FNET
FNET is a wide-area power system frequency measurement system. Using a type of phasor measurement unit known as a frequency disturbance recorder, FNET/GridEye is able to measure the power system frequency, voltage, and angle very accurately. These measurements can then be used to study various power system phenomena, and may play an important role in the development of future smart grid technologies. The FNET/GridEye system is currently operated by the Power Information Technology Laboratory at the University of Tennessee in Knoxville, Tennessee, and Oak Ridge National Laboratory in Oak Ridge, Tennessee.
History
A phasor measurement unit is an important tool that is used to monitor and study electric power systems. The first PMUs were developed at Virginia Tech in the late 1980s. These devices measure the voltage, frequency and phase angle at buses within the power system. By utilizing the Global Positioning System, a PMU can provide a timestamp for each measurement. This allows measurements taken from different PMUs to be accurately compared.A PMU is typically installed at an electrical substation. This process can be quite expensive and time-consuming, costing tens of thousands of dollars per device and requiring several months of effort. The high cost of installing PMUs has limited their use in the electric power industry.
In 2000, researchers led by Virginia Tech faculty member Yilu Liu began the development of a low-cost phasor measurement network that could be installed at the low-voltage distribution level of the power grid. Researchers at Virginia Tech received a NSF MRI grant from the National Science Foundation to develop the system, which became known as FNET. The first frequency disturbance recorder was developed in 2003 with support from TVA and ABB. The FNET system went online in 2004.
Since 2010, in partnership with the Department of Energy, FNET/GridEye has been developed into a wide-area grid monitoring network that covers the three major North American power grids and 16 of the largest grids around the world.
Frequency disturbance recorder
The frequency disturbance recorder, or FDR, is a GPS-synchronized single-phase PMU that is installed at ordinary 120 V outlets. Because the voltages involved are much lower than those of a typical three-phase PMU, the device is relatively inexpensive and simple to install.The FDR works by rapidly sampling a scaled-down version of the outlet’s voltage signal using an analog-to-digital converter. These samples are then processed via an onboard digital signal processor, which computes the instantaneous phase angle of the voltage signal for each sample. The device then computes the voltage angle, frequency and voltage magnitude at 100 ms intervals. Each measurement is time stamped using the information provided by the GPS system and then transmitted to the FNET/GridEye server for processing and storage. The frequency measurements obtained from the FDR are accurate to within ± 0.0005 Hz and angle accuracy could reach 0.02 degree.
An FDR requires only a power outlet, Ethernet port and a view of the sky. Thus, FDRs can be installed virtually anywhere, including substations, offices, and even private residences.
System architecture
Currently, FNET/GridEye collects data from over 300 FDRs, most of which are installed in the North American power grid. About 70 of these units are located in 30 of the other largest grids around the world.The FDRs transmit their measurements over the Internet to phasor data concentrators located at the University of Tennessee and Oak Ridge National Lab. These PDCs collect more than 4 GB of phasor data per day. The PDCs also forward data to an application server that performs near-real-time analysis of the data. Examples of the analysis applications are given below.