Issues with electrical power quality have become more frequent due to the widespread use of electronic devices and limitations placed on distribution lines. Consequently, there will be a growing concentration on monitoring power quality and monitoring power disruptions. Understanding power quality problems and identifying disturbances are crucial for electric compensation along with improving electrical safety. A modified S transform based on the sigmoid function is addressed for obtaining the characteristics of various power quality signals with better time–frequency (T-F) resolution as compared to other techniques. Thus, an assessment index was established to quantify the effect of different methodologies on signal. Various power quality signals are generated, and the performance of the modified S-transform is evaluated which shows the efficiency and accuracy of the method. From the results, it can be concluded that the proposed T-F method fulfills the requirements of various power quality signals and copes with the negative impact of noise and harmonics.