Optimal mechanical sag estimator for leveled span overhead transmission line conductor

Mechanical sag of the overhead transmission line (OTL) is a critical parameter for power system operation. However, remote locations of the conductor limit observability of sag. To monitor sag, distributed (DMS) or point measurement systems (PMS) are used. But, due to the limitation of DMS to use ruling span method, PMS is preferred. PMS requires sensors on every tower; as a result, sensor and data transmission requirements are high. This paper attempts to reduce the sensor requirement and estimate the sag in leveled span. To reduce the number of sensors and identify their location a linear integer programming based optimal sensor placement approach is proposed while keeping the redundancy intact. Using this, a reduced order, least-square based state estimator is proposed to estimate the sag in leveled span configuration. The estimator uses the conductor temperature and tension at one end of the span as input. Though, designed assuming ideal leveled span configuration, it is found to work for actual operating conditions. The performance of the proposed estimator is validated on the sag and tension data obtained with simulations on PLS-CADD™. Moreover, to eliminate the bad data, sensitivity based bad data elimination approach is presented. It allows replacement of bad data with almost exact values. The results show the robustness of the proposed approach.