As such, these substations act as the interference between transmission lines and subtransmission lines. Step down SubstationĪs mentioned earlier, step down substations decrease transmission line voltages down to subtransmission line levels, typically between 26kV and 69kV. A step up substation is shown in Figure 5.įigure 5: A step-up substation. Switching circuits are used to route power through the substation, allowing the operation to continue in the event of transformer failure or during required maintenance. The power required for the substation to operate is drawn from the substations’ input feed.
Transmission lines generator#
Step up substations contain high voltage transformers that boost the generator output voltage to a value between 115kV and 765kV, and provide power outputs in the thousands of kilovolt-amperes (kVA) and higher. Step-up SubstationĪn electrical power generating plans typically generate voltages between 2.3kV and 33kV. A Distribution substation connects subtransmission lines to the distribution lines that serve local utility customers. A Step-down Substation is connected between transmission lines and subtransmission or distribution lines.
A Step-up Substation connects the power generating plant to the transmission lines. There are several types of electrical substations, each connecting two or more elements in the power transmission system.
These transformers reduce the transmitted voltage to the levels shown in Figure 1. Note that power losses up to 5 percent of the total power transmitted along a transmission line are generally considered acceptable (though not desirable).Ĭorona Discharge: Power loss along transmission lines that occur when high voltages ionize the air surrounding the power lines.Īs shown in Figure 1, overhead transmission lines end at substation step down transformers. There is a limit, however, to how high the voltage can be increased to reduce I 2R losses.Īt extremely high voltage-more than 2000kV between conductor and ground- Corona Discharge losses so high that they can offset the reduction in I 2R losses. In this case, the power line loss is decreased by a factor of 100 2 = 10,000. You may recall that the power dissipated by a resistance can be found as:Ī step up transformer actually performs two functions:įor example, a generator step-up transformer that increases voltage by a factor of 100 decreases current by the same value. Two high voltage transmission line towers are shown in Figure 3. Transmission line towers like those represented in Figure 1 are identified by their size and shape.
Note that the voltages in the 365 kV to 765 kV range are sufficient to require extra transmission line precautions, such as increasing the distance between the lines to prevent Flashover (electrical arcing from one line to another). The most common transmission line voltages are 115kV, 138kV, 161kV, 230kV, 345kV, 500kV, and 765kV. Transmission lines begin at the step-up transformer and end at the substation step down transformer, and typically span a distance of 300 miles or less.įigure 1: An overhead transmission and distribution system.įigure 2 will give you a good idea of the complex network of transmission lines that supplies power across the continental United States.įigure 2: The U. A basic transmission line system is represented in Figure 1. Overhead transmission lines are used to transmit electrical energy in the form of three phases (3 AC.
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