This bundle define elements and commonly used components in excitation systems and contains definitions for excitation systems applied to synchronous machines. They include criteria, definitions, and test procedures for evaluating the dynamic performance of excitation control systems for synchronous machines as applied by electric utilities. They provide requirements and specific directions for the high-potential testing of complete excitation systems and their components using the most recent information manufacturers have made available. The standards supply the information to prepare a specification for the purchase of an excitation system; describe types of excitation systems and information required for sizing the excitation system. Mathematical models are included for computer simulation studies of excitation systems and their associated controls for three-phase synchronous generators. This bundle includes 7 active IEEE standards in the 421 family which are: IEEE Std 421.1-2007, IEEE Std 421.2-2014, IEEE Std 421.3-2016, IEEE Std 421.4-2014, IEEE Std421.5-2016, IEEE Std 421.6-2017