saadi-siemens

Siemens Pakistan Engg. CO LTD Internship
Report
Shaikh Saadi | Sir Syed University of Engg. & Technology, Karachi 1
Name: Shaikh Saadi
Department of Electronics
Sir Syed University of Engineering and Technology (SSUET)
INTERNSHIP REPORT
Business Unit: EM-TS
By SHAIKH SAADI
SUPERVISOR: Mr. UMAIR AHMAD

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PREFACE:
This report documents the work done during the summer internship at SIEMENS KARACHI
department EMTS, under the supervision of Mr. UMAIR AHMAD (PRIMARY
ENGINEER). The report first shall give an overview of the tasks completed during the period
of internship with technical details. Then the results obtained shall be discussed and analyzed.
I have tried my level best to keep report simple yet technically correct. I hope that I
succeeded in my attempt.
Kindly Regards,
 Shaikh Saadi.
AKNOWLEDGEMENT
First of all I thanks to ALMIGHTY ALLAH for giving me the opportunity to work as an
internee in Siemens Pakistan Engineering Company Ltd, a reputed and prestigious organization
of the country.
It is the indulgence to acknowledge my deep gratitude to Siemens who gave me an opportunity
to work as an engineer and not as a student. I am highly obliged for the kindness and great co-
operation provided by staff BU: EMTS of Siemens and to become an active part of this
department as an internee.
I thank Mr. Umair Ahmad, my supervisor, for giving me time of his busy schedule. His sincere
commitment and guidance helped me learn a lot from this internship.
During the course of my internship, I came into contact with almost all the staff working here
and found them invariably helpful. I would like to thank the following:
 Mr. Faizan Tahir
 Mr. Yasir Zaidi
 Mr. Hasan Nasir
 Mr. Ahmed Ozair
 Mr. Obaid Aqil
 Miss. Samreen Iqbal

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CONTENTS
1. Introduction………………….…………………………………………………………………………4
2. EM-TS…………………………………………………………..………………….……………….…5
2.1 Departments in EMTS…………….…………………………………………………….……...…6-7
3. Process Engineering in EMTS……...……………………..……………………………………………7
3.1. Grid Station………………………..……………………………………………………………….7
3.2. Switch Gears…………………………………..……………………………….………………......8
3.3 Types Of Switch gears.……………………………………………………………………………..8
3.3.1 Air Insulated Switch Gears………………………………………………………..………..…….8
3.3.2 Gas Insulated Switch Gears ………………..…………………………………………...............8-9
4. Transformer………………………………………………………………………………………..……..9
4.1 Types of Transformer…………………………………………………………………………..….9
4.1.1 Power Transformer………………………………………………………………………….....9-10
4.1.2 Instrument Transformer……………………………………………………………………….10-11
4.1.3 Distribution Transformer…………………………………………………………………….....11
5. Bus Bars………………………………………………………………………………………………...12
5.1 Electrical Bus Bar System………………………………………………………………………...12
5.1.1 Single bus bar arrangement………………………………………………………………………...12
5.1.2 With bus sectionalizer……………………………………………………………………………..12
5.1.3 Double bus bar arrangement…………………………………………………………………….12-13
5.1.4 Double circuit Breaker bus bar arrangement………………………………………………………13
5.1.5 One & a half circuit Breaker bus bar arrangement………………………………………………...13
5.1.6 Ring bus bar arrangement………………………………………………………………………….13
6. HV/LV Devices…………………………………………………….……………………………………...14
6.1 Disconnector…………………………………………………………………………………………14.
6.2 Circuit Breaker……………………………………………………………………………………….14
6.2.1 Types of Circuit Breaker…………………………………………………………………………...14
6.3 Earthing Switch…………………………………………………………………………….………. .14
6.4 Surge Arrester………………………………………………………………………………………..14
6.5 Contactor …………………………………………………………………………………………….14
6.6 Line Trap……………………………………………………………………………………………..15
6.7 Capacitor Bank…………………………………………………………………………………..…...15
6.8 Bushings ……………………………………………………………………………………………..15
6.9 Earth Shield Wiring………………………………………………………………………………….15
7. Relay………………………………………………………………………………………………………..16
7.1 Types of relay……………………………………………………………………………….……….16
7.1.1 Over current relay……………………………………………………………………….…………16
7.1.2 Phase balance current relay………………………………………………………………………..16
7.1.3 Distance relay……………………………………………………………………….……………..16
7.1.4 Earth fault relay……………………………………………………………………….…………...16
7.1.5 Buchholz relay….……………………………………………………………………….…………16
7.1.6 Overvoltage/Undervoltage relay…………………………………………………………………...16
8. Faults………………………………………………………………………………………………………..16
8.1 Types of faults………………………………………………………………………………….…….17
8.1.1 Persistent fault…………………………………………………………………………….17
8.1.2 Arcing fault………………………………………………………………………………..17
8.1.3 Transient fault……………………………………………………………………………..17
8.1.4 Symmetric fault……………………………………………………………………………17
8.1.5 Asymmetric fault…………………………………………………………………………..17
9. Conclusion………………………………………………………………………………………....17

