Esther Romero-Ramos

Improving the voltage regulation of secondary feeders by applying solid-state tap changers to MV/LV transformers

Voltage regulation at the subtransmission and distribution levels strongly relies on the use of transformer tap changers, implemented nowadays by means of sophisticated electromechanical mechanisms. The possibility of replacing such slow and prone-to-wear switches by electronic devices has been the subject of much interest in the last few veals, particularly at subtransmission levels. In this paper, the application of on-load electronic tap-changers to MV/LV distribution transformers is proposed and the operational benefits from their widespread use on a sample realistic feeder, both at normal and emergency conditions, are illustrated.

Enhancing the integration of renewable sources in distribution systems using DC-links

This work proposes the use of DC-links between existing radial distribution feeders so that full advantage is taken of their maximum capacity, which is particularly important when new distributed generators are to be connected at the distribution level. An optimization tool is developed to determine the optimum settings for the DC-link control variables, in order to maximize the penetration of dispersed sources subject to customary electrical constraints. Simulation results regarding two real networks are presented to illustrate the former advantages. Also, improvements in system operation resulting from the presence of DC-links are studied and discussed. A real loss model for the DC link is considered in all test cases.

Distribution transformer load allocation from substation measurements and load patterns

This paper proposes a new method to split the total load measured at the head of a distribution feeder into a set of individual loads served by those transformers connected to the feeder. For this purpose, a least-squares estimator is formulated, trying to reconcile hourly substation measurements of aggregated feeder load with historical 24-hour records of typical end-use demand profiles. The results of different tests are included to validate the proposed technique and illustrate its potential benefits and limitations.

DC link operation in smart distribution systems with communication interruptions

DC Links are proposed in the literature as a mean to enhance the system performance and facilitate the integration of dispersed generators in distribution grids. Their operation relies on a centralized controller which gathers the measurements acquired along the network to compute their adequate set points. This system architecture provides several technical benefits but strongly depends on communication infrastructures (meters, data concentrators, etc.) which may fail. When this happens the DC links may not work properly, even forcing the system operator to disconnect them until the communications are restored. This paper proposes operational strategies to avoid the malfunction or disconnection of DC links when communication interruptions occur. Several simulations are done to assess how these strategies affect the performance of the DC links. An actual Spanish 100-bus distribution system with a DC link is used as a test bench in different situations.

New insight into the possibilities of estimating secondary distribution transformer taps

This paper researches the future capability of estimating the fixed tap positions of MV/LV distribution transformers under the smart grid framework. The new available measurements allow improving state estimation, not only of system state but also of parameters as turns ratio of transformers, which turns to be essential for any application fed by state estimator. The nature of the measurements needed to estimate the current tap ratio of secondary distribution transformers is analyzed, as well as the quality of the estimated state. The real possibilities of this issue are critically evaluated under the current smart grid paradigm, pointing out the new opportunities arising from the increased visibility of the whole system.