Optimal procurement of ancillary services considering balance and system security criteria

Nowadays, processes of purchase of ancillary services reserves (AnS) and their further activation are mostly separated. A determination of the demanded volume of AnS reserves is based on the expected difference between generation and consumption. The final portfolio of requested AnS reserve type is composed of bids with the lowest price and possible power network limitations (i.e. an impact on system security aspects like branches' current limits, nodal voltage security ranges) are not considered in the AnS procurement process. In power network balancing, an activation of AnS reserves in a location operating close to system security margins may lead to possible violation of system security criteria and costly remedial action needs be triggered (e.g. redispatch on power plants), which results in a significant economic inefficiency and possible violation of reliable operation of the power system. Consideration of system security aspects in the procurement of AnS reserves will lead to an economically efficient allocation of procured AnS reserves, which will increase the reliability and security of power system operation. In this paper, the interval method of secure power injections is extended for needs of optimal AnS reserves purchase, which will take into account economic as well as system security aspects. Further, the use of the developed method for optimal and secure AnS portfolio determination is shown in the case study from the Czech transmission system.