of the previous two pages, because after the first event the system is usually not in equilibrium when the next discontinuity occurs. Determination of such a sequence of events requires a detailed transient load flow analysis at each change of network configuration (i.e., loss of generation, switching of lines, or change of load) coupled with a line-by-line examination of power flow and protection device setting, along with examination of machine stability limits at the power demands involved. This sort of analysis is tantamount to a complete simulation of the entire power network. In a study of this sort, it is impossible to make general statements about the magnitude and frequency of power shifts likely to cause large scale network shutdown. However, the potential for such situations does exist and the larger and more frequent the power fluctuations, the greater the probability of such an occurrence. 2,2.4 Northeast Blackout The Northeast Blackout is an example of instability problems which arose from the normal operation of protective devices. Before discussing the series of events leading to the blackout, it is necessary vo indicate some of the important characteristics of the Canada-United States Interconnection (CANUSE). Hydroelectric power constituted approximately 26 percent of the CANUSE generation and is largely concentrated in the Niagara Falls area. Most of this power is transmitted to loads located far from the generation site. Power which is generated by Power Authority of the State of New York (PASNY) plants in the Niagara Falls area is transmitted in large part by twin 345 kV lines from Niagara to Albany to New York City. Niagara and PASNY were interconnected with the Connecticut Valley Electric Exchange (CONVEX) and the New England Electric System (NEES) by one 345 kV line, one 230 kV and five 115 kV lines (see Figure 2.4.) Seven transmission lines carrying from 115 to 230 kV connect CANUSE with the Pennsylvania-New Jersey-Maryland (PJM) power pool.
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