25-08-2017, 09:32 PM
SCADA- IMPLEMENTED OVER POWER TRANSFORMER WITH REMOTE MONITORING SYSTEM
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INTRODUCTION
Nowadays, with the advancement of technology, particularly in the field of computers as well as micro-controllers, all the activities in our day to day living have become a part of information and we find computers and micro-controllers at each and every application. Thus, the trend is directing towards computer based project works. However, in this project work the basic signal processing of temperature, load current and input high voltage parameters related to the distribution transformers are monitored with analog electronics only. For measuring various parameters values, various transducers are used, and the output of these transducers are converted to control the parameters. The control circuit is designed using micro-controller. The outputs of all the three parameters are fed to the analog to digital converter for converting the analog information in to the digital information and this digital information is fed to micro-controller. The output of the micro-controller is used to drive the digital display, so that the value of each parameter can be displayed. In addition to the digital display micro-controller outputs are also used to drive four relays independently. These relays energize and de-energizes automatically according to the condition of the parameter. Out of four relays one relay is treated as common relay and energizes automatically whenever any parameter exceeds its preset value. This relay contact is used to break the supply to the transformer primary. The remaining three relays are used for the three different parameters, to transmit the information about the failure parameter. For example, if the load is more than the rated load, then immediately the micro-controller energizes one relay out of these three relays and this relay contact is used to provide supply to the low frequency oscillator, which produces a perfect square wave of 1 KHz approximately. This low frequency is fed to transmitter as a modulating wave, which is super imposed over the carrier and transmitted as a modulated wave. Like wise for other two parameters, two different low frequencies are generated. The idea of generating three different low frequencies is to identify the failure parameter and to transmit the failure information.
BLOCK DIAGRAM AND BRIEF DESCRIPTION
The block diagram of the project work “Implementation of wireless communication in supervisory control and data acquisition system of a distribution transformer using microcontroller & computer” is explained. For better under standing, the total block diagram is divided into various blocks and each block explanation is provided in this chapter. The complete block diagram of this project work is provided at the end of this chapter.
LOAD MONITORING CIRCUIT:
For monitoring the load current continuously, Current Transformer (CT) is used. The current transformer is used with its primary winding connected in series with load carrying the current to be measured and, therefore, the primary current is dependant upon the load connected to the system and is not determined by the load (burden) connected on the secondary winding of the current transformer. The primary winding consists of very few turns and, therefore, there is no appreciable voltage drop across it. The secondary winding of the current transformer has larger number of turns, the exact number being determined by the turn’s ratio. The ammeter, or wattmeter current coil, are connected directly across the secondary winding terminals. Thus a current transformer operates its secondary winding nearly under short circuit conditions. One the terminal of the secondary winding is earthed so to protect equipment and personnel in the vicinity in the even of an insulation breakdown in the current transformer.
HIGH VOLTAGE MONITORING CIRCUIT:
Transformer failures have many causes and one of the main causes is over voltage. The primary of the distribution transformer or any other transformer primary is designed to operate at certain specific voltage, if that voltage is more than the rated voltage, then immediately the transformer primary may burn because of over voltage. To protect the transformer, burning due to over voltage, this voltage monitoring and control circuit is used in this project work.
In this project work for generating high voltage, autotransformer is used so that the line voltage can be increased to more than 240V. For monitoring the line voltage, a step-down transformer of 6V-0-6V center-tapped secondary is used as a line voltage sensor. As this transformer primary voltage increases, according to that secondary voltage also raises, and this secondary voltage is rectified, filtered and it is applied to the analog to digital converter for converting the analog information in to the digital information.
TEMPERATURE SENSING CIRCUIT:
The methods of temperature measurement may be divided into two main classes according as the exchange of heat between the testing body and the hot system takes place by contact or by radiation across a space. In the contact methods, thermometers or thermocouples are used and they are immersed in solids or liquids. The thermodynamic equilibrium between the hot body and the testing body is established by material contact. In the non-contact methods, the thermodynamic equilibrium is established by the radiation emitted as excited atom and molecules in the hot body return to the ground state.
For monitoring the transformer body temperature, SL100 general purpose NPN switching transistor is used and it is having ‘TIN’ metal body, so that it can absorb the heat properly. This transistor can be placed over the transformer body, where the transformer radiates maximum heat. The exact location where the transistor is to be installed using suitable clamp should be determined on the ease of access and the degree of accuracy obtainable at the given point.
MICRO-CONTROLLER:
Micro-controller unit is constructed with ATMEL 89C51 Micro-controller chip. The ATMEL AT89C51 is a low power, higher performance CMOS 8-bit microcomputer with 4K bytes of flash programmable and erasable read only memory (PEROM). Its high-density non-volatile memory compatible with standard MCS-51 instruction set makes it a powerful controller that provides highly flexible and cost effective solution to control applications.
Micro-controller works according to the program written in it. The program is written in such a way, so that the output from the ADC will be converted into its equivalent voltage and based on the magnitude of the voltage, it calculates the parameter value. Now this magnitude is again digitalized and fed to 7-segment display unit through the latch.
Micro-controllers are "embedded" inside some other device so that they can control the features or actions of the product. Another name for a micro-controller, therefore, is "embedded controller". Micro-controllers are dedicated to one task and run one specific program. The program is stored in ROM (read-only memory) and generally does not change. Micro-controllers are often low-power devices. A battery-operated Microcontroller might consume 50 milli watts. A micro-controller has a dedicated input device and often (but not always) has a small LED or LCD display for output. A micro-controller also takes input from the device it is controlling and controls the device by sending signals to different components in the device.
DIGITAL DISPLAY:
The output of the micro-controller is used to drive the digital display, for this purpose four 7-segment common anode displays are used for measuring the line voltage, transformer body temperature and load current. These displays are used to display the data received from the Microcontroller through the latches. The segments of each display are called A, B, up to G. In order to reduce the numbers of connections needed to address each of the LED’s (Light Emitted Diode), the anodes of the LED’s of each seven-segment display have been connected together.
F.M RECEIVER:
The FM receiver is located at the remote end. The first stage of this remote end unit is the F.M. Radio Receiver, which is designed with Phillips IC TEA 5591A. In the circuit diagram an LED indicator is connected at Pin No.7 of 5591 IC, which glows brightly, if the receiver is tuned perfectly with the transmitter.
The F.M. receiver, which operates at 100 MHz, will have an intermediate frequency of 10.7 MHz and bandwidth of 200 KHz. This IC consists of a built in RF amplification circuit. It matches the input impedance of the antenna. This IC consists of F.M. Detector including amplifier of modulated signal (RF amplification). Two sections of LC are provided and a ceramic filter is used to filter the IF of 10.7 MHz.
FREQUENCY TO VOLTAGE CONVERTER:
The output of the signal amplifier is converted into DC voltage in proportion to the tone frequency, with the help of phase locked loop IC 4046 and Multi-plexer IC 4053. The amplified signal is fed to the in signal (Pin NO.14) of the device, which is the input of the phase comparator. The other input of the phase comparator is fed from the internally generated voltage controlled oscillator (VCO), whose frequency is set with the help of external capacitor connected between Pin 6 and 7, here PLL is used for synchronization. The output of the PLL is fed to the Multiplexer. The signals of the phase comparator – I and phase comparator – II are fed so that the output is multi-plexed with the hlp of IC4053. The output of the F/V converter is fed to the Analog to digital converter circuit for converting the Analog information into digital pulses. The circuit design of phase locked loop with multiplexer and its associated circuitry is shown below.