Most of the turbines are running above 1500 rpm. Either Proximity probe or velocity sensor is used to take the bearing displacement measurements which were given as online readings.Is it correct to monitor displacement instead of velocity in case of turbines. Comments ?

Gevenag

No! You need both. And in addition if a monitoring program is utilized I would collect independant acceleration readings which could be mandantory depending on frequency of interest. Need more data???

Displacement is not well defined for turbines. One can still (and may) get shaft riders for absolute displacement. Particularly with a 1500 rpm machine shaft relative will have far superior frequency response than shaft riders. However, they are different measurements.

One may also have some type of contraption to measure shaft relative and shaft absolute in which case one also has casing measurement(s).

Given the value (assumed) of your equipment, you should be able to justify casing and shaft measurements. The shaft absolute using shaft relative probes may not be popular in your country but are worth considering. x-y measurement configurations are most often used today (but not in the old days).

Additionally, it may be useful to measure at the couplings, shaft measurement. It can be useful to have measurements on either side of couplings, but one must justify costs.

Right now, we have only casing displacemnt measurements only and the turbine is operating at 3000rpm. As Mr.Sam pointed out, we collect the displacement, vel, accn in all the bearings with the help of portable analyzer.If I want to provide proximity probe, it involves drilling of bearing top covers and purchase of proximity probe.How can I justify.

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How can I justify?

I assume you are in the best position to justify this.

If you only measure casing vibration the first criticals may look good. You may not want to put probes on this to see the shaft relative. No news is good news?