Monitoring System Of Transformer Engineering Essay

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Transformers have a long service life if they are operated at its full load conditions. However, their life is significantly reduced if they are overloaded, resulting in unexpected failures and loss of supply to a large number of customers thus effecting system reliability. Overloading and ineffective cooling of transformers are the major causes of failure in distribution transformers. Transformer follows Bath-curve relation type curve (Fig no. 1) for taking place fault in it.

FIG. NO 1

BATH -CURVE

The first phase indicates fault occurring due to improper service handling of transformer because it is new, second phase indicates fault occurring constantly and third phase fault are due aging problems. [5]

Online monitoring of key operational parameters of transformers can provide useful information about the health of transformers which will help the utilities to optimally use their transformers and keep transformer in operation for a longer period. This will also help identify problems before any sudden failure which can result in a significant cost savings and greater reliability. There are various fault occurred in transformer which causes damaged to the transformer if they are not diagnosed at quick time. It is thus important to monitor transformer continuously. Online monitoring is the solution for continuously observing the health of transformer. With the advancement in technology various technique are used for monitoring continuously the transformer. The global system for mobile communication (GSM) is the best among them.

II.FAULTS IN TRANSFORMER

1) Overvoltage : When the voltage in a circuit or part of it is raised above its upper limit, this is known as overvoltage. The conditions may be hazardous. Depending on its duration, the overvoltage event can be transient a voltage spike or per manent, leading to a power surge . Electronic and electrical devices are designed to operate at a certain maximum supply voltage, and considerable damage can be caused by voltage that is higher than that for which the devices are rated.Due to this Overvoltage there may be Mal-operation of Circuit -Breaker or other accessories can be take place and hence Power system may get collapse.Thus monitoring of such faults becomes necessary .

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2) Single phasing : Single phasing is an unwanted condition where one phase in a three-phase power system is missing, due to a tripped breaker or other condition. With just two lines hot, there is no phase rotation and thus the power delivered to the load is single-phase. This is very bad for most three-phase loads with reduced power and continuously drawing current.

3) Temperature : Hot spot of the winding is the maximum limit of the load capability. Previously the hot spot is calculated by knowing the measurement of oil temperature and of load of current. Abnormal temperature readings almost always indicate some type of failure in a transformer. For this reason, it has become common practice to monitor the hot spot, main tank, and bottom tank temperatures on the shell of a transformer.

4)Moisture :The presence of water in the oil can lead to reduction in the dielectric strength of transformer oil also ageing of oil is also affected .Thus all this can lead to electrical breakdown of transformer oil. This is very critical situation therefore continuous monitoring of operation is required to protect transformer from all of this.

5) Gas in Oil Analysis: The two principal causes of gas formation within an operating transformer are electrical disturbances and thermal decomposition especially in Oil. During the natural aging process of the oil and insulating parts, especially in the case of thermal or electrical failures, cracked gases form, and are dissolved in the oil. The rate of decomposition and the type of gases evolved during operation; result in thermal overloading and electrical faults. Thus analysis of gas in oil is important for protect the Transformer against such fault. Dissolved Gas Analysis is one method by which different gases can be finding out in transformer oil. The gases forms like Hydrogen (H2), Methane (CH4), Acetylene (C2H2), Ethylene (C2H4), and Ethane (C2H6). Further, when cellulose insulation is involved, thermal decomposition or electric faults produce Carbon monoxide (CO), and Carbon dioxide (CO2). Following table shows the various fault can be occurred because of gases formation in oil. [9]

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TABLE NO. 1

Different Types of Fault Occur

Fault Type

Gases Responsible

Corona

Hydrogen , Acetylene

Insulator Effect

Carbon Monoxide, Carbon Dioxide

Arc Formation

Acetylene and Hydrogen

Sparking

Methane and Ethane

Overheating

Methane and Ethylene

Method of Dissolved Gas Analysis:

Traditionally Dissolved Gas Analysis has been carried out by taking a sample of oil from the transformer, sending it to a laboratory and waiting for the results. Unless there was any suspicion of a problem in the transformer, samples might be taken at intervals of up to 1 year, depending on the maintenance report of the operator. This means that a fault that develops over a shorter period of time then the sampling interval can be missed, leading to possible catastrophic failure of the transformer . Manual sampling can also lead to errors in the analysis. Results can vary from laboratory to laboratory, and even between users of the same equipment Units.

