What Spread Spectrum Time Domain Reflectometry Means for the Utility Market

Electric utility systems become more complex each day as new features, technologies and capabilities are added.

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By Ron Vogel

Electric utility systems become more complex each day as new features, technologies and capabilities are added. Smarter ways of generating and distributing electricity, such as smart metering and alternative energy sources, raise the complexity level and create a need for more real time information. To meet these new needs, there are new technologies that have been incubating and are now ready to be brought to market.

A New Technology Brought to Market

If something goes wrong with these new systems, the utility immediately wants to know about it and how to provide reliable electric power for its customers. But, what happens when intermittent conditions trip sensors? Crews respond, shut down power, and check the circuits and equipment at the trouble area. They find nothing, however, because the conditions that caused the intermittent condition do not exist when they are on-site.

What if a technician could look into the electrical conditions of any size cable at any voltage, while they are energized and carrying current, to see intermittent shorts or arc faults occurring and instantly be able to locate the exact location of these events? What if you could detect, locate and time stamp the event and characterize the problem while the electricity continued to flow? A new technology is making its way to market, and the impact on how faults are discovered and corrected will change the utility field.

The new technology is an advanced form of Spread Spectrum Time Domain Reflectometry (SSTDR), and it is being developed for commercialization by two American companies for applications in the electrical utility market, as well as other electrically oriented industries.

Traditional Time Domain Reflectometry (TDR) technology has long been used by electrical utilities to help locate cable failures, cable length information and cable problems that are not visually apparent. These forms of TDR technology, some more than 40 years old, are limited to unpowered dark cables because the voltage and current conditions interfere with the type of reference pulses the older testers use.

Spread Spectrum technology was first used during World War II in secure submarine communications. In the 1990s, Qualcomm developed a version of this concept to help cell phones connect over frequency signals that would degrade and block cell signals. The reason someone in Hong Kong can dial a number in the US and reach the right person is primarily because of Spread Spectrum implementation. What has successfully happened in the wireless world is about to happen in the wired world.

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Time Domain Reflectometry Capabilities

SSTDR technology promises to revolutionize the way a utility will use TDRs to find and fix cable faults, both underground and overhead. It will make it easier to see what is happening and where it is happening on live energized circuits on all equipment types and over all conditions, at any voltage or current level, transmission or distribution.

A traditional TDR cable fault finder sends a generated pulse through a cable to seek out variances, such as opens and shorts. The reflected pulse is compared with the delay at the speed of light, which is translated into a distance measurement to the "event." Old style TDR's can only work correctly when the cable they are "shooting" is unpowered. This is because the line's voltage noise interferes with the pulse, and, therefore, the reflection gets lost in this noise.

Advanced SSTDR resolves this limitation by generating pulses at a broad selection of frequencies that spread over the spectrum and skip through noise and signal impediments on the cable, while it is energized, to find exactly where the fault occurs, when it occurred and what its characteristics are. So, cable faults can be found, pinpointed and characterized without taking the circuit down and out of the system. In addition, unlike older TDR technology, SSTDR can perform dynamic testing that can monitor an energized cable system while it is under load or stress and wait for a fault to occur. This is useful in instances of intermittent arc fault conditions caused by wind, water intrusion or rogue voltage surges.

Locating buried cable faults will be easier and won't require damaging cable to find the exact location of the fault as is now done with some thumping techniques. By generating selective pulses at specific frequencies, locating pinholes in underground cable will become easier, cost less and be less intrusive to the overall system.

The technology's sensitivity and flexibility offer another possibility. By using new, patented capacitive coupling techniques, utility technicians will be able to clamp onto conductor insulation without touching bare conductor or disconnecting anything-and continuously monitor the lines to detect, locate and wirelessly report intermittent problems.

Who is Using the Technology?

Advanced SSTDR technology is now embedded in new flightline test equipment for the US Navy on aircraft carriers. Advanced SSTDR is a natural addition for aerospace applications to find arc faults in aircraft wiring that cannot be detected in installed wiring systems. It is being used by Halliburton to develop safer monitoring systems for offshore drilling rigs. Volvo is using it to develop 24/7 monitoring of the entire electrical control systems on their new heavy-duty trucks.

Schneider Electric has tested the technology on energized lines up to 33 kV, and it has performed flawlessly. So, utility applications are being investigated by this company and others who design and produce equipment for power systems.

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What it Means for Utility Systems

The detection, location and characterization of intermittent electrical faults on live energized conductors can now be easily done, which will create safer electrical networks and allow service organizations to keep networks running smoothly. Smarter street lighting systems that self report outages of strings of lights or individual lamp failures can be designed into existing equipment with embedded modules. Smart grids can become smarter and more informative for the owners.


An emerging technology such as SSTDR will make a lasting and important contribution to the utility industry in the form of handheld, portable test equipment and embedded in electrical control systems as a safety feature for every cable run.

Advances such as this will enhance newer smart grid system reliability. As they say, knowledge is power, and SSTDR technology will provide more knowledge to electrical grid owners on all transmission and distribution levels.

About the author: Ron Vogel is CEO of T3 innovation and can be reached at rvogel@t3innovation.com. T3 Innovation is dedicated to providing the latest and most effective handheld test equipment technology.

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