What you need to know about dielectric strength and breakdown voltage
Dielectric strength is a decisive property of insulating materials that describes their ability to withstand high electric voltages without an electrical breakdown. It plays a central role in electrical engineering, particularly in the design and selection of insulating materials for electrical devices and systems. This article covers the basics, measurement methods and influencing factors of dielectric strength.
GOBA processes polyester films and insulation materials with defined dielectric strength for demanding applications.
What is dielectric strength and why is it important?
Definition of dielectric strength
Dielectric strength is the maximum electric field strength that an insulating material can withstand before it breaks down electrically. It is expressed in kilovolts per millimetre (kV/mm).
Why is it important?
A high dielectric strength guarantees the safety and efficiency of electrical systems, since it prevents short circuits and sparking. It is particularly important for materials used in high-voltage systems or power transformers.
How is dielectric strength measured?
Dielectric strength is measured under controlled conditions to achieve precise and comparable results.
Measurement method
- Breakdown voltage: The voltage is increased continuously until an electrical breakdown occurs.
- Use of electrodes: Electrodes are used to distribute the field strength uniformly over the material.
- IEC 60243 series of standards: This standard describes the methods for measuring the dielectric strength of insulating materials.
Important parameters
- Humidity: Influences the conductivity of the material.
- Temperature (°C): Higher temperatures can reduce the strength.
- Field distribution: A homogeneous electric field strength is critical for accurate results.
What role does the electric field strength play?
The electric field strength indicates how strong the electric field is in a material. It has a decisive influence on when a breakdown occurs. Materials with a high dielectric strength can withstand higher field strengths before ionization occurs.
Influence of the field strength on the breakdown voltage
- Homogeneous materials: Withstand higher field strengths.
- Air inclusions: Reduce the strength, as they promote pre-discharges and ionization.
Influence of materials on dielectric strength
Insulating materials
- Plastics: Materials such as polyimide (PI) and PTFE offer high dielectric strengths and are used for electrical insulation.
- Ceramics and mica: Excellently suited for applications with extreme voltages.
Factors influencing dielectric strength
- Composition: Purity and homogeneity increase the strength.
- Moisture: Reduces the strength through increased conductivity.
- Ionization: Can weaken the dielectric barrier, leading to breakdown.
How does measurement of the breakdown voltage work?
Methods
- Direct current (DC): For long-term tests in which the stability of materials is examined.
- Alternating current (AC): Short-term tests for dynamic loads.
The role of electric voltage in measurement
The voltage is increased continuously until the insulator can no longer hold the maximum load. The point of failure is defined as the breakdown voltage.
Which factors influence dielectric strength?
Temperature
High temperatures can weaken the molecular structure, which reduces the strength.
Ionization
A strong electric field can ionize the molecules of a material, which irreversibly weakens the insulating property.
Chemical purity
Contaminants such as trapped air cavities or moisture can strongly influence the strength.
What role do plastics play in dielectric strength?
Plastics such as polyimide (PI) and polycarbonate (PC) offer a high dielectric strength, which makes them ideal for applications in electrical engineering. Their ease of processing and flexibility make them preferred materials for insulation in transformers, printed circuit boards and cables.
Where can I find references and further information?
Reliable sources
- IEC 60243 series of standards: Official standards for measuring dielectric strength.
- Literature: Technical books and specialist journals are good starting points for in-depth information.
- Online databases: Technical lexicons and manufacturer websites provide up-to-date information.
GOBA Takeaway
Dielectric strength is an indispensable material property in electrical engineering. It determines how well an insulating material can withstand high voltages and contributes significantly to the safety and efficiency of electrical systems. A sound knowledge of the influencing factors and measurement methods enables the optimal selection of materials for specific applications.