Trending vs Waveform

Ever since introduced to the area of power quality and its definitions by my first manager, Azmi Rahmat, it has become a pet-peeve for me everytime someone used the words “trending” and “waveform” interchangeably.

To put the record straight, it is not the SAME.

And it has become my personal way in differentiating a PQ engineer from a non-PQ engineer 🙂

waveform vs trending
Waveform (top) vs Trending (bottom)

In relating to this, I had a previous experience whereby the Customer demanded to know why their voltage dip duration is far off from utility’s official voltage dip results at 22kV. Their monitoring was at low voltage side (230V Phase voltage / 400V Line voltage).

While it is known fact that nearer to the loads, the dip recovery may be slightly slower. However this was incredibly long (I was firstly given the trending only).

long recovery trend
Long recovery trend

Only after I compared with their recorded waveforms, then I realised (and chuckled too); their monitoring system had a wrong time scale!

long recovery wave
20 cycles = 2000ms ???
Singapore: 50Hz System. 1 cycle = 20ms