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HVDC is used for long submarine cables where AC cannot be used because of cable capacitance. The integrated Dynamic Cable Rating (DCR)/Real Time Thermal Rating (RTTR) solution makes it possible to run the network to its maximum. Because of this phenomenon, conductors must be periodically transposed along the line so that each phase sees equal time in each relative position to balance out the mutual inductance seen by all three phases. Voltage-based regulation is complex to use in mesh networks, since the individual components and setpoints would need to be reconfigured every time a new generator is added to the mesh. When electrical energy is transmitted over very long distances, the power lost in AC transmission becomes appreciable and it is less expensive to use direct current instead. High-voltage power transmission allows for lesser resistive losses over long distances. Single-wire earth return is also used for HVDC over submarine power cables.

Single-wire earth return (SWER) or single-wire ground return is a single-wire transmission line for supplying single-phase electrical power to remote areas at low cost. For transmission systems with low power factor, losses are higher than for systems with high power factor. Lowering line sag at high temperatures can prevent wildfires from starting when power lines touch dry vegetation. Traditional power lines use a steel core surrounded by aluminum strands (Aluminium-conductor steel-reinforced cable). This was invented in 1930, but not available outside military use until after World War 2 during which a telegraph cable using it was laid across the English Channel to support troops following D-Day. Merchant transmission projects in the United States include the Cross Sound Cable from Shoreham, New York to New Haven, Connecticut, Neptune RTS Transmission Line from Sayreville, New Jersey, to New Bridge, New York, and Path 15 in California. A 2024 report found the United States behind countries like Belgium and the Netherlands in adoption of this technique to accommodate electrification and renewable energy.

The rate of transmission expansion needs to double to support ongoing electrification and reach emission reduction targets. A reconductoring project in southeastern Texas upgraded 240 miles of transmission lines at a cost of $900,000 per mile, versus a 3,600-mile greenfield project that averaged $1.9 million per mile. Current flowing through transmission lines induces a magnetic field that surrounds the lines of each phase and affects the inductance of the surrounding conductors of other phases. Applications for a new transmission line typically include an analysis of electric and magnetic field levels at the edge of rights-of-way. The field strength was 1.6 kV/m, and became the interim maximum strength standard for new transmission lines in New York State. No adverse health effects have been substantiated for people not living close to power lines. Submarine connections up to 600 kilometres (370 mi) in length have been deployed. Series resistance and shunt conductance are considered to be distributed parameters, such that each differential length of the line has a corresponding differential series impedance and shunt admittance. Spiraling, which refers to the way stranded conductors spiral about the center, also contributes to increases in conductor resistance.

Sony has developed a biological battery that generates electricity from sugar in a way that is similar to the processes observed in living organisms. The transmission system operator is Red Eléctrica de España (REE) and the wholesale electricity market operator is Operador del Mercado Ibérico de Energía - Polo Español, S.A. Spain was the first country to establish a regional transmission organization. The terminal characteristics of the transmission line are the voltage and current at the sending (S) and receiving (R) ends. For this approximation, the voltage and current are identical at the sending and receiving ends. Voltage is stepped down before the current is sent to smaller substations. Loops can be normally closed, where loss of one circuit should result in no interruption, or normally open where substations can switch to a backup supply. Corona and resistive losses can be estimated using a mathematical model. It has been estimated that waste would be halved using this method, since the necessary refrigeration equipment would consume about half the power saved by the elimination of resistive losses. Rolling blackouts (also called load shedding) are intentionally engineered electrical power outages, what is electric cable used to distribute insufficient power to various loads in turn. Additional projects are in development or have been proposed throughout the United States, including the Lake Erie Connector, an underwater transmission line proposed by ITC Holdings Corp., connecting Ontario to load serving entities in the PJM Interconnection region.