Direct Current Systems

DOE-HDBK-6004-99

Direct Current Systems

The facility direct current power for safety-class systems should be provided by several independent

DC systems as required for normal and abnormal plant operations. Each safety-class DC system will

consist of one independent 125 VDC battery, battery charger, and a DC control center. DC motor

control centers will be provided where required for motor-operated valves and pump motors as

indicated above.

Each DC subsystem will be of adequate size to provide control and switching power to safety-class

systems and components. The DC power systems should be designed so that no single failure will

result in conditions that prevent safe shutdown of the fusion facility. Redundant safety-class loads

will be distributed between the redundant DC subsystems.

The DC systems will operate ungrounded. A DC ground detector relay for each system will be

provided to annunciate an undervoltage condition.

All batteries will have sufficient capacity to supply power to the DC systems for the time period

specified in the safety analysis without the support of the charger.

The capacity of each battery charger will be based on the largest combined demands of the various

steady-state loads and the charging capacity required to restore the battery from the design minimum

charge state to the fully charged state within 12 hours under any facility operating condition.

Calculations for battery sizing will be in accordance with the method presented in IEEE-485. The

Class 1E system design should be in conformance with IEEE 308.

Vital Instrumentation and Control Power Supply

Independent ungrounded vital instrumentation and control power supplies should be provided to

supply emergency/back-up power to instruments and controls systems credited in the safety analysis

report. Each vital AC power supply will consist of an inverter, distribution panel, and manual transfer

switch. Normally, the distribution panel will be supplied by the inverter. Each inverter will be

supplied by a 480 VAC safety-class power source and a separate safety-class 125 VDC subsystem.

A backup supply will be provided to each vital AC bus from a safety-class AC regulating type

transformer through a manual transfer switch. The capacity of each regulating transformer should

be adequate to meet the largest demand of any of the two vital AC distribution panels to which each

regulating transformer may be connected.

Motors

All motors for safety-class equipment should be rated, manufactured, and tested in accordance with

NEMA Standard MG-1 and other applicable USA and ISC standards.

All motors should be sized to ensure operation within the temperature limits given in NEMA

Standard MG-1. All DC motors should be rated at 120 and 240 volts. The voltage rating of the AC

motors, in general, should be as in Table II-4 following: