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1. SHORT CIRCUIT STUDY IN
ELECTRICAL TECHNOLOGY
A Technical seminar Report Submitted in partial fulfillment of the
requirement for the degree of
BACHELOR OF TECHNOLOGY
In
ELETRICAL AND ELECTRONICS ENGINEERING
BY
K.V.V.S.CHAKRADHAR (06J21A0241)
Under the esteemed guidance of
CH.VENKAT, B.TECH
Asst.prof,EEE- Dept.JBREC.
Department of Electrical and Electronics Engineering
JOGINPALLY B.R. ENGINEERING COLLEGE
Yenkapally, Moinabad Mandal, R.R.District
Affiliated to J.N.T. University, Hyderabad
1

2. JOGINPALLY B.R. ENGINEERING COLLEGE
Yenkapally, Moinabad Mandal, R.R.District
Affiliated to J.N.T. University, Hyderabad
BONAFIDE CERTIFICATE
This is to certify that the Technical seminar report entitled
“SHORT CIRCUIT STUDY IN
ELECTRICALTECHNOLOGY” is being submitted by
K.V.V.S.CHAKRADHAR (06J21A0241), in technical
fulfillment for the award of the degree of Bachelor of
Technology in Electrical and Electronics Engineering to the
Jawaharlal Nehuru technological university, as a record of
bonafide work carried out by him under my guidance and
supervision. The result embodied in the Technical seminar
report has not been submitted to any other University or
Institute for the award of any degree.
PROJECT GUIDE HEAD OF THE DEPATRMENT
CH.VENKAT M.Kondalu,M.Tech,(Ph.D),
Asst.prof, EEE-Dept.JBREC HOD, EEE, JBREC
EXTERNAL EXAMINER
2

3. ACKNOWLEDGEMENT
We express our profound sense of gratitude for the administration
of JOGINPALLY B R ENGINEERING COLLEGE for giving
us an opportunity to take up the TECHNICAL SEMINAR work in their
organization
We express our great pleasure to have opportunity to take up the
TECHNICAL SEMINAR work under the guidance of D.N.RAO M.E,
Ph.D PRINCIPAL of JOGINPALLY B R ENGINEERING
COLLEGE whose invariable references, suggestions, and
encouragement have immensely helped us in the successful completion
of this TECHNICAL SEMINAR.
We express our sincere thanks and gratitude to Mr.
KONDALU M.Tech (Ph.D) Associate Professor and HEAD OF
THE DEPARTMENT of ELECTRICAL AND
ELECTRONICS ENGINEERING for valuable help and
encouragement throughout the TECHNICAL SEMINAR work.
We are very much thankful to Mr.CH.VENKAT, B.TECH
EEE DEPARTMENT for his excellent guidance AND
encouragement throughout the TECHNICAL SEMINAR work.
We thank all of teaching and non-teaching staff members of EEE
department for their extended cooperation.
3

4. INDEX
CONTENT : Pg.No
1. ABSTRACT……………………………………………..5
2. INTRODUCTION………………………………………7
3. WHAT IS SHORT CIRCUIT?........................................8
4. SHORT CIRCUIT TYPES …………………………….9
5. REASONS OF SHORT CIRCUIT…………………….13
6. EFFECTS OF SHORT CIRCUIT…………………….17
7. PREVENTION METHODS ………………………….19
8. ADVANTAGES OF SHORT CIRCUIT STUDY…….27
9. CONCLUSION………………………………………..29
4

