What do you mean by Turbovisory or Turbine supervisory system?
Turbovisory or Turbine supervisory system is the monitoring of a Turbine. It supervises the condition of turbine and informs to an operating person. It also ensures the parameters do not exceed maximum allowable limit.
What is the significance of Turbine supervisory system?
Turbines are heavy & high speed machines, failures of machine lead into unrecoverable losses. So in case of any abnormality turbine should stop automatically. This is taken care by Turbine supervisory system.
What are the equipments or systems used in Turbine supervisory system?
Vibration probes: These probes are used for sensing shaft or bearing casing vibrations. Generally two probes are fitted at 900 apart at X & Y-directions to measure the shaft vibrations. These vibrations are measured in microns, mills or mm/sec.
Speed probes: Speed sensors are generally Magnetic Pick up unit (MPU) type. These are fitted at teethed portion of turbine shaft for measurement. Generally 2 MPUs are used to measure the shaft speed, one for speed sensing & other for controlling.
Axial shift probes: This probe is fitted at the turbine front end to measure the axial displacement of shaft. Axial displacement probe of the shaft is generally set between +/- 0.4 to +/- 0.6 mm.
Bearing temperature measuring sensors: These are used to sense the bearing metal temperature or bearing drain oil temperature. For measuring bearing metal temperature, RTD is inserted into drilled hole & touches the white metal & to measure the oil temperature RTD sensor touches the drain oil only.
Differential expansion probes: During abnormal operation conditions like quick start up, wrong SOP & uninform temperature distribution in casing & turbine rotor there could be the possibility of rubbing among turbine internals. To measure & monitor these gaps differential expansion probes are used & trips the turbine if these gaps increase beyond set values.
Casing temperature measuring sensors: Generally turbine casing thickness is very large around 150 mm &it depends on turbine operating parameters. So it is very much necessary of uniform distribution of temperature throughout the casing thickness.
And also the difference between top & bottom casing temperature of turbine should be very less.
Casing expansion measurement probes/sensors: These sensors are used to measure absolute expansion of casing. During startup &subsequent loading conditions turbine casing thermal expansion is must. Generally LVDTs are used for casing expansion measurement.
ESV opening indication: This is used to indicate the actual position of valves.
Eccentricity: This is very important supervision system. This is used to measure the mechanical bow. This may happen due to sudden trip of turbine & unavailability of barring device. Standstill position of turbine rotor for long time
Why do vacuum breaker valves are provided on steam condensers?
During tripping of turbine due to any of the above reasons like bearing vibration, temperature, axial shift, differential expansion etc, the vacuum breaker valve opens to bring down the turbine rotor speed to zero at the earliest time