William A. Chisholm

Insulators for icing and polluted environments

PREFACE. ACKNOWLEDGMENTS. 1. INTRODUCTION. 1.1. Scope and Objectives. 1.2. Power System Reliability. 1.3. The Insulation Coordination Process: What Is Involved? 1.4. Organization of the Book. 1.5. Precis. 2. INSULATORS FOR ELECTRIC POWER SYSTEMS. 2.1. Terminology for Insulators. 2.2. Classification of Insulators. 2.3. Insulator Construction. 2.4. Electrical Stresses on Insulators. 2.5. Environmental Stresses on Insulators. 2.6. Mechanical Stresses. 3. ENVIRONMENTAL EXPOSURE OF INSULATORS. 3.1. Pollution: What It Is. 3.2. Pollution Deposits on Power System Insulators. 3.3. Nonsoluble Electrically Inert Deposits. 3.4. Soluble Electrically Conductive Pollution. 3.5. Effects of Temperature on Electrical Conductivity. 3.6. Conversion to Equivalent Salt Deposit Density. 3.7. Self-Wetting of Contaminated Surfaces. 3.8. Surface Wetting by Fog Accretion. 3.9. Surface Wetting by Natural Precipitation. 3.10. Surface Wetting by Artificial Precipitation. 4. INSULATOR ELECTRICAL PERFORMANCE IN POLLUTION CONDITIONS. 4.1. Terminology for Electrical Performance in Pollution Conditions. 4.2. Air Gap Breakdown. 4.3. Breakdown of Polluted Insulators. 4.4. Outdoor Exposure Test Methods. 4.5. Indoor Test Methods for Pollution Flashovers. 4.6. Salt-Fog Test. 4.7. Clean-Fog Test Method. 4.8. Other Test Procedures. 4.9. Salt-Fog Test Results. 4.10. Clean-Fog Test Results. 4.11. Effects of Insulator Parameters. 4.12. Effects of Nonsoluble Deposit Density. 4.13. Pressure Effects on Contamination Tests. 4.14. Temperature Effects on Pollution Flashover. 5. CONTAMINATION FLASHOVER MODELS. 5.1. General Classifi cation of Partial Discharges. 5.2. Dry-Band Arcing on Contaminated Surfaces. 5.3. Electrical Arcing on Wet, Contaminated Surfaces. 5.4. Residual Resistance of Polluted Layer. 5.5. dc Pollution Flashover Modeling. 5.6. ac Pollution Flashover Modeling. 5.7. Theoretical Modeling for Cold-Fog Flashover. 5.8. Future Directions for Pollution Flashover Modeling. 6. MITIGATION OPTIONS FOR IMPROVED PERFORMANCE IN POLLUTION CONDITIONS. 6.1. Monitoring for Maintenance. 6.2. Cleaning of Insulators. 6.3. Coating of Insulators. 6.4. Adding Accessories. 6.5. Adding More Insulators. 6.6. Changing to Improved Designs. 6.7. Changing to Semiconducting Glaze. 6.8. Changing to Polymer Insulators. 7. ICING FLASHOVERS. 7.1. Terminology for Ice. 7.2. Ice Morphology. 7.3. Electrical Characteristics of Ice. 7.4. Ice Flashover Experience. 7.5. Ice Flashover Processes. 7.6. Icing Test Methods. 7.7. Ice Flashover Test Results. 7.8. Empirical Models for Icing Flashovers. 7.9. Mathematical Modeling of Flashover Process on Ice-Covered Insulators. 7.10. Environmental Corrections for Ice Surfaces. 7.11. Future Directions for Icing Flashover Modeling. 8. SNOW FLASHOVERS. 8.1. Terminology for Snow. 8.2. Snow Morphology. 8.3. Snow Electrical Characteristics. 8.4. Snow Flashover Experience. 8.5. Snow Flashover Process and Test Methods. 8.6. Snow Flashover Test Results. 8.7 Empirical Model for Snow Flashover. 8.8. Mathematical Modeling of Flashover Process on Snow-Covered Insulators. 8.9. Environmental Corrections for Snow Flashover. 8.10. Case Studies of Snow Flashover. 9. MITIGATION OPTIONS FOR IMPROVED PERFORMANCE IN ICE AND SNOW CONDITIONS. 9.1. Options for Mitigating Very Light and Light Icing. 9.2. Options for Mitigating Moderate Icing. 9.3. Options for Mitigating Heavy Icing. 9.4. Options for Mitigating Snow and Rime. 9.5. Alternatives for Mitigating Any Icing. 10. INSULATION COORDINATION FOR ICING AND POLLUTED ENVIRONMENTS. 10.1. The Insulation Coordination Process. 10.2. Deterministic and Probabilistic Methods. 10.3. IEEE 1313.2 Design Approach for Contamination. 10.4. IEC 60815 Design Approach for Contamination. 10.5. CIGRE Design Approach for Contamination. 10.6. Characteristics of Winter Pollution. 10.7. Winter Fog Events. 10.8. Freezing Rain and Freezing Drizzle Events. 10.9. Snow Climatology. 10.10. Deterministic Coordination for Leakage Distance. 10.11. Probabilistic Coordination for Leakage Distance. 10.12. Deterministic Coordination for Dry Arc Distance. 10.13. Probabilistic Coordination for Dry Arc Distance. 10.14. Case Studies. APPENDIX A: MEASUREMENT OF INSULATOR CONTAMINATION LEVEL. APPENDIX B: STANDARD CORRECTIONS FOR HUMIDITY, TEMPERATURE, AND PRESSURE. APPENDIX C: TERMS RELATED TO ELECTRICAL IMPULSES. INDEX.

