Oleh: Muhammad Sholeh Wijaya, ST.
Introduction
The gas turbine is a rotating machine that produce energy from a stream of combustion gases. It has an upwards compressor coupled to a downwards turbine, and a combustion chamber in the middle. Energy is added in the gas stream in the burner, where the air is mixed with the fuel and ignited. Combustion increases the temperature, velocity and volume of the gas stream. It is then directed through a nozzle through the turbine blades, turning the turbine and powering the compressor. The gas turbine discussed by the author in this bulletin is the CAR-3600 Centaur 50/5702 at KRA platform PT Star energy. Gas Turbine serves to drive the centrifugal compressor. In this bulletin the author will discuss how the process of handling unbalance cases on a Power Turbine with a velocity sensor without using a key phasor (RPM Sensor). Technical data unit information as follows.
Measurement Layout
Finding and Recommendation
Finding :
- Old Centaur 50 Turbine engine is exchanged with new Turbine engine, When unit are being started, found high vibration at PT Turbine.
- The problem is suspected from unbalance peak 1X rpm PT
Recommendation :
- Pdm perform trim balance at Power turbine
Trim Balance Process
Founded Unbalance Indication at Power Turbine.Highest at 0.69 mm/s RMS on Speed at 70% NPT, trim balancing with using Four Run Method is the only way to Balancing unit without keypashor (zero point). Vibration alarm NPT : 0.5 Ips rms and shutdown at : 0.8 Ips rms.
Configuration :
Noted for the next finding if we found the same cases:
- Balancing job with no phase has several deficiency:
- Need more unit start stop during balancing step, unit reach target operating RPM/ NPT.
- High spot phase shifting un-able to be monitored.
- Balancing sequence and procedure repetition.
- Duration of balancing job much longer than with phase method.
- Power Turbine proximity probe (already attached on unit) unable to be use with compressor proximitor, during balancing job on power turbine. There was possibility different specification between sensor cable and proximitor.
Recommendation for PDM team :
- During next schedule unit shut down, coupling assembly at Gear Box and power turbine side, proposed to be balanced on machine shop, in order to minimize correction weight attached at this component, since there were correction mass installed around 9.8 gr. All bolts of coupling and spacer mounting should be weighed and marking.
- Modification/ fabrication cover coupling for balancing activities purpose, with transparent material such as glass and or acrylic, in order to applied photo tach sensor for balancing with phase angle method.