Generator load drop

For FCC applications, a rigorous analysis typically involves transient evaluations of expander coupling failures, generator load drops, compressor and surge system operation, and control valve malfunctions. The results of these evaluations permit optimum selection of control valves and control strategies. 

A generator load drop of 100% is shown in Figure 4-89. For a valve elosure time of 1 see, a 5% overspeed is predieted. Note the eompari-son to the power reeovery string in Figure 4-83, where a 10% overspeed was predieted with a 10 see valve elosure. The mueh larger rotor inertia of the full power reeovery string allows the use of a slower and less expensive valve. 

If a system disturbance requires extra generating capacity, the generator may drop speed, reducing the frequency proportionately. The under-frequency relay 81-G will detect such a condition and operate a systematic load shedding in a programmed manner in order to meet the load demand. If the abnormal condition persists, the generator is taken off the main supply system. 

Figure 4-83. Speed versus time plot during generator full load drop (PRS string).

The savings generated by variable-speed pumping increase as the load drops off. 

Generator load surge is attributed mainly to the reduction in frequency of the grid. The resulting increase in steam consumption by the turbine will cause the pressure to drop in the coolant circuit, with the appearance of steam possible at the MCP inlets, cavitation failure of these pumps and impaired thermal conditions of the fuel channels. 

The small nuclear cogeneration plant SAKHA-92 [11] is a small-size power source intended for generation of electric power and district heating. The maximum electric power supplied to the consumer is 1000 kW. Low-grade heat output falls in the range of 1200 to 3000 kW at electric load drop. 

When controlling SOFC systems, the main control parameter is the electrical power output of the system. This AC output is determined by the inverter connected to the SOFC stack. The fuel supply to the stack must follow the DC power demand by the inverter, which is needed to deliver the required AC power. This is more complicated than controlling gas turbines, whose power output is related directly to the fuel flow. In the case of a SOFC/GT hybrid system, power control is even more complicated since both the gas turbine generator and the SOFC stack deliver power. A major concern in load following is the risk of retaining residual unburned hydrogen and carbon monoxide in the stack, due to a sudden load drop [3 5], which can be difficult to handle. 

The most dramatic evolution of a microwave power source is that of the cooker magnetron for microwave ovens (48). These magnetrons are air-cooled, weigh 1.2 kg, generate weU over 700 W at 2.45 GHz into a matched load, and exhibit a tube efficiency on the order of 70%. AppHcation is enhanced by the avaHabiHty of comparatively inexpensive microwave power and microwave oven hardware (53). The cost of these tubes has consistently dropped (11) since their introduction in the eady 1970s. As of this writing (ca 1995), cost is < 15/tube for large quantities. For small quantities the price is < 100/tube. 

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