Views:3 Author:Site Editor Publish Time: 2021-04-28 Origin:Site
Common causes of impact on thin film capacitors
Reasons for problems in use:
1. The high operating voltage causes the premature phase-shifting capacitor to be phased out prematurely, the power loss and heat generation of the capacitor are proportional to the square of the operating voltage, the operating voltage is increased, so that the temperature of the capacitor increases significantly, and under the action of the long-term electric field, it will accelerate the aging of the capacitor insulation
2. Operating overvoltage causes damage to the capacitor, and when the parallel capacitor group is cut off, it may cause the oscillation process of an inductive capacitor circuit. Thus, the operating voltage is generated, and during the cut-off process, if the circuit breaker is rekindled with an arc, it will cause a strong electromagnetic oscillation with a higher overvoltage value. The magnitude of this overvoltage is related to the size of the cut capacitor and the bus side capacitor, as well as to the potential difference between the contacts when the arc is rekindled.
3. Charged closing shall cause the explosion of the capacitor, and any capacitor group rated voltage shall prohibit the charge closing. Each time the capacitor block re-closes, it must be carried out after the switch disconnects the capacitor from discharge 3min.
Damage to the phase shift capacitor due to excessive operating temperature:
1. The ambient temperature is too high, the current YY type and YL type transfer capacitor surrounding air temperature system according to a 25-40C design. The requirement that the ambient temperature does not exceed 40'C is difficult to meet in many parts of our country. Therefore, the new low-pressure reactive compensation device, the surrounding air temperature is designed at a 30-55C.
2. Outdoor capacitors direct sunlight, phase-shifting capacitors open-air installation in substations or distribution lines on the road, due to direct sunlight, due to over-temperature operation reasons. The annual damage rate is very high, some can reach about 10%. Especially in the outdoor iron distribution box, poor heat dissipation, summer damage rate is particularly high. In addition, in the hot weather suddenly heavy rain, can also concentrate on causing damage.
3. Insufficient ventilation and cooling
Effects of network off-secondary harmonics:
1. Make the operating current and output reactive power of the capacitor group exceed the rating significantly.
2. When the supply voltage waveform in a harmonic frequency. Harmonic resonance overvoltage may occur when approaching the natural frequency of the network
Shadows of switchgear performance:
When the capacitor is removed, it does not generate excessive voltage if the switch is not reburned and is switched off. There is also no overcurrent. Improving the ability of the switch to cut capacitive current is an important aspect of reducing accidents and extending the life of capacitors.
Reasons for affecting the capacity size of thin film capacitors:
The capacity size of thin film capacitors depends on the size of the film metal layer area, so the decrease in capacity is mainly due to the influence of external factors on the metal coating, the reduction of the area. During the production of capacitors, trace amounts of air exist between the film layers and are difficult to eliminate completely. When the capacitor is operating, the air may be ionized under the action of an electric field. After air ionizing produces ozone, ozone is an unstable gas, at room temperature self-decomposition into oxygen, is a strong oxidant, low concentration can be instantaneously completed oxidation. The metal coating of the metalized film (component Zn/Al) oxidizes immediately after encountering the oxygen of ozone decomposition, resulting in transparent and non-conductive metal oxides ZnO and Al2O3, which actually shows that the plate area is reduced and the capacitor capacity decreases. Therefore, eliminating or reducing the air between the membrane layers can slow down the decay of electrical capacity. When the air between the membrane layers is invaded by external water, the penetration potential of the air will be reduced, speeding up air ionization, producing a large amount of ozone, metal coating of the oxide metallized film, the capacity of the capacitor will rapidly decline.