Design and Construction

DOE-HDBK-1092-98

2. A hazard exists when a capacitor is subjected to high currents that may cause heating and

explosion.

3. When capacitors are used to store large amounts of energy, internal failure of one capacitor

in a bank frequently results in explosion when all other capacitors in the bank discharge into

the fault. Approximately 104 J is the threshold energy for explosive failure of metal cans.

4. High-voltage cables should be treated as capacitors since they have the capability to store

energy.

5. The liquid dielectric and combustion products of liquid dielectric in capacitors may be toxic.

6. Because of the phenomenon of "dielectric absorption," not all the charge in a capacitor is

dissipated when it is short-circuited for a short time.

7. A dangerously high voltage can exist across the impedance of a few feet of grounding cable

at the moment of contact with a charged capacitor.

8. Discharging a capacitor by means of a grounding hook can cause an electric arc at the point

of contact. (See 10.10.1.2.3).

9. Internal faults may rupture capacitor containers. Rupture of a capacitor can create a fire

hazard. Polychlorinated-biphenyl (PCB) dielectric fluids may release toxic gases when

decomposed by fire or the heat of an electric arc.

10. Fuses are generally used to preclude the discharge of energy from a capacitor bank into a

faulted individual capacitor. Improperly sized fuses for this application may explode.

10.10.1.2 DESIGN AND CONSTRUCTION

The following cautions in design and construction should be considered:

1. Isolate capacitor banks by elevation, barriers, or enclosures to preclude accidental contact

with charged terminals, conductors, cases, or support structures.

2. Interlock the circuit breakers or switches used to connect power to capacitors.

3. Provide capacitors with current-limiting devices.

4. Design safety devices to withstand the mechanical forces caused by the large currents.

5. Provide bleeder resistors on all capacitors not having discharge devices.

6. Design the discharge-time-constant of current-limited shorting and grounding devices to be

as small as practicable.

7. Provide suitable grounding.

10.10.1.2.1 AUTOMATIC DISCHARGE DEVICES

1. Use permanently connected bleeder resistors when practical.

2. Have separate bleeders when capacitors are in series.

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