Under the action of an electric field, a destructive discharge occurs inside the insulator, the insulation resistance decreases, the current increases, and the phenomenon of damage and perforation occurs.
Power capacitors are widely used as the main electrical components of reactive power compensation devices in low-voltage power distribution systems. However, because capacitors are in a state of being carried for a long time, they are often affected by overcurrents caused by various abnormal factors in the power grid.
When the voltage and current in the system exceed the rated current of the capacitor, the internal dielectric loss of the capacitor will increase, overheating will accelerate the insulation aging, and the service life of the capacitor will be reduced. In severe cases, the dielectric may be broken down.
The reasons for capacitor breakdown are:
1. Poor sealing leads to oil leakage: due to poor sealing of the assembled casing, moisture enters the interior, which reduces the insulation resistance; or the oil level drops due to oil leakage, resulting in pole-to-shell discharge or component breakdown.
2, drum belly and internal free: due to internal corona, breakdown discharge and internal free, the capacitor under the action of overvoltage, so that the initial free voltage of the component is reduced below the working electric field strength, so that the insulation accelerates aging, gas, The internal pressure of the capacitor is too large, causing the belly
3. With charge closing: the capacitor group of any rated voltage is forbidden to be charged and closed. The capacitor group is re-closed every time, and it must be executed after the switch is disconnected for 3 minutes, otherwise the closing moment will be triggered by the charge superposition. Wear phenomenon.
In order to prevent the explosion of capacitors, the capacitors on the market are mostly self-healing. The function of the capacitors is that the partial breakdown of the dielectric caused by the capacitor overvoltage can quickly heal itself and resume normal operation, which greatly improves the reliability.
Capacitor self-healing principle:
The electrode of the metallized film adopts zinc-aluminum composite technology, and the thickness of the electrode is very thin. When the inside of the capacitor is overloaded or the temperature is too high, the phenomenon of click-through occurs, the electrode around the breakdown point is ionized, and the breakdown point makes the electrode medium layer gas. Separate, create an insulation zone, and the capacitor returns to normal operation.
Generally speaking, when the capacitor is broken down, the ion ions at the breakdown point form a protective layer to ensure that the capacitor can work normally.
Post time: Jul-18-2019