Here are some examples of the high voltage power lines that criss-cross North America.

The North American bulk power system has evolved into four major networks (power grids), which also include smaller groupings or power pools. The major networks consist of extra-high-voltage connections between individual utilities designed to permit the transfer of electrical energy from one part of the network to another. These transfers are restricted, on occasion, because of a lack of contractual arrangements or because of inadequate transmission capability.

The four networks are:

• the Eastern Interconnected System, consisting of the eastern two-thirds of the United States and Canada;
• the Western Interconnected System, consisting primarily of the Southwest and areas west of the Rocky Mountains;
• the Texas Interconnected System, consisting mainly of Texas; and
• the Quebec Interconnected System, consisting of Quebec, Newfoundland and Labrador.

Texas is not interconnected with the other networks (except by certain direct current lines). The other three networks have limited interconnections to each other. Both the Western and the Texas Interconnect are linked with different parts of Mexico. The Eastern and Western Interconnects are completely integrated with most of Canada or have links to the Quebec Province power grid. Virtually all U.S. utilities are interconnected with at least one other utility by these three major grids. The exceptions are in Alaska and Hawaii. The interconnected utilities within each power grid coordinate operations and buy and sell power among themselves.

Why aren’t they all connected?  Just like many other slowly evolving standards, by the time we realized it would be worthwhile to cover the entire continent with electrical service, too many different variations had been built.  The bottom line is that the ‘flavor’ the electricity in each system is not compatible with that of its neighbors.  For example, the electricity in Quebec is out of phase with that in the Eastern system – to convert from one to the other, you have to convert it first from alternating current (AC) into direct current (DC), and then back into alternating current in the proper phase.  In the process, you lose some of the power, making it an expensive conversion.

But converting electricity is an integral part of the entire transmission process.  Electricity is commonly generated at relatively low voltages, stepped-up to higher voltages for transmission, and then stepped-down as it nears its destination.  Let’s take a look at the lower voltage stages of the transmission process.