Load–frequency control management in island operation

•Cooperation of turbine governors with supervisory load frequency control is investigated in an island operation.•Different modes for load/speed control of steam turbines are described.•A new mode for the load frequency control is introduced.•Several case studies are presented in order to prove feasibility of proposed control modes.•A combination of turbine speed control and centralised LFC proves advantages of both conceptions.

This paper analyzes particular cases of active power and frequency control strategies in island operation when a part of the system is electrically separated from the main interconnected system. This operation condition occurs rarely on a transmission system level; however, the control systems on all levels should be adjusted accordingly and transmission system operators should have a plan prepared to manage such an extraordinary situation. A number of possibilities for the cooperation of turbine control modes and supervisory control of frequency and active power are investigated and evaluated in the paper. A new mode for LFC suitable for island operation is proposed and tested as well. All of the examined possibilities are simulated by a dynamic power system model. The results prove correctness of the proposed solution for operating turbine control in a decentralised way in the island operation. Following the successful transition to island operation, the new LFC mode can be used for centralised automatic frequency control during the island resynchronisation phase.