Power Quality April 2026 · 5 min read
Good power quality is the foundation of a reliable electrical installation. When the supply is clean and stable, equipment runs as designed, energy is used efficiently, and maintenance costs stay low. When it isn’t, the consequences show up in ways that are expensive and often difficult to trace back to the real cause.
Most facility managers do not think about power quality until something goes wrong. A motor that keeps failing, a computer system that keeps crashing, or an energy bill that seems too high relative to production output are all classic signs of underlying power quality problems. Understanding what good power quality means, and what happens when it is poor, is the first step to protecting your investment in electrical equipment.
Power quality describes how closely the electrical supply at any given point matches the theoretical ideal: voltage at the correct level, at 50 Hz, with a clean sinusoidal waveform, balanced between phases, and free from interruptions and transients.
In practice, every supply deviates from the ideal to some degree. The question is whether those deviations fall within the limits that connected equipment can tolerate. When they do not, the equipment is affected. The main power quality parameters that matter for NZ industrial and commercial facilities are:
| Parameter | Description | Typical Cause |
|---|---|---|
| Voltage magnitude | Over or undervoltage | Network loading, cable voltage drop, transformer taps |
| Voltage sags | Short-duration voltage drops | Motor starts, network faults, large load switching |
| Harmonics | Waveform distortion | VSDs, LED lighting, UPS systems, switching power supplies |
| Power factor | Ratio of real to apparent power | Inductive loads, motors, fluorescent lighting |
| Voltage unbalance | Voltage difference between three phases | Uneven single-phase loading, blown fuses |
| Transients | Short-duration voltage spikes | Lightning, capacitor switching, motor interruption |
Harmonics cause transformers and motors to run hotter than their nameplate rating allows. Voltage sags cause sensitive electronics to reset or trip. Transients damage insulation. None of these effects are immediately obvious, but they accumulate over time and show up as equipment failing years earlier than it should. The cost of replacing a motor or transformer that should have lasted another decade is rarely attributed to power quality, but often that is exactly what caused it.
A voltage sag lasting 80 milliseconds is enough to trip a variable speed drive or reset a programmable logic controller. On a production line where a VSD trip requires a 30-minute restart procedure, one sag event costs significantly more than the electricity consumed in an entire shift. Sites with frequent unexplained production stoppages often find a power quality monitor reveals the root cause within its first week of operation.
A low power factor means your facility is drawing more current from the network than the useful work requires. Some NZ network operators charge reactive power penalties if your power factor falls below 0.95. Harmonic currents also add to cable and transformer losses without contributing to useful work, increasing both energy consumption and heat generation.
Equipment stressed by poor power quality requires more frequent maintenance and earlier replacement. VSD cooling fans, motor windings, and transformer insulation all degrade faster under abnormal supply conditions. The maintenance cost consequence of ignoring power quality is real but diffuse, which is why it often goes unaddressed.
NZ industrial sites face some specific power quality challenges. The widespread adoption of variable speed drives in dairy, food processing, and manufacturing has significantly increased harmonic distortion on many networks and within site installations. Rural sites often experience greater voltage fluctuation than urban sites. Coastal environments add corrosion risk to monitoring equipment if not correctly specified.
The NZ Electricity Authority publishes Electricity Authority Technical Code A (previously ECP 34), which sets power quality obligations on network operators, including voltage quality limits. Network operators also have obligations under their distribution codes regarding the quality of supply they must deliver. If your site is experiencing supply quality below these limits, there may be a basis to require the network operator to investigate and remediate.
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