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Digital excitation systems

Improve plant response to variable grid conditions and raise operator awareness

Traditional synchronous machine-based power generation is gradually being replaced by renewables like wind and solar energy. Wind and solar, however, are intermittent and do not provide the required system inertia for transient rotor angle stability, nor the reactive power needed for voltage stability support. 

To ensure the stability and reliability of a power system containing a large volume of renewables, it is crucial that the synchronous generators maintain stability over a broad range of operating conditions. In addition, the grid operator should be able to monitor operating parameters, such as loading angle, in real time in both normal and transient states.

In conventional excitation systems, the excitation control system parameters are set during the commissioning process and remain fixed throughout the lifetime of the system. The fact that the power system evolves and changes its properties over time is rarely taken into consideration.


Breaking with tradition

ABB’s latest generation of excitation systems, UNITROL® 6000, breaks with this tradition of inflexible parameters. Equipped with fast and accurate measurement sensors, UNITROL 6000 continuously measures the electrical output variables of the synchronous machine and analyzes the data collected. Using advanced transducers, measurement techniques and built-in algorithms, UNITROL 6000 automatically tracks changes in external grid impedance (Xe). Awareness of the correct Xe-value is important as it influences the settings of the key excitation system controllers.

Knowledge of Xe is also instrumental to the operation of the Extended Kalman Filter-based (EKF) state estimator. The state estimator allows for rapid and accurate calculation of the generator states that are important for the proper operation of the power system stabilizers (PSS). For instance, correct calculation of the generator’s angular speed enables the PSS to operate over a broad range of frequencies. 

In addition, the state estimator provides fast and reliable estimates of the generator’s load angle, which informs the power plant operator of the closeness to the steady-state stability limit of the generator. This information raises the operator’s situational awareness and helps maintain reliable and safe operation of the power plant as it contends with uncertain and variable grid conditions.

UNITROL 6000 is part of ABB’s offering of excitation products and synchronizing equipment for the power generation industry. The portfolio is the most comprehensive and proven on the market, extending from the smallest to the largest power requirements and covering all power generation applications.


UNITROL 6000 - In Control 01 17
UNITROL 6000

  • Automatically regulates generator output
  • Stabilizes the grid
  • Avoids critical generator states
  • Communicates potential problems early to operators

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