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FNET (Frequency monitoring Network) is a wide-area power system frequency measurement system. Using a type of phasor measurement unit (PMU) known as a Frequency Disturbance Recorder (FDR), FNET 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 system is currently operated by the Power Information Technology Laboratory at Virginia Tech and the University of Tennessee, Knoxville. [1]


Phasor measurement units are an important tool 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, the PMU can provide a timestamp for each measurement. This allows measurements taken from different PMUs to be accurately compared. [2]

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.[3] The high cost of installing PMUs has limited their use in the electric power industry.

In 2000, researchers at Virginia Tech began the development of a low-cost phasor measurement network that could be installed at the low-voltage distribution level of the power grid.[4] Researchers at Virginia Tech received $262,000 in funding from the National Science Foundation to develop the system, which became known as FNET. [5] The first Frequency Disturbance Recorder was developed in 2003, and the system went online in 2004. [4]

Frequency Disturbance Recorder[edit]

Generation II FDR

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 (1,440 times per second) 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 timestamped using the information provided by the GPS system and then transmitted to the FNET server for processing and storage. The frequency measurements obtained from the FDR are accurate to within ± 0.0005 Hz.[4]

An FDR requires only a power outlet, Ethernet port, and a view of the sky (for the GPS antenna). Thus, FDRs can be installed virtually anywhere, including substations, offices, and even private residences.

System Architecture[edit]

FNET FDR locations as of September, 2010

Currently, FNET collects data from over 80 FDRs, most of which are installed in the North American power grid. A small number of units are located in other countries, such as France, Italy, Germany, and China.

The FDRs transmit their measurements over the Internet to phasor data concentrators (PDCs) located at Virginia Tech and the University of Tennessee. These PDCs collect more than 2.5 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.


A variety of applications have been developed using the FNET platform. Some operate in near-real-time, while others are used for offline analysis.

Event detection and location[edit]

The sudden addition or removal of large amounts of load or generation in a power system leads to changes in frequency. For example, a generator trip causes a decline in frequency, whereas load shedding results in an increase in frequency. The change in frequency is proportional to the size of the tripped generator or the amount of load shed. These changes propagate in both space and time throughout the grid. Since the geographical location of each FDR is known, as is the time of each measurement, it is possible to estimate both the size and location of these events.[6]


The FDR data are also used to “replay” power system events through intuitive animations. Both frequency and angle data can be used for this purpose, as shown in the images that have been removed.

Oscillation detection[edit]

Power system oscillations can occur as the result of generator trips, load shedding or faults, though some have no obvious cause. Such oscillations are usually not harmful, provided they are quickly and sufficiently damped. FNET uses both the phase angle and frequency data to detect oscillations and provide real-time alerts.[7]

Interarea Oscillation Modal Analysis[edit]

Once an oscillation has been detected, the system can perform modal analysis using the multichannel matrix pencil technique. This analysis can reveal the dominant oscillation modes and show which parts of the power grid tend to oscillate together.[7]

See also[edit]


  1. ^ FNET Website
  2. ^ Phadke, A.G.; Thorp, J.S., "HISTORY AND APPLICATIONS OF PHASOR MEASUREMENTS," Power Systems Conference and Exposition, 2006. PSCE '06. 2006 IEEE PES , vol., no., pp.331-335, Oct. 29 2006-Nov. 1 2006.
  3. ^ NASPI Responses Summary to Questionnaire on PMU Installation and Maintenance
  4. ^ a b c Zhian Zhong; Chunchun Xu; Billian, B.J.; Li Zhang; Tsai, S.-J.S.; Conners, R.W.; Centeno, V.A.; Phadke, A.G.; Yilu Liu; , "Power system frequency monitoring network (FNET) implementation," Power Systems, IEEE Transactions on, vol.20, no.4, pp. 1914- 1921, Nov. 2005.
  5. ^ NSF Award Information
  6. ^ Gardner, R.M.; Wang, J.K.; Yilu Liu, "Power system event location analysis using wide-area measurements," Power Engineering Society General Meeting, 2006. IEEE , vol., no., pp.7 pp., 0-0 0
  7. ^ a b Y. Zhang, P. Markham, et al., "Wide-Area Frequency Monitoring Network (FNET) Architecture and Applications," Smart Grid, IEEE Trans. on, vol. 1, no. 2, Sept. 2010, pp. 159-167.

External links[edit]