vibration analysis component faults spectrum time wave ......actually causing the increases in...

ANTARA STEEL MILLS | LABUAN EQUIPMENT: 1223 Motor & Gearbox VIBRATION ANALYSIS REPORT Data Collection Date: 26/7 – 20/12/2018

Prepared by Rotary Machinery Section of 7

Vibration Analysis

Component Faults Spectrum Time Wave Enveloping Cross Phase

Motor AC Non VFD

Imbalance Yes - - Slight

Eccentric stator : soft foot None - - -

Eccentric Rotor None - - -

Loose Rotor bar Yes - - -

Cracked Rotor bar Yes - - -

Beating Yes Yes - -

Rotor Bow None None - None

Bearing – NDE None None None -

Bearing –DE None None None -

Rotating Looseness None None - None

Coupling Motor-Gearbox

Misalignment None - - None

Gearbox Input Shaft Gear : Pinion

Bearing DE None None None -

Bearing NDE None None None -

Gear Fault None None None -

Gear Resonance None

Gearbox Intermediate or Output

Bearing DE None None None -

Bearing NDE None None None -

Gear Fault - - - -

Gear Resonance None

Coupling Driver-Driven

Misalignment - - - -

Driven Pump Compressor Fan

Imbalance - - - -

Rotating Looseness - - - -

Bearing – DE - - - -

Bearing – NDE - - - -

Cocked Bearing - - - -

Bent Shaft - - - -

Resonance - - - -

Cavitation - - - -

Flow Turbulence - - - -

Vane Pass - - - -

Structure Baseplate Piping

Structural Looseness - - None

Structural Weakness - - Slightly Flex

Resonance None

**Note: Bearing condition steps: Good -> Early Stage 1 (5 kHz-40 kHz) -> Early Stage 2 (1khz-5kHz) -> require replacement: Intermediate or premature Stage 3 (0-1kHz) -> Late Stage 4 (0-1kHz noise)



Finding(s)

1. Overall vibration trending jumped from 3 to 11mm/s and consistent till present.

2. FFT at high resolution shows strong 1x in horizontal direction as well as 1x harmonics (1x-4x)

with pole pass frequency sidebands. A pattern of rotor bar faulty, or other faults shorted end

rings, rotor laminations.

3. Time waveform with beating phenomenon which gives audible modulating growling noise at

site.

4. Time waveform is asymmetrical indicates impacts is directional.

5. FFT: 2xLF amplitude varies up and down. Rotor bar frequency with 2LF sideband shows fault

on the rotor bar (loose joint)

6. Motor speed fluctuates: without load 1491/1482/1477 with load 1450/1444/1428 rpm

7. Motor Body temperature 35-44’C

8. Gearbox starts to pick up strong vibration from the motor.

Action(s) taken

1. Repair worn out hinge bolt for gearbox and motor's mounting base – Material Sec.

2. Repair leak through from backstop flange and top up oil for gearbox. – Material Sec.

3. Retighten all the bolts

Suggestion(s)

1. Carry out Motor Current Signature Analysis, MCSA, to further determine faults and severity

damage of rotor bar.

2. Rotary don’t have special SKF Current clamp that can be connected to our vibration device

to carry out the Motor Current analysis.

3. Below are some reference and faults example:



4. Monitor other signs of severe damage: the motor will run hot, the motor will lose Power, the

motor amps will constantly drift up and down, and the speed of the motor will continually

fluctuate. The damage or vibration energy will transmit to other machine and it will

progressively damage the gearbox gears.

5. Other technologies and field experience to determine the root cause are advisable.

Notes:

1X-5X with PPF sidebands



PPF sidebands

Rotor bars faulty



Beating sound



Latest data

Machine name POINT name Date/Time Last value Units

Motor 1 Vel H 20/12/2018 10.5 mm/s

Motor 1 En3 H 20/12/2018 0.9 gE

Motor 1 Vel V 20/12/2018 5 mm/s

Motor 2 Vel H 20/12/2018 8.6 mm/s

Motor 2 En3 H 20/12/2018 0.9 gE

Motor 2 Vel A 20/12/2018 2.9 mm/s

Gearbox 3 Vel H 20/12/2018 4.6 mm/s

Gearbox 3 En3 H 20/12/2018 1.5 gE

Gearbox 3 T H 20/12/2018 0.6 g

Gearbox 3 Vel V 20/12/2018 6.8 mm/s

Gearbox 3 Vel A 20/12/2018 2.9 mm/s

Gearbox 3 En3 A 20/12/2018 1.8 gE

Gearbox 4 Vel H 20/12/2018 4.1 mm/s

Gearbox 4 En3 H 20/12/2018 0.3 gE

Gearbox 4 T H 20/12/2018 0.6 g

Gearbox 4 Vel V 20/12/2018 7.7 mm/s

Gearbox 4 Vel A 20/12/2018 2.8 mm/s

Gearbox 4 En3 A 20/12/2018 1.4 gE

Gearbox 5 En3 H 20/12/2018 0.8 gE

Gearbox 5 T H 20/12/2018 0.4 g

Non Route Motor Low

frequency 1H

5/10/2018 14 mm/s

Non Route Motor High

frequency 1H

5/10/2018 0.3 g



Notes

VIBRATION SPECTRUM ANALYSIS - This test can detect cracked or loose bars while

under load. Under load, the vibration will modulate at a rate equal to the number

of poles times slip frequency. With a broken rotor bar, the amplitude of the beat

increases with load. A cracked rotor bar can also cause localized heating of the

rotor which causes uneven expansion and rotor bowing. This results in an

unbalance and a strong 1 times running speed vibration as well as the side bands

related to slip frequency. Loose rotor bars may give similar symptoms and also

will show vibration at rotor bar passing frequencies. This test will not show up at

no load running because a broken rotor bar cannot carry current. When it is in an

area of high flux, the magnetic forces on the rotor are unbalanced. Since the

current flow through the rotor bar is proportional to slip, at no load when rotor

current is low, the bar has virtually no magnetic forces acting on it.

Todd A. Hatfield, VP Engineering & Repair

Today many instruments incorporate the use of computer algorithms to

automatically identify the frequency peaks of interest and the amplitudes of these

peaks to aid in analysis. What appears to be a very challenging task becomes

quite simple with the aid of industrial designed software. Of the various methods

put forth in this article, no single test will definitively prove the presence of a rotor

bar defect. Understanding why these peaks are where they are, and what is

actually causing the increases in amplitude, allows us to better analyse the

condition of our machines. The use of these methods will also provide additional

clarity to the vibration data. Luckily, very few rotor bar defects lead to

catastrophic motor failure. All of the data analysis methods described in this

article have trend able indicators. Trend the relative amplitudes for motors,

compare these results to other motors of the same design, and make an educated

decision that is practical concerning motor criticality. The presence of broken bars

will cause an increase in overall motor losses and a decrease in motor efficiency.

The additional heat generated from the added current will also further increase

the rate of insulation degradation in the stator. Taking routine data on your

motors, analysing that data as described above and trending this data over time

will allow you the confidence to “make the right the call”.

Drew Norman is currently working with Baker Instrument Company, an SKF

Group company

vibration analysis component faults spectrum time wave ......actually causing the increases in...

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