Yes, you can file RTI Application to National Thermal Power Corporation (NTPC).
National Thermal Power Corporation Limited (NTPC) is an Indian Public Sector Undertaking incorporated under the Companies Act 1956 and is promoted by the Government of India. NTPC was conferred Maharatna status by the Union Government of India in the Year 2010. Thus, NTPC is a Public Authority as per Section 2 (h) of the RTI Act 2005 and comes under the ambit of the Act.
Hence, you can apply RTI Applications to NTPC by paying the prescribed fee either Online or Offline mode.
To know the further procedure for filing RTI's Online, please refer https://onlinerti.com/how-to-file-rti-online-for-center