EPRI sensors utilize a current pick-up (guard electrode) on the insulator being monitored that is isolated from ground to facilitate measurement. For disk insulators, the guard electrode is in the form of a special clip-on arrangement while, on substation or post insulators, a simple metal band is used. Typical installations are illustrated in Fig. 8.
There are already over 150 sensors installed at a range of sites worldwide. Some have been operational for 5 years and continue to provide data to act upon. Examples of installation locations are shown in Fig. 9.
Sensor Operations Overview
There are two basic applications for obtaining data captured by the leakage current monitors:
1. Data is downloaded during periodic rounds inspection through a portable interrogator with an antenna. Inspection period is not pre-determined and could vary according to need or opportunity. Sensors and communication are designed so that data can be collected via fly-by or drive-by inspections at up to 100 km/h.
2. Sensors are continuously interrogated via a dedicated sensor base station. In this mode, it is possible to resolve the times when leakage current events occur. With this operation strategy, automatic alarms can be triggered to indicate need for insulator cleaning or times when there is significant risk for flashover.
Basic architecture of the dedicated leakage current system is shown in Fig. 9. There are 3 basic components to the system for data collection, storage and presentation:
1. The wireless sensors networking protocol uses the IEEE 802.14.5 standard; operating in the 2.45 GHz frequency band. Each sensor in the wireless network can be configured to broadcast at set intervals ranging from 5 to 120 seconds. All data packets transmitted by the sensors are collected by the ZAP (Wireless Access Point), which reassembles and stores the sensor data in memory. Bin levels on the sensors can also be wirelessly reset and calibrated.
2. Sensor Base Station: The base station is the main on-site data collection point. Each base station is equipped with a ZAP, data logger, cell modem, battery/solar panel, and peripheral sensors. The base station consists of the following components with the functions described:
• ZAP(Wireless Access Point): Collect and store data from EPRI wireless sensors.
• The ZAP can be integrated with utility asset health systems directly, using Modbus or DNP3, or integrated into the EPRI Research Sensor Network, as described below.
• Data logger: Interrogates the ZAP for wireless sensor data (via RS232 modbus), and collects data from peripheral sensors such as wind, temperature/humidity, and door alarm. All collected data are stored in a circular buffer.
• Cell Modem: Allows the EPRI VDV server to pull data from the data logger- Battery/Solar Panel: Main power source of the base station. Without sunlight, the base station will remain operational for up to 7 days.
3. EPRI VDV Server: For the EPRI Research Sensor Network all base stations in the field report back to a central data server. This server is configured to pull data from the field at fixed intervals throughout the day (if necessary it also perform post processing on the data). Data collected are then stored in a MySQL database. A web interface is also available for accessing and viewing the collected data. Additional password protection and access control are available to only allow certain users to access the data stored on the server. Email alarms can be generated and sent to both utility and EPRI personnel.
Data is made accessible to users via an automatically generated web page, shown in Fig. 10. Leakage current activity is shown in 3 formats: 1. development of bin counts over time (top graph); 2. highest current measured during latest monitoring interval (middle graph), and 3. algorithms that have been developed to trigger alarms (bottom graph). A summary of sensor locations and visible alarms with important weather parameters are shown on a dashboard (as in Fig. 11).
EPRI’s approach to wireless leakage current monitors sees leakage current on insulators monitored using a robust, low-installed-cost device that allows widespread applications to monitor insulator performance under polluted conditions. The sensor has been deployed at a number of sites to demonstrate its utility and robustness. For utilities, the goals are obtaining information on when to conduct insulator washing and collecting information for dimensioning insulation with respect to pollution. A key aspect of the EPRI system is that the leakage current sensor is just one of a range of sensors that have been developed to address a range of transmission assets and issues so as to form a suite. New sensors for the suite are continually being developed and commercialized based on industry needs. Basic development of the EPRI leakage current sensor concept is now final and sensors are now commercially available.