Career Episode 1

v Introduction

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CE 1.1

My first career episode is based on the
project ‘GSM Based Substation Load Switching’.

This project was my graduation project, during the time of study of Bachelors of Electrical and Electronics Engineering
at Jawaharlal Nehru Technological
University. I spearheaded the project as part of my curriculum in 3rd
year  2nd semester of my
course . The project was based in Hyderabad/

CE 1.2

project was about reducing the power instability in residential and office
premises. The project involved operating the loads with micro switches to avoid
huge switchgears in some of the switching systems. The use of digital phase
selection systems allowed the relay to trigger according to phase selection.

Automation in phase selection was needed in the areas where power consumption
was more.

CE 1.3

prime objective of this project was to develop a digital phase selector that
acted as a backup power supply if any of the main lines failed. If in single-phase
lines 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 the
wastage of power and time. The switching was achieved using high frequency
technology that utilized infrared radiation. IC MCT2eE was responsible for the
switching action and capable of reducing arcing, which occurs in three phase
lines due to mechanical switching. Transistors and MOSFETS provided the
required trigger pulses for switches. The project was mainly intended to
operate 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 the
GSM modem from mobile phone, which was fed as input to the micro controller. In
the second stage, a return feedback message was sent to the mobile from GSM
modem and the temperature at the place where the devices were being operated
was obtained.

CE 1.4

I carried out below mentioned activities and
tasks during the project;

Prepared a work schedule to compete for all the tasks timely

Studied scholarly articles and publications to
get the basic knowledge of automated load switching

Studied electronic circuit design books,
watched online tutorials and got help from professionals to strengthen my
circuit designing abilities

Built three types of relay driver circuits
using basic engineering knowledge

Distributed the tasks evenly among all team
members to ensure smooth progress of the project

Reported the issues encountered and prepared
proposals to resolve those issues

Recorded experimental results and waveforms
along with other calculations to get them approved by the project supervisor

Presented the final report and presentation
and amended them according to the instructions of the project supervisor and

CE 1.5

Hierarchy of the project is given below;


v Personal Engineering Activity

CE 1.6

Before initiating this project, I developed a
strong understanding of the project scope. I studied a number of publications
and research papers to strengthen my theoretical knowledge. Using online and
offline sources, I devised various circuit diagrams for testing and choosing
the best one. I also prepared a project schedule to carry out all the tasks in
an efficient manner. Then I arranged a kick off meeting with my team in the
presence of the project supervisor and coordinator. I discussed my initial research
with them and shared the schedule and circuit designs. In return, they gave their views which I took in
consideration. My team members also shared their research and we worked with
mutual consent. The project coordinator broke down all the tasks and I
distributed them to each team member. I followed the engineering
accountabilities for keeping the design as per the standard requirements. I
followed the IEEE standards while carrying out design activities. Apart from
this, all the material used was complied with RoHs.

CE 1.7

During this project, I designed a circuit for
soft switching which consisted of cable connectors, toggle switches, relay
drivers, bases with ICs, pull up and pull down resistors, and PNP transistors
to turn on and off. I used only one octal D-type latch and IC 74LS373. The
circuit that I built had multiple features. The first feature was an individual
on/off control. For turning on the action,
the switch S1 was pressed and a low logic was sent to data input pin D0. The
same level appeared at the data input pin Q0 because I connected the latch
enable pin LE (active high) to Vcc and used resistor R9 to pull down the output
enable OE (active low). After releasing S1, Q0 returned to the low state and
this level implied that transistor T1 would turn on with the help of diode D9
and activate RL1. LED1 also glowed to indicate that channel1 is on because of
the LED indication feature of this circuit. The switching off action works in
the same way when RL1 is deactivated. I assigned another emergency off control
feature to the emergency switch S17 which disabled all the outputs of IC1. The
immediate on control feature worked upon pressing S18 which applied low logic
to data inputs D0 and D7 using D17 and D24. To control more devices, similar circuits
can be built and cascaded.

CE 1.8

To stop the major problem of power interruption in the distribution system, I used digital phase
selector in combination with an inverter to perform automatic switching. In a
digital phase selector, the phase sensing/ switching block, control logic
block, relay driver section, and power supply unit got simultaneous signals so
it was hard to understand which block operated first. I used an inverter to
give power to the digital phase selector which was more reliable and did not
need any manual operation. When the system operated normally, the inverter was
fully charged and in the case of any fault, it provided backup. The NOT gate in
the inverter sent a low signal to the relay driver under faulty situations and
the relay powered the next unflawed line. In this way, I managed to protect the single phase load. In the case of a
three phase fault, all the phases became unavailable so I used another port of
the relay driver to make a separate
connection to alternate power sources
like inverter or battery.

