How does the Environment Affect Capacitor Performance?
The performance, shelf life, and service life of all capacitors depends largely on the environmental conditions in which they are exposed. Not only must the relationship of a single environmental factor to the capacitor, but also the effect of different combinations of these environmental factors be considered. The main environmental factors that affect the performance and life of capacitors are ambient temperature, humidity, vibration, shock, acceleration and atmospheric pressure, etc. The impact of these single environmental factors is briefly discussed as follows.
- High temperature
The high working environment temperature around the capacitor is very important to its application. The temperature rise accelerates all chemical and electrochemical reactions, the dielectric material is easy to age, and the service life of the capacitor decreases with the increase of temperature. The change of the capacitance with the increase of temperature depends on the relationship between the dielectric constant of the medium and the temperature. The capacity with a positive temperature coefficient increases with the increase of temperature, and the capacity with a negative temperature coefficient decreases with the increase of temperature.
As temperature increases, electron activity increases, so insulation resistance decreases with increasing temperature. The dielectric strength also decreases as the temperature increases, so the operating voltage must be reduced when the upper limit of use temperature is increased. High temperature oxidizes the metal, increasing the contact resistance, which increases the resistance and thus the loss.
- Low temperature
The material becomes brittle, the epoxy resin cracks, and the protective effect is lost. Moisture penetrates into the capacitor and reduces the electrical performance.
- High and low temperature shock
The thermal expansion and contraction generate internal stress, resulting in alternate condensation, freezing and evaporation, which cracks the encapsulation layer, which leads to the infiltration of water vapor and accelerates the deterioration of capacitor performance.
- High humidity
The water vapor condenses on the surface of the capacitor and is absorbed, which reduces the insulation resistance of the capacitor and causes leakage and arcing. The dielectric constant increases, and the dielectric loss increases. When water vapor enters the internal metallization layer of the capacitor and is corroded, the capacity will become smaller and the loss will increase.
- Alternating heat and humidity
After the water vapor is adsorbed on the surface of the capacitor, it absorbs and diffuses, and the effects of respiration and heated condensation can accelerate the penetration of the water vapor into the capacitor, making the performance of the capacitor worse as mentioned above.
Under the same relative humidity, when the temperature increases, the number of water molecules increases and the formation of molecular gaps is accelerated. Water molecules can enter these gaps from the surrounding air and penetrate into the interior of the medium. With the same humidity, the lower the temperature, the higher the relative humidity and the more moisture the capacitor will absorb.
Vibration, shock and acceleration are the main dynamic environments, which can cause mechanical damage or damage to capacitors, and small changes in capacitor structure cause capacitance changes. In addition, it may also cause lead breakage and poor contact.
Low pressure environment
Capacitors are used in high-altitude environments. As the height increases, the air pressure decreases, and the air resistance decreases. The capacitor will produce arcing and corona phenomena, and the withstand voltage strength of the capacitor will decrease. In addition, in the case of thin air, it is difficult to dissipate heat. The temperature rise of the capacitor will increase.
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