【正文】 o can analyze the data and diagnose/solve the problems.Power quality had bee an issue of increasing interest since the late interest in PQ involves all three parties concerned with the power business:utility panies,equipment manufacture,and electric power are many reasons for the growing concern with PQ.Visualization software packs a large amount of information into a single putergenerated image, enabling viewers to interpret the data more rapidly, and more accurately than ever before. This kind of software will bee still more useful, even indispensable as electricity grids are integrated over evrlarger areas, as transmission and generation bee petitive markers, and as transactions grow in number and plexity.00Tracking and managing these burgeoning transaction flows puts operating authorities on their mettle. While the electric power system was designed as the ultimate in plugand –play convenience, the humble wall outlet has bee a gateway to one of the largest and most plex off manmade objects. For example, barring a few islands and other small isolated systems, the grid in most of North America is just one big electric circuit .It enpasses billions of ponents, tens of millions of kilometers of transmission line, and thousands of generators with power outputs ranging from less than 100 KW to 1000MW and beyond . Grids on other continents are similarly interconnected.In recent years, a further plicating factor has emerged .Along with the broadening integration of power systems has e the increased transfer of large blocks of power from one region to another. In the United States, because of varying local power loads and availability, utilities purchase electricity from distant counterparts and independent suppliers exploiting price differentials to economize on costs .For one , the Tennessee Valley Authority , which provides power to more than 8 million residents in seven states using over 27000 km of transmission lines , handled a mere 20000 transaction requests through its service territory in 1996 , pared to the 300000 in 1999 .The next effect is that data once of interest mainly to small cadres of utilities now must be municated to the new entities being established to manage restructured grids. In the United States, that means independent system operators(ISOS) and regional transmission organization( RTOs ), which have to be able to grasp fastchanging situations instantaveously and evaluate corrective strategies nearly as fast .Power marketers’ needs , too , bee more urgent, as access to the grid is opened and petition among generators is introduced across the United States and elsewhere . They must be able to see just how much existing and proposed transactions will cost, and the availability of electricity at any time and point in the system .Finally , concepts like power flow, loop flow, and reactive power, which once mattered only to the engineers directly involved in grid operations , now municated to public service missions and the consumervoters to whom such boards are answerable .In short , whether the client/user is a power marketer, a grid operator or manager , a public authority, or a member of the public , power system visualization tools can aid their prehension by lifting the truly significant above background noise .Such tools can expedite decisionmaking for congestion management , power trading , market organization, and investment planning for the long term.The visualization tools illustrated here are available from Power World Corp, Urbana, Illinois , Visualization tools offered by others rely on updated text, ABB, Alstom ESCA, GE Harris, and Siement, for example , offer tools that are part of larger energy management systems packages .The usual reason that a large transfer of power can be hard to handle is that there are few mechanisms to control its route through the transmission system from generator to distant load. Often that route is indirect, dictated by the impedances of the lines and places where power enters or leaves the system. In effect, a single transaction between a generator and a utility spreads throughout a large portion of the gridaphenomenon termed loop flow.(To be sure ,current can be and is directly guided during highvoltage directcurrent[HVDC] transmission. And ac current is being nudged in desired directions by devices like phaseshifting transformers and series pensation capacitors, often lumped together as flexible ac transmission (FACT) devices. However very few of these devices are available in most large power systems, so in effect transmission flower are not controllable.)The percentage of a transfer that flows on any ponent in the grid a transformer, say is known, in language developed for the . Eastern interconnect, as the power transfer distribution factor (PTDF). A transaction that would send power through an overload ponent, in a direction to increase the loading , may not be allowed , or if already under way , may have to be curtailed . The . procedure for ordering such curtailments is known as transmissionline loading relief (TLR).Its developer was the North American Electric Reliability Council(NERC) ,the utilities’ voluntary reliability organization in Princeton , New Jersey . To reiterate, a grid ponent owner that detects overloading serves notice with the relevant authorityan ISO or RTO, for exampleand asks for relief . The independent operator , or whoever , thereupon orders loading relief measures . For the ponent in question , any transaction involving a distribution factor higher than a predetermined levelset by NERC at 5% of the transactionis a candidate for curtailment . If more than 5% of the power transferred as part of a transaction will go over a grid ponent subject to a TUR, the transaction may be scaled back or canceled Those TLR measures in turn will affect other existing and proposed transaction , requiring further nearinstantaneous analysis by utili