Primary energy has the potential to bring challenges to the reliability, economic, and eco-friendlinessof global electric power systems. The concept of electric power security are proposed, including many factors thatare not considered in power system reliability analysis,such as coal supply for power system, fuel price for electricity power market, carbon emissions of power generation, and so on. It is broader than power system reliability and security, which means that providing energy in the form of reliable, economical, and ecofriendly electric power. Following an account of existing blackout defence methods and systems, the processes of transforming various kinds of primary energy into electric power and the interactions between them are described, particularly with regard to flows of energy, capital, and information. Factorsthat limit the liquidity of these flows are defined as '"gen-eralized congestion", and the challenges presented byprimary energy are named "primary energy congestion".China's dilemma on coal supply for power generation is presented in some detail as an example of primary energy congestion. To cope with impacts of the primary energy on electric power systems, an idea is introduced to extend the scope of existing coordinated black out defence systems toan integrated tool to provide decision support to power system operators accounting for primary energy congestion.