system generation capacity, the introduction of such a power source may increase the number of transients of the power network and cause frequent redistributions of power flow throughout the network. The SPS should be designed so that any fluctuations in output power occur as slowly as is necessary to allow earth-bound regulator systems to correct for them without creating significant transients. Section 2.2.2 provides a discussion of the transient in system frequency due to system dynamics resulting from a loss of generation capacity. This transient is of concern because off-frequency operation has a severely adverse effect on many types of load elements and also places undue stress upon generator turbines as a result of governor operation at other than design frequencies. In Section 2.2.3 the effects of protection devices operation on machine stability is discussed, indicating the potential for large scale network instability as a result of switching operations. An example of stability problems is found in the Northeast blackout where a variation in the load caused a normally functioning protection device to initiate a sequence of events resulting in loss of power to most of the northeastern United States. This incident is discussed in some detail in Section 2.2.4. 2.2.2 System Dynamics After the loss of a generator unit in an electric power network, a frequency transient will occur whose precise characteristics are a function of many factors; e.g., the magnitude of power loss with respect to the remaining generation, the time constants of the remaining generators and the dynamics of the governors attached to the network. The detailed solution for such transient problems is complex, and in most instances, it is possible only to deal with average system properties. In so doing, it is necessary to apply weighting factors to the properties of each of the generators in the network. There are many ways in which these factors may be selected, but the basic analysis is unaltered.
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