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1. INTRODUCTION
SIEMENS HISTORY:
Siemens was founded in Berlin by Werner von Siemens in 1847. As an extraordinary
inventor, engineer and entrepreneur, Werner von Siemens made the world's first pointer
telegraph and electric dynamo; inventions that helped put the spin in the industrial revolution.
He was the man behind one of the most fascinating success stories of all time - by turning a
humble little workshop into one of the world's largest enterprises.
As Werner had envisioned, the company he started grew from strength to strength in every
field of electrical engineering. From constructing the world's first electric railway to laying
the first telegraph line linking Britain and India, Siemens was responsible for building much
of the modern world's infrastructure.
Siemens is today a technology giant in more than 190 countries, employing some 440,000
people worldwide. Work in the fields of energy, industry, communications, information,
transportation, healthcare, components and lighting has become essential parts of everyday
life.
SIEMENS IN PAKISTAN:
Siemens Pakistan Engineering Company Limited was founded in 1953 as a private company
and in 1963, the company was registered as a Public Limited Company. Siemens enjoys a
leading position in Pakistan in the business areas of Power, Automation and Control,
Information Technology and Industrial solutions. Siemens is the country’s No. 1 supplier of
high-voltage grid stations, switchgear products and systems, power distribution, and network
consultancy. The Automation and Drives Group is the only major local supplier with 35 years
of experience in the local manufacture of diesel generating sets to meet customer-specific
demands from clients on both the domestic and international markets. The success story
continues with the Medical Solutions Group, which is the leading supplier of state-of-the-art
equipment to major hospitals.
VISION:
To remain market leader and technology pace setter in the engineering and electronics
industry by utilizing the high-tech engineering expertise of the Siemens Group worldwide. To
maintain strong and prominent local presence.
COMPANY STRUCTURE:
Siemens Pakistan is working in all aspect of engineering. Its operations are categorized in
following divisions:
 Energy Sector
 Health care
 Industry & Infrastructure
 Cities Sector

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2. ENERGY MANAGEMENT TRANSMISSION SOLUTION
(EMTS):
In this department, high voltage transmission process is done. After the generation of power
from the generators, voltage is generated with high amount of current. This voltage is transfer
to a substation where it is step up to a high voltage due to which the current is reduced. This
is done to reduce current losses while the transmission of power. Then again it is step down
up to medium voltage by a step down transformer for further process.
The power is then transfer through power lines from where we can extract it to those places
where it is to be use. The various equipments are use for the protection and safety of the
transmission system such as surge arrestors, circuit breakers, disconnector with earthing
switches. Voltage transformers use to measure the voltages by step downing the voltage and
then measuring it. Current transformers use to measure the current passing through the line
by step downing the current to a measurable ratio (for example 500A=1A, by this ratio the
meter can easily measure the current and we can detect the actual current by multiplying the
real quantity with the answer). Power transformers use to step down large amount of voltage
to medium voltages (for example 132KV to 11KV).
Different relays are connected to a current transformer for various purposes. They detect the
fault and then signaled the circuit breaker to trip in order to protect the system. Bus bars act
as a common node. It is a low impedance conductor to which several electrical connections
can be made. Surge arrestors and shield wires use to protect the transmission system from
high voltage surges or lightning effects. Shield wires also protect from different losses as
well.
This department is divided into different sub groups performing alternative tasks. From the
proposal of the project till its execution, each group containing several engineers performs its
procedure on the basis of the client’s request. Following are the sub groups in EMTS
department.

