Motor Inertia Calculation Motor Inertia Calculation tiftif (Electrical) (OP) 8 Sep 17 22:17 I have a 1750HP IM 13.2kV RPM = 3600 & MVA is 1.424. H=1/2Jw^2/MVA. I do not know H. I need to get J which is written as J=2H (s). Anyway to estimate some reasonable value for J? RE: Motor Inertia Calculation 7anoter4 (Electrical) 9 Sep 17 05:39 It is difficult to appreciate the inertia moment since for modular type it could be 8 kg.m^2[190 lb-ft^2] and for cast iron 40 kg.m^2[950 lb-ft^2]. It would be better if you could ask the manufacturer.