INTEGRATION OF SPS WITH UTILITY SYSTEM NETWORKS Bjorn M. Kaupang General Electric Company Introduction This paper will discuss the integration of SPS power in electric utility power systems. Specifically treated will be the nature of the power output variations from the spacecraft to the rectenna, the operational characteristics of the rectenna power and the impacts on the electric utility system from utilizing SPS power to serve part of the system load. Dynamic Power Variations in the SPS System As a first approximation the SPS system consists of a constant power source working into a constant load. However, in practice the available power degrades slowly over the 30 year lifetime and it is modulated by infrequent but relatively rapid fluctuations. Table 1 lists some of the conceivable sources of relatively rapid power variations in the SPS system. They are listed approximately in sequence of the associated total yearly loss of energy. It can be seen that among the listed items only the first two, maintenance and eclipse produce 100% outage and both of these fall into the scheduled down time category. These two sources cause scheduled down times of 1.36% and 1% respectively. The remaining effects are small and essentially random. Total energy loss is less than 2.7% per year if shut down and start up times associated with eclipses are also considered. When it is necessary to implement scheduled or unscheduled output power level variations from the spacecraft several methods can be considered. Table 2 shows 7 methods to control the power input into the rectenna. Reduction of power to zero will require a maximum .45 sec. Rectenna Inverter Control and Operation The power conditioning system that has been recommended for the SPS is the current fed, line commutated inverter. This type of system is in common use in HVDC power transmission. Synchronous condensers control the ac voltage and the supply of reactive power. The SPS should operate at full available output. To accomplish this, the inverter must present to the rectenna the optimum load impedance. It is assumed that the rectenna is basically resistive in nature and there is an optimum de load resistance for maximum power transfer. Normally the system would be. operated at optimum resistance so that the rectenna would reflect a minimum of power. The power level would be adjusted at the satellite and would usually be set at maximum available power. If power reduction is required by utility considerations and it could not be accomplished at the satellite, the converter power can be adjusted by means of moving the resistance off optimum. Of course, RF power would be reradiated but that might be acceptable under the circumstances.
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