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2.1.
i. PROPOSAL DEPARTMENT:
The Proposal Manager will have the responsibility of coordinating all phases of the
company’s proposal process in response to government and commercial requests for
proposals. The ability to meet deadlines, a commitment to teamwork, and detailed follow-
through will be the key to success in this role.
ii. PROCUREMENT DEPARTMENT:
The procurement department is the office responsible for the acquisition of supplies, services
and construction in support of the authority’s business. The procurement department is the
entity within both authorities authorized to issue invitations to bid, requests for proposal,
request for quotation and issue contracts. It purchases orders, develops term contracts and
acquires supplies and services.
iii. PROJECT DESIGNING:
Project designing consist of two divisions:
1. Primary Designing 2. Secondary Designing
 Primary Designing:
In primary designing, the design of the project is made on the premises of the client. In this
department, all designing are performed such as layouts, earthing calculation, cable singling,
lightning protection and electrical designing. The design of a project is made on different
virtual software such as AutoCAD. The design consists of all the components that are ordered
by the client and place accordingly on its request. After the completion, it is checked by the
client for his satisfactory and then it is parallel to the next division i.e. secondary designing.
 Secondary Designing:
After the primary design is complete, the secondary designing is performed. Secondary
designing is based on the control and protection of the design. For the safety and protection
Proposal
Department
Procurement
Department
Project
Designing
Project
Execution
Primary
Designing
Secondary
Designing
ENERGY MANAGEMENT TRANSMISSION SOLUTION
(EMTS)

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of the transmission system and components, this department adds several appliances and the
design undergo another process to make the protection and safety at its best level.
iv. PROJECT EXECUTION:
In this department, the project executing consists of the processes used to complete the
work defined in the project plan to accomplish the project's requirements. Execution process
involves coordinating people and resources, as well as integrating and performing the
activities of the project in accordance with the project management plan.
3. PROCESS ENGINEERING IN EMTS
3.1. GRID STATIONS:
A substation or grid station is a part of an electrical generation, transmission,
and distribution system. Substations transform voltage from high to low, or the reverse, or
perform any of several other important functions. Between the generating station and
consumer, electric power may flow through several substations at different voltage levels.
Substations may be owned and operated by an electrical utility, or may be owned by a large
industrial or commercial customer. Generally substations are unattended, relying
on SCADA for remote supervision and control.
A substation may include transformers to change voltage levels between high transmission
voltages and lower distribution voltages, or at the interconnection of two different
transmission voltages. The word substation comes from the days before the distribution
system became a grid. As central generation stations became larger, smaller generating plants
were converted to distribution stations, receiving their energy supply from a larger plant
instead of using their own generators. The first substations were connected to only one power
station, where the generators were housed, and were subsidiaries of that power station.
3.2. SWITCH GEARS:
In an electric power system, switchgear is the combinations of electrical disconnect
switches, fuses or circuit breakers used to control, protect and isolate electrical equipment.
Switchgear is used both to de-energize equipment to allow work to be done and to clear
faults downstream. This type of equipment is directly linked to the reliability of
the electricity supply.
Typically, switchgears in substations are located on both the high- and low-voltage sides of
large power transformers. The switchgear on the low-voltage side of the transformers may be
located in a building, with medium-voltage circuit breakers for distribution circuits, along
with metering, control, and protection equipment. For industrial applications,

