In WSN-based utility monitoring systems, tiny wireless sensor nodes are installed on electric utility equipment and monitor the parameters critical to each equipment’s performance based on a combination of measurements, such as status, temperature, voltage, and current. This measured data is then transmitted to a control center (sink node) that analyzes the data from each sensor. Electric utility personnel are notified concerning any potential problems as an advanced warning system. This enables utility personnel to repair or replace the equipment before its’ performance drops or it fails entirely. In this way, catastrophic equipment failures and the associated repair and replacement costs can be prevented in a timely manner. In Figure 1, the architecture of our testbed is presented.

Fig. 1. Architecture of the BWN-Lab sensor network testbed monitoring the underground utility distribution system.

Our test-bed includes 20 TMote-Sky motes, which have Chipcon CC2420 radio chips that are compliant with the 802.15.4 standard. Specifically, Tmote-Sky motes operate in the 2.4 GHz ISM band with an effective data rate of 250 kbps, which is a much higher data rate than older radios. The higher data rate allows shorter active periods further reducing energy consumption. Tmote-Sky motes also integrate programming, computation, communication and sensing onto a single device. The integrated design provides an easy to use sensor mote with increased robustness, which is crucial for electric system automation applications.

In this project, we also made extensive measurements to quantify the use of external antennas in indoor, outdoor and underground sensor network environments. To connect the external antennas to the TMote-Sky motes, we soldered an SMA (Sub-Miniature ver-A) connector to the circuit board, while also disconnecting the internal antenna and changing the location of one capacitor on the board. Note that the Tmote Sky motes come with 3.1 dBi internal antennas. In our experiments, we integrated two different external antennas: i) HyperLink 8 dBi omni-directional antenna, and Titanis 4 dBi omni-directional antenna. In Figure 2 and 3, we present the sensor modules integrated with the external antennas, and show our experimental sites in outdoor and underground network environments, respectively. Note also that we made the underground field tests in underground Georgia Power distribution system.

Fig. 2. Sensor modules integrated with external antennas: a) 4dBi omni-directional, and b) 8 dBi omni-directional antennas.