Vacuum Capacitors Introduction
1. Preamble
Our company has a 30 years experience in manufacturing vacuum capacitors since the former company began in 1970s. We are making about 70 models vacuum capacitors. We have the ability for developing, trial manufacturing and mass-producing.
2. How to identify the Vacuum Capacitors
2.1 What is vacuum capacitor
Just as its name implies, vacuum capacitor is a capacitor with vacuum medium. The plates of the capacitor, which is sealed in a high vacuum container, are series concentric cylinders made by High conductive oxygen free copper. As the cylinders are shaped by series precise mold, vacuum capacitors have reliable performance and hardly bring out arc and electric corona.
2.2.
Classification of Vacuum capacitors
Vacuum ceramic capacitors |
Fixed vacuum ceramic capacitors
|
General fixed vacuum ceramic capacitors |
Adjustable fixed vacuum ceramic capacitors |
Variable vacuum ceramic capacitors |
Convection cooling variable vacuum ceramic capacitors |
Air cooling variable vacuum ceramic capacitors |
Water cooling variable vacuum ceramic capacitors |
2.3 How to show the capacitor model
According to Chinese standard, the type of vacuum capacitor should be named after the first letter (capital) of the Chinese pronunciation except capacitor, which is denoted by "C". such as vacuum ceramic capacitor:
By now, adjustable fixed vacuum ceramic capacitors and air cooling variable vacuum ceramic capacitors haven't been made by Chinese company. As China is just on beginning of making water cooling vacuum ceramic capacitors, there is not Chinese standard for the name, we just similarly named the capacitors as the original standard.
3. Performance and application of vacuum
3.1 Vacuum capacitors are widely used in:
Broadcast communication equipment
Vacuum capacitors are used in medium wave, shortwave and ultra shortwave transmitters, act as the tuning, coupling, wave sieving, counteracting component.
Plasma deposition and etching equipment for semiconductor manufacturing.
High frequency industrial equipment for high frequency heating and brazing.
Medical instruments. Medical analysis instruments and treatment instruments
High-energy physics. High-energy particle accelerator.
Power equipment. Medium waste test equipment.
3.2 Performance of vacuum capacitors
Vacuum capacitors have higher withstanding voltage, smaller volume, lower loss and more reliable performance than capacitors with other medium. The particular performance includes the following:
Rated voltage-Due to the excellent insulation of vacuum and the dustproof and moistureproof performance, vacuum capacitors have high rated voltage when the dimension and the volume are certain. It can achieve hundreds thousands of voltage.
Small loss and high rated current-As vacuum capacitors are made with vacuum medium, low loss ceramic shell and oxygen-free copper plate, it can carry large RF current under general convection cooling, even the frequency is very high. The carrying RF current can achieve thousands of amperes.
Save space-to a certain capacitance and rated voltage, vacuum capacitors need smallest space.
Wide capacitance range-the ratio of the biggest capacitance to the smallest achieve 150:1, from several pf to thousands of pf, it is an ideal component for wide range tuning.
self cured ability for excessive voltage-Vacuum capacitor can withstand instantaneous excessive voltage, which will permanently damage other sort of capacitors.
Work in high altitude-vacuum airproof allow vacuum capacitor to work in high altitude without performance decrease.
4. Structure of vacuum capacitors
Vacuum ceramic capacitors can be separated into two types by the structure.
The plates of the capacitor are fixed, as drawing A, is fixed vacuum ceramic capacitors.
One plate of the capacitor is moveable, as drawing B, is variable vacuum ceramic capacitors.
5. Technical parameter of vacuum capacitors
5.1 Top work temperature
Top work temperature of capacitors: 120 °C
5.2 Cooling mode
Convection cooling if no special request
5.3 Installation
No special request.
5.4 Temperature quotiety
No more than 100X10-6
5.5 Turning direction for enlarging capacitance of variable capacitors
Counter-clockwise
5.6 Collision
Peak acceleration: 100m /s 2 Pulse duration 16ms; collision times :10000
5.7 Vibration
Vibration direction: determined by the product specification. Frequency range: 5~55Hz.Swing: 20m / s 2 or determined by the product specification. Duration: determined by the product specification.
6. Primary technical parameters of vacuum capacitors
6.1 capacitance
fixed capacitor: the tolerance is ± 5% when the capacitance is more than 50 pF, the tolerance is ± 10% when the capacitance is 5 to 50 pF.
6.2 peak test voltage
Peak test voltage is the maximum voltage (50/60Hz), a capacitor can withstand for one minutes without causing internal or external arcing, through which shows the general condition of a capacitor.
6.3 peak RF working voltage:
This is the maximum peak RF voltage that can be continuously applied to a capacitor without reducing the capability of withstanding instantaneous excessive voltage. Usually RF working voltage corresponds to 60%~70% of the peak test voltage, which is the recommend safe data for your selecting capacitors.
6.4 Maximum RF current
Maximum RF current is the RF current permitted to flow the capacitor at working voltage, maximum capacitance and a certain frequency.
6.5 Medium waste
The medium waste should be than 10x10-4 ,or less
6.6 DC leakage current
DC leakage current is no more than 15uA.
6.7 Turning torque (for variable capacitor)
Turning torque should accord with the product specification.
7. Cooling method for vacuum capacitors
Different cooling methods permit different RF current, there are three types of cooling method:
Convection cooling
Air cooling
Water cooling
8. Storage of vacuum capacitors
Vacuum capacitors should be stored in a vertical position, in a clean, dry place.
Capacitors should take high voltage processing to maintain the voltage hold-off capability when a capacitor is stored more than 3 months.
High voltage processing of water-cooling capacitors should be sure of no water in capacitors.
9. Shipping of vacuum capacitors
For shipping, use the original package whenever possible. Variable capacitors must be kept at minimum capacitance and turn back the turning screw 3~4 cycles.
10. Testing of vacuum capacitors
For AC testing, the AC power should be 50/60Hz, capacitors' ceramic must be free from any vapor, oil or other contaminator to void external breakdown, and variable capacitors should be set to maximum capacitance.
Test voltage is the peak working voltage.
For DC testing, capacitors' ceramic must be free from any vapor, oil or other contaminator to void external breakdown, and variable capacitors should be set to maximum capacitance. DC testing is permitted only after capacitors passed AC testing.
Test voltage is the peak working voltage.
Caution: After DC testing, the capacitor must be completely discharged before next operation. There will bring out some load current after DC testing, it is dangerous.
11. Installation of vacuum capacitors
Before installation, capacitors parameters should get the requirement and be clean.
Cooling method for vacuum capacitor is determined by applied RF current of the capacitor.
One end of capacitor must be connected by soft, short and wide copper strip.
During installation, capacitors should avoid twisting or bending force to prevent distortion of the seal part that connects ceramic and metal.
12. Maintenance
Under normal operating conditions, the capacitors do not need much maintenance. They should be free from dust and kept in dry environment. The unglazed ceramic envelope can be cleaned with detergent and clean water.
The lead screw should be periodically lubricated with oil or special grease.
|