△P is the fraction of the total power being generated, g The above result indicates that a sudden reduction in generation capacity (assuming the system is able to absorb the loss of generation with available spinning reserve) will create an approximately sinusoidal frequency transient whose peak value is directly proportional to the magnitude of the power loss; this helps to define the required stability of the output of the satellite power system. If for example, a 2% change in frequency is the maximum to be tolerated, the satellite power system would have to maintain its generation level so as to produce maximum power fluctuations of no more than .12 of the total network generation at the time of the change in the SPS output. If the total power pool demand were 30 GWe, the maximum allowable fluctuation would be 3.6 GWe. If the total power pool demand were 10 GWe, the maximum allowable fluctuation would be 1.2 GWe. Normally, a power pool will have sufficient generation capacity on-line to meet the expected load plus a certain amount of spinning reserve; the required amount of spinning reserve is equal to either a percentage of the maximum expected load (typically 3-7% of the system load) or to the output of the largest generator on-line, which ever is larger. This ensures that the system will be able to absorb any unexpected loss of generation without large frequency changes. The large size of the SPS will probably require a significant increase in the level of spinning reserve and the operating cost of the power pool would consequently increase. The modern use of load shedding relays have reduced the probability of large scale system shutdowns occurring as a result of the sudden loss of generation capacity. These relays disconnect part of the load so that the system can still meet the larger part of the load. Even if the spinning reserve were provided for the example given, the sudden loss of the SPS output would force a loss of load operation of the relays whenever the total load is less than 42 GW.
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