Magnetic Field Monitoring on HVdc Transmission Lines Using a UHF-RFID Tag

High-voltage direct current (HVdc) transmission lines are gaining more attention as an integral part of modern power system networks. Monitoring the dc current is important for metering and development of dynamic line rating control schemes. However, this has been a challenging task and there is a need for remote sensing methods with high accuracy and dynamic range. Conventional methods require direct contact with the high-voltage conductors and utilize bulky and complex equipment. In this paper, we introduce a UHF radio frequency identification (RFID)-based sensor to monitor the dc current of an HVdc transmission line. The sensor is comprised of a passive RFID tag, with a custom design antenna, integrated with a Hall effect magnetic field device. The dc current is measured by monitoring the dc magnetic field around the conductor using the Hall effect device. The internal memory of the RFID tag is encoded with the magnetic field data. The RFID tag enables remote wireless interrogation using a conventional RFID reader. The unique advantage of this approach is that the sensor does not require batteries and does not need additional maintenance during its lifetime. This is an important feature in a high voltage environment where any maintenance requires either an outage or special equipment. The UHF RFID-based magnetic field was fabricated and tested in a laboratory experimental setup, which consists of a 34 mm diameter aluminum conductor typically used in a 500 kV HVdc system carrying a dc current of up to 1200 A. The sensor was attached to the conductor such that the Hall effect device was 30 mm from its surface. A dc current in the range of 100–1200 A was measured with an accuracy of 5% for a reader-to-sensor distance of 3 m.