The research paper published by IJSER journal is about Transformer Health Condition Monitoring Through GSM Technology 1

ISSN 2229-5518

Transformer Health Condition Monitoring Through

GSM Technology

Vadirajacharya.K, Ashish Kharche, Harish Kulakarni, Vivek Landage

Abstract—. Transformers are a vital part of the transmission and distribution system. Monitoring transformers for problems b efore they occur can pre- vent faults that are costly to repair and result in a loss of service. Current systems can provide information about the sta te of a transformer, but are either of- fline or very expensive to implement. Transformers being the essential part of power transmission system are expensive, as is the cost of power interru p- tions. Because of the cost of scheduled and unscheduled maintenance, especially at remote sites, the utility industry has beg un investing in instrumentation and monitoring of transformer. On-line transformer diagnostics using conventional technologies like carrier power line communication, Radio frequency based control system, and Supervisory control and data acquiring systems, Distributed control systems and Internet based communications are having their own limitations. GSM is an open, digital cellular technology used for transmitting mobile voice and data services.

This project objective is to develop low cost solution for monitoring health condition of remotely located distribution transformers using GSM technology to preent premature failure of distribution transformers and improving reliability of services to the customers. An Embedded bas ed hardware design is devel-

oped to acquire data from electrical sensing system. It consists of a sensing system, signal conditioning electronic circuits, advanced embedded hardware for middle level computing, a powerful computer network for further transmission of data to various places. A powerful GSM netwo rking is designed to send data from a network to other network for proper corrective action at the earliest. Any change in parameters of transmission is sensed to protect the entire transmission and distribution. The performance of prototype model developed is tested at laborato ry for monitoring various parameters like transformer over load, voltage fluctuations, over temperature, oil quality and level etc.

Index Terms. Power system faults, transformer health monitoring, GSM technology, micro controller

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1 INTRODUCTION

n recent years, increased emphasis has been placed on power reliability and economy. In particular, major changes in the utility industry have caused increased interest in more econom- ical and reliable methods to generate and transmit and distribute electric power. In this regard monitoring the health of equipment constituting the system is critical to assure that the supply of power can meet the demand. As has been seen recently in northern grid failure on 30th and 31st July 2012 due to inefficient load management functions lead to wider blackout, leaving al- most 700 million people without electricity in six northern states
of our country.
The main concern with transformer protection is protecting the transformer against internal faults and ensuring security of the protection scheme for external faults[2]. System conditions that indirectly affect transformers often receive less emphasis when transformer protection is specified. Overloading power trans- formers beyond the nameplate rating can cause a rise in tempera- ture of both transformer oil and windings. If the winding temper- ature rise exceeds the transformer limits, the insulation will dete- riorate and may fail prematurely. Prolonged thermal heating weakens the insulation over time, resulting in accelerated trans- former loss-of-life. Power system faults external to the trans- former zone can cause high levels of current flowing through the transformer. Through-fault currents create forces within the trans- former that can eventually weaken the winding integrity. A com- prehensive transformer protection scheme needs to include pro- tection against transformer overload, through-fault, and over ex- citation, as well as protection for internal faults.

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Vadirajacharya.K. is working as Associate Professor in Electical Engg
Ashish Kharche, Harish Kulakarni,& Vivek Landag students of Final year

B.Tech. Electrical Engg at Electrical Engineering Dept , Dr.Babasaheb

Ambedkar Technological University, Lonere, Raigad , Mharastra,India

This paper focuses on liquid-immersed transformers because the majority of medium and high-voltage transformers are of this type.Transformer fault analysis is discussed in section-II, while section III describes about designing of microcontroller for moni- toring of transformer health. The prototype model development is discussed in section IV. While programme execution and testing is discussed in section V.

