A Vibration Based Condition Monitoring Systemfor Power Transformers

He Ting-ting, Wang Jing-di, Guo Jie, Huang Hai, Chen Xiang-xianand Pan JieDepartment of Instrumentation Science and Engineering,Zhejiang University,Hangzhou,310027,China

School of Mechanical Engineering,The University of Western Australia, Western Australia 6009, Australia

AbstractThis paper is concerned with the design and devel-opment of an on-line condition monitoring system for large powertransformers utilizing signals such as transformer vibration,voltages, currents, temperature and state of switches. The systemconsists of two parts which communicate each other via Ethernetor series port. The formal is a front-end computer subsystem usedfor data acquisition and processing, and the latter is a remotecomputer subsystem for analyzing and monitoring transformersoperating conditions. It provides a reliable real-time serviceto power industry by integrating the transformers electricalproperties with the mechanical properties for detecting potentialproblems in power transformers. The developed system hasbecame useful platform for an on-going project on the conditionmonitoring and fault diagnosis for large power transformers.

Keywordsvibration method; condition monitoring; powertransformer

I. INTRODUCTIONPower transformers are one of the most expensive and

critical assets in power system. The safe operation of powernetwork relies on the reliability of power transformers. Fail-ures in power transformers can lead to interruptions in electricsupply and carry great costs [1]. The condition monitoringand fault diagnosis techniques have been used to detecttransformers abnormity and faults. They can not only preventthe occurrence of unexpected incidents, but also performthe condition maintenance instead of regular maintenance toprolong transformers life and reduce operating costs greatly.

Compared with oil chromatographic analysis method, vi-bration technique has demonstrated potential to detect trans-formers mechanical fault such as displacement, deformation,looseness or abrasion of core, winding and OLTC (on load tapchanger). Further more, the technique can be applied withoutinterfering the normal operation of transformers [2] [3].

According to the recent literatures, the existing on-linecondition monitoring and fault diagnosis systems have somelimitations [2]. They were mainly used for experimental stud-ies, not suitable for practical applications. Also only vibrationsignals were monitored while other parameters which affecttransformer vibration were ignored (i.e. voltages, currents,temperature, switch-on or off of air fans and pumps). There isalso a lack of study of the general properties of transformervibration in relation to the transformer fatigue and failures.

To effectively implement the practical application and fun-damental research in the field of transformer condition moni-toring, using the advanced embedded system technology andcommunication network technology, this paper proposes a

Large power transformer

Vibration sensors

Voltage, current transducers

Temperature sensors

Digital sensors

The front-end data acquisition subsystem

The remote computer subsystem with the function software

Ethernet RS-232

1 temperature signal

8 switch signals

4 voltage signals

4 current signals

4 vibration signals

Fig. 1. architecture of TCMS

vibration-based multi-parameter (including transformer volt-ages, currents, temperature and switches) power transformercondition monitoring system [4].

II. SYSTEM ARCHITECTUREThe target of this system is to judge power transformers

condition by monitoring and analyzing its vibration.Takinginto account the affects of transformer voltages, currents,temperature, air fans and oil pumps on vibration signals,the system will monitor all these signals simultaneously toimprove its effectiveness and accuracy.

Based on these demands, the architecture of desired Trans-former Condition Monitoring System (TCMS) is depicted inFig.1. TCMS includes the front-end subsystem and the remotecomputer with functional software. The front-end subsystemcan be installed near the transformer to carry out the tasksof sampling, processing, displaying and storage of all signals.The functional software in the remote computer communicateswith the front-end subsystem through Ethernet or serial inter-face and performs displaying, analyzing, storage, managementof signals and parameter setting of the whole system. The twosubsystems are developed on different platforms. They can beexecuted in a distributed environment and possible changesmade in one of them do not affect the others.

III. FRONT-END SUBSYSTEMThe front-end subsystem carries out data sampling, pro-

cessing, displaying, storage and communicating with remotecomputer. It is designed based on embedded system architec-ture employing embedded computer and embedded operating

978-1-4244-2487-0/09/$25.00 2009 IEEE

system. The main components include sensors, conditioningcircuits, A/D module, CPU module, operating system, andapplication software. These elements are described more indepth below.

A. SensorsTCMS uses 21 external sensors: 13 analog and 8 digital.There are four ICP piezoelectric accelerometers for vi-

bration measurement, the sensitivity and supply voltage ofwhich are 500 MV/g and 24V respectively. Three of them arepositioned on transformers oil tank, just under each phasewhere core and winding vibration can be most effectivelydetected [5]. Another one is used to capture OLTCs vibrationsignal.

