The document discusses various types of power system faults including their causes, classification, and effects. It describes symmetrical and unsymmetrical faults, noting that unsymmetrical faults like line-to-line and line-to-ground faults are more common. The document also summarizes different types of faults that can occur in key power system equipment like generators, transmission lines, and distribution lines. It provides details on fault detection and analysis methods as well as protection devices used to isolate faults, such as current transformers, potential transformers, circuit breakers, and different types of relays.

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-BY: ENGR. MART NIKKI LOU M. MANTILLA, REE, RME

2.  Fault is an abnormal condition , caused by equipment failures such as
transformers and rotatory machines and environmental conditions.
 These fault causes interruption to electric flows, equipment damage, death
of humans, birds and animals.
 Some causes of power system faults are lightning, heavy winds, birds,
excessive loading conditions, insulation breakdown, winding flashover ,
etc.
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3.  There are different types of faults at different levels from power generation
to power distribution.
 Basic classification of Power system faults :
 1. Generation faults
 2. Transmission faults
 3. Distribution faults
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4.  Faults occur when voltage and current deviate from their normal values under which
the system operates safely.
 Under fault condition high current flows thus damaging the equipment, so its
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detection and analysis is necessary to select suitable design of switchgear equipment ,
electromechanical breakers and other protective devices.
 These are mainly of two types:
 1. Symmetrical Faults
 2. Unsymmetrical Faults

5.  These are very severe types of faults and occur infrequently in the power system as
balanced faults.
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 These are mainly of two types line to line to line to ground fault (LLLG) and line to line
to line (LLL).
 Only 2 to5% of the total faults are symmetrical faults.
 Analysis of fault is easy and is required for selecting set-phase relays, protective
switchgear rating, etc.

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8.  Very common and less severe.
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 Mainly three types namely line to line fault (L-L), line to ground fault (L-G), double line
to ground fault (L-L-G).
 Most common type and around 65-70% faults are unsymmetrical faults.
 Conductor make contact with line or ground.
 There occurrence can cause unbalance in the system.
 Impedance values are different in each phases causing unbalanced current to flow in
each phase.

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12.  Generators are the most important part in the whole plant.
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 Generator faults are serious faults since they cause severe and costly damage to the
insulation , windings and the core.
 They may cause severe mechanical damage to shafts and couplings.
 Faults in generators occurs :
1.In stator
2.In rotor

13. 1. Phase to Phase fault
Under normal condition, the current in phase 1 (i1) is equal to current in phase 2 (i2).
The current values in the CT secondaries are also equal, which is i1=i2 then no current
will flow through the relays.
If a fault is generated in phase 1, current i1 and i2 are no longer equal, i1 will be very
much higher than i2, therefore i1 and i2 are not equal.
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14. 2. Inter-Turn fault
 In the generators, instead of single path for each phase, double layer windings are
used. That means for each phase there will be two parallel paths. So if there is an inter
turn fault between the two parallel paths of each phase then there will be heavy fault
current. This mainly happens due to the insulation damage between two conductors
of parallel paths of each phase.
 Under normal condition, the current flowing through the two parallel paths of each
phase of the stator winding will be same and no current will be flowing through the
relay but under this fault the currents will be different.
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15. 3. Stator earth Faults
Any fault involving earth results in shift of the neutral point from its actual
position which can be detected by measuring the voltage across the
grounding resistor . The protection is provided for the 95% of the generator
stator conductor. Because for the rest 5% region nearer to the neutral point
,if there is fault then the voltage induced in the secondary side of the NGT
will be very very less.
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16. Rotor Faults
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 This type of fault is basically caused due to insulation failure or due to ageing of
insulation or vibration of rotor.
 Occurrence of this type of fault bypasses the field current through the ground
which ultimately isolates the flow of current through the rotor windings.
 This results in unsymmetrical flux distribution.
 Hence air gap flux is distorted and the rotor windings get displaced and touches
the stator which results in sever damage in the bearing.

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18.  (1)Category IV (Minor):
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 -Here in this kind of fault all the primary function of the system can be done but
repair is to be done urgently.
 (2) Category III (Marginal):
 -This kind of faults are slightly severe than Category IV Faults there is some kind of
reduction in the ability to perform primary Function.
 (3)Category II (Critical)
 -This Faults lead to loss of primary function.
 (4)Category I (Catastrophic)
 -After this fault has occurred the system becomes inappropriate to work on.

