Harvesting electro-magnetic (EM) energy, in combination with industrial grade rechargeable lithium batteries, enables emergency repair crews to pinpoint disruptions in the electrical power transmission lines to speed repairs and reduce labor costs.
by Sol Jacobs, Tadiran Batteries
High voltage electrical power transmission lines form the backbone of America’s power grid: a vital asset that demands intelligent management and oversight to protect against disruptions to regional energy markets.
It is becoming essential for electrical power grid managers to have access to near real-time data that offers actionable intelligence regarding the operational status of transmission lines, thus enabling emergency repair crews to pinpoint potential line breaks to promote faster response and less system downtime.
High voltage power lines are also inherently dangerous and inaccessible, so the equipment being installed must be highly durable to provide long-life reliability to reduce long-term maintenance costs, because the electrical power grid is simply no place for unproven or short-lived technologies. A long-term solution uses harvested magnetic energy
Southwire Company, LLC, a leading manufacturer of wire, cable and associated products for the distribution and transmission of electricity, recently developed a wireless line/connector sensor that supports the power grid by providing real-time status of electrical transmission assets. The line/connector sensor mounts directly on a bare overhead transmission conductor, where it harvests energy from the power line’s magnetic field to measure conductor temperature, sag on the transmission line, and electrical current on the line. These readings are transmitted, typically every 30 seconds, to a base station using 2.4 GHz RF communications.
The line/connector sensor requires sufficient line current to fully recharge a AA-size industrial grade rechargeable Lithium-ion (Li-ion) battery that stores enough energy to provide approximately 45 days of continuous sensor operation during extended periods where there is no line current. The strength of the magnetic field is also constantly changing, including many periods when line current drops below the threshold required for energy harvesting, and the rechargeable Li-ion battery serves to balance out theses fluctuations.
Unlike consumer grade Li-ion batteries, industrial grade Li-ion rechargeable battery can deliver high pulses of short duration (5A for a AA-size cell) required for wireless communications. Consumer grade Li-ion cells have other limitations, including limited life expectancy (5 years and 500 recharge cycles), restricted temperature range (0°C – 40°C), and crimped seals that may leak. By contrast, industrial grade Li-ion batteries can operate for up to 20 years and 5,000 full recharge cycles, with an extended temperature range of -40°C to 85°C, and a glass-to-metal hermetic seal to protect against leakage.
Supercapacitors were not appropriate for this application for numerous reasons, including lower reliability, linear discharge characteristics that do not allow for use of all the available energy, low capacity, low energy density, short duration power due to high self-discharge (up to 60% per year), and the need for cell balancing for supercapacitors linked in series. Supercapacitors are also extremely bulky, whereas utility line crews prefer more lightweight and ergonomic solution.
Combining an energy harvesting device with a 20-year industrial grade Li-ion battery proved to offer the most economical solution because is reduces long-term maintenance costs, thus resulting in a lower total cost of ownership.
Tadiran Batteries, Lake Success, NY. (516) 621-4980. www.tadiranbat.com