5. ABSTRACT
Short circuit study in electrical technology
Short Circuit (Fault Current) studies are required to
insure that existing and new equipment ratings are
adequate to withstand the available short circuit energy
available at each point in the electrical system. Fault
currents that exceed equipment ratings are capable of
extensive equipment damage and are a serious threat to
human life
On large systems, short circuit studies are required to
determine both the switchgear ratings and the relay
settings. No substation equipment, motor control
centers, breaker panels, etc. can be purchased without
knowledge of the complete short circuit values for the
entire power distribution system.
The short circuit calculations must be maintained and
periodically updated to protect the equipment and the
lives. It is not necessarily safe to assume that new
equipment is properly rated.Fires from electrical cords
or from wiring devices are increasing in these years. The
reason is supposed to be the increase of electrical power
dissipation for domestic use.
DELIVERABLES OF SHORT CIRCUIT STUDY
A typical short circuit study includes:
 Short circuit calculations, which highlights any
equipment that is ascertained to be underrated as
specified
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6.  Suggested modifications to rectify the underrated
equipment; (trip sizes within the same frame, the
time curve characteristics of induction relays, CT
ranges, etc.).
The Protective Device Setting and Coordination Study is
the suggested follow on analysis to develop the
coordination curves, highlighting areas lacking
coordination. Presentation of a protective device study
would include a technical evaluation with a discussion
of the logical compromises for best coordination
The building/facility may not be properly protected
against short-circuit currents. These currents can
damage or deteriorate equipment. Improperly protected
short-circuit currents can injure or kill maintenance
personnel.
Recently new initiatives have been taken to require
facilities to properly identify these dangerous points
within the power distribution of the facility.This is the
main reason for requirement of study about short circuit.
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7. INTRODUCTION
Fires from electrical cords or from wiring devices are
increasing in these years. The reason is supposed to be
the increase of electrical power dissipation for domestic
use.
A circuit breaker is used to protect the circuit from
overcurrent or short-circuit. If the conductors do not
touch directly and they are shorten by an arcing along
the carbonised insulating material, the current flows
intermittently.
This is the reason why a circuit breaker does not cut off
the current more than 100 Amps and fire hazardous
sparking continues.
Peak value of the short-circuit current is limited by the
resistance of the circuit. In typical conditions the circuit
breaker does not cut off the intermittent current under
about 200 Amps in peak value. This condition is easily
made when an extending cord of about 10 meters long is
used.
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8. India has approximately 60000 fires a year. The number
of fires related to electrical cause or electrical appliances
are shown in table 1. Although insulating materials have
been increased their quality, the number of electrical
fires have not been decreased.
Table 1: Loss of lives in Andhra Pradesh due to
fires
Year No.of fire accidents No.of lives lost
1996 12741 79
1997 13569 184
1998 12459 58
1999 14456 81
2000 16987 123
2001 12584 58
2002 12999 78
2003 18456 156
2004 16271 249
2005 15631 183
2006 17452 129
2007 18975 149
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9. Short circuit arcing was made intentionally in this study.
Although insulating materials have been increased their
quality, fires are still caused by these failures. It is
necessary to doubt about their safety and to make a
study on the mechanism of the beginning of short circuit
arcing in order to prevent these fires.
A short circuit (sometimes abbreviated to short or s/c)
in an electrical circuit is one that allows a current to
travel along a different path from the one originally
intended. The electrical opposite of a short circuit is an
"open circuit", which is an infinite resistance between
two nodes. It is common to misuse "short circuit" to
describe any electrical malfunction, regardless of the
actual problem.
What is short circuit?
A short circuit is a fault. It means there is a very low
resistance conducting path from one side of a
component to the other. For example a wire might have
come loose which connects two sides of a circuit
together. Or perhaps there's some moisture on the
surface of a component that means current can bypass it.
The wire or the moisture 'shorts' the circuit because the
length of the conducting path back to the battery has
decreased.
9

10. Simple activity showing the effect of shorting out a
bulb.
A short makes the circuit behave as if the component
wasn't there. The component stops working (it isn't
there, after all) and the current everywhere in that circuit
will increase, which can damage other components or,
in extreme cases, cause a fire.
So how can we explain shorts? A very misleading way
of explaining them is to say that current takes the easiest
path
Shorting out a single component
which is in series with others
When you connect a wire across the terminals of a bulb
you're effectively creating a little parallel circuit. The
thing with parallel circuits is that the effective resistance
is less than the smallest resistance. In this case the
smallest resistance is just the wire, and this has a very
low resistance indeed.
10