19.  (1)Level E (Extremely Unlikely):
 -In this case the probability of occurrence of fault is less than 0.001.
 (2)Level D (Remote)
 -In this type of fault the probability of occurrence of fault is more than 0.001 but
less than 0.01.
 (3)Level C (Occasional)
 -In this type of fault the probability of occurrence is more than 0.01 but less than
0.1.
 (4)Level B (Reasonably Probable)
 -Probability of occurrence of the fault is more than 0.1 less then 0.2
 (5)Level A (frequent)
 -In this category of fault the probability of occurrence of the fault is more than 0.2. 19

20. Value Detection Criteria
1 Level F Good Identification
2 Level E Fair Identification
3 Level D Good detection and rough
identification
4 Level C Fair Detection
5 Level B Rough Detection
6 Level A Complementary test
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21. 1. Winding failure
2. Bushing failure
3. Tap changer failure
4. Core failure
5. Tank failure
6. Protection system failure
7. Cooling System failure
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26. FAILURE TYPE PN
1. Winding 6-30
2. Bushing 24-48
3. Tap Changer 28-52
4. Core 6
5. Tank 18
6. Protection System 22-64
7. Cooling System 26-48
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27. The main philosophy about protection is that no protection of power system can
prevent the flow of fault current through the system, it only can prevent the
continuation of flowing of fault current by quickly disconnect the short circuit path
from the system.
 Zones of Protection
 Lighting arresters
 Current transformers
 Potential Transformers
 Circuit Breakers
 Relays, etc.
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28.  Power system is divided into several zones.
 Zones are divided to separate monitoring of different equipment by separately
checking their performance.
 Division of zones is based on the operation of the relays.
 A relay will operate in a particular zone and thus will protect that zone from the
future faults.
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30.  A lightning arrester is a device to protect the
insulation and conductors of the system from the
damaging effects of lightning.
 The lightning arrester is located close to the
equipment that is to be protected.
 They are usually connected between phase and
ground in an AC system and pole and ground in case
of the DC system.
 It provides a low resistance path to ground the
lighting.
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31.  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 a transmission line
using an ammeter.
 There are three basic types of current
transformers: wound, toroidal and bar.
 They can step-down current levels from
thousands of amperes down to a standard output
of either 5 Amps or 1 Amp for normal operation.
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32.  Potential transformer or voltage transformer
gets used for stepping down the system voltage
to a safe value which can be fed to low ratings
meters and relays as they work on low
voltages.
 The potential transformer is mainly classified
into two types, i.e., the conventional wound
types and the capacitor voltage potential
transformers.
 It is used for a metering purpose, for
protection of the feeders, for synchronizing the
generators and feeders, for protecting the
impedance of the generators, etc.
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34.  Circuit breakers defend the generator rotor and stator against failure generated by
a component on the load side of the circuit.
 It can be operated safely under huge current carrying condition.
 During the interruption of massive current, there would be large arcing in between
the switching contacts, circuit breaker quench these arcs in circuit breaker in a safe
manner.
 This function can be automatic, manual or a combination of both depending on the
failure.
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35.  Reactance relay :
 It is a high speed relay which consists of two elements.
 An overcurrent element and a current voltage directional element, the former
develops positive torque and the later one opposes the current element depending
on the phase angle between the current and the voltage.
 It develops maximum negative torque when current lags by 90⁰.
 They are very suitable as a ground relay for ground fault because its reach is not
affected by fault impedance.
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36.  Impedance Relay :
 It’s operation depends upon the impedance between the point of fault and the point
where relay is installed.
 It includes a voltage element from PT and current element fed from CT
.
 Secondary of the CT produces deflecting torque and restoring torque is produced by
the voltage of PT
.
 Under normal conditions restoring torque is more than deflecting torque, hence
relay will not operate but under faulty condition current becomes quite large while
the voltage drops.
 Thus deflecting torque becomes more than the restoring torque and the relay starts
which close the no contact of the relay.
 They provide primary and backup protection for AC transmission and distribution
line against three phase, phase to phase and phase to ground faults.
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37. Time Distance Impedance Relay 40

38.  The differential relay operates when the difference between two or more similar
quantities exceeds a predetermined value.
 Under normal condition, the phasor sum of the quantities will be zero and hence
there will be no current flowing through the relay.
 But due to any abnormality if the balance is broken, the phasor sum will no longer
be zero and current will flow through the relay coil thereby relay being operated.
 It is mainly of two types:
1. Current Balance Differential Relay
2. Voltage Balance Differential Relay
 This is the most common protective device for generators, motors, buses, reactors,
capacitors, etc.
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40. Circuit Diagram
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41. Subsystem internal diagram
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44. THANK YOU….