IEEE Std 308:2020 pdf free download – IEEE Standard Criteria for Class 1EPower Systems for Nuclear PowerGenerating Stations
5.3.1 General
DC power systems include power supplies and distribution systems arranged to provide power to Class 1Edc loads and for control and switching of Class 1E power systems. Features such as physical separation,electrical isolation, redundancy, and qualified equipment shall be included in the design to aid in preventing amechanism by which a single design basis event can cause redundant equipment within the station’s Class 1Epower system to be inoperable.For guidance, refer to IEEE Std 946TM. Design requirements shall include thefollowing:
a) Class 1E electric loads shall be separated into two or more redundant load groups.
b)The protective actions of each load group shall be independent of the protective actions provided by redundant load groups.
c) Each of the redundant load groups shall have access to a power supply that consists of one or morebatteries and one or more battery chargers.
d) Each load group shall have its own battery charger (or chargers) with no automatic interconnectingprovisions.Two or more chargers may have a common ac power supply if the consequences of the lossof the power supply to the load group under design basis conditions are acceptable.
e) The batteries shall have features so that common-cause failures are minimized between redundantbatteries.For further guidance, refer to IEEE Std 484TM
f) For passive reactor designs, battery chargers shall be Class 1E to provide proper isolation from the non-Class 1E power supply and to reliably maintain the Class 1E batteries in a charged state to performtheir safety function.
g) The system and battery charger shall be designed so that faults or failures internal to the charger are prevented from unacceptably affecting the dc system.
5.3.4.2 Function
Each battery charger shall furnish electric energy for the steady-state operation of connected loads requiredduring normal and post-accident operation while its battery is being restored to or maintained in a fully chargedstate.
5.3.4.3 Capability
The capacity of each battery charger shall be based on the largest combined demands of the various continuoussteady-state loads plus charging capacity to restore the battery after the bounding design basis event dischargeto a state in which the battery can perform its design basis function for subsequent postulated operational anddesign basis functions. The time period considered for sizing the charger shall be as stated in the design basisof the plant.IEEE Std 946 should be reviewed for guidance and recommendations on sizing battery chargers.
For passive reactor designs using batteries with extended duty cycles of 24 h to 72 h, restoration of the batterychargers following a loss of power event is a high priority. Provisions shall be made to allow for restoration ofreliable permanent or temporary power to the battery chargers prior to the end of the design discharge cycle toprovide continuous dc system supply in a loss of power event.
5.4.2.3 Independence
Distribution circuits to redundant equipment shall be physically and electrically independent of each otherin accordance with IEEE Std 384.No provision shall be made for automatically interconnecting redundantload groups. If nonautomatic interconnecting means are furnished, provisions shall be included that preventparalleling of the redundant I&C power system sources.No provision shall be made for automaticallytransferring 1&C loads between redundant power sources.