Short-Circuit calculation -Ppt-Slides - Copy.ppt

ABSTRACT
 Short Circuit (Fault Current) studies are
required to ensure 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

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.
 India has approximately 60000 fires a
year.
 These fire accidents are occurred due to
short circuit.

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
 A short circuit 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.

A wire might have come
loose which connects two
sides of a circuit together
Shorting out a single
component which is in series
with others

A diagram of the shorting circuit in transformer is
below.

Figure shows Normal and short circuit conditions

Prevention of short circuit
 When the cables of the electrical appliances are
worn out or it's not connected properly a short
circuit may occur.
 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

 DISCOLORED OR LEAKING
TRANSFORMER
 BEFORE YOU ENERGIZE THE
EQUIPMENT, LOOK FOR: SHORTS
 LOOSE, BROKEN, OR CORRODED
CONNECTION
 DAMAGED RESISTORS OR CAPACITORS
 ENERGIZE THE EQUIPMENT AND
LOOK FOR: SMOKING PARTS

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.

Benefits of short circuit study
 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.

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.

Short Circuit (Fault) Analysis
FAULT-PROOF SYSTEM

not practical

neither economical

faults or failures occur in any power system
In the various parts of the electrical network
under short circuit or unbalanced condition,
the determination of the magnitudes and phase
angles

Currents

Voltages

Impedances

Application of Fault Analysis
1. The determination of the required mechanical
strength of electrical equipment to withstand
the stresses brought about by the flow of high
short circuit currents
2. The selection of circuit breakers and switch
ratings
3. The selection of protective relay and fuse
ratings

4. The setting and coordination of protective
devices
5. The selection of surge arresters and insulation
ratings of electrical equipment
6. The determination of fault impedances for use
in stability studies
7. The calculation of voltage sags caused resulting
from short circuits

8. The sizing of series reactors to limit the short
circuit current to a desired value
9. To determine the short circuit capability of
series capacitors used in series compensation of
long transmission lines
10. To determine the size of grounding
transformers, resistances, or reactors

Three-phase Systems
)2
base MVA3
(base voltage, kV
base kVA3
(base voltage, kV )2
1000
ZB  LL
ZB  LL

Per Unit Quantities
B
pu
B
pu
B
pu
Base impedance (Z )
actual impedance
BaseVoltage (kV )
V
Base Current (I )
actual current
Z 

actual voltage (kV)
I 

Changing the Base of Per
Unit Quantities
pu[new]
B[new]
[new]
[new]
B[new]
[old]
pu[old]
[old]
pu[old]
Z
Z
base kVA
basekV
Z
base kVA[old]
base kVA[old]
Z

Z()
2
1000

Z base kV 2
1000
Z() 
base kV 2
1000

actual impedance, Z()

Changing the Base of Per
Unit Quantities
B[new]
pu[new]
[new]
[new]
B[new]
[old]
pu[old ]
[old ]
pu[old]
Z
Z
base kVA
basekV
Z
base kVA[old]
base kVA[old]
Z

Z()
2
1000

Z base kV 2
1000
Z() 
base kV 2
1000

actual impedance, Z()

kVA Base for Motors
kVA/hp hp rating
1.00 Induction < 100 hp
1.00 Synchronous 0.8 pf
0.95 Induction 100 < 999 hp
0.90 Induction > 1000 hp
0.80 Synchronous 1.0 pf

Power System Short Circuit
Calculations
Classification of Power System
Short Circuits

Shunt Faults
• Single line-to-ground faults
- occurs when one of the power lines comes
into direct contact with the ground or any
other low-impedance path. This creates an
unintended current flow from the power
line to the ground, bypassing the electrical
load and protective devices.

Shunt Faults
• Double line-to-ground faults
- A double line-to-ground (2LG) fault involves
a short circuit between two phase conductors
b and c and ground. As with the line-to-line
fault, there is symmetry with respect to the
principal phase a. In double line-to-ground
fault, the two lines contact with each other
along with the ground.
• Line-to-line faults

Shunt Faults
• Line-to-line faults
-A line-to-line fault, also known as a phase-to-
phase fault, is a type of electrical fault that
occurs when two phases of an electrical
system come into direct contact with each
other or with a ground. When a line-to-line
fault occurs, it can result in a short circuit
between the affected phases, causing a sudden
surge of electrical current. This surge can lead
to overheating, equipment damage, power
outages, and potential hazards

Shunt Faults
• Three-phase faults
- Three-phase faults occur in electrical systems
when all three phases come into contact with each
other or with ground, leading to a simultaneous
short circuit. These faults can result from various
causes such as equipment failure, insulation
breakdown, or external factors like lightning
strikes. Detecting and isolating these faults quickly
is essential to prevent widespread outages,
equipment damage, and ensure the safety of
personnel and the integrity of the electrical system.

Series Faults
One-line open faults
Two-line open faults

Short-Circuit calculation -Ppt-Slides - Copy.ppt

More Related Content

Similar to Short-Circuit calculation -Ppt-Slides - Copy.ppt (20)

Recently uploaded (20)

Short-Circuit calculation -Ppt-Slides - Copy.ppt