Do medium organic film capacitor
is plastic film, metal foil or metallic thin film electrode, made by winding way,
Except for laminated structure)
, with polyester film dielectric and the most widely used polypropylene film dielectric.
Organic dielectric materials are mostly synthetic polymers, abundant raw materials, wide variety, is conducive to the development of organic dielectric capacitor.
Compared with inorganic capacitor, its main weakness is: organic medium easy to aging, the performance of the capacitor will gradually decrease;
The thermal expansion coefficient of organic medium is bigger, the stability of the capacitor is poorer;
Organic medium heat resistance is poor, the working temperature of condenser and ceiling is restricted.
To distinguish between dielectric materials according to our country now use mainly have two medium polyester film and polypropylene film;
According to the electrode type to distinguish: metal foil and metalized film two structures.
In winding way to distinguish: inductive winding and non-inductive winding shows two ways of specific features in the following table: organic film points polarity organic film and nonpolar organic film, made of polar organic film capacitor is better than allowing people, high temperature resistant, resistant to high intensity of music, etc.
Made of nonpolar organic film capacitor has the loss tangent tg values in the delta of small, high insulation resistance, dielectric absorption coefficient is small, has a negative temperature coefficient, etc.
The two most common types of organic film capacitor use 1.
Polyester film capacitor characteristics: 1)
Small size, large capacity, notably the metallized polyester film capacitor size smaller.
Use the wide temperature: -
Polypropylene capacitor as: a 40 '* + 85 ° C)
Positive temperature coefficient of capacitance 4)
Tan delta loss increases with increased frequency is bigger, so should not be used in high frequency circuit.
The characteristics of polypropylene film capacitor is: 1)
Very low loss at high frequency tan delta 0 or less.
Polyester capacitor tan delta 1 or less.
And in a very wide frequency range loss change is very small, suitable for high frequency circuit.
Within 100 KHZ)
Smaller negative temperature coefficient;
High insulation resistance,
IR≥10° MQ ）
High dielectric strength, suitable for high voltage film capacitor.
Organic film capacitor advantage at present, the high volume of organic film capacitor is mainly used in all kinds of inverter power supply, as support (dc
Capacitor is used, volume shrink film capacitor can be used instead of electrolytic capacitor, and has higher ability to withstand voltage;
Organic film capacitor self-healing introduced organic metallized film capacitor's biggest advantage is that it has self-healing capability, so it become one of the fastest growing capacitor current class capacitor.
Self-healing of metalized organic film capacitor there are two different mechanisms: one kind is discharge self-healing.
The other is a electrochemical self-healing.
I and W power consumption and increases quickly, so current results in the region of the metal electrode close to the defect of current density J1 = J = V/PI r12 has risen sharply in the bajaur heat will melt of the metallized layer, cause here fly between electrode arc, arc evaporation and soon scatter off the molten metal to form without the insulation of the metal layer isolation, arc extinguishing, realize self-healing 2, electrochemical self-healing aluminum metallized organic film capacitor under low pressure, often appear this kind of self-healing.
As the growth of the time, gradually formed AL2O3 insulation cover the defect and isolation, capacitor insulation resistance greatly improved thereby, achieve self-healing.
Self-healing the pros and cons of the biggest characteristic of metalized organic film capacitor is a self-healing capability, so the benefits of self-healing is the main, however, it also has disadvantages, one of the biggest harm is caused when the pulse current, bring circuit signal interference, reduce the important performance of the circuit -
Signal to noise ratio.
So for some special demanding circuit, such as hi-fi, high precision communication circuit, etc. , can't let organic film capacitor occurs at work.
Another harm of self-healing, is the use of capacitor has a capacity of gradually reduce.
If the electric capacity at work, since many times, will cause the capacitance and insulation resistance, large loss Angle increases significantly smaller, the capacitor failure quickly.
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