of the current (I²R), lower current drastically minimizes resistive losses over long transmission lines.

Explanation: Kelvin's law posits that the most economical conductor size for a transmission line is achieved when the sum of the annual cost of energy lost due to resistance and the annual capital charges associated with the conductor is minimized. This involves balancing material costs against operational energy losses.

Explanation: In AC transmission systems, the power factor is a measure of how effectively electrical power is being utilized. It represents the ratio of real power (doing work) to apparent power (total power delivered), with a lower power factor indicating a higher proportion of reactive power and thus lower efficiency.

Explanation: Transformers are crucial for adjusting voltage levels. They are used to *step up* voltage for efficient long-distance transmission and subsequently *step down* voltage for safe local distribution.

Explanation: Underground power transmission systems are significantly more expensive to install compared to overhead lines, although they offer advantages in terms of aesthetics and reduced susceptibility to weather.

Explanation: Transmission substations primarily function to *decrease* the voltage from high transmission levels to lower subtransmission or distribution levels, and to reroute power. Voltage is increased at generation points, not substations.

Explanation: Capacitor banks and reactors are key components used in power systems to inject or absorb reactive power, thereby managing voltage levels, improving the power factor, and enhancing overall transmission efficiency.

Explanation: Conductor transposition involves periodically swapping the positions of the three phases along a transmission line. This process ensures that each phase conductor experiences approximately equal inductance and capacitance, leading to balanced voltage and current distribution.

Explanation: Subtransmission operates at voltages lower than main transmission lines. It serves to step down power from the high voltages of the main transmission system to levels suitable for distribution substations.

Explanation: The thermal limit, which dictates the maximum current a conductor can carry without excessive sag or damage, is a critical factor limiting the capacity of a transmission line.

Explanation: Reconductoring refers to replacing existing transmission lines with higher-capacity ones in their original locations, rather than building entirely new lines elsewhere.

Explanation: Protective relays rely on robust communication systems to detect power system faults and coordinate actions, such as de-energizing faulted equipment, thereby ensuring grid stability and safety.

Explanation: Dedicated communication systems like microwaves and optical fibers are generally considered *more* reliable and controllable for critical transmission projects than common carrier services.

Explanation: Power-line communication (PLC) utilizes the power lines themselves to carry data signals, rather than using radio waves transmitted separately.

Explanation: Transmission costs constitute a relatively small fraction of a consumer's total electricity bill. For instance, in the UK, transmission costs are approximately 0.2 pence per kWh, significantly less than the total delivered price.

Explanation: Voltages commonly used for subtransmission in North America include 69 kV, 115 kV, and 138 kV. These voltages fall between the higher voltages used for main transmission and the lower voltages used for final distribution.

Explanation: Reconductoring is a process that involves replacing existing transmission conductors with new ones that have higher capacity, typically within the same existing infrastructure. This is often more cost-effective than constructing entirely new lines and is a common method for upgrading transmission capacity.

Explanation: While common carrier lines might be used in some contexts, dedicated communication systems (like fiber optics or microwaves) are often preferred for protective relaying due to their higher reliability and control, essential for rapid fault detection and system protection.

Explanation: Transformers are essential for adjusting voltage levels. They step up voltage to high levels for efficient long-distance transmission and then step it down to safer, usable levels for distribution to consumers.

Explanation: Underground transmission cables are less exposed to environmental factors such as storms, ice, and wind, making them less prone to weather-related disruptions compared to overhead lines.

Explanation: Transmission substations are critical nodes that reduce the high voltage of transmission lines to lower levels suitable for distribution networks and also serve to switch and reroute power flows.

Explanation: The frequency of the alternating current is a fundamental parameter of the system and does not directly limit the *capacity* of a transmission line in the same way as thermal limits, voltage drop, or system stability considerations.

Explanation: Reconductoring is a process that involves replacing existing transmission conductors with new ones that have higher capacity, typically within the same existing infrastructure.

Explanation: Protective relays are essential safety devices that continuously monitor electrical parameters, detect abnormal conditions or faults, and initiate rapid disconnection of faulted sections to protect equipment and maintain system stability.

Explanation: Dedicated communication systems such as microwaves and fiber optics are preferred for transmission projects because they provide superior reliability and control compared to common carrier services. This enhanced control is essential for the critical functions of fault detection and system management in power grids.

