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BASICPROTECTIVE RELAYING
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BASICPROTECTIVERELAYING
I. INTRODUCTION
A. Classification of Relays
B. Philosophy of Protection
C. Operating Principles
1. Electromechanical Relays
2. Static and Digital Relays
II. DIFFERENTIAL RELAY PROTECTION
A. Transformer Protection
B. Bus Protection
III. LINE PROTECTION
A. Distance Protection
B. Ground Protection
IV. Breaker Failure Protection
V. Auto Reclosing
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BASIC PROTECTIVE RELAYING
Relays are compact analog, digital, and numerical devices
that are connected throughout the power system to detect
intolerable or unwanted conditions within an assigned area.
They are, in effect, a form of active insurance designed to
maintain a high degree of service continuity and limit
equipment damage. They are Silent Sentinels.
I . I NTRODUCTI ON
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A. CLASSI FI CATI ON OF RELAYS
1. Protective Relays
2. Monitoring Relays
3. Reclosing Relays4. Regulating Relays
5. Auxillary Relays
6. Synchronizing Relays
BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
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1. PROTECTI VE RELAYS
Detect defective lines, defective apparatus, or other
dangerous or intolerable conditions. These relays generally
trip one or more circuit breakers, but may also be used tosound an alarm
2. VERI FI CATI ON OR MONI TORI NG RELAYS
One whose functions is to verify power system conditions
with respect to prescribed limits and to initiate or permit
automatic functions other than opening a circuit breaker
during fault conditions. These relays includes fault detectors,
alarm units, channel-monitoring relays, synchronism
verification, and network phasing.
BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
A. CLASSI FI CATI ON OF RELAYS
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3. RECLOSI NG RELAYS
Establish reclosing sequence for a circuit breaker following
tripping by protective relays.
4. REGULATI NG RELAYS
Are activated when an operating parameter deviates from
predetermined limits. Regulating relays function throughsupplementary equipment to restore the quantity to the
prescribed limits.
Ex: OFR, UFR
BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
A. CLASSI FI CATI ON OF RELAYS
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
A. CLASSI FI CATI ON OF RELAYS
5. AUXI LLARY RELAYS
Operates in response to the opening or closing of the
operating circuit to supplement or assist another relay or
device. These include timers, contacts-multiplier relays,
sealing units, isolating relays, lockout relays, closing relays
and trip relays.
6. SYNCHRONI ZI NG RELAYS
Assure that proper conditions exist for interconnecting two
sections of a power system.
Ex: Synchrocheck relay
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Branch of electric power engineering concerned with the
principles of design and operation of equipment (called
relays or protective relays) which detect abnormal
power system conditions, and initiate corrective action as
quickly as possible in order to return the power system to
its normal state.
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Relays are the Brains of the Fault Clearance System
Breakers are the Muscles
A CRUDE ANALOGY
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING
Continuously monitor the power system
Respond to abnormal conditions
Prevents equipment damage
Minimizes service interruption
WHAT PROTECTI VE RELAYS DO
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BASIC PROTECTIVE RELAYING
MINIMIZES DAMAGE
MINIMIZES EFFECT ON SYSTEM OPERATION
MAXIMUM POWER TRANSFER
HI -SPEED CLEARI NG OF FAULTS
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BASIC PROTECTIVE RELAYING
To prevent of limit damage to apparatus and all other
components of a transmission and distribution system.
PURPOSES OF PROTECTI VE RELAY
To isolate the affected part from the remainder of the
power system.
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BASIC PROTECTIVE RELAYING
SENSOR - Feeds system information to the relay
Ex: CT, PT
RELAY makes a decision as to the need for action
Ex: OCR, Distance/Differential/Voltage relays
SWITCHING OR CONTROLLING DEVICE physically
isolates or control the problem Ex: Circuit Breaker
THREE MEMBERS OF PROTECTI ON
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Fault Clearance System
PROTECTIONEQUIPMENT
Currenttransformer
Voltagetransformer
TELECOM DC-system
Circuit
BreakerMechanism
TripCoil
CIRCUIT BREAKER
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
B. PHI LOSOPHY OF PROTECTI ON
PowerSystem
Voltageand CurrentTransformer
RelayCircuit
Breaker
Decides whether systemquantities are normal or
abnormal
These devices changeelectrical quantities to level
relay can use, i.e. 5A,115V
*If quantities are normal,no signal sent.
