VishwakShenan S (GSM based Distribution Transformer Monitoring System)

GSM based Distribution Transformer Monitoring System 

ABSTRACT:
This project is about design and implementation of a mobile embedded system to monitor and record key parameters of a distribution transformer like load currents, oil level and ambient temperature. The idea of on-line monitoring system integrates a global service mobile (GSM) Modem, with a standalone single chip microcontroller and different sensors. It is installed at the distribution transformer site and the above parameters are recorded using the analog to digital converter (ADC) of the embedded system. The obtained parameters are processed and recorded in the system memory. If any abnormality or an emergency situation occurs the system sends SMS (short message service) messages to the mobile phones containing information about the abnormality according to some predefined instructions programmed in the microcontroller. This mobile system will help the transformers to operate smoothly and identify problems before any catastrophic failure.

BACKGROUND OF THE PROJECT ;

Abnormality in distribution transformer is accompanied with variation in different parameters like Winding temperature , Top and bottom oil temperatures, Ambient temperature, Load current, Oil flow (pump motor), Moisture in oil ,Dissolved gas in oil, Bushing condition, LTC monitoring, Oil level. However, we are dealing with oil temperature and load current. Online monitoring system consists of embedded system, GSM modem, mobile-users and GSM networks and sensors installed at transformer site Sensors are installed on transformer side which reads and measures the physical quantity from the distribution transformer and then it converts it into the analog signal. The embedded module is located at the transformer site. It is utilized to acquire, process, display, transmit and receive the parameters to/ from the GSM modem. The second is the GSM module. It is the link between the embedded system and the public GSM network. The third is utility module that has a PC-based -server located at the utility control center. The server is attached to GSM modem and received transmits SMS from/to the transformer site via the GSM module.

HARDWARE IMPLEMENTATION ;

This chapter explains regarding the Hardware Implementation of the project. It tells about the design and working of the design with the help of circuit diagram and explanation of circuit diagram in detail. It explains the features, programming and serial communication of ATmega 16L microcontroller. It also explains the different modules used in this project. 3.1 INTERFACING MODULE SCHEME The above scheme depicts the sequence of methodologies followed in the monitoring of distribution transformer via GSM technology.

 First sensors which are installed at the transformer site sense the various parameters of transformers and convert into analog signal to be processed in signal conditioning circuits 
 Next the SCC consisting of opamps and resistors manipulates the analog signal to a compatible value so that can be read by the embedded system. 
 Next the signal is passed through microcontroller. The ADC is used to read the parameters, built-in EEPROM is used to host the embedded software algorithm that takes care of the parameters acquisition, processing, displaying, transmitting and receiving. The built-in EEPROM is used to save the online measured parameters along with their hourly and daily averages.
  The GSM modem is interfaced with the microcontroller through RS 232 adapter by which it upload and download SMS messages that contain information related to the transformer parameters and status.
  This GSM modem then sends this SMS to mobile users containing information about parameters value of the distribution transformers.

SENSORS; 

Sensors are installed on transformer site which reads and measures the physical quantity from the distribution transformer and then it converts it into the analog signal. Sensor are used for sensing load current, ambient temperature, winding temperature, oil temperature and oil level. A sensor is a device which receives and responds to a signal when touched. A multitude of different measurable variables can be collected for on-line monitoring[1]. However, it is very rarely useful to use the entire spectrum. Therefore, sensor technology must be adjusted to the specific requirements of a particular transformer depending on their age and condition. Following general set-up of sensors for example is proposed[1]-[3] for the use at a Distribution transformer: 
• PT100 to measure top oil temperature 
• PT100 to measure ambient temperature 
• C.T to measure load current (single phase)
• Determination of voltage at measurement tap of bushing (three phase) 6 
• Estimation of oil pressure of bushing
• Sensor to measure humidity in oil • Sensor for measuring gas-in-oil content It is fundamental to measure the electrical variables load current and operating voltage directly at the transformer. A bushing-type current transformers is used for load current measurement. For the gas-in-oil detection a Hydran[3] sensor is used which reads a composite value of gases in ppm (H2 (100%), CO (18%), C2H2(8%), C2H4 (1,5%)). As hydrogen is a key gas for problems in the active part, an increase in the output signal of the sensor is an indication for irregularities such as partial discharge or hot spots. The evaluation of this measuring signal, together with the dependency on the temperature of the oil and the load current, provides a reliable basis for the continuous operation of the transformer. In the event of an increase of gas-in-oil content, an immediate reaction can be effected via an off-line dissolved gas analysis to determine the concentration of the other components dissolved in the oil in order to clarify the cause of the potential damage. A capacitive thin film[1] sensor is used for the detection of moisture in oil. There are several causes for an increase of water-in-oil content. After improper shipping and erection of the transformer on-site the oil can be contaminated with water. Breathing of the transformer can cause absorption of moisture by the oil in the conservator. Due to the fact that water is a result and also an origin of paper degradation the water-in-oil content is an important indicator for the condition of winding insulation. The voltage applied to the transformer is acquired at the measuring tap of the capacitor bushing by means of a voltage sensor. It acts with the capacity of the bushing as a voltage divider. This enables not only the measurement of the operational voltage but also the detection of overvoltages, because due to its design the voltage sensor has a bandwidth up to some MHz. The output of the voltage sensor is connected to a peak sampler to detect the amplitude of overvoltages by the monitoring system. 

