Powerline Carrier (PLC) Signalling
Risk Reduction Category
Technology Description
Powerline Carrier (PLC) Signaling was first developed around 1910-1920, becoming a mature technology by the 1930s [1]. While PLC might have been thought obsolete with the advent of fiberoptic cables, and Wi-Fi technologies, it remains an economic choice for utility powerline communications—and is widely used in transmission systems. Moreover, narrowband PLC offers greater security against data eavesdropping and falsification than other communication technologies [6].
However, the PLC signals may be affected by line impedance, transformers, conductors not being uniform or of the same specifications, three-phase line transpositions, and non-homogenous lines—all of which can reduce the strength of the conducted PLC signal. Above-ground-to-underground transmission cables have frequency/wavelength considerations [2].
While PLC may be used without license from the FCC, the narrowband frequencies that may be used are regulated by the FCC (between 9 kHz and 490 kHz). The PLC system operates on a non-interference, unprotected basis, that is, should it experience or cause harmful interference, the electric power utility shall stop using it or adjust the PLC operation such that the interference is remedied—particularly around 100 kHz [2]. This is the LORAN C navigational frequency band—90 kHz to 110 kHz—which went away around 2010 but appears to be coming back as eLORAN operating at the same frequency band [3].
A basic power-line carrier terminal for operation of a protective relay system might resemble the following simplified diagram [2].
Today’s gap in the 4kV to 34KV distribution systems space, is the lack of automatic detection and triggering of protection for the affected circuit segment. Today’s passive detection algorithms yield an undesirable number of false positive and false negatives. The false positives create increased outage durations for customers while the false negatives result in fire and safety concerns that go undetected.
A novel approach is the use of Powerline carrier (PLC) as a relatively low-cost technology to support this use case. PLC is an established one-way or two-way communication scheme whereby signals are injected onto conductors that are primarily used to deliver power. PLC has been used for communications and protection on the transmission system for many years. TWACS® is one example of a proprietary two-way communication protocol within the family of powerline carrier communications. This long-haul, low bandwidth technology is in use today by utilities and is ideal for simple messaging and control such as meter reading and demand response.
Technical Readiness (Commercial Availability)
Powerline carrier (PLC) has been available for many years in the transmission system. According to Aclara, a Hubbell company, more than 400 utilities use their product, TWACS® to collect revenue-critical meter data as well as monitor line conditions, detect faults or outages and monitor power restoration [5]. The technology has other uses such as real-time pricing and demand response [5].
Repurposing existing PLC technology or developing new PLC signaling technologies is an R&D question. Field trials with an active power line carrier or other signal injection technology may help manufacturers bridge the performance gap that today’s options yield. The concept is that a low-cost signal injection system (for example a variation of TWACS repurposed for protection) could be applied to the power distribution system and all the “listening” protective devices could appropriately respond in a coordinated way to de-energize the live downed conductor section.
The following list of manufacturers is the product of an Internet search using a general description of the technology as the search term. Sometimes more than one variation on the search term is used. The objective is to identify the most demonstration-ready products available in the category. Toward assessing demonstration readiness, the manufacturer websites typically provide useful information such as writeups of successful use cases or field demonstrations, number of deployments, or other indicators. Where lack of information exists online, further inquiry is made by phone. Generally, one to three frontrunners emerge as being most ready for a field demonstration. Preference is given to manufacturers who sell to the United States, or, if emerging technology, those who have participated in US-based field demonstrations.
Transmission Line PLC
Hubbell Power Systems
https://www.rflelect.com/images/products/CA10250E_RFL_PLC_Solutions_Catalog.pdf
Siemens
General Electric (GE)
https://www.gegridsolutions.com/communications/power-line-carrier.htm
Medium and Low Voltage Line PLC
General Electric (GE)
https://www.gegridsolutions.com/communications/catalog/e-terrapowercom.htm
Hubbell Power Systems
Implementations / Deployments
PLC might be used to send commands around the electric power grid and may serve to open faulted circuits very quickly and likewise reclose after arc clearing—although no PLC supplier was identified online as specifically emphasizing this possibility for wildfire prevention.
This gap poses an important Research and Development opportunity. While a few passive monitoring approaches are being used and being demonstrated, none of the technology identified to date fully resolves the false positive and false negative challenges. Field trials with an active power line carrier or other signal injection technology may bridge this gap.
Innovations as of Mid 2023
Potential Enrichment Work Opportunity
References
[1] AIMS Electronics and Electrical Engineering 2022, Volume 6, Issue 3: 265-284. doi: 10.3934 /electreng.2022016 Power line communication: A review on couplers and channel characterization Martial Giraneza, Khaled Abo-Al-Ez https://www.aimspress.com/article/doi/10.3934/electreng.2022016?viewType=HTML
[2] https://www.pes-psrc.org/kb/report/060.pdf
[4] https://www.rflelect.com/images/products/CA10250E_RFL_PLC_Solutions_Catalog.pdf
[6] https://nessum.org/media/technology-blog/what-is-power-line-communication