Entendendo os Sistemas de Proteção de Máquinas
Proteção de máquinas — also called equipment protection or machine safeguarding — refers to the monitoring-and-control systems that automatically detect dangerous operating conditions (vibração exceeding safe limits, excessive temperatures, abnormal pressures) and execute protective actions (alarms, then automatic shutdowns) to prevent catastrophic equipment damage, safety hazards or environmental releases. By design these systems prioritise preventing damage over maintaining production, and they are built fail-safe: a sensor fault or a loss of power drives the machine to a safe stop rather than allowing it to keep running blind.
Machinery protection is deliberately distinct from monitoramento de condições. Condition monitoring tracks equipment health to plan maintenance, giving early warnings over weeks or months. A protection system instead provides immediate emergency response, executing an automatic shutdown within seconds once a critical threshold is breached. The two are complementary — one buys planning time, the other prevents the bang — but they answer to different requirements.
1. Protection System Components
Sensors (permanently installed)
- Sondas de proximidade measuring shaft displacement relative to the bearing.
- Acelerômetros mounted on the bearing housings.
- Temperature sensors (RTDs and thermocouples).
- Pressure and flow transmitters.
- Axial position sensors watching the thrust end.
- Typically redundant — two or three sensors per measured parameter.
Hardware de monitoramento
- A dedicated protection-system processor.
- Real-time signal processing.
- Voting logic (2-out-of-2 or 2-out-of-3).
- Relay outputs that command the shutdown.
- Kept separate from the DCS/PLC so its integrity does not depend on the process-control network.
Shutdown logic and actuators
- Hardwired trip circuits — not software-only.
- Solenoid valves for turbine trips.
- Circuit breakers for motor trips.
- Fail-safe design: loss of power causes a trip.
2. The API 670 Standard
Requirements for turbomachinery
API 670 is the industry standard for machinery-protection systems:
- Effectively mandatory for turbomachinery above roughly 10,000 HP.
- Specifies the sensor types and quantities.
- Defines the voting logic and redundancy.
- Sets the alarm and trip delay times.
- Requires the system to be independent of process control.
Typical sensor configuration per API 670
- Radial vibration: two XY proximity-probe sets — four probes per bearing — capturing the shaft’s vibração radial.
- Axial position: two axial displacement probes.
- Teclado: dois phase-reference sensores.
- Bearing temperature: two temperature sensors per bearing.
- Total: typically 12–20 channels per machine.
3. Protection vs. Condition Monitoring
| Aspecto | Monitoramento de Condições | Sistema de proteção |
|---|---|---|
| Propósito | Detecção precoce de falhas para planejamento | Prevenir danos catastróficos |
| Tempo de resposta | Horas a semanas | Segundos |
| Limiares | Menor (alerta antecipado) | Maior (perigo imediato) |
| Ações | Notificações, ordens de serviço | Desligamento automático |
| Reliability focus | Precisão | Fail-safe operation |
| Redundância | Opcional | Obrigatório |
Integração
- Modern installations combine both functions in one platform.
- The same sensors can serve protection and condition monitoring at once.
- Each function uses its own processing and níveis de alarme.
- The protection pathways stay independent and hardwired regardless.
4. Protection Parameters
Vibração
- Shaft displacement: proximity-probe measurement, with a typical trip around 25 mils (635 µm) peak-to-peak.
- Bearing-housing velocity: a trip of roughly 0.5–0.6 in/s (12–15 mm/s) is typical.
- Aceleração: used for high-frequency protection.
Setting those numbers sensibly means relating them to recognised severity zones; the modern general guideline, ISO 20816-1 (which supersedes the older ISO 10816), frames the alarm-and-trip thinking, and for steam turbines and generators a dedicated ISO 20816-2 vibration-limits calculator turns those zones into concrete values.
Posição
- Axial position: trips on excessive shaft movement, the classic signature of rolamento axial failure.
- Differential expansion: rotor growth relative to casing growth.
- Excentricidade: rotor position within the folga do rolamento, useful for spotting a arco térmico at slow roll.
Temperatura
- Bearing-metal temperature (typically a 110–120°C trip).
- Bearing drain-oil temperature.
- Winding temperatures on motors and generators — a generator bearing temperature monitor helps set realistic limits.
5. Voting and Redundancy
2-out-of-2 (AND logic)
- Both sensors must agree before the machine trips.
- Impede deslocamentos indevidos devido à falha de um único sensor.
- Risk: both sensors must be working — there is no protection if both fail.
2-out-of-3 (majority voting)
- Any two of three sensors agreeing causes a trip.
- Best reliability, since it tolerates one failed sensor.
- More expensive (three sensors).
- Preferred for máquinas críticas.
Bypass and testing
- Individual channels can be bypassed for testing or maintenance.
- All protective channels can never be bypassed simultaneously.
- Bypass controls are key-locked.
- Bypasses reset automatically after a set time.
6. Testing and Maintenance
Functional testing
- Periodic full-system tests, quarterly to annually.
- Simulate trip conditions.
- Verify the encerramento actually executes.
- Exercise every redundant channel.
- Document the results.
Calibração do sensor
- Annually, or per the equipment specification.
- Verify the trip setpoint.
- Test the overall system response time.
- Maintain calibração records.
Manutenção do sistema
- Keep sensors clean and functional.
- Verify the power supplies.
- Check relay and actuator operation.
- Update software and firmware as needed.
7. Where Portable Diagnostics Fit Alongside Protection
A permanently installed protection system tells you que a machine is in danger and trips it; it rarely tells you por que. That root-cause question is answered with portable diagnostics. When a protection trip flags rising shaft displacement or bearing vibration, an engineer follows up with a portable two-channel analyser such as the Conjunto de equilíbrio-1a, measuring 1× deslocamento, amplitude and phase in the machine’s own bearings to distinguish unbalance from misalignment or looseness — and, where unbalance is the cause, to correct it on-site and verify the result before the unit is returned to service. In this way monitoramento de vibração, protection and portable balancing form a continuum: protection prevents the failure, condition monitoring forecasts it, and field diagnostics fix it.
Machinery protection systems are the safety net that prevents catastrophic failures by shutting equipment down automatically when dangerous conditions appear. While condition monitoring provides the early warnings that drive planned maintenance, protection systems deliver the immediate emergency response that makes them mandatory on critical turbomachinery and high-value rotating equipment, where a failure could carry severe operational, safety or environmental consequences.
