What should be done when there is abnormal expansion of the housing of a high-voltage capacitor?

In the power system, high-voltage capacitors are crucial equipment for reactive power compensation, improving power factor and ensuring voltage quality. Their stable operation is of utmost importance. If any abnormal expansion such as bulging or deformation is observed on the capacitor's shell, immediate attention must be given, as this is usually a serious warning sign of an internal fault. Failure to handle it properly may lead to catastrophic accidents.

Ⅰ. The cause of abnormal expansion: Why is this a "danger signal"?

The expansion of the capacitor casing is not an accidental occurrence. The fundamental cause lies in the generation of excessively high pressure inside. The main contributing factors include:

1. Internal component breakdown: This is the most common cause. The insulating medium inside the capacitor (such as polypropylene film) may undergo local breakdown due to aging, manufacturing defects, or overvoltage after long-term operation. At the moment of breakdown, an arc is generated, which decomposes the insulating oil (or insulating gas) and produces a large amount of gas (such as hydrogen, methane, ethane, etc.).

2. Overcurrent or overvoltage operation: If the system voltage is too high, there are severe harmonics, or frequent inrush currents are applied, it will cause the capacitor to operate under long-term overload conditions, leading to overheating, accelerating the aging and decomposition of the insulating medium, and thereby generating gas.

3. Excessive environmental temperature: The installation site has poor ventilation and heat dissipation, and the ambient temperature exceeds the permitted limit, resulting in excessive temperature rise of the capacitor and increased internal pressure.

II. How to handle: Take immediate action and strictly follow safety procedures

Step 1: Immediately and urgently shut down (power off)

Primary operation: Do not hesitate! Immediately disconnect the faulty capacitor's reactive power compensation branch from the power grid by using a circuit breaker or load switch.

Step 2: Complete discharge and isolation

Force discharge: After the capacitor is disconnected from power supply, there are still a large amount of charges remaining on its two poles, with extremely high voltage and being extremely dangerous. A special discharge rod must be used. First, the discharge rod should be reliably grounded through a qualified grounding wire that has been inspected. Then, the two connection terminals of the capacitor should be fully discharged multiple times.

Step 3: Replace the treatment, no repair allowed

Correct approach: The entire capacitor unit must be replaced with a new one of the same model and specification. Before replacement, it is necessary to check whether the associated reactors, fuses, switching devices, etc. are functioning properly, and analyze the potential system causes of the capacitor failure (such as whether there are issues like excessive voltage or excessive harmonics). This is to prevent the newly replaced equipment from experiencing similar failures again.

The abnormal expansion of the casing of a high-voltage capacitor is an extremely dangerous fault signal, directly indicating internal faults and the risk of explosion. The handling principle is: immediately cut off the power supply, fully discharge, forcibly isolate, and professionally replace. Any delay, negligence or attempt to repair will likely lead to serious personal and equipment accidents. Safety first, prevention foremost, is the fundamental principle for dealing with such issues.