GIS and Transmission Insulation Coordination

Over the last several years, climate issues have been dominating the news. Headlines, such as the historic rainfall, the widest and most intense hurricane ever recorded (think of Milton), and the frequency of tornadoes like we have never seen before, are becoming too common. The impact on society has been devastating. When we witness videos of tornadoes and hurricanes, they are almost always accompanied by stunning lightning displays. For those of us in the power business, lightning can be a significant hazard to the grid, particularly the high voltage system. Remember when your parents told you never to sit under a tree during a thunderstorm? Well, that’s because trees are tall and are a great target for lightning. What could be taller than the huge transmission towers that can rise 150 to 200 feet above the ground, depending on the voltage level?

Lightning is Bad for Electric Transmission

Lightning strikes on transmission systems can cause them to fail. Failure is due to a flashover of the protective insulation of the equipment and the integrity or lack of integrity of the grounding of the towers. Remember your parents telling you that a car is the safest place to be during a thunderstorm? That’s because rubber tires are great insulators.

To protect transmission systems from the hazards of lightning, transmission engineers perform a workflow called insulation coordination. This process happens during engineering and design for new transmission lines and analytics for existing ones. It is quite a complex process using well-developed, sophisticated simulation software. The process involves modeling lightning strikes and selecting the right protection equipment to thwart them. From a very simplistic perspective, a lightning strike hits a transmission line, and then it is like a wave, similar to a water wave that travels down the line until it hits a barrier, such as an insulator. If the height of the wave, measured in voltage, is higher than the insulator’s rating, it flashes over in its quest to find ground. The behavior resembles a storm surge wave and splashing over a sea wall. Once a flashover occurs, the transmission line fails and trips out, potentially leaving thousands in the dark. The engineers use this simulation to insert protection equipment and ensure that all the insulation ratings, like sea walls, needed to protect against storm surges, are high enough to prevent the flashover. A similar wave is also produced during switching operations, such as tripping or opening a substation breaker. Insulation coordination involves both lightning and surge protection.

Modeling the Network is Critical

So, what data do the engineers need? Two categories. The first and most obvious is a completely connected transmission network data set. This data set should include all the pieces and parts of the transmission system. The other includes everything outside the transmission system that impacts the analysis. This data includes historical weather patterns and places where lightning is most likely to strike. Don’t believe the myth that lightning never strikes twice. There are places where lightning frequently strikes and where it hardly ever does. Environmental factors include pollution, proximity to salt contamination, humidity, and areas prone to wildfires where smoke is more likely to occur. These factors impact the insulation strength. For example, a salty, dusty, or dirty insulator lowers its strength to fight off a lightning wave.

Recall that lightning loves to go to ground. The nature of the grounding is critical. Soil type impacts the resistance of the ground. The land topology and surrounding vegetation are all factors that must be considered when designing new systems or analyzing existing ones. GIS has managed these climate and environmental factors for decades.

GIS Manages All This Data

While GIS historically managed network data, it was never precise or comprehensive enough to model a complete transmission system. Now, it can, with the ArcGIS Utility Network.

In the past, insulation coordination did not fully leverage the GIS.

Why not? Many insulation coordination products extract network data from power system applications such as power flow analysis. Yet power flow analysis does not require some of the essential elements needed for insulation coordination. They don’t include lightning protection or grounding data. Thus, the insulation simulation data must be supplemented with additional data from other sources.

Good News and Bad News

The bad news for insulation coordination is that no single data source exists. This practice leads to inconsistency and duplication of data. Thus, some of the insulation coordination data has to come from many sources: some from the GIS, some from power flow data, some from real-time systems, other data from private equipment databases, and many other sources. This situation isn’t good for solid, error-free data management.

The good news is that the non-network data from GIS is readily available via web services for insulation coordination simulations. We know that GIS has always managed the land and environmental data. Now that the GIS comes with a comprehensive network data model, which is built to include protective equipment and grounding information, most of the data needed for insulation coordination can come from the GIS. The framework is there. All that is needed is to populate the data into the GIS network.

The Transmission System Digital Twin is On the Horizon

A concept raised by some leading utilities is the notion of a digital twin of the transmission system. This representation would include a realistic model of the as-built system, including substations and transmission lines, the land features, real-time weather, and integration with SCADA and other operating systems. This twin would provide the transmission system’s past, present, and future state. Utilities are beginning to examine ways to build this twin, leveraging imagery, LiDAR, and Building Information Models (BIM) accessed by GIS to provide a complete modern network model and all the essential non-network information for analysis, visualization, and stakeholder engagement.

So, when lightning strikes, we ensure that as we expand the grid, we have a solid source of grid data for all to use.

For more information on insulation coordination, refer to IEEE Standard 1313.1, and for detailed stories about GIS and Modern Network Management for electric utilities, click here.