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a transformer and switchgear line-up may be combined in one housing, called a
unitized substation.
3.3.
3.3.1. AIR INSULATED SWITCH GEAR:
Air Insulated Switchgear (AIS) is the most common type of
medium voltage equipment with the largest installed base. Its
life cycle is generally quite long, so the service strategy applied
is extremely important to guarantee the required reliability over
time.
FEATURES OF AIS:
 AIS is cost effective
 Requires large amount of space
 Climatic effect damages the system
 Is less reliable than GIS
3.3.2. GAS INSULATED SWITCH GEAR:
In this type of switchgear, all the necessary components of switchgear can be assembled in
very limited space. GIS is a kind of metal enclosed switchgear. That means, all the equipment
of the electrical switchgear are enclosed by gas tight metal enclosure and SF6 gas is used as
insulation between live parts of the equipment and earthed metal enclosure. This type of
switchgear, means, and gas insulated switchgear is available from 12 KV system to 800 KV
system. For establishing electrical substation in very limited place this type of SF6 insulated
electrical switchgear plays the major role.
In gas insulated medium voltage switchgear, vacuum technology is used as interrupting
purpose and SF6 gas is used as insulation material. Although for both interruption and
insulation, SF6 gas is used in many medium voltage GIS system. But for such equipment
rated SF6 gas pressures are different for interruption and insulation. SF6 gas pressure for
insulating purpose is generally kept below 2.5 bar whereas SF6 gas pressure for interrupting
purpose is ranged from 5 bar to 7 bar
FEATURES OF GIS:
 GIS is far more costly than AIS
 Requires less space
 Is safer in operation
 Has higher protection against ambient condition
 Is more reliable
TYPES OF SWITCH GEARS
GAS
INSULATED
AIR
INSULATED

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4. TRANSFORMER:
A transformer is an electrical device that transfers electrical
energy between two or more circuits through electromagnetic
induction. Commonly, they are used to step-up or step-down
the voltages of alternating current in electric power
applications. It is also called “TRAFO”.
4.1. TYPES OF TRANSFORMERS:
1) POWER TRANSFORMER:
Generation of electrical power in low voltage level is very
much cost effective. Hence electrical power is generated in
low voltage level. Theoretically, this low voltage level
power can be transmitted to the receiving end. But if the
voltage level of a power is increased, the current of the
power is reduced which causes reduction in ohm or I2
R
losses in the system, reduction in cross sectional area of the
conductor i.e. reduction in capital cost of the system and it
TYPES OF TRANSFORMERS
POWER
TRANSFORMERS
INSTRUMENT
TRANSFORMERS
DISTRIBUTION
TRANSFORMER

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also improves the voltage regulation of the system. Because of these, low level power must
be stepped up for efficient electrical power transmission. This is done by step up transformer
at the sending side of the power system network. As this high voltage power may not be
distributed to the consumers directly, this must be stepped down to the desired level at the
receiving end with the help of step down transformer. These are the uses of electrical power
transformer in the electrical power system.
Two winding transformers are generally used where ratio between high voltage and low
voltage is greater than 2. It is cost effective to use auto transformer where the ratio between
high voltage and low voltage is less than 2. Again three phase single unit transformer is more
cost effective than a bank of three single phase transformer unit in a three phase system. But
still it is preferable to use than the later where power dealing is very large since such large
size of three phase single unit power transformer may not be easily transported from
manufacturer's place to work site.
2) INSTRUMENT TRANSFORMER:
Instrument transformers are high accuracy class electrical devices used to isolate or transform
voltage or current levels. The most common usage of instrument transformers is to operate
instruments or metering from high voltage or high current circuits, safely isolating secondary
control circuitry from the high voltages or currents. Instrument transformers are also sub-
divided into two parts i.e. Current transformer (C.T) & Voltage transformer (P.T).
 CURRENT TRANSFORMER (C.T):
A current transformer (CT) is used for measurement of alternating electric currents (AC).
Current transformers, together with voltage (or potential) transformers (VT or PT), are known
as instrument transformers. When current in a circuit is too high to apply directly to
measuring instruments, then a current transformer helps us produce an alternating current in
its secondary winding which is proportional to the current being measured in its primary.
Outputs of current transformers are commonly used in metering and protective relays in
the electrical power industry. Current transformers reduce high voltage currents to a much
lower value and provide a convenient way of safely monitoring the actual electrical current
flowing in an AC transmission line using a standard ammeter. There are three basic types of
current transformers.
1. Wound
2. Toroidal
3. bar-type
INSTRUMENT
TRANSFORMER
CURRENT
TRANSFORMER
POTENTIAL
TRANSFORMER

