This document discusses fault analysis in power systems. It introduces symmetrical components for analyzing unbalanced faults and describes different types of faults including single line-to-ground, line-to-line, and double line-to-ground faults. It also discusses overcurrent relays for fault protection and describes an algorithm using symmetrical components to discriminate between faults and non-fault events like transformer energization. The algorithm is tested on a simulated distribution system and able to correctly identify fault and non-fault conditions.

1. FAULT ANALYSIS
Submitted by:-Malay niraj
Roll no.:-1307438
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2. CONTENT
 INTRODUCTION
 PROTECTION SYSTEM
 SYMMETRICAL COMPONENT
 FAULT
 OVERCURRENT RELAY
 ALGORITHM
 SIMULATION DISTRIBUTION SYSTEM
 RESULTS
 CONCLUSION 2

3. INTRODUCTION
 The concept of symmetrical
components for enhancing
protection scheme by providing a
practical technology for
understanding and analyzing
power system operation during
unbalanced condition. 3

4. PROTECTION SYSTEM
What is need of protective system ?
 In order to maintain steady state of
power system by taking correct and
quick remedial action during any faulty
condition.
Properties of a good protective system
Automatic
Quick
Minimum amount of disruption 4

5. SYMMETRICAL COMPONENT
 Unbalanced systems are difficult to handle.
 It provide balanced analysis of an unbalanced
system
 The unbalanced three phase system can be
transformed into three balanced phasors
 Positive Sequence
 Negative Sequence
 Zero Sequence
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6. POSITIVE PHASE SEQUENCE
 Each have the same magnitude.
 Each positive sequence voltage or
current quantity is displaced 120°
from one another.
 The positive sequence quantities
have a-b-c, counter clock-wise,
phase rotation.
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7. NEGATIVE PHASE SEQUENCE
 Each have the same magnitude.
 Each negative sequence voltage
or current quantity is displaced 120°
from one another.
 The negative sequence quantities
have a-c-b, counter clock-wise,
phase rotation.
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8. ZERO PHASE SEQUENCE
 Each zero sequence quantity has the same magnitude.
 All three phasor with no angular
displacement between them, all in phase.
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9. 9
FAULT
o General Causes of fault
 Fault due to lightning
 Tree limbs falling on the line
 Wind damage
 Effects of fault
 Flow of excessive current
 Abnormal voltages
 Induces over voltages on neighbouring
equipments.
 Hazards to human, equipment and animals

10. TYPES OF FAULTS
• Balanced Faults :
– Three-phase fault
• Unbalanced Faults :
– Single line to ground fault
– Line to line fault
– Double line to ground fault
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11. UNBALANCED FAULTS
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12. SINGLE LINE TO GROUND FAULT
 The most common type of fault is the single line to
ground fault:
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13. 13
 The SLG fault can be described by the following
voltage and current relationship:
Ib=0 & Ic=0
Va=IaZf
 The Sequence current can be given as:

14. LINE TO LINE FAULT
 It occurs when two conductors are short circuited.
 There is no zero sequence component due to
absence of ground return path.
 The positive and negative sequence components
are connected in parallel.
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15. DOUBLE LINE TO GROUND FAULT
 In double line to ground fault two line conductors
come in contact with each other and ground .
 The networks are connected in parallel.
 For the zero sequence component it requires to add
an external impedance of Zf+3Zg
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16. OVER CURRENT RELAY
 Short-circuit currents are generally several times (5
to 20) full load current. Hence fast fault clearance is
always desirable on short circuits.
 A relay that operates or picks up when it’s current
exceeds a predetermined value (setting value) is
called Over current Relay.
 Over current includes short-circuit protection, and
short circuits can be:
 Phase faults
 Earth faults
 Winding faults
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17. TYPES OF OVER CURRENT RELAY
I. Instantaneous Over current (Definite Current)
Relay
II. Definite Time Over current Relay
III. Inverse Time Over current Relay (IDMT
Relay)
i. Moderately Inverse
ii. Very Inverse Time
iii. Extremely Inverse
IV. Directional over current Relay
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18. ALGORITHM
 The criterion function for discriminating fault from
non fault switching is defined as follows :
R= |I1|-|I2| / |I1|+|I2|
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19. SIMULATED DISTRIBUTION SYSTEM
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20. RESULTS
Several non faults events are applied to
this system along with some short circuit
events a different time.
The discrimination of fault from a non
fault event could be done by representing
two cases
 Transformer energizing
 Fault
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21. TRANSFORMER ENERGIZING
 Various inrush current condition were simulated.
 Various parameters which have considerable effect
on the characteristic of the current signal were
changed and was analysed.
FAULT
 In this case a single line to ground fault occurs.
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22. 22
NON FAULT CONDITION
WHEN VALUE OF R>=.35s
FAULTY CONDITION WHEN
VALUE OF R<.35s

23. 23
THREE PHASE CURRENT
BEFORE FAULT
THREE PHASE CURRENT
AFTER FAULT

24. CONCLUSION
 Simple method of improving over current relays
operation by algorithm, based on different
behaviour of the current amplitudes. Based on
the differences, a criterion function R is defined
such that undesirable operation of the over
current relays to the switching is prevented.
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