Aspirants who pursue masters with minimum 55% marks can apply for CSIR OR UGC NET Exams.
As you pursued M.Tech in Power Systems High Voltage Engineering, you can appear in both the exams.
For UGC NET Exam you should apply for Electronic Sciences and for CSIR NET Exam you should apply for Physical Sciences.
Both the exams are organised for the same purpose. Make your own decision that in which subject or you are most interested.
Hope The information is helpful to you!