Electric Fields on AC Composite Transmission Line Insulators

This paper provides an overview of the electric field (E-field) distribution on transmission line composite insulators applied in alternating current applications. Factors that affect the E-field distribution are discussed as well as the influence of the E-field distribution on the short and long term performance. Modeling and measurement methods are reported and examples of calculated E-field magnitudes determined are presented together with corona ring application information. This paper was developed by the IEEE Task force on electric fields and composite insulators.

Selection of Line Insulators With Respect to Ice and Snow—Part II: Selection Methods and Mitigation Options

Special measures may be needed to select line insulators for transmission and distribution lines in locations exposed to freezing conditions. This second part of the paper describes the strength of typical line insulation in these conditions and then deals with selection and mitigation methods based on the in-service stresses described in Part I.

Selection of Line Insulators With Respect to Ice and Snow—Part I: Context and Stresses

Special measures may be needed to select line insulators for transmission and distribution lines in locations exposed to freezing conditions. This first part of the paper describes the environmental and electrical stresses encountered in service that influence the risk of flashover on line insulators. Part II of the paper describes the strength of typical line insulation in these conditions and deals with selection and mitigation methods.

Real-Time Overhead Transmission-Line Monitoring for Dynamic Rating

This paper discusses the wide range of real-time line monitoring devices which can be used to determine the dynamic thermal rating of an overhead transmission line with the power system operating normally or during a system contingency. The most common types of real-time monitors are described including those that measure the line clearance, conductor temperature, and weather data in the line right of way. The strengths and weaknesses of the various monitoring methods are evaluated, concluding that some are more effective during system normal and others during system contingency conditions.

50 years in icing performance of outdoor insulators

During the last 50 years a significant technical advance, namely in our understanding and control of switching-surge overvoltages, has had some unintended and adverse consequences when designers took full advantage of the possibility of reduced insulator dimensions. Glaze ice accretion can produce harmful effects, especially on closely spaced or large-diameter station post insulators and bushings. Partial or full bridging of the leakage distance occurs for moderate ice-accretion levels and reduces insulator reliability during melting in saturated conditions. Colocation of HV or EHV substations with roads or expressways on which deicing salt is spread has proved particularly problematic. The DEIS has played an important role as a forum for exploring icing flashover physics and as a sponsor of improved test methods and applications guidance.

Key Considerations for the Selection of Dynamic Thermal Line Rating Systems

Recent reviews have shown that many methods can be used for estimating the dynamic thermal capacity of overhead transmission lines. A number of approaches are described and key features of each system are organized. Data from field trials provide a unique basis for assessing the variation in ten different parameters. Characteristics of distributed measurement systems are underscored and contrasted against point measurements systems.

A coupled computational fluid dynamics and heat transfer model for accurate estimation of temperature increase of an ice-covered FRP live-line tool

Controlled laboratory tests validated a hypothesis that extremely light (~2-3 μg/cm2) levels of Equivalent Salt Deposit Density (ESDD) with no Non-Soluble Deposit (NSDD) can reduce voltage withstand capability of Fiberglass-Reinforced Plastic (FRP) hot sticks under cold-fog conditions near the freezing point, where the tool surfaces are fully wetted by the environment or alternately surrounded by fog. However, the source of moisture in flashovers at temperatures below -13 °C was not established. The mechanism of tool surface wetting was explored through coupled Computational Fluid Dynamics (CFD) and Heat Transfer mathematical equations for a FRP hot stick modeled in Commercial software, COMSOL Multiphysics. The results show that the flow of partial discharge current could be sufficient to raise the temperature of an iced pollution layer just below freezing, where the cold-fog flashover mechanism prevails.

Grounding of overhead transmission lines for improved lightning protection

Improved grounding can be a cost-effective method to improve power quality by reducing the number of lightning flashovers on shielded overhead transmission lines. Improvements can be valued against benchmark values of cost per avoided customer momentary dip. Effectiveness of improvements can vary widely because the local soil resistivity varies with a wide statistical distribution. A portable impulse Zed-Meter00AE; can be used to measure the local transient response of transmission tower ground electrodes.

Editorial: Flashover of Ice- and Snow-Covered Insulators

The 15 papers in this special issue focus on the subject of flashover of ice- and snow-covered insulators.