11. Simulation A full explanation of what happens when a
bulb is shorted out.Now you've reduced the resistance of
the series circuit and so the current everywhere
increases. The current through the unshorted bulb
increases and so it gets brighter. But brightness isn't just
a function of current.
You have a low resistance (the shorted bulb) in series
with a higher resistance (the unshorted bulb) and this
changes the way the voltage is shared around the
circuit. The bigger resistance takes a bigger share of the
total voltage. So the second bulb is bright for these two
reasons, bigger current through it AND bigger voltage
across it. Remember that voltage and current are
connected. The current through the second bulb can
only increase because the voltage across it is bigger.
In the same way the shorted bulb has a very low voltage
across it so the current through it is very small and that's
why it's out. The wire doing the shorting has the same
voltage across it as the bulb but it also has a very low
resistance so the current through the wire is big. The
current through the wire and the current through the
bulb add up to the current through the unshorted bulb.
Shorting out a whole circuit
11

12. This is exactly the same as saying that the power supply
is shorted out. In this case the explanation of why the
bulb goes out is slightly different
Animation showing different ways of shorting out a
whole circuit by connecting one terminal of a battery
directly to the other.
Again we've introduced a parallel circuit and the parallel
circuit has an effective resistance of a little bit less than
the wire. This means that there isn't really any
resistance anywhere in the circuit and so the current
supplied by the battery becomes very big. So the battery
has to work very hard.
When you work very hard you sweat a lot and this is
similar to what the battery does. The chemical reactions
in the battery take place very rapidly and lots of the
energy released gets turned straight into heat rather than
being given to the charges in the circuit. This means the
voltage is a lot less than it should be. The voltage across
the components is very low and so none of them work.
This type of short can cause a battery to get very hot. It
may even explode!
12

13. How does a short circuit happen?
When the cables of the electrical appliances are worn
out or it's not connected properly a short circuit may
occur. A short circuit has a very low resistance that
almost all electric current flow through it. It'll affect the
operation of the electrical appliances. Owing to the
heating effect the excess electric current would produce
a large amount of heat without a fuse or a circuit breaker
a fire may be occured when there's a short circuit.
A short circuit is an abnormal low-resistance connection
between two nodes of an electrical circuit that are meant
to be at different voltages. This results in an excessive
electric current (overcurrent) limited only by the
Thevenin equivalent resistance of the rest of the network
and potentially causes circuit damage, overheating, fire
or explosion. Although usually the result of a fault, there
are cases where short circuits are caused intentionally,
for example, for the purpose of voltage-sensing crowbar
circuit protectors.
In circuit analysis, the term short circuit is used by
analogy to designate a zero-impedance connection
between two nodes. This forces the two nodes to be at
the same voltage. In an ideal short circuit, this means
there is no resistance and no voltage drop across the
short. In simple circuit analysis, wires are considered to
be shorts. In real circuits, the result is a connection of
nearly zero impedance, and almost no resistance. In
such a case, the current drawn is limited by the rest of
the circuit.
Examples
13

14. An easy way to create a short circuit is to connect the
positive and negative terminals of a battery together
with a low-resistance conductor, like a wire. With low
resistance in the connection, a high current exists,
causing the cell to deliver a large amount of energy in a
short time.
A large current through a battery can cause the rapid
buildup of heat, potentially resulting in an explosion or
the release of hydrogen gas and electrolyte, which can
burn tissue and may be either an acid or a base.
Overloaded wires can also overheat, sometimes causing
damage to the wire's insulation, or a fire. High current
conditions may also occur with electric motor loads
under stalled conditions, such as when the impeller of an
electrically driven pump is jammed by debris; this is not
a short, though it may have some similar effects.
In electrical devices, unintentional short circuits are
usually caused when a wire's insulation breaks down, or
when another conducting material is introduced,
allowing charge to flow along a different path than the
one intended.
In mains circuits, short circuits may occur between two
phases, between a phase and neutral or between a phase
and earth (ground). Such short circuits are likely to
result in a very high current and therefore quickly
trigger an overcurrent protection device. However, it is
possible for short circuits to arise between neutral and
earth conductors, and between two conductors of the
same phase. Such short circuits can be dangerous,
particularly as they may not immediately result in a
large current and are therefore less likely to be detected.
14

