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Power System Frequency Estimation for Protection Application in Accordance with IEC 60255-181

Abasnejad, Mohamad Ali | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56690 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Hajipour, Ehsan
  7. Abstract:
  8. The frequency of the system is one of the important network parameters that must be continuously monitored. In new power networks, due to the fact that inverter loads and renewable power plants have increased, frequency estimation has faced many problems. Due to the fact that these renewable power plants have little inertia, the networks that include these power plants are faced with rapid frequency changes in the presence of network incidents and transients such as load shedding and power plant blackout or fault, and therefore they should Be equipped with accurate frequency relays or relays to detect the rate of frequency changes. Also, the increase in the amount of harmonic pollution of the network due to inverter loads or converters used in high voltage direct current (HVDC) systems makes it difficult to accurately estimate the frequency and rate of change. Due to the inherent changes in the power grid in recent decades, the requirements of the protection algorithm implemented in frequency relays have also undergone changes. For this purpose, the IEC 60255-181 standard presented in 2019 has proposed very strict tests - such as harmonic test and frequency gradient changes in some tests, etc. - to confirm the performance of the frequency estimation algorithm in a frequency relay. Also, the relevant standard includes tests related to the frequency change rate function (ROCOF). This thesis seeks to implement a frequency protection function in a practical way. In this thesis, we are not looking for the simulation of inverter sources or transient states, and we will only test the signals mentioned in the standard on the frequency relay. The frequency protection function includes various parts such as pre-processing filter, input signal generation, frequency estimation algorithm, post-processing filter and protection function logic. In this thesis, the study of various solutions for the design of each of these subsections of the protective function has been studied. In the frequency estimation algorithm design section, two methods of crossing zero and angle difference have been selected for implementation on the frequency relay. Finally, the protection function of the proposed frequency estimation has been implemented on a real digital relay and it has been shown that it is able to satisfy all tests of the IEC 60255-181 standard and its performance is compatible with the industrial relays available in the market
  9. Keywords:
  10. IEC 60255-187-1 Standard ; Zero Crossing Detection ; Frequency Prediction ; Frequency Protection ; Angle Difference ; Rate of Change of Frequency (ROCOF)

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