EITI

Insulation coordination is the process of coordinating the insulation level of electrical equipment and its associated surge arresters with the expected overvoltages that occur on the power system. Substation equipment as well as transmission lines and cables all require properly applied surge arresters for reliable operation. 
This section covers:

• Insulation coordination purpose and objectives
• Types of overvoltages and their causes
• Insulation types and strengths
• Overvoltage limitation
• Basic definitions
• Apply Insulation Coordination procedures to Reduce Failure Risk

• Probability distributions – Gaussian – Weibull
• Risk of failure analysis

The overvoltages that occur on power systems are due to internal causes (switching surges and temporary overvoltages) and external causes (lightning). The power system could be designed to withstand these overvoltages by using very large air insulation clearances, but it would be extremely costly and impractical to do so. The role of surge arresters is to limit the overvoltages to lower levels that provide a safety margin below the actual design voltage withstand capability of the equipment or circuit insulation. This allows more practical designs, greater system reliability and significant cost savings—key benefits of knowing how to use surge arresters in the insulation coordination process.

This section covers:

• Temporary overvoltages – faults – load rejection – resonance
• Slow front overvoltages – line switching – making and breaking reactive currents – others
• Fast front overvoltages – lightning – direct strokes – back flashovers
• Very fast front overvoltages – disconnect switch operation in GIS

• Internal and external insulation
• Self- and non-self-restoring insulation
• Air
• Liquids and gases
• BIL—basic lightning impulse insulation level

• Rated withstand voltage determination
• Test sequences 3/0, 3/9 and 15/2
• Test correction factors
• Altitude correction factors
• Pollution

• Types: silicon carbide and metal oxide without and with gaps
• Rated voltage and energy considerations
• Protective and related characteristics
• Selection procedure

• Substations
• Transmission lines
• Distribution

Metal oxide and silicon-gapped arresters are fundamentally different and cannot be applied on the same basis. While gapped arresters are voltage limited, metal oxide arresters are thermally limited devices. Various international, U.S., and Canadian standards are available to aid in the application of these devices, but they differ substantially in essential details related to arrester application.

Using clear examples based on these standards, this course will provide valuable understanding of how to correctly apply modern metal oxide arresters. Because the impact of metal oxide surge arresters on insulation coordination cannot be understated, your instructor will address this subject in detail.