Transmission Lines

Transmission lines are often called power lines. The network of all these lines, linked by transformers down to successively lower voltages, is known as the grid. Internal connections of the grid lines must be changed frequently as demand varies across a country during the day, and different power stations close down through failure or the need for maintenance work. A transmission line is a connecting line between a source and a load.

EFFICIENCY

Long cables connecting communities to sources of electrical power are expensive. Efficient placing of electrical generating stations can reduce energy costs. The closer an electrical power station is to its place of use, the less energy that is wasted due to resistance on the lines. People concerned with the efficiency of the system recommend that thermal stations should be used within a 10 mile radius to reduce the wasted heat on the system. None of the power used in the Pennridge School District comes from within a 10 mile radius of the community.

Throughout South Eastern Pennsylvania there are not a lot of power plants. One power plant that we do have is located in Limerick in Montgomery County. There also are others nearby along the Delaware Bay and the Maryland shore. Power in our area also comes from Martins Creek, north of Easton, PA.

TRANSMISSION LINE USES

In addition to electrical power lines, there are also many other types of transmission lines. Transmission lines are used by amateur radio operators and for coaxial cable (cable TV). Another type of transmission lines is parallel wire lines.

CHOOSING TRANSMISSION LINE CABLES

The highest voltage lines use a group of three or four wires which gets some of the advantage of a single thick cable at much lower cost. The advantage of using the highest voltage possible is to keep the current as low as possible for a given power. Lower currents can be carried on thinner, and therefore cheaper, cables.

Transmission lines have many different voltages. Our school district contains 69,000 volt power lines. Each power line starts out at 500,000 volts, but it may change. as the power is transferred and transformed down, eventually the lines into the home are 240 volts.

SAFETY CONCERNS

For many years the U.S. government has been studying the dangers of living near transmission lines. Since the late 1960's and early 1970's, the studies have concluded that there are no dangers living near transmission lines.

LIGHTNING

There are two ways that transmission lines are grounded so that if lightning strikes they don't explode. The first way is that the highest point on pole (static wire) is positioned there so it will take a direct hit by the lightning instead of the conductors. The second way is each transmission has a ground wire and the same type of grounding grid applied to it. The type of soil in the ground depends what type of grid it is.

During a storm sometimes the power line goes down. There is usually one outage for every ten miles of line in ten years. Since the power lines have a chance of falling down, they need to build lines away from the highway. Power lines are usually built through rural areas to reduce the amount of exposure.