Although there are dozens of sub-branches in Electrical engineering, but only a few of them are evergreen. For best design capstone projects, it is a good idea to do something that captures your imagination and hopefully others.
Here, evergreen means engineering project field which is high in demand in industrial markets. The below mentioned Electrical engineering field has very Promising Strategies for Advancement in Knowledge.

• Core Electrical
  • Design and development of electrical machine like
    • Transformer for current limiting, harmonic reduction, its optimisation in size, weight, cost, efficiency etc.
    • Motors like linear induction motors, Tubular motors.
• Power System(Substation/Transformer/Transmission Line) Monitoring And Control, data acquisition, load balancing.
• Power Quality i.e Sag, Swell, pf, short circuit current, inrush current, transient mitigation technique.
• Home/Industrial/Base Station/office/ agricultural Automation
• Protection and Control Electrical Equipment (Motor control and protection relay, Transformer protection, line protection etc.
• Smart Grid Appliances like theft proof smart energy meters, Remote terminal units, Intelligent electronics devices.
• IOT and artificial intelligence based Automation, Control and monitoring system.
• Renewable Energy Sources (Solar/Wind/wave) implementation, application, optimisation etc.
• Security System in Industry/Home/Office
• Robotics and its application.
• Electrical Vehicle
• Electrostatic ionisation and its application in agricultural spraying equipment, industrial spray painting etc.

If you are searching project idea for academic submission you have those limits.

1. Time
2. Money
3. Material
4. Proper Guidance (Especially in Indian Education System)

Be aware it before selecting any topic. It’s my worst experience in my last year.