Career Episode 1v IntroductionCE 1.1 My first career episode is based on theproject ‘GSM Based Substation Load Switching’.This project was my graduation project, during the time of study of Bachelors of Electrical and Electronics Engineeringat Jawaharlal Nehru TechnologicalUniversity. I spearheaded the project as part of my curriculum in 3rdyear 2nd semester of mycourse .
The project was based in Hyderabad/India.CE 1.2 Thisproject was about reducing the power instability in residential and officepremises. The project involved operating the loads with micro switches to avoidhuge switchgears in some of the switching systems. The use of digital phaseselection systems allowed the relay to trigger according to phase selection.Automation in phase selection was needed in the areas where power consumptionwas more. CE 1.3 Theprime objective of this project was to develop a digital phase selector thatacted as a backup power supply if any of the main lines failed.
If in single-phaselines any line failed, the power was transferred to the remaining two lines.The scope of this project was to create a device that mainly reduced thewastage of power and time. The switching was achieved using high frequencytechnology that utilized infrared radiation.
IC MCT2eE was responsible for theswitching action and capable of reducing arcing, which occurs in three phaselines due to mechanical switching. Transistors and MOSFETS provided therequired trigger pulses for switches. The project was mainly intended tooperate devices like fans, lights, motors, etc. via a GSM based mobile phone.The important components of this system were; GSM modem, sensors (temperature,current, voltage), switches like the relay switch, and the micro controller was the brain of this system.This project worked in two stages.
First,the micro controller was programmed to send a particular format of SMS to theGSM modem from mobile phone, which was fed as input to the micro controller. Inthe second stage, a return feedback message was sent to the mobile from GSMmodem and the temperature at the place where the devices were being operatedwas obtained. CE 1.4I carried out below mentioned activities andtasks during the project; Prepared a work schedule to compete for all the tasks timelyStudied scholarly articles and publications toget the basic knowledge of automated load switchingStudied electronic circuit design books,watched online tutorials and got help from professionals to strengthen mycircuit designing abilitiesBuilt three types of relay driver circuitsusing basic engineering knowledgeDistributed the tasks evenly among all teammembers to ensure smooth progress of the projectReported the issues encountered and preparedproposals to resolve those issuesRecorded experimental results and waveformsalong with other calculations to get them approved by the project supervisorPresented the final report and presentationand amended them according to the instructions of the project supervisor andcoordinator CE 1.5Hierarchy of the project is given below; v Personal Engineering ActivityCE 1.
6 Before initiating this project, I developed astrong understanding of the project scope. I studied a number of publicationsand research papers to strengthen my theoretical knowledge. Using online andoffline sources, I devised various circuit diagrams for testing and choosingthe best one. I also prepared a project schedule to carry out all the tasks inan efficient manner. Then I arranged a kick off meeting with my team in thepresence of the project supervisor and coordinator. I discussed my initial researchwith them and shared the schedule and circuit designs. In return, they gave their views which I took inconsideration.
My team members also shared their research and we worked withmutual consent. The project coordinator broke down all the tasks and Idistributed them to each team member. I followed the engineeringaccountabilities for keeping the design as per the standard requirements. Ifollowed the IEEE standards while carrying out design activities. Apart fromthis, all the material used was complied with RoHs.
CE 1.7 During this project, I designed a circuit forsoft switching which consisted of cable connectors, toggle switches, relaydrivers, bases with ICs, pull up and pull down resistors, and PNP transistorsto turn on and off. I used only one octal D-type latch and IC 74LS373. Thecircuit that I built had multiple features. The first feature was an individualon/off control. For turning on the action,the switch S1 was pressed and a low logic was sent to data input pin D0.
Thesame level appeared at the data input pin Q0 because I connected the latchenable pin LE (active high) to Vcc and used resistor R9 to pull down the outputenable OE (active low). After releasing S1, Q0 returned to the low state andthis level implied that transistor T1 would turn on with the help of diode D9and activate RL1. LED1 also glowed to indicate that channel1 is on because ofthe LED indication feature of this circuit. The switching off action works inthe same way when RL1 is deactivated. I assigned another emergency off controlfeature to the emergency switch S17 which disabled all the outputs of IC1. Theimmediate on control feature worked upon pressing S18 which applied low logicto data inputs D0 and D7 using D17 and D24.
To control more devices, similar circuitscan be built and cascaded. CE 1.8 To stop the major problem of power interruption in the distribution system, I used digital phaseselector in combination with an inverter to perform automatic switching.
In adigital phase selector, the phase sensing/ switching block, control logicblock, relay driver section, and power supply unit got simultaneous signals soit was hard to understand which block operated first. I used an inverter togive power to the digital phase selector which was more reliable and did notneed any manual operation. When the system operated normally, the inverter wasfully charged and in the case of any fault, it provided backup. The NOT gate inthe inverter sent a low signal to the relay driver under faulty situations andthe relay powered the next unflawed line. In this way, I managed to protect the single phase load. In the case of athree phase fault, all the phases became unavailable so I used another port ofthe relay driver to make a separateconnection to alternate power sourceslike inverter or battery.CE 1.9 In the duration of this project, I also designed a relay drivercircuit to drive DC relays.
