Renewable technologies such as wind and solar energy are becoming powerful tools in the fight against climate change. Over the last few decades, their cost has declined while their effectiveness has improved exponentially. Nevertheless, the wider implementation of renewables poses a number of challenges, including the issue of how to deal with fault current.
This post is one of the articles published by a small cohort within our UK team, including Dr Mahmoud Elkazaz, James Wilson, Sean McConnon, Jonathan Cervantes, Carlos Ferrandon-Cervantes, Adam Harper, Raj Hirani. This group meets regularly to collaborate on topical issues of the day, shares the researching and writing effort across the team, and presents internally before publishing.
What is fault current?
Fault current is the current produced by a power-generating technology when a fault occurs. This is when some part of the electrical infrastructure becomes short-circuited. One example would be when a power line hits a tree during a storm. Higher fault current means more energy is transferred during these fault events. Because of this, it is also a measure of the electrical strength of a particular point in the network.
Electrical power systems are always designed to be protected from such fault currents, which are often magnitudes higher than normal currents. Equipment such as switches must be designed to handle the maximum possible fault current in a particular area and at the same time. Relays react to fault current by measuring its level and shutting off faulty equipment.
Converter/inverter fault current
To provide the right kind of power to the grid, most battery, solar, and wind technologies include some form of converter or inverter. Compared to fossil-fuel-based technologies such as coal generators – which are spinning and have momentum – most converter technologies do not provide significant fault current.
At first sight, this may appear to be a positive characteristic. After all, the larger the fault current, the greater the danger. In reality, low fault current puts protection relays into a very dangerous zone. Where protection relays can not adequately detect fault current, they may be unable to switch off whatever is causing the fault current. So, people may be walking around a system where fault current is traveling in the ground – too low for the protection relay to detect and turn off – but more than enough to cause serious harm or fatality.
This means that when an electrical network is primarily or entirely renewable, we need new techniques and ways of thinking to ensure the system’s safety.
Dealing with low fault current from renewable systems
The good news is that there are more and more ways of dealing with this fault current issue. One such method is to use multiple setting relays or multiple relays that can determine when renewable generation is connected and adjust settings accordingly.
A further method is the use of technologies that can provide fault current. Synchronous condensers are an older technology developed in the 1950s that is finding new life in the age of renewables. It is essentially a flywheel for the electrical system providing both reactive power and fault current.
Finally, an increasing number of converter and inverter manufacturers are creating particular technology that can deliver greater fault current.
How PSC can help with renewables implementation and protection
PSC has long-standing expertise in both protection systems and renewable technologies and can help any client find the safest and most effective way of implementing renewables along with their associated protection systems.