Modelling of the Protection Relays of STATCOM
Nuuttila, Markus (2019)
2019
Sähkötekniikan DI-ohjelma - Degree Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2019-08-07
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-201907022399
https://urn.fi/URN:NBN:fi:tuni-201907022399
Tiivistelmä
Selective, fast and reliable protection measures are essential for the electric power system, particularly for the transmission network operating at high power levels. Due to the dependence of the society on electric power, the protection systems are critical in minimizing the risks of personal injuries, economical losses and interruptions in the supply of electricity. For the same reason, the power quality is another important issue in the modern transmission systems. To compensate reactive power and reduce the harmonic content in the grid, power electronic solutions such as static synchronous compensators (STATCOMs) and static VAr compensators (SVCs) have been developed. The complex control systems of these compensators require an efficient design method, and simulations with Matlab and Simulink are used widely for this purpose. However, the protection system is still often designed conventionally by verifying the setting calculations with intensive stability tests in laboratory. Moreover, the effect of the trips on the control system must be analysed manually.
In this thesis, Simulink models for overcurrent and differential protection functions were implemented to reduce the need for testing. Two different commercial protection relay models were analysed for both functions with the results compared to each other and the standards defining the functions. For the overcurrent protection, a simplified simulation model was also created according to the standard. Particularly, operating characteristics of the functions as well as the differences between the relay models were examined by visualising them with the Simulink modelling. In the comparison of the performance of the relays, the focus was on the operating speed. The models were verified first with idealized unit test schemes and finally with a control system model from an actual STATCOM project.
In the tests performed, the simulation models succeeded in detecting the simulated problems and tripping the circuit accordingly to the specifications from manuals and standards. The harmonic blocking of differential protection, the reset process of the timers, as well as the sampling were identified as the main differences between the relay models. However, limited information is often available on these features. Therefore, the further development of them will require more detailed modelling of their structures and applications. Another challenge related to the stability simulations was found to be the large computational capacity required by the control system model.
Based on the successful results from this thesis, the simulation models will be developed further with the stability simulations in future commercial projects. In addition, new models will be developed to cover more typical functions found in STATCOM and SVC applications, as well as to include the setting calculations.
In this thesis, Simulink models for overcurrent and differential protection functions were implemented to reduce the need for testing. Two different commercial protection relay models were analysed for both functions with the results compared to each other and the standards defining the functions. For the overcurrent protection, a simplified simulation model was also created according to the standard. Particularly, operating characteristics of the functions as well as the differences between the relay models were examined by visualising them with the Simulink modelling. In the comparison of the performance of the relays, the focus was on the operating speed. The models were verified first with idealized unit test schemes and finally with a control system model from an actual STATCOM project.
In the tests performed, the simulation models succeeded in detecting the simulated problems and tripping the circuit accordingly to the specifications from manuals and standards. The harmonic blocking of differential protection, the reset process of the timers, as well as the sampling were identified as the main differences between the relay models. However, limited information is often available on these features. Therefore, the further development of them will require more detailed modelling of their structures and applications. Another challenge related to the stability simulations was found to be the large computational capacity required by the control system model.
Based on the successful results from this thesis, the simulation models will be developed further with the stability simulations in future commercial projects. In addition, new models will be developed to cover more typical functions found in STATCOM and SVC applications, as well as to include the setting calculations.