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June 2002 IBEW Journal
As many communities struggle with ever-increasing traffic congestion and air pollution, transportation planners study light rail systems built in North American cities over the last 30 years as part of a potential solution. What is Light Rail? In the United States, "light rail" is the modern term for an old mode of transportation: trolley or streetcar. It has elements of several other forms of public transportation. Light rail supporters point to several factors that define modern light rail systems. They are environmentally friendly with little or no emissions; use existing right-of-way, street medians or segregated street lanes; are flexible enough to transport passengers to work, into historic districts and pedestrian malls; provide a smooth, speedy, safe ride; carry more passengers than a bus but fewer than heavy rail; and provide affordable transportation with passengers usually boarding at street-level rather than from high platforms such as a subway. History and In the early days of mining, horses were used to pull the ore deposits to the surface. To ease the burden on the horse, the vehicle containing the ore was set on rails. The same principle applied on land, where passenger trams pulled by horses became a means of public transportation. The first horse-drawn street tramway was constructed in New York in 1832. Steam, compressed air, gas and petrol engines were early forms of streetcar propulsion that were tried and discontinued for various reasons. In 1879 German engineer Werner von Siemens (1816-1892) developed an electric dynamo that generated power at a fixed point and supplied the power to the line by an overhead wire or through a rail. American engineer, inventor, and pioneer in electric railway transportation Frank J. Sprague (1857-1934) built the first electric street railway in Richmond, Virginia, in 1887. He is the considered "the father of the electric railway" and among his many designs for electric railways were the automatic brake and the multiple unit system control. With Spragues multiple unit system, electric traction motors were placed in each car of the train. All of the traction motors were commanded in unison by relays energized by train-line wires. Sprague is also credited as co-inventor of the electrified third rail for electric rail lines and todays systems still benefit from his designs. The Disappearance Electric streetcars provided an inexpensive and efficient method of public transportation from the 1880s until the 1930s. Increasing congestion of vehicle traffic, the streetcars lack of speed and cost of maintenance caught up with the streetcars in the 1930s. In an effort to replace streetcars with buses, oil and rubber corporations purchased privately owned streetcar companies and closed them. The streetcar was replaced by the bus for mass transportation and a grassy median in the boulevard often hides the old tracks. Canada Leads the Light Rail The first modern streetcar systems, now called light rail, were deployed in Canada. Edmonton began its service in 1978, followed by Calgary in 1981. Borrowing ideas from Canadian systems, light rail systems were soon built in San Diego, Sacramento, Portland, Toronto, Los Angeles, St. Louis, San Jose, Salt Lake City and several other Canadian and American cities. Light Rail Propulsion Systems There are many different electric rail vehicles currently in operation in North America. The systems are powered by alternating current (AC) or direct current (DC). Diesel mechanical and diesel electric powered light rail vehicles are also available but are more popular in Europe than in the United States or Canada. (In North America, Ottawa has diesel mechanical light rail and New Jerseys Hudson Bergen line is running diesel electric.)
The DC traction electrification systems range from 600 to 800 VDC. Electrical substations feed power to the system. In the event one substation fails, the use of load sharing ensures that electricity will continue to be supplied by substations on either side of the bad section. A pantographa diamond-shaped device on the roof of the light rail vehicleallows current from the overhead contact wire to feed the motors. Most vehicles are equipped with two to four motors per car, geared to the wheels. An elementary DC motor consists of four principal components: a field coil, an armature or rotor, a commutator and a set of brushes. The field coil is stationary and the armature rotates (see diagram). The stationary brushes maintain the electrical contact with the rotating commutator, and the commutator provides the current to the rotating armature. When the electromagnetic field created by the stationary field coil interacts with the magnetic field in the rotating armature, torque is produced. It is this torque that powers the system. The function of the commutator is to change magnetic polarity by sequentially energizing and de-energizing the windings of the armature. A shaft is connected to the armature and turns as the armature turns. A pinion, connected to the shaft, drives a gearwheel. The gearwheel is shrunk onto the axle and drives the wheels of the vehicle. Electrical energy is transformed into the rotary motion that propels the vehicle. For many years, the DC motor provided the necessary torque for railway operation and was the preferred motor for electrical traction. Advances in power electronics and increased efficiency have led to the 3-phase AC motor in some North American light rail systems. The 3-phase AC motor is an induction motor with a rotor and a stator but, unlike the DC motor, it does not require current to flow to the rotor from the power source. An electromotive force is applied to the rotor through electromagnetic induction from the stator. The rotor turns as the result of the interaction between its magnetic fields produced by the induced current from the stator and the electromagnetic field caused by the current flow in the stator. The 3-phase voltage supply used to feed this type of motor utilizes three conductors, each connecting at a point one-third or 120 degrees into the normal cycle period (see diagram). There is no electrical connection between the rotor and the stator. The 3-phase AC motor needs no brushes; thus, the rotor can be made of steel laminations rather than the large number of windings necessary in other motors. Variable frequency drives allow the speed of the motor to be controlled.
The 3-phase AC motor is cheaper and sturdier than most other motors of its size. The Future of Light Rail Because light rail runs on electricity, there are practically no emissions compared with other forms of mass transit. The six Canadian cities that have light rail systems are either building extensions to the current systems or have plans for future extensions. There are currently 25 light rail systems in the United States and many of them are planning to extend their systems. With a number of other communities in some stage of the planning process, the future looks promising for light rail to become a permanent element in the mass transit system. The IBEW is closely following developments in the light rail industry and is ready to provide the skilled workers that will be required as the industry expands.
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