| Open Access Same-time Information System |
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| CATEGORIES ABOUT OPEN ACCESS SAME-TIME INFORMATION SYSTEM | |
| electric power transmission systems | |
| electricity distribution | |
| united states department of energy | |
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OPERATION The "Open Access" policy for transmission service in the United States was created by Federal Energy Regulatory Commission (FERC) Order 888, and the OASIS system to support it by Order 889, both issued April 24, 1996. US power line owners were compelled by Order 888 to open their power lines to competitive use, while reciprocity agreements extended this competitive market for transmission service into jurisdictions in Canada and Mexico. The capacity to carry electricity on a given power line is limited. A transmission customer, such as an electric utility wishing to buy power from another power company, requests service from a transmission owner by submitting a Transmission Service Request (TSR) to the owner's OASIS node (web site) for a specified power level and duration. The transmission owner approves or denies requests based on a set of rules published in a tariff posted on the OASIS node and filed with FERC. When there are more requests for a transmission line than the amount of service available in a given period, the transmission line is said to be congested. The tariff determines which TSRs are approved and in what amount. Where a tariff also defines an energy market, the market price for power at each location is partly determined by the congestion. A long-distance power transaction may require a number of transmission reservations with multiple owners to move the power from the source to the destination. Regional Transmission Organizations (RTOs) are groups of transmission owners that have placed their transmission assets under the control of the RTO to simplify the process of managing transmission in the region. In these cases, the RTO has a single OASIS node in place of each transmission owner. Each RTO is commonly associated with a regional power market that manages the supply of energy and other ancillary services. Physically, power divides according to the laws of electricity across parallel power lines, so the whole power system must be operated cooperatively to supply the correct amount of power at each destination. Demand for power is always changing, and Generator s increase or reduce their output to the grid to match demand because power can not be stored. Unpredicatable events sometimes happen to make the amount of power flowing on a power line exceed its normal capacity limit, despite the system of OASIS reservations. To stay within safe operating limits, power flowing on a line is cut back using a procedure called Transmission Loading Relief (TLR). Generators supplying power to the power line have to reduce their output, while other generators closer to the load increase their output to compensate for the reduction. Conditions can persist where generators supplying power to a line in TLR do not follow their obligation to reduce their output. Prolonged overloading can result in transmission equipment damage or electrical shorts from overheated high voltage power lines that sag too close to the ground and contact trees. Automatic Protection Systems instantly disconnect power lines and generators when unsafe conditions are detected. A series of line disconnections caused the massive 2003 North America Blackout when generators in the east could not respond quickly enough to the loss of power from the U.S. midwest. SEE ALSO EXTERNAL LINKS
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