This thesis investigates the capacity expansion of distribution substation of each service area considering PV system penetration to achieve the cost effectiveness of substation investment to comply with the service reliability. With the land use planning of Kaohsiung City Government, the load density of each small area for the target year is derived according to the final floor area and development strength of the land base. The load forecasting of each small area is then solved by considering the load growth of each customer class and a Markov model is applied for the forecasting of solar energy, which is then included in the expansion planning of substations. The forecasting of annual peak loadings for each area over the future 20 years is performed by the time series method based on the historical load data and load type of customers served. The forced outage rate ¡]FOR¡^ of main transformers in the substations is used to solve the loss of load expectation¡]LOLE¡^ according to the peak loading of each service area. By this way, the capacity expansion planning of main transformers to meet the service reliability can therefore be derived. To further enhance the distribution system planning, the capacity transfer capability of main transformers and the tie line flow capacity between different areas are considered too. It is found that the expansion planning of main transformers by the proposed methodology can provide better cost effectiveness of transformer investment to satisfy the service reliability as well as the system peak loading.

Wind power generation influences on the quality of the power grid. Because wind velocity is consistently changing this change causes unstable wind power generation. Since more wind power is expected to be used in the future, it is crucial to study the influence of the wind penetration level on normalized-damping ratio and damped-resonant frequency. In this thesis three types of calculated data were used to analyze the effect of wind penetration level on the Texas power grid: the percentage of wind power generation in Texas, generator-unit trip damping coefficient, and damped-resonant frequency. The percentage of wind energy was calculated from wind data provided by the Electric Reliability Council of Texas. The damping coefficient and damped-resonant frequency values are the indicators of power system stability and were calculated from synchronized phase data from the Texas power grid. The synchronized phase measurements were collected from the University of Texas at Austin and the wind farm near the Mc-Donald observatory. The data analyzed in this paper were from September 2009 to February 2010. The wind data were correlated to the grid-stability indicators which allowed us to interpret the status of the power grid according to the wind penetration level. When the wind penetration level increased over 11 %, five generator trip events occurred with damping coefficient values ten times higher than those of the regular unit trips. Moreover, during those events, damped-resonant frequency values rose nearly four times higher than the frequency values of other events. The results of this study may lead us to the conclusion that simply increasing the capacity of wind power generation will cause the power system to become unstable, and this will result in low quality of electricity. Therefore, further study is needed to determine the optimum amount of wind power generation without causing instability in the power grid. / text

The Swedish Energy Agency has a target to increase solar photovoltaics (PV) power production by up to 5-10% of the total electricity demand by the year 2040. The PV potential for the residential market is high and its contribution to the total installed PV capacity is expected to increase significantly. The technical requirements should be met to keep high reliability and good power quality at the customers, therefore, it is important for planning reasons to proactively find the maximum amount PV power that can be connected at each low-voltage network without violating the performance of the grid. This amount is known as the hosting capacity. A method for PV hosting capacity estimation by taking overvoltage and transformer overload as performance indices was developed in this thesis. The method does not require any knowledge about the topology of the network. The overload hosting capacity can be estimated for any combination of customers having PV power and for the overvoltage hosting, the minimum at each penetration level can be estimated. The method was implemented on four low-voltage networks located in a typical Vattenfall medium-voltage network and the comparison of the estimation results to a power flow simulation showed good correspondence. It was shown how the impact of PV power in adjacent secondary substations can be accounted for. Using SS-EN50160 voltage limits, the studied networks were able to handle 3-7 times the PV penetration level needed (8 kWp at 20% of the customers) to achieve the national goal in Sweden without grid investments.