Condition monitoring of induction motor with a case study

Condition Monitoring of Induction Motor with A Case Study, Pravin P. Joshi, M.R.Bachwad,
Journal Impact Factor (2015): 7.7385 (Calculated by GISI) www.jifactor.com
www.iaeme.com/ijeet.asp 10 editor@iaeme.com
1,2
Electrical Department, Govt. College Engineering, Aurangabad, Maharashtra, India
ABSTRACT
This Paper discuss about latest development on condition monitoring of induction motor like
motor current signature analysis(MCSA), Vibration analysis, shaft voltage measurement as well as it
also focus on traditional method like temperature measurement analysis. Both methods provide
status of motor for condition maintenance. It also discusses each method merits and demerits. It also
analyzed data which we obtained during monitoring.
Keywords: Conditional Monitoring, Temperature Monitoring, Vibration Analysis, MCSA, Shaft
Voltage
I. INTRODUCTION
Condition monitoring means the continuous evaluation of the health of plant and equipment
throughout its serviceable life. Idea of planned shutdown can be possible due to introduction of
condition monitoring. Monitoring should be designed to pre-empt faults, whereas protection is
essentially retroactive. Condition monitoring can, in many cases, be extended to provide primary
protection, but its real function is always being to attempt to recognize the development of faults at
an early stage. Schedule Outages in the most convenient manner, resulting in lower down time and
lower Capitalized losses. Expenses occurred due to forced outage can be minimized by condition
monitoring. Continuous condition monitoring of certain critical items of plant can lead to Significant
benefits:-
• Greater plant efficiency,
• reduced capitalized losses due to breakdown,
• Reduced replacement costs [1]
In this paper condition monitoring done on following motor whose specification can be listed as-:
The design specifications of fans include:
Rating: 300 KW
Speed: 1,480 rpm
No of pole: 4 Pole
Rated Current: 33.8 Amps
Volts: 6600 V
CONDITION MONITORING OF INDUCTION MOTOR WITH A
CASE STUDY
Pravin P. Joshi1
, M.R.Bachwad2
Volume 6, Issue 6, June (2015), Pp. 10-15
Article ID: 40220150606002
International Journal of Electrical Engineering & Technology (IJEET)
© IAEME: www.iaeme.com/IJEET.asp
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
IJEET
© I A E M E

II. TEMPERTURE MONITORING
In this type of monitoring temperature received from various location like winding
temperature ,motor bearing temperature(driving & non driving) , fan bearing temperature (driving
and non driving ). This measurement can be done by local temperature gauge or RTD (pt-100 or Cu-
53) or thermocouple (J, K, R, S type). It can also do by IR type temperature gun or modern thermal
image camera. Since temperature measurement is continuous process, we can put alarm and tripping
at particular setting with the help of temperature switch.
During condition monitoring we identified hotspot zone of motor. If winding temperature
maintains on higher side it gives indication of motor insulation degrading and insufficient motor
cooling method. By improving cooling method condition does not improve it clearly suggestion
regarding motor insulation. As per condition we decide to change motor cooling methods. Similarly
if we found bearing temperature maintain on higher side first check bearing cooling arrangement
then check alignment and improper coupling. With the help of simple observation of temperature
reading we can conclude healthiness of motor. Hence temperature monitoring is essential and
primary step of condition monitoring. [3]
Table1:-Bearing temperature
Table2:-Winding temperature
Day1 Day2 Day3
SLOT1 41 43 42
SLOT2 41 44 42
SLOT3 42 43 42
SLOT4 42 43 42
III VIBRATION MONITORIONG
The most commonly used method for rotating machine is called as vibration analysis.
Various instruments are available to measure vibration. Measurement can be taken on machine
bearing casing with accelerometers to measure casing vibration. Eddy current transducer provides
radial displacement of the shaft. The coordination between vibration analysis and other maintenance
technologies can extend the life of the equipment and minimize the maintenance cost. [2]
Vibrations reading have been taken on two instruments namely CSI 2120 & CSI2130. All
data collected from the CSI 2120/2130 machinery health analyzer can be transferred to the AMS
suite: Machinery health manager application for final analysis, trending, comparison with results
from other diagnostic technologies, decisive problem diagnosis, and implementation of corrective
actions.
Day1 Day2 Day3
MOTOR DRIVING 39 40 40
MOTOR.NON DRIVING 40 40 40
FAN DRIVING 43 42 43
FAN NON DRIVING 42 43 43

