“Does frequency changes during a voltage dip?” – A favourite question among many. The answer is “Yes”.
This will be quickly followed by “But why our power quality monitor did not show significant changes in the frequency values even though a voltage dip event was captured?” The general answer is that the standard (IEC 61000-4-30) does not require it to measure such detailed changes in frequency values.
With the voltage waveforms captured, it is technically possible to calculate the frequency values during a particular event (say a voltage dip). Here’s an example, where the event waveforms were post-processed (via the Dranetz Dranview 7 software).
Such post-processing feature is very useful especially in generator load-test applications, where one will be interested to know both the voltage and frequency changes during every step-load change. An example is shown below. One just need to ensure that the pre/during/post event waveforms were set to be captured properly (i.e enough cycles). The software will do the rest.