Now therefore it is important to monitor such DGA analysis online. Online monitoring not only automized system but also reduced the manual mistakes. Continuous online monitoring helps to keep record of transformer health at every instant .By monitoring and record key operation of transformer is not only thing to be considered but it is necessary .[ 12 ]

6) Vibration: Transformer vibration (and consequently noise) is caused by the magnetostriction of the core laminates (the extension and contraction of the core lamination. Under alternating fluxes, this extension and contraction takes place twice during a normal voltage or current cycle .This means that transformer is vibrating twice of the frequency of supply resulting in vibration to occur mainly at 120 Hz. This vibration level depends on the transformer construction and design. Vibration level shall increased by through fault current, phase to ground or phase to phase fault. Thus monitoring is necessary for any kind of vibration in the Transformer.

III.GLOBAL SYSTEM FOR MOBILE COMMUNICATION

Above fault identification techniques can be useful for identify various fault ,but it is always be helpful to have a continuous operation of transformer health because it causes least disturbance to the Transformer .Thus we proposed one method called as Global System for Mobile communication ( GSM ) helps to record operation of transformer and convey its data continuously to the operator by sending massage regarding transformer health .Previously SCADA system are used to monitor and record such key operation of transformer but since this system is complex and it is expensive to use .Thus GSM is the best alternative to it .Further the network of GSM technology is wider than other network hence it is flexible to use . [3]

IV.DESCRIPTION OF METHODOLOGY

The proposed on-line monitoring system consists of Global Service Mobile (GSM) Modem, with chip microcontroller and different sensor. It is installed at the transformer site and the finding parameters recorded using the analog to digital converter (ADC) of the embedded system. The acquired parameters are processed and recorded in the system memory. If there is any abnormality or an emergency situation the system sends SMS (Short Message Service) messages to designated mobile telephones containing information about the abnormality. Also, it sends SMS to a central database via the GSM modem for further processing. This mobile system will help the system to run under reliable condition and identify problems before any failure.

V.BLOCK DIAGRAM

The block diagram of proposed model is as follows. [11]

VI . Ways of detecting various faults for online monitoring of Transformer

1) Measurement of Over-voltage : To measure overvoltage we used step down transformer in our project. The transformer connect across the phase and neutral of each phases (R, Y, B), which step down voltage from 300v AC (max) to 5 volt AC, further

This voltage will be converted to DC by means of rectifier and give it to the input of ADC, the ADC will convert this signals in equivalent digital signals and give it to microcontroller. Further microcontroller compares these digital signals with the settled overvoltage (250v) and under voltage (180v) If the signals is greater than 250 volt and less than 180volt then the microcontroller trips the contactor. If in case of phase failure the microcontroller treat this fault as a under voltage because if any phase is not available that means the voltage is less than 180 v (0 volt is less than 180 volt) in this case also microcontroller trips the contactor.

2) Single Phasing : Single phasing can be prevented by using single phasing preventer. Single phasing preventer is an electronic circuit which prevents the three phase electronic operated electrical machines from single phase cut off, phase reversal and phase imbalance .

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3) Temperature Monitoring: In order to make on-line monitoring possible, thermocouples are placed externally on the transformer and provide real-time data on the temperature at various locations on the transformer. High main tank temperatures have been known to indicate oil deterioration, insulation degradation, and water formation.

4) Moisture: Online monitoring can be used to improve the accuracy of Oil .Moisture sensors available can easily detect the presence of any moisture.

