When a voltage dip lasting a few milliseconds stops a factory production line, or the lights in a residential area start to flicker, the phones at the distribution company start ringing. The customer assumes the grid is to blame. The network operator often suspects the disturbance started inside the customer's own installation. Underneath, most power quality disputes come down to one question: where did the disturbance come from?
Three Disturbances, Three Different Characters
The three most common power quality problems behave very differently in physical terms:
- Voltage sag (dip): A short-lived drop in voltage well below nominal. EN 50160 defines a dip as an event where the residual voltage falls to between 90% and 5% of the declared voltage, lasting from 10 milliseconds to one minute.
- Harmonics: Components at whole multiples of the fundamental frequency. They appear when non-linear loads draw non-sinusoidal current from the grid.
- Flicker: Repetitive voltage fluctuations that cause visible light flicker. Flicker severity is expressed as short-term (Pst) and long-term (Plt) values.
Each one has different sources, spreads through the network differently and has different effects, so root cause analysis relies on different clues for each.
What's Behind a Voltage Sag?
Most voltage sags are caused by short-circuit faults on the network. A fault on one feeder pulls the voltage down on every other feeder fed from the same busbar until protection clears it. So a customer who has nothing to do with the fault still feels the sag.
Customer-side events can also cause local sags, for example large motors starting, transformers being energized or sudden load steps. A useful clue for telling the two apart is how the current at the measurement point behaves during the sag. If the cause is downstream of the measurement point, on the customer side, current usually rises sharply. If the cause is upstream, on the grid side, current stays flat or falls.
Harmonics: The Fingerprint of Non-Linear Loads
Now that power electronics are everywhere, harmonics are no longer just a heavy-industry problem. Variable speed drives, rectifiers, arc furnaces, LED lighting, IT equipment and inverters all inject harmonic currents. Those currents flow through the network impedance, distort the voltage and affect every other customer supplied from the same point.
Two standards often come up together here. EN 50160 deals with distortion on the voltage side, while IEEE 519 recommends limits both for voltage distortion and for the current distortion a customer injects into the grid (TDD). The difference matters. Voltage distortion is a shared result, but current distortion usually reflects how a particular customer's installation behaves.
Flicker: The Quality Problem You Can See
Of all power quality problems, flicker is the one customers notice most directly. Typical sources include arc furnaces, welding equipment, large compressors and loads that switch on and off frequently. Variable generation such as wind turbines can also contribute under certain conditions.
Flicker severity changes over time, so a one-off measurement can be misleading. The quickest way to the source is usually to correlate Pst values with the time of day, with a particular customer's operating schedule or with load changes on a specific feeder.
Why Root Cause Analysis Is Hard
Identifying the source sounds simple in theory but gets harder in practice:
- A measurement at a single point shows only one side of the disturbance. You need several points compared on the same timeline.
- Analyzers from different vendors produce data in different formats, and without time synchronization you can't correlate them reliably.
- Disturbances are brief. An event that wasn't captured at millisecond resolution can't be investigated afterwards.
- Source identification is a judgement about likelihood, not a verdict, so it needs long-term data behind it.
Settling the Liability Boundary with Data
Power quality disputes often turn into commercial or legal questions as much as technical ones. When there's lost production, damaged equipment or a contract disagreement, data is the strongest argument either side has. A consistent record showing when an event happened, how severe it was and which direction it came from moves the conversation from assumption to evidence.
Root Cause Analysis with GeoEner PQM
GeoEner PQM captures voltage sags, swells, interruptions and transients at millisecond resolution and raises alarms instantly. It tracks individual harmonics, THD, Pst/Plt flicker, negative sequence and TDD, and can optionally audit voltage and current against IEEE 519.
Its root cause analysis helps determine whether a disturbance originated upstream on the grid side or downstream on the consumer side. Data from analyzers of any brand is collected via Modbus, OPC UA and REST, standardized in one time-series archive and kept for 10 years, so past events can be compared on the same basis.
PQM is built for distribution companies, industrial facilities, organized industrial zones and large consumers, and it helps clarify liability boundaries on the shared grid with data.
Conclusion: From Guesswork to Evidence
You can't eliminate harmonics, flicker and voltage sags completely. But once you know where they come from, you can deal with them on the right side and with the right measures. That depends on continuous, synchronized measurement data processed with a standard methodology.
To trace the sources of power quality events on your network with data, contact us and request a GeoEner PQM demo.
