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Seminar: Faculty Candidate, Electrical Engineering
April 10, 2015 @ 10:00 am - 11:00 am
The recent progress in renewable energy (RE) technologies has led to the erection of RE power plants (REPPs) up to the order of several hundred megawatts. Unlike their predecessors, which generally appeared in the form of dispersed generation (DG) coupled mainly with distribution systems, such large REPPs are naturally part of transmission networks and hold non-negligible proportions of the generation. As a result, the fault ride-through requirement has become an essential part of modern transmission grid codes. On the other hand, RE-based DGs have become pervasive in many modern distribution systems, enabling the formation of microgrids. In order for a microgrid to be fault-resilient and capable of frequently switching between the grid-connected and islanded modes, these DGs must remain connected to the system during disturbances. This presentation discusses the challenges brought about by the fault ride-through requirement now affecting protection of transmission and distribution systems with which RE-based sources are integrated.
On the transmission level, the performance of distance relays that are installed at an REPP substation and protect the neighboring line will be explored. The analyses include squirrel cage and doubly-fed induction generator-based wind farms, as well as full-scale converter-interfaced REPPs. The exclusive fault behavior of REPPs will be reviewed to identify possible relay maloperations and their root causes. The relay malfunctions discussed in this presentation are restricted to the systems with REPPs, and are not among the known distance relay failures that can occur in conventional power systems. Modified protection algorithms that retain non-delayed fast tripping of distance relays over the entire length of the line in the presence of a communication link with minimal bandwidth requirement will be discussed and evaluated.
On the distribution level, the presentation highlights the effects of RE-based DGs on fault type classification methods. Protective devices of smart and fault-resilient microgrids are not expected to trip the healthy phases during unbalanced short-circuits. Thus, some utilities as well as relay manufacturers have started contemplating single- and double-pole tripping for distribution systems. Selective phase tripping demands fault type classification. It will be shown that existing industrial methods misidentify the fault type in microgrids that include photovoltaic and/or Type IV wind DGs. Using phase and sequence voltages, two new classifiers are proposed to determine the fault type for not only microgrids with different DGs, but for any three-phase system.
Although microgrids have been extensively studied in recent years, no commercial relays have been manufactured for such systems to date. The presentation will finish by describing the challenges that should be met to develop a microgrid relay for systems with high RE penetration. Specifically, the problems associated with directional overcurrent relaying in the presence of RE-based DGs will be elaborated on, and the future directions for potential solutions will be introduced.
Ali Hooshyar received the PhD degree in electrical engineering from the University of Waterloo, Waterloo, ON, Canada in 2014. As a Postdoctoral Fellow at the University of Toronto’s Center for Applied Power Electronics (CAPE), he is currently investigating protection of microgrids with high renewable energy penetration for CanmetENERGY of Natural Resources Canada. His research interests include protection and control of renewable energy systems and smart grids.