How Does The Steam Turbine Trip System Work | Faisal Ahmed

🔧 Purpose of the Trip System

The trip system is designed to immediately shut down the steam turbine during unsafe or abnormal conditions to prevent damage to:

The turbine

Generator

Connected mechanical systems

Plant personnel and environment


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⚙️ Working Principle – Step by Step

1. Continuous Monitoring

Sensors and protection devices constantly monitor critical parameters:

Overspeed (RPM too high)

Low lube oil pressure

High bearing temperatures

High shaft vibration

External signals (e.g., fire, manual emergency trip)



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2. Detection of Fault / Hazard

When any monitored parameter exceeds the safe limit:

A trip signal is generated (electrical or mechanical)

Sent to the trip solenoid valve or mechanical trip mechanism



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3. Activation of Trip Mechanism

Once the trip signal is received:

The trip solenoid is de-energized

This causes loss of hydraulic control oil pressure

As a result, the main steam stop valves and control valves slam shut


This action instantly cuts off steam flow to the turbine.


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4. Turbine Shutdown (Coast Down)

The turbine slows down gradually using stored rotational energy

Turning gear (ratchet motor) may engage to slowly rotate the shaft and prevent bending

Auxiliary systems (like emergency lube oil pumps) remain active to protect the turbine during coast-down



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🔄 Reset After Trip

To restart the turbine after a trip:

1. Identify and resolve the root cause of the trip


2. Reset all protective relays and trip devices


3. Rebuild hydraulic and control pressures


4. Follow the normal startup procedure




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📌 Common Trip Conditions & Devices

Condition Device Type

Overspeed Electronic overspeed sensor or bolt
Low lube oil pressure Pressure switch / transmitter
High bearing temperature RTDs / thermocouples
High vibration Proximity probes
Emergency shutdown/manual trip Push buttons or remote signal
Fire or high exhaust temperature Flame sensors, thermocouples



Faisal Ahmed I&C Engineer