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Frequency anti-islanding protections use frequency measures to determine an islanding condition, which are usually filtered to eliminate high frequency components. Digital relays can use different frequency estimation methods, which could lead to different results between different methods and filter lengths. This paper compares three frequency estimation methods found in digital relays against noise, harmonics, DC decays, steps and slopes of frequency, showing their intrinsic differences. Islanding events are simulated to show the importance of investigating frequency measurement methods and filter lengths before performing any protection study.

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