Electrical Services
Power Quality & Harmonic Studies
Measuring what is actually on your power system — harmonics, distortion and power factor — and fixing what the measurement finds.
Power quality problems are expensive and invisible. Equipment fails early, transformers run hot, breakers trip for no traceable reason, and nobody connects any of it to the waveform. Harmonic distortion is the usual culprit, and it has grown steadily worse in commercial buildings for the same reason efficiency has improved: almost every modern load is a non-linear electronic one.
Where the harmonics come from
A linear load draws current smoothly in proportion to voltage. A non-linear load draws it in pulses, and those pulses inject harmonic currents back into your distribution system at multiples of the fundamental frequency.
Almost everything worth installing in the last two decades is non-linear:
- LED drivers — the retrofit that saved your energy bill also added harmonic current
- Variable frequency drives on motors, pumps and fans
- UPS systems and server-room switch-mode power supplies
- EV charging equipment
- Electronic ballasts, dimmers and lighting control gear
- Welding equipment, induction heating and arc furnaces
- Solar inverters and battery storage systems
What it actually costs you
Harmonic currents do no useful work but they still heat conductors. The visible consequences arrive as apparently unrelated maintenance problems, which is why the underlying cause so often goes undiagnosed for years.
- Transformers running hot and derating, or failing early
- Neutral conductors overloaded — triplen harmonics add rather than cancel on the neutral
- Nuisance breaker tripping with no traceable overload
- Capacitor bank failure and resonance conditions
- Motor overheating, vibration and shortened bearing life
- Poor power factor and utility penalty charges
- Sensitive electronics misbehaving in ways nobody can reproduce
What IEEE 519 requires
IEEE 519 is the standard governing harmonic limits, and it applies at the point of common coupling — the interface between your facility and the utility, not at each individual load inside the building. That distinction matters, because a single noisy load can be well within tolerance at the PCC while a building full of moderately noisy loads is not.
The standard sets two things: a limit on voltage distortion, and a limit on the current distortion your facility injects back into the utility system. The current limit is expressed as Total Demand Distortion and is not a fixed number — it scales with the ratio of available short-circuit current to your maximum demand current. A stiff service can absorb more harmonic current than a weak one, so the same load profile can be compliant in one building and non-compliant in another.
For voltage, systems at 69 kV and below are generally held to 8% total harmonic distortion with individual harmonics limited to 5%. Typical allowable current TDD lands between 5% and 20% depending on system strength.
How we run a study
A power quality study is a measurement exercise, not an inspection. We log at the point of common coupling and at suspect distribution points, over a period long enough to capture your real operating cycle rather than a convenient afternoon.
- Power quality logging at the PCC and selected panels, typically 7 to 30 days
- Voltage THD and current TDD measured against IEEE 519 limits
- Individual harmonic spectrum analysis, with attention to the 3rd, 5th, 7th and 11th
- Neutral current measurement — frequently the finding that surprises people
- True power factor, displacement power factor and demand profile
- Transformer loading and derating assessment
- Voltage sag, swell and transient capture
- Written report with findings, compliance status and prioritised mitigation
Fixing what the study finds
Mitigation is chosen against the specific spectrum measured, not bought off a shelf. Line reactors and DC chokes on drives are the cheapest intervention and often sufficient. Passive harmonic filters tuned to a dominant order handle a concentrated problem. Active harmonic filters correct dynamically across a range and suit variable load profiles. Multi-pulse or low-harmonic drives address the issue at the source when equipment is being replaced anyway.
On the distribution side, K-rated or harmonic-mitigating transformers, oversized neutrals and load rebalancing across phases are frequently part of the answer. We size and specify against your measured data, then re-measure after installation to verify the correction actually worked — which is the step most often skipped.
Common questions
How do I know if we have a harmonics problem?
The usual signals are transformers running hotter than their loading explains, neutral conductors carrying more current than any phase, repeated unexplained breaker trips, capacitor failures, or sensitive equipment behaving unpredictably. Any one of those justifies measurement. The only way to know is to log it — harmonics are invisible to a standard clamp meter reading true RMS current alone.
Does our utility require IEEE 519 compliance?
Many utilities reference IEEE 519 in their interconnection or service agreements, particularly for larger commercial and industrial accounts, and can require correction or apply penalties. Requirements vary, so we confirm what your specific service agreement says as part of the study.
Did our LED retrofit cause this?
It may well have contributed. LED drivers are non-linear loads, and converting an entire building at once can raise harmonic current noticeably. This is not an argument against LED — the energy savings are real — but it is a reason to measure afterwards on large retrofits, especially in facilities that already carry significant drive or UPS load.
How long does a study take?
Logging typically runs 7 to 30 days to capture a representative operating cycle, including weekly variation. A one-hour snapshot is close to worthless because harmonic profiles change with what is running. Reporting follows within about a week of the logger coming out.
Ready to talk about your project?
Tell us what you need and we will give you a straight answer on scope, schedule and cost. No obligation, and no pressure if it turns out we are not the right fit.