Gas Insulated Substations (GIS) for Enhanced Resiliency

By George Becker

Resiliency is defined as “a means to withstand and to rapidly recover from disruption.” The “Grid of the Future” must be resilient. Electrical substations must also be resilient and operate safely and reliably irrespective of the environments in which they reside. Grid reinforcement efforts should improve substation reliability, inherently enhance emergency response and improve recovery strategies related to naturally or human-caused events that damage electric substations.

Natural events such as severe weather are the primary cause of unplanned power outages in the United States. There is a range of natural events that can cause high impact damage to an electric substation, including storms, earthquakes, floods, wildlife etc. The severity and impact of recent weather events such as superstorms, large scale tornado outbreaks, coastal flooding, inland river flooding and severe thunderstorms with strong straight-line winds have prompted substation owners to examine design strategies to limit potential damage from such occurrences.

Human-caused physical attacks and criminal activity directed at electric substations can be high impact events that cause significant damage and have long lasting effects. As a result of recent criminal attacks on critical substations, many utilities are examining design strategies to mitigate the effects of criminal activity directed at substations in conjunction with limiting potential damage to substations, due to natural events.

Historically, substation designs for the most part have been based on standardized engineering practices and traditional air insulated technology. Given the challenges associated with the threats posed by high impact naturally and human-caused physical events, many utilities are turning to gas insulated technologies as a more resilient solution to harden their substation infrastructure.

The key to designing a truly resilient substation is to methodically assess what could happen and the vulnerabilities within the substation that need to be addressed. While the NERC requirements are focused on addressing a physical attack, substations fail for other reasons as well. Most of the utilities approach the assessment and subsequent planning from a more holistic perspective that includes physical attack, natural disasters or simply age-related failures.

Effective prevention of most catastrophic damage to substations can be achieved by using gas insulated switchgear as part of the design of substations that are critical to the electric grid and vulnerable to major threats.

Gas insulated substations provide the substation owner with the following advantages with respect to substation design and cost while enhancing resiliency:

• A smaller substation footprint (area and perimeter) that can be located inside a hardened building, underground structure or elevated structure.
• Expansion of the security perimeter of the substation.
• Reduced construction time and schedule commissioning risks during construction.
• More easily located near load centers and critical infrastructure.
• More easily disguised and aesthetically pleasing with the design option for no overhead line entry (“out of sight, out of mind”).
• Approximately 15 times the reliability of an air insulated substation performing the same operation.

To show the combined value of the above points, consider elevating an entire transmission substation to avoid coastal flooding or inland flooding due to severe weather. It is undoubtedly challenging, due to the amount of space required for increased electrical clearances at higher voltages. Even if AIS (air-insulated substation) equipment is raised out of projected storm surge or flood levels, the substation will remain “outdoors” and is still vulnerable to other elements of the tropical cyclone.

Based on prior installations and case studies, elevating transmission substations with “indoor” GIS (gas-insulated switchgear) has proven to be an excellent solution to ‘flood-prone’ areas, especially near the coasts. The successful protection of substation equipment from malicious, human-caused physical attack requires a layered security approach. The widely accepted asset protection basic philosophy is best approached through three steps:

• The application of concentric rings of security measures
• Inner most layers of security protect the most critical assets
• A structured process for evaluating protection based on impact and risk

GIS provides the substation owner with a pre-engineered substation design that enables the substation owner to employ construction methods for substations that reduce the impact of Human-Caused Physical Threats and enhance resiliency. GIS designs can expand the outermost layer of security by adding buffer distance in addition to strong wall/barriers. GIS designs also allow for more concentrated mid-layer and maximum innermost security.

Designing a substation that is truly immune to most human-caused physical threats is challenging. GIS designs are an effective method to protect a substation and its associated electrical equipment from severe damage from a malicious, human-caused physical attack. GIS designs allow for the following substation design attributes with respect to protection from such attacks:

• Reduced area of the substation, flexible compact arrangements
• Reduced exposed perimeter of the substation, significantly reduced cost for perimeter protection
• Expanded security buffer, hence, intruder neutralization devices can be more easily installed
• More concentrated fixed cameras with analytics at the perimeter
• More effective pan-tilt-zoom camera coverage with analytics
• Concentrated close proximity security layers with less potential for penetration
• More concentrated thermal imaging cameras with analytics
• “Out of sight, out of mind” to blend into surroundings and hidden from aerial imagery
• No line-of-site to equipment for projectile weapons
• Switchgear is completely enclosed with fire protection
• Transformers and reactors can be enclosed and covered with grating overhead to minimize air assault
• Relay control rooms can be located at the interior of the complex to enhance protection
• Interfaces to transmission and distribution system can be more easily concealed underground

The use of gas insulated substation designs is an effective method to protect a substation and its associated electrical equipment from severe damage from a naturally occurring catastrophic event or a malicious, human-caused physical attack. At the same time, it is a cost effective strategy that results in enhanced substation resiliency and higher reliability, due to a reduction in substation area and perimeter, the ability to shield equipment and minimize exposure to external threats. The benefits employing GIS designs contribute to the overall resiliency of the transmission system.

Edited by Panos Moutis