Influence of direct air-cooled units on primary frequency regulation in power systems

The performance of air-cooled units is significantly affected by meteorological conditions because they use the ambient air directly as the cooling medium. The purpose of this study is to determine the influence of air-cooled units on grid stability under extreme meteorological conditions. Based on the characteristics of air-cooled units, cooling air face velocity and temperature are two main meteorological factors taken into consideration. A dynamic model of the air-cooled units is developed. Since grid frequency is a representation of grid stability, the above model is then applied to a mathematical model to analyse the primary frequency regulation process of a grid. A coefficient to measure the primary frequency regulation ability (PFRA) is defined and the calculation of PFRA is put forward. To increase the reliability of the study, the performance of the grid under different meteorological conditions is also studied in frequency domain. Case studies under generator tripping and steep load rising conditions are studied. The corresponding PFRA and the maximum capacity proportion of air-cooled units are calculated. This study provides a constructive guide for the operation of air-cooled units under different meteorological conditions.