Fig 1:- motor inboard vertical vibration
Most vibration analysis instrument today utilizes a Fast Fourier Transform (FFT) which
converts the vibration signal from its Time domain representation into its equivalent frequency
domain. Frequency analysis tends to be most useful on machines that employ rolling bearing.
During condition monitoring we get various reading of vibration at its different location like
vertical rotor, horizontal rotor, shaft, by knowing its critical value (as per IEC standard), we can
easily understood its severity.
During detailed analysis (as its role of condition monitoring engineer), we observed vibration
spectrum and finding peaks in it. By observations we can conclude following result-
-1X RPM - Balance; Alignment; Resonance - the turning speed vibration of a system
indicates a multitude of inherent vibration situations, this finding must be followed by further
analysis. Turning speed vibration is usually indicative of misalignment, unbalance, or numerous
other problems.
-2X RPM - Alignment; Looseness -. This is usually indicative of coupling misalignment or
system looseness (i.e. bearing, coupling, etc.). It should be noted that this vibration is acceptable for
operating conditions and the last reading indicates levels well below the alert limits.
-Sync (3X-8X) - Looseness; Excessive bearing clearances -. This is usually indicative of
looseness (i.e. bearing, coupling, shaft, etc) or excessive clearances within the bearings.
-NonSynch (1X-8X) - Looseness; Cavitations; Belt; Bearing - This is usually indicative of
looseness of the bearing or coupling.
-NonSynch (>8X) - Cavitations; Driven component; Bearing -This is probably indicating
vibration seen from the system, which has numerous frequencies, bearing frequencies, and flow
frequencies.
-2X Line frequency (120Hz) – Stator eccentricity; Soft foot; Electrical vibration -. This is
usually indicative of electrical or motor anomalies within the system [4]
III MOTOR CUURENT SIGNATURE ANALYSIS (MCSA)
This technique is been now widely used. This technology enables the testing of operating
equipment to identify rotor bar analysis and high resistance joints problem. As a preventive
maintenance tool, MCSA can be used to perform one time test or periodic testing to track and trend
motor performance. MCSA allows for remote non intrusive testing of the testing of the equipment
being monitored. This test analyzes the current waveform using complex mathematics. This
technique of evaluating motor condition by performing an FFT of the motor current has been
verified.
Route Waveform
02-Apr-15 15:20:37
RMS = .0625
PK(+/-) = .1820/.2016
CRESTF= 3.23
0 1 2 3 4 5
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
Revolution Number
Acceleration in G-s
Motor Inboard Vertical
Route Spectrum
02-Apr-15 15:20:37
OVERALL= 1.00 V-DG
PK = .9975
LOAD = 100.0
RPM = 1479. (24.65 Hz)
0 20000 40000 60000
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Frequency in CPM
PK Velocity in mm/Sec
Freq:
Ordr:
Spec:
1479.3
1.000
.589

In order to perform this test motor must be at 75-100% load. the closer to 100% full load ,the
better the test will be. with portable data collector and in route mode or analyzer mode. Data is
collected using clamp and spectrum display of CSI motor view RBMware module [7]
Fig 2:- rotor current spectrum
Table 3:-spectrum data
When one is trying to make a decision on whether or not he should continue to operate
critical motors, he now has a tool in addition to vibration analysis with which he can not only
confirm the presence of problems, but also assess their severity. Purely mechanical problems can
cause a motor to appear to have significant electrical problems when being evaluated by either motor
current or vibration analysis of given data
III.I)Let’s first examine line frequency(LF), number of pole (NP) and two times line frequency
(2FL) as it shows close side of an eccentric rotor will first be attracted to the north, and then to the
south pole, at each pole, the force itself will vary at 2 X the frequency of the magnetic field relative
to the eccentricity. It is important to have a high resolution in the spectral analysis in order to allow
one to separate electrical from mechanical problems. We must be able to separate 2FL from motor
running speed harmonics. s. The reason for this is to distinguish the pole pass frequency. Pole pass
frequency (Fp) is determined by slip frequency times the number of poles.
III.II) One indication of a problem with the stator is a simple current unbalance greater than 3%.
Combination of two tests (vibration program and current signature analysis) is used to confirm and
verify motor problems. A good idea when testing a high voltage motor is to stop the motor when
taking a vibration analysis to see if the vibration immediately diminishes. This would indicate either
electrical problems or a slow amplitude decrease that indicates nothing but a pure vibration problem.
III.III). If there is a fault in the rotor circuit, then the spectrum will have two prominent features
when displayed with the ‘Y’ axis as a logarithmic function. At the 50 Hz line frequency, there will
be a large spike. To the left at a distance equal to the rotor slip times the number of poles (Fp, the
pole-pass frequency) there will be another spike of energy. These spikes can be labeled ‘A’ and ‘B,
respectively. The amplitudes will have to be obtained from the software display because it is
SPECTRUM COMPARE
RPM 1484
%LOAD 74%
Amps 21.1
LF - NPxSF 49.06 Hz
SLIP 207
0
10
20
30
40
50
60
70
Frequency in Hz
dB Amps
Freq:
Ordr:
Spec:
49.88
2.017
60.00

