What is a corona discharge and how does it arise in power lines?
Definition and formation process of the corona discharge
A corona discharge is a physical phenomenon that occurs when the electric field strength near a current-carrying conductor exceeds a critical threshold. The ionisation of the surrounding air generates a faintly luminous plasma around the conductor. The discharge occurs preferentially at sharp edges or surface irregularities, since the electric field strength is highest there.
Corona-resistant insulation materials such as mica-based insulants are standard in high-voltage applications.
Positive and negative corona discharges: differences and effects
Positive corona discharge: Electrons are removed from the air, creating positive ions. This type of discharge is generally more stable.
Negative corona discharge: Electrons are emitted into the environment, which promotes the formation of secondary electron avalanches. This form of discharge frequently produces more ozone.
Electric field strength and ionisation of the air
Ionisation of the air occurs when the electric field strength exceeds the dielectric strength of the air (about 30 kV/cm under standard conditions). This produces free electrons that collide with other molecules and release further electrons. This electrical discharge results in the emission of UV light and can be visible as a bluish glow.
What effects do corona discharges have on power lines?
Energy losses and efficiency reduction
Corona discharges lead to energy losses by removing charge carriers from the air and dissipating current. In high-voltage lines in particular, this can reduce energy efficiency.
Ozone formation and environmental impact
The ionisation of the air generates ozone (O₃), a reactive gas that is harmful to the environment in large quantities. Corona discharges therefore contribute to a local increase in ozone concentration.
Noise emission and electromagnetic interference
Acoustic emissions: Corona discharges generate crackling noises that can be heard near high-voltage lines.
Radio interference: The discharges emit electromagnetic waves that can affect radio communication and electronic equipment.
How can corona discharges be measured in power lines?
Measurement methods and instruments for corona discharges
Various methods are used to detect corona discharges:
- Optical methods: special cameras capture the UV light emitted by the corona
- Acoustic measurements: microphones detect the characteristic crackling of the discharges
- High-frequency measurements: electromagnetic waves emitted by the discharge are detected
Interpretation of measurement results and limit values
Measurement results are presented in the form of corona intensity maps. International standards and guidelines (e.g. IEC 60270) define which values are acceptable and which measures must be taken.
What techniques are available to reduce corona discharges?
Optimisation of conductor geometry and surface condition
Corona discharges occur particularly at sharp edges and uneven surfaces. Optimising the conductor geometry can distribute the electric field more evenly and minimise the discharge.
Use of corona rings and other protective devices
Corona rings are metal rings placed around high-voltage lines to distribute field strength evenly. This reduces ionisation of the air.
Adjusting operating voltage and insulation techniques
- Voltage reduction: a slight reduction in operating voltage can significantly decrease corona formation
- Use of improved insulators: high-quality insulating materials and specially coated conductors minimise electrical discharge
How does the environment influence the formation of corona discharges?
Weather and climate effects on corona discharges
Humidity and rain increase the likelihood of corona discharges, since water droplets act as additional charge carriers. Dry air, by contrast, reduces the risk.
Altitude dependency and air humidity
- Higher humidity reduces the dielectric strength of the air, causing corona discharges to occur more frequently
- At higher altitudes with lower air pressure, corona formation can increase, since the air molecules are further apart
What role do corona discharges play in the planning of high-voltage lines?
Consideration of corona effects in design
When constructing high-voltage lines, the effects of corona discharge must already be taken into account during the planning phase to minimise efficiency losses and environmental impact.
Economic aspects and cost-benefit analysis
- Energy losses from corona discharges cause additional operating costs
- Investments in optimised conductor geometries and protective measures can reduce maintenance costs in the long term
How is research into corona discharges developing?
Current research approaches and innovations
- Use of AI-assisted measurement techniques to accurately detect and predict corona discharges
- New conductive coatings that improve surface condition and minimise corona intensity
Future challenges and solution approaches
- Further development of environmentally friendly high-voltage technologies to reduce ozone formation caused by corona discharges
- Optimisation of grid voltage and insulation materials to minimise energy losses from electrical discharges
GOBA Takeaway
Corona discharges are an unavoidable phenomenon in high-voltage lines but can be minimised through targeted measures. Advances in materials technology, insulation processes and measurement techniques help to reduce efficiency losses and environmental impact. Research is increasingly focused on intelligent monitoring systems and new materials that allow even better control of corona discharges.