Overview


A low frequency event occurs when the measured system frequency falls below a predefined lower threshold set by the user.

The low frequency threshold is defined as a deviation from the nominal frequency (50 Hz or 60 Hz), configured by the user.


Low Frequency Detection Method

The detection algorithm operates as follows:

 A low frequency variation event begins when the measured frequency (10/12 cycle) on phase 1 falls below the lower bound threshold and ends when the measured frequency (10/12 cycle) on phase 1 falls above the threshold plus hysteresis.

Low Frequency Measurement Specifications

  1. Measurement Method:
    Digital filtering to extract the fundamental signal, next determine zero crossing, calculating the period of each cycle, accordingly get the frequency of each cycle, and finally estimate the frequency of 10/12 cycle by averaging the frequency each cycle within 10/12 cycle.
  2. Recorded Event Information
    • Frequency Level: measured frequency at event start and end.
    • Start Time: event start timestamp.
    • Event Duration: time interval between Event IN and Event OUT.
    • Worst Case: Minimum value of frequency 10/12 cycle crossed the threshold.
    • Min Value: lowest frequency recorded during the event.
    • Max Value: highest frequency recorded during the event.
  1. Event Threshold: Defined as a deviation from the nominal frequency (range: 0.1 Hz to 9.9 Hz, step 0.1 Hz).
  2. Event Start: Beginning of a measurement window where the frequency falls below the threshold.
  3. Event End: Beginning of a measurement window where the frequency rises above the threshold plus hysteresis (0.1 Hz).
  4. Polyphase system treatment: Not applicable.
  5. Stored Waveforms: Event waveforms are recorded for each detected event.


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