Why can’t we monitor the same signals with our own vibration analysis setup?

Because the VEWS system uses raw (unfiltered) acceleration signals, 20 kHz bandwidth or greater. It is very common that your signals might be routed through various high and low pass filtering and sometimes converted from Acceleration into Velocity. Both factors make it impossible to use the signals for further conditioning and signal processing.

Why can’t we use our own accelerometers already fitted to the gas turbine?

The existing accelerometers typically have a very low signal to noise ratio. This means that weak signals are not picked up efficiently. Such accelerometers are fitted only to detect high levels of unbalance. For bearing monitoring, accelerometers must function with a low signal to noise ratio.

Why are additional accelerometers fitted to the gas turbine with the DT system compared to the standard arrangement?

For simple unbalance detection, the energy produced from the turbine can easily be picked up by only one or two accelerometers. However, for detection of bearing signals, accelerometers must be positioned in the vicinity of each bearing support module for precise monitoring.

Why can’t we detect bearing degradation with our own instrumentation setup?

There are too few accelerometers fitted, and their sensitivity is normally too low. In addition, standard systems have no hardware or software installed that is capable of signal processing required to detect the specific type of signals needed for bearing degradation diagnostics.

Why is it so demanding to do measurements and analysis to gas turbines?

Because all weak signals are buried in the gas-path noise, and in the energy produced by the main rotor. Special experience, equipment and software is needed to “clean” this up.

Why is unbalance detection not sufficient for gas turbine diagnostics?

Unbalance is a very important parameter to trend; however, unbalance is often related to SECONDARY faults. As an example: Aero-derivative gas turbines have ball and roller element bearings for the support of the rotor. In the early stages of the bearing degradation, the VEWS defines this as a PRIMARY fault before any major catastrophe occurs. With conventional systems, if a bearing fails, the bearing must be totally damaged before an unbalance occurs and no pre-warning of pending breakdown is possible. The time between severe unbalance noted, and machine failure is therefore very short and implications can be severe.

What is the main difference between the Dynatrend system, and conventional systems?

Although the Dynatrend VEWS system can perform the same simple functions of a conventional condition monitoring system, it does far more. The VEWS is built with capability to monitor and diagnose high frequent AND acoustic signals from accelerometer loops fitted to gas turbines, gearboxes, fans, windmills etc.
Typically areas of monitoring:
* Rolling element bearing condition
* Blade passing energy
* Foreign or dropped object damage events
* Internal rubbing
* Unbalance
* Combustion energy