The paper presents technical studies performed to review the values of the Normal Infeed Loss Risk (NILR) and Infrequent Infeed Loss Risk (IILR) in the Transmission System Security Standard (TSSS). The objective is to facilitate the connection of the largest power station in Oman, which is Sur 2000 MW IPP, to the Main Interconnected Transmission System (MITS), while complying with the requirements of the TSSS. The full output of 2000 MW of Sur power plant is expected to available in 2015; therefore the MITS model of 2015 is used in the studies using the DIgSILENT professional software. The model includes static and dynamic representations of each generating unit with its synchronous generator, turbine, speed governor, exciter, and automatic voltage regulator; in addition to representation of the network transmission lines, transformers and loads. System studies have been performed to assess the dynamic performance of the MITS when it is subjected to various levels of loss of power infeed at Sur power plant. The objective is to make sure that both voltage and frequency are within the allowable limits, stability is maintained and no overloading before and after the loss of power infeed. The studies presented in this paper are corresponding to the following expected demand levels in 2015: • Minimum demand of 1760 MW • Off-peak demand of 3000 MW • Peak demand of 5560 MW The results have shown that the following reviewed values of the normal and infrequent loss of infeed risks should be used to facilitate the connection of the 2000 MW Sur IPP: • The NILR is 500 MW at system demands above 3000 MW falling to 390 MW at system demands below 2000 MW. • The IILR is 780 MW at system demands above 3000 MW falling to 500 MW at system demands below 2000 MW.