Insulation Coordination: Overvoltage Protection

Insulation Coordination Purpose

• The main goal of insulation coordination is to protect electrical equipment against overvoltages.

Insulation Level Factors

• A critical factor for determining insulation levels is the voltage rating of the system.

Overvoltages Considered

• Temporary, switching, and lightning overvoltages are all considered during insulation coordination.

Basic Insulation Level (BIL)

• BIL indicates the withstand voltage under lightning impulse conditions.

Switching Overvoltages

• Capacitor switching is the primary cause of switching overvoltages in power systems.

Limiting Overvoltages

• Surge arresters are commonly used to limit overvoltages.

Insulation Coordination Optimization

• Insulation coordination optimizes the design of electrical insulation systems.

Primary Standard

• The primary standard for insulation coordination is IEC 60071.

Flashover

• A flashover involves a complete breakdown of insulation that leads to short circuits.

Insulation Level Selection

• Expected overvoltages and system performance needs mainly determine insulation levels.

Objectives

• The key objective of power systems insulation coordination is to achieve a balance of cost-effectiveness and reliability

Affecting Factors

• Voltage stress primarily impacts the insulation performance of electrical equipment.

Surge Arresters

• Surge arresters prevent voltage surges from damaging insulation.

Temporary Overvoltages

• Capacitor switching contributes to temporary overvoltages.

Creepage Distance

• Creepage distance is measured along the surface of an insulator between two conductive parts.

Insulation Strength Parameters

• Lightning impulse withstand voltage defines insulation strength against lightning impulses.

Insulation Coordination and Surge Arresters

• Coordination is vital to avoid excessive insulation costs while maintaining protection.

Basic Insulation Level (BIL) Selection

• System voltage and expected overvoltage levels affect BIL selection.

High Voltage Systems

• In high-voltage systems external insulation failure often results from contaminants and moisture accumulation.

Protective Gaps

• Protective gaps allow safe overvoltage dissipation using controlled arcing.

Insulation Failure

• Dielectric breakdown is the type of insulation failure that happens when electric stress surpasses the insulating material's strength.

Shielding Electrodes

• A main goal for shielding electrodes is to distribute electric field stress evenly.

Mitigating Lightning Overvoltages

• Using surge arresters is an effective way to mitigate lightning overvoltages.

Withstand Voltage

• Withstand voltage is the highest voltage an insulation system can endure without failure.

Insulation Material Selection

• Dielectric strength and thermal stability are key factors when selecting insulation material for high-voltage applications.

Margin of Insulation Coordination

• The difference between operational voltage and insulation breakdown voltage defines of insulation coordination.

Determining Insulation Level

• Environmental conditions, like humidity and pollution, play a major role in establishing insulation levels.

Transformer Insulation Failure

• Internal insulation failure in transformers can arise from insulation aging and degradation.

Extra High Voltage (EHV) Systems

• Insulation coordination in EHV systems minimizes insulation failure risks from overvoltages.

Impulse Voltage

• Impulse voltage refers to a high transient voltage that has a very short duration.

Analyzing Insulation Coordination

• Overvoltage withstand testing is commonly used to analyze insulation coordination

Basic Insulation Level (BIL) Indication

• A higher BIL indicates a higher tolerance to impulse overvoltages.

Insulation Thickness

• Maximum expected overvoltage impacts insulation thickness.

Medium-Voltage Systems

• In medium-voltage power systems the main goal of insulation coordination is to prevent equipment damage from surges.

Insulation Coordination Studies

• Transformer cores are not key components in insulation coordination studies.

Insulation Failure Mechanism

• Long-term exposure to high voltage stress will cause partial discharge.

Grading Rings

• Grading rings reduce voltage stress along insulator surfaces.

Transient Overvoltages

• Proper grounding and surge protection are most effective for reducing the impact of transient overvoltages.

Pollution Effects

• Pollution decreases insulation resistance, increasing flashover risk.

Switching Surges

• Switching surges cause insulation breakdown and system failures in EHV systems.

High Voltage Transmission Lines

• Dielectric strength is the most important parameter when selecting insulation for high-voltage transmission lines.

Voltage Stress

• Impulse overvoltage stress is most commonly associated with failures

Polymer v Porcelain Insulators

• Polymer insulators provide better mechanical strength and pollution resistance than porcelain.

Underground Cables

• High levels of moisture and contamination increases the risk of insulation failure in underground cables.

Corona Rings

• Corona rings distribute electric field stress and prevent corona discharge.