by Melissa C. Lott
According to reports released over the past 6 months, the Tennessee Valley Authority (TVA) and Southern Company have successfully deployed networks of distributed power flow control devices to relieve stress on the nation’s electricity grid. These reports document findings from two on-going large-scale projects that could represent an economic option for solving a national grid modernization challenge.
These devices were developed by Smart Wires, an aptly named start-up company based in Oakland, California. This company was one of the first technology start-ups funded by ARPA-E under their Green Electricity Network Integration (GENI) Program.
Today, Smart Wires is home to three core technologies – the PowerLine Guardian, Router, and Commander. The first two devices are power flow control hardware that are attached directly to transmission lines, while the third is a control and data aggregation software suite that is used to manage fleets of the devices once they have been installed within the transmission grid. The PowerLine Guardian was the core technology deployed in both the Tennessee Valley Authority (TVA) and Southern Company projects.
The TVA installation was completed in 2012 and included 100 first generation PowerLine Guardians installed on a 7.5-mile segment of the TVA Knox-Douglas 161 kilovolt (kV) transmission line. The Guardian devices and associated communications infrastructure created a meshed network capable of communicating over GSM frequency bands. This pilot project represented the first utility-scale deployment of Smart Wires technology and was supported by funds from ARPA-E.
The TVA system includes three main components:
1. PowerLine Guardians – devices attached directly to the transmission wires to increase line impedance and measure the state of that portion of the transmission grid.
2. PowerLine Commander – the software side of the system, which includes a graphical user interface (GUI), data aggregator and logger, operator log, and alert generator that the grid operator uses to manage the PowerLine Guardian fleet.
3. Cellular Enabled PowerLine Guardian – the communication bridge between the Guardian devices and the PowerLine Commander.
After initial testing, these devices were used by TVA over a continuous 12-month period in order to evaluate their ability to:
1. Reduce loading on the Knox-Douglas Line and shift this load to two alternate semi-parallel lines (a.k.a. power flow control) to varying degrees.
2. Provide real-time sensing capabilities of the devices themselves with a goal of having at least 95% of these devices available for power flow control and data collection after one year of operation.
A 2014 report by Smart Wires and TVA confirmed that the pilot system had met both of these goals. Overall, according to their 2014 report, the network has allowed grid operators to more closely monitor the status of the Knox-Douglas transmission line, effectively push power away from this heavily loaded transmission line onto lines with more available capacity, and respond to an array of interruptions and events that could threaten the grid’s reliability.
One of the key lessons learned in this large-scale pilot project was that acoustic vibration from the PowerLine Guardian devices can have a significant effect on noise levels in the transmission right of way. According to Smart Wires, this noise has been successfully reduced in their current device using a combination of an improved bolt design and increased torque on the bolts that secure the Guardian units to the transmission lines.
2013: Commercial project kicks-off with Southern Company’s Georgia Power
In March 2013, Smart Wires and Southern Company successfully completed the installation of 33 PowerLine Guardian units on two 115-kW transmission lines (the Grady-Moreland and Grady-West End). These lines are managed by the Georgia Power Company, the largest of the four electric utilities currently owned and operated by Southern Company. The network of devices was brought online in April 2013 and run continuously for a 16-month period to test their performance.
Over the 16-month period, the devices were allowed to operate in four different modes:
1. Standby – the PowerLine Guardian unit is not able to commuicate or inject impedance into the system because the current on the transmission line is not high enough to power the device.
2. Monitoring – there is enough current available to power the device, but no impedance is being injected into the line.
3. Injection – the magnetizing inductance of the unit is being applied to the line to increase its impedance. Note that, because the operator can place individual devices in a variety of modes, the total injected impedance on the line can be changed along a range of values.
4. in extremis – where the unit protects itself from extreme conditions that could hurt the hardware (for example, fault-inducted current).
According to the report released by Smart Wires in January 2015, the network of devices was used to inject about 75% (on average) of the total possible impedance that could be achieved using the system.
Furthermore, 31 of the 33 units installed in March 2013 were still online at the end of 2014. The other two were removed from service due to failures, one due to a problem with the electrical connection between the top and bottom halves of the device, which was rectified for the current device through an improved connection design. After the initial deployment and test period, Southern Company decided to expand the system, doubling the number of installed PowerLine Guardians and working towards integration of the PowerLine Commander software with its existing Energy Management System (EMS).
Both the TVA and Southern Company projects are ongoing. According to Smart Wires, it expects to install its PowerLine Router technology in 2016. This technology will be able to not only increase power line impedance (like the PowerLine Guardian) but also directly decrease line impedance.