The plans to reduce the energy-related greenhouse gas emissions stimulate the deployment of electronically interfaced renewable resources. The increased penetration of such intermittent sources together with phasing conventional power plants out and the installation of High Voltage Direct Current (HVDC) links for long-distance more efficient transmission, reduces the stored inertia in any electrical grid. This leads to a more vulnerable power system and increases the significance of studying the corresponding stability aspects. Decreasing the inertial response of a power system deteriorates the quality of both frequency and rotor-angle stability which are the dynamics of interest in this study. The thesis explores the role of the location of low inertia on varying the power system’s dynamics. This is to be conducted in isolation of all other factors that could affect the study outcomes, such as dealing with the same system’s inertia value upon lowering the inertia in different locations. To accomplish this objective, it is essential to analyze the inertia distribution of the examined power system following the alterations of inertia reduction location. Accordingly, an inherently previous work methodology, that estimates the relative distance of the system’s components to Center Of Inertia (COI), is utilized throughout this study. Both frequency response and small-signal stability are analyzed in light of the inertia distribution results. The thesis examines two different power systems, a small two-area model and a bigger more realistic power system. The former model, known as Kundur model, helps in building a conceptual process to apply the methodology and to benchmark the dynamics of interest. While the latter is a reduced model of the Swedish transmission grid, known as Nordic 32 model. Different scenarios of low inertia are considered to capture the current trend of integrating more Renewable Energy Sources (RES) and phasing out more conventional plants. DIgSILENT Powerfactory is the weapon of choice in this study. It is utilized to assess both the frequency stability by performing electromechanical transients’ simulations, and small-signal stability following modal analysis simulations.  Results show that the alterations of low inertia location are associated with variations in Instantaneous Frequency Deviation (IFD), Rate Of Change Of Frequency (ROCOF) and the damping ratio of the most critical inter-area oscillation mode. These variations have different levels of significance. Variations of the latter two metrics have the most considerable effects from the stability’s perspective. They can be utilized to prioritize the phasing out process of the conventional power plants, and to choose one of the scenarios of a specific low inertia location over the others. This helps in fulfilling proper long-term planning and short-term operation from the system operator’s perspective.

The increasing amount of renewable energy sources is applying more and more pressure on today’s power system. Additionally, plannable sources of energy, which are mostly non-renewable, are being decommissioned at a high rate to combat climate change. The decommissioning of non-renewable producers and the increasing number of intermittent sources of energy are causing an increasingly volatile power system. In addition to the lack of plannable production, the inertia from synchronously rotating machines is decreasing due to the lack of contribution from renewable sources. The inertia of a power system assists in slowing down large frequency changes. When a notably large difference between production and consumption occurs in a power system with low inertia, components which can quickly counteract these effects by supplying the system with active power, are needed. The low inertia can also cause problems to the synchronicity of the synchronously rotating machines in the system, namely the rotor angle stability. A lack of rotorangle stability can cause the synchronicity of the synchronously rotating machines to be questioned. Fast frequency response units supply the power system with active power for a short period of time to reduce the rate of change of frequency and frequency deviation, which in turn allows the self-regulating units more time to adjust their production. Furthermore, these units can improve rotor angle stability. Such units can consist of batteries which are both serially and parallel connected with their associated control unit. This thesis aims to, with the help of the power system analysis program PowerFactory, and its associated dynamic simulation tools, formulate a methodology which can be used in power system models to locate the best placement for fast frequency response units. The results show that the formulated methodology can be used to find the best position of fast frequency response units for frequency deviation-, rate of change of frequency- and rotor angle stability support.