Explanation: While AC is predominant, High-Voltage Direct Current (HVDC) is also utilized for specific applications, such as long-distance transmission, submarine cables, and interconnecting asynchronous grids.

Explanation: HVDC is primarily employed for very long-distance transmission, submarine cables, and interconnecting asynchronous grids, where it offers superior efficiency compared to AC over such distances.

Explanation: Advanced conductors like ACCC (Aluminum Conductor Composite Core) utilize composite materials, such as carbon fiber, for their core instead of steel. This design allows them to operate at higher temperatures with reduced sag, thereby increasing transmission capacity and safety.

Explanation: HVDC technology is particularly well-suited for interconnecting AC grids operating at different frequencies (asynchronous) and for transmitting power over long submarine distances where AC's capacitive effects become prohibitive.

Explanation: Carbon fiber composite conductors are significantly lighter and stronger than traditional steel-reinforced aluminum conductors, allowing for greater transmission capacity and reduced sag.

Explanation: Superconducting cables offer the potential for virtually lossless power transmission. However, they require cryogenic cooling, typically using liquid nitrogen for high-temperature superconductors, which is a specialized refrigeration process, not standard refrigeration.

Explanation: Single-Wire Earth Return (SWER) systems utilize a single conductor wire and the earth itself as the return path for the electrical current, making it a distinct configuration from systems using two wires.

Explanation: While the Inga-Shaba line is noted for its significant length (1,700 km), the highest capacity transmission line mentioned is the Zhundong-Wannan HVDC line in China, rated at 12 GW.

Explanation: The North Sea Link, connecting Norway and the UK, is indeed cited as one of the longest submarine power cables, with a length of 720 km, alongside other notable examples like the NorNed cable.

Explanation: Advanced conductors like ACCC utilize composite cores, enabling them to withstand higher operating temperatures with reduced sag. This increased thermal capacity allows for higher current flow and thus greater transmission capacity.

Explanation: HVDC technology is particularly well-suited for interconnecting AC grids operating at different frequencies (asynchronous) and for transmitting power over long submarine distances where AC's capacitive effects become prohibitive.

Explanation: Superconducting cables, by eliminating electrical resistance, offer the significant potential for virtually lossless power transmission. This could dramatically improve efficiency and reduce energy waste, although the associated cooling costs are a consideration.

Explanation: Single-Wire Earth Return (SWER) is an economical method for transmitting electricity, particularly in rural areas, which utilizes a single conductor wire and the earth as the return path for the electrical current.

Explanation: The Inga-Shaba line in the Democratic Republic of Congo is identified as the longest power transmission line mentioned in the source material, spanning approximately 1,700 kilometers.

Explanation: Prior to AC transmission advancements, the inability to efficiently step up DC voltage for long-distance transmission necessitated locating generating plants close to their loads, leading to a model of distributed generation.

Explanation: William Stanley, Jr., working with George Westinghouse, developed a practical series AC transformer in 1885, which was instrumental in demonstrating a viable AC lighting system.

Explanation: The 1884 Turin exhibition demonstrated the first long-distance *AC* power transmission line, not DC.

Explanation: Both Nikola Tesla and Galileo Ferraris independently developed the concept of the induction motor operating on polyphase AC current in 1888.

Explanation: Rotary converters and motor-generators were primarily used to *integrate* older AC and DC systems with the developing universal AC grid, acting as interfaces rather than replacements for AC systems.

Explanation: The 1891 Frankfurt exhibition demonstrated the first use of *three-phase* AC for long-distance power transmission, not single-phase.

Explanation: The 1884 Turin exhibition featured the first long-distance AC transmission line, utilizing transformers to demonstrate the feasibility of transmitting AC power over extended distances.

Explanation: The 1891 Frankfurt exhibition was a pivotal event that demonstrated the first successful long-distance, three-phase AC power transmission system. It transmitted electricity over approximately 175 km from Lauffen am Neckar to Frankfurt, proving the viability of this technology.

Explanation: Before the advent of AC transmission, the primary limitation was the inability to efficiently step up DC voltage for long-distance transmission. This necessitated locating generating plants in close proximity to the loads they served.

Explanation: The Ferranti effect is characterized by a voltage *increase* at the receiving end of medium-length transmission lines, particularly under no-load or light-load conditions, due to the line's capacitance.