Parameter Sensors Used 
Phase Current Current Transformer
Phase Voltage Voltage Transformer
Oil temperature Thermistor, 
TPT-32 4 Oil Level R-Series
Rxl oil level sensor
Winding Temperature RTD Sensors 
Gas Content in Oil Hydran Sensor

 POWER SUPPLY 

Power supply is the circuit from which we get a desired dc voltage to run the other circuits. The voltage we get from the main line is 230V AC but the other components of our circuit require 5V DC. Hence a step-down transformer is used to get 12V AC which is later converted to 12V DC using a rectifier. The output of rectifier still contains some ripples even though it is a DC signal due to which it is called as Pulsating DC. To remove the ripples and obtain smoothed DC power filter circuits are used. Here a capacitor is used. The 12V DC is rated down to 5V using a positive voltage regulator chip 7805. Thus a fixed DC voltage of 5V is obtained. 8 A 5V regulated supply is taken as followed: Each of the blocks is described below: 
 Transformer - steps down high voltage AC mains to low voltage AC. 
 Rectifier - converts AC to DC, but the DC output is varying. 
 Smoothing - smoothes the DC from varying greatly to a small ripple. 
 Regulator - eliminates ripple by setting DC output to a fixed voltage. 

 TRANSFORMER
 Transformer is the electrical device that converts one voltage to another with little loss of power. Transformers work only with AC. There are two types of transformers as Step-up and Step-down transformer. Step-up transformers steps up voltage, step-down transformers steps down voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains voltage to a safer low voltage. Here a step down transformer is used to get 12V AC from the supply i.e. 230V AC. 

9 3.4.2 RECTIFIERS 

A rectifier is a circuit that converts AC signals to DC. A rectifier circuit is made using diodes. There are two types of rectifier circuits as Half-wave rectifier and Full-wave rectifier depending upon the DC signal generated. 

3.4.3 SMOOTHING 

Smoothing is performed by a large value electrolytic capacitor connected across the DC supply to act as reservoir, supplying current to the output when the varying DC voltage from the rectifier is decreasing. The diagram shows the unsmoothed varying DC and the smoothed DC. The capacitor charges quickly to the peak of the varying DC and then discharges as it supplies current to the output. Here the capacitor of 330uF is used as a smoothing circuit. 
3.4.4 VOLTAGE REGULATION

 Voltage regulators produce fixed DC output voltage from variable DC (a small amount of AC on it). Fixed output is obtained by connecting the voltage regulator at the output of the filtered DC. It can also be used in circuits to get low DC voltage from high DC voltage (for example we use 7805 to get 5V from 12V). Two types of voltage regulators are 1. fixed voltage regulators (78xx, 79xx) 2. Variable voltage regulators (LM317) 

3.5 MICROCONTROLLER

 Microcontroller is defined as a system on computer chip which includes number of peripherals like RAM, EEPROM, etc. required to perform some predefined task. There are number of popular families of microcontrollers which are used in different applications as per their capability and feasibility to perform various task, mostly used of these are 8051, AVR and PIC microcontrollers. In this subject we will introduce you with AVR family of microcontrollers. AVR is an 8-bit microcontroller belonging to the family of Reduced Instruction Set Computer (RISC). In RISC architecture the instruction set of the computer are not only fewer in number but also simpler and faster in operation. The other type is CISC . We will explore more on this when we will learn about the architecture of AVR microcontrollers in following section. 10 The microcontroller transmits and receives 8-bit data. The input/output registers available are also of 8-bits. The AVR families controllers have register based architecture which means that both the operands for an operation are stored in a register and the result of the operation is also stored in a register. Discussing about AVR we will be talking on Atmega16 microcontroller, which is 40-pin IC and it belong to mega AVR category of AVR family. Some of the key features of Atmega16 are: 

· 16KB Flash memory 
· 1KB SRAM 
· 512 Bytes EEPROM 
· 40-Pin DIP 
· 8-Channel 10 bit ADC 
· Two 8 bit Timers/Counters 
· One 16 bit Timer/Counter 
· 4 PWM Channels 
· In System Programmer (ISP) 
· Serial USART · SPI Interface 
· Digital to Analog Comparator.