*If quantities are abnormalsignal is sent to breaker toopen.
Functional Diagram of Relaying
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Electrical Diagram of Relaying
Protected
Device
Circuit Breaker
Trip Coil
Current Transformer
Relay
Operating
Coil
Relay Contacts
Station Battery
Power
System
Conductor
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
B. PHI LOSOPHY OF PROTECTI ON
Dependability
Relays must detect designated abnormalsystem conditions on the power system
Speed
Relay systems should operate as quickly aspossible in order to minimize the duration of
system disturbances
Economy
The cost of the relay system should be as lowas possible
Security
Relays must never misinterpret normalcurrents and voltages as conditions which
require tripping
Selectivity
Relay systems should only trip as much ofthe system as necessary to de-energize
distressed components
Reliability
It is not possible to build a system which will never fail.
DESI GN CRI TERI A
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
1. Loss of Dependability
relay R1 does not operate on this fault
Reliability of Protection System
2. Loss of Security
relay R5 operates through breaker B5 for the same fault
before breaker B2 clears the fault
Example :
R1
R2
R3
R4
R5
B1
F
B3
B4
x
B5
B2
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING
Correct and Desired
Correct but undesired
Incorrect Tripping
Failure to trip
GENERAL CLASSI FI CATI ON OF RELAY OPERATI ON
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BASIC PROTECTIVE RELAYING
Poor application
Incorrect setting
Personnel error
Equipment malfunction
CAUSES OF I NCORRECT RELAY OPERATI ON
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
usually associated with major system components usually delimited by circuit breakers
must overlap to prevent any system component from being
unprotected
ZONES OF PROTECTION
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Generator ProtectionG
M
Low Voltage Switchgear Protection
Power Transformer Protection
High Voltage Switchgear Protection
Transmission Line Protection
High Voltage Switchgear Protection
Motor Protection
ZONES OF PROTECTI ONS
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING
System Configuration
Existing system protection and difficulties
Degree of protection required
Existing preferences, operating procedures and practices
Possible future expansion
Fault study
Maximum load and current transformer ratios
Potential transformer locations, connections and ratios
Impedance of the lines and transformers
I NFO NECESSARY FOR RELAY APPLI CATI ON
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BASIC PROTECTIVE RELAYING
1. Thou shall trip all faults within thy zone of protection
irrespective of changes in generation.
2. Thou shall trip these faults at high speed, yea, thou
shall make thy tripping decisions in terms of a second
split into a hundred parts.
3. Thou shall not trip faults outside thy zone of protection
except in back-up assistance to a failing brother.
4. Thou shall not trip under heavy load conditions even
though thy coils do carry much current.
5. Thou shall not trip during power swings, denying always
the temping surges of current and voltage.
MAJOR COMMANDMENTS FOR AN I DEAL RELAY
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Principle of Overlapping Protectionaround a Circuit Breaker
CT for Zone B
CT for Zone A
ZONE A ZONE B
B. PHI LOSOPHY OF PROTECTI ON
Dead Tank Breaker and Breakers With SeparateCurrent Transformers on Both Sides of Breakers
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Principle of Overlapping Protectionaround a Circuit Breaker
B. PHI LOSOPHY OF PROTECTI ON
Live Tank Breaker and Breakers With SeparateCurrent Transformers on One Side Only
CT for Zone BCT for Zone A
ZONE A ZONE B
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
PRIMARY PROTECTION
A set of protective functions assigned to a zone
Optimum speed and sensitivity
Main protective function for the zone
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
BACKUP PROTECTION
A second set of protective functions assigned to a zone
Anticipates failure of primary function
May sacrifice speed or sensitivity for economy
B. PHI LOSOPHY OF PROTECTI ON
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Primary relays for zone which also provide backup protection for
an adjacent zone.
Remote Backup:
B. PHI LOSOPHY OF PROTECTI ON
Local Backup:
Use of additional relays on a zone to provide backup
protection separate considerations for relay and
breaker failure.
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
C. Relay Operating Principles
1. Plunger - Electromagnetic Attraction
2. Hinged Armature - Electromagnetic Attraction
3. Induction Disk - Induction
4. Induction Cup - Induction
5. Static Relay
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
DEFI NI TI ONS
Operation - Relay output changes state.
