See this depends upon which department you are placed in. One cant predict this kind of thing. Since BHEL has a presence in the following areas 

• Renewable Energy
• Defence & Aerospace
• Oil & Gas
• Power
• Industry
• Transportation
• Water Management Systems
• Transmission

BSNL is into communication so electronics plays a major role here. 

What is to be understood is PSUs are Govt entities so career growth is pretty chartered. If you check their career pages they will have listed a lot of information. check that out too.