General Safety Design Guidance

DOE-HDBK-6004-99

high voltage (35-115 kV). The voltage supplied to the facility loads can be lower (13.8 kV) since

the load will be significantly less. The switchyard will also contain the various high voltage breakers

and disconnect switches.

Downstream from the switchyard, the electrical power distribution system is divided into two main

parts, namely the fusion facility distribution system and the plant distribution system.

The fusion facility distribution system is primarily a high voltage system (35-115 kV) designed to

supply the heavy (and often pulsed) loads for fusion facility operation. Included in this distribution

system are the magnet power supplies and various plasma fueling and heating power supplies. Also

included in this system will be the static volt-ampere-reactive (VAR) compensation and any energy

storage equipment required.

The facility distribution system generally consists of four types (IV, III, II and I) of power to supply

those loads which are required to operate independently of the Fusion Facility Distribution System.

The four types of power supply are defined as follows:

Type IV (Non-Safety Class): Interruptible AC supply for those loads which can be interrupted

indefinitely without resulting in plant damage or safety hazards to either on-site personnel or the

public. Type IV power is supplied by the grid. This type of power supplies the normal facility

operating loads.

Type III (Safety Class): Interruptible alternating current (AC) supply for those loads which can

be interrupted briefly (5 minutes) without resulting in plant damage or safety hazards, but where

longer interruptions may cause such problems. Type III is supplied from Type IV (grid) power

when available, or by emergency (standby) generators. This type of power supplies loads which

are needed to achieve and maintain the fusion facility in a safe condition. In the event of loss of

grid power, the emergency generator power will fulfill the requirements.

Type II (Safety Class): Uninterruptible AC supply for those loads requiring a very secure

continuous power supply. This class of power is obtained by the use of inverters (or motor

generators) driven by Type I power.

Type I (Safety Class): Uninterruptible direct current (DC) supply for those loads requiring the

most continuity of supply. This type of power is supplied by batteries, which are continuously

recharged by Type III power through battery chargers fed from Type III MCCs. This class of

power supplies safety and protective (DC) loads which must be available at all times.

General Safety Design Guidance

Electrical system functions should be designated safety functions if they are credited in the facility

safety analysis in order to meet prescribed safety criteria. Systems or components needed to perform

safety functions should be designated safety-class systems or components. Components which do

not perform safety functions but whose failure causes the failure of a safety function should be

designated safety-class components.