Pickup - Relay operating quantities of sufficientmagnitude to cause operation.
Reset - Relay restored to quiescent (at rest) state.
Dropout - Relay operating quantities reduced to belowmagnitude required to cause operation.
C. Relay Operating Principles
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Relay Contact Sense:
Normally open "a"
Normally close "b"
Defined as the state of the contact with the relay de-energized.
DEFI NI TI ONS
C. Relay Operating Principles
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Fig. 1 PLUNGER CONSTRUCTI ON
SOLENOID
COIL
ARMATUREMOVING
CONTACT
FIXED CONTACT
Type of Relays
C. Relay Operat ing Principles
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
Fig. 2 HINGED ARMATURE CONSTRUCTI ON
ARMATURE
ELECTROMAGNET
MOVING
CONTACT
FIXED
CONTACTHINGE
POINT
Type of Relays
C. Relay Operating Principles
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
FIXED
CONTACT
MOVING
CONTACT
DISK
SHADING
RING
COIL
MAGNETSHAFT
Fig. 3 SHADED POLE INDUCTION DISK
Type of Relays
C. Relay Operating Principles
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BASIC PROTECTIVE RELAYING(I. INTRODUCTION)
MAGNET
UPPER COIL
DISK
LOWER COILS
Fig. 4 WATTMETER INDUCTION DISK
Type of Relays
C. Relay Operating Principles
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BASIC PROTECTIVE RELAYING
II. The Differential Concept
Reliability Selectivity
Economy
Security Speed
Most relays system achieve objectives thru:
Desensitize for security
Slowdown for security & selectivity
Increase sensitivity for reliability
and other compromises
Differential Protection
Profoundly simple
Inherently secure
Highly reliable
Fast
Reasonably economical
S C O C G
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BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
87
Identify a PROTECTIVE ZONE
Line Transformer Generator
Motor Bus
Provide CTs at all terminals of the zone Interconnect the CTs appropriately Install a relay to measure the error current
BASIC PROTECTIVE RELAYING
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87
For an EXTERNAL fault or through load:
CTs see identical primary current
Produce similar secondary currents Secondary currents circulate in CT secondary No current flows through relay
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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87
For an INTERNAL fault:
CTs see different primary current
Produce different secondary currents Secondary currents OPPOSE in CT secondary Current in relay is the sum of secondary currents
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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Requirements:
CT at each power connection to the connected zone All CTs have same rating Careful attention to CT connection Note that differential protection provides only PRIMARY protection
cannot provide backup protection for adjacent zones. Operating quantity is i1-i2 Provides protection on a per phase basis requires three sets ofequipment for three phase protection
Prefer identical (similar) current transformer
i1-i2
I1 I2
i1 i2
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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Gas Detection and Analysis
Rate of Change of Pressure
Current Differential
Overcurrent
Overexcitation
A. Transformer Protection
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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A. Transformer Protection
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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Type 900 Fault Pressure Relay
A. Transformer Protection
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
A. Transformer Prot ect ion
Differential ConsiderationsInrush Current
Op
R R
Typical FaultCurrent
Typical InrushCurrent
20
0
20
0
When the transformer is firstenergized, there is a magnetizingcurrent inrush which will appearonly on the source side.
Inrush current is rich in harmonics, specially low order events. Harmonic restraint provides relay security.
Environmental Harmonics. CT performance.
BASIC PROTECTIVE RELAYING
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A very important part of the power system at various point
along the bus, transmission line and or other circuits are
connected through circuit breakers.
B. Bus Protection
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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300A
300A
300A
4
5
6
300A
1
300A
2
300A
3
ALL C.T. RATIOS 100/1
5
5
5
5
55
55
55
55
3A
3A
3A3A
3A
3AZEROAMPS
DIFF RELAY
OP.COIL
SIMPLE CURRENT DIFFERENTIAL CIRCUITCONFIGURATION
B. Bus Protection
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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3000A
3000A
3000A
4
5
6
18000A
3000A
1
3000A
FAULT OUTSIDE THE PROTECTED BUS
2
3000A
3
ALL C.T. RATIOS 100/1
5
5
5
5
55
55
55
55
30A
30A
30A150A
30A
30A
DIFF RELAY
15000A
ZEROAMPSOP.