For this purpose, I used DC voltage rating asspecified on relay’s data sheet and a zenerdiode. I used the zener diode toeliminate high voltage spikes from the relay circuit when the relay opens andcloses. The coil of a relay acts as an inductor so to understand the effect oflarge current across the coil, I used the mathematical relation V=LdI/dt. Toprevent the circuit from any damage caused by transient voltage spikes, Iplaced a reverse biased diode in parallel to the relay. In this way, the diodeconducted current in reverse bias when the voltage was about to cross a certainthreshold and grounded excess voltage. I used a relay with a 9V rating so I fed 9V DC to the resistor. CE 1.10 In the same way as DC relay driver circuit, I built an AC relaydriver circuit.
I supplied AC power to the relay as per the specifications inrelay’s datasheet. Unlike DC relays, here I could not use a diode as atransient suppressor because AC power alternated after each half cycle. Usingtwo reverse biased diodes in parallel was also worthless because the currentdid not reach the coil of the relay. To resolve this issue, I placed an RCseries network across the coil in parallel. The capacitor absorbed excesscharges and the resistor helped in discharging them. In this way, I designed an AC relay driver circuit thatturned on and powered the loads effectively.CE 1.
11 Using my incredible technical and circuitdesigning skills, I designed another relay driver circuit that utilizedarbitrary control voltage (AC/DC). This circuit was efficient because it didnot use datasheet rated voltages as it contained a transistor which amplifiedthe current leading from base to emitter so the relay required much less powerto operate. The components I used were a 6-9V relay, 2N2222 transistor, zener diode, 1K? resistor, and 9V battery or DCpower supply. As no voltage/input current was applied to the transistor’s baselead, the transistor’s emitter-to-collector channel was open and it blockedcurrent flow through relay’s coil. However, if rated voltage and input currentwere applied to the base lead, the transistor’s emitter-to-collector channelopened allowing the current to flow through the relay’s coil.CE 1.12 Another task that I accomplished during thisproject was to prepare a Rectangular Pulse Excitation – Long Term Prediction(RPE-LTP) coding scheme used by GSM. I sampled the voice signal at 8000bits/secand quantized it to get a 13bit resolution corresponding to a bit rate of104kbits/sec.
I gave this signal to a speech coder (codec) which compressedthis speech into a source-coded speech signal of 260 bit blocks at a bit rateof 13kbit/sec. When the codec achieved a compression ratio of 1:8, the VoiceActivity Detector (VAD) present in the codec decided whether to turn on or offthe transmitter under the control of the Discontinuous Transmission (DTX). TheDTX helped in reducing the power consumption and increasing battery life. TheSilence Descriptor (SID) replaced the missing speech frames by syntheticbackground noise and the frame flagged as a Bad Frame Indicator (BFI) wasdiscarded. CE 1.13 Circuit designing requires the use of variousformulas so I used some of them to justify my design.
I performed calculationsto meet the required specifications of each component to get the desired output.I used Kirchhoff’s Voltage and Current Law and Ohm’s Law to solve the circuitwith respect to each node and loop. Moreover, I calculated desired values ofresistances, capacitances, andinductances using basic electronic circuit formulas.CE 1.14The project put mytechnical abilities to test and I succeeded in achieving every task using myprior engineering knowledge. I took guidance from various web resources,journals, books, and tutorials.
If I faced any difficulty, I always informedthe project supervisor and other team members. Good communication helped us tocome up with an effective solution. I also attended various conferences andseminars on simulation software during the project, which improved my circuitsimulation skills. CE 1.
15 I made sure that allthe project activities were carried out following the on health and safetyprocedures. I advised my team to take every necessary precaution while dealingwith electrical equipment. As we were dealing with three-phase 415V supply,manual changeover could lead to fire accidents so I prioritized theinstallation of the digital phase selector so that none of the lives wererisked. I ensured that the diodes were rated to handle the current equivalents,supplied to them, before giving power to the circuit. I took safety measuressuch as the installation of the fuse inthe circuit to prevent any damage to it. I made sure that the scrap materialsand failed components were disposed of to keep the working area clean.
CE 1.16 In this project, I usedProteus software to carry out circuit simulations and verify my calculations.Software simulation was necessary to test whether or not the components with anestimated value could be used to provide the desired output before actuallypurchasing them. I also used the Microsoft Office Program to record results,prepare a report and presentation. CE 1.17 Throughout thisproject, I accomplished my tasks as a responsible team member. I keptinteracting with my team at all times to motivate them. I monitored theprogress of the project to make sure everything was going smoothly.
I simulatedthe circuit on simulation software before ordering the components to save extracosts. I arranged weekly group meetings with my team members to discuss variousproject matters with them. The outcome of each meeting and the project progresswas reported to the project supervisor. In the final meeting, I presented theproject in front of all the team members, project supervisor and projectcoordinator.
vSummaryCE 1.18 The project of GSMBased Substation Load Switching was a great success for me as it proved to bean alternative source of power backup for the utility supply on which mostindustrial and commercial applications were dependent. I was able to accomplishit on time, which made it even more praiseworthy. This project featured all thehardware components that were reasoned out and placed carefully, thuscontributing to the best functioning of the unit. It gave me an environment togroom myself in the field of engineering.
It also improved my socialinteraction and dealing skills. My company recognized me for my qualityperformance and efforts that I put into this project. CE 1.19The future aspects ofthis project can be extended using GPRS technology. This will help in sending the monitored andcontrolled data to any place in the world. The temperature controlling systemslike coolant can also be used in places where maintenance of temperature levelis needed. Industrial equipment can besupervised from our personal computers by connecting wireless camera by usingGPRS and GPS technology. Automated switching of the devices can be carried outusing personal computers making everything so convenient.