In our last post, I briefly explored how electricity is produced and delivered over the transmission and distribution systems to customers.
In this post I want to review the three physical “laws” which govern the transmission and distribution of electricity. As with a number of topics in these early posts, this information will become useful once we begin to discuss the policy issues being discussed today.
First, electricity travels at the speed of light. This means that generating resources can be located over a wide region and still meet “local” demand. For example, the electricity that supplies mid-Atlantic customers can come from local generating plants or from generation resources in the southeast or Midwest. Generation planners refer to an interconnected generation/transmission supply region as a “power pool.” The “power pool” which serves the mid-Atlantic states includes states as far west as Illinois.
Second, electricity generated at a power plant follows the “path of least resistance” and cannot be directed over specific power lines to specific customers. So, when a power plant injects power into the grid, we do not know exactly where that power goes, we just know that it goes onto the grid and is delivered to customers. The path over which electricity flows from a specific generating station to its ultimate use – i.e. the lights in your house – cannot be predetermined.
Third, the amount of electricity used at any point of time (known as the “load”) must be matched exactly by the amount generated (known as supply). There is very little tolerance in an electric system for “imbalances” between supply and load.
Any significant supply-load imbalances (i.e. either too much or not enough electricity being generated at a moment in time) must be corrected very quickly. If this correction does not occur rapidly (remember the first law – electricity travels at the speed of light), voltage reductions or black-outs may occur as protective devices at generating stations will shut the stations down to protect critical equipment from power surges.
The imbalances occur for large quantities of power – i.e. when a major generating plant or high voltage transmission line suddenly goes out of service. Generating equipment is designed to adjust automatically to the continual smaller variations in demand that result from motors and lights being turned on and off or from a tree limb taking down a local distribution line
In the next post I’ll discuss who is responsible for supplying your electricity.