The Frequency Maintenance Schedule is prepared for the tackling of those failures in the power system which are accompanied by significant changes in frequency; electricity supply to consumers is automatically interrupted and generating plants are disconnected from the network usually by means of frequency relays which are installed in compilance with the Frequency Maintenance Schedule:
- on power plant equipment so as to automatically respond to frequency changes;
on transmission and distribution system equipment so as to automatically interrupt electricity supply to those consumers who are connected to such equipment; or
on the equipment of consumers directly connected to the transmission or distribution systems so as to automatically interrupt electricity supply to these consumers.
The Frequency Maintenance Schedule is provided in Annex 3 to Regulation of the Ministry of Industry and Trade No. 80/2010 (in Czech), on a state of emergency in the power sector and the content of emergency plans as well as in ČEPS Operational Instruction PI 620-6. The amount of power tripped off and the various frequency stages are specified in the Transmission System Grid Code in compliance with the Energy Act, Article 24, paragraph 10f) and in the Distribution Systems Grid Code in compliance with the Energy Act, Article 25, paragraph 10g). Frequency relay installation points are determined by the Transmission System Operator and Distribution System Operators, respectively.