5) DGA Analysis: Nowadays DGA usually consists of three steps:

i) Sampling of oil in an airtight glass tube made up of borosilicate of capacity 150 ml to 250 ml.

ii) The DGA technique involves extracting or stripping the gases from the oil and injecting them into a gas chromatograph (GC). Detection of gas concentrations usually involves the use of a flame ionization detector (FID) and a thermal conductivity detector (TCD). Most systems also employ a methanizer, which converts any carbon monoxide

And carbon dioxide present into methane so that it can be burned and detected on the FID, a very sensitive sensor.

iii) The separated gases are detected by thermal conductivity detector for atmospheric gases, by flame ionization detector for hydrocarbons and oxides of carbon.

Following fig no. 3 [13] shows the Gas Chromatography technique:

FIG. NO 3

Thus at present, gas chromatography is the main method which can achieve the fault diagnosis by the on-line monitoring to the dissolved gases in the transformer oil.

But it has many disadvantages, such as the aging, Pollution and saturation of chromatogram columns and it takes a long time consuming much carrier gases during the monitoring process. Concerning these disadvantages, on-line monitoring to the groups of dissolved gases through the gas sensor array is suggested. [7]

VII. Conclusion

Due to daily increased load of power system it is important to maintain system Reliability .As transformer plays important role in power system by maintaining reliability it is important that we should keep transformer from daily fault occurring in it just by observing its key parameter so that such fault cannot result in bigger failure also apart from these sharing of data information is also essential using new technology at reduced cost . System to expert systems can be used to achieve all the parameters test and analysis of automation every system is automated in order to face new challenges in the present day situation. Automated systems have less manual operations, so that the flexibility, reliabilities are high and accurate. Hence every field prefers automated control systems. Especially in the field of electronics automated systems are doing better performance. [10]

VIII. References

[1] Guiyin Yu, and Lu Zhang, " Application of Electrical Transformer Online Monitoring System '' International Conference on Intelligent Control and Information Processing August 13-15, 2010 - Dalian, China

[2] Abdul-Rahman AI-Ali, Abdul Khaliq & Muhammad Arshad, "GSM-Based Distribution Transformer Monitoring System" Dubrovnik, Croatia IEEE MELECON 2004, May 12-15, 2004

[3] Constantin Daniel Oancea, Member, IEEE GSM Infrastructure Used for Data Transmission' The 7 th international symposium on advanced topicin electrical engineering, Bucarest May 11-14 2011

[4] Fagarasan, Sorina Costina, Sergiu St. ILIESCU3, " Monitoring and Diagnosis Methods for High voltage power Transformer " U.P.B. Sci. Bull., Series C, Vol. 70, No. 3, 2008

[5] Cbengtsson ABB Transformers AB Ludvh, Sweden,"Status and Trends in Transformer Monitoring"IEEE Transactions on Power Delivery, Vol.11, No. 3, July 1996

[6] J.C. Burgos , E. Pagan , B. Garcia ," Experiences in Managing Transformers through Maintenance Operations and Monitoring Systems 21, rue d'Artois, F-75008 Paris http://www.cigre.org,May 2004[7] Lynn Hamrick ESCO Energy Services,"Dissolved Gas Analysis for Transformers Winter 2009-2010 NETA WORLD

[8] A. Kingsmill S. Jones Application of new condition Monitoring Technologies in the Electricity Transmission Industry, Transgrid University of Australia

[9] Fredi Jacob "Dissolved Gas Analysis, Past Present Future ACTI Inc. - Jan 21, 2003.

[10] Brian D Sparling, Jacques Aubin,"Power Transformer life extension through better monitoring

[11] A review by Vidhata Technologies

[12]Sherif S.M.Ghoneim,"Advances in electrical Engineering sy stem , Volume 1 2012, ISSN 2167-633

[13] Online transformer monitor site preparation guide ,Model T M Series ,August 27 2008