COIL
B. Bus Protection
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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3000A
3000A
3000A
4
5
6
3000A
1
3000A
2
3000A
3
ALL C.T. RATIOS 100/1
5
5
5
5
55
55
55
55
30A
30A
30A30A
30A
30A
DIFF RELAY
18000A
180AOP.
COIL
FAULT INSIDE THE PROTECTED BUS
B. Bus Protection
BASIC PROTECTIVE RELAYING(II. THE DIFFERENTIAL CONCEPT)
BASIC PROTECTIVE RELAYING
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BASIC PROTECTIVE RELAYING
Distance Relays
V
Z1 Z2 Z3
Zload
Fault
I
Er
Normal Conditions:
I =V
Z1 + Z2 + Z3 + Zload
Er = VZ2 + Z3 + Zload
Z1 + Z2 + Z3 + Zload
and Zr = I
Er
-1
= Z2 + Z3 + Zload
and
With Fault:
I =V
Z1 + Z2
Er = VZ2
Z1 + Z2
Zr =
I
Er
= Z2-1
I I I . LI NE PROTECTI ON
BASIC PROTECTIVE RELAYING
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X
R
+ load with lagging pf
- load with leading pf
The R-X Diagram the language of relay engineering
Distance Relays
BASIC PROTECTIVE RELAYING(III. LINE PROTECTION)
BASIC PROTECTIVE RELAYING
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Transmission Line Applications
(First Zone)21
21
Provide fault detection for middle section of the line withno intentional delay for speed
Must under reach end of the line for selectivity (typicallyset 80-90% of line impedance)
Distance Relays
BASIC PROTECTIVE RELAYING(III. LINE PROTECTION)
BASIC PROTECTIVE RELAYING
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21
21
Provide fault detection in the end zones
Must over reach the end of the line for selectivity(typically set 120% of line impedance)
Ideally will not over reach first zone in adjacent line segments
But must be selective with first zone of adjacent lines
Distance Relays
Transmission Line Applications(Second Zone)
BASIC PROTECTIVE RELAYING(III. LINE PROTECTION)
BASIC PROTECTIVE RELAYING
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Source of Failure:
Relay Failure
Communication Channel FailureInstrument Transformer FailureBattery FailureBreaker Mechanism FailureBreaker Electrical Failure
Wiring Failure, Relay Breaker
Backup
X
X
RemoteBackup
X
XXX
BreakerFailure
XXX
Local Backup
BASIC PROTECTIVE RELAYING
I V. BREAKER FAI LURE PROTECTI ON
BASIC PROTECTIVE RELAYING
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Primary/Secondary
Main A
Main B
Redundant Relaying Systems
Fully functional both high speed Complementary technology
Different manufacturers
Separate current transformers Separate breaker trip coils
Separate station batteries
Local Backup
BASIC PROTECTIVE RELAYING(IV. BREAKER FAILURE PROTECTION)
BASIC PROTECTIVE RELAYING
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Breaker Failure
FD
Main B
Main A
Fault Detector:
Must detect any fault which the primary/secondaryrelays can detect
Usually an instantaneous overcurrent relay
Local Backup
Rs
Rp
BASIC PROTECTIVE RELAYING(IV. BREAKER FAILURE PROTECTION)
BASIC PROTECTIVE RELAYING
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Causes of Most Transmission Line Faults:
Lightning induced flashover
Insulator contamination Trees or brush growing into the line
Animals and birds
Most (80-90%) of Transmission Line Faults are non-persistent if the fault is de-energized promptly
After the Ionized Air in the Vicinity of the Fault Dissipatesthe line can be re-energized
V. Automatic Reclosing
BASIC PROTECTIVE RELAYING
BASIC PROTECTIVE RELAYING
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Single Pole Trip and Reclose:
Trip and reclose only the faulted phase
Applied most often on EHV lines
Greater assurance of successful reclose
Maintain power transfer and synchronism throughtwo healthy phases
Require more complex relaying (phase
discrimination)
Require more expensive breakers
Deionization time is considerably longer
BASIC PROTECTIVE RELAYING(V. AUTOMATIC RECLOSING)
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