Answer first
Short Answer
A power quality assessment records voltage, event timing, and equipment behavior so a plant can distinguish voltage sags, interruptions, harmonics, transients, and process-side causes.
A 30-day monitoring period is a practical project starting point, not a guarantee that every event will be captured.
The deliverable should connect measured events to the first trip in the process and compare protection architectures before procurement.
Suggested start30-day monitoring, extended when event frequency requires it.
Measured dataRMS voltage, depth, duration, phase, count, harmonics, transients, timestamps.
Business outcomeDefine the lowest practical protection boundary before buying equipment.
When This Applies
- The plant sees unexplained VFD or control trips.
- Events are recurring but utility and process records do not align.
- The protected load and required ride-through boundary are unclear.
- A capital project needs auditable baseline data and acceptance criteria.
What the Assessment Records
| Data | Purpose | Typical location |
|---|---|---|
| RMS voltage and residual voltage | Classify sag depth and affected phases | PCC and sensitive feeder |
| Duration and event count | Build the voltage-duration exposure profile | Time-synchronized meters |
| Harmonics and transients | Avoid misclassifying a different power-quality issue | Source and load side as needed |
| VFD trip timestamps and codes | Connect electrical events to equipment behavior | Drive and control logs |
| Process sequence | Identify the first failure that propagates to the line | PLC, historian, and operator records |
Four Questions the Report Must Answer
- What happened at the electrical supply?
- Which equipment trips first?
- How often and under what operating conditions does it occur?
- What is the lowest-cost protection architecture that preserves the required process boundary?
Calculation Example
If a plant records six qualifying trips per year and each event causes an estimated USD 40,000 production loss plus USD 8,000 restart cost, the planning loss exposure is 6 × (40,000 + 8,000) = USD 288,000 per year.
Limitations / When Not to Use
- A fixed 30-day window may miss rare events; monitoring duration should reflect known frequency.
- A single meter at the PCC may not identify the first internal trip.
- Metering data without synchronized VFD, PLC, and process records can leave causality unresolved.
- A report should not recommend equipment using unverified vendor claims or missing load data.
Recommended Assessment Workflow
1. Collect one-line diagram and trip history2. Place synchronized meters at source and sensitive load3. Correlate waveforms with VFD / PLC / process timestamps4. Define voltage-duration and load-power envelope5. Compare protection boundaries and alternatives6. Write acceptance test plan before procurementTraceable sources
Sources / References
- IEC 61000-4-30: Power quality measurement methods. Measurement and interpretation methods for voltage dips, interruptions, harmonics, transients, and other power-quality parameters. Accessed 2026-08-24.
- IEEE 1159-2019: Monitoring Electric Power Quality. Recommended practice for describing, measuring, and interpreting power-quality phenomena. Accessed 2026-08-24.