Abstract The power grid reliability impacts could be significant when a large amount of variable wind generation is integrated  with the electric power system。 The widely used deterministic reliability assessment method is invalid when modeling intermittency of wind energy sources。 The energy based probabilistic reliability assessment models are required in system reliability impact assessment in order to consider the stochastic characteristic of wind resources。 This paper investigates different stochastic characteristics in wind energy integration, including resource availability, generation facility outages and transmission availability。 A probabilistic framework of reliability modeling for renewable resource integration such as wind energy conversion system  is proposed in this paper。 Using the proposed reliability models and framework, the cost of wind energy integration with the power gird for maintaining system adequacy and  reliability can be evaluated realistically。 The IEEE Reliability Test System (IEEE-RTS) system is utilized to demonstrate the developed models and methods。84216

I。 Introduction

Renewable energy resources such as wind and solar energy conversion systems play an important role to eliminate reliance on fossil fuels as well as in reducing the greenhouse gas emissions。 With the wind energy technology advancements in the past couple of decades, it is expected that a large amount of electric energy supply requirements will be met by non-conventional energy sources such as wind, solar and geothermal technologies。 Many countries have adopted aggressive Renewable resource Portfolio Standard (RPS) targets in order to reduce their reliance on imported oil, and on environmentally harmful fossil fuels。 For  example,  in the state of California, a 33% RPS target by 2020 is under consideration [1]。 Wind resource integration with the power system has received increased attention by power system researchers and engineers in both planning and operation phases。  Intermittency  and  variability  of  energy   production

associated with any renewable technologies need to be reflected and accurately modeled in system reliability performance assessments。

The inability of modeling the stochastic characteristics of power system is not a new problem for widely deterministic methods; however, it becomes a serious problem when considering the integration of wind resources with the power system。 For example, in the current practice of system planning, the deterministic method is used in generation interconnection to identify and to resolve the stability issues [2]。 The transmission upgrades identified based on the worst case scenarios may be underutilized if the capacity factor of wind resource is low。 A solution that has been used in deterministic study is to adopt a de-rated capacity as the target capacity of transmission upgrade [3]。 The selection of the de- rated target capacity is normally based on the average of historical data or field measurements。 The deterministic reliability assessment is a snapshot study that is difficult to cover all possible scenarios。 The system addition identified by deterministic methods cannot adequately model power system capability to accommodate different types of generation technologies including intermittent  sources。  The probability of loss of load may increase when wind resource penetration and system load increase [4 and 5]。

Probabilistic reliability techniques are required to model the impacts of wind energy resources on system reliability and adequacy。 The energy-limited and intermittent characteristics of wind generation, especially wind generation, have been studied using the probabilistic reliability assessment techniques。 The capacity state probability model of energy- limited generation in probabilistic reliability assessment has been developed in [6 and 7]。 The capacity state probability model of wind generation output is dependent of wind speed and wind turbine outage [8 and 9]。 The impacts on system reliability from wind generation have been investigated based on probabilistic reliability assessment from different view points [4, 5, 10 and 11]。 It has been recognized that the system reliability may be degraded when wind generation penetration increases in power system, because of the intermittent characteristic of wind resource。 The requirements of additional