Figure

THE SANTA CLARA DEMONSTRATION PLANT The Test Program has begun and the Plant has produced its Rated Power Output to allow the start-up of multiple-stack systems. The initial open circuit voltages for the sixteen stacks were equal to within 0.5%, with stack voltages of 251+/-1 Volt (See Figure 2). The successful conditioning of these 16 stacks simultaneously was a significant project milestone. A period of tuning and adjusting the AC/DC inverter control system followed the conditioning operations. While the inverter had been extensively tested during the BOP pre-test activities, this final tuning was required because it had not been operated with the fuel cell stacks. After the initial tuning was completed, the initial grid connect was made at a power level of 200 kW. In the initial phase the PCU was deliberately tripped to verify that the power plant system could ride through inverter trips as the inverter was adjusted further. Once that was completed the power ramp was continued, and on the afternoon of May 2,1996 the plant reached the design level 2.0 MW gross AC, delivering 1.8 MW net AC to the Santa Clara electric system(See Figure 3).

This initial phase of power plant operations was approached in a conservative manner, focusing on characterizing the plant operations while minimizing operational risks. Two of the auxiliary burners in the system - which are meant to be shut down during normal operations - were kept running in order to minimize the impact of a trip caused by the inverter or any of the BOP equipment. This approach was maintained as the plant was ramped to and above the rated power level. Within these limitations the highest efficiency achieved by the power plant was 43.6% (7820 Btu/kWh LHV). This was achieved at a power output of 1.93 MW net AC to die grid. Throughout the ramp to this higher power level, the stack performance exceeded the projection used in the plant design calculations, indicating that the target efficiency of 6850 Btu/kWh is achievable, once supplemental natural gas use is stopped.

Beginning approximately 520 hours into the plant operation, intermittent anomalies were observed in some of the stack voltages. In order to determine the cause of these events, the power plant was shut down and cooled to ambient temperature for inspection. . The cause was determined to be parasitic electrical currents, caused by a breach of the electrical isolation between the fuel cell stacks and the gas distribution piping. FCE has completed the process of cleaning or replacing the damaged dielectric piping. As of the writing of fliis paper, the power plant restart was in progress. FIGURE 2 OPEN CIRCUIT STACK VOLTAGES The 16 stacks had very uniform open circuit voltages.

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