9- 2.1 System Similarities

Each available power-source system provides a different degree of power continuity and independence, or isolation, from the plant auxiliary-power system In general, each system has a form of stored energy for providing power to the critical bus during an unacceptable frequency or voltage excursion and during the time interval when it becomes necessary to disconnect the normal source of power and transfer to the standby power source Each system has a means of isolating the unacceptable normal power source and initiating the alternate source (if one is provided) before the stored energy of the system is depleted Automatic reconnection to the normal source, after it has returned to a stable condition for a given period, is also a common feature

8- 2.2 Energy Storage Methods

The five major ways to provide stored energy for a standby power system are

1 Pneumatic (stored air or gas) systems

2 Hydraulic accumulation systems

3. In-house or on-site steam-driven turbogenerator systems

4. Inertia, flywheel with and without eddy-current coupling systems

5. Storage-battery-supported systems

The first four systems are commonly used with rotating machinery, and the last is associated with static* systems

The last two methods are electrical in nature and have had the greatest acceptance Each of the last two methods is used to improve the quality of the power normally provided by the plant auxiliary-power source by acting as a filter or buffer When they are combined with a diesel- dnven generator backup, they also provide reliable protec­tion from prolonged power outages Storage-battery systems are normally combined with static battery charging rectifiers and either static inverters or d-c to a-c motor—

•“Static’ as used here means “no moving parts ” generator sets to provide short-time power continuity Static inverters, with and without output transfer switch­ing, have also gained wide acceptance as reliable sources of a-c power for critical loads