2 TRANSFORMER FAULT ANLYIS

A power transformer consists of a set of windings around a mag- netic core. The windings are insulated from each other and the core. Operational stresses can cause failure of the transformer winding, insulation, and core. The power transformer windings and magnetic core are subject to a number of different forces during operation:[3]
1. Expansion and contraction caused by thermal cycling
2. Vibration caused by flux in the core changing direction
3. Localized heating caused by eddy currents in parts of the wind- ing, induced by magnetic flux
4. Impact forces caused by fault currents.
5. Thermal heating caused by overloading.
These operating limits only considered the thermal effects of transformer overload. Later, the capability limit was changed to include the mechanical effect of higher fault currents through the transformer. Power transformer faults produce physical forces that cause insulation wear. These effects are cumulative and should be considered over the life of the transformer.[2]. The following discussion highlights on different capability limits of transformer

2.1 Over Load

Over current is the current flowing through the transformer re- sulting from faults on the power system. Fault currents that do not include ground are generally in excess of four times full-load

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The research paper published by IJSER journal is about Transformer Health Condition Monitoring Through GSM Technology 2

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current; fault currents that include ground can be below the full- load current depending on the system grounding method. Over current conditions are typically short in duration (less than two seconds) because protection relays usually operate to isolate the faults from the power system. Overload, by contrast, is current drawn by load, a load current in excess of the transformer name- plate rating. In summary, loading large power transformers be- yond nameplate ratings can result in reduced dielectric integrity, thermal runaway condition (extreme case) of the contacts of the tap changer, and reduced mechanical strength in insulation of conductors and the transformer structure. Three factors, namely water, oxygen, and heat, determine the insulation life of a trans- former. Filters and other oil preservation systems control the wa- ter and oxygen content in the insulation, but heat is essentially a function of the ambient temperature and the load current. Current increases the hottest-spot temperature (and the oil temperature), and thereby decreases the insulation life span.[2]

2.2 Over Temeperature

Excessive load current alone may not result in damage to the transformer if the absolute temperature of the windings and transformer oil remains within specified limits. Transformer ratings are based on a 24-hour average ambient temperature of
30°C (86°F). Due to over voltage and over current, temp. of oil increases which causes failure of insulation of transformer wind- ing.[2]

2.3 Over Exicitation

The flux in the transformer core is directly proportional to the applied voltage and inversely proportional to the frequency. Over excitation can occur when the per-unit ratio of voltage to fre- quency (Volts/Hz) exceeds 1.05 p.u. at full load and 1.10 p.u. at no load. An increase in transformer terminal voltage or a decrease in frequency will result in an increase in the flux. Over excitation results in excess flux, which causes transformer heating and in- creases exciting current, noise, and vibration.[2]

2.4 Oil Level Fault

Oil mainly used in transformer for two purposes one is for cool- ing of transformer and another use is for insulation purpose. When temperature of transformer goes high, oil level in trans- former tank decreases due to heating effect. For normal operation of transformer oil level should maintain at required level. If oil level decreases beyond required level, it affect cooling and insu- lation of the transformer.

3 DESIGN OF MICROCONTROLLER BASED TRANSFORMER HEALTH CONDITION MONITORING KIT

fig.1. It consist of current transformer, power transformer, ther- mister, oil sensor, micro-controller (89S51), converter (ADC0808), LCD display, GSM modem and relay. Normally in transformer, failure occurs due to voltage and current fluctuation, overheating, change in oil level etc. In this project, to sense these fault we have used current and power transformer, temperature sensor, oil sensor respectively.
Fig.1. Basic block diagram.
All these sensors are connected to converter (ADC0808) and dig- ital output from converter is given to micro-controller 89S51. MC89S51 has four ports viz. P1, P2, P3 and P0 to which we will be connected to address lines, GSM model and LCD respec- tively. When fault occurs due to above any reason then change in ratings will be shown on LCD and quick SMS will go to control room via GSM modem. A brief discussion about components used is as given below
Sensors play a vital role in effective implementation of the project. As we are interested in monitoring over current , over temperature and oil level following sensors are selected and suit- able designed with respect to prevailing conditions of power sys- tem and rating of transformer to be protected.

3.1.Current and Voltage Transformer

Current or voltage instrument transformer are necessary for iso- lating the protection & control. The behavior of current and volt- age transformer during and after the occurrence of fault is critical in electrical protection since error in signal from transformer can cause mal operation of the relays.

3.2. Thermistor

Thermistors are special solid temperature sensors that behave like temperature-sensitive electrical resistors. No surprise then that their name is a contraction of "thermal" and "resistor". There are basically two broad types, NTC-Negative Temperature used mostly in temperature sensing and PTC-Positive Temperature Coefficient, used mostly in electric current control.

Features :

• Low cost solid state sensor • Standard resistance tolerances down to ±2% • High sensitivity to changes in temperature• Suita- ble for temperature measurement, control and compensation • Excellent mechanical strength.

