Power system reliability is one of the most important issues in modern energy market. Revenues of the generation companies are associated with competition in a market filled with risk and uncertainty. Speculating economic aspects and the high costs of new transmission lines, on one side, and formation of fast fault clearing systems and advanced control systems, on the other side, encourage system operators to maximize their generation and transmission capacities. By recent progress in insulation technology, transmission voltage has reached 1000kv while output voltage of conventional generators is limited to about 30kv and hence, step-up transformer is needed to connect these generators to the power system. Voltage output limitations in generators and utilizing step-up transformers are accompanied with some problems like limited power output, increased loss, reduced system stability and so on. Hence, increased generators output voltage for omitting intermediate step up transformers and direct connection to the network has remained as a goal. Answering this need, a new generator known as Powerformer TM was introduced to the market in 1998 in which the traditional stator windings were replaced with some kind of XLPE cables. Applying this newly developed structure enables increased output voltage that nowadays is increased up to 155kv. Meanwhile, the new structure made some changes in utility. In this thesis, after introducing Powerformer TM and its structure, effect of this generator on system reliability is evaluated. Achieving this task, based on the available data, reliability of the Powerformer TM is estimated and then the effect of this generator on generation system reliability is evaluated. Based on these investigations, the required installed capacity and system spinning reserve are determined. Cost of supplied energy considering units availability is an other criteria which is discussed. One other spotlight in Powerformer TM characteristics is it's competence on short term over current capacity in emergency cases. The effect of this capability on power system reliability is also assessed through well-being evaluation using steady-state security considerations.
