Design of millimeter wave based sag measurement and monitoring system for overhead transmission lines in a smart grid

Abstract

In smart grid, power transmission monitoring and control is a crucial part. Electrical power transmission capacity of an overhead transmission line is dependent on the sag of that line. Power transmission through a transmission line can be increased with the decrease in sag. Thus, real-time sag monitoring is required for effectively using the transmission lines for transferring power. In this thesis, two simple, yet effective millimeter wave (mmWave) based techniques of measuring sag of overhead transmission line are proposed. These techniques can be used for measurement and monitoring of real-time sag of overhead transmission lines. The first technique only uses a single transmitter in each transmission line and a single transceiver. The transmitter sends mmWave signal to the transceiver. Simulation results demonstrate that based on the received power at the transceiver, sag of overhead transmission line can be measured effectively. Impact of different system parameters, namely, shadow fading, number of samples, horizontal distance between transmitter and transceiver, and horizontal displacement on the accuracy of the calculated sag for practical 132 kV, 230 kV and 400 kV transmission lines is comprehensively investigated. However, this technique suffers from large error, requires ground wire and strict alignment between the transmitter and the transceiver. To overcome the drawbacks of the first technique, another mmWave based technique is proposed that uses parabolic approximation. In the second technique, a transmitter and a transceiver along with an angle of arrival (AoA) sensor are used for each transmission line. Impact of system parameters on the accuracy of the calculated sag is also investigated for 132 kV, 230 kV and 400 kV lines. This technique shows significant improvement in accuracy of sag calculation compared to the first technique, though the accuracy degrades with error in AoA measurement. Network parameters for establishing communications among the devices in the proposed techniques are rigorously studied. Trade-offs between latency and sensitivity with bandwidth, and latency and percentage average error with number of samples are also investigated. Moreover, the proposed techniques are compared with the existing techniques of measuring sag of overhead transmission lines in terms of accuracy, hardware requirements and so forth.