Simulation Studies of Emergency Transfer System and Load Sequencing in Indian Pressurized Heavy Water Reactor

Electrical Power Supply System in Indian Pressurized Heavy Water Reactor (PHWR) based Nuclear Power Plants consists of Offsite (Grid) power supply and Onsite (Turbo-generator, Diesel Generators, Battery) power supply. Power supply from Grid and/or Turbo-generator is normally used and is called as Preferred Power Supply. On loss of Preferred Power Supply, restoration of power supply to emergency buses from Diesel Generators and sequential load restoration of safety loads is crucial in maintenance of reactor safety. Emergency Transfer System plays a vital role in automatic restoration of power supply and systematic load restoration to avoid tripping of diesel generators on overload. Designing transfer logic by considering all failure scenarios and deciding load sequence to avoid overloading of Diesel Generators are challenging tasks during design stage. Lack of verification of this system during design stage may lead to rework during site testing stages. This paper explains step by step methods and simulations adopted to verify Emergency Transfer & load restoration scheme and to study diesel generator performance during sequential restoration of major loads. Challenges in simulation such as unavailability of motors resistance and reactance values, simulation of dynamic operations of field equipment, modelling of Diesel Generator system are addressed in this paper.