CE 1.9

In the duration of this project, I also designed a relay driver
circuit to drive DC relays. For this purpose, I used DC voltage rating as
specified on relay’s data sheet and a zener
diode. I used the zener diode to
eliminate high voltage spikes from the relay circuit when the relay opens and
closes. The coil of a relay acts as an inductor so to understand the effect of
large current across the coil, I used the mathematical relation V=LdI/dt. To
prevent the circuit from any damage caused by transient voltage spikes, I
placed a reverse biased diode in parallel to the relay. In this way, the diode
conducted current in reverse bias when the voltage was about to cross a certain
threshold 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 relay
driver circuit. I supplied AC power to the relay as per the specifications in
relay’s datasheet. Unlike DC relays, here I could not use a diode as a
transient suppressor because AC power alternated after each half cycle. Using
two reverse biased diodes in parallel was also worthless because the current
did not reach the coil of the relay. To resolve this issue, I placed an RC
series network across the coil in parallel. The capacitor absorbed excess
charges and the resistor helped in discharging them. In this way, I designed an AC relay driver circuit that
turned on and powered the loads effectively.

CE 1.11

Using my incredible technical and circuit
designing skills, I designed another relay driver circuit that utilized
arbitrary control voltage (AC/DC). This circuit was efficient because it did
not use datasheet rated voltages as it contained a transistor which amplified
the current leading from base to emitter so the relay required much less power
to operate. The components I used were a 6-9V relay, 2N2222 transistor, zener diode, 1K? resistor, and 9V battery or DC
power supply. As no voltage/input current was applied to the transistor’s base
lead, the transistor’s emitter-to-collector channel was open and it blocked
current flow through relay’s coil. However, if rated voltage and input current
were applied to the base lead, the transistor’s emitter-to-collector channel
opened allowing the current to flow through the relay’s coil.

CE 1.12

Another task that I accomplished during this
project was to prepare a Rectangular Pulse Excitation – Long Term Prediction
(RPE-LTP) coding scheme used by GSM. I sampled the voice signal at 8000bits/sec
and quantized it to get a 13bit resolution corresponding to a bit rate of
104kbits/sec. I gave this signal to a speech coder (codec) which compressed
this speech into a source-coded speech signal of 260 bit blocks at a bit rate
of 13kbit/sec. When the codec achieved a compression ratio of 1:8, the Voice
Activity Detector (VAD) present in the codec decided whether to turn on or off
the transmitter under the control of the Discontinuous Transmission (DTX). The
DTX helped in reducing the power consumption and increasing battery life. The
Silence Descriptor (SID) replaced the missing speech frames by synthetic
background noise and the frame flagged as a Bad Frame Indicator (BFI) was

CE 1.13

Circuit designing requires the use of various
formulas so I used some of them to justify my design. I performed calculations
to 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 circuit
with respect to each node and loop. Moreover, I calculated desired values of
resistances, capacitances, and
inductances using basic electronic circuit formulas.

CE 1.14

The project put my
technical abilities to test and I succeeded in achieving every task using my
prior engineering knowledge. I took guidance from various web resources,
journals, books, and tutorials. If I faced any difficulty, I always informed
the project supervisor and other team members. Good communication helped us to
come up with an effective solution. I also attended various conferences and
seminars on simulation software during the project, which improved my circuit
simulation skills.

CE 1.15

I made sure that all
the project activities were carried out following the on health and safety
procedures. I advised my team to take every necessary precaution while dealing
with electrical equipment. As we were dealing with three-phase 415V supply,
manual changeover could lead to fire accidents so I prioritized the
installation of the digital phase selector so that none of the lives were
risked. I ensured that the diodes were rated to handle the current equivalents,
supplied to them, before giving power to the circuit. I took safety measures
such as the installation of the fuse in
the circuit to prevent any damage to it. I made sure that the scrap materials
and failed components were disposed of to keep the working area clean.

CE 1.16

In this project, I used
Proteus software to carry out circuit simulations and verify my calculations.

Software simulation was necessary to test whether or not the components with an
estimated value could be used to provide the desired output before actually
purchasing them. I also used the Microsoft Office Program to record results,
prepare a report and presentation. 

CE 1.17

Throughout this
project, I accomplished my tasks as a responsible team member. I kept
interacting with my team at all times to motivate them. I monitored the
progress of the project to make sure everything was going smoothly. I simulated
the circuit on simulation software before ordering the components to save extra
costs. I arranged weekly group meetings with my team members to discuss various
project matters with them. The outcome of each meeting and the project progress
was reported to the project supervisor. In the final meeting, I presented the
project in front of all the team members, project supervisor and project


CE 1.18

The project of GSM
Based Substation Load Switching was a great success for me as it proved to be
an alternative source of power backup for the utility supply on which most
industrial and commercial applications were dependent. I was able to accomplish
it on time, which made it even more praiseworthy. This project featured all the
hardware components that were reasoned out and placed carefully, thus
contributing to the best functioning of the unit. It gave me an environment to
groom myself in the field of engineering. It also improved my social
interaction and dealing skills. My company recognized me for my quality
performance and efforts that I put into this project.

CE 1.19

The future aspects of
this project can be extended using GPRS technology. This will help in sending the monitored and
controlled data to any place in the world. The temperature controlling systems
like coolant can also be used in places where maintenance of temperature level
is needed. Industrial equipment can be
supervised from our personal computers by connecting wireless camera by using
GPRS and GPS technology. Automated switching of the devices can be carried out
using personal computers making everything so convenient.