15. Possible effects include unexpected energisation of a
circuit presumed to be isolated. To help reduce the
negative effects of short circuits, power distribution
transformers are deliberately designed to have a certain
amount of leakage reactance. The leakage reactance
(usually about 5 to 10% of the full load impedance)
helps limit both the magnitude and rate of rise of the
fault current.
A short circuit may lead to formation of an arc. The arc,
a channel of hot ionized plasma, is highly conductive
and can persist even after significant amount of original
material of the conductors was evaporated. Surface
erosion is a typical sign of electric arc damage. Even
short arcs can remove significant amount of materials
from the electrodes.
A short circuit is an accidental path of low resistance
which passes an abnormally high amount of current. A
short circuit exists whenever the resistance of a circuit
or the resistance of a part of a circuit drops in value to
almost zero ohms. A short often occurs as a result of
improper wiring or broken insulation
Reasons for short circuit occurs
A short circuit is simply a low resistance
connection between the two conductors supplying
electrical power to any circuit. This results in excessive
current flow in the power source through the 'short,' and
may even cause the power source to be destroyed. If a
fuse is in the supply circuit, it will do its job and blow
out, opening the circuit and stopping the current flow.
15

16. A short circuit may be in a direct- or alternating-current
(DC or AC) circuit. If it is a battery that is shorted, the
battery will be discharged very quickly and will heat up
due to the high current flow.
Short circuits can produce very high temperatures due to
the high power dissipation in the circuit. If a charged,
high-voltage capacitor is short circuited by a thin wire,
the resulting huge current and power dissipation will
cause the wire to actually explode.
Arc welding is a common example of the practical
application of the heating due to a short circuit. The
power supply for an arc welder can supply very high
currents that flow through the welding rod and the metal
pieces being welded. The point of contact between the
rod and the metal surfaces gets heated to the melting
point, fusing a part of the rod and both surfaces into a
single piece.
How do we locate short circuit?
Along a wire, there should be a place where some
insulation is burnt where short occur. Some times you
might also want to locate a place where there is a lapse
of electrical connection, or where there is a break along
the wire. To locate wires that are broken you can
measure the resistance with a multimeter. First shut off
all power
16

17. to item and wires that you are going to test. Set to
measure resistance at the highest setting. Place one lead
at the beginning or end of the wire and then place the
other lead the other end of the wire. With the
measurement of infinite resistance or very high
resistance, that means that there is a break in that wire.
With zero or very little resistance, that means the wire is
good. Safety is a large concern. The following images
show some steps of the setup. There are areas available
17

18. for double-checking setup before taking actual
measurements. The motor contactor below is used to
cause the transformer to short circuit to show a fault.
Below (Fig 2) is the short circuit part of the test circuit.
On the left side is a current transformer that was used to
measure the current through the shorting circuit. The
fuse box on the right has fuses which we blew to stop
the short circuit. The small black wires coming off of
the side of the contactor are connected to a switch.
When the switch is flipped, the short circuit is then
working. After a few cycles (or 1/10 of a second), the
fuses blow and the short circuit is no longer conducting
current. This prevents damage to the transformer. The
other small black wires connect to the relay and as soon
as the short circuit turns on, the relay starts collecting
data.
Figure 2
18