Explanation: The 'black box' model simplifies transmission line analysis by focusing solely on the terminal characteristics (input and output voltages/currents) without requiring detailed knowledge of the internal components.

Explanation: In the context of a lossless transmission line, the surge impedance (or characteristic impedance) is the ratio of voltage to current. When a line is terminated with its surge impedance, there are no reflections, and the voltage profile is uniform.

Explanation: The short line approximation, typically used for lines under 80 km, *includes* the series impedance (resistance and reactance) but *ignores* the line's capacitance and shunt conductance, simplifying the model.

Explanation: The medium line approximation is generally applied to transmission lines ranging from approximately 80 km to 250 km. For lines longer than 250 km, the long line model, which treats parameters as distributed, is more appropriate for accurate analysis.

Explanation: The long line model treats transmission line parameters (resistance, inductance, capacitance, and conductance) as *distributed* along the line, utilizing the Telegrapher's equations for analysis. Lumped elements are characteristic of the short line approximation.

Explanation: The Ferranti effect is characterized by a voltage *increase* at the receiving end of medium-length transmission lines, particularly under no-load or light-load conditions, due to the line's capacitance.

Explanation: The short line approximation is typically applied to transmission lines shorter than 80 km (50 miles). In this model, only the series impedance is considered, while the line's capacitance and shunt conductance are ignored, simplifying the calculations.

Explanation: A wide-area synchronous grid connects generators and consumers operating at the *same* frequency. Interconnecting grids with different frequencies requires specialized converters.

Explanation: Historically, transmission and distribution were often managed by the same entities. The separation into specialized companies largely occurred with the liberalization of electricity markets in the late 20th century.

Explanation: HVDC links act as asynchronous barriers, enabling them to disconnect parts of a network experiencing faults or instability, thereby preventing the propagation of cascading failures across the grid.

Explanation: Rolling blackouts, also known as load shedding, are *planned* and controlled power outages implemented during periods of insufficient generation capacity to prevent a complete system collapse. They are a deliberate measure to manage demand when supply is critically low.

Explanation: Electricity transmission is generally considered a natural monopoly and is typically regulated as such, often managed by independent Transmission System Operators (TSOs) or Regional Transmission Organizations (RTOs).

Explanation: FERC Order 888, issued in 1996, was a landmark regulation in the United States that mandated public utilities to offer open and non-discriminatory access to their transmission services, fostering competition in the wholesale electricity market.

Explanation: The prevailing scientific consensus indicates that electromagnetic radiation from power lines at typical exposure levels does not conclusively cause significant long-term health problems. While some studies have suggested correlations, these findings are often debated and lack definitive causal proof.

Explanation: A primary challenge for merchant transmission projects, which are developed outside traditional utility rate-making processes, is securing adequate revenue. This involves ensuring that all beneficiaries of the transmission service contribute fairly to its cost, often referred to as the 'toll'.

Explanation: The US federal government has identified the American power grid as being susceptible to cyber-warfare. This concern highlights the need for robust cybersecurity measures to protect critical infrastructure from digital threats.

Explanation: Interconnecting multiple generating plants allows for the dispatch of the most efficient units to meet demand, reduces capital costs through shared standby capacity, and enhances overall system reliability.

Explanation: Electricity transmission is generally considered a natural monopoly and is typically regulated as such, often managed by independent Transmission System Operators (TSOs) or Regional Transmission Organizations (RTOs) to ensure fair access and system reliability.

Explanation: The prevailing scientific consensus indicates that electromagnetic radiation from power lines at typical exposure levels does not conclusively cause significant long-term health problems. While some studies have suggested correlations, these findings are often debated and lack definitive causal proof.

Explanation: A primary challenge for merchant transmission projects, which are developed outside traditional utility rate-making processes, is securing adequate revenue. This involves ensuring that all beneficiaries of the transmission service contribute fairly to its cost, often referred to as the 'toll'.

Explanation: The US federal government has identified the American power grid as being susceptible to cyber-warfare. This concern highlights the need for robust cybersecurity measures to protect critical infrastructure from digital threats.

Explanation: HVDC links act as asynchronous barriers, enabling them to disconnect sections of the network experiencing faults or instability, thereby preventing the propagation of cascading failures across the grid and maintaining overall grid stability.