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 Wound current transformers: The transformers primary winding is physically
connected in series with the conductor that carries the measured current flowing in the
circuit. The magnitude of the secondary current is dependent on the turns ratio of the
transformer.
 Toroidal current transformers: These do not contain a primary winding. Instead, the
line that carries the current flowing in the network is threaded through a window or hole in
the toroidal transformer. Some current transformers have a “split core” which allows it to be
opened, installed, and closed, without disconnecting the circuit to which they are attached.
 Bar-type current transformers: This type of current transformer uses the actual cable or
bus-bar of the main circuit as the primary winding, which is equivalent to a single turn. They
are fully insulated from the high operating voltage of the system and are usually bolted to the
current carrying device.
 POTENTIAL TRANSFORMER (P.T):
Potential transformer or voltage transformer gets used in electrical
power system for stepping down the system voltage to a safe value
which can be fed to low ratings meters and relays. Commercially
available relays and meters used for protection and metering, are
designed for low voltage. There are three primary types of potential
transformers.
1. Electromagnetic
2. Capacitor
3. Optical
 Electromagnetic potential transformer: The electromagnetic potential transformer
is a wire-wound transformer
 Capacitor potential transformer: A capacitor voltage transformer (CVT or CCVT),
is a transformer used in power systems to step down extra high voltage signals and
provide a low voltage signal, for metering or operating a protective relay.
 Optical potential transformer: An optical voltage transformer exploits the electrical
properties of optical materials.
 DISTRIBUTION TRANSFORMER:
A distribution transformer is a transformer provides the
final voltage transformation in the electric power distribution system,
stepping down the voltage used in the distribution lines to the level
used by the customer. If mounted on a utility pole, they are
called pole-mount transformers. If the distribution lines are located at
ground level or underground, distribution transformers are mounted
on concrete pads and locked in steel cases, thus known as pad-mount
transformers, they usually don't operate at full load.
Tap Changer:
It is used to control the voltage in transformer; it is places in the primary side of transformer
because minimum voltage is found in primary side.

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5. BUS BARS:
DEFINITION: A bus bar is an electrical conductor, maintained at a specific voltage and
capable of carrying high currents, usually to make a common connection between several
circuits in the system.
5.1. ELECTRICAL BUS BAR SYSTEM:
There are many different electrical bus system schemes available but selection of a particular
scheme depends upon the system voltage, position of substation in electrical power system,
flexibility needed in system and cost to be expensed.
Some common types of bus bars are discussed below:
5.1.1. SINGLE BUS BAR ARRANGEMENT:
Single Bus System is simplest and cheapest one. In this
scheme all the feeders and transformer bay are connected to only
one single bus.
Advantages:
1) This is very simple in design.
2) This is very cost effective scheme.
3) This is very convenient to operate.
Disadvantages:
1) One major difficulty of this type of arrangement is that,
maintenance of equipment of any bay cannot be possible without
interrupting the feeder or transformer connected to that bay.
5.1.2. SINGLE BUS BAR ARRANGEMENT WITH BUS SECTIONALIZER:
If a single bus bar is sectionalized with circuit breaker, it will
give more advantage then the previous scheme. If there are more
than one incoming and the incoming sources and outgoing feeders
are evenly distributed on the sections, interruption of system can be
reduced to a good extent.
Advantages:
1) If any of the sources is out of system, still all loads can be fed by
switching on the sectional circuit breaker or bus coupler breaker.
2) If one section of the bus bar system is under maintenance, part
load of the substation can be fed by energizing the other section of
bus bar.
Disadvantages:
In the case of single bus system, maintenance of equipment of any bay cannot be possible
without interrupting the feeder or transformer connected to that bay.
5.1.3. DOUBLE BUS BAR ARRANGEMENT:
In double bus bar system two identical bus bars are used in such a
way that any outgoing or incoming feeder can be taken from any of
the bus. Every feeder is connected to both of the buses in parallel
through individual isolator. Any feeder at any time can be transferred
from one bus to other.

