When Power Conditioners Go Bad

We recently came across what appeared to be the worst power quality (as measured by voltage waveform, distortion, and regulation) we’ve ever seen (Fluke 1750 power analyzer). Power quality this poor is rather inexplicable – hard to imagine anything working well with this sort of power.

However, we’ve been analyzing power quality data for this particular client since 2003 (over 4000 individual reports) so we researched our surprisingly complete and useful database, and realized that we had reviewed this same site and same piece of equipment several years back (2009 and 2010), using an RPM 1650 power analyzer. At that time, the power quality was not only much better, it was nearly perfect. The equipment, in fact, appeared to be supplied via a UPS or power conditioner (make and model not indicated).

Since the power conditioner or UPS was dedicated to the medical imaging system, no other loads within the facility were affected. Clearly, the device feeding the equipment has failed or aged out of useful service – and needs to be bypassed (to start) and then repaired or replaced. We think you’ll agree….

Snapshot New

Voltage waveform (Phase B) in 2015 shows high levels of voltage distortion. Voltages were also highly imbalanced across three phases.

Snapshot Old

Voltage waveform (Phase B) in 2010 shows nearly perfect voltage with very low levels of distortion.

Harmonics New

Voltage harmonics (2015) show 3rd, 7th, 9th, and 13th far higher than 5% of fundamental, with total harmonics exceeding 25% THD.

Harmonics Old

Voltage harmonics (2010) were very low – with a small peak near the 33rd harmonic, typical of UPS or power conditioner switching frequency.


Voltage and Current RMS logs (2015) show high voltage, many voltage swells, and poor regulation. Voltage imbalance (across all phases) was also very high.


Voltage and current RMS logs (2010) show very tight regulation, with small fluctuations related to load changes, typical of a static power converter.