Overview


Transient events are short-duration voltage disturbances that occur in electrical power systems. They are characterized by sudden and brief changes in voltage, which may cause equipment malfunction or damage.

Transients can result from various sources, including lightning strikes, switching operations, capacitor bank switching, and equipment failures.


Transient events are generally classified into two types:

• Impulsive transients: High-amplitude, short-duration voltage spikes, typically caused by lightning or switching events.

• Oscillatory transients: Ringing waveforms that oscillate around the nominal voltage, usually caused by switching operations or system interactions.

The Inspector detects only impulsive transients. 


Transient Detection Method


The detection algorithm operates as follows:


  • The input signal is processed using a digital high-pass filter to remove the fundamental frequency component.
  • The filter is designed with the following characteristics:
    •  Cut-off frequency: 2.5 kHz  
    •  Gaussian window (standard deviation: 10)  
    •  Number of coefficients: 100  
    •  Group delay: 5 samples  
  • Each phase voltage signal is buffered over a 200 ms window.
  • The filtered signal is continuously monitored and compared against the configured transient threshold.
  • When the filtered signal exceeds the threshold, a transient event is detected.
  • Multiple threshold crossings within the same event window are counted as transient occurrences.
  • The event ends when all phase signals remain below the threshold.


Transient voltage Measurement Specifications

  1. Measurement Method: Transient events are detected from sampled voltage waveforms after removing the fundamental frequency component (50/60 Hz).


  1. Recorded Event Information:
    • Voltage Level: Instantaneous voltage value at event start (% or V).  
    • Phase: Phase at which the event is detected.  
    • Start Time: Timestamp of the event start.  
    • Frequency: System frequency at the event start.  
    • Triggering Transient Width: Duration of the transient that triggered the event (minimum detectable width).
    • Event Duration: Total time interval between event start and event end.  
    • Worst Case: Maximum peak voltage recorded during the event (with corresponding phase).  
    • Transients Count: Total number of transient occurrences detected within the event duration.
    • Transient Width: Duration during which the threshold is exceeded  
    • Transient Count: Number of transient occurrences within the event window  
        (Simultaneous transients across phases are counted as one event)
  1. Measurement Band: 2.5 kHz to 4 kHz  
  2. Minimum Detection Width: 31.25 µs  
  3. Event Start: The event starts when a peak value exceeds the threshold within the 200 ms aggregation window.
  4. Event End: The event ends when no transient activity is detected within the aggregation window across all phases.
  5. Polyphase System Treatment: A transient event starts when any phase exceeds the threshold and ends when no phase shows transient activity.
  6. Stored Waveforms : 
    • Event IN: A waveform is saved starting 1 ms before and 2 ms after the detected peak.  
    • Event OUT: A waveform is saved starting 1 ms before and 2 ms after the last detected peak within the event.  
  1. Event Threshold: Defined as an absolute value relative to the peak voltage after removing the fundamental component.


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