In short. Power-quality problems look similar on the surface: equipment trips, flickers, overheats. Each has different causes and tests. Match your symptom to the right measurement and study before buying a stabiliser, filter or UPS, so the fix fits the cause.
Symptom to study map
| Symptom | Possible cause | Measure or study |
|---|---|---|
| Equipment resets or trips at random | Voltage sags, swells, interruptions | Power-quality recorder; event analysis |
| Lights flicker | Fluctuating loads, weak supply | Flicker measurement; voltage-drop and motor-starting study |
| Hot neutrals or transformers, tripping capacitors | Harmonics | Harmonic measurement and study |
| Motors overheat, three-phase unbalance | Voltage unbalance | Unbalance measurement; load distribution study |
| Electronic equipment damaged | Transients, surges, earthing issues | Surge and earthing assessment |
| High bills, low power factor | Reactive power demand | Reactive power and power-factor study |
| Low voltage at remote loads | Voltage drop, weak source | Load flow and cable study |
| Generator voltage hunting or distortion | Non-linear loads, regulator interaction | Harmonic and generator-load study |
| Phase loss or reversal trips | Utility supply issues | Protection relay review; supply monitoring |
Step-by-step approach
- Describe the symptom, time of day, which equipment and how often.
- Install a power-quality analyser at the incoming supply and at the affected load.
- Capture for at least a week, including the problem periods.
- Compare events with load changes and utility events.
- Choose the study and the solution accordingly.
Typical solutions by cause
- Sags and interruptions: UPS, static voltage stabilisers, ride-through devices. See UPS and critical power.
- Slow voltage variation: servo stabilisers or transformer tap changes. See servo stabilisers.
- Harmonics: filters, reactors, different drives.
- Unbalance: redistribute loads, independent-phase regulation.
- Surges: surge protection devices coordinated with earthing.
- Low power factor: capacitor banks, detuned if needed.
Why measurement first
Buying a stabiliser for a sag problem does nothing if the real cause is harmonics, and a filter does nothing for interruptions. Measurement shows the actual phenomenon and its frequency. See voltage and power-quality monitoring.
Worked illustration
A plant reports that its CNC machines reset several times a week. A recorder shows voltage sags of 25 to 30 per cent lasting 100 to 300 ms, coinciding with a large compressor starting on the same feeder. The solution is soft starting the compressor, or a ride-through device on the machines, not a harmonic filter. The measurement turned a vague complaint into a specific cause and a cheaper fix.
Match the problem to the study
| Symptom | Likely cause | Study or check |
|---|---|---|
| Lights flicker when a motor starts | Voltage dip | Motor-starting study |
| Voltage rises on generator, AVR unstable | Leading power factor from capacitors | Reactive power review |
| Distorted waveform, hot neutral or alternator | Harmonics | Harmonic measurement and study |
| Capacitor bank failing | Resonance | Resonance scan |
| Motors overheating with normal loading | Voltage unbalance | Unbalance measurement |
| Equipment damage after storms | Surges | Surge protection and lightning risk |
| Sensitive loads resetting | Sags or transients | Power quality logging |
| Frequency hunting | Governor tuning or load character | Transient and governor review |
Steps
- Log voltage, current and frequency with a power quality analyser at the incomer and at a suspect load.
- Correlate events with operations.
- Pick the study from the table.
- Define the data to collect.
Do not guess
Money spent on filters or oversizing without measurement can miss the real cause. See surge protection and harmonics.
Common mistakes
- Choosing equipment before measuring.
- Measuring for too short a time.
- Ignoring the generator as a cause when on standby.
What to send us
Send your symptoms, equipment affected and any recordings. Send your application details. See also power-quality problem to technology guide.
Questions engineers ask
How long should I record power quality?
At least a week to capture normal cycles and events; longer for intermittent problems.
Is a stabiliser the answer to voltage problems?
For slow voltage variation, yes. It does not fix interruptions or harmonics.
What if the problem only occurs on the generator?
Check generator regulation, harmonics from non-linear loads and step loading.
Do I need a standard to compare against?
Yes, for example EN 50160 for supply voltage characteristics and IEEE 519 for harmonics.
This guide gives general principles. Diagnosis needs measurements at your site.