Advanced optimization techniques for voltage support planning in self-dispatch systems present several opportunities for transmission system operators. Before an initial implementation of such techniques in daily operation, the expected benefits are usually assessed. However, such an assessment is subject to high uncertainties related to the expected participants' behavior. A proper assessment of consequences of applying optimization for voltage support planning requires an ex-post analysis with several years of operational data. This paper contains a breakdown of relevant impacts based on five years of operational data from the Swiss transmission system. It discusses the challenges of increasing penetration of renewable energy sources on the transmission system voltages and identifies drawbacks of the voltage support planning applied in Switzerland. Finally, it quantifies potential improvements, such as moving the voltage planning closer to real-time in order to account for intraday market activity.

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