Three-phase systems can also be classified as single or double circuit systems. In a three-phase AC system, the wires carry three alternating currents that reach their peak values at different times. In alternating current (AC) transmission, the movement of the electric charge periodically reverses direction. Both have their advantages however, “three-phase alternating current” is the most common method used around the world. Power is transmitted through the wires via alternating current or direct current. As a result, high voltage towers are usually built to withstand so-called 50 or 100-year storms to ensure weather conditions don’t interrupt the flow of electric service. Transmission lines and towers have to withstand a range of environmental adversities, from high winds to freezing temperatures, where ice and snow deposits might otherwise cause a line or tower to collapse. With height requirements comes a complementary need for stability. Clearance requirements can vary widely, but a range of 60-150 feet is common. One of these key requirements involves how high off the ground the wires must be at their lowest point (known as “clearance”). The two primary answers are safety and reliability.īecause of the high voltages used, local, state and federal regulations place certain requirements on how the transmission lines can be built, primarily in the interest of safety. A common question asked about overhead wires, particularly during the planning process, is why such large steel towers are needed.
While electricity can sometimes be transmitted underground, “bulk” transmission systems often involve the use of overhead wires. Thus today, as energy travels hundreds or thousands of miles from where it is generated, high voltage lines of 230, 500 or 765 kilovolts ensure electricity is delivered quickly and with minimal energy loss. The higher the voltage, the better the system is able to overcome resistance and minimize losses. The solution to the resistance problem is to increase the voltage (or the “pressure”) at which electricity is pushed through the wires. Not a big deal for very short distances but the longer the wire, the greater the resistance and the greater the losses.
Wires create resistance to the flow of energy and that resistance creates small losses on the amount of energy being transmitted. Electricity has to be transmitted through wires. Transmission lines were the only way to get the power to where it was needed.Ĭonnecting remote generation plants with customers also came with a small problem. Newer, bigger power plants came on line, but were far away from their load centers.
The need for bulk transmission came about as demand for electricity grew and small power plants that could only serve their local area became inadequate. The transmission system, which delivers electricity to you at the astonishing speed of 186,000 miles per hour (almost the speed of light) is what makes this possible.Īs presented in Understanding Transmission, the electric system involves generation, transmission and distribution. What this means is electricity must be generated and provided at the very moment it is needed. Something many people are surprised to learn is that electricity, by its very nature, cannot be stored – at least not economically in any appreciable quantities (beyond what you find in a battery).
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