Power transformers must be evaluated under impulse tests. For that, it is necessary to compare voltage and current waveforms corresponding to reduced-level and full-level voltages. Any difference may correspond to a failure in the transformer under test. This test is based on the principle that there is no change in the generation of the impulse voltage. However, with chopped waveforms, many impulse generators have significant differences in the time of chopping that make difficult to get a conclusion on the test result. This paper presents a new algorithm that generates reduced-level chopped voltage and current waveforms, with arbitrary chopping time, from a couple of reduced voltage of full and chopped waveforms. In this way, it is possible to compare full-level voltage chopped waveforms with reduced-level ones with different chopping times.