Power Transmission

Electric power, because it can be efficiently and economically transported over long distances is the basis for modern power transmission and distribution. More specifically, power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation.

The history of electric power transmission did not begin until the late 19^th century. The earliest electric generation was with direct current (DC), which could not easily be increased in voltage for long-distance transmission. Different voltages – requiring separate generators – were required for streetlights, electric motors in factories, streetcars, and lights in homes. In addition, generators had to be relatively near their loads (a mile or less for low voltage devices). Electric companies ran different lines for the different classes of loads their inventions required

The development of alternating current or AC, electric power improved the reliability, economy, and safety of long-distance power transmission. Electrical energy distributed as alternating current may be increased or decreased with a transformer. This allows the power to be transmitted through power lines efficiently at high voltage, which reduces the energy lost as heat due to resistance of the wire, and transformed to a lower and safer, voltage for use.

There are hundreds of power plants located throughout North America that generate electricity. These plants are connected to transformers that step up the voltage of that electricity so it can be transmitted. These are connected by high-voltage overhead power transmission lines that carry the electricity long distances across the country. Underground power transmission by high-voltage cables is used in dense urban areas and in high-voltage direct-current underwater connections. In the United States, the entire electricity grid consists of hundreds of thousands of miles of high-voltage power lines and millions of miles of low-voltage power lines with distribution transformers that connect thousands of power plants to hundreds of millions of electricity customers all across the country.

The most common type of alternating electric power transmission, and thus the most common for generation and distribution, is 3 phase power.  Typical voltages for long-distance power transmission are in the range of 155,000 to 765,000 volts in order to reduce line losses. A typical maximum transmission distance is about 300 miles (483 km).

After the electricity has traveled a long distance, it is distributed to a neighborhood substation transformer, a specialized piece of power transmission equipment. This steps down the electrical voltage and transmits the energy through smaller, lower voltage lines. The energy is then distributed to poles which step down the energy once again and eventually send a safe amount of electricity into your home.

The electric power is then put to work in lighting, telephones, stoves and ovens, refrigeration, heat ventilation and air conditioning, hot water heaters, washers and dryers, TVs, computers, security systems, internet, LED lighting, etc.  With the growth of technology, electric power transmission and storage systems have become interconnected by the development of regional and national electrical power grids.