19. A diagram of the shorting circuit is below.
19

20. Figure shows Normal and short circuit conditions.
A short is caused by improper wiring. Note the effect on
current flow. Since the resistor has in effect been
replaced with a piece of wire, practically all the current
flows through the short and very little current flows
through the resistor. Electrons flow through the short (a
path of almost zero resistance) and the remainder of the
circuit by passing through the 10-ohm resistor and the
battery. The amount of current flow increases greatly
because its resistive path has decreased from 10,010
ohms to 10 ohms. Due to the excessive current flow. the
10-ohm resistor becomes heated. As it attempts to
dissipate this heat, the resistor will probably be
destroyed.
EFFECTS OF SHORT CIRCUIT
Short circuit currents play a vital role in Influencing the
design and operation of equipment and power
20

21. system and could not be avoided despite careful
planning and
Design, good maintenance and thorough operation of
the system.
This paper discusses the short circuit analysis conducted
in KSO
Briefly comprising of its significances, methods and
results. A result sample of the analysis based on a single
transformer is
detailed in this paper. Furthermore, the results of the
analysis and
its significances were also discussed and commented.
Home electrical circuits may have a number of
problems:
 Too many lamps or appliances on one circuit;
 Faulty wiring within the house;
 Defective wall switches or receptacles;
 Defective cords or plugs;
 Defective circuits within appliances.
 Short circuits happen when a hot wire touches a
neutral or ground wire; the extra current flowing
through the circuit causes the breaker to trip or
fuse to blow.
Although it's often easy to tell when you have a short
or overloaded circuit—the lights go dead when you plug
in the toaster oven—it isn't always as simple to tell
where in the system this has occurred.
21

22. Start by turning off all wall switches and unplugging all
lights and appliances. Then reset the circuit breaker. Pull
the lever to off and then to on again to reset a circuit
breaker with a lever switch. If a fuse is blown, it must be
replaced. Unscrew the fuse to replace it with one with
exactly the same amperage rating (both circuit breakers
and fuses should be sized according to the wire used in
the circuit they protect).
- If the breaker trips immediately: the problem may be a
short circuit in a receptacle or switch.
- If the breaker does not trip again, turn on each switch
one at a time and check if and when the breaker trips
again.
- If turning on a switch causes the breaker to trip, there's
a short circuit in a fixture or receptacle controlled by the
switch.
-If turning on the switch makes no difference, the
problem is in one of the appliances connected to the
switch.
- If the circuit went dead when you plugged in the
appliance, the problem is probably in the cord or plug.
- If the circuit went dead when you turned on the
appliance, the appliance itself is defective.
Table 2
22

23. Causes and effects of short circuit :
Causes Effects
1. Over temperatures due to
excessively high over current.
2. Disruptive changes causes by over
voltage.
3. Arcing caused by moisture together
with impure air especially on
insulators.
1. Power supply interruptions.
2. System components damage or
destruction.
3. Development of unacceptable
mechanical & thermal stresses in
electrical operational equipments.
HOW CAN WE PREVENT
SHORT CIRCUITS?
Whenever you are working with electricity, the proper
use of safety precautions is of the utmost importance to
remember. In the front of all electronic technical
manuals, you will always find a section on safety
precautions. Also posted on each piece of equipment
should be a sign listing the specific precautions for that
equipment. One area that is sometimes overlooked, and
is a hazard especially on board ship, is the method in
which equipment is grounded. By grounding the return
side of the power transformer to the metal chassis, the
load being supplied by the power supply can be wired
directly to the metal chassis. Thereby the necessity of
wiring directly to the return side of the transformer is
eliminated. This method saves wire and reduces the cost
of building the equipment, and while it solves one of the
problems of the manufacturer, it creates a problem for
you, the technician. Unless the chassis is physically
23

