## 3 Non-Linear Load Effect on Operation of Low-Power Synchronous Generator  
A flow chart of the computer model that was used in the study is shown in Figure 8. The turbogenerator in the model served a resistive and inductive load of 1.8 + \(j\)0.6 MWA. Distortion of the current and voltage sine waveform was carried out by consistently increasing the rectifier power with a simultaneous reduction of the main load of the turbogenerator so that the total load remained unchanged. The results of computer-aided simulation are summarized in Table 5 and illustrated in Figures 9 and 10. Figure 10: _Cont._  
An increase in harmonic components of load current led to an increase in stator and rotor currents of the turbogenerator (Figure 9) while maintaining the balanced load flow. The results of the study also showed that when the voltage and current waveforms deviated more from the sine waveform, the amplitude of the forced oscillations of the excitation current of the generator at a frequency multiple of 300 Hz increased, which led to additional losses and extra heating (Figure 10c,d). This circumstance is due to the fact that the higher harmonics in the turbogenerator stator current curve create magnetic fields rotating in the forward and reverse directions with the harmonic frequency. These fields, rotating asynchronously with respect to the rotor, are superimposed on the magnetic field of the fundamental frequency and induce high-frequency currents in the rotor circuits. If there are odd harmonic currents in the stator winding, even harmonic currents are induced in the rotor winding as a result of the interaction of magnetic fields. Figure 10: Waveforms of stator currents (**a**) and rotor currents (**b**) of the generator and their harmonic content (**c**,**d**) at \(k_{U\!a}=15.6\%\). Thus, an increase in the harmonic distortion of the load current was accompanied by a growth of stator and rotor currents and the occurrence of forced oscillations of electrical and mechanical parameters of the generator. This should be considered when introducing DG units into RPSSs. Failure to consider these factors can lead to rapid wear and tear of equipment and even breakdown of generators. In addition, given significant deviation from the sine waveform, the stability margin was reduced, and the probability of the generator switching into asynchronous operation increased. Experiments run on the simulation model showed that when the generator served a rectifier load, the power of which was 85% of the rated generator power, and an additional load was connected, the system lost stability, and the generator started asynchronous operation. When serving linear loads of the same power, ARE and ARS effectively dampened the disturbances introduced into the system. The waveforms of the rotor speed of the turbogenerator that illustrate these conclusions are shown in Figure 11: the load was 85% of the rated power of the turbogenerator. In this experiment, the sine-wave distortion coefficient of the voltage waveform reached \(k_{U}=30\%\), while the RMS value of the excitation current increased by 55% compared with the operation that served a linear load. These circumstances, which also take place in real-world operation of RPSSs, must be taken into account as well when deciding on the settings of the ARE and ASR of generators of DG units. Thus, the loss of stable operation of the synchronous generator is due to the incorrect operation of the regulators and an additional increase in the stator and rotor currents, which reduces the actual stability margin. On the basis of computer-aided simulation it was found that the following effects took place when the harmonic distortion of the load current increased:  
1. The stator and rotor currents of the generator were significantly increased. For example, at \(k_{Ua}=15.6\%\), the RMS value of the stator current increased by 32% compared with the load flow when there was no rectifier load.