Electrical Energy Transport

Pipelines transmit a large amount of energy, but electric power lines transmit a similar amount. To compare these two types of transmission techniques it will be useful to review some of the characteristics of the electric power transmission system.

Electrical systems share some of the characteristics of a pipeline distribution system. Electricity is produced and fed into the distribution system at central locations. It is transported to users over a distribution network. The electric distribution network is made of copper and aluminum wires rather than the pipeline's iron, steel or plastic pipes. The wires fan out from central and substation distribution centers to serve individual customers. At the point of generation, the voltage, equivalent to the pressure in a pipeline, is very high. The high voltage must be handled with great care to prevent arching. As the wires divide and subdivide on their way to the customer the voltage is lower and lower. As the voltage drops the danger from arcing becomes less. In virtually all parts of the world electric power lines can be seen distributing energy. Despite its wide use, electricity is a mediocre method of transmitting energy.

A major problem is power loss during transmission. Resistance in the transmission wires turns a portion of the electrical energy into heat. This heat is lost to the surroundings and performs no useful task. The amount of heat produced is a function of the voltage used on the transmission line, its length and the diameter of the wire. Very little energy is lost from short, fat wires operating at very high voltage. Short wires do not go anywhere, and fat wires are expensive, hard to string and difficult to support. These factors lead to electrical transmission systems made up of thin wires operating at the highest possible voltage. 156

The higher the voltage the more difficult it is to insulate the voltage from the surroundings and the more difficult it is to switch the power off and on. High voltage can create electric arcs. The lengths of these arcs depend on the shape of the electrodes, temperature, humidity, atmosphere circulation, and the presence of ionizing radiation. At room temperature, normal pressure and 50% humidity, a 2.5-centimeter spark will form between two sharp points at 12,000 volts. At 50,000 volts, the spark is 13 centimeters long and at 100,000 volts, it can span nearly 40 centimeters. To achieve low loss, crosscountry lines are operated at more than 300,000 volts. Local distribution lines are operated at more than 10,000 volts. Insulators used to handle these high voltages must be large and of high quality to prevent arcing to the support structure. The high voltage wires also must be prevented from coming close to any grounded conductor or, at a minimum, power will be lost. In the worst case, arcs will initiate fire and destruction.

In the early days of electric power, Thomas A. Edison wanted to use direct current. He found it required very thick wires to transmit energy with low loss. Raising the voltage to decrease these losses made the design of the generator difficult and compelled the user to handle very high voltages, voltages so high the potential for arcs, fires and hazards were extreme. It is difficult to convert direct current from low to high voltage for transmission and back to low voltages for safe use. Because of these shortcomings Edison's direct current transmission lost out to Dr. Steinmetz's alternating current. The electric current voltage is reduced by transformers before local distribution. Figure 4.3 shows an electrical distribution point in North East Ohio. It is not very decorative and in this case, trees were

156 Barthold, L. O. and Pfeiffer, H. G., "High Voltage Transmission", Scientific American, Vol. 210, No. 5, May 1964, Page 38

planted to hide the transformers. Of course, in a few years the trees will be trimmed to prevent their contact with the high voltage wires.

Figure 4.3 Electrical Distribution Point

High voltage Wires with Transformers Feeding Local Wires

Figure 4.3 Electrical Distribution Point

High voltage Wires with Transformers Feeding Local Wires

With alternating current, it is possible to use a transformer to step the voltage up or down. This permits the generator to operate at its optimum voltage. A transformer is used to step the voltage up to a high value for relatively low loss transmission on thin lines. Near the user, a second transformer reduces the voltage. The voltage from this transformer is safe and easy to handle. On the low voltage, user side of the third transformer the wire size is increased to reduce losses. This is acceptable because of the relatively short run from the transformer to the user. This combination of optimum generator operation, step-up conversion to high voltage for low loss transmission and voltage step-down conversion for safe use by the customer has provided the basis for the electric system worldwide.