necessary to use amplitudes accurate to four decimal places. . To determine the condition, perform
the following calculation:
Log (A/B) times (65)
• 54-60 dB = Excellent
• 48-54 dB = Good
• 42-48 dB = Moderate
• 36-42 dB = Cracked rotor bars or other source of high resistance.
• 30-36 dB = Multiple sources of high resistance.
• < 30 dB = Severe damage [5]
Table 4:- Result data of MCSA
IV. SHAFT VOLTAGE MONITORING
"Shaft current can flow in rotating machinery as a consequence of electromagnetically
developed voltages in the shaft or frame'’. These shaft currents are produced by circulating currents
which transfer through the motor bearings in order to complete a shaft-to-frame loop.
According to Costello, the four potential sources of shaft current in motors are (1)
electromagnetic, (2) electrostatic, (3) external voltages supplied to the rotor windings, and (4)
magnetic dis- symmetries in electrical windings.
Regardless of the source, shaft current can be easily measured. A measurement is made by
connecting a shaft brush between the shaft near a bearing and the frame with a short piece of low
resistance conductor [5]. To measure the current, a I ohm resistor should be placed in series with the
brush and conductor cable.
According to IEC-34-12 shaft voltage may not exceed 500 mV. But No specific guidelines as
to thresholds levels are available. IEEE standard 112-1991 [5] recommends measuring peak voltage
which is equivalent to the dc offset plus the peak amplitude of line frequency. However, the standard
does not suggest any maximum values. Shaft currents are undesirable, allowable shaft current
amplitudes should be low. Some experts recommend that both the dc component and the line
frequency component be below 3-5 mA. Whenever, shaft currents are present, the source of
circulating currents should be determined [3] Techniques used to minimize this problem include:
insulation, alternate discharge paths, Faraday shield [6]
Table 5:- Shaft voltage reading
Date DAY1 DAY2 DAY3 DAY4
Reading 5Mv 5mV 6mV 5mV
V. CONCLUSION
Different technique available for condition monitoring provides various data to diagnosis
healthiness of motor. By knowing different parameter preventive maintenance scheduled can be
planned. This paper has focused all aspect to monitoring right from data acquisition, data analysis
and conclusion. During temperature monitoring we found the all temperature is in limit. Motor has
better insulation and cooling. While during vibration analysis all vibration are in limit. While MCSA
SPECTRUM
(dB)
LF - NPxSF
AMLITUDE
LINE
FREQ
AMP
CALC
DELTA
ADJUSTED
DELTA
ESTIMATED
BROKEN BAR
Percent
Current
Unbalance
Comparison 7.94 60.00 52.06 50.53 0.9 13%

we found that motor is being in healthy condition. Shaft voltage parameters indicate it has good
grounding and shielded cable. Still various technique available for condition monitoring but it will
beyond scope of this paper. Condition monitoring is emerging tool and it is becoming asset of
today’s engineering field.
VII.FUTURE SCOPE
Condition monitoring is emerging topic, as new development and technique always in
progress. Stator flux monitoring is also developing topic. Now we are using various methods for
condition monitoring .Latest development taking place in composite module for complete
assessment of motor module. It may possibility that some of methods will become regular exercise to
monitoring data rather than conditional.
VIII. REFERENCES
1. Condition monitoring of rotating electrical machine by peter tanver, pp.68–73
2. Wikipedia condition monitoring
3. Proactive Motor Monitoring- S.V.Bowers, W.A.Davis, K.R.Piety
4. Diagnostic Vibration Analysis on Two-Pole Motor Following Multiple Rotor Problems- Amy
Wathen, Ray Saxton
5. http://www.lselectric.com/motor-current-signature-analysis-2/
6. Wikipedia shaft voltage
7. CSI machine health analyzer motor view module
8. Raichel Mathew and Aswathy Mohandas P, “A Bridgeless CUK Converter Based Induction
Motor Drive For PFC Applications” International Journal of Electrical Engineering &
Technology (IJEET), Volume 5, Issue 12, 2014, pp. 191 - 196, ISSN Print : 0976-6545, ISSN
Online: 0976-6553.
9. Santosh D. Gadekar and A. A. Bhole, “A New Boost Regulator Based Induction Motor Drive”
International Journal of Electrical Engineering & Technology (IJEET), Volume 6, Issue 5,
2015, pp. 1 - 7, ISSN Print : 0976-6545, ISSN Online: 0976-6553.
10. Diviya Radhakrishnan and Reshma P S, “An Enhanced Controller For Shunt Active Filter In
Soft Starting of Induction Motor” International Journal of Electrical Engineering &
Technology (IJEET), Volume 5, Issue 12, 2014, pp. 149 - 155, ISSN Print : 0976-6545, ISSN
Online: 0976-6553.

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