VIbration of Electrical Problem

1. Vibration of Electrical Problem
Vibration Diagnostic for Industrial Electric Motor Drives
Aji Nur Sahid
(15/379029/TK/42971)
Arya Mahendra P
(15/379034/TK/42976)
Emmanuel Glodias Boggy Sanjaya
(15/379043/TK42985)
Dimas Jati Paggayuh
(15/379041/TK42983)
Kelas B
Anggota Kelompok :

2. Introduction
The fault detection and diagnosis is very important in system safety. The fault detection and diagnosis process has been
developed over the years and uses various techniques such as analytical approaches, knowledge-based systems
technique, etc. Different types of electrical motors are present in processes and equipments and are important and
decisive component. Induction motors are running in noisy environment and produces also noice. The vibration caused
by these leads to damages.
Monitoring and analyzing the vibration in different places of the motors the cause of the vibration can be discovered. It
is also important to disccover and solve these problems in time

3. What is?
By far the most widely employed electric motrol in industrial drives, is the induction motor and this application note
applies to this type of electric motor. Engineers should be able to relate some of the principles to synchronous motors
or generators etc. The vibration problems relating to this case (induction motor) are combination of two groups which
can be called “mechanical” and “magnetic” according how they arise.
To help determine which of two groups of vibration are present, the maintenance engineer can listen the beats. A beat
is identified as an oscillatory amplitude of vibration, due to closely spaced frequency components alternately
reinforcing then canceling each other.
The absence or the null of the beats may indicate there is the only a mechanical problem. Then, the presence of the
beats can indicate mechanical and magnetic problem.
More can be discovered about the problem by disconnecting the electric supply ( “a power trip test” ), this will
distinguish the mechanical and the magnetic component of vibration, since magnetic component will disappear
immediately after electrical power is removed. The effect of this method should be observed by changing amplitude of
the vibration on a spectrum analyzer

4. Types
1. Magnetic Vibration in Induction Motors
2. Mechanical Vibration in Induction Motors

5. Types
1. Magnetic Vibration in Induction Motors
The induction machine is shown in simplified form in Fig. 1. Current is produced in
the rotor onductors,which is proportional to the difference in speed between the
rotating field,produced by the current in the 3 phase Stator windings and the rotor
itself. This current Produces a Rotor field Which interacts With the stator field to
generate force on the rotor.
The field in the rotor rotates in synchronism with the rotating field in the stator; both
advance 2-pole pitches relative to the stator, for each cycle of line frequency, i.e. at
synchronous speed. The rotor of the induction motor does not rotate at synchronous
speed, but instead slips backwards through the rotating field. The rate of slip is the
difference between synchronous speed and rotor speed. Since synchronous speed
depends on the line frequency and the number of poles in the machine, it is conve-
nient to use the per-unit slip as defined in Fig. 1., and define slip frequency as per-
unit slip x line frequency. This definition of slip frequency applies to all motors
regardless ofthe number of poles. The slip frequency is the actual frequency of the
current in the rotor conductors, and the rotating fields advance relative to the rotor
by 2-pole pitches for each cycle of slip frequency. Motor torque is produced where
balanced forces exist on either side of the rotor. If the forces of attraction are not
balanced, then vibration results. Thiscan be related to current or air-gap variations in
induction motors.

6. Types
2. Mechanical Vibration in Induction Motors
A brief description of the 'mechanical‘ vibration problems resulting from faults
occurring on the rotating shaft is appropriate, since these problems are often
interdependent with 'magnetic' vibrations as described already. For a thorough
treatment of shaft and bearing vibrations.

7. Characteristics and Causes
1. Thermal bending of the rotor
Uneven electrical circuits in the rotor bars generates an uneven heat distribution in the rotor. This
causes a deformation, bending, of the rotor which results in unbalance.
2. Eccentricity in the air gap
If the air gap is not uniform it generaties unbalance forces on the rotor which in turn induce a
vibration at 120 Hz (2xLF).
3. Loose rotor
Sometimes the rotor skid on the axle, depending on the temperature. This generates a vibration
1xRPM and harmonics. Factors provoking this fenomenon are sudden changes in load or line
frequency.
4. Eccentric rotor
If the rotor is not entirely round this will cause vibrations at 1xRPM. It will also generate
unbalanced magnetic forces resulting in vibrations at a frequency corresponding to the slip
frequency multiplied with the number of poles.
5. Loose windings
If the stator windings are slightly loose the vibration level at 120 Hz will increase. This causes
scraped thread isolation which leads to short circuit between the windings. It can also be short
circuit between the windings and earth, which leads to stator breakdown.

8. Characteristics and Causes
6. Problem with rotor bars:
An important cause of problem in elctrical motors is that the rotor cracks. This mainly happens to
motors often exposed to starts with load. During start the current in the rotor bars become very
high as the speed of the rotor is much lower than the synchronous speed. The electric current
causes heated rotor bars, causing them to expand in relation to the rotor itself. The difference i
resistance between the rotor bars result in turn in uneven heating and uneven expansion. This
leads to cracks in the joint between the bars and the shortning rings. When a crack appears the
resistance in the bar increases, which in turn increases the heating and thereby enlarge the crack.
The current also becomes larger in the other rotor bars as the current has been reduced in the
broken bar.
7. Electrical motor problem
Electrical motors have the same mechanical faults that like other rotating machines, but there are
also some specific faults for electrical motors.

9. Spectrum
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).

10. Spectrum
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
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.

11. Spectrum
Narrow-band vibration components due to 'magnetic' &
'mechanical' problems, separately identified using 'zoom'
analysis

12. Journal Sources
• http://www.sciencedirect.com/science/article/pii/S 2212017315000791
• 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