24. grounded to the ship's ground (the hull), the chassis can
be charged (or can float) several hundred volts above
ship's ground. If you come in contact with the metal
chassis at the same time you are in contact with the
ship's hull, the current from the chassis can use your
body as a low resistance path back to the ship's ac
generators. At best this can be an unpleasant experience;
at worst it can be fatal. For this reason Navy electronic
equipment is always grounded to the ship's hull, and
approved rubber mats are required in all spaces where
electronic equipment is present. Therefore, before
starting to work on any electronic or electrical
equipment, ALWAYS ENSURE THAT THE
EQUIPMENT AND ANY TEST EQUIPMENT YOU
ARE USING IS PROPERLY GROUNDED AND
THAT THE RUBBER MAT YOU ARE STANDING
ON IS IN GOOD CONDITION. As long as you follow
these simple rules, you should be able to avoid the
possibility of becoming an electrical conductor.
TESTING :
There are two widely used checks in testing electronic
equipment, VISUAL and SIGNAL TRACING. The
importance of the visual check should not be
underestimated because many technicians find defects
right away simply by looking for them. A visual check
does not take long. In fact, you should be able to see the
problem readily if it is the type of problem that can be
seen. You should learn the following procedure. You
could find yourself using it quite often. This procedure
is not only for power supplies but also for any type of
electronic equipment you may be troubleshooting.
(Because diode and transistor testing was covered in
24

25. chapter 1 and 2 of this module, it will not be discussed
at this time. If you have problems in this area, refer to
chapter 1 for diodes or chapter 2 for transistors.)
BEFORE YOU ENERGIZE THE EQUIPMENT,
LOOK FOR: SHORTS - Any terminal or connection
that is close to the chassis or to any other terminal
should be examined for the possibility of a short. A
short in any part of the power supply can cause
considerable damage. Look for and remove any stray
drops of solder, bits of wire, nuts, or screws. It
sometimes helps to shake the chassis and listen for any
tell-tale rattles. Remember to correct any problem that
may cause a short circuit; if it is not causing trouble
now, it may cause problems in the future.
DISCOLORED OR LEAKING TRANSFORMER -
This is a sure sign that there is a short somewhere.
Locate it. If the equipment has a fuse, find out why the
fuse did not blow; too large a size may have been
installed, or there may be a short across the fuse holder.
LOOSE, BROKEN, OR CORRODED
CONNECTION - Any connection that is not in good
condition is a trouble spot. If it is not causing trouble
now, it will probably cause problems in the future. Fix
it.
DAMAGED RESISTORS OR CAPACITORS - A
resistor that is discolored or charred has been subjected
to an overload. An electrolytic capacitor will show a
whitish deposit at the seal around the terminals. Check
for a short whenever you notice a damaged resistor or a
damaged capacitor. If there is no short, the trouble may
be that the power supply has been overloaded in some
25

26. way. Make a note to replace the part after signal tracing.
There is no sense in risking a new part until the trouble
has been located.
ENERGIZE THE EQUIPMENT AND LOOK FOR:
SMOKING PARTS - If any part smokes or if you hear
any boiling or sputtering sounds, remove the power
immediately. There is a short circuit somewhere that
you have missed in your first inspection. Use any
ohmmeter to check the part once again. Start in the
neighborhood of the smoking part. SPARKING - Tap or
shake the chassis. If you see or hear sparking, you have
located a loose connection or a short. Check and repair.
If you locate and repair any of the defects listed under
the visual check, make a note of what you find and what
you do to correct it. It is quite probable you have found
the trouble. However, a good technician takes nothing
for granted. You must prove to yourself that the
equipment is operating properly and that
no other troubles exist.
If you find none of the defects listed under the visual
check, go ahead with the signal tracing procedure. The
trouble is probably of such a nature that it cannot be
seen directly-it may only be seen using an oscilloscope.
Tracing the ac signal through the equipment is the most
rapid and accurate method of locating a trouble that
cannot be found by a visual check, and it also serves as
check on any repairs you may have made. The idea is to
trace the ac voltage from the transformer, to see it
26

