Abstract/Summary

Thermal limits of overhead transmission lines create network constraints that can result in curtailment of renewable energy generation. Thermal limits are conventionally static and based on worst-case, non-cooling ambient weather conditions, leading to under-utilization of overhead lines. Utilization can be increased and network constraints reduced by rating overhead lines dynamically, based on actual conductor temperature. Installation and maintenance of temperature and weather sensors along an overhead line is expensive and laborious. A more cost-effective solution is to derive average conductor temperature from overhead line impedance parameters, which can be calculated from measurements of electrical signals at each line end. Synchronized phasor measurement technology is becoming increasingly available in substations to capture voltage and current signals with high accuracy and reporting rates. It is known that the substation instrumentation channel can introduce significant systematic errors to the phasor measurements, which in turn cause inaccurate line impedance parameter and temperature values. This thesis presents novel methods for accurate, real-time monitoring of overhead line impedance parameters using synchronized phasor measurements that have systematic errors. In contrast to previous research, the time-variance and temperature dependence of line resistance as well as compensation of systematic errors is taken into account in the system model to increase parameter estimation accuracy. In addition, an algorithm for the selection of the best parameter estimates from different measurement sets is given. The effectiveness of the novel methods is demonstrated in several case studies on measurement data from simulations and an actual overhead line. The results show that the identified correction factors compensate systematic measurement errors, leading to a reduction in impedance parameter estimation errors of at least one order of magnitude compared to existing methods. Furthermore, the accuracy of real-time estimation of average conductor temperature was increased by at least one order of magnitude relative to previously proposed methods.