Insulation Coordination Studies

1. Insulation Coordination

Transient overvoltage is one of the major concerns for high voltage (HV) substations and transmission systems. Overvoltage and Insulation coordination studies are very important for the economical way of designing the insulation level of equipment in HV air insulated substation (AIS), gas-insulated substations (GIS), and transmission systems.

The Insulation coordination studies are the process to determine the insulation strength of equipment in relation with the operating voltage and transient overvoltage, or it is the process to verify that the selected insulation level of the equipment is sufficient for the safe operation under transient overvoltage caused by the switching and lightning.

The main purpose of Insulation coordination studies is to reduce the number of failures, cost of design, installation, and operation. The standard insulation level of equipment, procedure, and modeling guidelines for IC studies are presented in IEEE/IEC/CIGRE standards.

2. Standard Procedure for Insulation Coordination Studies

The IC studies can be carried out according to IEC 60071 (Part-1 to Part-4), IEEE C62.82.1, IEEE 1313.2-1999, CIGRE WG C4.23, and CIGRE WG 33.01 standards. As per the standards, the IC study consists of the following steps.

Step-1: Determine the maximum overvoltage (i.e., voltage stresses).

To determine the peak overvoltage, transient simulation case studies can be performed. The result of transient simulation and analysis can provide the peak overvoltage for the following cases:

• Temporary overvoltage (TOV)

• Slow front overvoltage (SFO)

• Fast front overvoltage (FFO)

• Very fast front overvoltage (VFFO)

The amplitude, duration, and wave-shape of voltage stresses are determined by transient simulation and analysis.

Step-2: Select the insulation strength (i.e., standard insulation level) from the Standards

Step-3: Compare the determined maximum overvoltage with the standard insulation level

Step-4: Suggestion to reduce the voltage stresses by proposing the surge arrester, improving the grounding system, or providing any other recommendations.

References

• IEEE. "IEEE Standard for Insulation Coordination-Definitions, Principles, and Rules." IEEE Std C62. 82.1-2010 (Revisión de IEEE Std 1313.1-1996) (2011).

• International Electrotechnical Commission. "Insulation co-ordination—Part 2: Application guidelines." International Standard, IEC (2018): 60071-2.

• "IEEE Guide for the Application of Insulation Coordination," in IEEE Std 1313.2-1999, vol., no., pp.1-68, 15 Nov. 1999, doi: 10.1109/IEEESTD.1999.90576.

• IEC, TR. "60071-4: 2004, Insulation co-ordination–Part 4.

• Cigré, W. G. "Procedures for Estimating the Lightning Performance of Transmission Lines—New Aspects (C4. 23)." Technical Brochure 839 (2021).

• SC, CIGRE. "Guide to procedures for estimating the lightning performance of transmission lines." CIGRE Technical Brochure 63 (1991).

• LaForest, J. J. Transmission-line reference book. 345 kV and above. No. EPRI-EL-2500. General Electric Co., Pittsfield, MA (USA). Large Transformer Div.; General Electric Co., Schenectady, NY (USA). Electric Utility Systems Engineering Dept., 1981.