A recent article in Linkedin claimed that in the last few months solar and wind has provided about 14% of total US electrical energy. That seemed large until one realized that the electric grid provides only 20% of all energy needed. The percent of total energy provided by wind and solar is less than 3% and getting from 3% to 100% will be a huge challenge. It is unlikely that the industry can grow wind and solar resources to achieve net-zero emissions by 2050 per US policy, which is essential to combat climate change and keep global temperatures increases below 1.5°C.
To get to net-zero many issues need to be carefully considered. One leading issue is the electric distriution grid protection or the ability to identify and isolate faults on the system. These systems have the potential to cause chaos as we trend toward clean energy. The electric grid is a collection of wires, cables, towers and poles. The transmission grid is a real grid that can send power between two points in either direction. It is possible to put power into the grid in one location and take it out in several other locations far away.
The distribution system is not a grid at all. It is designed to deliver power from a substation to users. The system was never intended to deliver power from users to a substation. This seems strange, as the two systems are made from the same components that transmission systems use to deliver power in either direction.
Some Distribution Infrastructure Is 100 Plus Years Old and Potentially Dangerous
When electric utilities started, with Thomas Edison in 1883, there were lines that went from the generating station on Pearl St in New York to Edison’s customers. As the systems grew, these distribution systems were built in many cities, and today, some of the older cities have operating distribution systems installed more than 100 years ago. These systems were cutting edge when installed, but in many cases, they have remained in a similar state since installation. in 2021, one of my students brought a piece of a cable that had just been taken out of service from a local distribution system in a small town. The conductor was strands of copper wire wrapped around a hemp rope used to carry the overall weight of the conductor. That cable was installed more than 100 years ago and was replaced recently.
A Transmission Protection System Is Used to Identify and Isolate Faults
Transmission systems have experienced a different history and the systems are more modern and sophisticated. In the 1950s, high voltage lines were generally either 138 kV or 230 kV. Growth was rapid and energy delivered doubled every 10 years. At any time in the mid-century, half of the transmission system was less than 10 years old. Today the backbone voltages for transmission range between 500 kV and 735 kV.
A transmission protection system is used to identify and isolate faults. A lightning strike that hits a tower and causes a flashover fault must be isolated within a few cycles to maintain system stability. The protection systems located in substations monitor line voltages and currents and can detect even small faults rapidly. These systems can identify line and the direction of where the fault is located. The actual fault may be on a given line, or on a line that is connected to the next substation in the grid. The protection system needs to be able to locate the fault and clear it rapidly.
Communications between line ends are the key tool to doing this well. If there is a fault that appears to be on one line, the system will send a signal to protection systems at the other end of the same line, and if the other end sees a fault that is toward the initial station, both ends of the line are tripped immediately. This system has worked well but has been dramatically helped with the introduction of fibre optics.
Innovative Maintenance Systems Changed the Monitoring Game
Early in my career, utilities built dedicated microwave radio systems that provided communications for transmission system protection. These systems were costly to install and maintain. The sites were often on mountain tops, with heavy loads of snow in winter, requiring cable cars, snow cats, or helicopters for maintenance. Fibre optic technologies have totally changed these systems. Our transmission grid is now well protected with sophisticated protection and control systems. Today, our transmission grid is designed and operated to allow faults to occur with no loss of service. There is always another path available and in operation that can seamlessly replace any single loss.
Distribution Systems Need Advanced Systems
Distribution facilities need protection system advance. Existing distribution protection is almost the opposite of the transmission protection, based largely on concepts that have been in use for 100 years. Most distribution is either designed or operated in a radial fashion. A failure of any single feeder may result in a power loss for everyone on the entire length of that feeder. Faults are detected with crude overcurrent systems that operate in almost identical fashion to a household fuse or circuit breaker. There have been some advances over the years, but the principles remain largely unchanged.
The addition of renewable energy sources or storage via distributed energy resources (DER) systems are causing real strain for the utility protection engineers. If a distribution feeder is long and has enough DER devices connected that can provide the current drawn by a fault further down the line, the substation may not even detect the fault and the line may remain in service, without isolating the fault, becoming a fire hazard. Some utilities have been shutting down distribution lines during periods of heat and wind. The presence of a high penetration of DER facilities may exacerbate this situation.
To combat these pressures and needs, it is time to migrate some of the options that have been successful in protecting the transmission grid. Policy may require a module in every DER site that can detect a fault and communicate back to the substation protection system—and there may be another hurdle.
Protection engineers are conservative and careful. They are unlikely to accept a DER vendor giving signals to the protection system, so a module created by the same group that designed the protection system will likely need to be installed with the DER system. Communications are available at low cost through internet or cellular systems. Unlike the transmission system that need to clear faults in less than 0.1 second, a distribution fault that is cleared in several times than length of time would likely be ample.
The world around the power grid has advanced dramatically in the last 100 years. Transmission systems have grown with these advances but the distribution system, to a large extent, remains locked in the past. There is almost certainly a big opportunity for people with systems to advance distribution protection to advance, allowing much higher penetration of DER facilities in what will soon be Grid 2.0.
Energy without Hot Air 