How Dangerous is EMI for Drones?
Electromagnetic interference (EMI) is a tricky subject for drone operators in the electric utility space. With EMI - an invisible and inconsistent threat - there is a wide variety of experiences among professionals that fly drones to conduct inspections of electric utility infrastructure such as power lines and substations. Some operators encounter repeated failures, while others none at all in their experience flying drones. Through extensive research and outreach, Manifold Robotics has sought to understand how EMI has an effect on inspection operations and how often it may strike.
Electromagnetic fields (EMF) from power utility infrastructure consist of electric and magnetic energy that is naturally emitted from (respectively) the changing voltage and current of electricity passing through power lines and storage equipment within substations. The higher the voltage and current, the stronger the electromagnetic fields will be, and therefore greater risk of electromagnetic interference (EMI) to a drone. Drones can experience the negative effects of EMI in a number of ways – GPS accuracy loss or failure, compass and IMU instability, communications interference, motor failure, and more unexpected malfunctions. These issues can appear in the beginning of a flight, or more frighteningly can lead to sudden failure without any previous indication of threat.
Aerial Inspection (Source: EPRI)
There is no doubt that drone manufacturers are doing a better job of protecting their drones against EMI, probably as a response to numerous incidents and the home-made solutions users have employed to harden drones against EMI. Today we’re seeing inspections with drones that get as close as 10 feet from high-voltage transmission lines without problems, or even flying between transmission phases (operators: please respect the minimum approach distance)! Unfortunately, not all drones – even the seemingly well-shielded ones – are immune from the threat of EMI. In the past year, for example, we’ve heard of incidents with industry-leading drones experiencing “fly-aways” (GPS and/or compass failure) or instantaneous flight shutdown most likely from motor failure. Cases like these, we found, are generally due to overwhelming amounts of interference coming from high voltage and/or current draw.
Besides relying on shielding, pilots currently have only a few other techniques to mitigate the adverse effects of a power line’s electromagnetic field, and are limited to protecting only a few components such as the IMU. Right off the bat, to maintain stability it is imperative to calibrate the IMU sensor before going out to the field to fly, in an area free of strong magnetic interference. The other technique is using tools like an e-field reader to monitor the EMF strength in the area-of-interest while on the ground. Even when these tools are available to use (they are seldom handy for drone operators), this method is cumbersome at best. The pilot can only get the EMF levels from their ground position, and if they choose to estimate what the EMF is close to the power line, it requires too many assumptions concerning power line morphology. As such, EMF levels cannot be accurately predicted where the drone is actually flying. This problem, as common as it is, has not been met with technological solutions and is often shrugged off.
So how does a pilot understand how much of a threat EMF is to their drone? One way the Manifold Robotics team is changing this is by equipping an EMF sensor to a drone itself. This novel approach provides real-time feedback on EMF strength from the drone - a big step away from the previous approach based on estimates. Furthermore, with interactive software the pilot can set EMF thresholds, so that it either flags warnings or automatically avoids areas where EMF exceeds the preset value.
EMF detection has many applications that the Manifold team is taking advantage of and EMF hazard avoidance is a base-level feature that will finally improve pilot situational awareness of the environments they fly in. This puts more power into the hands of users, and allows them to understand the invisible and deceiving threat they’re always up against.