Four current sensors and four voltage sensors are used tomonitor currents and voltages. For both voltages and currents,three sensors are positioned on the high-voltage side or low-voltage side of the A, B, C phase (Generally, voltage ismeasured in high-voltage side, current is measured in low-voltage side), another may be positioned on the other side ofa phase.

The temperature signal is captured by one PT100 sensorwhich has a temperature coefficient = 0.00392oC1 . Thisone is used for measuring the temperature of the coolantoil such that its influence on vibration can be analyzed andprocessed.

Finally, the eight digital sensors monitor the status of theoil pump, air fans and OLTC of the power transformer. Thesesensors are relay contacts that show the ON or OFF status ofthe aforementioned elements.

B. Conditioning circuitBefore sampling, outputs of the sensors need to be condi-

tioned. The function of the circuits used to adjust accelerationsignal includes ICP sensors power supply, vibration signalsisolation, amplification, 50Hz trap filtering and anti-aliasingfiltering. The conditioning circuit for voltage and currenttransducer outputs which should be converted to 1-5 V or4-20 mA standard signal by voltage and current Hall sensorsfirst performs current / voltage conversion (for current signal),signal anti-aliasing filtering and amplification to suit the A/D module input range. Temperature signal is modulated byPT100 sensors typical conditioning module. Switch signalsare isolated from conditioning circuit and converted to TTLlevel signals by using optocouplers.

C. Acquisition module (A/D module)The data-acquisition card used is a PCM-3718H module

from Advantech Company and has the following characteris-tics: 100 KHz for DMA mode, 16 analog input channels, 12bits resolution, 2 eight bits digital input/output channels.D. CPU module

Since TCMS front-end subsystem is installed near the fieldtransformers and requires high reliability, the hardware core isbased on PC/104 module up to industrial standard and CPUmodule is PCM-3350 based on X86 architecture.

E. SoftwareConsidering the requirement for real-time ability, the front-

end subsystem is developed using Windows CE operatingsystem and the Visual C++ programming environment. Itis a multithread application where three threads are beingexecuted concurrently (Fig 2). Sampling thread performs thesampling, processing and storage of all signals. For all theanalog sensors, 4000 samples are acquired with a samplingrate of 4000 Hz and the interval between two acquisitionsis 10 seconds. In order to get the current conditions ofin-service transformers, the measurements are divided intotwo groups: dynamic and static. The dynamic one includesvibrations, voltages and currents real-time waveform. Thestatic one includes peak values, harmonic amplitudes from 100to 800 Hz (vibration), RMS values (vibration, current, voltageand temperature) and switch values. The program interfacedisplays the results of sampling process, in which a set ofbar chart is designed to show static datas real-time change.Along with 10 seconds cycle of sampling and data updates, themain thread updates the corresponding values, so transformerscurrent state can be monitored intuitively. Communicationthread is responsible for receiving and transmitting data (allmeasurements and parameter setting) with remote subsystemand has been divided into two parts for serial port and networkrespectively.

IV. REMOTE SUBSYSTEMThe remote subsystem performs analysis and management

of data from front-end subsystem and parameters setting forthe whole system. After packing needed parameters into arequest frame according to a specified protocol, the remotesubsystem initiates a communication with the front-end sub-system. Then, the front-end subsystem responds to the requestby performing corresponding setting or just returning thewanted data back. Finally, the remote subsystem performsvarious analysis and processing of the received data subjectto administrators requirement.

The functional software has been developed using Lab-VIEW graphic application development environment fromNational Instruments [6] [7]. Data analysis module analyzesinstantaneous data, real-time data, trend data and alarm data.Instantaneous data (vibration, voltage and current data sampledduring transformers transient process such as start-up andshut-down) is used to monitor the transient state of transform-ers while real-time data is used to monitor transformers stateduring continuous running. Trend analysis, including day trendand annual trend which was calculated from the real-time data,will show transformers state trend in one day and one year.When the real-time vibrations peak to peak value exceedsthreshold value three times, alarm will be triggered and detailof the incident will be recorded by front-end subsystem. Inaddition, raw and processed data can be stored and inquired.

