The article discusses issues related to ensuring secure operation of the National Power System. The tasks of transmission system operators in that scope were presented and the power demand of the Polish National Power System on critical days in terms of power generation and demand was characterized. The article also presents the causes and course of events which took place in August 2015 when there was a critical imbalance in the Polish National Power System leading to the introduction of limitations. Then, the possibilities and types of costs connected with the possibilities of balancing the system in the periods of peak loads were characterized. The summary of the article contains the presentation of conclusions related to power balancing in the power system and reduction of related costs.
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