The use of graphical dynamic system simulation software is becoming more popular as economic demands require reducing time and cost of development and troubleshooting equipment. Nuclear power plants pose unique problems in this regard because installed equipment must be available to support the plant safety function, so it is not available to support qualification testing of new designs or troubleshooting in the case of equipment malfunction. Commercial design processes have similar constraints due to the high cost of prototype development.
This paper discusses recent successes in using modular system simulation software to support the implementation of improved speed control governors installed on emergency diesel generators. The original governors are to be replaced as part of an overall control system upgrade. However, the engine operator needed to demonstrate that the replacement governors would provide adequate transient performance and no degradation in engine or generator response during fast loading and full load rejection per United States Nuclear Regulatory Commission (USNRC) Regulatory Guide 1.9. A dynamic system model was developed using MATLAB/SIMULINK software, which the authors have used in other similar modeling tasks. The system model includes a torque-predictive engine model (including sub-models of the turbocharger and fuel injection system), speed control governor, and plant emergency electrical loads. This model was validated using the engine vendor's qualification test stand data and results from periodic utility surveillance tests.
Through use of the model, the performance of the EDGs with replacement governors was predicted to be the same as with the original governors. In addition, it was shown that the performance could be enhanced to comply with the intent of the regulatory guide. Further, by using the model, stability and tuning analyses were accomplished to predict the system adjustments required prior to installation, thus reducing the time to implement the modification. Finally, a modified governor system design was analyzed to determine if improved system response could be attained.