Notching
BSRIA Power quality guide (AG 2/2000) was written by C C Pearson and V Uthayanan and published by BSRIA in July 2000. It states:
Waveform distortion is defined as a steady state deviation from an ideal sine wave of power frequency, principally characterised by the spectral content of the deviation.
There are five primary types of waveform distortion:
- dc offset
- harmonics
- interharmonics
- notching
- noise
Notching is a periodic voltage disturbance caused by the normal operation of power electronics devices when current is commutated from one phase to another.
Since notching occurs continuously, it can be characterised through the harmonic spectrum of the affected voltage. However, it is generally treated as a special case. The frequency components associated with notching can be quite high and may not be readily characterised with measurement equipment normally used for harmonic analysis.
Figure 1 shows an example of voltage notching from a three-phase converter that produces continuous dc current. The notches occur when the current commutates from one phase to another. During this period, there is a momentary short circuit between two phases, pulling the voltage as close to zero as permitted by system impedances.
See also: Notch.
--BSRIA
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