The Power Supply

Boss to secretary: - "Mrs Simpson, there are 2 500 employees in this company, and everyone seems to have heard about your new baby. So I´ve decided to move you to our PR-department!"

Electric power is needed to keep the beam traffic running. In the FLYWAY® design, the power is fed regionally and backed up by UPS in order to achieve resiliency. This is a technical page, where we try to be as detailed as practicable.

While several solutions are possible, we will here only deal with the FLYWAY® design. We will look att how power is supplied, how it is converted to the right voltage and frequency for use and how we endeavour to feed electricity back to the power supply system when braking the cars.

Distribution and Transformation Electric power is needed for: Powering the beam vehicles Powering the lifts and swiveling systems of the vehicles Providing lighting along the beams and in the passenger cabins Providing power for communication and computers in nodes and vehicles. Figure 2 Electrical power for powering the propulsion cars is taken from the local electric utility. From three phase high voltage AC it is converted to 750 volt DC at local substations throughout the system. For resiliency against sabotage and accidents, the network is divided into suitable geographical areas, where each such area is supplied from a local transforming station. An example of this is shown in the illustration above, where the borders between distribution areas are shown as red lines (the beams are depicted as thin blue lines). The capacity of each station should preferably be about twice what is needed, so that it can temporarily supply a neighboring area with electric power, if need be. Each substation should contain: Transformers and rectifiers for production of the DC voltage UPS (Uninterrupted Power Supply) in the form of batteries for about 5 minutes normal power supply Electric generators for temporarily keeping traffic moving From the substation, the 750 volt DC power is supplied through the inside of nearby poles to the power rail mounted in the systems´ horizontal beams. Each substation supply power to the beams within its own distribution area. This power distrubution network is isolated from neighboring areas, but can be connected by switches to one of it´s neighbors when the need arises. By reason of their dimensions, the power rails have very low electrical resistance, so the process of transformation and distribution to the vehicles should not have lower than 90% efficiency. When considering this efficiency, the actions of individual beamcars come into play, such as whether they are negotiating curves, accelerating, cruising, decelerating or braking. The power can be distributed i 2 ways: As 750 volt DC. Converted to 3-phase AC-voltage. In the DC-case, the beamcars could generally use either of 2 alternatives for handling the power: The 750 volt DC supplied through the power rail is used as it is by vehicles using DC-powered motors, or The power is converted by the vehicles into variable AC-voltage and frequency, commensurate with the power requirement and speed the vehicles have at the moment. In both cases, the traction motor feeds the voltage back into the power rail when the car is slowing down or braking. This method of braking both conserves the vehicles´ kinetic energy for re-use later on (or by other vehicles) and reduces wear on the friction brakes.

The shortest way between 2 points is undoubtedly a straight line. So why is it that lightning travels such a jagged way from the thunderclouds down to earth (or vice versa)? Well, the reason why clouds get electrically charged in the first place is not completely understood. But whenever air of different temperatures meet, this always results in turbulence, and the more so the greater the temperature difference. An upward motion of moist air, coupled with the downward motion of water droplets and ice (which are condensed out of moist air being cooled), produces a strong positive electric charge on the top of the cloud, and an equally strong negative charge at the bottom. As long as this motion of moisture in both directions keeps up, the two charges are prevented from meeting up with each other. Instead, the negative bottom charge attracts a positive charge in the earth, and this charge assembles at high points, nearest the cloud, since it is attracted to the opposite charge in the cloud. Figure 5 What next happens is that when the voltage is high enough, so-called "leaders" poke into the air from the clouds, at those points where the air is sufficiently moist. Since water is a good electrical conductor, the leader that meets the least resistance soon attracts electrons from the cloud in its path, forming an electrical "channel". Surrounding this channel is a "corona sheath" of some 50 feet in diameter, consisting of a negative electrostatic field. The electric field force across this sheath is typically 9 000 volts/centimeter (cm). Depending on air moisture, the voltage in the channel could vary about 50 volts/cm. As the corona nears earth, "streamers" shoot out in the air, following the paths of most moisture. The channels follows in the path of those streamers closest to the positive earth potential. Since the channels follows a "prepared" path, it quickly catches up with the streamers, and has to wait while they continue to search for paths of least resistance. This step-by-step process can actually be seen, and it follows a crooked path because air moisture is very uneven. Each leg in this stepping process is somewhere between 10 and 80 meters in length, and the legs grow shorter as the corona nears the earth. At the same time, the "leader" speeds up until it reaches some 300 meters/milli-second. The corona, when it moves, keeps about 1/4 the speed of light. When the "leader" reaches about 10 meters above flat ground (or 100 meters above a high object) a corresponding, positively charged, leader rises from the ground. When these two meet, the discharge occurs, and it can be as high as 200 000 Ampere! The FLYWAY® vehicles could use inverters which convert the 750 volt direct current into variable voltage/variable frequency 3 phase alternating current. When vehicles are going down sloping beams or braking, their motors become generators, and the inverters convert their output into electric DC-power. In the case of the power being supplied as 3-phase AC, there are 2 options as well: The beamcars could use AC-powered asynchronous motors. They could use the same system as in point 2 above, but without the need for AC/DC inverters.

