The compressed gas capacitors are manufactured for COMET especially by CONDIS SA of Fribourg, Switzerland. These high-power devices are used for high frequency applications in the long wave (LW) and medium wave (MW) ranges up to 1.6 MHz.
Intensive research and long-term experience in precision manufacturing guarantee high performance and ultimate reliability.
2. Applications
Main applications are
in transmitters and antenna systems for radio broadcasting.
Other
applications in high frequency equipment.
3. Design
The compressed gas
capacitors are manufactured with either fixed or variable capacity in two
diameters: 350 mm and 500 mm. The height of the capacitors depends on the
performance requirements.
The electrodes consist of polished aluminium plates with different profiles for fixed and variable capacitors. Operating voltage and capacitance range are determined by number, geometry and distance of the electrodes.
The dielectric medium is sulphur hexaflouride gas (SF6) at a nominal gauge pressure of 5 bar (72.5 lb./sq.in.). SF6 is an inert and non-toxic gas, with high availability.
The steel tank is copper-coated on the inner surface and tested up to a pressure of 9 bar. The ceramic insulator is subjected to test at a pressure of 15 bar (217.5 lb./sq.in.).
A valve is provided for filling and evacuating the capacitor. The internal pressure is indicated by a switch pressure gauge, and a safety valve with a threshold of 7 bar protects against overpressure.
An external sphere-sphere spark-gap protects the capacitor against overvoltages and internal flashovers.
4. Technical Data
The compressed gas
capacitors are designed for a maximum current which is limited by the
temperature of the air, the operating voltage and the frequency. At a low
capacitive reactance (i.e. C-max.) it may be impossible to apply the rated
voltage due to the current level. At a high capacitive reactance (i.e.
C-min.) it may be impossible to apply the rated current due to the voltage
level. These characteristics have to be checked by our engineering
department for each type according to the load curves.
| Ø 500 mm | Ø 350 mm | ||
| Max. operating voltage, peak value: | 80 kV | 30 kV | |
| Max. current: | 800 A | 500 A | |
| Capacitance (typical): | 5.000 pF - 50.000 pF | 5.000 pF - 50.000 pF | |
| Tolerances on C-max.: | - 0 % / + 10 % | - 0 % / + 10 % | |
| Tolerances on C-min.: | - 5 % / + 0 % | - 5 % / + 0 % | |
| Tolerances on fixed C: | - 5 % / + 5 % | - 5 % / + 5 % | |
| Variation of
Capacitance: with temperature at 60°C: |
< 140 x 10-6/° C | < 140 x 10-6/° C | |
| with pressure at 7 bar: | < 2.4 x 10-6/bar | < 2.4 x 10-3/bar | |
| Loss Factor tand : | < 10-4 | < 10-4 | |
| Internal Inductance (1 ... 20 nF): | 100 ... 300 nH | 100 ... 300 nH | |
| Max. permissible Temperature, measured on head: | 100° C | 100° C |
