Fulfilling the task given from mechanical vibration class of mechanical engineering major, Universitas Gadjah Mada.

1. ELECTRIC PROBLEM VIBRATION
By : Muhammad Miftahul Azhar 15/385245/TK/43907
Muhammad Ezra Fikriardhi 15/385246/TK/43908
Pri Hestuwati 15/385250/TK/43912
Riyando Laksana Aji 15/385257/TK/43919

2. One of electric component which is has electric vibration problem is
electric motor in the rotating machnine. This problem can cause
damage the machine or other machine which is vibrations transmited
to that machine. And then this will result in reducing machine lifetime.
That damage because of excessive vibration or resonance.
WHAT IS IT ?

3. 1. Thermal bending of the rotor: Uneven electrical circuits in the rotor bars generates an
uneven heat distribution in the rotor. Because of that, it will causes deformation, then
bending, and then vibration which result in rotor unbalance.
2. Eccentricity in the air gap: Because of this problem, it will induce a vibration at 120Hz
(2xLF ). It because air gap is not uniform
3. Loose rotor: Rotor skid on the axle, depending on the temperature. This problem will
generates a vibration 1xRPM and harmonics because load changed or line frequency changed
4. Eccentric rotor: It because rotor is not completely round. This problem will cause vibration
1xRPM and generate unbalanced magnetic forces.
5. Loose windings: cause of this problem is stator winding which is slightly loose, the the
vibration level at 120 Hz will increase. The worst, this problem leads to stator breakdown.
TYPE AND CAUSE

4. • There are two spectra necessary to detecting electrically-related
problems. Each example that follows is taken on one or the other :
1.High frequency (200 x RPM).
2.High resolution (12kcpm Fmax w/ 1600 lines is usually sufficient).
SPECTRUM

5. • There are also certain terms and frequencies which must be defined :
1. FLine = Electrical line frequency - normally 60 Hz (3600 cpm) or 50 Hz (3000 cpm).
2. 2 x FLine = Torque Pulse Frequency.
3. P = # of poles on the motor. The number of poles is how the speed of the motor is controlled. The
greater the number of poles, the slower the motor runs. It always even number
4. FSynch =. It is the speed of the rotating magnetic field that is generated and the speed the
rotor tries to attain (it will never quite reach that speed).
5. FSlip = Slip frequency = FSynch - rotor RPM (actual speed)
6. FPole = Pole pass frequency = P x FSlip
7. WSPF = # Winding Slots x RPM
8. RBPF = # Rotor Bars x RPM
SPECTRUM

6. To analyze electric vibration, it is important to look for presence of a peak or
patterns of peaks. But the most important aspect is we must look for increasing
amplitudes. If it is detected in our machine, we must see if the amplitudes are
trending up or not. Then additional testing can also be performed, like surge
testing, current testing, etc.

7. Electrical fault in induction motor
Electric faults produce a vibration with a specific frequency.
Through monitoring and analizing the vibration spectrum these
specific frequencies can be detect and through these we can detect
usages, slackness and forces which act and produce the fault. If the
amplitude of these vibrations reach a certain level the fault can be
detect and identify.

8. Vibration sources in electrical motors
1. Electrical causes
• Flux variation around the stator which produce a variation of attractive force between the stator
and rotor
• Broken rotor bar: if a rotor bar is broken in this bar will be no current and no magnetically
field. This will create a magnetic unbalance the two opposite side of the motor. The unbalance
creates a magnetic force which rotates with rotational speed and modulates at the
frequencyequel to the slip frequency times of the number of poles.
• Short circuit of a part of the winding
• Rotor bar passing frequency vibrations: high frequency vibration appears when current is
induced the rotor bars under the load. The induced current creates around the bars a magnetic
field and this generates an attracting force with radial and tangential component to the stator
teeth and vibrations will appear. These high frequency vibrations are related to electrical noise.

9. Vibration sources in electrical motors
2. Mechanical causes
• Motor unbalance: all rotating machinery, induction motor must be balanced to have an easy
and quite operating. The rotor is an important part of induction motors, this balance influence
the whole working of the motor. By non-symmetrical rotor heating appears the thermal
unbalance. Every rotor shows a changing in vibration at transition from cold state to hot state.
Another cause of unbalance of the driven machine. This can appears when there is a rigid
coupling between the two machines or the unbalance of the driven machine is great.
• Improper base : vibration near to the motor feet must be less than 30% of the vibration
measured at the motor bearing
• Usage of the bearing: bearing vibrations are present in all type of rotating system and motors.
Anti-friction bearing are an important part of the motor. The bearing usage influences the
whole rotating system.

10. Vibration measurement methods
The vibration of a system can be expressed as a displacement or as a velocity or as
acceleration. Generally a velocity spectrum is analyzed. Electrical and mechanical
sources of vibration are ata different frequency and phase angle and or one type of
vibration may modulate the other type of vibration and result a vibration with variable
amplitude and phase. For induction motor is used the determination of the displacement
for shaft vibration measurement and velocity housing vibration measurement.

11. MS VARIATION

12. SPRING MASS

13. MR VARIATION

14. Conclusion
Electrical motor vibration caused by any reasons mentioned in
upper parts is important and require steady monitoring in critical
places, bearing, motor feet, motor housing, etc. can prevebt hard
faults. It was shown for motor vibration study mechanical system
with two degree of freedom must be considered. Analyzing the
system behavior in accordance with the frequency can be
observed that for all kind of variation in the system (fault
appearance) amplitude and phase variation occurs in the variation
signal. This can be useful in fault warning.

15. Reference
• http://www.sciencedirect.com/science/article/pii/S
2212017315000791
• http://www.vibrationschool.com/mans/SpecInter/
SpecInter32.htm
• http://www.vtab.se/training/vibration-
school/electrical-motor-problem/?lang=en
• http://www.ee.co.za/article/electrical-machine-
vibration-causes-controls-2.html
• https://pdfs.semanticscholar.org/d18a/9da4279a7
cd30eaf3f5d7c475713e8c0ceac.pdf
• https://www.bksv.com/media/doc/BO0269.pdf