The U.S. electricity network is immense, consisting of nearly 160,000 miles of overhead high voltage transmission lines, thousands of substations and millions of miles of local transmission lines, per the U.S. Energy Information Administration.

Distribution towers, grids and stations are capital investments that utilities must maintain to provide energy stability. Power outages due to system faults are unacceptable for utilities and customers. To ensure that aerial transmission lines and equipment operate reliably, utilities have moved away from antiquated reactive maintenance to condition-based and predictive maintenance strategies, which improve flexibility and cost control in their inspection techniques.

Complete sensor arrays for drones and helicopters are increasingly part of this solution. Together, powerful instruments and cutting edge aircraft create a solution to gather data and imaging on power lines and grid equipment. These inspections gather the data a utility needs to operate on a predictive maintenance plan, which helps identify potential points of defect so preemptive service can be scheduled.

This maintenance strategy pinpoints possible equipment before it impacts service, thereby optimizing maintenance strategies and resources, and saving utilities the costs of emergency repairs from unplanned outages.

Symptoms and effects of corona discharge

Figure 1. Corona discharge captured on a dead end string. Source: Ofil Ltd.Figure 1. Corona discharge captured on a dead end string. Source: Ofil Ltd.Corona discharge is the electrical breakdown and ionization of a fluid that surrounds a high voltage conductor. In the case of overhead transmission lines, it occurs when the electric field exceeds the dielectric value of the air. It is evident by an audible hissing or crackling, or at night a blue or purple glow due to the discharge’s ultraviolet (UV) wavelengths.

For utilities, this presents major challenges. Corona discharge is a significant waste of energy and a 2010 Stanford study found that U.S. transmission losses represent up to $24 billion per year. Corona discharge also damages important insulation materials, and if left unchecked will lead to equipment failure.

Corona discharge also represents a risk to the community and environment. Besides the obvious electrical hazard, it can interfere with nearby sensitive RF equipment. Corona discharge also creates harmful ozone gas and can disorient UV-sensitive animals, such as migratory birds.

Tools of the trade

UV and infrared cameras are non-destructive testing (NDT) equipment that detect anomalies on power lines. These technologies complement each other; UV cameras detect voltage-related cocona partial discharge and arcing, and thermal cameras detect current-related hot spots. The inspection conditions and timing do not typically concur, and the instruments measure different parameters. Yet the technologies are complementary and together give a better overview of equipment condition.

These cameras and sensors can be employed on foot via manual inspection. However, it is more efficient to mount these on helicopters or drones. Aerial inspections permit imaging of transmission lines from additional angles. Determining the right instrument suite and aircraft depends on a number of variables.

Helicopters offer the advantage of being able to quickly and independently survey up to hundreds of miles of power lines, even in challenging terrain. Helicopters can carry more or heavier instruments than a drone. There are established operating standards for copters, which limits how close they can get to substations, but offer clear operating parameters and regulations.

On the downside, helicopters are expensive to operate, and utilities contract this service out, at costs of $2,500 per hour or more. These services often must be scheduled weeks or months before. The sensor arrays can be challenged by the speed and pitch of the aircraft, but high quality instruments can compensate for this.

As a result of some of helicopter limits, drones are increasingly being implemented for power line inspections. They are inexpensive to fly and operate, and can be easily deployed and owned by the utility. Generally, they can also fly closer to the lines than helicopters, and because of this are better suited for distribution and railway catenary systems.

However, inspection flights are a careful tradeoff of sensor array weight versus battery power and flight time. Drones also have shorter ranges than helicopters and must be launched in the flight area by an operator. These vehicles are also more vulnerable to the RF interference of corona discharge than a helicopter. Finally, drone regulations are patchworked and evolving.

Ofil’s aerial inspection solutions

To get the best return on investment for aerial inspection, both helicopters and drones should be outfitted with the best cameras and sensors available. Since 1993, Ofil Ltd. has been providing premium solutions to the global market.

Figure 2. From left to right: DayCor ROM HD, DayCor MicROM HD and DayCor ROMpact. Source: Ofil Ltd. Figure 2. From left to right: DayCor ROM HD, DayCor MicROM HD and DayCor ROMpact. Source: Ofil Ltd.

The DayCor ROM HD is a high-definition imaging and lidr suite for aircraft. The exact sensors can be tailored to the customer’s needs, including UV, infrared video and still cameras or laser ranging. GPS monitors and reports geolocation. It is installed in a remote controlled turret that is gyro stabilized and vibration insulated for steady imaging and high accuracy. And the turret is compatible with both FAA and EASA aircraft mounts.

The DayCor MicROM HD camera is a high-definition UV and visible light camera in a small, lightweight footprint that is gimbal-ready and ideal for mounting on drone platforms. This ensures the best possible range and flight time from the drone. MicROM HD accepts data from secondary environmental or GPS systems to map locations. The camera can also be programmed to work with the drone controller.

Finally, the DayCor ROMpact is a high-resolution imaging solution for drones, helicopters and stationary installations, as well. It is an ultra-lightweight, dual imaging solution for corona discharge inspection and equipment monitoring. Video feeds can be streamed wirelessly to a remote monitor; it can also be stored to an external memory.

Figure 3. From left to right, visible imaging, UV imaging and composite imaging from Daycor technologies. Source: Ofil Ltd.Figure 3. From left to right, visible imaging, UV imaging and composite imaging from Daycor technologies. Source: Ofil Ltd.

Overall, Ofil offers the most comprehensive solution for drone and helicopter power line inspections. Utility companies will be able to identify corona discharge much more quickly and can take the appropriate measures to prevent further power line degradation. Ofil even includes training with their systems to ensure that a team is ready for the next round of inspections.

To learn how Ofil can elevate electrical utility inspections, visit their website.