Sneaky Voltage Swell Events

Long time, no post! A pandemic will do that to you . . . suffice it to say I am healthy, relatively happy, and staying busy with both my engineering work (mostly stable through the troubles) and my yoga studio work (very different these days but busier than ever with online classes and the need to provide appropriate technology).

Today’s engineering bon-bon involves a trio of voltage swell events. Seemingly caused by a short circuit (another facility load fault, perhaps utility lighting arrestors) that causes a 1/4 cycle drop-out on one phase and resultant voltage swell following. The swell has a serious overvoltage, likely to cause problems for many types of equipment / power supplies.

This event was captured as a minor RMS voltage swell (5.1% above nominal) – but the peak voltage is very high (540 V vs 395 V normal). Note the ~30 Amp peak current swell.
This event was barely detectable as an RMS voltage swell (4.8% above nominal) – once I recognized the nature of these events, I went looking for more and came up with just this one. Almost no resultant current swell.
This is the big smoking gun event. Even though it did not register as a sag / swell event at all (the voltage drop-out being balanced by the following swell, just 3.25% over nominal) it was captured as a current swell (the highest current event over 6 weeks of data capture) – 650 Amps waveform peak. Something within the client load saw this event as a problem and drew a slug of current.

I’m just the hired gun reviewing the data, pulling out events and issues, writing a report. So I won’t be following this to a resolution or further troubleshooting on site. But this is a good example why automated report writing is not always sufficient – the Fluke 1750 analysis tools would see these events as minor voltage swells (if that). It takes a human being with some experience (I’ve reviewed over 5000 power quality data sets since 2003) to see something unusual, scratch one’s head, and dig in a bit deeper.