Special protection systems based on generator tripping are implemented to protect power systems against the loss of synchronism following extreme contingency events. Such countermeasure is particularly effective when the circuit breakers of the tripped generators are opened soon after the fault is cleared. This paper presents a new method that enables quick real-time predictions of transient instability and the number of generators that must be tripped. The proposed method uses local measurements only and is based on quick prediction of the magnitude of the power-angle characteristic. The proposed method has been validated by simulation tests performed for a large-scale real power system and detailed models of power system elements. INDEX TERMS power system transient stability, real-time instability prediction, generator tripping, special protection scheme

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Power system transient stability can be effectively improved by applying shunt braking resistors. This paper proposes multi-objective heuristics-based optimization for shunt braking resistor sizing. The proposed approach addresses three objectives: transient angle stability, transient voltage response, and mechanical stress of the turbine-generator shaft. The optimization problem was solved using a Python implementation of the multi-objective evolutionary NSGA-II algorithm. Based on the optimization model, comprehensive tests for multimachine IEEE 39-bus power system including single-and multi-objective simulations were performed. Pareto sets for various sets of objectives are obtained and discussed. The results show the complexity of the shunt braking resistor optimization process. Optimization studies were complemented by simulation tests performed for assessing of the impact of optimal shunt braking resistor on power system dynamic response. Detailed discussion of test results has confirmed the correctness of the proposed approach.

The generation structure in the European power systems is continuously changing towards an increasing share of non‐synchronous energy sources. This leads to significant challenges in maintaining frequency stability due to declining system inertia. In this study, a novel concept of demand response very fast active power control (DR VFAPC) capability using in a direct way the braking energy in electric trainsets being in motion is presented. In order to assess the potential to ensure DR VFAPC capability by freight railway carriers and examine the impact of such service on frequency dynamics, a simplified mathematical model of Polish power system representing the frequency regulation process has been developed. The impact of basic characteristics of the freight train transport, as well as the selected power system parameters on the DR VFAPC operation, has been studied. In conclusion, current technical constraints of implementing the presented idea and future works have been discussed.