As part of a program to provide an infrastructure for transmission line and substation monitoring, EPRI in the U.S. has developed remote sensors to monitor the condition of important assets. This INMR article from 2015, contributed by Andrew J. Phillips and Chris S. Engelbrecht of EPRI USA and M. Major of SWRI reviewed this program and its results.
The main goal behind this program was to obtain a cost effective platform that enables installation of numerous sensors over a transmission system. These sensors would provide for increased condition awareness, resulting in improved reliability as well as reduced maintenance costs. All sensors are communicated to with the same radio frequency (RF) system that collects data from sensors and integrates it with Utility Asset Health Systems. An overview of the sensor package demonstrated at over a dozen utilities is shown in Fig. 1.
Sensors under development and commercialization include:
• Conductor sensors to monitor temperature, conductor movement & vibrations;
• Structure motion & vibration sensors;
• A ground wire sensor to detect lightning & fault current;
• A sensor to monitor geo-magnetically induced currents;
• A radio frequency interference sensor to detect arcing or other discharges at substations or on lines;
• An arrester condition monitoring sensor;
• A disconnect sensor that monitors its temperature, current & inclination of switch arm;
• Physical security sensor;
• A bushing sensor;
• Underground cable sensors (5 different types).
The sensor suite also includes an insulator leakage current sensor, designed as a robust, low-cost device to allow widespread application on lines and at substations to monitor insulator performance under polluted conditions.
Monitoring Leakage Current
Insulator leakage current measurement can be done with various degrees of sophistication, including:
• Capturing detailed oscillograms of leakage current surges, or bursts, and/or the supply voltage (as in Fig. 2);
• A date and time stamped array of peak leakage current amplitude measured over a given time period (as per Fig. 3);
• Binned leakage current peak values over an extended time period (as shown in Fig. 4). It should be noted that it is not possible to determine exactly when the highest leakage current pulse occurred with this methodology unless data retrieval is very frequent. Retrieval rate is every 5 months in the example shown.
• Time stamped binned leakage current peak values. In this case the binned current peak values are retrieved from the leakage current monitor at relatively short time intervals (e.g. 10 minutes). This way, both time and severity information is obtained about leakage current events, which can also be correlated with available weather data. An example of such time stamped binned leakage current data is presented in Fig. 5.