This system (Fig 9.12) consists of a synchronous motor, fed from the utility power system, which drives a synchronous generator, which, in turn, feeds the critical a-c load. Simultaneously, a small induction motor is driving a flywheel at a speed considerably in excess of the syn­chronous generator speed. The flywheel is not coupled to the generator under normal operation since the eddy current coupling between the generator and flywheel is not energized. When an unacceptable excursion in voltage or frequency occurs on the plant auxiliary-power system, the power-source feed is disconnected and the eddy-current coupling is energized, thereby coupling the flywheel to the generator. The stored energy of the flywheel then serves to drive the generator at synchronous speed in the same manner as described for the system shown in Fig 9 11 The present system (Fig 9 12), by excluding the eddy-current coupling from being energized during normal operation, operates at a much greater efficiency than the svstem shown in Fig. 9.11.

addition, a second in-line d-c motor, normally floating on the battery system, is instantaneously available to drive the system if the plant auxiliary-power system fails This system suffers from the ills common to all s) stems with rotating equipment, including increased maintenance and wear, when compared to static systems In addition, the duration of operation after the failure of the utility source is limited by the battery capacity

(b) Static Rectifier—Motor-Generator—Battery Sys­tem. During normal operation of the system (Fig 9 14), utility-line power is rectified and applied to the d c motor that dnves the a-c generator supplying power to the critical a-c load. The rectifier is sized to accommodate any normal d-c load in addition to the power required by the d-c motor and the power needed to maintain the battery at full charge. On failure of the plant auxiliary-power system, the d-c motor is supplied with power from the batteries, thereby maintaining the continuity of the a-c generator

With the exception of improved efficiency, this system has the same characteristics as the system described in Sec 9-5 6, and, in addition, the frequency excursion of the generator output during transfer from normal utility supply to flywheel operation may exceed acceptable limits

9- 5.8 Battery-Supported Motor-Generator Isolated Systems

(a) Motor-Generator—Motor-Battery System In the normal operation of the isolated system (Fig. 9.13), an a-c motor, fed from the plant auxiliary-power system, drives an a-c generator, which, in turn, feeds the critical a-c load. In

prime mover. The length of emergency operation is limited by the capacity of the battery. Adding a backup internal — combustion engine to drive the generator directly would, of course, greatly extend the length of emergency operation.

The base system affords satisfactory operation during short-term transients because of the extremely effective filtering action of the battery and motor—generator com­bination.

9- 6 CONCLUSIONS

The material of this chapter aids in selecting and specifying high-reliability power sources Only the major electrical systems have been discussed because they are the most commonly used in nuclear power reactor plants.

In determining which type of system is best, an important aspect is responsibility. A given system may be designed and specified and the component parts purchased and assembled by the purchaser The purchaser thereby assumes the responsibility for satisfactory system opera­tion.

An alternative procedure, and one that usually guaran­tees satisfactory results, is to specify the required parame­ters of the power source The system supplier then submits a quotation and assumes the responsibility for system operation to meet the specifications This latter procedure is recommended.

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