Arc Detection Technology for Manholes

Utilities are continuously seeking technology that will create safer working environments for their employees.

11 05 Up07 01 Manhole

Utilities are continuously seeking technology that will create safer working environments for their employees. In the area of manholes, utilities can find great value in technology that will alert workers of the presence of low-voltage system cable faults (arcing) in underground structures. The Electric Power Research Institute (EPRI) and Consolidated Edison of New York (Con Edison) collaborated to develop such a technology.

The result of this collaboration is the development of a prototype safety device that warns workers of electrical arcing before they enter a structure and monitors for arcing as crews work. The prototype unit is fully functional as an arc-detection system and detects arcing events with very high sensitivity and minimal false alarms. The technology can also serve as a component for additional field data acquisition. The first phase of the research has been completed and the prototype system is now being field tested to confirm its capabilities and that it meets reliability and positive detection objectives.

How the System Works

Using this technology is straightforward. The measurement system is connected to a sensor pod, and the pod is lowered into the manhole prior to worker entry. Similar to the concept of checking for gas before entering a structure, the sensor pod obtains a spectral sample of the existing electromagnetic conditions within the manhole. If the system senses cable arcing, the unit will alarm and alert the workers to the potential arcing concern. Even after determining that the manhole is safe to enter, the worker keeps the sensor with them as a warning indicator in case a nearby arcing event begins while they are inside the manhole.

In the past, there have been no devices that have been considered field usable to accurately accomplish arcing detection and alarm objectives. Most arc detection systems require the user to clamp a sensor around the cables to be measured, which is not feasible if the objective is to scan the structure prior to entry. The only non-contact device suitable would be an amplitude modulation (AM) radio receiver, but the radio receiver is not capable of distinguishing between real arcing and the many other arc sources that might cause false alarms.

Past Work Leads to New Developments

EPRI has been engaged in extensive arcing measurement research over the past two decades. This research has led to many key developments in arc fault recognition and location within power systems. It is through this body of knowledge that the basic characteristics of arcs have been understood.

The industry now has a better understanding that the very nature of the arc itself, having sharp rise times and erratic states with various periods, generates a broad spectrum of frequency emissions from interharmonics around the power frequency to radio frequencies extending into the range to hundreds of megahertz. It is because of this broad spectrum of emissions that several key signatures can be extracted, and, through digital signal processing, detecting an arc in its early stages can be achieved with a high level of confidence.

This project was designed to build on earlier proof-of-concept testing by EPRI, which suggested that even small, low-current arcs emit discernable signatures that can be picked up by properly configured, off-the-shelf hardware. This led EPRI and Con Edison to collaborate to test various hardware devices and filtering algorithms under both laboratory and field conditions. This was aided through the use of the Con Edison Cable and Splice Center for Excellence, an advanced lab environment suited for this effort. The overall plan was to develop a system that detects arc faults with very high sensitivity and minimal false alarms.

Benefit for the Industry

“Initial results have been promising,” said Neil Weisenfeld, department manager for Distribution Cable Systems and team leader for this project at Con Edison. “Worker and public safety is a top priority for Con Edison, and, if this system can be optimized and then commercialized, there is a significant potential to improve safety for our employees and advance the state of the art in detection of low-voltage arcing.”

In addition to improving worker safety, the arc detection technology developed for this project might be useful in addressing other problems utilities face in operating underground cable systems. Manhole events and cable failures are often related to arcing events, and the ability to detect arcing may have implications in reducing the risk of manhole events and improving the reliability of low-voltage cable systems.

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