3.3 Oil Level Sensor

Oil level sensor is float connected angular potentiometer. Float is immersed in oil and its mechanical output is given to angular potentiometer. When there is any mechanical movement of float, there is voltage generation corresponding to mechanical move- ment of float. That voltage is used for oil level monitoring.

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3. 4. Analog to Digital Converter

The heart of this single chip data acquisition system is its 8-bit analog-to-digital converter. The pin diagram and block diagram of ADC 0808 is s as shown in fig.2 and 3 respectively[4]. The converter is designed to give fast, accurate, and repeatable con- versions over a wide range of temperatures. The converter is par- titioned into 3 major sections: the 256R ladder network, the suc- cessive approximation register, and the comparator. The convert- er’s digital outputs are positive true.
The ADC0808, ADC0809 offers high speed, high accuracy, min- imal temperature dependence, excellent long-term accuracy and repeatability, and consumes minimal power[6].

Features :

1. Easy interface to all microprocessors operates ratio metrically
or with 5 VDC or analog span adjusted voltage reference;
2. No zero or full-scale adjust required 8-channel multiplexer with address logic.


Fig. 2Pin and block diagram of ADC0808
Fig.3.Pin diagram of AT89S51 μ Controller

3.5. Micro Controller

In this project a low power, high performance8 bit microcontrol- ler (AT 89S51) is used. The pin diagram of AT89S51 is as shown in fig.3. The AT89S51[5] is a low-power, high-performance CMOS 8-bit μC with 4K bytes of In System Programmable Flash memory. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. It has following features:
• Compatible with MCS®-51 Products
• K Bytes of In-System Programmable (ISP) Flash Memory
• 4.0V to 5.5V Operating Range
• 128 x 8-bit Internal RAM
• 32 Programmable I/O Lines
• Dual Data Pointer

3.6. GSM Modem


A GSM modem is a specialized type of modem which accepts a SIM card, and operates over a subscription to a mobile operator, just like a mobile phone.
Fig.4. GSM Modem
We are using the FARGO MAESTRO 20 GSM as shown in fig.4. This is a powerful GSM/GPRS Terminal with compact and self- contained unit. This has standard connector interfaces and has an integral SIM card reader. The modem has a DB9 connector through which a speaker and microphone can be connected al- lowing audio calls being established, but this feature is not uti- lized in this project as only data transfer is needed.

Features & Specification

• Cellular frequency 900/1800MHz
• Easy to use
• Serial port DB9 connector
• Antenna length is 120mm
3.7. MAX 232
The MAX232 device is a dual driver/receiver that includes a ca- pacitive voltage generator to supply EIA-232 voltage levels from a single 5-V supply. The MAX232 was the first IC which in one package contains the necessary drivers (two) and receivers (also two), to adapt the RS-232 signal voltage levels to TTL logic. It became popular, because it just needs one voltage (+5V) and generates the necessary RS-232 voltage levels (approx. -10V and
+10V) internally. This greatly simplified the design of circuitry. The pin configuration of MAX 232 is as shown in fig.5.

Fig.5. Pin configuration of MAX 232
It has features like operating from a Single 5-V Power Supply,
operates up to 120 kbit/s Two Drivers and Two Receivers 30-V Input Levels Low Supply Current 8 mA Typical..

4. PROTOTYPE MODEL DEVELOPMENT

As shown in the fig.6 microcontroller 89S51 is the main control- ling element to which PT on input side, CT on load side, ther- mister and float sensor are connected. These four sensors are

