Theistareykir Geothermal Power Plant, Performance of the Plant During Varying Grid Situations

Abstract

The challenges in operating Landsvirkjun’s new 2x45 MWe geothermal powerplant at Theistareykir in North East Iceland involve guaranteeing that the plant responds reliably with different scenarios that can arise in operation of the grid. The plant strengthens a relatively weak electrical grid in NE Iceland and provides electricity for high energy intensive industries in the area. The location of the plant is rather remote and connects to a single 220 kV transmission line going from Húsavík to Krafla geothermal power plant where it connects to the main grid. Geothermal power plants in Iceland are generally run as base load whereas hydro plants handle fluctuations in grid load, but technically geothermal power plants have the potential to contribute to grid stability and flexibility in power balancing services. Due to the location of Theistareykir Geothermal Power Plant, it is required to respond quickly to load variations and provide stability to the grid. In addition, transmission line failures and other unforeseen disturbances can create situations where the plant is cut off from the main grid and islanded, requiring the plant to actively control the grid frequency. Furthermore, combining the faster response of steam turbines with the response of the hydro plants has the potential to be beneficial for overall transmission system stability by coordinating the response of the units. This paper will describe the efforts made to enable the plant to perform reliably, tests that have been performed and the experience gained after more than 1 year in operation. The turbine units have been implemented with functions that have been shown to enable the units to contribute to the control of grid frequency and, in situations where the area is cut off from the main grid, to actively control the islanded grid frequency. The development of a Smart Grid scheme utilizing Wide-Area-Controls will be described and how it aims to control the response of the power plant in more optimal way compared to conventional local controls, for variety of different and complex system disturbance in the weak transmission grid. The plant has demonstrated that steam supply and auxiliary systems have sufficient redundancy and capability to handle varied operational conditions. Furthermore, the paper describes results of extensive testing that has been done on the active grid to simulate the situations that can arise and show the response of the plant.