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7/27/2019 Principles and Philosophy of Protective Relaying
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PRINCIPLES AND PHILOSOPHY
OF PROTECTIVE RELAYING
P1-COURSE PRESENTATION
BYENGR.W.A ASONMWONRIRI
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PERSONAL INFORMATION
NAME: Engr. Wilfred Amen Asonmwonriri (MNSE)
DATE OF BIRTH: September 1970
Married
Protection Engineer
FORMAL EDUCATION
M.ENG(POWER AND MACHINES)
B.ENG(ELECTRICAL AND ELECTRONICS)
PROFESSIONAL AND TECHNICAL EDUCATION
Travelling waves systems: QUALITROL
Power System Engineer ing:Power System Training Institute: - New Delhi
Protective Relay Testing using Omicron Test set :OMICRON
Conditi on-Based evaluation of power transformer:HIVOTEC-UNILAG
Reyrol le Protective Relays ApplicationsREYROLLE
Power system traini ng methods(Israel Electricity Training School. Tel-Aviv)
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PRINCIPLES AND PHILOSOPHY OF
RELAYING PROTECTION
The electric power system is designed to generateand supply energy to meet the demands of theusers on a continuous basis.
It comprises of many diverse equipment that arevery expensive
The whole system must be kept in operationcontinually without major breakdown so as toprevent severe disruption to the normal routinesof modern society
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To keep the power system in operation
continually adequate protection must be
provided.
Protective relays detect abnormalities or faults
and eliminate such abnormalities by isolating
the smallest portion of the system.
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Faults on transmission line
possible causes Lightning
Switching
Pollution Salt storms
Growing trees
Bush fires Damage or sabotage
The most often!
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RELAYS
Relays are the devices, which monitor the conditions of acircuit/device and give instructions to isolate it underunhealthy conditions.
The conditions of a circuit or equipment are monitoredfrom the electric power system parameters, the most basicof which are voltage, current, frequency and power.
The power system parameters have predetermined values
under healthy conditions.
. Any shift from this normal behaviour therefore, could bethe result of a fault condition.
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PRIMARY AND SECONDARY RELAYS
PrimaryRelays are the first line of defense in thesystem. They are generally high-speed relays. Theprimary relay scheme is designed to remove
minimum equipment from service. Secondary Relays also called backup relays are
intentionally delayed in their operation so as togive the primary relays a chance to operate first.
The backup relays scheme is independent of theprimary relay scheme and operates if the primaryrelay scheme fails to operate.
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ELECTRICAL POWER SYSTEM DEVICE
NUMBERS AND FUNCTIONS
1 Master Element
2 Time Delay Starting or Closing Relay
3 Checking or Interlocking Relay
4 Master Contactor
5 Stopping device
6 Starting Circuit breaker
7 Anode Circuit breaker
8 Control Power Disconnecting Device
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9 Reversing Device
10 Unit Sequence Switch
11 RESERVED FOR FUTURE APPLICATION
12 Over Speed device
13 Synchronous Speed device
14 Under Speed device
15 Speed or frequency matching device
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16 RESERVED FOR FUTURE APPLICATION
17 Shunting or Discharge switch
18 Accelerating or Decelerating device
19 Starting to Running Transition Contactor
20 Electrically Operated Valve
21 Distance Relay
22 Equalizer Circuit breaker
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23 Temperature Control device
25 Synchronizing or Synchronism Check device
26 Apparatus Thermal device
27 Under Voltage relay .
28 Flame Detector .
31 Separate Excitation device
32 Directional Power relay
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37 Undercurrent or under power relay
40 Field relay
50 Instantaneous over current or rate of rise relay
51 A.C. Time Over current relay
52 A.C. Circuit breaker
55 Power Factor Relay
81 Frequency Relay
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59 Over voltage Relay
63 Pressure switch
64 Ground Protection Relay
65 Governor
67 A.C Direction or Over-current Relay
79 A.C. Reclosing relay
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Power system protection is realized byprotecting the different primary equipmentthat variously constitute the power system.
