Overview


Total Harmonic Distortion (THD) is a key parameter in power quality monitoring. It represents the level of harmonic distortion in the electrical signal, which may affect equipment performance and system reliability.

THD events can be analyzed to identify distortion sources and take corrective actions.

Harmonic distortion can result from non-linear loads such as power electronics devices (e.g., inverters and converters), arc furnaces, welding machines, and fluorescent lighting. Additional causes include poor power factor correction, unbalanced loads, and improper grounding.

The Inspector device measures harmonic content and calculates THD values, providing both real-time monitoring and historical data.

A THD event is triggered when the measured THD value exceeds a user-defined threshold.

THD Detection Method

The detection algorithm is developed and implemented as follow:

  • In single-phase systems, a THD event begins when the THD value exceeds the THD threshold and ends when the THD value is equal to or below the THD threshold minus the hysteresis.
  • In polyphase systems, a THD event begins when the THD value of each channel separately fall above the THD threshold and ends when THD value of each channel separately is equal to or lower than the THD threshold minus the hysteresis.


Voltage THD & Current THD Measurements Specifications

  1. Measurement Method :THD is calculated in accordance with IEC 61000-4-7.
  2. Analysis window width : 10/12 cycles
  3. Window point count: Rectangular  (2048 points)
  4. Recorded Event Information:
    • THD Level: measured value at event start and end
    • Phase: corresponding phase at event start and event end
    • Start Time: event start timestamp
    • Frequency: system frequency at event start
    • Event Duration: time interval between Event IN and Event OUT
    • Worst Case: maximum THD value recorded during the event
    • Minimum Value: lowest THD value recorded during the event
    • Maximum Value: highest THD value recorded during the event
  1. Event Threshold: Voltage: 0.0% to 100.0%
  2. Event Start :Beginning of a measurement window where the THD value exceeds the threshold.
  3. Event End :Beginning of a measurement window where the THD value falls below the threshold minus hysteresis.
  4. Polyphase system treatment : A THD event starts when any phase exceeds the threshold and ends when all phases return below it.
  5. Stored Waveforms: Event waveforms are recorded for each detected event.


Created with the Personal Edition of HelpNDoc: Make Help Documentation a Breeze with a Help Authoring Tool