Power Quality
April 2026 · 8 min read
Poor power quality is one of the most common causes of unexplained equipment failure on NZ industrial sites. This guide covers what power quality monitoring involves, the issues we see most often at Clive Wilson, and how to set up effective monitoring for your facility.
Power quality problems are often invisible until something expensive fails. An unexplained drive trip, a burned motor winding, or persistent metering errors are all frequently traced back to supply conditions that a basic power quality monitor would have flagged months earlier. Based in Invercargill, Clive Wilson Switchboards incorporates power quality metering into switchboard builds across New Zealand and has seen firsthand what poor power quality does to industrial plant.
Power quality refers to how closely the electrical supply at a given point matches the ideal: voltage at the right level, at the correct frequency, with a clean sine wave and balanced phases. When the supply drifts outside acceptable limits, connected equipment may fail early, operate inefficiently, or behave unpredictably in ways that are hard to trace back to the root cause.
The main parameters monitored on NZ industrial sites include:
New Zealand industrial facilities have specific challenges. Many run a mix of older plant and modern variable speed drives (VSDs), which together create harmonic distortion the older equipment was never designed for. Rural and coastal sites often experience voltage fluctuations that are not an issue in well-supplied urban networks. As energy costs rise, losses from poor power factor and harmonic heating have a direct dollar impact.
VSDs, UPS systems, switching power supplies, and LED lighting all generate harmonic currents that distort the supply waveform. Harmonics cause transformers and cables to run hotter than they should, interfere with protection relays and metering, and can cause nuisance tripping of sensitive equipment. As sites add more inverter-driven equipment, harmonics become an increasing concern in both new and retrofit installations.
Voltage sags are short drops in supply voltage caused by faults on the network or large motor starts on site. They last milliseconds to a few cycles but that is long enough to reset sensitive control equipment or trip drives. Sites with frequent unexplained trips often find voltage sags are the root cause once monitoring is installed.
A low power factor means your facility is drawing more current than the actual work requires. Network operators in New Zealand can charge reactive power penalties if your power factor falls below their threshold. Power factor correction equipment must be sized using real monitoring data to work correctly and avoid creating resonance issues with harmonic sources on site.
Three-phase motors are sensitive to unbalance between phases. A 2% voltage unbalance causes roughly 8% additional heating in motor windings, significantly shortening motor life. On sites with single-phase loads spread unevenly across phases, unbalance can be substantial and is often overlooked.
| Parameter | Common Cause | Equipment at Risk |
|---|---|---|
| Harmonics | VSDs, LED lighting, UPS | Transformers, motors, meters |
| Voltage sags | Motor starts, network faults | PLCs, drives, computers |
| Low power factor | Inductive loads, motors | Network charges increase |
| Voltage unbalance | Uneven single-phase loads | Three-phase motors |
| Transients | Switching, lightning | Control electronics, insulation |
The right approach depends on what you need to know. A portable power quality analyser run over two to four weeks gives a useful snapshot and is a practical starting point for most audits. Permanently installed metering at key points in your switchboard provides ongoing visibility and the ability to correlate events with equipment problems in real time.
Typical monitoring points include:
Data is logged and reviewed to identify trends, set alarm thresholds, and build a baseline for future comparison. At Clive Wilson Switchboards, we incorporate power quality metering into switchboard builds including selection, configuration, and integration with BMS or SCADA systems where required.
Class A analysers (to IEC 61000-4-30) provide the highest accuracy and are required for contractual or compliance measurements, for example when a network operator is involved in a dispute. Class S instruments are suitable for most site surveys and ongoing monitoring applications.
Key features to look for:
If your site is experiencing unexplained equipment failures, high energy bills without obvious cause, nuisance protection tripping, or you are adding significant new loads such as large VSDs or a UPS system, a power quality assessment is worthwhile. A specialist can identify root causes from the data and recommend targeted solutions rather than trial and error.
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