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Fig.6. Prototype model of microcontroller based transformer health condition monitoring kit.
used to monitoring transformer parameters (voltage, current, temperature & oil level) Initially input from mains lines to load is monitored by CT current transformer. This CT gives the current level based on load used by costumer. Output of the CT is current and ac which is rectified and made voltage by signal conditioner circuit consisting of 10 ohm resistor; diode and capacitor. The output of the CT is fed to the ADC0808 for converting analog voltage to digital voltage. ADC0808 does conversion of analog signal into digital by successive approximation method and with the help of clock pulses, which is generated by NOT gate IC, this NOT gate produces 50kHz clock and give it to ADC. The output of the ADC is 8 bit which is fed to the microprocessor for further processing of the data. When power supply is switched on, mi- crocontroller starts program execution from zero memory loca- tion. The microcontroller has four input parts, which are contains
8 lines for input or output. In our project 4 lines of microcontrol- ler are used for giving address selection input and ALE signal to ADC for selecting sensor line, after this microcontroller receives
8 bit output from ADC. This output is digital equivalent of power consumption. Microcontroller gets another I/p from maximum limit setting switches, which are connected on pin 10,11,12,13. This gives maximum limit of power which consumer can use during peak time. The peak time pulse are received from real time clock, which is connected on pin no 16&17.This all infor- mation is displayed on LCD which is connected on pin 32 to40.The functions of microcontroller is continuously check power consumption of customer by means of CT, ADC and get digital I/p. This I/p is compare with maximum limit setting. Dis- play both those data on LCD. If the I/p ie power consumption exceeds the maximum limit then initially an alarm is sent telling consumer to reduce power consumption. This alarm is given by microcontroller through pin 14, and a transistor amplifier giving signal to a buzzer. After some time delay, microcontroller again check power consumption by customer, if it decreases then alarm stops or else microcontroller gives another trigger signal on pin
15, which signal is amplified by transistor & fed to relay. This relay switches off the supply to consumer for predetermined time limit. After this time limit completion again the supply resumes to consumer & microcontroller check the power consumption
again. If consumer exceeds his maximum limit setting again then he gets alarm & cycle is continuous.

5. PROGRAM EXECUTION AND TESTING

The project is based on microcontroller programming. The pro- gram for microcontroller in embedded C language. program writ- ten burned into microcontroller and saved as Hex file. For AT89S51 controller Atmel programmer is used. Program hex file is compiled in µcontroller flash compiler. This compiler converts program into machine language code as well as check program for error if any error found notifies and these errors are corrected manually. Then it successfully executed in compiler. After com- piling program in µcontroller flash compiler, it is burned into AT89S51 microcontroller with the help of universal program burner kit FP8903 programmer which is connected to computer. After successful program burning, microcontroller becomes ready for use.
In testing, after successful program burning, microcontroller is mounted on its base and kit becomes ready for testing. For testing In program kit has provided with following four parameter of transformer:
1. 180 >Voltage > 260 -- Voltage Fault
2. Temperature > 400C--- Temperature fault
3. Power > 125W -- Over load
4. Oil level < 10 ml --- Oil level fault
Therefore any change occurred in above rating during running of project model, these changes is shown in LCD and same data obtained in SMS and at the same time transformer gets discon- nected from supply with the help of relay. Results obtained dur- ing testing as per given input and fault conditions on LCD are as follows:

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6. CONCLUSION

Transformers are among the most generic and expensive piece of equipment of the transmission and distribution system. Regular monitoring health condition of transformer not only is economi- cal also adds to increased reliability. In the past, maintenance of transformers was done based on a pre-determined schedule. With the advancement of communication technology now it is possible to receive fault information of transformer through GSM tech- nology remotely to the operator and authorities so one can able to take possible solution before converting fault in to fatal situa- tion. Depending upon fault analysis a prototype model of micro- controller based transformer health monitoring kit is developed in laboratory. Using digital controller analysis results are regularly updated. During abnormal conditions exceeding specified limits information is immediately communicated through GSM tech- nology to the operator and also to concerned authority for possi- ble remedial action. This type of remote observation of health condition of transformer not only increases the life of transformer increases mean down time of transformer there by increased reli- ability and decreased cost of power system operations.

REFERENCES

[1] Bajjuri Praneeth Kumar & Boda Vamsee Krishna Babu, “SMS Remote

Controller” paper presented in Embedded System –Fall 2005

[2] Ali Kazemi & Casper Labuschagne ,“Protecting Power Transformers

From Common Adverse Conditions”, paper presented at the Ga -Tech

and the Western Protective Relay Conferences, New Berlin” in 2005

[3] T.S.Madhavrao, “Power System Protection- Static Relays”. TMH Pub- lication.

[4] National Semiconductor Corporation, “ADC 0808”, journal published, America, October 1999.

[5] Atmel Corporation, “ AT 89S51”, literature journal published, CA,

December 2003 3. National Semiconductor Corporation, “ Voltage

Regulator LM 7805” journal published, America, May 2003.

[6] R.P.Jain, “Modern Digital Electronics”, TMH Publication 2003

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