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 VIBRATION AND AXIAL

DISPLACEMENT MONITORING C M &  U   s

C M &  U   s

   G   A   S   T   U   R   B   I   N   E   S

   G   A   S   T   U   R   B   I   N   E

   SINTRODUCTION

It is normal for all machines, even in peak performanceconditions, to vibrate and make noise. The level ofvibration is dependent on the operating condition of a

mechanical system: when vibration increases, deviatingfrom an acceptable level, it is a sure indication that somecomponent is deteriorating.Development of reliablevibration measurement instrumentation now gives ussufficient information for a detailed analysis of thestate of health of any mechanical component. Analysisof vibration signals, combined with experience andfamiliarity with the machine are the keys to relativelyaccurate troubleshooting.

BENEFITS

Although machinery protection alone is sufficientreason for equipping critical machine parts withsupervisory instrumentation systems, monitoring

systems can be of advantage for other reasons.They are essential for diagnostic and predic-

tive maintenance, which is a growing industrytrend and replacing preventive maintenance wher-ever possible as preventive maintenance general-ly has a high economic penalty which is notalways justified in technical terms. A predictiveinstead of a preventive approach means operatingon a machine or component just when needed,and no service as long as the system is runningreliably. Early identification of machinery problemstherefore offers a number of benefits, including:1) shutdowns can be timed;2) replacement parts can be prepared in advance,

saving time;3) elimination of defects causing vibration

significantly reduces noise.

RADIAL VIBRATION

Two no-contact proximity probes are mounted off-set 90°, on the bearing cap.The proximity probe signals are sent to a controlroom monitor, which:

• displays the peak-peak value of the signal from each

probe• performs alarm and trip functions on each probe• provides the power supply for field probes.

A third probe, a Keyphasor probe, is installed justoff the shaft. The Keyphasor acts as a phase ref-erence, ie, it generates a pulse every time a notchmade in the shaft passes under the probe.

GE Power Systems Oil & Gas 

Nuovo Pignone 

CM&Us TU/GA15-9/2002

DUAL VIBRATION 

MONITOR 

POWER 

SUPPLY 

SYSTEM 

MONITOR 

FIELD CONTROL ROOM 

NO CONTACT

PROBES

LOCAL

PROXIMITOR ZENER

BARRIER

X 

Y 

ORBIT 

DUAL THRUST 

MONITOR 

Figure 1

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Headquarters

via F. Matteucci, 2 - 50127 Florence (Italy)Tel. +39/055 4238280 - Fax +39/055 4238308E-mail: info.service@np.ge.comwww.ge.power.com

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By correlating the signals from the two proximity probesand the keyphasor, an elliptical wave shape is dis-played (for instance on a 2-channel oscilloscope) rep-resenting the shaft orbit.By simply observing deviations from the ideal orbit pat-tern, it is possible to identify any defects or irregulari-ties. Every defect generates a characteristic vibrationmode and is represented in the form of a particularvibration frequency. Analysis of vibration frequenciesidentifies many types of problems including, for exam-ple, unbalance of rotating parts and reduction of the oilfilm which lubricates journal bearings.Fig. 1 shows the string of instruments from field tocontrol room.

AXIAL DISPLACEMENT

No-contact probes are also used to measure rotor

axial displacementThe installation comprises two probes which guaranteeredundancy. The average values of the signals fromthe probes can be displayed on a dedicated monitorintegrated in the previously described radial vibrationmonitoring system.Fig.2 shows a mechanical drawing of a bearing equippedwith radial and axial vibration probes and a keyphasor.

INSTALLATION AND MACHINE MODIFICATIONS

Fig. 3 shows the arrangement for probes on singleand two-shaft machines.The bearing cap and outer casing have to be drilled to

install the probes. In addition, the area of the shaftexposed to the probe must be burnished.All modifications can be done on site with modificationdrawings supplied by Nuovo Pignone.

SCOPE OF SUPPLY

For single-shaft turbines:

• 2 axial displacement probes on the thrust bearing;• 2 radial vibration probes for bearing n°1;

• 2 radial vibration probes for bearing n°3;

• 1 keyphasor,

• extension cables and

proximitors for all probes;• local junction box for

installing proximitors;

• cable sheathing up to the junction box;

• control room monitor to suitthe number of probes;

• Zener barriers for each probe(if necessary);

• mechanical modificationdrawings for installing theprobes and wiring diagram.

 VIBRATION AND AXIAL

DISPLACEMENT MONITORINGFor two-shaft turbines:

• 4 axial displacement probes on the thrust bearings(2 per bearing);

• 2 radial vibration probes for bearing n°1;• 2 radial vibration probes for bearing n°4;• 1 keyphasor for bearing n°1;• 1 keyphasor for bearing n°4;• extension cables and proximitors for all probes;

• local junction box for proximitors;

• cable sheathing up to the junction box;

• control room monitor to suit the number of probes;

• Zener barriers for each probe (if necessary);

• probe installation modification drawings and wiringdiagram.

Interconnecting cables between the local junction box,barrier and monitors can be supplied on request.

TWO-SHAFT TURBINES

 PGT5/2 PGT10 PGT25 MS5002 MS3002

TWO-SHAFT TURBINES

 PGT5/2 PGT10 PGT25 MS5002 MS3002

V vertical probeH horizontal probe

A axial displacement probe

K keyphasor

SINGLE-SHAFT TURBINES

 PGT5/1 MS5001 MS6001 MS7001 MS9001

SINGLE-SHAFT TURBINES

 PGT5/1 MS5001 MS6001 MS7001 MS9001

V vertical probe

H horizontal probe

A axial displacement probe

K keyphasor

A

V

K

V

HH

 bearing 2(only for MS7001

 and MS9001)

 bearing 3 bearing 1

V

K

H

 bearing 2

   b  e  a  r   i  n  g   3 bearing 1

A

V

K

H

   b  e  a  r   i  n  g   4

A

 KEYPHASOR

 RADIAL

VIBRATION 

 PROBE

 AXIAL

 DISPLACEMENT 

 PROBE

A

 KEYPHASOR

TURBINEC

SECTION A-A

 RADIAL

VIBRATION 

 PROBE

 AXIAL

 DISPLACEMENT 

 PROBE

 RADIAL

VIBRATION 

 PROBE

 AXIAL

 DISPLACEMENT 

 PROBE

Figure 3

Figure 2