27. change to pulsating dc at the rectifier output, and then
see the pulsations smoothed out by the filter. The point
where the signal stops or becomes distorted is the place
look for the trouble. If you have no dc output voltage,
you should look for an open or a short in your signal
tracing. If you have a low dc voltage, you should look
for a defective part and keep your eyes open for the
place where the signal becomes distorted.
Signal tracing is one method used to localize trouble in a
circuit. This is done by observing the waveform at the
input and output of each part of a circuit.
Let's review what each part of a good power supply does
to a signal, as shown in figure 4-51. The ac voltage is
brought in from the power line by means of the line
cord. This voltage is connected to the primary of the
transformer through the ON-OFF switch (S1). At the
secondary winding of the transformer (points 1 and 2),
the scope shows you a picture of the stepped-up voltage
developed across each half of the secondary winding-the
picture is that of a complete sine wave. Each of the two
stepped-up voltages is connected between ground and
one of the two anodes of the rectifier diodes. At the two
rectifier anodes (points 4 and 5), there is still no change
in the shape of the stepped-up voltage-the scope picture
still shows a complete sine wave.
Complete power supply (without regulator)
27

28. However, when you look at the scope pattern for point 6
(the voltage at the rectifier cathodes), you see the
waveshape for pulsating direct current. This pulsating dc
is fed through the first choke (L1) and filter capacitor
(C1) which remove a large part of the ripple, or "hum,"
as shown by the waveform for point 7. Finally the dc
voltage is fed through the second choke (L2) and filter
capacitor (C2), which remove nearly all of the
remaining ripple. (See the waveform for point 8, which
shows almost no visible ripple.) You now have almost
pure dc.
No matter what power supplies you use in the future,
they all do the same thing - they change ac voltage into
dc voltage.
Component Problems
The following paragraphs will give you an indication of
troubles that occur with many different electronic circuit
components.
28

29. TRANSFORMER AND CHOKE TROUBLES. - As
you should know by now, the transformer and the choke
are quite similar in construction. Likewise, the basic
troubles that they may develop are comparable.
• A winding can open.
• Two or more turns of one winding can short
together.
• A winding can short to the casing, which is
usually grounded.
• Two windings(primary and secondary) can short
together.
• This trouble is possible, of course, only in
transformers.
When you have decided which of these four possible
troubles could be causing the symptoms, you have
definite steps to take. If you surmise that there is an
open winding, or windings shorted together or to
ground, an ohmmeter continuity check will locate the
trouble. If the turns of a winding are shorted together,
you may not be able to detect a difference in winding
resistance. Therefore, you need to connect a good
transformer in the place of the old one and see if the
29

30. symptoms are eliminated. Keep in mind that
transformers are difficult to replace. Make absolutely
sure that the trouble is not elsewhere in the circuit
before you change the transformer. Occasionally, the
shorts will only appear when the operating voltages are
applied to the transformer. In this case you might find
the trouble with a megger-an instrument which applies a
high voltage as it reads resistance.
CAPACITOR AND RESISTOR TROUBLES. - Just
two things can happen to a capacitor:
• It may open up, removing the capacitor
completely from the circuit.
• It may develop an internal short circuit. This
means that it begins to pass current as though it
were a resistor or a direct short.
You may check a capacitor suspected of being open by
disconnecting it from the circuit and checking it with a
capacitor analyzer. You can check a capacitor suspected
30

