3.0 Inlet volute
There no real problems with this component except for the condition of the trash screen which should be monitored to check for break up of the mesh.
There are advisory service bulletins on this matter. Three locations on the volute are used for seismic vibration monitoring.
Unfortunately the casing can act as a vibration amplifier and
disproportionately indicate that the turbine is in distress. It is not unknown to record velocities in excess of 20 mm/sec rms. See the vibration section for more on this subject.
The casing carries two RTDs for inlet air temperature measurement. The outputs from these are utilised for control purposes. If required compressor washing injection nozzles or spray bars are also fitted to this component.
4.0 Inlet Bearing Housing
This component is cast from aluminium alloy but is vulnerable to distortion and oil leaks. There are numerous A forms and service bulletins that have attempted to address the problems.
The current design of the TB inlet bearing housing is vulnerable to oil leaks from the joint faces and/or the threaded fasteners. Various modifications have been introduced over the years in an attempt to deal with the problem.
5.0 Compressor
5.1 General.
For the TB5400 at full load ISO conditions, the twelve stage compressor absorbs roughly equal work per stage delivers about 21 kg/sec of air. This is achieved with a pressure ratio of just over 7:1 at a discharge temperature of
about 275 C.
In terms of its mechanical construction the rotor is a multi-disc assembly with the rotor blades located between the discs in dovetails and held together with a central tension bolt. The LP blade stages and disc air washed faces are normally coated to provide corrosion resistance.
The rotor journals are prepared to accommodate displacement vibration equipment even though perhaps only about 20% of TB turbines are so fitted.
It is not permissible to repair the CT journal using a re-chroming process because this procedure has resulted in service failures. These incidents have always occurred during significant transient events and it is believed that it is as a result of rapid changes to the temperature of the cooling air that passes through the unprotected centre of the journal.
5.2 Inlet Guide Vanes.
For the TB3000 the IGVs were fixed at +15 degrees, but for the other ratings the vanes change between +28 and -5 degrees as the load passes through about 1500 hp. These angles are calibrated by the use of a setting block which fixes distances between the mechanism and the casing. There is no modulation; it is just a flip flop mechanism that moves quickly between the two set points and is driven by P2 air pressure.
This normally occurs at 52 psi rising and 48 psi falling. For turbines operating at high altitude where the pressures will be lower the mechanism is fitted with a weaker spring and the transition takes place at circa 44 psi. Apart from a sudden change of compressor speed the changeover happens quite smoothly.It is not unknown for surging to be a problem on dirty or old turbines.
It normally occurs around the IGV change over point which may be the result of a set up error. Surging at other times, especially during run up, may be indicative of errors in the fuel schedule. Correct operation of the inter stage blow off valves may also cause surge problems.
There no real problems with this component except for the condition of the trash screen which should be monitored to check for break up of the mesh.
There are advisory service bulletins on this matter. Three locations on the volute are used for seismic vibration monitoring.
Unfortunately the casing can act as a vibration amplifier and
disproportionately indicate that the turbine is in distress. It is not unknown to record velocities in excess of 20 mm/sec rms. See the vibration section for more on this subject.
The casing carries two RTDs for inlet air temperature measurement. The outputs from these are utilised for control purposes. If required compressor washing injection nozzles or spray bars are also fitted to this component.
4.0 Inlet Bearing Housing
This component is cast from aluminium alloy but is vulnerable to distortion and oil leaks. There are numerous A forms and service bulletins that have attempted to address the problems.
The current design of the TB inlet bearing housing is vulnerable to oil leaks from the joint faces and/or the threaded fasteners. Various modifications have been introduced over the years in an attempt to deal with the problem.
5.0 Compressor
5.1 General.
For the TB5400 at full load ISO conditions, the twelve stage compressor absorbs roughly equal work per stage delivers about 21 kg/sec of air. This is achieved with a pressure ratio of just over 7:1 at a discharge temperature of
about 275 C.
In terms of its mechanical construction the rotor is a multi-disc assembly with the rotor blades located between the discs in dovetails and held together with a central tension bolt. The LP blade stages and disc air washed faces are normally coated to provide corrosion resistance.
The rotor journals are prepared to accommodate displacement vibration equipment even though perhaps only about 20% of TB turbines are so fitted.
It is not permissible to repair the CT journal using a re-chroming process because this procedure has resulted in service failures. These incidents have always occurred during significant transient events and it is believed that it is as a result of rapid changes to the temperature of the cooling air that passes through the unprotected centre of the journal.
5.2 Inlet Guide Vanes.
For the TB3000 the IGVs were fixed at +15 degrees, but for the other ratings the vanes change between +28 and -5 degrees as the load passes through about 1500 hp. These angles are calibrated by the use of a setting block which fixes distances between the mechanism and the casing. There is no modulation; it is just a flip flop mechanism that moves quickly between the two set points and is driven by P2 air pressure.
This normally occurs at 52 psi rising and 48 psi falling. For turbines operating at high altitude where the pressures will be lower the mechanism is fitted with a weaker spring and the transition takes place at circa 44 psi. Apart from a sudden change of compressor speed the changeover happens quite smoothly.It is not unknown for surging to be a problem on dirty or old turbines.
It normally occurs around the IGV change over point which may be the result of a set up error. Surging at other times, especially during run up, may be indicative of errors in the fuel schedule. Correct operation of the inter stage blow off valves may also cause surge problems.
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