# Verification Methodology for Simulation Models of the Synchronous Generator on Transients Analysis
## 4 Results and Discussion
### The Results of Three-Phase Fault on the Generator in the Dynamic Simulation Model  
Figures 15 and 16 show the results obtained for the observed two power plants in real power networks HPP 1 and HPP 2, after the simulation of the three-phase fault at the generator terminals in HPP 1. The fault is initiated at 0 s, which is the moment when the voltage in one phase is equal to zero. In Figure 15, it can be seen that the currents of all three phases increase. It can also be observed that there is a voltage drop in all three phases (the voltage is 0) in HPP 1. In HPP 2, there is almost no voltage drop and a small increase in currents can be noticed. Short-circuit currents are higher in HPP 1 because it is electrically closer to the fault location. Figure 16 shows the machine speed, excitation voltage, and mechanical power for the two observed power plants, HPP 1 and HPP 2, when the three-phase fault occurs in HPP 1 at the generator terminals. Speed value was set at 1 p. u., which corresponds to the synchronous speed in the steady state, and a minimal change in speed is visible. In response to increased excitation voltage in HPP 2, transients occur as the behavior approaches the new steady state. Voltage goes to 2.5 p. u., which is the regulator output limit; 1 p. u. corresponds to the excitation voltage at no load. The variation of the excitation voltage caused by the voltage regulator does not significantly influence the values of the electrical and mechanical parameters of the generator where the short-circuit occurred, but  
Figure 14: The phase currents obtained by the FEM calculation. Figure 13: Detail of magnetic field just above the slot half a period after short-circuit. does affect the parameters that occur on the generator that is farther from the fault location. Due to the function of the voltage regulator on the generator that is farther away from the fault location, the phase voltages do not show a significant deviation from the nominal value, and the asymmetry of the phase currents is reduced. In the dynamic simulation model, the generator no-load characteristic is considered, and the calculation of the transient with and without the influence of saturation can be performed. Since the machine is low-saturated at the rated voltage, i.e., the saturation factor of the magnetic circuit is only 1.05, no significant differences were observed between the currents obtained by the dynamic simulation model, with or without taking the magnetic saturation into account. The presented values used for comparison of the two analyzed methods shown in Figure 17 are with saturation. In Figure 17, the currents in phase \"w\" obtained by the FEM calculation with the dynamic model are presented. The peak value of current obtained by the dynamic model is 25.48 kA; with the FEM, it is 27.87 kA, which is a deviation of 9.38%. This is the current of the phase in which the voltage was zero at the time of the short-circuit. Figure 16: Machine speed, excitation voltage, and mechanical power. Figure 15: Phase currents and voltages in generators built in the model. Since the actual sudden short-circuit current can only be determined by measuring on a produced machine in real conditions, its exact amount is not known. The dynamic model uses the parameters of the equivalent diagram, obtained by measuring with standard methods that are usually performed at low voltages on such large machines. Those conditions cause the obtained reactances to always be higher than the actual ones. Therefore, the peak value of the sudden short-circuit current obtained by the dynamic model is less than that obtained by the FEM. There is a small phase shift between the waveforms due to a change in the rotational speed considered in the dynamic simulation model, while in the FEM it is calculated with a constant speed during the transient. The FEM calculation takes into account the actual form of the produced machine as well as the actual conditions under which the transients occur. The actual state of saturation can only be obtained by the FEM.