Estimation of reactive power export and import capability for non-utility generators

Non-utility generators (NUG's) are typically required by their electric power sales agreement to have the capability to supply power to the purchasing utility near unity power factor. With the advent of large combustion turbine generators, many NUG's are simple or combined cycle facilities with generating capacities in excess of 100 MW. Utilities are recognizing that these large NUG facilities can be significant contributors to the reactive power [megavars (MVArs)] flow needed to support system requirements and transmission level grid voltages. NUG's are now being dispatched for MVAr export and import activities to meet utility requirements. The ability of a NUG to export or import MVArs is highly dependent on the actual transmission intertie voltage level. Unless plant-specific studies are performed, this capacity can be difficult to ascertain for the NUG operating and engineering personnel. This paper presents a method, based on system load-flow studies, for estimating the capacity of a NUG to export or import MVArs at a given transmission intertie voltage level. It also explores other key variables which determine the ability of a NUG to export or import VArs. This methodology can be used to aid operating personnel at existing facilities or as a guide during the design of a new facility.