Peak load times vary by region largely due to the industry High Resolution Textures mix. The New York Times reported that American hackers from the United States Cyber Command planted malware potentially capable of disrupting the Russian electrical grid. Submarine HVDC systems are often used to interconnect the electricity grids of islands, for example, between Great Britain and continental Europe, between Great Britain and Ireland, between Tasmania and the Australian mainland, between the North and South Islands of New Zealand, between New Jersey and New York City, and between New Jersey and Long Island. The opinion also limited the voltage of new transmission lines built in New York to 345 kV. The 287.5 kV (Hoover Dam to Los Angeles line, via Victorville) and 345 kV (Arizona Public Service (APS) line) are local standards, both of which were implemented before 500 kV became practical. Although advanced lines can cost 2-4x more than steel, total reconductoring costs are less than half of a new line, given savings in time, land acquisition, permitting, and construction. For a long transmission line, these lower losses (and reduced construction cost of a DC line) can offset the cost of the required converter stations at each end.

The power transmitted by an AC line increases as the phase angle between source end voltage and destination ends increases, but too large a phase angle allows the systems at either end to fall out of step. SIL, the voltage drops from sending end and the line consumes VARs. For this approximation, the voltage and current are identical at the sending and receiving ends. The terminal characteristics of the transmission line are the voltage and current at the sending (S) and receiving (R) ends. Voltage and frequency can be used as signaling mechanisms to balance the loads. This efficiency delivers a larger proportion of the generated power to the loads. Such facilities are nuclear, coal or hydroelectric, while other energy sources such as concentrated solar thermal and geothermal power have the potential to provide firm power. 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. Rolling blackouts (also called load shedding) are intentionally engineered electrical power outages, used to distribute insufficient power to various loads in turn.

Blackouts occur when the grid fails completely. This is an everyday occurrence in AC systems, but one that can become disrupted when AC system components fail and place unexpected loads on the grid. 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. Factors that affect resistance and thus loss include temperature, spiraling, and the skin effect. The lossless line approximation is the least accurate; it is typically used on short lines where the inductance is much greater than the resistance. If too much current is drawn, conductors may sag too close to the ground, or conductors and equipment may overheat. Voltage is stepped down before the current is sent to smaller substations. For a given amount of power, a higher voltage reduces the current and thus the resistive losses. 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. The conductors' mutual inductance is partially dependent on the physical orientation of the lines with respect to each other.

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. The heating of short line conductors due to line losses sets a thermal limit. Adding transmission lines is difficult due to cost, permit intervals, and local opposition. Hydro and wind sources cannot be moved closer to big cities, and solar costs are lowest in remote areas where local power needs are nominal. Connection costs can determine whether any particular renewable alternative is economically realistic. In any AC line, conductor inductance and capacitance can be significant. The mutual inductance seen by a conductor of the phase in the middle of the other two phases is different from the inductance seen on the top/bottom. The Western Interconnection has two primary interchange voltages: 500 kV AC at 60 Hz, and ±500 kV (1,000 kV net) DC from North to South (Columbia River to Southern California) and Northeast to Southwest (Utah to Southern California). One example of a long DC transmission line is the Pacific DC Intertie located in the Western United States.

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