The purpose of this research is to develop models which can be used to produce realistic test waveforms for the evaluation of protection systems used for generators and transformers. Software models of generators and transformers which have the capability to calculate voltage and current waveforms in the presence of internal faults are presented in this thesis. The thesis also presents accurate models of current transformers used in differential current protection schemes. These include air gapped current transformers which are widely used in transformer and generator protection. The models of generators and transformers can be used with the models of current transformers to obtain test waveforms to evaluate a protection system. The models are validated by comparing the results obtained from simulations with recorded waveforms.