| Summary: | Svenska Kraftnät is (together with the other transmission system operators of the Nordic power system) responsible for keeping balance between the generated and demanded power in the Nordic power system. Spontaneous load variations and system disturbances, however, lead to power imbalance followed by frequency variations. The frequency deviations can be limited to an acceptable level by the spinning reserve, mainly by hydro power control. But there are also other system properties which have a great influence on the frequency and system stability. The frequency and voltage dependence of the loads have a direct influence on the power balance. The load naturally decreases because of the frequency and voltage drop that occurs in case of a sudden drop of a generating unit. Moreover, the emergency power control of the HVDC-transmission is activated at lower frequencies. This Master thesis is based on studies performed with the simulation program PSS/E. The work results in a comprehensive investigation regarding the Nordic model of frequency control. The system design is of great importance in PSS/E. Therefore the turbines including their control systems and models for the frequency and voltage dependence of the loads are examined in detail. Further deeper analysis regarding the modelling of the spinning reserve in PSS/E is performed. New models are developed as an alternative to the existing model of the spinning reserve in PSS/E. Their effect on the power balance is examined to determine if the modification of the spinning reserve has any significant impact on the frequency control or stability of the system, that has to be considered before the new model is implemented in PSS/E.
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