Insulation Coordination Studies

What are Insulation Coordination Studies?

• Insulation coordination studies can be used to select the proper insulation level for the power system equipment or to check whether the selected insulation level of the equipment is sufficient to withstand the transient overvoltage.

• The transient overvoltage can be generated due to internal problems such as ground faults, line and load rejection, switching operation, energization of line and transformer, and resonance. Also, it can be generated due to external problems such as lightning (i.e., shielding failure and back flashover).

• Insulation coordination studies can be classified into 4 categories based on the characteristics of transient overvoltage. They are temporary overvoltage (i.e., power frequency overvoltage), slow front overvoltage (i.e., Switching overvoltage), fast front overvoltage (i.e., lightning overvoltage), and very fast front overvoltage studies.

What is the Importance of Insulation Coordination Studies?

The main purpose of insulation coordination Studies is:

• To select the proper insulation level for the power system equipment in the system/substation.

• To verify the selected insulation levels of the equipment are sufficient for safe and secure operation and also to withstand the temporary, switching, and lightning transients.

• To avoid damage to the system/substation equipment.

• To avoid the interruption of supplies to the customers and circuit interruption.

How Do We Perform Insulation Coordination Studies?

• Step-1: Data collection such as single line diagram (SLD), substation layout, transformers, transmission line conductor, tower, and insulator, surge arrester, system short circuit level, site conditions, substation equipment such as circuit breaker, disconnector, capacitive voltage transformer, bus post insulator, etc.

• Step-2: Modeling the study system/substation for temporary, switching, and lightning overvoltage studies using PSCAD/EMTDC software.

• Step-3: Preparation of simulation case studies for temporary, switching, and lightning overvoltage studies scenarios based on the clients requirement.

• Step-4: Preparation of technical report and submission to clients.

What Standards can be Referred for Insulation Coordination Studies?

• IEC 60071-1 - Insulation co-ordination - Part 1: Definitions, principles, and rules.

• IEC 60071-2- Insulation co-ordination – Part 2: Application guidelines.

• IEC 60071-4 – Insulation co-ordination — Part 4: Computational guide to insulation co-ordination and modelling of electrical networks.

• CIGRE WG C4.23 - Procedures for Estimating the Lightning Performance of Transmission Lines – New Aspects.

• CIGRE WG 33.01 - Guide to Procedures for Estimating the Lightning Performance of Transmission Lines.

• IEEE Std 1313.2™-1999 (R2005) - IEEE Guide for the Application of Insulation Coordination.

• IEEE Std C62.82.1™-2010 - IEEE Standard for Insulation Coordination—Definitions, Principles, and Rules.

• IEEE Std 1243-1997 - IEEE Guide for Improving the Lightning Performance of Transmission Lines.

• EPRI Transmission Line Reference Book - 345 kV and above.

• IEEE Std C62.22™-2009 - IEEE Guide for the Application of Metal-Oxide Surge Arresters for Alternating-Current Systems.

• IEC 60099-5:2018 - Surge arresters - Part 5: Selection and application recommendations.