Tripping parameters of turbine and related logic’s
By Interlocks, we are ensuring the safety of Steam turbine and its accessories.
Steam turbine and generator together have hell a lot of interlocks for the safety and reliability of the units. I’ll try to cover the major one,
All these interlocks are usually based on the supervisory probes/sensors provided by OEM to make sure the turbine parameters should not jump the safe limits. And if they act, they either trip the machine or shutdown it.
- Bearing Vibration - Probes are provided on almost every bearings for measuring bearing vibration (sensor type- displacement/velocity/or Acceleration) and they trip the machine in case high vibration crosses specific limits.
- Bearing temperature. - High temp. Alarm and then Trip.
- Differential Expansion (It indicates the relative expansion of Turbine casing and Turbine rotor - Will have trip limits on both +Ve and -Ve side) and Absolute Expansion (Measures the expansion of casing relative to Bearing pedestal ).
- Lube Oil temperature - Alarm - Not trip usually.
- Lube Oil Pressure- Low pressure trip.
- Steam parameters - Low steam flow and temperature- Trip.
- Vacuum deterioration- High Exhaust Pressure-Low Vacuum - Trip.
- High Hotwell level - Trip.
- Overspeed - Trip (Usually 3 or 6 sensors - Voting logic - 2 out of 3/ 4 out of 6).
- High Exhaust temperature - Trip.
- If Both CEPs (Condensate Extraction pump ) are unavailable - Trip.
- If Both Vacuum pumps are unavailable - Trip.
- If upstream Steam source (Boiler or HRSG) Trips - ST Trip.
- Control/Hydraulic oil pressure ( Operating the Main steam stop and control valves ) Low- Trip
Author : Bhola Shanker