Transformers are remarkably efficient, ranging from 88% to 96%. Few things have efficiency this high. Despite their high efficiency, every time the voltage is converted, 4% to 12% of the energy is lost in the transformers as heat. Depending directly on the distance between the generator and the customers, more power is converted to heat in the transmission lines. The power converted to heat is lost and reduces the efficiency of the energy distribution system. 157

When transmitted over long distances alternating current is subject to a loss other than resistance. Alternating current used in the United States cycles at a rate of 60 times per second. The 60-cycle current can generate 60 cycle radio waves. This can be observed as the buzz heard on a car radio when driving near high voltage power lines. Like electrical resistance, this radiation results in a loss of power. The amount of power radiated is affected by the condition of the lines and their length. The wavelength of a 60-cycle radio wave is about 5000 kilometers. As the length of a transmission line approaches one fourth of a wavelength (1250 kilometers), more and more power is lost by radiation. When the line length reaches 1250 kilometers, more than half of the power input is radiated as

157 Coltman, John W., "The Transformer", Scientific American, Vol. 258, No. 1, January 1988, Page 86

essentially useless 60 cycle radio waves. The radiation affect places limits on the distance 60-cycle alternating current can be transmitted without severe loss

Commercial systems for conversion of high voltage alternating current to high voltage direct current are in use today. These systems allow the transport of electric power distances over long distances, but the equipment for conversion has internal resistance and conversion losses and it is very expensive. High voltage direct current systems are used only in locations where the input power cost is quite low and the source far from the customers. This combination is most often found with hydroelectric power generation facilities located at sites remote from large cities. For example, In the United States a direct current line carries power from the waterpower projects on the Columbia River, in Washington State, to San Francisco. These special circumstances demonstrate high voltage direct current transmission can be used successfully. However, ultra high voltage direct current transmission is little used in most power distribution systems.

In a large system, power lost in transmission is dependent on factors such as the number of transformers, the length of the transmission lines, the size of the wires, the type and number of customers and the peak voltage used. The very best systems deliver less than 80% of their generator output to the customer and many deliver much less. 158

When the efficiency of the transport of energy as a chemical fuel is compared to the efficiency of electric energy transport, one can wonder why electricity is used at all. It survives and grows because of the low cost and simplicity of the end-use electrical conversion devices. Today's electric lights may use more energy than gaslights, but they are far more convenient, can be controlled with great ease and present little fire hazard. Small electric motors incorporated in home appliances and manufacturing equipment are extremely convenient and simple to use. In applications where large amounts of energy are used, such as home heating and cooking, gas is more cost effective and is often selected for this purpose in preference to electricity when both are available.

Small motor driven appliances could be operated with little gas burning internal combustion engines at higher energy efficiency, but enormously reduced convenience, flexibility, and reliability. The electronic gadgets in the home: TV, video recorders, radio, stereo sound systems and microwave ovens, all require electricity for operation. To supply these devices with energy as gas or oil would not only require engines, but generators and local wires as well. Because of the convenience of electric devices the relatively less efficient electric power distribution systems will, in the near term, remain a useful method of transporting energy. 159

For all its convenience, electricity has one colossal shortcoming as an energy-handling medium. Electricity cannot be stored. At all times, the power plant operators are adjusting the output of the generators to match the needs of the users. This can create difficulties if the user changes his needs at a rapid rate. To account for these changes most systems have a hierarchy of generating capability. First are the base load generators. These consist of large coal fired or nuclear generators operated at a constant output power level. These generators produce electric power at the lowest cost, but require hours to start (ramp up) and to shut down. The next level of generators consists of intermediate size units capable of more rapid ramp up and down. The intermediate units are fueled with coal or the very cheapest low-grade oil. The final level is made up of peaking units that can start from cold to full power in a matter of minutes. The peaking units often burn relatively expensive gas or diesel quality

158 Snowden, Donald P., "Superconductors for Power Transmission", Scientific American, Vol. 226, No. 4, April 1972, Page 84

159 Ross, Marc, "Improving the Efficiency of Electricity Use in Manufacturing", Science, Vol. 244, No. 4902, April 21, 1989, Page 311

fuel oil. Thus the power generated by these units' costs up to 10 times more than power produced by the base load generators. 160

In normal operations, the base load generators operate at all times. During the early morning hours, the intermediate generators are activated to supply the basic power for the operation of routine daily activities. Under some conditions, intermediate generators may carry the total load. On a very hot summer afternoon, when the demand for electricity to drive air conditioning is at its peak, it may be necessary to bring the peaking units into operation to carry the short term peak load.161

As the day progresses the loading process is reversed. As the demand, drops the peaking units are shut down followed by the intermediate units. Finally, late in the evening, all extra power is shut off and the base load generators supply the modest needs through the late night and early morning hours.

This system works well as long as events follow the predicted course. When events deviate, a series of problems can result starting with slight brownouts to momentary interruptions progressing on to long interruptions and finally disaster such as happened in the northeast section of the United States in the 1960s when a multi-state area was without power for several days. Power outages are usually a result of weather conditions that rapidly change the demand in unexpected ways or violent weather that damages parts of the system.