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Advantages:
Double Bus Bar Arrangement increases the flexibility of system.
Disadvantages:
The arrangement does not permit breaker maintenance without interruption.
5.1.4. DOUBLE CIRCUIT BREAKER BUS BAR
ARRANGEMENT:
In double breaker bus bar system two identical bus bars are used
in such a way that any outgoing or incoming feeder can be taken
from any of the bus, it is similar to double bus bar system. Only
difference is that here every feeder is connected to both of the
buses in parallel through individual breaker instead only isolator
& there is no use of bus-coupler.
Advantages:
Maintenance or any problem occurs in one bus line, the other can
be used for the transferring of power.
Disadvantages:
It is very costly.
5.1.5. ONE AND A HALF CIRCUIT BREAKER BUS BAR
ARRANGEMENT:
This is an improvement on the double breaker scheme to effect saving
in the number of circuit breakers. For every two circuits only one
spare breaker is provided. In figure two feeders are fed from two
different buses through their associated breakers and these two feeders
are coupled by a third breaker which is called tie breaker. Normally all
the three breakers are closed and power is fed to both the circuits from
two buses which are operated in parallel. The tie breaker acts as
coupler for the two feeder circuits.
Advantages:
During any fault on any one of the buses, that faulty bus will be cleared instantly without
interrupting any feeders in the system since all feeders will continue to feed from other
healthy bus.
Disadvantages:
This scheme is much expensive due to investment for third breaker.
5.1.6. RING BUS BAR ARRANGEMENT:
It provides a double feed to each feeder circuit, opening one
breaker under maintenance or otherwise does not affect supply
to any feeder
Disadvantages:
If any one of the circuit breaker in ring loop is switched off the
reliability of system becomes very poor as because closed loop
becomes opened.

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6. HV/LV DEVICES:
A device designed to close, open, or both, one or more electrical circuits are called switching
devices.
6.1. DISCONNECTOR:
A disconnector, disconnect switch or isolator switch is used to ensure that an
electrical circuit is completely de-energized for service or maintenance. Such
switches are often found in electrical distribution and industrial applications.
High-voltage isolation switches are used in electrical substations to allow
isolation of apparatus such as circuit breakers, transformers, and transmission
lines, for maintenance. The disconnector is usually operates in no-load
condition. Disconnector can be operated either manually or automatically.
6.2. CIRCUIT BREAKER:
A circuit breaker is an automatically operated electrical switch designed
to protect an electrical circuit from damage caused by overload or short
circuit. Its basic function is to detect a fault condition and interrupt
current flow. Unlike a fuse, which operates once and then must be
replaced, a circuit breaker can be reset either manually or automatically.
6.2.1. TYPES OF CIRCUIT BREAKERS:
There are three types of circuit breakers:
 High Voltage Circuit Breaker
 Medium Voltage Circuit Breaker
 Low Voltage Circuit Breaker
6.3. EARTHING SWITCH:
It is usually connects with isolator in parallel & its main function is to earth one
or both ends of disconnector, whichever is required.
6.4. SURGE ARRESTER:
A surge arrester is a device to protect electrical equipment from over-voltage
transients caused by external (lightning) or internal (switching) events. Also
called a surge protection device (SPD or transient voltage surge
suppressor (TVSS), this class of device is used to protect equipment in
power transmission and distribution systems, usually connects with power
transformer.
6.5. CONTACTOR:
A contactor is an electrically controlled switch used for switching an electrical
power circuit, similar to a relay except with higher current ratings. A contactor is
controlled by a circuit which has a much lower power level than the switched circuit.
Contactors are used to control electric-motors, lighting, heating, capacitor banks,
thermal evaporators, and other electrical loads.

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6.6. LINE TRAP:
A line trap is a high frequency stopper, acts as a low pass filter.
When there is a need to send communication signals far away we
send it by the help of transmission lines. At the receiving end a line
trap is connected which obtains the desire communication signals
and block others, also called wave trap. Line traps are cylinder like
structures connected in series with HV transmission lines. Its range
is from (40 kHz-1000 kHz).
6.7. CAPACITOR BANK:
A capacitor bank is a grouping of several identical capacitors interconnected in parallel or in
series with one another. These groups of capacitors are typically used to correct or counteract
undesirable characteristics, such as power factor lag or phase shifts inherent in alternating
current (AC) electrical power supplies. Capacitor banks may
also be used in direct current (DC) power supplies to increase
stored energy and improve the ripple current capacity of
the power supply.
Single capacitors are electrical or electronic components
which store electrical energy. Capacitors consist of two
conductors that are separated by an insulating material or
dielectric. When an electrical current is passed through the
conductor pair, a static electric field develops in the dielectric which represents the stored
energy.
6.8. BUSHINGS:
A bushing is an insulated device, in an electrical power system that allows an
electrical conductor to pass safely through a (usually) earthed conducting barrier
such as the wall of a transformer or circuit breaker. Bushings are needed on:
 Transformers
 Buildings
 Gas-Insulated Switch Gears (GIS)
 Generators
 And Other High Voltage equipment
6.9. EARTH SHIELD WIRING:
The earth shield wiring is used for lightning protection.

