The present investigation carries out the study of requirements in the IEC and ANSI/IEEE international standards, analysis and recommendations of several specialists in transformer testing and impulse voltage testing systems for distribution and power submerged, in insulating liquid in order to carry out the sizing of an impulse voltage test generator for transformers up to 10 MVA, class 69 kV up to an altitude of 3,000 m above sea level (masl). The sizing indicates the step-by-step description of the characteristics and technical requirements that the system must have in order to carry out impulse voltage tests, both in peak voltage, as well as in the specific front and tail times. The results were verified through 87 simulations of 40,000 data each in Matlab/Simulink. Additionally, the simulations were evaluated with the results of high voltage laboratory tests on power transformers. The values obtained during simulation and laboratory tests are excellent since the deviations are less than 3% in voltage level, 8% and 12% in front and tail times, when the latter have a tolerance of 30% and 20%, respectively. This study provides the methodology and exemplifies the sizing of the main components of impulse voltage testing systems for distribution and power transformers.