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.