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7. RELAY:
A relay is an electrically operated switch. It is use as a switching or indicates any problem in
power lines. Relays are used where it is necessary to control a circuit by a low-power signal
(with complete electrical isolation between control and controlled circuits), or where several
circuits must be controlled by one signal.
7.1.TYPES OF RELAY:
As, there are many types of relays but I discussed here very few.
 7.1.1. Over Current Relay:
It indicates the current which exceed in outgoing feeder & then produce tripping. In an over
current relay or o/c relay the actuating quantity is only current. There is only one current
operated element in the relay, no voltage coil are included. It is connected with generation
and transmission bay, sometimes called protective relay.
 7.1.2. Phase Balance Current Relay:
The phase balance current relay is designed to provide protection against unbalanced phase
currents by operating to trip the circuit breaker when a fixed percentage of unbalance exits
between any two phases. It will, therefore; protect motors under load when the desired
sensitivity cannot be obtained by a voltage operated relay. It is mostly used in distribution
bay.
 7.1.3. Distance Relay:
The function of distance relay depending upon the distance of fault in the line, the relay
operates depending upon the impedance between the point of fault and the point where relay
is installed. These relays are known as distance relay or impedance relay. It is mostly used in
generation bay, sometimes called protective relay.
 7.1.4. Earth Fault Relay:
This relay is a definite time relay suitable for earth fault protection of generators, motors,
transformers, capacitor banks, shunt reactors and radial feeders in distribution networks.
 7.1.5. Buchholz relay:
Buchholz relay is a safety device sensing the accumulation of gas in large oil-
filled transformers, which will alarm on slow accumulation of gas or shut down the
transformer if gas is produced rapidly in the transformer oil. The contacts are not operated by
an electric current but by the pressure of accumulated gas or oil flow.
 7.1.6. Overvoltage/Undervoltage Relay:
It provides protection to equipment where either an over voltage or under voltage condition is
potentially damaging. When used as an under voltage relay, they provide protection to
equipment that is required to operate above a minimum voltage. When used as an over
voltage relay, they protect equipment against excessive voltage conditions. It is usually
connects in distribution bay.

Report
8. FAULTS:
A fault is any abnormal electric current in an electric power system. In three-phase systems, a
fault may involve one or more phases and ground, or may occur only between phases. In a
ground fault or earth fault, charge flows into the earth. If only some phases are affected, the
resulting "asymmetrical fault".
8.1.TYPES OF FAULTS: Some types of faults are discussed below.
1. PERSISTENT FAULT:
A persistent fault does not disappear when power is disconnected. Faults in
underground power cables are most often persistent due to mechanical damage to the
cable. This is temporary fault.
2. ARCING FAULT:
Where the system voltage is high enough, it causes an electric arc forms between
power system conductors and ground, engineers use arc fault circuit interrupter to
avoid it.
3. TRANSIENT FAULT:
It occurs in overhead power lines due to lightning or bird or an other animal in
contact.
4. SYMMETRIC FAULT:
In a polyphase system, a fault may affect all phases equally which is a symmetrical
fault or balanced fault.
5. A SYMMETRIC FAULT:
If only some phases are affected, in a polyphase system then the resulting
asymmetrical fault or unbalanced fault.
SOME CAUSES ARE:
 Line-to-Line: A short circuit between lines, due to a broken insulator.
 Line-to-Ground: A short circuit between one line and ground, due to lightning or
other storm causes damage.
 Double line-to-Ground: It happens due to two lines come into contact with the
ground.
9. CONCLUSION:
As an internee I have learned a lot here, met new people and have new experience. I have
achieved several of my learning goals; however for some conditions do not permit. The
internship was good to find out my strength and weaknesses. This helped me to improve my
skills in coming time. After my BACHELORS I think I can start my working career.
During my internship period I performed some tasks and experiments as well. The tasks
include matching of power cables, AutoCAD designing, & working in healthy environment
with experienced people.
I will always recommend students to do their internship at Siemens Karachi, as it is a great
place to learn and groom your abilities.

saadi-siemens

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