In short. Power-quality problems look alike on the surface: equipment trips, lights flicker, cables run hot. Each has its own causes and needs its own measurement or study. Match the symptom, and whether it happens on mains, on the generator or on both, to the right study before buying a stabiliser, filter or UPS. That way the fix suits the actual cause.
Who this page is for: For facility managers and plant engineers facing trips, dips, overheating or failures and wanting to know what to investigate.
Key facts
- Start with the symptom and when it happens.
- Problems only on generator often point to the set itself, or to how the loads interact with it.
- Problems on both supplies usually point to the site’s own loads; problems only on mains point to the incoming supply.
- Measure before buying equipment.
- Record events with time stamps to link cause and effect.
- One problem may need two studies.
Symptom to study
| Symptom | Likely cause | Study or measurement |
|---|---|---|
| Breakers or drives trip | Settings, dips, earth faults | Protection coordination and event recording |
| Lights dip when motors start | Starting current | Motor-starting study |
| Hot neutrals, cables or transformers | Harmonics or overload | Harmonic measurement and load study |
| Flicker on generator | Governor, voltage regulator or load swings | Generator test and transient check |
| Low power factor charges | Reactive load | Power factor study |
| Electronics or capacitors fail early | Harmonics, resonance or surges | Harmonic and surge study |
Worked example: three complaints traced (illustrative)
| Complaint | When | Finding | Fix |
|---|---|---|---|
| Office lights flicker | Generator only | Voltage regulator hunting with a large UPS load | Regulator retuned; alternator checked for harmonic load |
| Drives trip in the plant | Both supplies | Deep dips when a 75 kW compressor starts | Soft starter on the compressor |
| Capacitor bank failing | Both supplies | Resonance with drive harmonics | Detuned bank |
A stabiliser bought for the office flicker would not have fixed a regulator problem on the generator. See harmonic screening and motor starting.
Do not buy correction equipment before measuring. The wrong device can hide the symptom for a while, or make the real cause worse.
Symptom record
| Symptom | Date and time | Mains or generator | Loads running |
|---|---|---|---|
Common mistakes
- Buying a fix before measuring.
- Not noting whether it happens on generator.
- No time stamps on events.
- Treating several symptoms as one.
What to send us
Send a description of the symptom, when it happens and any readings. WhatsApp 98852 01608 or use the application engineering enquiry.
Evidence note. The examples are illustrative.
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.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and Service Engineer, Reddy Generators. Last updated 8 November 2026.