Partial discharge facts for kids

A partial discharge (PD) is a small electric discharge that happens inside the insulation of electrical equipment. Think of it like a tiny spark or a mini-lightning bolt that doesn't fully cross the gap between two conductors. Instead, it just zaps a small part of the insulation.

This happens when electrical equipment is under stress from high voltage. It's often caused by tiny air bubbles or cracks, called "voids," inside the insulating material. These voids can be in solid materials like plastic or liquid materials like oil. Over time, these small discharges can slowly damage the insulation, which might lead to bigger problems for the equipment.

What is a Partial Discharge?

A partial discharge is a tiny electrical spark that occurs within the insulating material of electrical equipment. It's called "partial" because it doesn't completely bridge the space between two metal parts that carry electricity. Instead, it only happens in a small, weak spot within the insulation.

Imagine an electrical cable with a protective layer around it. If there's a tiny bubble or gap inside that protective layer, electricity can try to jump across that gap. This small jump is a partial discharge. It's not a full short circuit, but it's a sign that the insulation isn't perfect.

Why Do Partial Discharges Happen?

Partial discharges usually happen because of small flaws in the insulating material. These flaws can be:

• Tiny air bubbles: Sometimes, during manufacturing, small air pockets get trapped inside solid insulation.
• Cracks or gaps: Over time, insulation can develop tiny cracks due to heat, stress, or aging.
• Contamination: Dirt or moisture can get into the insulation, creating weak spots.

When high voltage is applied to the equipment, the electric field becomes very strong around these flaws. This strong field can cause the gas (like air) inside the void to break down electrically, creating a small spark. This is similar to how lightning forms in a cloud, but on a much smaller scale.

Where Can We Find Partial Discharges?

Partial discharges can occur in many types of high-voltage electrical equipment. This includes:

• Power cables: The underground or overhead lines that carry electricity.
• Transformers: Devices that change voltage levels in power grids.
• Switchgear: Equipment used to control and protect electrical circuits.
• Generators and motors: Machines that produce or use electricity.

Anywhere there is high voltage and insulating material, there's a chance for partial discharges to occur if the insulation has flaws.

Why Are Partial Discharges Important?

Even though they are small, partial discharges are a big deal for electrical equipment. Here's why:

• Damage over time: Each tiny spark slowly wears away the insulation. Over months or years, this damage can grow.
• Equipment failure: If the damage gets too bad, the insulation can completely fail. This leads to a full electrical breakdown, which can cause equipment to stop working, sometimes with a loud bang or fire.
• Costly repairs: Replacing damaged high-voltage equipment is very expensive and can cause power outages.
• Safety risks: In some cases, equipment failure due to PD can pose safety risks to people nearby.

Engineers regularly test electrical equipment for partial discharges. Finding them early helps prevent major failures and keeps our electricity supply reliable and safe.

Images for kids

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  Partial discharge test set with partial discharge meter, manual test adapter for semiconductors (for example optocoupler) and computer with control software from MPS Mess-& Prüfsysteme.

See also

In Spanish: Descarga parcial para niños