V. TESTSTCMS has been tested on a 220KV power transformer

at a transformer substation of Ningbo. Vibration on high-

data sampling

vibration, voltage, current, temperature and switch signals

data processing

p-p values, RMS values , mean values , switch

values, harmonics

vibration p-p values exceed the threshold

3 times

alarm status recording, zero

alarm times

alarm data

reckoning of real-time trend

real-time trend points %30=0?

day trend calculation

one point value of

day trend

day trend points %12=0?

year trend calculation

one point value of

year trend

end

start

system initialization and startup

10 seconds past ?

start sampling

wait

update graphics

wait

communicate with the remote

computer?

select data type

send data

Yes

No

Yes

No

Yes

No

Yes

No

Yes

No

Sampling thread Main thread Communication thread

acquisition card initialization

Fig. 2. Three process running within the front-end subsystem

Fig. 3. vibration of A, B phase (LV)

Fig. 4. spectra of vibration in A, B phase, (LV)

voltage side, low-voltage side, air fans and oil pumps has beenmeasured.

The key results are summarized as follows:

Fig. 5. spectra of vibration in B phase, (LV)

Fig. 6. spectra of vibration in B phase, (HV)

1 Fig.3 shows vibration waveforms of A, B phase in low-voltage side and Fig4 shows their spectra. As we can see,core and windings fundamental frequency is 100Hz, and otherharmonics exist due to power harmonic and magnetostrictions

Fig. 7. spectra of vibration in C phase, (HV)

Fig. 8. spectra of vibration in A phase side, (HV)

nonlinearity [2].2 Comparison between Fig.5 and Fig.6 shows 100Hz,

200Hz and 300Hz harmonics in low-voltage side have greateramplitude which could be due to winding in lower-voltageside having more severe vibration.

3 For high-voltage side, vibration of the A phases sideis showed in Fig.8. As can been seen, the harmonic contentis very similar to the vibration of the B phase and C phase(Fig.6, Fig. 7) which has largest amplitude in 400Hz, thisphenomenon is caused by Transformer windings natural fre-quency which is always an important index to judge windingsdeformation [2] [5].

These data are very useful for further detection of trans-formers mechanical condition.The harmonic components re-veal the cause which leads to vibration and the amplitudesreveal core and windings mechnical condition such as dis-placement,deformation,looseness and abrasion.Further studyincluding modeling, signal separation and feature extractionwill benefit from the whole system for its accuracy andreliablity.

VI. CONCLUSION

We have designed and developed an on-line conditionmonitoring system for power transformers utilizing the vi-bration signals and other signals such as voltages, currents,temperature and switches status. Based on embedded systemarchitecture, the front-end subsystem establishes a real-timeand reliable interactive control and analysis environment using

communication and network technology. The functional soft-ware of the remote subsystem is designed based on LabVIEWplatform and realizes signal real-time analysis, trend analysis,instantaneous analysis, alarm analysis and data managementfor power transformer monitoring. The system was tested andused in laboratory and in the field. The results show that TCMSsatisfies the requirements of practical on-line monitoring forlarge power transformers and is also useful as a reliable systemplatform for the further work of condition monitoring and faultdiagnosis for power transformers.

ACKNOWLEDGMENTThe authors would like to thank all the project group

members for their hard work.This work was supported by the National High-tech

R&D Program (863 Program, China) through Grant No.2007AA04Z439 and the International Cooperation Project ofZhejiang Province (Grant No. 2008C24004).

REFERENCES[1] F. Poza, P. Marino, M. Ubeira, and F. Machado, Programmable electronic

instrument for condition monitoring of in service power transformers,Instrumentation and Measurement Technology Conference, 2004. IMTC04. Proceedings of the 21st IEEE, vol. 3, pp. 21262131, May 2004.

[2] B. Garcia, J. C. Burgos, and A. M. Alonso, Transformer tank vibrationmodeling as a method of detecting winding deformations - part i:Theoretical foundation, IEEE Transactions on Power Delivery, vol. 21,no. 1, pp. 157163, 2006.

[3] J. Shengchang, L. Yongfen, and L. Yanming, Research on extractiontechnique of transformer core fundamental frequency vibration based onolcm, Power Delivery, IEEE Transactions on, vol. 21, no. 4, pp. 19811988, Oct. 2006.

[4] M. Sanz-Bobi, A. Garcia-Cerrada, R. Palacios, J. Villar, J. Rolan, andB. Moran, Experiences learned from the on-line internal monitoring ofthe behaviour of a transformer, Electric Machines and Drives ConferenceRecord, 1997. IEEE International, pp. TC3/11.1TC3/11.3, May 1997.

[5] B. Garcia, J. C. Burgos, and A. M. Alonso, Transformer tank vibrationmodeling as a method of detecting winding deformations - part ii:Experimental verification, IEEE Transactions on Power Delivery, vol. 21,no. 1, pp. 164169, 2006.

[6] LabVIEW Measurements Manual, National Instruments, 2001.[7] LabVIEW User Manual, National Instruments, 2001.

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