Uninterrupted rotor shaft vibration monitoring on turbomachines - no more bridging of the trip contacts during startup

The startup of a turbomachine is a highly stressed and critical operation phase in which most of the severe damages are caused; in this respect it is comparable to the take-off of an airplane. Still, continually a quite dangerous monitoring practice can be observed: it is common that during startup machine operators deactivate the monitoring of the rotor shaft vibration in order to get the machine running without any interference of trip alarms.

Turbomachines in industrial use (turbocompressors, turbines, generators, big pumps, fans/blowers, …) are permanently monitored regarding rotor shaft vibrations. When a specified vibration level is exceeded, the machine will be shut down automatically.
For the monitoring of sleeve bearings, usually the rotor shaft vibration is contactlessly measured by means of eddy current probes. The measuring system supplies a 4 to 20 mA signal, proportional to the peak-to-peak vibration. Commonly the limit values are monitored with a central control system (DCS or PLC).

Based upon experience, most of the damages especially occur during startup. A lot of damages can be detected only by vibration monitoring. From this point of view, it is negligent to deactivate the vibration monitoring system during startup. Still it is common practice in the industry around the world to do so! Many companies are not aware of the risk that this might lead to massive machine damage, production loss and even to personal injury!


Why do many turbomachinery operating companies still bridge the rotor vibration monitoring during startup?

1. Most of the turbomachines are driven by an electric motor via a spur gear unit. The gear mostly is designed in that way that the driven shaft is lifted within the bearing due to torque. The lifting of the shaft will be recognized by the rotor vibration monitoring system as an increase of the vibration level. Due to the bearing clearance being higher than the trip limit, the limit value would be inevitably exceeded and the machine would automatically be shut down at every startup trial! Mostly the increase of the vibration level even exceeds the measuring range.

2. A lot of turbomachines are operated in supercritical condition; this means that on the way to their normal operation speed, they have to pass a resonance range, which might cause rotor vibrations exceeding the trip limit.


Of course those "normal peaks" must not lead to a shutdown; however simply deactivating the rotor shaft vibration monitoring temporarily is not a convincing technical solution either. Although the machine can be started in this way, but the rotor vibration is not monitored, thus the machine is unprotected until the normal operation speed is reached! It is recklessly disregarded that damages, which could be detected only by monitoring the rotor vibration, in fact stay undetected. The situation becomes disastrous, if the vibration sensor is hit and destroyed by an extreme deflection of the shaft. A destructed eddy current sensor will not supply a signal that exceeds the trip limit; that means that even after reactivating the rotor vibration monitoring after the startup phase, the machine will not be shut down automatically anymore!

kmo turbo has developed a new and universal vibration transmitter (kmo-VibroUniT), offering a smart logic for the event controlled adaption of the measurement range (kmo-TripMaster, patent pending). Besides a lot of other benefits, the system enables to completely monitor the rotor vibrations without the need of bridging trip contacts, especially during the critical startup of a turbomaschine.

kmo-VibroUniT can be combined with measurement components (sensor + cable + conditioner/oszillator/proximitor) of any supplier. The measuring range is freely adjustable. It can be universally used for the measuring of the rotor/shaft vibration or the axial shaft position of new machines as well as existing machines.

Further information: http://www.kmo-turbo.de/downloads/200905_kmo-VibroUniT_eng.pdf

kmo turbo is a German engineering company based on decades of turbomachinery experience. Besides troubleshooting, commissioning and the proficient retrofit of used machines kmo turbo develops, manufactures and distributes innovative solutions for the control and vibration monitoring of rotating equipment of all manufacturers. Over the years kmo turbo has build a reliable network of partners and specialists. Thereby kmo turbo is able to provide high quality and outstanding products at attractive pricing. All products are designed for maximum operational benefit.

Downloads: http://www.kmo-turbo.de/include/downloads.htm

kmo turbo GmbH
Friedrichstr. 59
88045 Friedrichshafen
Germany

Mr. Roland Klauber
Phone: +49 7541 95289-13
Email: roland.klauber@kmo-turbo.de

This release was published on openPR.