When a beamcar is braking or slowing down, it uses its motor as an electric generator, feeding power back into the power rails, to help power other vehicles. Considering the need for emergency braking, the motors are dimensioned for this braking. The power output at such times, i.e. when the propulsion motors function as generators, could at times very well exceed propulsion requirements, i.e. the power produced when braking can at times exceed the power consumption when accelerating. Estimated maximum accelerating would be about 1.4 meters/second2. Thus, emergency braking could in most situations be handled solely by the propulsion motors, but this does not obviate the need for the mechanical emergency brake, as a safety precaution. The light-blue area in the figure at right indicates that equipment which is aboard the beamcar.

Figure 7

In case of power failure Each station should have its own uninterrupted power supply (UPS), which consists of electrical batteries with enough stored energi to keep its own region going, at least until in-site generators get started. Should the UPS also fail, or distribution of power not function everywhere, then the affected beamcars would have to rely on their on-board batteries. The capacity of these batteries should normally be sufficient to get each car to the nearest available berth. The need for batteries in the beamcars has been debated. The drawbacks are: The beamcars will be heavier. Batteries consitute an added investment. Batteries have to be maintained and replaced after 3 - 5 years. Maintenance and replacement costs money. UPS-systems can (and do) occasionally fail, but it is felt that there is no need for batteries in the vehicles. As stated above, the FLYWAY UPS-design allows for supplying one neighboring area with power as well, in case of power failure. Thus, if this is implemented with sensors that control automatic power-switches between neighboring areas, a neighboring UPS will jump to the rescue, should the local UPS fail. This is roughly illustrated to the right (figure 9). The green area has 6 immediate neighbors (numbered) which are connected together by cables, that both can carry electric power and sensor information. Thus, if for instance area 5 suddenly loses power, this would be detected by the power supply station in the green area, and also (of course) by area 5´s other neighbors. These have a priority list. Let´s say that area 6 should be the primary backup for area 5. Then, area 5 would start getting backup-power from area 6.

Figure 9 But; the case could be that area 6 has a malfunctioning UPS, or is already supplying backup-power to another area. In that case, the backup-supplier that comes next on the priority list would jump into action, if available, and so on. As can be seen, small areas with many immediate neighbors makes for secure backup-power. The green area has 6 neighbors, any of whom could come the aid of the green area. Should a stranded beamcar that carries a cabin with passengers on board nevertheless lose all power supply from the outside, there are still options available. The best thing to do is of course to wait a few minutes, to see if power is not restored. Failing that, the beamcar should be able to lower its cabin, on the spot where it happens to be, if this is possible. For this reason, each car carries information about ground conditions for all beams, i.e. information about where it is possible to lower the cabin, and how far down from the beam the ground is. The beamcar´s battery should, however primarily be used for maintaining its computer, data communications and on-board lighting, even if this means that the car won´t move. The nodes in the beam network might need batteries as well, for the sole purpose of maintaining communications and keeping their computers going. These would be small, maintenance-free rechargeable batteries.