Simulation of Small Scale Pumped Hydro Power Plant with Permanent Magnet Generator during Faults
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- Institutt for elkraftteknikk 
This master thesis is a further investigation of the possibilities to utilize the permanentmagnet synchronous machine technology in small scale pumped hydro power, as a continuationof the specialization project, fall 2014. The focus of this thesis is how thepumped storage plant will operate during four different fault situations. A theoretical survey is done to get a better understanding of how voltage and frequencydeviations in the synchronous machines connected grid affect in generator operation.Available design criteria standards for synchronous generators are reviewed, and a summaryof these are formed. The fault period during a short circuit of a synchronousmachine has been set in focus, and the different torque contributions during and afterthe short circuit fault have been investigated. The simulation models are made in Matlab Simulink SimPowerSystems(MSPS), and thecorresponding control circuits for each of the simulation cases are developed here. Bothsimulation models are established from existing blocks in the simulation program, onewith an electrical machine equipped with rotor damper windings and one without. Eachof the simulation cases are performed on both simulation models, and the results andconclusions follow each of the four cases. A full short circuit simulation case is done in both motor and generator operation. Forgenerator operation the results show that the generator that is equipped with damperwindings have a smaller rate of rise of the rotational speed increase during the fault, thanthe generator without the damper windings. The damper windings contributes with aspeed 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 alarger speed reducing torque, and that the rotational speed has a steeper speed reductionduring the fault than for the model without damper windings. In motor operation thiseffect leads to that the simulation model without damper windings is able to withstanda 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 damperwindings speed reducing torque is considered as a disadvantage. For the simulation case during minor voltage and frequency variations, both of thesimulation circuits are able to withstand the tested simulation case. This shows thatthe requirements for this simulation case are not the most demanding to meet with apermanent 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 lowestvoltage plateau. The FIKS requirements that are the background for this simulationcase are considered more demanding to fulfill with a permanent magnet synchronousmachine configuration. Since the simulation models consist of the electrical machine,connected directly to the grid, an insertion of passive elements as transmission linesor/and transformers between the grid and the electrical machine would add a dampingeffect to the system, and possibly better simulation results. The main conclusion is that damper winding are considered as a advantage both duringthree phase short circuit and after a fault in generator operation. In motor operationthe result is more complex, where the damper winding contribute with a negative contributionduring a three phase short circuit, and with a positive effect after a fault.