Impact of thermal uprating and emergency loading of OHL networks on interconnection flexibility (original) (raw)
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Network planning evaluation implementing time varying thermal ratings
Contemporary transmission networks are not fully utilized due to increased uncertainty and security buffers resulting mainly from the inefficient operation and planning, currently based on conservative predetermined thermal ratings. However, in a smart operation scheme, which considers time varying thermal ratings of transmission assets, operation and planning could be optimized to facilitate the proliferation of generation expansion projects while maintaining required levels of reliability. This paper presents a methodology which enhances the current methods of network element ratings by incorporating a more detailed modelling of the overhead line (OHL) properties. Three thermal rating models, static (STR), seasonal (SeTR) and time varying (TVTR), are implemented for comparative studies, under both deterministic and probabilistic frameworks with an aim to identify the most cost-effective and optimal flexible network operation plan in today's congestion-driven and competitive power markets. In addition, the effects of line outages on transmission losses in the electric power networks are presented, quantifying the transmission losses in a realistic manner due to the incorporation of real thermal ratings. The IEEE 24-bus RTS is used under sequential modeling to validate the methodological enhancements and to evaluate network performance. The system annual operating costs are reduced when using the proposed TVTR model.
Dynamic thermal ratings for overhead conductors enable increased loadability of transmission lines during weather conditions that are favorable for conductor cooling. This could provide several benefits, including the accommodation of extra variability and uncertainty in line flows occasioned by increased penetration of intermittent renewable energy sources (IRES) in power networks. However, there are concerns over perceived increased risk of violating thermal limits if prevailing ambient weather conditions are worse than the forecasted values used to calculate the real-time ratings. This paper develops a methodology for the determination of safety factors to be applied in the calculation of real-time dynamic line ratings in order to ensure safe operation of transmission lines. Analyses using real-time weather data show significant increases in line loadability even with the application of the safety factors.