What is Creepage and Clearance?

Key Concepts:

• Clearance: Shortest distance through air between two uninsulated conductors.
• Creepage: Shortest distance along the surface of an insulating material between two uninsulated conductors.
• Arc Over (Arc Discharge): Ionization of air leading to current flow across the isolation barrier.
• Tracking: Breakdown of insulation material creating a conductive path across the isolation barrier.
• Comparative Tracking Index (CTI): A measure of a material's susceptibility to tracking.
• Pollution Degree: A rating of environmental conditions affecting creepage and clearance requirements (1-4).

1. Introduction to Creepage and Clearance

• Tim Lafy, Texas Instruments Isolation Product Marketing Manager, introduces the concepts of creepage and clearance as they relate to high-voltage isolation barriers.
• These terms define the necessary distances between conductors to prevent electrical breakdown.

2. Clearance Explained

• Definition: Clearance is the shortest distance through air between two uninsulated conductors.
• Measurement: The video shows diagrams illustrating how to measure clearance distance in different scenarios.
• Importance: Adequate clearance prevents "arc over" or "arc discharge."
• Arc Over (Arc Discharge) Details: Arc over occurs when the air becomes ionized, creating a conductive path and allowing current to flow across the isolation barrier, effectively shorting it.

3. Creepage Explained

• Definition: Creepage is the shortest distance between two uninsulated conductors along the surface of an insulating material.
• Measurement: Diagrams illustrate how to measure creepage distance, emphasizing the surface path.
• Importance: Sufficient creepage prevents "tracking."
• Tracking Details: Tracking is the degradation of the insulation material's surface, forming a conductive path that shorts the isolation barrier.

4. Comparative Tracking Index (CTI)

• Different insulating materials have varying susceptibility to tracking.
• The Comparative Tracking Index (CTI) is a rating that quantifies a material's resistance to tracking.
• The CTI level of a material directly influences the required creepage distance in a design. Lower CTI materials require greater creepage distances.

5. Environmental Considerations: Pollution Degree

• Creepage and clearance cannot be considered in isolation from the operating environment.
• Pollution Degrees: Four levels (1-4) categorize environmental conditions based on the presence of conductive contaminants.
  • Pollution Degree 1: Little or no non-conductive dust.
  • Pollution Degree 4: Conducting dust (e.g., graphite, metal), condensation, rain, or snow.
• The required creepage and clearance distances increase significantly with higher pollution degrees due to the increased risk of conductive paths forming.
• Safety standards provide tables specifying creepage and clearance distances based on voltage levels and pollution degrees.

6. TI Isolation Products

• Texas Instruments (TI) offers a range of digital and analog isolation devices with varying creepage and clearance specifications.
• These products are designed to meet diverse design requirements and safety standards.
• Viewers are directed to www.ti.com/isolators to explore TI's isolation product offerings.

7. Conclusion

• The video emphasizes the importance of understanding and properly implementing creepage and clearance requirements in high-voltage isolation designs.
• Considering voltage levels, insulation material properties (CTI), and environmental conditions (pollution degree) is crucial for ensuring safe and reliable operation.