Most electric systems have a dozen or more power interruptions during the spring and summer when thunderstorms are common. Lightning strikes some part of the system. The surge of voltage causes protective circuits to cut the power off for a short time. If the protective circuits are inadequate, lines and transformers are damaged causing interruptions lasting for hours while the equipment is repaired. Lightning induced power surges can occasionally cause a section of a system to fail resulting in interruptions requiring several days to repair. Ordinary storms, tornadoes and hurricanes have winds capable of knocking down wires and poles. Often, interruptions in electric service can be repaired in a few hours but when many poles and kilometers of wire must be replaced, the interruption can last for weeks.

In winter, lightning is not a severe problem, but snow and ice can collect on power lines and tear them down. This results in interruptions that last for a number of days because thousands of kilometers of wire must be replaced. Winter interruptions are less common than summer interruptions, but when they occur they often last longer because the damage is greater and the repair crews have a difficult time working in ice and snow. 162

Underground transmission of electric power over long distances is impractical. Long distance transmission requires high voltage. Most ground is somewhat electrically conductive so very thick, high-quality insulation is needed to protect the lines from arcing. The thick insulation is expensive and the installation of thick and stiff transmission lines is difficult. Consequently, long distance underground transmission of electricity is quite costly and is used only in specialized situations. One of the common uses for underground transmission lines is in the final run from the local transformer to the private home. This is usually a short length of thick wire carrying a relatively low voltage. The short path keeps the cost of the thick wire to an acceptable level. Thin insulation is acceptable because

160 Glavitsch, Hans, "Computer Control of Electric-Power Systems", Scientific American, Vol. 231, No. 5, November 1974, Page 34

161 Kalhammer, Fritz R.' "Energy Storage Systems", Scientific American, Vol. 241, No. 6, December 1979, Page 56

162 Abelson, Philip H., "Reliability of Electric Service", Science, Vol. 245, No. 4919, August 18, 1989, Page 689

the low voltage. In some locations high priced underground transmission lines are used to provide power to industrial sites because overhead lines are not possible.

The country is crossed and re-crossed by above ground high voltage power lines for implementation of the distribution system. Plant growth must be prevented close to the lines because trees and other vegetation are sufficiently conductive to short circuit the high voltage. For much the same reason building cannot be allowed near the lines. As a consequence, all of the cross country power transmission lines have a swath of clear-cut ground about 50 meters wide along their path. These are not pleasing to the eye. The clear-cut path requires frequent cutting and trimming to maintain its effectiveness. Because of the danger from arcs, the land under the lines has few uses.

The high voltage alternating current induces small electric currents in everything near the path of the transmission line. At a distance, the effect is weak but it becomes stronger close to the power line. This effect is commonly observed as the buzz in a car radio that gets stronger as you near the transmission line. Fragmentary data indicate the tiny electric currents produced in people living near the power line can cause health problems. We live with and tolerate the power lines because they are necessary for the use of electric power. 163'164

Figure 4.4 Electricity Distribution

Surface Manifestation Located every 200 to 800 meters

Figure 4.4 Electricity Distribution

Surface Manifestation Located every 200 to 800 meters

The power lines trudge across the country delivering electric energy at relatively low efficiency and marginal reliability. In performing this task, they provide visual insult and possible environmental harm. The nation's pipelines transmit a similar amount of energy, but most of us are unaware of their existence. When compared to electric power lines, pipelines carrying a chemical fuel are more

163 "Biological Effects of Power Frequency Electric and Magnetic Fields", Office of Technology Assessment, Report No. OTA-BP-E-53, United States Government Printing Office, May 1989

164 Edwards, Diane D., "ELF: The Current Controversy", Science News, Vol. 131, February 14, 1987, Page 107

efficient, more reliable, invisible and only harm the environment by accidental leakage. The major justification for the transmission of electricity stems from its ability to directly power electronic devices of the user. These include common every day items such as electric lights, electronic devices (radio, TV, VCRs), small motors and controls.

The foregoing discussion of electric power transmission is presented to display that pipelines carrying a chemical fuel are far more efficient, reliable and environmentally benign at delivering energy than are electric wires carrying electricity. Under most circumstances pipelines are buried a meter or two underground and are protected from the destructive effects of weather. Pipelines of any size can be buried without significant problems. Pipeline failures are limited to the occasional break due to materiel failures, digging for construction and earthquakes. To reap the full advantages of the use of pipelines for the transportation of energy it is necessary to transmit most energy as a chemical fuel.165

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