Source: Deepak Divan, William Brumsickle et Joseph Eto, A New Approach to Power Quality and Electricity Reliability Monitoring – Case Study Illustrations of the Capabilities of the I-Grid™ System, Ernest Orlando Lawrence Berkeley National Laboratory, Avril 2003
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For many customers who require highly reliable power, les services publics fournissent à double flux; c'est à dire, un service à un centre provient de deux lignes de transmission indépendantes. Under normal conditions, the plant load is shared by the two transmission lines. When a problem arises on one of the lines, plant loads are switched nearly instantaneously to the other line. In other words, the two lines provide redundant paths to ensure near continuous electric service to a customer.
Description
A large automobile assembly plant (3,200 workers) is supplied from a dedicated substation that is fed from two separate transmission lines. An I-Sense monitor was located on each transmission line. See Figure 1.
A grid event occurred during which the monitor on one line recorded a voltage sag of 4.8 cycles (0.09 seconde) followed immediately by a complete interruption that lasted 9.8 seconde; the other monitor recorded a similar voltage sag followed by return to normal voltage and no subsequent interruptions. These data indicate that a fault occurred on the first transmission line, and a voltage sag was propagated from one line to the other. See Figure 2.
The physical cause of the event was later reported: a windstorm caused a line-line fault at the point of entry of Transmission Line #1 into the substation. The fault was initially fed by both transmission lines, causing a voltage sag on all downstream load buses. Circuit breakers subsequently disconnected the faulted transmission line, leaving all plant loads connected to the remaining Transmission Line #2.
Discussion
This case study demonstrates the operation of a dual feed when a fault occurs: un transfert automatique est initiée à partir de l'alimentation en défaut de l'alimentation unfaulted,,en,Cette stratégie permet la restauration automatique de la puissance de l'installation,,en,permettant un redémarrage des processus interrompus,,en,L'infrastructure transmission à double alimentation signifiait que cette société a connu seulement un cycle de quatre,,en,second,,en,chute de tension plutôt qu'une interruption de plusieurs heures de services,,en,la chute de tension était suffisamment grave pour provoquer des interruptions de processus,,en,Dans le commerce du matériel d'atténuation de chute de tension disponible aurait gardé tous les processus en cours d'exécution critiques lors de cet événement,,en,pour cent de la tension est restée pendant la chute,,en,et Correcteurs d'affaissement peuvent compenser jusqu'à,,en,pour cent tension restante,,en. This strategy allows automatic restoration of power to the facility, permitting a restart of interrupted processes. The dual transmission-feed infrastructure meant that this company experienced only a four-cycle (0.07second) voltage sag rather than a several-hour interruption of service. Cependant, the voltage sag was sufficiently severe to cause some process interruptions. Commercially available voltage sag mitigation equipment would have kept all critical processes running during this event; 68 percent of voltage remained during the sag, and sag correctors can compensate down to 50 percent remaining voltage.
Cet exemple montre comment le pouvoir peut être très fiable doté de deux alimentations utilitaires, mais aussi que l'utilisation de deux aliments n'élimine pas les baisses de tension de courte durée qui peuvent aussi causer des temps d'arrêt du processus,,en,Ligne Schéma de cas,,en,Les événements enregistrés sur Feeder,,en,Un affaissement de deux lignes pour quatre cycles,,en,suivie de la tension nominale pour un cycle,,en,suivie d'une interruption complète pour,,en,suivi d'un retour à la normale,,en,sans interruption ultérieure,,en,les formes d'ondes d'événements sont affichés ci-dessous,,en,Notez que les parcelles d'événements,,en,sont de,,en,exactement la même durée totale,,en,Notez également que le début de l'événement,,en,est visible dans le tracé de l'événement,,en,Waveforms de l'événement,,en,ERNEST ORLANDO LABORATOIRE NATIONAL LAWRENCE BERKELEY,,en.
Figure 1. Line Diagram for Case #1
Events recorded on Feeder #1: A two-line sag for four cycles, followed by nominal voltage for one cycle, followed by complete interruption for 9.8 seconde, followed by return to normal.
Events recorded on Feeder #2: A two-line sag for four cycles, with no subsequent interruption.
Event waveforms are shown below. Note that the plots of events 263(#1) et 251(#2) are of
exactly the same total duration. Note also that the beginning of event 264 is visible in the plot of event 263.
Figure 2. Cas #1 Event Waveforms
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