The aim of the project was to increase thermal power plant reliability throughout evaluation of power flow regimes of power plant, short circuit studies and protection coordination and optimization. As an analysis tool EA-PSM revealed as reliable, accurate, fast task solving tool.

Thermal power plant has two electrical generators with capacity of 24MW, interconnected to 6kV network, also as 913 MW thermal capacity.

The necessity of the project had arisen due to mal operation of protection due to external or internal faults. Electrical network is supplied by two 110/35/6kV transformers. The main electrical equipment is supplied through current limiting reactors and has 6kV nominal voltage. High length cable network creates high-level capacitive currents which are reduced at the fault place using arc suppression coils (Peterson coils). The EA-PSM modelled network consists of: 204 busses; 263 branches like power transformers, cable lines, reactors; 36 asynchronous electric motors with 6kV nominal voltage; 12 variable frequency drives, connected to 6kV network.

Protection coordination and settings optimization is critical due to requirements of generators island operation.

Fig. 1. Part of the 6kV network in EA-PSM
Fig. 1. Part of the 6kV network in EA-PSM

Protection tracking function allowed simulate protection behavior in big picture. The simulation results due to fault at bus depicted in Fig. 2. Protection Tracking allows initiate fault at any bus, for any kind of fault, for minimum or maximum systems short circuit power, also as add arc resistance at fault place. Protection Tracking evaluates protection, auxiliary relay time delays, circuit breaker disconnection time, also as protection relay return time.

Fig. 2. Simulation of protection behavior. Protection tracking function
Fig. 2. Simulation of protection behavior. Protection tracking function.
Fig. 3. Low voltage circuit breaker, overcurrent, directional groundfault and undervoltage protection models
Fig. 3. Low voltage circuit breaker, overcurrent, directional groundfault and undervoltage protection models

The study reviled protection mal operation for some faults and some fault places. Overall 135 circuit breakers with nominal voltage 6kV including 3 stage over current protections, under voltage protections and directional ground fault protection were studied. Low voltage 0.4kV network was modelled partly, limiting to 6/0.4kV transformers and low voltage side circuit breaker.

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