What is the difference between surface leakage current and leakage current?
Electrical systems must be reliable and safe, yet surface leakage current and leakage current present significant risks to the functionality and safety of electrical installations. These uncontrolled currents can cause dangerous material fatigue, malfunctions or even fires. In this article we examine the causes, risks and preventive measures for surface leakage and leakage currents in electrical engineering.
GOBA supplies insulation materials with high creepage current resistance for electrical engineering applications.
Definition and formation of surface leakage current
Surface leakage current refers to unwanted electrical currents that flow along the surface of an insulator rather than being conducted within a conductor. This effect occurs particularly in the presence of moisture, contamination or deposits that increase the electrical conductivity of the insulation surface.
Characteristics and causes of leakage current
Leakage current, in contrast, describes electrical currents that flow through the insulation itself, not along the surface but through the material. This can be caused by ageing, mechanical stress or material fatigue. Leakage currents are particularly critical in low-voltage installations, as they can represent a latent fire hazard.
Effects on electrical systems and safety
Both types of current are potentially dangerous, as they:
- Cause malfunctions in electrical equipment
- Reduce the service life of insulating materials
- Increase fire risks in electrical installations
- Can cause electric shocks to people
Which factors promote the formation of surface leakage currents?
Influence of humidity and air moisture
High humidity and condensation promote the conductivity of surfaces. Moisture settles on insulators and forms a conductive layer that facilitates surface leakage currents. This occurs particularly in unheated or poorly ventilated areas.
Role of contamination and deposits
Dust, soot, salts or chemical reactions on insulation materials can form conductive deposits. Industrial environments with pollutant load and corrosion are particularly affected.
Importance of the surface condition of insulators
Insulators with a rough or porous surface are more likely to absorb contaminants or moisture. Smoother surfaces reduce surface leakage current formation, while materials such as silicone or glass-fibre-reinforced plastic have special hydrophobic properties that prevent surface leakage currents.
How does material fatigue affect the formation of surface leakage and leakage currents?
Ageing processes in insulating materials
Over time, insulating materials age through thermal and mechanical stress, reducing their dielectric strength. Plastics in particular lose their insulating effect through micro-cracks and degradation.
Influence of UV light and ozone on insulation materials
Long-term UV radiation and ozone can make insulating materials brittle and cracked. Overhead-line insulators in particular are strongly exposed to these conditions and require special protective measures.
Effects of operating temperature and thermal stress
Elevated operating temperatures accelerate the ageing of insulating materials. This leads to increased oxidation and degradation, impairing or destroying the insulation.
What preventive measures exist against surface leakage and leakage currents?
Selection of suitable insulating materials and substrates
Durable materials with high moisture resistance (e.g. polyester films, glass-fibre-reinforced plastic or silicone) minimise the risk of surface leakage currents.
Regular maintenance and cleaning of electrical components
Electrical installations should be cleaned and inspected regularly to remove deposits and contamination.
Optimisation of creepage distances and air clearances
Extended creepage distances and larger air clearances reduce the risk of partial discharges and surface leakage currents. In high-voltage lines in particular, creepage distance extensions are implemented through insulated covers or special insulators.
How can surface leakage and leakage currents be measured and monitored in practice?
Measurement methods and instruments for detecting surface leakage currents
Surface leakage currents are usually measured with special insulation resistance testers. A rule of thumb is: the lower the insulation resistance, the higher the risk of surface leakage currents.
Monitoring systems for leakage currents in low-voltage installations
Modern leakage current monitoring systems detect even small fault currents and can trigger alarms to prevent greater damage.
What dangers do surface leakage and leakage currents pose to people and equipment?
Risk of electric shocks and electrical accidents
An excessively high surface leakage current can electrify contact surfaces, posing a significant electric shock risk to people.
Potential damage to electrical and electronic devices
Leakage currents can damage sensitive electronic components or cause entire systems to fail.
Fire hazard from surface leakage and leakage currents
The greatest danger of surface leakage currents is potential fire formation, as local overheating or arcing can lead to a short circuit or ignition of the insulating materials.
GOBA Takeaway
Surface leakage and leakage currents pose serious risks to electrical safety and the longevity of insulating materials. Through the targeted use of high-quality insulating materials, regular maintenance and the use of modern monitoring systems, these risks can, however, be significantly reduced.
The key measures in summary:
- Selection of durable insulating materials (e.g. silicone, glass-fibre-reinforced plastic)
- Regular cleaning and maintenance of insulation surfaces
- Extended creepage distances to increase insulation
- Measurement methods and monitoring systems for early detection
- Protection against moisture and contamination, particularly in harsh environments