A faulted component needs to be isolatedfrom the entire grid as quickly as possible to
prevent the fault from spreading to otherparts of the grid and to prevent damage toequipment and personnel.
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Main purposes of protective relays
To ensure uninterrupted power supply.
To reduce equipment damage.
To maintain quality of service.
To guarantee safety of life and property.
To ensure operation of equipment at peakefficiency.
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ATTRIBUTES OF PROTECTIVE RELAYING
(a) Sensitivity
A relay must be sensitive to the least fault
conditions for which it has been configured.
(b) Reliability
It must be relied upon at all times to respondto any fault by relaying signals that will cause
the faulty part to be isolated.
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(c) Selectivity
The relay must be able to discriminate between
faults and abnormal conditions.
(d) Simple
For a relay to be effectively used, itsconstruction and operation has to be simple in
nature.
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(e) Speed of Operation
To be able to prevent damage to the associatedequipment the relay is protecting, it must act
fast before the damage is done.
(f) Cost
The relay should not be so expensive as tooutweigh the benefit of using it to protect theassociated equipment.
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CATEGORIES OF FAULTS
Single phase to ground fault
Double phase to ground fault
Three phase to ground fault
Phase to phase fault
Three phase fault.
The commonest, in occurrence, of the above faultconditions, is the single phase to ground faultwhich is about 70%.
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Protective relaying was introduced in practice asearly as the first power systems were invented tomake sure that faults are detected and damagedor faulted components are taken out of service
quickly.
Faults occur randomly and may be associated
with any component of the power system.
The longer the fault duration, the larger is theextent of damage.
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EFECTS OF FAULTS IN A POWER
SYSTEM
Over heating
Over voltage (surge)
Over load
Fire disaster Unbalanced loading
Loss of synchronism
For the faults and abnormal conditions enumeratedabove protective relays are designed to isolate andreduce damage to the system equipment.
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RELAY PERFORMANCE
Performance of relays can be classified as:
Correct
Incorrect
Inconclusive.
Incorrect Operation
This can be due to the following factors:
Incorrect Relay Setting
Personnel Error
Equipment Malfunction
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Incorrect tripping may be either failure to trip or falsetripping.
Failure to trip can be caused by faulty associated
instrument transformer, circuit breakers, control cablesand wiring and station batteries.
Inconclusive Operation
This is the last resort when no evidence is availableeither for a correct or incorrect operation. Quite often,this is a personal involvement.
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RELAY OPERATING TIME
Relays can be classified in terms of their operatingtimes as follows:
High Speed Relays - operate in less than three (3) cycles Slow speed relays - operate in three (3) cycles or more
Time delay relays - have built in time delay facility toallow co-ordination with other relays within the power
system. Instantaneous relays - have no deliberate time delay
facility. They operate instantaneously.
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BASIC COMPONENTS OF A
PROTECTION SYSTEM CURRENT TRANSFORMERS
VOLTAGE TRANSFORMERS
CAPACITOR VOLTAGE TRANSFORMERS
CIRCUIT BREAKERS
RELAYS
CONTACTORS
DC BATERRY BANKS
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EQUIVALENT CIRCUIT OF A CVT
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BASIC COMPONENTS OF LINE
PROTECTION
PROTECTION
EQUIPMENT
TRIP
COIL
TELE
COM
DC SYSTEM
FAULT
VOLTAGE
TRANSFORMER
CURRENT
TRANSFORMER
CIRCUIT BREAKER
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ZONES OF PROTECTION
For effective protection of the system with
minimum part disconnected during fault,
protection zones are mapped out.
