Answer first
Short Answer
In a chemical or petrochemical process, a brief voltage sag can trip a drive, pump, compressor, fan, cooling system, lubrication system, or control layer and trigger a wider process shutdown.
The engineering goal is to maintain the safe critical process boundary, not to keep every site load energized.
Protection selection must follow the process hazard review, electrical data, equipment limits, and site change-control procedures.
When This Applies
- A brief sag initiates a process trip or emergency shutdown sequence.
- Rotating equipment auxiliaries must remain available to protect machinery or process conditions.
- A small set of drives controls a much larger continuous process.
- The restart duration and off-spec production loss materially exceed the electrical event duration.
Map Electrical Trips to Process Consequences
| Load group | Possible consequence | Protection question |
|---|---|---|
| Process pumps | Flow interruption, pressure deviation, or loss of feed | Must the motor ride through, coast, or restart in sequence? |
| Compressors | Unit trip, recycle action, or long restart | Which main and auxiliary systems must remain coordinated? |
| Cooling fans / pumps | Temperature or condensing-pressure excursion | What thermal time constant defines the required interval? |
| Lubrication systems | Machinery protection action | Are pumps, controls, and backup sources all inside the protected boundary? |
| DCS / PLC / instruments | Loss of control or interlock state | Can control power be hardened separately from motor loads? |
Calculation Example
For an illustrative 800 kW protected boundary requiring 1 second of ride-through, the ideal energy demand is 800 kJ, or about 0.222 kWh. The actual system must be sized using load dynamics, converter losses, recovery sequence, overload, and the site's defined safety margin.
Alternative Solutions
- Separate UPS protection for DCS, PLC, and instrumentation.
- VFD DC-bus support for selected critical rotating equipment.
- Whole-line Dynamic Voltage Restoration for mixed loads on a critical feeder.
- Battery or generator-backed continuity for longer outages.
- Network, protection, process-control, or operating changes when they reduce risk more effectively.
Limitations / When Not to Use
- No ride-through change should bypass a plant trip, interlock, or safety-instrumented function without formal review.
- Electrical continuity does not prove process safety or mechanical suitability.
- A generic voltage-duration target is insufficient without equipment and process acceptance criteria.
- Hazardous-area, environmental, fire, and site standards must be confirmed for the proposed installation.
Recommended Architecture
Define the safe process boundary with operations and process safety, identify the first electrical failure inside that boundary, then compare DC-bus, feeder-level, UPS, and hybrid options. Acceptance testing should confirm both electrical ride-through and the intended process response.
Traceable 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.