Hum of capacitor
from the perspective of the mechanism of hum appear, there are several possibilities.
First, in the condition of voltage, the medium between the two layer plate (
The organic film)
, under the action of electric field, because of alternating electric field force alternating elastic deformation, resulting in a elastic vibration, and then a hum.
The causes of hum were generally higher, and as the voltage rise and fall, field strength increase/decrease and change.
And the causes of hum tend to occur on the solid capacitors, rarely appears in oil-immersed capacitor.
Second, the core package package, or in addition to the core of the appendages, including gasket, cables, fuses, bundling rope, etc. , have vibration space, in the condition of voltage, or between the poles, or core package between the shell and formed an alternating electric field.
Under the action of electric field force, the existing space appendages vibration, vibration produced by hum.
Thus causes the hum is generally low.
Third, existing in the circuit of harmonic component is bigger, it is also triggered before two kinds of hum one of the causes of noise causes of film capacitor now contains a variety of high order harmonic of power grid, and mainly exists in the form of electric current, the capacitance is just like to return it, if someone USES electric welding near, or silicon controlled phase modulation of high power electric equipment, capacitance of electrode vibration and noise.
Besides harmonic current to the destruction of the capacitance effect is very big, CBB capacitor electrode is sprayed on the metal film on the film, in under the action of instantaneous large current near parts easy to stand at the ends of the ohm heat, make the film melting caused by short circuit, although the CBB capacitance of short-circuit self-healing ability, but after the healing of the ESR get bigger, more easy to fever, vicious circle, soon complete failure.
Because of the thin film thermal conductivity is small, cannot use the appearance to judge the internal temperature of instantaneous local temperature rise, so it's best to check the specifications of the manufacturer, should have restrictions to wave pulse current, the unit product should be the current time, such as according to seconds, according to ms.
It is possible that the current is too large, didn't also give current limiting resistor.
2 uf good quality capacitor is absolutely not low price.
The whole circuit volume that is smaller than the same ability of power frequency transformer.
Film capacitor noise test pressure test 1, using pressure tester for the capacitance of the electrode pressure, casing pressure test, to ensure the withstand voltage of capacitor quality, time of the test set, press 'timing adjustment' select test time (
Such as thin film capacitor plus 2 times the Un, 2 s no permanent breakdown)
To 'manual' and 'time' button, adjust to the 'timing' gear.
2, to adjust the voltage type, thin film capacitor selection 'AC' gear, electrolytic capacitor choose 'DC' gear;
Open the tester power supply, press the switch tester handles, according to the product technical parameters adjusting test voltage (
The unit for KV)
2 times, generally choose the Un test voltage, set of 'leakage' in general to 0.
2 ma for the push.
3, then the zero line connected to one side and capacitance tester, wire - a probe
- - - - - -
Client contact with capacitance at the other end, and the handle of the button, after completion of the 'timing' time, if the 'super' leakage tester indicator light is not bright, warning buzzer not ring, shows that the test qualified.
Withstand voltage test between 4 and shell, the UN AC660V or less, the test voltage to 3000 VAc, 10 s, test time for UN AC660V or higher, test voltage to 6000 v, 10 s, test time according to the state of 'super' leakage indicator judging if they are qualified.
And withstand voltage test of electrolytic capacitors, in strict accordance with the portable line with technical parameters by the test, in case the capacitance blasting test voltage is set too high.
Generally the noise of the film capacitor, work in some specific occasions, such as cross line, step-down communication occasions such as film capacitance noise may exist, this is because the gap between film, under the action of alternating electric field in vibration.
At the current technology and statistics to see that film capacitance noise had no obvious effect on the performance of the condenser.
It generally results from the reason of the manufacturing process, the technological progress can significantly improve or solve this problem, so ouyi electronic advice must choose qualified, the manufacturer of high quality, good manufacturer production of film capacitors can be done without noise or noise is small.
If it is can't accept the noise, can choose to replace the film capacitance.
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