31. of being leaky with an ohmmeter; if it reads less than
500 kilohms, it is more than likely bad. However,
capacitor troubles are difficult to find since they may
appear intermittently or only under operating voltages.
Therefore, the best check for a faulty capacitor is to
replace it with one known to be good. If this restores
proper operation, the fault was in the capacitor.
Resistor troubles are the simplest. However, like the
others, they must be considered.
• A resistor can open.
• A resistor can increase in value.
• A resistor can decrease in value.
You already know how to check possible resistor
troubles. Just use an ohmmeter after making sure no
parallel circuit is connected across the resistor you wish
to measure. When you know a parallel circuit is
connected across the resistor or when you are in doubt
disconnect one end of the resistor before measuring it.
The ohmmeter check will usually be adequate.
However, never forget that occasionally intermittent
troubles may develop in resistors as well as in any other
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32. electronic parts. Although you may observe problems
that have not been covered specifically in this chapter,
you should have gained enough knowledge to localize
and repair any problem that may occur. The continuous
rating of the main components such as generators,
transformers, rectifiers, etc., therefore determine the
nominal current carried by the busbars but in most
power systems a one to four second short-circuit current
has to be accommodated. The value of these currents is
calculated from the inductive reactance of the power
system components and gives rise to different maximum
short-circuit currents in the various system sections.
DAMAGES
Damage from short circuits can be reduced or prevented
by employing fuses, circuit breakers, or other overload
protection, which disconnect the power in reaction to
excessive current. Overload protection must be chosen
according to the prospective short circuit current in a
circuit. For example, large home appliances (such as
clothes dryers) typically draw 10 to 20 amperes, so it is
common for them to be protected by 20–30 ampere
circuit breakers, whereas lighting circuits typically draw
less than 10 amperes and are protected by 15–20 ampere
breakers. Wire gauges are specified in building and
electrical codes, and must be carefully chosen for their
specific application to ensure safe operation in
conjunction with the overload protection.
In an improper installation, the over current from a short
circuit may cause ohmic heating of the circuit parts with
poor conductivity (faulty joints in wiring, faulty contacts
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33. in power sockets, or even the site of the short circuit
itself). Such overheating is a common cause of fires. An
electric arc, if it forms during the short circuit, produces
high amount of heat and can cause ignition of
combustible substances as well.
ADVANTAGES OF SHORT CIRCUIT STUDY
Short Circuit Analysis uses the point-to-point method to
calculate fault currents at various points in an electrical
system up to 600V. Calculations can be made from the
utility transformer secondary to the utilization
equipment in an electrical system. Printouts are
available for each calculation, and the help system
guides you through the calculations.
Benefits :
 Save time by easily obtaining the short circuit
magnitude at each point in the power system.
 Design safer systems by comparing the
calculated fault current to the ratings of installed
equipment.
 Increase design reliability by supporting proper
selection of circuit protection equipment for
protection and coordination.
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34.  Reports ac and dc current for 4 user defined
times.
 Reports zero crossing time of total current.
How to perform short-circuit
calculations.
Performing short-circuit calculations requires an
understanding of various system components and their
interaction.
It's very important to understand the meaning of the
term "short-circuit fault." Basically, a short-circuit fault
in a power system is an abnormal condition that
involves one or more phases unintentionally coming in
contact with ground or each other. Thus, short-circuit
protection is necessary to protect personnel and
apparatus from the destructive effects of the resulting
excessive current flow, which is caused by the relatively
low impedance of the short-circuit fault connection.
To provide the required protection, we must determine
the extent of short-circuit current at various points of our
 Reduce the risk a facility could face and help avoid catastrophic losses.
 Increase the safety and reliability of the power system and related equipment.
 Evaluate the application of protective devices and equipment.
 Identify problem areas in the system.
 Obtain recommended solutions
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35. power distribution system. This determination requires a
calculation.
CONCLUSION
Finally from this short circuit study, We have to learn
about short circuit And we can clarify from some
doubtable question like, what is short circuit?, how it
happens?, when it happen?, why it happens?. And also
learn prevention methods of short circuit. We can know
the advantages about short circuit study.
35

36. Short Circuit (Fault Current) studies are required to
insure that existing and new equipment ratings are
adequate to withstand the available short circuit energy
available at each point in the electrical system. Fault
currents that exceed equipment ratings are capable of
extensive equipment damage and are a serious threat to
human life.
Recently, 23000 fire complaints a year from all over
state. There are lot of fire accidents are occurred due to
these short circuit. To protect the buildings from these
short circuit, we have to learn about this short circuit
phenomenon.
REFERENCE
36

37. 1. www.google.com short circuit phenomenon
2. www.howstuffworks.com electrical stuff
3. IEEE journals on short circuit phenomenon
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