Motor Protection Zone
Generator Protection Zone
Transformer Protection Zone
Bus bar Protection Zone
Lines Protection Zone
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Zones of Protection
To limit the extent of the power system that is disconnected when
a fault occurs, protection is arranged in zones
Zones of protection should overlap, so that no part of the power
system is left unprotected
Location of the CT connection to the protection usually defines
the zone
Unit type protections have clear zones reach e.g Diff. Relay, REF
relay
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RELAY OPERATING TIME
Relays can be classified in terms of theiroperating times as follows:
High Speed Relays - operate in less than three (3)cycles
Slow speed relays - operate in three (3) cycles ormore
Time delay relays - have built in time delayfacility to allow co-ordination with other relayswithin the power system.
Instantaneous relays - have no deliberate timedelay facility. They operate instantaneously.
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DEVICES PERFORMING MORE THAN
ONE FUNCTION
If one device performs two relatively important functions in an
equipment so that it is desirable to identify both of these functions,
this may be done by using a double device function such as: 50/51 -
An over-current relay with an instantaneous element and an inverse
element.
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SUFFIXNUMBERS
If two or more devices with the same function number and suffix letter (if
used) are present in the same equipment then these are distinguished as
follows 52x-1, 52x-2, 52x-3 etc
SUFFIX LETTERS
Suffix letters are used with device numbers for various purposes. The
meaning of each suffix letter or combination of letters should be clearly
indicated in the legend on the drawings or publications accompanying the
equipment.Example: 52 TC Tripping coil of the breaker
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COMMONLY USED LETTERS
R - Raising relay or for remote operation
L - Lowering relay or for local operation
O - Opening relay or contactor
C - Closing relay or contactor
CS - Control Switch
CC - Closing Coil TC - Trip Coil PB - Push Button
G - Generator T - Transformer L - Line F - Feeder etc
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REPRESENTATION OF DEVICE
CONTACTS
There are almost in all electrical devices,
particularly in circuit breakers and relays, a set
of contacts which are normally open and
another set of contacts which are normallyclosed.
When the device operates, the contact
position reverses. Those normally openbecome closed and vice versa.
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CARRER GUIDE FOR YOUNG
PROTECTION ENGINEERS
The protection engineer is saddled with ensuringthe reliability and stability of the power system.
As a protection engineer you are an electricalengineer with specialisation in power systemsand protection systems.
It is obviously a great field as it forces you to fullyunderstand the technical aspects of the powerindustry.
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The major challenges facing the young
protection engineers
Bridging the gap between schooling and thereal world as most engineering students arebombarded with abstractions without ideas of
the big picture let alone a sense of the valueof work they will be doing.
Entry level position and qualification isanother challenge as the protection engineer
requires a solid foundation in electric powersystems to be successful.
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A deep understanding of the operation of all theelements of the power system is required as onecannot protect an equipment which operation hedoes not know.
He requires a solid understanding of manytechnical features of the power systemincluding:machine design parameters,bus
configuration, trip circuits, symmetricalcomponents,fault currents, unbalanced powerflow and much more
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For an early success in the protection
engineering career the young engineer should
undergo the following:
He should be made to pass through training
courses that are tailored specifically for
protective relaying.
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He should place himself on a continousprofessional development program by accessingpower system references and training materialswhich include textbooks,relay manuals, standards
and technical papers.
He should place himself on a continousprofessional development program by accessing
power system references and training materialswhich include textbooks,relay manuals, standardsand technical papers.
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The young engineer needs to develop good
hands-on-the job skills with ability to stay on
the job untill he gets result.
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The young engineer should be passionate
about his work as he requires the positive
mental attitude that goes with love for work
to succeed.
He needs to be quick and able to learn new
things all the time
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He needs a mentor for guidance as he
progresses in his career.
He needs to develop or join an existing
professional network or peer group in the
industry.
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This is quite a lot to ask of any one person but the
professional and psychological reward can be very
great.I cannot imagine a better field to begin a
power engineering career than protective relayingas the challenges it provides are endless and the
learning process a life- long one.