D-C Energy Storage Capacitors

Capacitors operating on direct current are used in a variety of applications, such as

• d-c power supply filters
  • X-ray equipment
  • Radar equipment
  • Particle accelerators for nuclear research
• Intermittent duty pulse forming
  • Small surge generators
  • Linear accelerators
• Other energy storage applications
  • Capacitor discharge welding
  • Flash tube light sources

Energy storage capacitors for rapid discharge involving relatively high amounts of energy (several thousand joules) are used in nuclear fission studies, hydraulic metal forming, and electric plasma research. In these applications energy is stored to be released subsequently in microseconds. Such rapid discharges involve large currents, and the construction of the capacitor must be strong enough to withstand the mechanical forces developed by these high currents. In addition it is necessary to minimize the internal inductance of the capacitor to permit rapid release of the energy. The effect of inductance in series with capacitance is discussed in Section 1-16.

Energy storage capacitors used in some of these operations are rated from 1 to 100 μf at voltages between 3 and 100 kv, usually storing between 1 and 3 kj (kilojoules); this means that the higher voltage ratings apply to the lower capacitance ratings. Since their internal inductance is less than 0.1 μh they are able to produce peak discharge currents of 100 ka (kilo-amperes) routinely. Constant-current sources are preferred to constant-voltage sources because the efficiency of the former is considerably greater than that of the latter, which, according to Section 1-16, cannot exceed 50 percent.