Knowledge of capacitor safety protection

When the power is turned off after the capacitor is charged, the charge in the capacitor may still be stored for a long time. This charge is sufficient to produce an electric shock, or to destroy connected instruments. A disposable camera flash module, charged by a 1.5V AA dry battery, may seem safe, but the capacitor in it can charge up to 300V, and the electric shock produced by 300V can be very painful and possibly fatal.

Many capacitors have a low equivalent series resistance (ESR) and therefore generate a high current in the event of a short circuit. Before servicing equipment with large capacitors, make sure the capacitors have been discharged. For safety reasons, all large capacitors need to be discharged before assembly. If the capacitor is placed on the substrate, a bleeder resistor can be connected in parallel beside the capacitor. In normal use, the leakage current of the bleed resistor is small and will not affect other circuits. In the event of power failure, the bleed resistance can provide a path for capacitor discharge. A high voltage capacitor must be stored with its terminals short-circuited to ensure that its stored charge is discharged, because if the capacitor is suddenly discharged during installation, the resulting voltage can be dangerous.

Large, older oil-immersed capacitors contain polychlorinated biphenyls (PCBS), so they need to be disposed of properly when discarded. If not disposed of properly, PCBS can enter groundwater and contaminate drinking water. Polychlorinated biphenyls are carcinogens that can affect the human body in small amounts. If the size of the capacitor is large, it is more dangerous and needs to be extra careful. New electronic parts are no longer PCBS.

Capacitors operating at high voltages and strong currents

High voltage capacitors can suffer catastrophic damage when operating beyond their nominal voltage. A failure of the insulation material can cause an electric arc in a small unit filled with oil (which normally acts as a barrier to air), causing the insulating liquid to evaporate, causing the capacitor to bulge, crack, or even explode, which can spread flammable oil everywhere, catch fire, and damage nearby equipment. Cylindrical glass or plastic capacitors in hard packaging are more likely to burst than those in rectangular packages, which are not easy to crack under high pressure.

Capacitors that operate in RF circuits and long term in high current environments

Capacitors used in RF circuits and long term operation in strong current environments can overheat, especially the reel at the center of the capacitor. Even if the external environment temperature is low, but these heat can not be dissipated in time, concentrated in the interior may quickly lead to internal high heat resulting in capacitor damage.

Capacitor group operating in high energy environment

In a group of capacitors working in a high-energy environment, if one of them fails, the current is suddenly cut off, and the energy stored in the other capacitors will rush to the faulty capacitor, which is likely to cause a violent explosion.

High voltage vacuum capacitor

High voltage vacuum capacitors emit certain X-rays even when used correctly. Proper sealing, fusing, and preventive maintenance can help reduce these potential hazards.