Simulation of Small Scale Pumped Hydro Power Plant with Permanent Magnet Generator during Faults

This master thesis is a further investigation of the possibilities to utilize the permanent magnet synchronous machine technology in small scale pumped hydro power, as a continuation of the specialization project, fall 2014. The focus of this thesis is how the pumped storage plant will operate during four different fault situations. A theoretical survey is done to get a better understanding of how voltage and frequency deviations in the synchronous machines connected grid affect in generator operation. Available design criteria standards for synchronous generators are reviewed, and a summary of these are formed. The fault period during a short circuit of a synchronous machine has been set in focus, and the different torque contributions during and after the short circuit fault have been investigated. The simulation models are made in Matlab Simulink SimPowerSystems(MSPS), and the corresponding control circuits for each of the simulation cases are developed here. Both simulation models are established from existing blocks in the simulation program, one with an electrical machine equipped with rotor damper windings and one without. Each of the simulation cases are performed on both simulation models, and the results and conclusions follow each of the four cases. A full short circuit simulation case is done in both motor and generator operation. For generator operation the results show that the generator that is equipped with damper windings have a smaller rate of rise of the rotational speed increase during the fault, than the generator without the damper windings. The damper windings contributes with a speed reducing torque, which acts as an advantage in the generator mode of operation. For motor operation the same effect is seen, that the motor with damper windings has a larger speed reducing torque, and that the rotational speed has a steeper speed reduction during the fault than for the model without damper windings. In motor operation this effect leads to that the simulation model without damper windings is able to withstand a longer short circuit on the machine terminals, than the model with damper windings, because its speed deviation after the fault is smaller. In motor operation the damper windings speed reducing torque is considered as a disadvantage. For the simulation case during minor voltage and frequency variations, both of the simulation circuits are able to withstand the tested simulation case. This shows that the requirements for this simulation case are not the most demanding to meet with a permanent magnet synchronous machine. In the "fault-ride-through" test does none of the simulation circuits operate stable after the main test, with 85 % voltagedrop and a 0,40 seconds time duration at the lowest voltage plateau. The FIKS requirements that are the background for this simulation case are considered more demanding to fulfill with a permanent magnet synchronous machine configuration. Since the simulation models consist of the electrical machine, connected directly to the grid, an insertion of passive elements as transmission lines or/and transformers between the grid and the electrical machine would add a damping effect to the system, and possibly better simulation results. The main conclusion is that damper winding are considered as a advantage both during three phase short circuit and after a fault in generator operation. In motor operation the result is more complex, where the damper winding contribute with a negative contribution during a three phase short circuit, and with a positive effect after a fault